ENGI 9605 – Advanced Wastewater Treatment

Winter 2011 Faculty of Engineering & Applied Science

Chapter 1: Introduction

1

(1) Source of wastewater flowsDomestic discharges from residential,

commercial, and institutional facilitiesIndustrial discharges from different

industriesInfiltration groundwater seepage that enters

sanitary sewer through cracks in pipe joints and manholes

Inflow water that enters through drains which is relatively unpolluted source of water

Storm water runoff from rain

Municipal wastewater 2

1.1 Wastewater flows

3(Viessman

et al., Water supply and pollution control, 2009)

4

Pollutants in domestic wastewater

(Tchobanoglous

et al., Wastewater Engineering, 2003)

5

(2) Wastewater sewer system

receive liquid wastes from the city buildings, houses, institutions, and other entities) and transport them to the treatment plant

consists of the collection pipes and appurtenances, such as manholes, pumping stations, and others

6

Types of sewer systemsSanitary Sewer carries domestic, industrial, and infiltration/inflowStorm Sewer carries storm waterCombined Sewer carries both

Sources of municipal wastewater in relation to collector sewers and treatment(Hammer, Water and Wastewater Technology, 2004 )

7

Protect surface-water qualityProtect public healthMeet legal requirements

(1) Why treat wastewater?

How to evaluate water quality?

Obtain wastewater characteristicsCompare them with water quality standards

8

1.2 Wastewater characteristics

(2) Physical characteristics

Total solids (TS) residue left in a drying dish after evaporation of a sample of water or wastewater and subsequent drying in an oven

Solids

(Viessman

et al., Water supply and pollution control, 2009)

9

Total suspended solids (TSS) nonfilterableresidue that is retained on a glass-fiber disk after filtration of a sample of water or wastewater

Total dissolved solids (TDS) = TS - TSS

(Viessman

et al., Water supply and pollution control, 2009)

10

important in assessing the effectiveness of treatment processes (e.g., secondary sedimentation, effluent filtration, effluent disinfection)

Particle size distribution

(Tchobanoglous

et al., Wastewater Engineering, 2003)

Analytical techniques applicable to particle size analysis of wastewater contaminants 11

Turbidity determinationNephelometer scattering of light from particlesTurbidimeter interference to light passage in a

straight lineNTU is commonly usedSamples with turbidities > 40 NTU must be diluted

Turbidity Result of interference of passage of light through the water containing suspended materials

normally used for process control

12

Schematic diagram of a turbidimeter

and a nephelometer

(Zhang, Chemistry for Environmental Engineering, 2005 )

13

Apparent color caused by suspended matter determined on the sample “as is”True color caused by colloidal vegetable or organic extracts remove suspended matter by centrifugation then determine color of clarified liquid1 standard unit of color

= 1 mg/L of Pt (as K2

PtCl6

)Nessler tubes 0 ~ 70 color units

Color-comparison tubes (Nessler

tubes)

Color used along with composition and concentration in describe wastewater refers to the age of wastewater

(Zhang, Chemistry for Environmental Engineering, 2005 )14

Temperature has important effects on chemical reactions and reaction rates, aquatic life and the suitability of the water for beneficial uses

Temperature of wastewater normally higher than that of the local water supplyWithout treatment river and lake water that has been artificially warmed can be considered to have undergone Thermal PollutionGas solubility decreases with increasing temperature

warm water contains less oxygen than cold waterOptimum temperature for biological activity 25 ºC to 35 ºC

15

Estimation of temperature effects on reaction rates

Thus, if we know θ and K1

at temperature T1 we can get K2 at temperature T2 16

K = A RTEae /−

K1

= A 1/ RTEae −

K2

= A 2/ RTEae−

Ea Activation energy; A preexponential factor R gas constant = 8.31 J/mol/K

(2) Inorganic chemical characteristics

When placed in water, most inorganic compounds dissociate into electrically charged atoms referred to as ions atoms linked in ionic bondCan be classified into two

Metal (e.g., Pb2+, Hg2+, Cu2+)Non-metal (e.g., H+,OH-, HCO3

-, CO32-, Cl-, NO3

-)

17

pH and acidity/alkalinitypH condition of a solution related to [H+]pH = -

log[H+] determined by a pH meter

Acidity/Alkalinity the ability of natural water to neutralize base/acid determined from a titrationAcidity = (Volume need to reach end point) ×(concentration of the strong base)Mineral acidity = [H+] + [H2CO3] − [OH-] titration to pH = 3.7 (methyl orange end point)Total acidity = [H+] + 2[H2CO3] + [HCO3

-]− [OH-] titration to pH = 8.3 (phenolphthalein end point)

18

Alkalinity = (Volume need to reach end point) ×(concentration of the strong acid) => titrated with 0.02 N H2SO4

Phenolphthalein alkalinity (mg/L) = [OH-] + [CO32-] − [H+]

titration to pH = 8.3Total Alkalinity = Bromcresol-Green alkalinity (mg/L) =[HCO3

