SEWAGE SLUDGE CHARACTERIZATION AND EVALUATION OF P

AVAILABILIW UNDER GREENHOUSE CONDITIONS

A thesis

Presented to

The Faculty of Graduate Studies

of

The University of Guelph

bv

GUDMUNDUR HRAFN JOHANNESSON

I n partial fulfillment of requirements

for the degree of

Master of Science

December, 1999

O Gudmundur H. Johannesson, 1999

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ABSTRACT

SEWAGE SLUDGE CHARACTERIZATION AND EVALUATION OF P

AVAILABILITY UNDER GREENHOUSE CONDITIONS

Gudmundur Johannesson,

University of Guelph, 1999

Advisor:

Dr. R.P. Voroney

The objective of the research was to evaluate sewage sludge as a

fertilizer, especially P availa bility. Twelve sewage sludges currently

used for land application were studied. Chemical analysis indicated

high variability in most properties and high quantities of N and P.

Quantities of P extracted by Mehlich-III were different and not related

to those extraded by Olsen bicarbonate. A greenhouse growth trial

was carried out using nine sludges to determine P uptake by

perennial ryegrass (Lolium perenne L.) grown in Guelph loam soil. P

uptake varied depending on sludge generation method and

application rate, ranging from 2 to 6% of applied P. At field rates,

sludge P availability was similar to that from monocalciurnphosphate.

There were significant residual effects of rates of sludge application

on soi1 bicarbonate extractable P levels. Plant P uptake did not

correlate with any sludge P pools measured.

Little a sand-grain, little a dew drop, Little the rninds of men:

All men are not equal in wisdom, The haff-wise are everywhere.

It is best for man to be middle-wise, Not over cunning and clever: The fairest life is led by those Who are deft at al1 they do.

It is best for man to be middle-wise, Not over cunning and clever:

No man is able to know his future, So let him sleep in peace.

It is best for man to be middle-wise, Not over cunning and clever:

The learned man whose lore is deep 1s seldom happy a t heart.

From: Havamal (Words of the High One);

W. H. Auden & P. B. Taylor Translation

Acknowledgements

1 would like to express my gratitude to my advisor Dr. R.P.

Voroney for accepting me as his student and supporting me for the

duration of the program. His effort to change a farmboy into a

scientist and a cityslicker has been appreciated.

Thanks to the members of my advisory cornmittee, professors L.

Evans and P. Groenevelt. My gratitude also to professors E.

Beauchamp and W. Chesworth for sewing on my examination

committee. The inputs and recommendations for changes and

improvements to the thesis, from al1 of these gentlemen, are

a ppreciated.

Thanks to al1 the graduate students in the department for their

friendship and support. They are mostly accountable for introducing

me to the past-time activities of Canadians, which have brought me

entertainment and some insight into the culture of the country. No

apologies will be made for lack of interest in hockey although Dave,

your effort was appreciated. Thanks also for the use of your monitor.

Sincere gratitude to al1 of the faculty, staff, and technicians in Land

Resource Science for their kindness and help throughout the progress

of the program. These people supplied me with the information and

skills necessary to carry out the research and tackle the simple

hurdles that challenge a foreigner who is also new to most things in

the academic world.

My deepest thanks to Goretty Dias for her endless friendship,

support, and help during the writing and defence of the thesis. Her

encouragement and kindness in times of distress are appreciated.

Kærar bakkir tit fjolskyldu minnar a islandi. Stuaningur og traust

Sem Pau sqndu mér var ometanlegur.

The research project was funded by OMAFRA and further financial

support was provided by The Phosphate Institute of Canada through

the Kenneth McAlpine Pretty Scholarship. Funding from The

Agricultural Productivity Fund in Iceland was also granted. My sincere

gratitude to al1 of these foundations.

Table of contents

List of Tables .............................................................................. v . * List of Figures ............................................................................ VII

1 . Introduction ........................................................................... 1 ................................. 1.1. Sewage sludge production techniques 2

......................... 1.2. Sludge production and utilization in Ontario 4 1.3. Land application of sewage sludge ...................................... 6 1.4. Sludge application management in Ontario .......................... 8

.................................... 1.5. Nutrient content of sewage sludge 10 1.6. Nutrient availability from sewage sludge ........................... 11 1.7. Nitrogen in sewage sludge ............................................... 12 1.8. Phosphorus in sewage sludge .......................................... 14 1.9. Indices of phosphorus availability ..................................... 16 1.10. Research objectives ...................................................... 17

2 . Sludge characterization .......................................................... 19 ...................................................................... 2.1. Summary 20

2.2. Introduction .................................................................. 21 2.3. Objective ...................................................................... 22 2.4. Materials and methods .................................................... 22

2.4.1. Sludge sampling ................................................... 22 2.4.2. Ana lytical methods ............................................... 23

2.4.2.1 Solids content ........................................... 24 2.4.2.2 Specific gravity .......................................... 24 2.4.2.3 Total nitrogen, phosphorus, and potassium .... 25 2.4.2.4 Inorganic nitrogen ..................................... 25 2.4.2.5 Olsen and Mehlich III extractable phosphorus 26 2.4.2.6 Total carbon .............................................. 27 2.4.2.7 Electrical conductivity and pH ...................... 27

2.4.3. Statistical analysis ................................................ 27 ......................................................................... 2.5. Results 28

2.5.1 Total nutrients ...................................................... 28 2.5.1.1 Phosphorus ............................................... 28 2.5.1.2 Nitrogen ................................................... 29 2.5.1.3 Potassium ................................................. 30 2.5.1.4 Carbon ..................................................... 30

2.5.2 Available nutrients ............................. .. ............... 30 2 S.2.1 Extractable phosphorus .............................. 30 2.5.2.2 Inorganic nitrogen ..................................... 32

iii

2.5.3 Other properties .................................................... 33 2.5.3.1 pH ........................................................... 33

................................. 2.5.3.2 Electrical conductivity 33 2.6 Discussion ..................................................................... 33 2.7. Conclusions ................................................................... 39

3 . Phosphorus availability ........................................................... 52 3.1. Summary ................................................................ 53 3.2. Introduction .................................................................. 54 3.3. Objectives ..................................................................... 55 3.4. Materials and methods .................................................. 55

3.4.1. Sludge ................................................................ 55 3.4.2. Soi! .................................................................... 56 3.4.3. Mineral fertilizer ................................................... 56 3.4.4. Control .............................................................. 57

..................................................... 3.4.5. Indicator plant 57 3.4.6. Experimental design ............................................. 58

.......................................... 3.4.7. Experimental methods 59 3.4.8. Data analysis ...................................................... 61

3.5. Results and Discussion ................................................... 61 3.5.1. Plant growth ........................................................ 61 3.5.2. Plant yield ........................................................... 63 3.5.3. Phosphorus concentration in plant tissue ................. 64 3.5.4. Phosphorus uptake ............................................... 65 3.5.5. Phosphorus availability .......................................... 68 3.5.6. Soil extractable phosphorus ................................... 71

3.6. Conclusions .............................................................. 74 4 . General conclusions ............................................................... 94

........................................................ 4.1. General conclusions 95 4.2. Further research .......................................................... 96

References ............................................................................... 98 Appendix A ........................................................................ 109 Appendix 6 ............................................................................ 114 Appendix C ............................................................................ 120 Appendix D ............................................................................ 129

List of tables

Table 2.1. Sludges analyzed and generation methods used at waste water treatment plants.. ........................................................ 41

Table 2.2. Parameters determined and types of analysis done on ......................................................... sewage sludge samples 42

Table 2.3. Properties of sewage sludges currently used for land ............................................................ application in Ontario 43

Table 2.4. Distribution and variability of data from analyses of 12 sewage sludge samples ......................................................... 44

Table 2.5. Correlation matrix for parameters from analysis on ................. sewage sludge and significance levels of correlation. 45

Table 2.6. Implications of applying current criteria for land application of sewage sludge in Ontario to sludges from facilities

.............................. using generated sludge for land application 46 Table 3.1. Selected properties of Guelph loam soi1 used for growth

experiment.. ..................................................................... 76 Table 3.2. Dry weight of sludges applied to soi1 in order to supply

given quantity of Pz05 for each P application rate in pot experiment .......................................................................... 77

Table 3.3. Percent recovery of applied P in pot experiment by treatment categories ........................................................... 78

........................................ Table 81. Plan of growth experiment 115 Table 82. Treatment codes, P application levels, and size of

experiment ...................................................................... 116 ........ Table 83. P application rate per pot, and per ha equivalents 117

............... Table 84. Seeding rates in pots and per ha equivalents 118 Table Cl. Yield of ryegrass (Loliurn perenne L.) using 9 different

sludges and minerai fertilizer as P sources at varying application rates in a greenhouse pot experiment ................................... 121

Table C2. Yield of ryegrass (Lolium perenne L.) using different sludges as P sources at varying application rates in a greenhouse

........ pot experiment. Data characteristics by sludge categories 122 Table C3. P concentration in ryegrass (Lolium perenne Lm) tissue

using 9 different sludges and mineral fertilizer as P sources at ........ varying application rates in a greenhouse pot experiment 123

Table C4. P concentration in ryegrass (Lolium perenne L.) tissue using different sludges as P sources at varying application rates in a greenhouse pot experirnent. Data characteristics by sludge categories ....................................................................... 124

Table C5. P uptake by ryegrass (Lolium perenne L.) tissue using 9 different sludges and mineral fertilizer as P sources a t varying

................... application rates in a greenhouse pot experiment 125 Table C6. P uptake by ryegrass (Lolium perenne L.) tissue using

different sludges as P sources a t varying application rates in a greenhouse pot experiment. Data characteristics by sludge categories ......................................................................... 126

Table C7. NaHC03 extractable P in Guelph loam soi1 as affected by 9 different sludges and mineral fertilizer used as P fertilizers at

........ varying application rates in a greenhouse pot experiment 127 Table CS. NaHCO3 extractable P in Guelph loam soi1 as affected by

different sludges used as P fertilizers a t varying application rates in a greenhouse pot experiment. Data characteristics by sludge categories ......................................................................... 128

List of figures Fig. 2.1. Total N, P, and K content of sewage sludge samples. Bars

................................................ represent standard error (g.,) 47 Fig. 2.2. Total N, P, and K content of sewage sludge samples by

..................... sludge types. Bars represent standard error (s,.,) 48 Fig. 2.3. Extractable P using NaHCO3 and Mehlich III methods, and

total P in sewage sludge samples. Bars represent standard error (s ) ........................................................................... 49 Y -*

Fig. 2.4. Available nutrients (N,P) as percent of total nutrients in sewage sludge estimated by Olsen and Mehlich III methods (P), and 2 M KCI extraction (N). Bars represent standard error (sY.J.. 50

Fig. 2.5. Available nutrients (N,P) as percent of total nutrients in sewage sludge estimated by Olsen and Mehlich III methods (P), and 2 M KCI extraction (N). Bars represent standard error (sY,) .. 51

Fig. 3.1. Sewage sludge P application rate effects on growth of ryegrass (Lolium perenne L.) at rates of 450, 900, 1350, 1800,

................. and 2250 mg PZO5 pot-' growing in Guelph loam soi1 79 Fig. 3.2. Yield difference between control treatment (no P applied)

and mineral fertilizer treatment at lowest P application rate ................................................ (receiving 450 mg PzOs pot-') 80

Fig. 3.3. Effects of three different sludges applied a t the same P rate (450 mg PzOs pot-') on growth of ryegrass (Lolium perenne L.) 81

Fig. 3.4. Yield of ryegrass (Lolium perenne L.) using sewage sludges and MCP as P sources at different levels. Control yield subtracted. Bars represent standard error (s,.,) ......................................... 82

Fig. 3.5. Yield of ryegrass (Lolium perenne L.), by treatment categories, using sewage sludges and MCP as P sources at different levels. Bars represent standard error (s,J .................. 83

Fig. 3.6. P content, by treatment categories, of ryegrass (Lolium perenne L.) tissue as a result of 9 different sludges and MCP used as P sources a t different rates. Bars represent standard error (s,.,)

.................................................................. ................... .... 84 Fig. 3.7. P uptake by ryegrass (Lolium perenne L.) using sewage

sludge and MCP as P sources at different rates. Bars represent .............................................................. standard error (s,,) 85

Fig. 3.8. P uptake of ryegrass (Lolium perenne L.), by treament categories, using sewage sludge and MCP as P sources at different rates. Bars represent standard error (s,.,) ................................ 86

Fig. 3.9. P uptake by ryegrass (Lolium perenne L.) as affected by ...................................................... rate of application of MCP 87

vii

1. Introduction

1.1. Sewage sludge production techniques Wastewater treatment plants (WWTP) generate two output

streams: sewage sludge and treated effluent. Sewage sludge is

generated through the removal of suspended solids and sludge from

the influent wastewater, and treated effiuent is discharged to

watercourses (see Appendix A).

Wastewater treatment ca n be a complicated process; several

different designs are used, utilising mechanical, biological, and

chemical methods, in various combinations (Rhyner e t al. 1995). The

difference between facilities depends mostly on the extent of water

purification and disposal method used for sludge. I n its simplest form

the treatment process can be seen as including up to three levels or

stages of treatments: primary, secondary, and tertiary.

I n primary treatment al1 wastes that either float or sink are

removed by screening. This primarily removes debris from the raw

sewage but most of the organic waste stays in the suspension or

solution. After the initial screening, most of the organic waste is

removed from the sewage through settling in tanks. From there the

organic waste is subsequently removed into separate sludge

treatment.

I n secondary treatment, the activity o f naturally occurring

microorganisms is encouraged to digest the organic residues in

2

aerobic and anaerobic environments. This result in flocculation of

solids produced by the microbial activity, which are removed from the

wastewater process into sludge treatment process.

Tertiary treatment of wastewater consists of physical (e.g.

filtration) and chemical processes (e.g. addition of lime, iron or

aluminium cornpounds) to flocculate solids and precipitate nutrients

(Smith 1996).

After initial thickening of sludge, biological activity is supported for

an extended time, mostly to reduce bulk and make the sludge more

manageable. This treatment of sewage sludge is also known as

stabilisation and it is required for sludge used for land utilization in

Ontario. About 75% of the sewage sludge produced in Ontario is

processed by anaerobic digestion (MOEE 1997). During stabilisation

the odour potential and number of pathogenic organisms is reduced,

and some mineralization of plant nutrients occurs (Ministry of

Agriculture and Food, Ministry of the Environment, Ministry of Health

1986).

I n some parts of the world, composting of sewage sludge has

become increasingly popular, and lime addition is also used (Bruce e t

al. 1984). The addition of precipitants can occur at various stages of

the wastewater treatment process, depending on the design of the

facility. A t some WWTP, increasing solids content by various methods

is practiced t o reduce bulk and make the sludge more manageable for

utilization or disposal.

Sludge value as a fertilizer and soi1 amendment depends to a large

degree on the combination and extent of processes descri bed above,

especially chemical treatments.

1.2. Sludge production and utilization in Ontario

The quantity of sewage sludge generated in Ontario is significant

and keeps growing due to increasing population and increasing

standards of wastewater purification.

The current annual production in Ontario is estimated t o be about

344,000 dry tonnes of sludge, according to survey results on sludge

production in Ontario (MOEE 1997). Disposa1 methods used do still

favour destruction over recycling o f this material. Only about 33% of

sewage sludge generated is land applied, about 25% is incinerated

and more than 4O0/0 is still landfilled.

Anaerobic digestion is the most commonly used for sludge

treatment in Ontario. Of sludge generated annually by WWTP

responding to a resent survey, 76O/0 is anaerobically digested, 3O/0 is

aerobically digested, 4 1 is stored in tagoons, and 17O/0 is generated

through other processes (MOEE 1997).

Sludge used for land application must meet the standards set by

MOEE for utilization on agricultural land. The majority of sludge

generated does comply with MOEE guidelines, 74% of the total

sludge produced meeting regulation all the time, and l l O / o meeting

guidelines in 51-99% of the analysis conduded. The quality of sludge

(as defined in management guidelines) should therefore not be the

limiting factor to increasing agricultural recycfing of this material.

Sludge is defined as 'good quality sludge' if it meets MOEE

standards. It is further estimated that 80% of total sludge production

in Ontario can be classified as 'good quality sludge'. Still only 43% of

this high quality sludge is utilised, and the remainder is either used

as landfill (13%) or incinerated (44%).

There is considerable variation between regions in Ontario (as

defined by MOEE) in terms of percent of sludge generated, which is

used for land application. I n the Northern Region, only a very small

fraction of sludge generated is land applied, about 1%. More

surprisingly in the Central Region, land application is not the

prevailing method of sludge management. Only about 27% of the

generated sewage sludge in this area is land applied. There is

therefore considerable scope to enhance quality, and especially

utilization of sludge in Ontario.

1.3. Land application of sewage sludge The following review is focused on management of land-applied

sewage sludge, but the same management strategies also apply to

other recycled material of organic origin, which have been termed

biosolids. This includes sewage sludge, animal manure, food waste,

and paper sludge, as the most common materials for generation o f

biosolids.

Land application of material of organic origin is an ancient method

of recycling nutrients and beneficial factors for plants and soils.

Before urbanization of the world this was possible without problems,

but increasingly denser population created problems by offsetting the

balance between number of people and available arable land. Further

this development created favourable conditions for pathogens which

led to major epidemics for centuries. One major reason for the

construction of sewage systems was the need to reduce the risk of

epidernics of that kind. As cities grew in size, the need to treat

sewage to a higher level became more important as pollution of

water systems and aquatic ecosysterns became increasingly severe.

In some areas industrialkation was also a major source of pollution

from sewage effluent.

The sludge generated by sewage treatment reflects the nature of

the raw sewage entering WWTP. The quality of the sludge further

depends on the efficiency of treatment systems in generating a

product beneficial for soi1 ecosystems, agriculture, and health of

humans as well as animals.

To accomplish this, regulations and management strategies are

essential.

Better knowledge of the impact of sewage sludge on the

environment, along with increased public pressure, has over the last

2 to 3 decades led to introduction of guidelines (legislation) for

disposal of sewage sludge to agriculture (Bruce et al. 1984). Many

countries have recently reviewed these guidelines in order to provide

higher levels of protection for the environment, as well as for animal

and human health (Bruce et al. 1990; Paulsrud and Nedland 1997;

Bouldin 1997; McBride 1998). These stricter guidelines have resulted

in a general trend for promoting a higher level of sludge treatment

before disposal. This trend is Iikely to continue in the near future and

will result in an even higher production of sewage sludge than occurs

now. In Europe, the quantity produced from 1990 to 2006 is

estimated to rise by 50-60% (Smith 1996). This rise in quantity

produced, along with stricter limitations on disposal, will result in the

need for more land suitable for spreading of sewage sludge.

1.4. Sludge application management in Ontario

Guidelines for land application of sewage sludge in Ontario were

first published in 1978, and since then have been used without any

major changes. These guidelines have been reviewed and currently

apply to al1 material of waste origin, used for land application (MOEE,

OMAFRA 1996). The purpose is to maximize beneficial aspects of

sludge application to soils and for plant growth, while rninimizing

potential downsides of the utilization.

All aspects of sewage sludge generation, hauling, spreading of

sludge, suitability of soils for sludge application, and crop

management are covered in this publication. Major factors used as

criteria are :

Sludge:

3 Must be stabilized for pathogen and odour reduction;

> Metal content within acceptable levels for final sludge product

(defined for aerobic, dewatered, and dried sludge); and

2 Ratio of inorganic N to rnetals within acceptable levels

(anaerobic sludge).

Spreading sites:

Minimum distances are defined from spreading site to

residences, surface watercourses, water wells, groundwater

table, and bedrock;

Spreading is not allowed when ground is frozen or snow

covered ;

Slopes of 6-9% (depending on soi1 permeability) are upper

limits for sludge application;

Spreading practices should aim at reducing risk of runoff and

soil compaction; and

Waiting periods are required to reduce risk from pathogenic

organisms in the sludge, with time limits depending on land use

or crop grown.

Soils:

Organic carbon content of soils can not exceed 17O/0 of weight

(Le. they have to be mineral soils);

Metal content has to be below standards defined as normal for

Ontario soils;

Phosphorus extractable by sodium bicarbonate (Olsen method)

has to be below 60 mg kg-' in top 15 cm layer of soil; and

Acidity has to be above pH 6 (except for lime-stabilized sludge);

Crop management:

Sludge can only be applied every fifth year (4 years for

commercial sod);

Anaerobic sludge application can never exceed 135 kg ha-' plant

available N in the sludge (Ammonium + Nitrate forms);

Aerobic, dewatered, or dried sludge application can never

exceed 8 tonnes of solids ha-'; and

Application load must be Iimited by nutrient requirements of the

crop grown.

1.5. Nutrient content of sewage sludge Sewage sludge contains considerable amounts of nitrogen and

phosphorus and has significant inorganic fertilizer replacement value

for these major plant nutrients. The origin and treatment o f sewage

sludge affects bath the quantity and availability of nutrients for crop

growth. Micronutrients are also present to a variable extent based on

origin and treatments of sludge.

The quantity of nutrients in sewage sludge varies considerably but

in general average values of total N and P are 3.8% and 2.2%,

respectively on a dry matter basis (Smith 1996). I n an extensive

survey of sewage sludge in USA Sommers (1977) found average

values for N and P to be 3.9% and 2.5% on a dry matter basis,

respectively.

10

I f these latter values are used to estimate N and P in sludge

produced in Ontario (344,000 tonnes year-'), the quantities of N and

P are equivalent to 13,400 and 8,600 tonnes annually, respectively.

At current market costs ($ 0.75 kg-'), these nutrients are worth

about $16.5 million. It should be stressed though that the variability

in nutrient content can be high between different sludges. Every

attempt to increase utilizatior! of sludge has therefore monetary as

well as environmental value.

Nutrient content of sludge has been found to Vary considerably and

is one of the sludge properties that have to be taken into

consideration. Sommers (1977) reported values from less than 1%

up to alrnost 18% for N and from less than 1% to more than 14O/0 for

P in a study using more than 250 sludges from across the USA. The

sludges containing extreme values of these nutrients were few.

The potassium content o f sewage sludge is low, and will not be of

concern when sludge is land applied. Most sources estimate K content

to be less than l0/0 (Sommers 1977; Wen et al. 1997b).

1.6. Nutrient availability from sewage sludge The availability of plant nutrients in sewage sludge has been found

to be hig hly variable. According to Ontario recommendations for

sludge use in agriculture, inorganic forms of N ( N H ~ + + NO<) in the

sludge are readily plant available in the first growing season. The acid

soluble P in sludge is estimated to be 40% as available to plants as

mineral fertilizer P (Ministry of Agriculture and Food, Ministry of the

Environment, Ministry of Health 1986). Other sources report highly

variable availability indices for plant utilization of N and P in sewage

sludge; the estimated availability of P ranges from almost none (Wen

1994) to that of chemical P in the form of superphosphate (Coker e t

al. 1986). As sewage sludge is generally low in potassium, it is

considered to be of little concern; however, its amount in sewage

sludge should be estimated for each case (MOEE, OMAFRA 1996).

1.7. Nitrogen in sewage sludge As mentioned earlier, the average nitrogen content of sewage

sludge is around 3.8%, which includes ammonium, nitrate and

organic forms. Amounts o f each form depend mostly on the extent of

treatment, which can alter the forms drastically (Sommers 1977).

Sommers (1977) reported that 50-9O0/0 of total N could be in organic

form, depending on the solids content of the sludge. The composition

of the organic N compounds in the sludge included amino acids,

hexoamines and proteinaceous material. A major portion of the

organic form was hydrolyzable. During aerobic digestion, organic

nitrogen is transformed into ammonium, and depending on

treatment, a variable part of the ammonium is converted into nitrate.

Volatilization losses of N during the aerobic treatment process can

consequently be considerable (Sommes 1977). Losses of sewage

sludge N can also be considerable after land application. Beuchamp et

al. (1978) measured 60% loss in inorganic N after surface application

of anaerobically digested sludge in the field.

The fertilizer value of N from sewage sludge is variable depending

on sludge treatment and soi1 environment. Factors affecting

utilization of nitrogen in soils are temperature, rainfall,

immobilization, and ammonia volatilization or denitrification

processes.

Reported values of available N from sewage sludge, as compared

to fertilizer N Vary from 45 to 85% in the first growing season, with

the higher values more frequently reported (Coker et al. 1987).

These values represent the N fraction in inorganic forms, mostly

ammoniacal N (Smith 1996). I n a four-year experiment Coker and

CO-workers (1987) found 25% of total N in sludge to be plant

available. Subsequent release of N from the organic fraction is

inversely proportional to the extent of its decomposition, but in

general its release is slow (Coker et al. 1987; Wen et al. 1995).

Coker and his CO-workers (1987) reviewed earlier research work and

reported values for digested sludge in relatively narrow range of 14%

to 18% organic N release in the first year after application. These

researchers reported an average value o f 8.8O/0 per year release in a

three-year experiment. Parker and Sommers (1983) reported values

ranging from 4% to 29% of sludge N being subjed to mineralization.

This difference was largely explained by different processes used in

the sludge production, an explanation supported by many other

researchers (e.g. Wen et al. 1997a; Hall 1984; Parker and Sommers

1983). Soon et al. (1978) found sludge N to be half as available as

ammonium nitrate fertilizer to plants. The resulting levels of nitrate in

the soi1 following application were similar both from sludge and

mineral fertilizer source (NH4N03).

1.8. Phosphorus in sewage sludge In developed countries, annual P discharge into sewage systems is

about 1 kg per capita, largely from detergents (de Haan 1981). This

number is likely to be much higher in developing countries where

rules for protection of the environment are not as strict as in North

America and Western Europe. With conventional treatment of

sewage, up to 90% of P in the treated effluent can be removed and

ends up in the sludge. Precipitants used for sewage treatment are

mostly soluble salts of iron or aluminium, but also calcium [Ca(OH)2],

or biological methods can be used (Coker and Carlton-Smith 1986).

Recent advances in sludge treatment have made possible even more

efficient P removal for recycling through advanced biological

treatment and subsequent chemical precipitation (Valsami-Jones

1999).

Crop requirements o f phosphorus are usually 1/10 to 1/5 that of N,

but the quantity of P in sewage sludge is often closer to being half o f

the N content. Because of foreseeable stricter rules for P removal

from wastewater, the amount of P in sludge is Iikely to increase

(Smith 1996). Therefore, the potential danger of applying phosphorus

in excess of crop needs has become a concern (McCoy et al. 1986;

Smith 1996). This may lead to accumulation of P in soils and

potentially create an environmental hazard if P becomes mobile

through changes in environmental factors, such as precipitation,

temperature, and pH (Rydin and Otabbong 1997; Rydin 1996). All o f

these factors are known to affect the availability and mobility of P in

soils. Excess P in soi1 can block uptake and lead to micronutrient

deficiency in plants of copper, iron, and zinc (Kirkham 1982).

P content of sludge can Vary considerably and common ranges are

1.2-3.0% (Somrners 1977). Furrer et al. (1984) reported a sludge P

content of 3.5% with a range of 1.2 to 9.5% for sludge from

treatment plants with P precipitation processes, (P elimination

processes are mandatory for waste water treatment plants in

Ontario). Kirkham (1982) concluded that phosphorus concentration in

sludge generated with chemical and biological methods, depended on

the characteristics of the wastewater, the type and quantity of

precipitant used, and stage of chemical addition during the

wastewater treatment process.

Forms of P in anaerobically digested sludge, which have undergone

tertiary treatment, are mostly inorganic (-70°/0) and the remainder

(30%) is in an organic recalcitrant form (Sornmers 1977).

Consequently most researchers have focused on the inorganic

compounds of phosphorus in sludge when studying their fertilizer

value.

The method of sludge production affects forms of P, with the use of

chemicals to precipitate P creating species of lower solubility than

biological treatment. Carliell and Wheatley (1997) found more than

20% of the total P in biological sludges to be soluble or loosely bound

as opposed to 3% in sludge treated by ferric sulphate [Fez(SO&].

1.9. Indices of phosphorus availability The availability of P to plants depends on type of soi1 and its

properties, especially its clay content and pH. Considering the fact

that the inorganic compounds of sewage sludge, which include Al, Fe,

Si, and Ca, resemble those found in soils, sirnilar methods, as are

used for soi1 P analysis can be used for characterization of sludge P

(Hani et al. 1981). Various procedures have been used for

characterization of P in sludge and sorne of them have application to

Ontario soils (Bates 1990; Nesse e t al. 1988).

Phosphorus availability indices attempt to simulate root uptake. A

successful availability index shows high correlation between research

data (concentration of soi1 test P) and crop response (Cox 1994).

Countless different extractants have been tested since the first ones

were developed in the 1940's. Although some have been highly

useful in a given area, a soil-P extractant with applicability over range

of geographical condition, still has not been found. The complication

is due to different conditions in the form of soi1 types and

environrnental factors, which ma kes correlation over varying

geography difficult in practice (Olsen and Sommers 1982; Dahnke

and Olson 1990; Fixen and Grove 1990).

I n North America only a few availability methods have become-

widely used with the Olsen, Bray-Pl, and Mehlich-III indices being

the most common. The success of each method is largely based on

regional soi1 characteristics and to a lesser extent on the type of

agriculture and crop used (Cox 1994).

1.10. Research objectives Advances in waste water treatment processes and increasingly

stringent standards for environmental protection cal1 for revaluation

of management strategies for land application of sewage sludge. High

17

P contents in sludge and uncertainty about its fate in soi1 are of

interest in an attempt to understand the overall impact of sewage

sludge application to agricultural land.

The objectives of this study are to characterize the fertilizer

properties of sewage sludge, and to estimate plant availability of P

from sewage sludge.

2. Sludge characterization

2.1. Summary Twelve sludges were studied for their fertilizer value with emphasis

on P characteristics.

Sewage sludge samples currently used for land application in

Ontario were analysed for a range of characteristics affecting their

value as a fertilizer. These sludges represented differences in

geographical location and community size as well as generation

methods used in waste water treatment plants. In total 15 different

parameters were estimated with special emphasis on P.

Quantities of extractable nutrients (N, P) were somewhat different

according to procedures used and sludge generation methods. Olsen

and M-II I indices yield relatively different quantities of extractable P.

On average 7% of total P was extractable with sodium bicarbonate

but 72% was extracted with Mehlich III. Inorganic N (2 M KCI) was

significantly different according to digestion method used for

stabilization of sewage sludge. Significantly higher levels of soluble

salts were observed in anaerobically digested than aerobically

digested sludges.

Application of current management guidelines in Ontario, which are

based on applying 135 kg inorganic N ha-', t o the sludges under

investigation indicated that P loads from sewage sludge might reach

levels of 750 kg PzOs ha-' over a five year period. Average P loads

20

from anaerobic and aerobic sludges would be 320 and 590 kg Pz05

ha-', respectively.

2.2. Introduction Sewage sludge has been used as nutrient source for decades

(Kirkham 1982; Bates 1972). When material is evaluated for its

fertilizer value, total quantity of plant nutrients is of interest, as well

as chernical forms and subsequent plant availability (Terman and

Engelstad 1971). Chemical forms of the nutrients, as well as soi1

properties and environment, determine plant availability of nutrients

(Mengel and Kirkby 1987; Hani et al. 1981; Wen et al. 1997a,b).

Nutrient content of sludge, to a large extent, is dependent on

sludge origin and methods used for its generation. (Rhyner et al.

1995; Krogmann et al. 1997; Hall 1984; Kyle and McClintock 1995).

Extent of sewage treatment and methods used in waste water

treatment plants can affect quantity of sludge produced, nutrient

content and forrns of nutrients in the sludge (Smith 1996; Bruce et

al. 1984).

Standard methods for agronomic evaluation of sludge are few.

Researchers have used methods developed for soi1 and plant

analyses, as well as procedures used for environmental studies to

estimate quantity and quality of sludge nutrients (Wen et al. 1997;

Sommers 1977; Hani et al. 1981; Coker and Carlton-Smith 1986;

Rydin and Otabbong 1997; Soon and Bates 1982).

2.3. Objective The objective of the research was to determine the chemical

properties of sewage sludges currently used for land application in

Ontario with emphasis on plant availability of phosphorus.

2.4. Materials and methods

2.4.1. Sludge sampling

When planning a sampling strategy, the decision was made to use

only siudges generated from wastewater treatment facilities that

comply with MOEE guidelines for application to agricultural land.

Therefore it was assumed that the sludges would not contain any

factors detrimental to plant growth.

The initial goal was to analyze sludges representing the variability

in production techniques, as well as in chemical cornposition. This

was done by using a recent survey result on sludge production and

management in Ontario (MOEE 1997). But as the diversity of sludge

production methods has decreased, only two major categories of

sludges were obtained; aerobically and anaerobically digested. All but

one of the facilities used alum for P removal. The facility using iron

generated dewatered sludge for landfill disposal, as the product did

not meet the criteria for land application because of excessive metal

levels. This sludge was sampled prior to dewatering although

chemicals for flocculation had already been added. Table 2.1 lists

sludges sarnpled and generation methods used at the wastewater

treatment facilities.

Sludges were sampled from facilities located in southern and

central Ontario in June, 1998. Samples were obtained from waste

water treatment plants during two separate sampling times, using

standard sampling procedures for sludge (EPA 1980). Sludges

represented the final product of sludges generated, or as close to that

state possible. Sludge samples were brought to the University of

Guelph and kept in storage at 4OC until analysed. For sarnpling, 25 L

plastic pails were used with subsamples taken and stored in 1 L

sampling bottles (Nalgene).

2.4.2. Analytical methods

When evaluating sludge for fertilizer properties one soon realizes

that not many standard procedures exist for sludge. Therefore

methods used here are the ones used either for soit, manure, plant,

or waste analysis, depending mostly on suitability for fertilizer

evaluation and resources available at the time. Ail analyses were

done in duplicate, including blanks and reference samples if

applicable.

23

Table 2.2 gives an overview of analysis carried out on sludge

samples. In total 15 different parameters have been estimated. The

difference between total and inorganic N is assumed to be in organic

form. Similarly, the difference between total and extractable fractions

of P is assumed to be in an occluded or fixed form, representing

organic and precipitated forms of P not readily plant available.

Organic C was determined from the difference between total C before

and after overnight ashing of samples.

2.4.2.1 Solids content

Total solids were determined by drying sludge samples in an oven

a t 10S°C for 24 hrs (APHA, AWWA, WEF 1995). Representative

samples (-120 g) were weighed into 500 mL glass beakers and put

in an oven previously set to desired temperature, and dried to a

constant weight.

2.4.2.2 Specific gravity

Specific gravity was determined using standard method for sludge

(APHA, AWWA, WEF 1995) by weighing out a known volume of

sludge and cornparing it to the weight of an equal volume of water at

the same temperature.

2.4.2.3 Total nitrogen, phosphorus, and potassium

Total N, P, and K were deterrnined by a rnodified ashing procedure

(Thomas et al. 1967) using sulphuric acid and hydrogen peroxide.

Analysis were carried out on liquid sludge samples to preserve

inorganic nitrogen potentially present. Using a syringe, 5 mL samples

were put into 250 mL digestion flasks followed by 5 mL concentrated

sulphuric acid (H2SOs). Samples were digested for at least one hour

in a heating block previously set to 22S°C. A few drops of hydrogen

peroxide (H202) were added six times, boiled for 15 min and sampfes

allowed to cool for 5 min between each additions. Samples were

made up to volume (250 mL) and leR to settle overnight.

Representative sub-samples were taken for analyses. N and P were

analysed using a Technicon Auto-Analyser (Technicon Instrument

Corporation, 1973a,b). K was analysed using a Varian SpectrAA-300

Atomic Absorption Spectrometer (AAS).

2.4.2.4 Inorganic nitrogen

. For inorganic N analysis, extraction by 2 M KCI (Keeney and Nelson

1982) and subsequent analysis by Technicon TRAACS 800 Auto

Analyzer (Bran and Lube, Technicon Industrial Systems, Elmsford,

N.Y.) was utilised. Using a pipette, a 5 m l sample was measured into

a glass bottle, 25 mL of 2 M KCI was added, and samples shaken for

30 min on a mechanical shaker. Samples were filtered through a

25

Whatman No. 42 filter, and the filtrate was kept in the fridge until the

analysis was done. Organic N was estimated by diffence between

total N and inorganic N measured as described above.

2.4.2.5 Olsen and Mehlich III extractable phosphorus

Two procedures frequently used to estimate availability of P in soi1

were used to estimate plant available P in the sludge samples, Olsen

procedure and Mehlich-III procedure. Sodium bicarbonate extractable

P (Olsen e t al. 1954) was estimated using a slightly modified

procedu re descri bed for study ing soils (Schoenau and Ka ramanos

1993). Liquid sludge (2.5 mL) was transferred to a glass flask using a

syringe, following by 50 mL of extrading solution. The samples were

shaken for 30 min, and filtered through Whatman No. 40 filter paper.

Mehlich III extractable phosphorus was similarly analysed following

the procedure of Mehlich (Mehlich 1985) as described by Tran and

Simard (1993) with minor modifications. Five mL of liquid sludge was

added to 50 mL of extraction solution. This solution was shaken for 5

min and filtered through Whatman No. 42 filter paper.

A Technicon Auto-Analyser was used for estimating concentration

of P in both Olsen and M-II I extractants (Technicon Instrument

Corporation 1973,b).

2.4.2.6 Total carbon

Total C was determined using LECO SC-444 Sulphur and Carbon

Analyzer (LECO Corporation, St. Joseph, Mi.). Inorganic C was

measured with the same instrument after ovemight (16 h) ashing of

samples in a muffler furnace set at 475 OC.

2.4.2.7 Electrical condudivity and pH

Electrical conductivity and pH were measured using an Accumet

Model 20 combined conductivity and pH meter. Measurements were

made on Iiquid sludge samples at room temperature.

2.4.3. Statistical analysis

Statistical analysis of the data was focused on determining the

variation within the range of sludges chosen for analyses. T-test,

regression, and correlation were used, as well as standard descriptive

calculations: i.e. average, median, minimum, maximum, and

standard deviation. For regression calculations SAS statistical

Program (SAS Institute Inc. 1994) was used utilising CORR procedure

(Spearman 's rank order correlation). Other calculations were made

using solutions available in Microsoft Excel 97 program.

2.5. Results

2.5.1 Total nutrients

2.5.1.1 Phosphorus

Current management practices for sludge in Ontario do not

consider P content or availability as a limiting factor for sludge

application rate. Instead, it is proposed that total P in sludge is 40%

generally

shown to

as plant available as mineral fertilizer P. Sludge is

in P but its bioavailability has been considered to be high

Vary in experiments.

Total P content of the sludges used for this study was in general

high compared to other forms of organic matter. One characteristic of

sludges is the high variation in chernical composition, here reflected

in P-contents ranging from 24 to almost 47 g kg-' (Table 2.3; Fig.

2.1), with an average of 38 g kg-' (Table 2.4). I n this study no

statistically significant difference (P<0.05) was observed between

anaerobic and aerobic sludges, based on difference in digestion

method (Fig. 2.2). The one sludge from a waste water treatment

plant using Fe compounds for precipitation of P did not show

significant difference from sludges generated using Al compounds.

2.5.1.2 Nitrogen

Management recommendations in Ontario use inorganic nitrogen

content as a criteria for sludge application to agricultural land. N in

inorganic form in sludge is used to control application rate, and the

ratio of inorganic N content to metal content is the criterion used for

lirniting metal loading to soils from anaerobically digested sludge

(MOEE and OMAFRA 1996).

60th total and inorganic N in this study showed wide ranges in

concentration. Total N ranged from 32 to 96 g kg" (Table 2.3, Fig.

2.1) with average of 59 g kg-' (Table 2.4). Some of the variability

might be explained by conditions at the time of sampling. The

wastewater treatment plants were sampled a t two different times and

it was not possible in some instances to obtain samples of sludges

representing the end product of sludge treatment processes. In some

cases sludge had just been shipped out for spreading, and these

sludge samples would be obtained as close to the final product as

possible. This may have resulted in incomplete digestion process at

the time of sampling, which could affect both quantity and forms of N

in the sludges. This variance can be considered to be within

variability in sludge treatment a t waste water treatment plants and

will therefore not create bias in the data. There was a significant

difference (Pc0.05) in nitrogen content of aerobic and anaerobic

sludges (Fig. 2.2).

2.5.1.3 Potassium

Management strategies do not put much emphasis on potassium

because of its low content in sewage sludge. As expected, the K

content of the sludges examined in this study was low, with few

extreme values (Fig. 2.1). The average K content was 6.3 g kg-' dry

matter, ranging from 2.6 g kg'' to 10.8 g kg-' (Table 2.3, Table 2.4).

2.5.1.4 Carbon

Carbon content of the sludge samples investigated was relatively

constant without any easily detectable trends. There was no

significant difference between aerobically and anaerobically digested

sludge. The C content ranged from 20 to 3S0/0, with an average of

26% (Table 2.3, Table 2.4). Most of the C was in organic form, with

inorganic C accounting for less than 0.0l0/0 of the total.

2.5.2 Available nutrients

2.5.2.1 Extractable phosphorus.

Using Olsen and Mehlich III procedures for estimating loosely

bonded P provided an opportunity to compare the effectiveness of

different extractants for assessing availability of sludge P. These

procedures are traditionally used for estimating plant available P in

soil, which does not have much in cornmon with sludge chemistry or

its physical properties. The sodium bicarbonate extractant is alkaline

(pH 8 .5 ) , while Mehlich III is acidic (pH 2.5). The quantity of P

extracted was very different for these two methods (Table 2.3, Fig.

2.3). The success of procedures will ultimately depend on the

relationship of extracted P to plant uptake, which is reported in

Chapter 3 of this thesis.

There is a highly significant difference (P<0.001) in extractability of

P using the two extractants investigated. While the Olsen extractant

only yielded a low proportion of total P in sludge samples, the Mehlich

III method extracted a relatively high proportion of the total P in

sludge samples studied (Fig. 2.4). There was no significant difference

a t the 0.05 probability level between sludge types based on digestion

method (Fig. 2.5). A slightly different level of significance was

obtained between aerobic and anaerobic sludge for the Mehlich III

method and the Olsen procedure (Pz0.07 vs. P=0.11, respectively).

The quantity of sodium bicarbonate-extractable phosphorus from

the sludge was low. On average approximately 7% (2.8 g kg-') of the

total P in sludge samples was recovered, ranging from 3 to l lO/o . A

weak correlation (rrO.11) was observed between total P and

extractable P using this method (Table 2.5).

The mean proportion of total P extracted with Mehlich I I I was 72%

(27.7 g kg-'), ranging from 5 1 to 88%. There is a good correlation

between total P and Mehlich III+ (r = 0.91, P<0.001).

Results from the two extractants correlated poorly with each other

(Table 2.5) , indicating that these two methods did not only differ in

quantity extracted but there were different mechanisms at work for

each of them (see discussion).

2.5.2.2 Inorganic nitrogen

The range of inorganic nitrogen content (Table 2.3; Fig. 2.4) varies

considerably, ranging from 1 to 78% of total N in the sludges. For

anaerobically digested sludge, where inorganic N is used as a criteria

for total application rate, the range was 47 to 77% of total N . A

significant difference (P<0.001) was observed between sludge

categories according to digestion method (Fig. 2.5). A high loss of N

through volatilization is a well known effect of aerobic digestion of

sewage sludge, making this finding logical.

A good correlation was found between inorganic N (sum of

ammonium and nitrate) and total N in the sludges (r=0.87,

P<0.001), (Table 2.5).

2.5.3 Other properties

2.5.3.1 pH

Sludges studied in this analysis did not show much variation in pH,

varying slightly from neutral. The average was 7.3 and ranged from

6.7 to 8.0 (Table 2.4).

2.5.3.2 Electrical conductivity

Considerable variation was observed in electrical conductivity

readings on sludges studied (Table 2.3). A significant difference was

evident between sludge digestion rnethods, with the anaerobically

digested sludge showing significantly higher (P<0.001) conductivity

than aerobically digested sludge (Table 2.4). The average

conductivity of al1 sludges was 4.7 mS cm-', with the anaerobically

digested sludge having an average of 6.2 mS cm-' white the

aerobically digested showed an average of 2.7 mS cm-'. Electrical

conductivity showed a significant correlation with many other

parameters determined in this study i.e., al1 forms of N, M - I I I

extractable P, and total C (Table 2.5).

2.6 Discussion I n general, findings of these analyses are similar to those reported

in the literature for comparable sludges. As methods used for sewage

sludge generation can alter composition and properties of the

product, it is important to know about the origin of sludges

investigated. Different methods used for analysis of sludges will also

contribute to differences in characteristics to some extent (Sommers

1977).

The values for total P in this study are similar to those found in the

literature for sludges generated from facilities with chemical and/or

biological P elimination treatments. Sommers (1977) reported an

average of 25 g kg-' total P from 250 sewage sludge samples

generated with a range of different methods. Markham (1982)

reported values of 30.4 g kg" for digested sludges with alurn used for

P precipitation, and 36.9 g kg-' in digested sludges with iron used for

P precipitation.

The two procedures used to estimate readily available P resulted in

totally different quantities of P extracted. Without calibration of these

numben with plant uptake in growth experiments, it is not possible

to comment on the relative value of these methods. That is dealt with

in Chapter 3 of this thesis.

Researchers studying sludge P under laboratory conditions have

found that a relatively large proportion of total P in sludge becomes

available. The extractability will depend on soi1 type, sludge type, and

time. Most of the available sludge P will originate from the inorganic

pool of P (-700/0 of total P) which in turn will include several different

pools (Rydin and Otabbong 1997; Fine and Mingelgrin 1996).

Compared with information from the literature, the N contents

found in this study are similar. Sommets (1977) reports an average

of 50 g N kg-' for digested sludge. Losses of nitrogen during aerobic

digestion, through volatilization, have been found to be considerable

and have led to different regulations for land application of sludge

depending on stabilisation method. Total solids applied is the criterion

for aerobically digested sludge while inorganic forms of nitrogen are

used to lirnit application rate of sludge generated with anaerobic

digestion (MOEE and OMAFRA 1996). It seems clear that these two

categories of sludge differ both in quantity and chemistry of N

present.

Values for potassium content for sludges analysed in this study are

on the higher end of what was found in the literature. Averages

values of 3.5 to 5.0 g kg-' seem to be applicable with a wide range of

seasonal as well as regional variability (Sommers 1977; Wen et al.

1997b).

Carbon content of sludge from domestic sewage systems is fairly

stable, but industrial sources can affect the quantity, especially food

and pulp industry. Normally, the main source of carbon in sewage

sludge is organic waste, mostly of human origin. Sommers (1977), in

a survey of sludge in the U.S., reported a mean value of 31% total C.

He cited sources estimating inorganic content ranging from 1 to 4*/0

identified as metal carbonates or soi1 minerals. The values found in

this study fall within a normal range for carbon content of similarly

derived sludges.

Table 2.5 presents the result of correlation between different

parameters analysed in this study. Some of these parameters are

highly correlated. Of most interest in this study are the relationships

of N and P with other characteristics. Inorganic N is well correlated

with total N (r=0.87, P<0.001), indicating that inorganic N might be

a good estimator for control of total N application from sludge. Total

P a:

Meh

P<O

well as Olsen P are poorly correlated to other parameters but

ich III shows significant relationships with total P (r=0.91,

001). There is little correlation between Olsen and Mehlich III

extractable P (r=0.04, ns at P10.05). This may imply that the values

obtained with each method reflect different pools or underlying

mechanisms. As the chemical characteristics of these two extractants

are different they are likely to extract P of different properties present

in the sludges. When these two methods are used to estimate

available P in soils they correlate well but yield a somewhat different

quantities of P extracted. Mehlich III procedure will, in general, yield

a higher quantities of P than the Olsen procedure (Wolf and Baker

36

1985; Bates 1990). P yielded from sludges by Mehlich III method, in

this study, exceeded that from Olsen method by about 10 times

greater quantity. It is not clear what causes this great difference in

response with these extradants used to analyse sludges. P in sludge

is largely acid soluble (Sommers 1976), while the Olsen extractant is

alkaline (pH 8.5). This may be a reason for low efficiency of this

method to retrieve sludge P, as observed during analysis of sludges.

The Mehlich III extractant has a pH of 2.5, which may explain why it

extracts a relatively high fraction of the total P in the sludges studied.

Table 2.6 presents the results of application calculations, according

to nutrient content of sludges analysed in this study. The assumption

is made that levels of metals in the sludges will not be limiting to

application rate. Using 8 tonnes biosolids ha-' and/or 135 kg

inorganic N ha-' as the maximum application rate for a 5-year period,

the resulting load of total nutrients will be considerable. Since there

seems to be a good correlation between inorganic N and total N

quantity (Table 2.5) , inorganic N input should also limit total N

loading. Other nutrients (P and K) are not significantly correlated with

factors used to control application rate. The load of total P (as P205)

is far higher than any crop will be able to utilise in the short term,

making a good estimate of bioavailable P necessary.

Stitl some assumptions have to be made about the mineralization

rate of organically-bound N and P. I n the current management

guidelines no estimate is provided for that quantity, but

mineralization of sludge organic matter can be considerable and an

attempt should be made to provide an estimate for plant available

nutrients from this source. In a field experiment, Kelling et al. (1977)

found significant levels o f available N and P present from a sludge

application up to two years aRer application. Application rate and soi1

type would affect the extent and rate of mineralization. Fine and

Mingelgrin (1996) concluded that 1/3 of organic PI which would be

less than 10% of total P, was readily available for microbial

degradation. They further reasoned that the mineral fraction of PI

usually more than 70% o f total P, would control the availability of P

to plants. The mineralization of sludge organic N in the field is

estimated to be 15% in the first growing season, but the release in

subsequent years is expected to be slower than the initial release

(Parker and Sommers 1983; Coker et al. 1987).

The high electrical condudivity observed in this study, especially

for anaerobically stabilized sludge (Table 2.4) may indicate high

levels of soluble salts. Rodgers and Anderson (1995) found soluble

sa lt content, measured as electrical conductivity, to increase linearly

with sludge application rate but not to a level that would normally

inhibit plant growth. These researchers concluded that one-tirne

sewage sludge application should not exceed 100 Mg ha-' to avoid

plant growth inhibition from high levels of soluble salts. As 75% of

sewage sludges generated in Ontario are anaerobically digested

(MOEE 1997), this fact might be of concern for management of

sludge in the province.

2.7. Conclusions The sludge samples showed considerable variation in chemical

properties used to define their fertilizer value. Up to a three-fold

difference between minimum and maximum values was observed for

content of plant macronutrients (N, P, K) and up to six-fold difference

for other properties. It is clear that it is necessary to develop

management strategy, which acknowledges that fact, and is aimed at

maximizing both the profit of utilising this material and the protection

of the environment.

The quantity of total P is higher in sewage sludge than other

fertilizer material of organic origin. Mehlich III extractable P may be a

good estimator of total P because of highly significant correlation

between these two factors. High P loads to soils from sludge can

potentially create problems and further research into the availability

of P in sludge are needed in Ontario.

Relatively high N quantity in sewage sludge, and the potentially

negative effect that nitrogen may have on the environment, makes it

logical to use nitrogen as a management factor for land application of

sludge. Inorganic N provides a good estimate to control application

rate of nitrogen.

High levels of soluble salts in anaerobically digested sludge may

potentiaily limit plant growth and affect soi1 structure.

Mineralization of nutrients from sludge can be considerable and

some estimate of that quantity should be included in guidelines for

land application of sludges.

Table 2.1. Sludges analyzed and generation methods used at waste water treatment plants

Sludge Digestion method P-precipitant

S l Aerobic Alum S2 Anaerobic Alum S3 Aerobic Alum S4 Anaerobic Alum SS Anaerobic Alum S6 Anaerobic Iron S7 Anaerobic Alum S8 Anaerobic Alum S9 Anaerobic Alum

SI0 Aerobic Alum S I 1 Aerobic Alum S12 Aerobic Alum

Table 2.2. Parameters determined and types of analysis done on sewage sludge sarnples

Parameters Total Organic Inorganic Available Fixed Other

N x x x* P X x** x***

Specific gravity Solids x * KCI extractable N, representing available N

** Olsen-9, and Mehlich II I-P

*** difference between total and extractable P () measurement made (can not be classified as 'total * )

Table 2.3. Properties of sewage sludges currently used for land application in Ontario

Sludge Total N Inorg. N Org. N Total P Olsen-P M III-P Total K Total C Solids Ec PH ,<g kg-' dem. O/i mS cm-' .

Average Median Minimum Maximum St. dev. C.V. (9.0)

Table 2.4. Distribution and variability of data from analyses of 12 sewage sludge samples Total N Inorg. N Org. N Total P Olsen-P M I I I -P Total K Total C Solids EC PH

g kg-' d m . O/O mS cm-' All sludges (n= 12)

Anaerobic (n=7) 68.5 42.3 26.2 39.2 2.3 30.3 5.7 270.0 2.8 6.2 7.4 75.7 45.4 22.5 37.3 1.9 26.9 6.1 250.0 2.7 5.7 7.5 43.7 23.5 17.6 35.0 1.3 23.8 2.6 231.0 1.8 5.5 7.0 95.5 60.7 50.2 46.8 3.9 37.3 9.7 353.0 4.4 8,4 7.7 18.4 14.9 11.1 4.4 1.0 5.8 2.4 460.0 0.9 1.0 0.2 26.9 35.3 42.3 11.2 42.6 19.3 42.4 169.0 33.8 16.5 3.0

Aerobic (n= 5) a

Average Median Minimum Maximum St. dev. CmV.(o/o)

59.2 29.2 30.0 38.1 2.6 27.7 6.3 263.0 2.4 4.7 7.3 59.5 29.9 26.4 38.5 2.8 27.0 6.1 256.0 2.2 5.6 7.4 31.6 0.3 17.6 24.2 1.3 14.7 2.6 200.0 1.2 1.4 6.7 95.5 60m7 55.4 46.8 3.9 37.3 10.8 353.0 4.4 8.4 8.0 21.6 21.4 12.1 5,6 0m8 6m8 2.3 410.0 0.9 2.1 0.4 36.4 73.5 40.4 14.6 32.4 24.6 37.1 154.0 37.7 43.8 5.7

Average Median Minimum Maximum St. dev. C.V. (%)

46.3 10.9 35.4 36.4 3.0 24.2 7.1 254.0 1.8 2.7 7.1 32.4 6.4 31.3 39.8 2.8 27.2 6.2 264.0 1.9 2.4 6.8 31.6 0.3 22.1 24.2 2.6 14.7 5.6 200.0 1.2 1.4 6.7 74.3 36.0 55.4 41.1 3.7 30.2 10.8 284.0 2.3 3.9 8.0 20.3 14.5 12.6 7.1 0.4 7.0 2.2 350.0 0.4 1.1 0.6 43.9 133.5 35.4 19.5 14.4 29.1 30.7 137.0 22.9 39.7 7.8

Table 2.5. Correlation matrix for parameters from analysis on sewage sludge and significance levels of correlation.

Inorg. N Org. N Total P Olsen-P M II I-P Total K Total C T.S. EC PH

Total N Inorg. N

Org. N Total P Olsen-P M III-P Total K Total C

T.S. EC

*,**,***; significant at 0.05, 0.01, and 0,001 levels respectively

ns; nonsignificant at the 0.05 level

Table 2.6. Implications of applying current criteria for land application of sewage sludge in Ontario to sludges frorn facilities usinq qenerated sludqe for land application

Dry W. Wet W. N Inorg. N P20s K Aerobic sludges (kg ha-')')

Si 8,000 384,722 252.5 2.0 753.9 45.2 S3 8,000 426,966 258.8 18.0 442.8 86.5 Si0 8,000 353,054 252.4 75.6 671.6 57.4 Si1 8,000 658,860 494.1 50.8 743.7 49.4 SI2 3,745 499,179 278.1 135.0 341.5 21.0 Average 7,149 464,556 307.2 56.3

Anaerobic sludges (kg ha-l)b) 93,575 174.3 135.0 156,359 284.4 135.0 130,303 250.8 135.0 130,662 181.6 135.0 201,382 272.9 135.0 75,841 210.8 135.0 139,904 222.4 135.0

Average 3,619 132,575 228.2 135.0 320.0 18.0

a) Maximum applications rate 8 tonnes ha-'. Nitrogen application rate can never exceed 135 kg inorganic N ha-' over a five year period

b) Maximum application rate 135 kg ha-' over five year period

3. Phosphorus availability

3.1. Summary A greenhouse growth study was carried out to estimate P

availability in sewage sludge. Nine different sludges, and a mineral

fertilizer, each applied at six rates (0, 450, 900, 1350, 1800, and

2250 mg Pz05 pot-'), and a control treatment were set out for

determination of relative P availability. The experiment was set up to

ensure that P was the only limiting factor for growth of ryegrass

(Lolium perenne L.), which was used as an indicator plant. Other

nutrients (NI K) were supplied in sufficient quantities, so as not to

restrict growth of plants.

The results showed varying availability depending on sludge

generation method and application rate. The availability was similar

to that reported in the literature for similar trials. There were

indications that current estimates used in Ontario guidelines for

sludge application to agricultural land may underestimate P

availability f rom sludge.

Additionally, there were sig n ificant residual effects of application

rate refleded i n bicarbonate extracta ble P from the soil, especially

h m mineral fertilizer.

3.2. Introduction Only a small fraction of total P in soi1 is in a form readily available

for plants. P concentration in soi1 solution and the phosphate buffer

capacity o f soils are the most important parameters controlling

phosphate supply to plant roots (Mengel and Kirkby 1987).

Sewage sludge can be successfully utilised to provide phosphorus

for plant growth, but may also potentially cause environmental

problems (Markham 1982; Rydin and Otabbong 1997).

Phosphorus in sewage sludge is present rnostly as phosphates, but

methods used during purification of sewage water and subsequent

sludge generation may advenely affect the plant availability of P

(Sommers 1977; Cox e t al. 1997; Frossard e t al. 1996; McCoy et al.

1986; Gestring and Jarrell 1982).

Bioavailability of fertilizers is determined through correlation

between applied nutrients and plant uptake. Chemical form of

nutrients, soi1 properties, choice of indicator plants, and

environmental factors determine how much will eventually be utilized.

Nutrient transfer from soi1 by volatilization, leaching, or erosion also

have to be considered so as to estimate the overall impact of the

application (Mengel and Kirkby 1987; Dahnke and Olson 1990; Cox

1994; Bates 1990; Wolf and Baker 1985).

Classical methods for agronomic and environmental evaluations

of phosphorus are applied to sewage sludge. Analysis of sludge P, use

of availability indices, and growth trials are used to estimate quantity,

forms, and availability of P (Folle e t al. 1995; Otabbong 1997; Kyle

and McClintock 1995; Coker and Carlton-Smith 1986; Soon et al.

1978; Wen et al. 1997a).

3.3. Objectives The objective of the experiment was to estimate availability of P

from sewage sludge. Difference in P supplying capacity based on

sludge origin and generation method was investigated.

3.4. Materials and methods 3.4.1. Sludge

Nine sludges, same as used for chemical analyses, were used in a

greenhouse growth trial, each applied at six different levels of total P.

The codes used to identify sludges are the same throughout the

experiment. Application rates were approximately 0, 450, 900, 1350,

1800, and 2250 mg P20s pot-', estimated to be equivalent to 0, 225,

450, 675, 900, 1125 mg PzOs kg-' soil. Additional mineral fertilizer,

providing N and K, was added repeatedly (2-3 tirnes) during the trial

to ensure that these nutrients would not limit plant growth. The total

application rate of each of these nutrients was at least 1500 mg pot-'

for the duration of the experiment. More detailed information on

experirnental design and methods can be obtained from Appendix B.

Sludge characteristics and analytical methods used for sludge

analysis are listed in Chapter Two of this thesis. An overview of their

properties can be seen in Fig. 2.1, Fig. 2.3, and Table 2.3.

3.4.2. Soil

Guelph loam soi1 was used as a growing medium. It was obtained

from a field at the Elora Experimental Station in November 1998,

sieved (< 2 mm) and mixed thoroughly before use. The soi1 from the

location sampled had been left as unfertilised land for more than 30

years, resulting in very low available P. Table 3.1 lists some findings

of the analysis conducted on the soi1 at the Soil and Nutrient

Laboratory, University of Guelph.

3.4.3. Mineral fertilizer

A mineral fertilizer treatment was included, using ammonium

nitrate (NH4NOi), superphosphate [Ca(H2P04)2 + CaS041, and

potassium sulphate (K2S04) as nutrient sources for N, P, and K,

respectively. Fertilizers were finely ground to enhance solubility of

nutrients and thereby optimise utilization by plants.

These nutrient sources were applied and mixed thomughly with

soi1 to approximately 10 cm depth. Additional N, and K fertilizer was

added during the trial as described for sludge treatments.

3.4.4. Control

The control treatment received N and K fertilizers, but no P. This

treatment was included to account for P uptake from soi1 and other

soi1 reactions that could interfere with availability of P originating

from sludge. Because of its extremely low Olsen P content (2 mg P

kg-'), this soi1 provides suitable conditions to study plant response to

additional P sources.

3.4.5. Indicator plant

Perennial ryegrass (Lolium perenne L.) was chosen as an indicator

plant, based on the fact that it has been proven to give a good

response to P over a wide range of application rates (Coker and

Carlton-Smith 1986).

The seeding rate was 0.5 g pot-', which is about 10 times the rate

recommended for field conditions (See Appendix 5). Using lower

seeding rates proved to be difficult in pradice; a lesser quantity of

ryegrass seed was difficult to weigh out with accuracy and it did not

cover the surface o f the pots sufficiently.

Because of the high application rates of sludge and mineral

fertilizer, there was a risk of affecting plant growth negatively,

especially at the early stage of plant growth. To provide protection for

the seeds during germination and initial root development, a seedbed

was prepared. The seedbed consisted of a layer of approximately 1.0-

1.5 cm of finely sieved and thoroughly mixed soil. At the time of

seeding, a thin layer of soil was applied on top of the sludge-soi1

mixture in the pots, seeding was carried out, and the seeds were

covered with another thin layer of soi1 and firmly pressed down by

hand. I n addition to providing protection from elements released from

nutrient sources at potentially toxic levels, this practice enhanced

retention of water necesSan/ for successful germination of seeds and

growth of plants at the early stage.

3.4.6. Experimental design

The sludge and mineral fertilizer treatments, each at five levels,

plus a control treatment resulted in a total of 56 treatments. The

experiment was laid out as a completely randomised design. While

most treatments contained three replications, some treatments could

only be carried out in duplicate, mostly because the quantity of

sludge necessary was underestimated.

The experiment was rerandomized once again during the trial so as

to rninimize the effect of any difference in environmental conditions

58

on the data. Environmental conditions in the greenhouse were

automatically controlled, making this practise almost unnecessary.

Throughout the design, preparation, and duration of the

experiment, measures were taken to minimize any possible

interference to the accuracy o f greenhouse growth experiments using

sewage sludge. Methods for this have been developed and tested,

and reported in the literature. This included the experimental design

and choice of appropriate indicator plant for the nutrient under

investigation. Choice of appropriate doses of nutrients for pot

experiments ensures that only the factor under investigation is

limiting for plant growth. Effort was made to avoid potentially toxic

effects of heavy loads of sewage sludge (Cox and Cochran 1946;

Terman 1974; Mortvedt and Terman 1978; Day et al. 1989; Folle et

al. 1995).

3.4.7. Experimental methods

The growth trial was located in teaching greenhouses at the

Department of Environmental Biology, University of Guelph. It was

initiated January 25, 1999 and plants were harvested March 21,

1999, resulting in an growth period of 55 days.

At the stait of the trial, problems arose due to low solids content of

the sludge used and high doses of sludges at upper P application

rates. This resulted in a range of 0.15 to 2.3 L of liquid sludge

59

required per pot to provide the desired quantity o f P for different

treatments (Table 3.2). I t was necessary to first concentrate the

sludges by drying, to allow it to be mixed with the limited volume of

soi1 used (approximately 2 kg pot-'). The procedure was to weigh out

required volume of sludges for each application into Mason jars and

to dry thern a t 55OC until their consistency was sufficiently thick to be

manageable.

The plants were grown in 3 L plastic pots, filled approximately to

2.5 L level with soi1 (2 kg dry soi1 per pot), and sludge added to the

pot and mixed in with the top 5-10 cm of soil. Additional N and K

fertilizer was added both at the outset of the experiment as well as 2-

3 times during the trial. Mineral fertilizer (MF) treatments were

handled the same way. Watering was provided manually, 1-2 times a

day, using both the weight of the pots and an estimate of the

required water, to control quantity of water supplied (see section

3.5.1).

A t the time of hawest, plant material was cut just above the soi1

surface, weighed and put into paper bags. It was dried to a constant

weight a t 6S°C, and weighed again. Samples were ground to pass

1-mm sieve and analysed for total P using a standard rnethod

(Thomas et al. 1967). Quantification of P was carried out using a

Technicon Auto-Analyser (Technicon Instrument Corporation, 1973b).

Soil samples were taken from every treatment at the time of

harvest. Samples were taken from the upper layer of each pot in the

attempt to obtain samples representing application rate of P. Samples

were dried t o a constant weight and analysed for Olsen-P (Olsen et

al. 1954; Schoenau and Karamanos 1993) at the Soil and Nutrient

Lab, University of Guelph.

3.4.8. Data analysis

Data were analysed as a randomized complete block design, using

SAS statistical program (SAS Institute Inc. 1994). Statistical analysis

included analysis of variance (ANOVA) using the General Linear Model

procedure (GLM) available in SAS. Further analysis included contrasts

(SAS Contrast statement) to investigate possible categories o f sludge

in terms of P supplying capacities. Some of the cornparisons (anova,

t-test, etc.) and regressions were carried out using resources offered

by Microsoff Excel 97 program.

3.5. Results and Discussion 3.5.1. Plant growth

Throughout the process of the experiment plants were monitored

carefully for any kind of visual symptoms of deficiency or toxicity.No

indication o f any such symptoms could be determined but

occasionally growth seemed to be slowed temporarily during the trial.

This may have been a fact due to lack of water, as discussed

further later on in this section.

After five days following seeding, the first seedlings emerged and

germination proceeded vigorously in the following days. The initiation

of plant growth was therefore normal without any problems or visual

symptoms of toxic effects in sludge treatments compared to mineral

fertilizer or control treatments.

A t the time of harvest, plants were still growing actively and no

visual evidence of diseases or restrictions to growth were observed

on the plants. The plant roots showed some visual difference

depending on sludge rate. It seemed that higher doses of sludge

restricted downward penetration of roots. Apparently mots did not

penetrate beneath the lower level of sludge distribution in the pots.

Further, root growth of plants fertilised with mineral fertilizer was

more vigorous and more evenly distrïbuted throughout pots than

roots from sludge treatments. This observation was supported with

the fact that during the experiment it seemed that sludge applications

resulted in the formation of a dense clod of soil-sludge mixture,

especially at higher levels. This resulted in a gap forrning at the edge

of some pots creating problems with watering, where by applied

water would pass through this opening and be lost through the

bottom of the pots without being absorbed by soils or utilised by

plants. By applying water generously, an attempt was made to

ensure that the plants did not suffer from shortage of water. This

made controlled uniform watering to al1 pots become difficult as the

problem was a fundion of sludge application rate, it was not

encountered at lower rates of sludge, or with the mineral fertilizer or

control treatrnent.

3.5.2. Plant yield

Yield of ryegrass from sludge treatments varied but there was a

general increasing trend from the lowest to the highest application

rate (Fig. 3.1). The mineral fertilizer treatment gave higher yield at

al1 rates than did sludge treatments, which showed a gradual increase

in yield without great variations within P rate (Fig. 3.4). An overview

of data distribution and variability is given in Appendix Cf Table C3.

The relatively large yield difference between the control treatment

and the lowest P application rate (Fig 3.2), and modest increase for

higher rates, suggest that the application rates used in this trial were

relatively high. Possibly, a more gradual increase in yield would have

been observed i f the difference in P application between the control

treatment and the treatments receiving P was not as high (Le.

increase from O to 450 mg PZO5 pot-' between the control and the

iowest P application rate). The low available P in the soi1 used for the

experiment sets the lower limits for nutrient availability. By using soi1

63

with higher initial P level, as often is the case in growth trials, this

phenornenon would not have been observed and the application

levels chosen rnight have proven too low.

Attempts were made to discover any differences within sludge

treatments that might originate from production methods used for

generation of the sewage sludges selected in this study. Comparison

of yield between different sludge types shows differences based on

the production methods used (Fig. 3.3), although numerically they

are not far apart (Table CZ) . This difference is refiected in plant yield,

both within application rate as well as across increasing P rate (Fig.

3.5). The difference between characteristics of anaerobic and aerobic

sludges was evident from chemical analysis of the sludges and the

literature supports this observation as well.

3.5.3. Phosphorus concentration in plant tissue

The average P concentration in plant tissue was 1.7-2.2 g kg-' for

sludge treatments, depending on application rate (Table C3).

Corresponding number for mineral fertilizer treatment was 1.2-4.3 g

kg-'. Plants growing on soi1 having low available P and no added P

fertilizer (control) contained 1.3 g P kg-'. More detailed analysis of

data is given in Table C4, where it can be seen that data variance is

relatively great (expressed as CV). A high variation in nutrient

concentrations in ryegass has been documented (Kelling and

64

Matocha 1990). Other possible reasons for the variability might

be effects from management of the growth trial o r environmental

variability in the green house. These explanations seem unlikely, as

the variation does not follow any pattern that can be related to

arrangement of pots, and management pradices were uniform

throughout the whole experiment.

Concentration of P as a function of sludge treatment was relatively

consistent for al1 categories, showing only a gradua1 rise between

application rates (Fig. 3.6). This was even more evident for the

mineral fertilizer treatment which showed a consistent rise in P

concentration as fertilizer application increased, except for lowest

application rate. A t the first two P rates, tissue concentration is

similar to sludge treatments, but at the three highest application

rates, tissue P concentration is higher than for any sludge treatment.

There is no obvious explanation for this, but it may be related to

differences in thé ability of sludges and minerai fertilizer to supply P

to plants.

3.5.4. Phosphorus uptake

By using the yield data of ryegrass and results of P concentration in

plant tissue, it is possible to estirnate total uptake of P from sludges

and mineral fertilizer used in the growth trial.

When examining the data from each treatment showing P

uptake as a function of application rate, it seems that variation was

high and response to increased nutrient rate was not consistent

(Table CS; Table C6). Whether al1 sludge treatments are grouped

together, or sludge type categories are used, it is evident that the P

uptake exhibited an increasing trend that may be expected for plants

at increasing levels of nutrients (Fig. 3.7; Fig. 3.8).

The drop in uptake a t the highest level(s) of sludge treatments is

likely due to some negative effects from sludges at high rates, or it

may be due to watering problems as discussed earlier. Hani et al.

(1996) observed negative effects of sludge application to soils. Their

conclusion was that often such effects might be related to metal

content of sludges. I n this study, the sludges used met the Ontario

guidelines for metal content as they came from facilities where land

application was practiced. Even so, the relatively high doses of

sludges used in the pot trials compared to field application rates may

have lead to accumulated metal content in the pots. The soluble salt

content of the sludges rnay also have contributed to restricted growth

at higher doses. Rodgers and Anderson (1995) suggested soluble

salts might cause toxic effects to plants at high levels of sewage

sludge application and could have caused restricted growth in trials

where sewage sludge was used. Effects of precipitants used for

removal of P are not likely to have affected plant growth. Ippolito

et al. (1999) did not find any toxic effects or elevated plant content

from use of alum as a precipitant in sludge generation.

Calculation of total P uptake leads to somewhat different findings

for mineral fertilizer treatment compared to sludge treatments. There

is not a significant difference between these two at lower levels, and

actually there seems to be a trend of reduced uptake of P from

mineral fertilizer source compared to the pooled sludge treatments

(Fig. 3.8). However at the two highest levels, uptake from the MF

treatment is 2.5 times higher than that of the sludge treatments (Fig.

3.7).

The difference observed earlier, between the properties of

anaerobically and aerobically digested sludge is also evident in

differences in uptake of total P in these categories. P availability from

anaerobically digested sludge is higher than that of aerobically

digested except at the highest level of application (Fig. 3.7).

I n contrast, somewhat different effects of application rate on P

uptake were observed. There is a difference in uptake between

sludge types in both quantity taken up and in patterns of plant

upta ke. Availa bility of P from aerobically digested sludge increases a t

the highest levels while anaerobic sludges show decreased uptake a t

rates greater than 900 mg PzOs pot-' (Fig. 3.8).

Uptake of P in this experirnent can be reasonably well-

explained by linear fundions (Fig. 3.9; Fig. 3.10). The correlation

coefficient for P uptake from sludges is relatively high if atl sludge

treatments are pooled ($10.71; Pc0.05) but part of the variability

can be explained by different characteristics of sludge types. By

separating sludge treatments into anaerobic and aerobic sludge

categories it c m be seen that the aerobic sludges follow a linear

function of P release more so than do anaerobic sludges (r2=0.92;

P < 0 . 0 1 vs. ?=0.56; ns at PS0.05). When a parabolic function was

applied to the data from anaerobic sludges, a much higher correlation

coefficient can be obtained (?=0.99). This may be due t o some

growth inhibiting factors, present to a different degree in sludges,

depending on generation method. Anaerobic sludges, analysed in this

study, showed significantly higher condudivity than did aerobic

sludge (Table 2.4). Therefore, high levels of soluble salts may have

contributed to this difference in P uptake between sludge categories.

This difference is visible both in yield and tissue concentration, but

more so in tissue concentration than yield (Fig 3.5; Fig. 3.6).

3.5.5. Phosphorus availability

When P uptake is estimated as a percent of applied P, the sludge

treatments show steadily decreasing uptake while the mineral

fertilizer treatment exhibits a more erratic pattern (Fig . 3.11). Pooling

68

al1 sludges, P availability ranges from 2 to 6% of total sludge P

applied (Table 3.3). The literature on similar greenhouse studies

reports varying recovery of P. Coker and Carlton-Smith (1986)

reported that relative availability of P from digested sludge was 60%

of that in superphosphate. The uptake of P from digested sludge by

spinach plants was 5-8O/0 of applied P. The NaHC03 extractable P

from sludge was far lower than the uptake by plants. Gestring and

JarreIl (1982) found P uptake by chard to be as good from sewage

sludge as MCP. They discussed the possibility of organic compounds

in the sludges competing with P for retention sites, enhancing the

availability of sludge P to plants. Organometallic phosphates may

have been present and their relatively high mobility may have

affected the availability of P from sludge as compared to mineral

fertilizer P. In a study on P availability in sewage sludge compost,

McCoy et al. (1986) found 0.2-1.0% of total P to be available, as

opposed to 3.5-11.0% from triple superphosphate. The results from

the literature are therefore similar to those obtained in our study

taking into consideration differences in sludge types and experimental

designs.

The percent recovery of P supplied by anaerobic sludges shows a

very high correlation (r2=0.99; P<0.001) with applied P, while

aerobic sludges show correlation to a lesser degree (r2=0.72; ns at

PSO.05) with applied P, as shown in Fig. 3.13. The recovery of P

from al1 sludges can be reasonably well described by a first order

equation having a correlation coefficient of 0.97 (Pc0.01) between

application rate and uptake.

Availability of P from mineral fertilizer treatment failed to show a

linear relationship with application rate. There is some inconsistency

in uptake with increasing application rate as shown in Fig. 3.12, but

in general the plant P availability from MCP seems higher than sludge

P. A t the lower rates of application rate the relative availability is

comparable between the MF and sludge treatments (Table 3.3). As

the application rate increased, the availability of sludge P decreased

while MCP availability was relatively stable. Part of this difference can

be explained by varying availability of P from sludges and mineral

fertilizer. The pool of readily available P in sludges may have been

more or less exhausted by plant uptake during the trial while

solubility from mineral fertilizer P is essentially 100% in water and

therefore readily plant available. I t has been indicated that the solid

part of sludges may absorb labile P and render it unavaiiable t o plants

(Cox et al 1997). They added both mineral fertilizer P and sewage

sludges at varying rates to soils and observed decreased P availability

with increased sludge application. The P fixing capacity of soils is

known to reduce P availability to a varying extent. I n this study,

potential P fixation by the soi1 should not have affected

treatments differently, as time was allowed for these reactions to

take place after sludge and fertilizer application and before plants

were seeded.

Application of results from pot experiments to field conditions can

be dif icult because of differences in environmental conditions. The

quantity of sludges applied in pot experiments is generally higher

than that applied in the field. I f cornmon conversions are used, the

lowest P application rate in this pot trial is similar to what could be

expected under Ontario management practices for sludge application

to agricultural land (Table 83; Table 2.6). At this rate, the recovery

(availability) of applied P was similar for sludges and mineral fertilizer

(Table 3.3; Fig. 3.7). The reason for decreasing availability of P from

sludges a t higher levels (Table 3.2) may be due to some physical or

chemical effects from the complex matrix of organic and inorganic

constituents in sludges as discussed above.

3.5.6. Soil extractable phosphorus

Effects of P loading rate from sludge and minera1 fertilizer were

reflected in increasing quantity of NaHC03 extractable P in the soi1

used in this trial (Fig. 3.13). All treatments showed a consistent

increase with increasing application rate, although varying somewhat

between sludges. The mineral fertilizer treatment resulted in 10-15

times greater extractable P than did sludge treatments (Table

C7), a phenornenon which has been observed in other trials. Gestring

and Jarrell (1982) observed consistently greater extractable P

(NaHCOs) from monocalciumphosphate (MCP) than sludge

treatments, the same effects as observed here. Gestring and Jarrell

observed only minor increases in soi1 extractable P from sludge

treatments. Here, 6 times more P was extracted from the highest

sludge application treatment than control treatrnent. The low initial

extractable P levels (2 mg kg-') in the soi1 used for this experiment

make even small changes appear relatively large nevertheless, the

general trend seems to be the same in this study as in reported

findings. Cox e t al. (1997) observed decreased extractable P (M-1)

when sludge was applied, but some increase from fertilizer P. In a

study of composted sewage sludge, McCoy et al. (1986) found a good

correlation between application rate and extractability of soi1 P

(NaHC03). Minerai fertilizers resulted in a somewhat higher quantity

extracted than composted sludge. Some authors have pointed out

differences in effects on soi1 P depending on P source, which may help

to explain differences between sludge and mineral fertilizer effects

found in this study. Folle et al. (1995) found that sludge and mineral

fertilizer addition significantly increased soi1 extractable P (M-1, Bray

Pl ) . Sludge application further increased Ca-P and Fe-P in the soil,

while the mineral fertilizer added primarily to the AI-P pool but

also to the Fe-P pool. Otabbong (1997) observed higher NaHC03

extractable P in soils amended with sewage sludge than in untreated

soil. He found most o f the additional P from sludge to be on a

inorganic form while the organic fraction in the soil remained

relatively stable. Soon et al. (1978) found sludge application increase

NaHCO3 extractable P, but to a lesser extent from alum sludge as

compared to calcium or iron sludges.

The increase in soi1 extractable P with higher application rates

suggests increasing risk of P losses under field conditions. P has been

shown to move in soil a t a low rate and erosion can also result in P

losses from soil. Magdoff e t al. (1999) argued that runoff water with

dissolved P>1 mg L-' would be rare under normal condition, as soi1

extractable P is not reflected well in P concentration of soi1 water.

Soon and Bates (1982) concluded that up to 2500 kg Pz05 ha-' from

alum treated sludge could be added to soils before NaHCO3

extractable would reach unacceptable levels (60 mg kg-') in the soil.

More Iikely, under some circumstances, P losses through soi1 erosion

may be a source for P transfer and subsequent effects on the

environment.

I n this study sornewhat different results were obtained by

separately assessing aerobically and anaerobically digested sludge,

especiall y at higher levels. Although the release pattern between

sludge categories was similar, extractability from anaerobic sludges

was greater, especially a t higher levels of application (Fig. 3.13).

The relationship between loading rate and extractability of P can be

descri bed by linear models with high correlation coefficients (Fig . 3.14). I f al1 sludges are pooled together correlation coefficient found

is 0.98 (P<0.001). Aerobically digested sludges lag behind anaerobic

sludges in slope, but both categories fit linear regression well as the

correlation coefficients indicate (r2=0.92, P<0.01 vs. ?=0.97,

P<0.001 respectively). The same is evident for mineral fertilizer

effects on extractability (?=0.90, Pe0.01) although the quantity

extracted is an order magnitude higher than that from sludge

treatments (Fig. 3.15).

3 .6 . Conclusions Sludge type and application rate significantly affected yield, tissue

concentration, and uptake of P by ryegrass (Lolium perenne L.).

Relative P availability varied with application rate but was comparable

to findings of similar experiments reported in the literature. Residual

effeds of sludge application rate and type on Guelph loam soi1

bicarbonate extractable P was also significant.

Plant P uptake showed a significant linear correlation with

application rate, especially for aerobically digested sludges. P

74

availability from sewage sludge, as a function of application rate,

was also exptained by a significant linear relationship.

A difference between sludge types was observed as a function of

both quantity of P supplied to plants (tissue concentration) and in

plant response to application rate (yield). The uptake of P from

aerobically digested sludge followed a linear model, while parabolic or

other models might be more appropriate for anaerobically digested

sludge. Further studies are necessary to determine if different P

management strategies are necessary for these two categories o f

sludge as is now practised for N in the Ontario management

guidelines for sludge application to agricultural land.

The availability of sludge P in this experiment was closely related to

application rate. Results of similar experiments reported in the

literature support the findings of this study. The current estimate

used in Ontario for availability of P from sludge may underestimate P

availability compared to results obtained in this greenhouse

experiment.

Residual effects of sludge on P in soi1 are evident using the Olsen

method. Under field conditions a risk of P loss would increase at

higher sludge application rates, especially if erosion of soi1 would

occur.

Table 3.1. Selected properties of Guelph loam soi1 used for qrowth experiment

Sand Silt Clay O.M. NaHC03-P PH O10 mg kg-'

Table 3.3. Percent recovery of applied P in pot experiment by treatment categories

Rate All sludge Anaerobic Aerobic Min. fert. mg Pz05 pot-' O/O P recovered

Fig. 3.1. Sewage sludge P application rate effects on growth of ryegrass (Lolium perenne L.) at rates of 450, 900, 1350, 1800, and 2250 mg P2O5 pot-' growing in Guelph loam soi1

79

Fig. 3.3. Effects of three different sludges applied at the same P rate (450 mg P2O5 pot-') on growth of ryegrass (Lolium perenne L.)

81

900 1350 1800 2250

P application rate (mg P2O5 pot-')

Fig. 3.4. Yield of ryegrass (Lolium perenne L.) using sewage sludges and MCP as P sources at different levels. Control y ield subtracted. Bars represent standard error (s,.,)

1 ' r --,--------- 1 1

, ! A . . A A A I I A A A - - " . . " V W V " V V

450 900 1350 1800 2250

P application rate (mg P205 pot")

-- - .

i3 All Q An

Aer El Min -- - --

Fig. 3.7. P uptake by ryegrass (Lolium perenne L.) using sewage sludge and MCP as P sources at different rates. Bars represent standard error (s,,,)

Anaeroblc (a) : y = 20.7 + 0 . 0 2 ~

R~ = 0.56 (ns at P<0.05)

y = 0 . 0 2 ~ + 10.45 Anaerobic (b) : R2 = 0.92 y = 5.6 + 0 . 0 7 ~ -0.00002~2 (P<O.Ol) R2 = 0.99

An i Aer

.

P Application rate (mg P205 pot-')

Fig. 3.10. P uptake by ryegrass (Lolium perenne L.) as affected by rate of application of different types of sludges

88

4. General conclusions

4.1. General conclusions It is clear that the potential agronomie value of sewage sludges is

substantial but there is also risk of negative effects if they are

improperly managed. Therefore it is important to maximize the

quality of the product that results from the purification of sewage

waters, namely sewage sludge. Assuming that this can be

accomplished, good management practices are the best strategy to

ensure that the hurnans, animals, and the environment are not a t

risk from sewage sludge inputs to soils.

I n this study, sludges proved to have high quantities of N and P but

lower K content. Other properties varied but some showed relatively

high values. Variation between sludges was also considerable for

most properties determined. High conductivity readings indicated the

need to investigate the impacts of soluble salt content in sewage

sludge on soils and plant growth at high application rates.

Applying sludges a t rates recommended in Ontario management

guidelines for sludge will result in varying loads of total P. The total

sludge P contents found in this study may indicate that accumulation

of P in soils may result from sewage sludge application. Guidelines for

sludge application rate do not adjust for variation in sludge P

contents, and subsequent fertilizer plans only indiredly recognize the

nutritional value of P present in sludges.

95

In a growth study sludges proved to be a good source of P for

plant growth. The difference observed between sludge types, which

was also noted during analysis, was refleded in somewhat higher P

upta ke for anaerobically digested sludges compared with aerobically

digested. Actual P uptake ranged from 2 to 6% of applied total P,

depending on application rate and sludge type.

Application rate of sludge P affected soi1 extractable P, measured

by the Olsen method. A significantly greater quantity of P was

extracted as application rate increased. There was also some

difference according to sludge type, again with more favourable

results for anaerobic sludges.

Linear models proved to explain the rdationship between

application rate of sludge P and most of the depended variables,

including plant P uptake, P availability, and soi1 extractable P.

4.2. Further research In order to further understand the underlying rnechanisms for

availability of P from sewage sludge additional research is needed.

Field studies are necessary to verify the findings in this pot

experiment under field condition, especially P availability.

Identification of pools of varying chernical forms and subsequent

availability in agronomic terms as well as biological impacts is also of

prime interest. That would enhance understanding of the effects, P in

96

sludges is likely to have on plants, soils, and the environment in

general. Investigation of the transformation and effects on soi1 P after

application is also important to enable qualitative as well as

quantitative management o f land application of sewage sludge. Other

sludge effects may also need to be studied more closely. For

instance, hig h electrical conductivity can, high application rate, affect

soils and plants negatively.

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Appendix A

Wastewater treatment

Sludge is generated as a product of the sewage water purification

process. The following text is a description of major steps involved in

wastewater purification and subsequent biosolids generation at waste

water treatment plants (Sources: Anonymous 1999a; Anonymous

1999b; Rhyner et. al 1995).

1. Plant Influent: Waste water enters the treatment facility

through the municipal sewer systern.

II. Coarse Bar Screen: When wastewater first enters a treatment

plant it passes through screens to remove pieces of wood, rock,

cloth, plastic and other objects. Most of these screenings are ground

up and returned for further processing. Anything that cannot be

ground up is taken to a landfill.

III. Gr i t Removal: The wastewater is then pumped into a series

of tanks. First, air is pumped through the water, suspending the

lighter, organic materials while the small, dense particles, called grit,

settle to the bottom. Grit, which is mostly sand and coffee grounds, is

pumped out of the tanks and taken to a landfill.

IV. Primary treatment: The wastewater flows into large settling

tanks, which allows suspended solids and organic material to sink t o

110

the bottom of these tanks. The raw sludge that settles t o the bottom

of these tank is removed and sent through a separate process of

sludge treatment.

V. Tertiary treatment, a: Partially treated wastewater is drawn

from the top o f the settling tanks and chemicals are added to remove

nutrients and solids if needed.

VI. Secondary treatment: In large aeration tanks, the partially

treated wastewater is mixed with oxygen to facilitate baderia growth.

The bacteria break down organic material and assimilate nutrients

from the solution.

VII. Tertiary treatment, b: The cleanest wastewater is drawn

from the top o f the aeration tanks. At this stage the water is already

quite clear, but chemicals or polymers may be added to concentrate

any remaining material. Once again, suspended particles settle to the

bottom and are removed to the sludge treatment process.

VIII. Disinfection: After final stages of treatment, water is

disinfected with chlorine or ultra-violet light to kill pathogenic

organisms.

IX. Water purity: Before the treated water is returned to the

environment, it is tested to ensure it meets provincial standards for

clarity.

X. Sludge thickening: Sludge removed at various stages of the

wastewater treatment process is initially treated to increase solids

content. This can be accomplished by settling in tanks but sometimes

biological, chernical, or physical treatment is also needed.

Xf. Sludge digestion: After the initial thickening process, sludge

is treated for 20-30 days in large, heated and enclosed tanks. Here,

bacteria break down (digest) the material, reducing its volume by

half. Digestion also significantly reduces odours and disease-

producing organisms, therefore this process is also referred to as

'stabilising ' the sludge.

XII. Dewatering Process: Vacuum filter, belt presses, or

centrifuge systems remove water from the processed sludge to

thicken it.

X I I I . Sludge disposal: The concentrated sludge, or biosolids, is

taken away for incineration, landfill, or land application.

Wastewater

PREUMINARY TREATM ENT

-phpical

PRIMARY TREATMENT

-physicaI -chernical

v Screening and grit removal

SECONDARY TREATMENT

- biological

Screenings and grit to landfill

TERTIARY TREATM ENT

-chernical -phpical

Sediment- ation

Activated Sludge thickening

sludge By dissolved air notation

Pnmary sludge thickening by

gravity b

Nutrient Removal Sludge thickening (N and P)

O

to a water course

- Sludge stabilization

. Biosolids for dis~osai

Chlorine UV radiation

Fig. Al. Processes involved in sewage water treatment and subsequent biosolids generation a t waste water treatment plants (after Rhyner et.al 1995).

v Sludge dewatering

v b Effluent discharged

Appendix B

Table 81. Plan of growth experiment

Factors Levels S2 S3 S4 SS S6 S7 S9 SI0 SI2 MF C

Table 82. Treatment codes, P application levels, and size of experiment

Codes P-levels Reps. # of pots

. .

Total 138

Table 83. P application rate per pot, and per ha equivalents -g pot-' mg kg-' soil* kg ha-'"

P pz05

200 458.4 229.2 458.4 400 916.8 458.4 916.8 600 1375.2 687.6 1375.2 800 1833.6 916.8 1833.6 1000 2292.0 1146.0 2292.0

* Approximately 2.0 kg soi1 pot'' ** 1 mg fertilizer per kg soi1 in pot is equivalent to 2 kg fertilizer per hectare in the field (furrow layer of soi1 equals 2,000,000 kg ha'', 1300 kg m'3, 0.15 m depth)

Table 84. Seeding rates in pots and per ha eauivalents

Seeding rate mg pot‘' mg cm-2 kg ha-'

50.9 0.2 20 76.4 0.3 30 101.8 0.4 40 127.3 0.5 50 152.7 0.6 60 178.2 0.7 70 203.6 0.8 80 229.1 0.9 90 254.5 1.0 100 381.8 1.5 150 509.0 2.0 2 0 0 ~ ) 1018.0 4.0 400

a) Recommended seeding rate for perennial ryegrass (Lolium perenne L.) is 15-20 kg ha-' b) 1 ha is equivalent to 100.000.000 cm2 c) 20 kg ha-' = (20 kg ha-' x 1000 g kg-' x 1000 mg g-l) / (100.000.000 cm2 ha-') = 0.2 mg d) Each pot is 7 inches (18 cm) in diameter giving surface area of g2*z= 254.5 cm2 e) The choice is approximately 0.5 g per pot (-200 kg ha") for this experiment

Window &\\\\\\\\\\\\\\V\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\U,\\\\\\\\\\\\\\\\\\\N\\\\\\\\\\\\\\W~\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\N\\\\\\\\\\\\\\\\\\\V

Walkway

Fig. 61. Arrangement of pots on greenhouse bench and its surroundings

Appendix C

Table Cl. Yield of ryegrass (Lolium perenne L.) using 9 different sludges and mineral fertilizer a s P sources at varying application rates in a qreenhouse pot experiment

Rate S2 S3 S4 S5 S6 S7 S9 SI0 SI2 MF

Table C2. Yieid of ryegrass (Lolium perenne L.) using different sludges as P sources at varying application rates in a greenhouse pot experirnent. Data characteristics by sludge cateqories

Applic. rate Average Median Minimum Maximum St. dev. C.V. (O/O)

mg Pz05 pot-' g pot-'

All sludge (n=9)

Anaerobic sludge (n=6) 450 8.8 8.7 6.8 10.8 1.4 16.2 900 10.0 10.0 8.5 11.9 1.1 11.2 1350 10.5 10.7 8.2 12.2 1.4 13.0 1800 10.5 10.6 8.6 11.8 1.2 11.7 2250 10.2 9.6 8.6 13.2 1.8 17.6

Aerobic sludge (n=3) 450 6.3 5.8 4.9 8.3 1.8 27.9 900 7.1 6.7 5.8 8.9 1.6 22.0 1350 8.2 8.8 6.7 9.3 1.4 16.8 1800 9.7 10.5 7.3 11.4 2.2 22.1 2250 9.9 10.6 7.7 11.4 1.9 19.5

Table C f . P concentration in ryegrass (Lolium perenne L.) tissue using 9 different sludges and mineral fertilizer as P sources at varying application rates in a qreenhouse pot experiment

Rate S2 S3 S4 S5 S6 S7 S9 SI0 512 MF

Table C4. P concentration in ryegrass (Lolium perenne L.) tissue using different sludges as P sources at varying application rates in a qreenhouse pot experiment. Data characteristics by sludqe cateqories

Applic. rate Average Median Minimum Maximum St. dev. C.V. (%)

mg pz05 pot-' 9 kg-'

All sludge (n=9) 450 1.67 1.84 0.15 2.35 0.68 40.8 900 2.04 2.18 1.04 2.72 0.59 29.1 1350 2.21 2.33 0.47 3.18 0.84 37.9 1800 2.24 2.13 0.67 3.15 0.76 33.8 2250 1.98 1.88 0.61 3.38 0.76 38.6

Anaerobic sludge (n=6) 450 1.67 1.78 0.15 2.35 0.80 48.1 900 2.14 2.28 1.04 2.72 0.63 29.4 1350 2.24 2.54 0.47 3.18 0.97 43.3 1800 2.17 2.26 0.67 2.97 0.84 38.8 2250 1.91 1.83 0.61 3.38 0.92 48.2

Aerobic sludge (n=3) 450 1.67 1.86 1.11 2.03 0.49 29.4 900 1.84 2.09 1.18 2.25 0.58 3 1.3 1350 2.16 2.17 1.48 2.84 0.68 31.4 1800 2.37 2.12 1.84 3.15 0.69 29.1 2250 2.11 1.88 1.87 2.60 0.42 19.8

Table CS. P uptake by ryegrass (Lolium perenne L.) tissue using 9 different sludges and mineral fertilizer as P sources at varyinq application rates in a qreenhouse pot experiment

Rate S2 S3 S4 S5 S6 S7 S9 SI0 SI2 MF

Table C6. P uptake by ryegrass (Lolium perenne L.) tissue using different sludges as P sources a t varying application rates in a greenhouse pot experiment. Data characteristics by sludge

- - - - - - - - - - - - - -

Rate Average Median Minimum Maximum St. dev. C.V. (%)

mg PzOs pot-'

All sludge (n-9) 450 30.7 32.3 3.3 57.0 15.9 51.8 900 42.9 41.6 22.6 74.0 18.0 41.9 1350 49.1 43.7 12.1 88.5 22.5 45.9 1800 51.4 51.1 18.1 78.3 17.1 33.3 2250 46.7 46.0 18.4 87.8 18.5 39.6

Anaerobic sludge (n=6) 450 33.3 35.5 3.3 57.0 18.2 54.5 900 49.9 49.5 22.6 74.0 18.1 36.3 1350 53.8 55.2 12.1 88.5 26.7 49.5 1800 51.7 50.1 18.1 78.3 21.6 41.8 2250 45.1 40.0 18.4 87.8 23.1 51.1

Aerobic sludge (n=3) 450 25.3 26.9 13.7 35.3 10.9 43.0 900 28.9 27.9 24.1 34.6 5.3 18.5 1350 39.6 43.5 31.5 43.7 7.0 17.6 1800 50.7 51.1 48.2 52.9 2.4 4.7 2250 49.9 49.1 46.0 54.5 4.3 8.6

Table C7. NaHC03 extractable P in Guelph loam soi1 as affected by 9 different sludges and mineral fertilizer used as P fertilizers at varying application rates in a qreenhouse pot experiment

Rate S2 S3 S4 S5 S6 S7 S9 SlO SI2 MF mg P205 pot-' mg P kg-'

O 3.0

450 7.0 3.0 3.0 3.0 4.0 10.0 4.0 8.0 7.0 47.0

900 9.0 7.0 16.0 8.0 7.0 14.0 12.0 13.0 7.0 123.0 1350 O 6.0 20.0 9.0 7.0 17.0 11.0 16.0 4.0 209.0 1800 20.0 8.0 13.0 7.0 18.0 17.0 17.0 17.0 10.0 305.0 2250 28.0 15.0 32.0 8.0 31.0 18.0 14.0 10.0 11.0 252.0

Table C8. NaHC03 extractable P in Guelph loam soi1 as affected by different sludges used as P fertilizers at varying application rates in a greenhouse pot experiment. Data characteristics by sludge cateqories

Rate Average Median Minimum Maximum St. dev. C.V. (%)

mg Pz05 pot-' mg P kg-'

All sludge (n=9) 450 5.4 4.0 3.0 10.0 2.6 47.8

900 10.3 9.0 7.0 16.0 3.5 33.5 1350 11.2 11.0 4.0 20.0 5.4 48.4

Anaerobic sludge (n =6) 450 5.2 4.0 3.0 10.0 2.8 53.9 900 O 10.5 7.0 16.0 3.6 32.5 1350 12.5 11.0 7.0 20.0 5.0 39.8 1800 15.3 17.0 7.0 20.0 4.7 30.5 2250 21.8 23.0 8.0 32.0 9.9 45.5

Aerobic sludge (n=3) 450 6.0 7.0 3.0 8.0 2.6 44.1 900 9.0 7.0 7.0 13.0 3.5 38.5 1350 8.7 6.0 4.0 16.0 6.4 74.2 1800 11.7 10.0 8.0 17.0 4.7 40.5

2250 12.0 11.0 10.0 15.0 2.6 22.0

Appendix D

I n this appendix, calculations from SAS statistical program are

presented. ANOVA (general linear Procedure) calculation were done

on data for plant yield, tissue concentration, and P uptake. It was not

possible to include al1 three variables in one model. Therefore the

effects of sludge generation method (anaeroblc sludge vs. aerobic

sludge) are estimated separetely. Similarly interaction could not be

investigated due to limited number of degrees of freedom.

D.1. Yield

General Linear Modefs Procedure

Class Level Information

Class Levels Values

RATE 5 450 900 1350 1800 2250

SLUDGE 9 SI0 SI2 S2 53 S4 S5 S6 S7 S9

TYPE 2 AerAn

Number of observations in data set = 45

Dependent Variable: YIELD

Source DF

Model 12

Error 32

Corrected Total 44

Source

RATE

SLUDGE

Source

RATE

SLUDGE

Sum of Squares

118.93700444

33.22642667

lS2.16343111

C.V.

10.82131

Type 1 SS

31.14445333

87.79255111

Type III SS

31,14445333

87.79255111

Mean Square F Value Pr > F

9.91141704 9.55 0.0001

1 .O3832583

Root MSE YIELD Mean

1.01898274 9.41644444

Mean Square F Value Pr > F

7.78611333 7.50 0.0002

10.97406889 10.57 0.0001

Mean Square F Value Pr > F

7.78611333 7.50 0.0002

10.97406889 10.57 0.0001

Class Levels Values

RATE 5 450 900 1350 1800 2250

SLUDGE 9 SlO SI2 S2 S3 S4 S5 S6 S7 S9

TYPE 2 Aer An

Number of observations in data set = 45

Dependent Variable: YIELD

Source DF Sum of Squares

Model 1 29.60693778

Error 43 122.55649333

Corrected Total 44 152.16343111

Source

TYPE

Source

TYPE

R-Square C.V.

O. 194573 17.92863

Mean Square F Value Pr > F

29.60693778 10.39 0.0024

2.85015101

Root MSE

1.68823903

YIELD Mean

9.41644444

DF Type 1 SS Mean Square FValue Pr > F

1 29.60693778 29.60693778 10.39 0.0024

DF Type III SS Mean Square F Value Pr > F

1 29.60693778 29.60693778 10.39 0.0024

D.2. Tissue concentration

General Linear Models Procedure

Class Level Information

Class Levels Values

RATE 5 450 900 1350 1800 2250

SLUDGE 9 Si0 SI2 S2 S3 S4 S5 S6 S7 S9

TYPE 2 Aer An

Number of observations in data set = 45

Dependent Variable: CONC

Source DF

Model 12

Error 32

Corrected Total 44

Source DF

RATE 4

SLUDGE 8

Source DF

RATE 4

SLUDGE 8

Sum of Squares

O. l48595S6

0.08472889

0.23332444

C.V.

25.11437

Type 1 SS

0.01819111

O. 13040444

Type III SS

0.01819111

O. 13040444

Mean Square F Value Pr > F

0.01238296 4.68 0.0002

0.00264778

Root MSE CONC Mean

0.05145656 0.20488889

Mean Square F Value Pr > F

0.00454778 1.72 O. 1704

0.01630056 6.16 0.0001

Mean Square F Value Pr > F

0.00454778 1.72 0.1704

0.01630056 6.16 0.0001

General Linear Models Procedure

Class Level Information

Class Levels Values

RATE S 450 900 1350 1800 2250

SLUDGE 9 SI0 SI2 S2 S3 54 SS S6 S7 S9

TYPE 2 Aer An

Number of observations in data set = 45

Dependent Variable: CONC

Source DF Sum of Squares Mean Square F Value Pr > F

Model 1 0.000 13444 0.00013444 0.02 0.8756

Error 43 0.23319000 0.00542302

Corrected Total 44 0.23332444

R-Square C.V. Root MSE CONC Mean

0.000576 35.94201 0.07364118 0.20488889

Source

TYPE

Source

TYPE

DF Type I SS Mean Square F Value Pr > F

1 0.00013444 0.00013444 0.02 0.8756

DF Type III SS Mean Square F Value Pr > F

1 0.00013444 0.00013444 0.02 0.8756

P uptake

Generaf Linear Models Procedure

Class Level Information

Class Levels Values

RATE 5 450 900 1350 1800 2250

SLUDGE 9 SI0 SI2 S2 S3 S4 S5 S6 S7 S9

TYPE 2 Aer An

Number of observations in data set = 45

Dependent Variable: UPTAKE

Source DF

Model 12

Error 32

Corrected Total 44

Source

RATE

SLUDGE

Source

RATE

SLUDGE

Sum of Squares

23.17777778

7.52992000

30.70769778

C.V.

25.18918

Type 1 SS

4.56372000

18.61405778

Type III SS

4.56372000

18.61405778

Mean Square F Value

1.93148148 8.21

0.235310

Root MSE UPTAKE Mean

0.48508762 1.92577778

Mean Square F Value Pr > F

1.14093000 4.85 0.0036

2.32675722 9.89 0.0001

Mean Square F Value Pr > F

1.14093000 4.85 0.0036

2.32675722 9.89 0.0001

General Linear Models Procedure

Class Level Information

Class Levels Values

RATE 5 450 900 1350 1800 2250

SLUDGE 9 SI0 512 S2 S3 S4 S5 56 S7 S9

TYPE 2 Aer An

Number of observations in data set = 45

Dependent Variable: UPTAKE

Source DF Sum of Squares Mean Square F Value Pr > F

Model 1 1.18795111 1.18795111 1.73 0.1953

Error 43 29.51974667 0.68650574

Corrected Total 44 30.70769778

R-Square C.V. Root MSE UPTAKE Mean

0.038686 43.0245 1 0.82855642 1.92577778

Source

TYPE

Source

TYPE

DF Type 1 SS Mean Square F Value Pr > F

1 1.18795111 1.18795111 1.73 0.1953

DF Type III SS Mean Square F Value Pr > F

1 1.18795111 1. 18795111 1.73 0.1953