-] + [OH-] + 2 [CO32-] − [H+] titration to pH = 4.5

End points for Acidity/Alkalinity titration(Zhang, Chemistry for Environmental Engineering, 2005 )

19

Nitrogen and phosphorus Known as nutrients or biostimulants essential to the growth of microorganisms, plants and animalsData required to evaluate the treatability of wastewater by biological processesForm of nitrogen

Form of phosphorus PO43-, HPO4

2-, H2PO4-, H3PO4

(Tchobanoglous

et al., Wastewater Engineering, 2003)

20

Dissolved oxygen

The concentration of DO in water is small precarious from ecological point of viewThe dissolution process

The equilibrium constant the Henry’s Law constant KH

)(dissolvedO(gas)O 22 ⇔

2O

2H PressurePartial

)(dissolvedOK =

21

The amount of a gas that will dissolve in a solution is directly proportional to the partial pressure of that gas in contact with the solvent.

Henry’s law constant Linkage of solubility and vapor pressure

Henry's Law

Pi = partial pressure of a contaminant i in the gas (atm)Cw

= concentration of the contaminant i in the solution (mol/m3)

KH

= Henry's law constant (atm

m3/mol)

KH

=w

i

CP

22

Chlorine (Cl2) used for disinfection of water supplies and wastewater effluent to prevent water-borne diseasesFree chlorine residuals Cl2 + HOCl + OCl−

Combined chlorine residuals NH2Cl + NHCl2 + NCl3

Total chlorine residuals = free chlorine residuals + combined chlorine residualsMeasurement of total chlorine residualsCl2

+ 2 I−

==> I2

+2 Cl−I2

+ starch ==> blue colorI2

+ 2Na2

S2

O3

==> 2Na2

S4

O6

+ 2NaI

Residual chlorine

23

MetalsChemical Adverse effectAntimony Blood disordersArsenic Skin damage, cancerBarium Increased blood pressureBeryllium Intestinal lesionsCadmium Kidney damageChromium DermatitisCopper Gastrointestinal, liver or kidney damageCyanide Nervous system impairmentLead Impaired mental developmentMercury Kidney damage, birth defectsSelenium Hair loss, circulatory problemsSodium High blood pressureSilver Thallium Blood, kidney, liver, intestinal effectsIron/ Manganese Stains laundry and fixtures 24

Hardness caused mainly by divalent metallic cations (e.g. Ca2+ , Mg2+ , Sr2+ , Fe2+ , Mn2+) determined by EDTA titrimetric methodEDTA = ethylenediaminetetraacetic acid (H4Y)M2+

+ EDTA [M-EDTA]complex

Total hardness = Ca hardness + Mg hardness (in most cases)

(Zhang, Chemistry for Environmental Engineering, 2005 )

Hardness

25

(3) Organic chemical characteristics

Organic compounds composed of a combination of carbon, hydrogen, and oxygen, together with nitrogen in some casesOrganic matter in wastewater a very large number of different synthetic organic molecules, with structures ranging from simple to extremely complex

proteins 46-60%carbohydrates 25-50%oils and fats 8-12%urea 26

Organic matter divided into biodegradable organics and non-biodegradable organics

biodegradable organics food to microorganism fast and easily oxidized by microorganism (e.g.,

starch, fat protein, alcohol)Non-biodegradable organics difficult to be biodegraded or toxic to microorganisms (e.g., pesticide, cellulose, phenol)

Organic matter characterization in wastewaterAggregate organic constituents (e.g., BOD, COD and TOC)Individual organic compounds (e.g., VOCs, pesticides, emerging organic compounds) 27

BOD (Biochemical oxygen demand)

BOD amount of O2 required by bacteria in the biochemical oxidation of organic matterHigh BOD value = high organic-matter concentration = poor water quality

–

Decomposition of organic matter is a slow process20 days decompose 95 to 99%

of organic matter 5 days decompose 60 to 70%

of organic matter

BOD5 the most widely used parameter to measure organic matter in both wastewater and surface water

28

Organic Matter – Classification

(Viessman

et al., Water supply and pollution control, 2009)

BOD test on wastewater sample29

(Viessman

et al., Water supply and pollution control, 2009)

BOD test on polluted surface water sample30

(Viessman

et al., Water supply and pollution control, 2009)

BOD reaction curve showing the carbonaceous oxygen demand (CBOD) and nitrogenous oxygen demand (NBOD) 31

Typical values of K for various waterThe equation for calculating BOD from a seeded laboratory test is expressed as:

PfBBDDBOD )()( 2121 −−−

=Where

D1

= DO of diluted seeded wastewater immediately after preparation, mg/LD2

= DO of wastewater after incubation, mg/LB1

= DO of diluted seed sample wastewater immediately after preparation, mg/LB2

= DO of seed sample after incubation, mg/Lf = ratio of seed volume in seeded wastewater test to seed volume in BOD test on seedP = volume of wastewater/volume of dilution water plus wastewater

32

Ultimate BOD (L0 )

BODt

= L (1 –

e-kt)Where

BODt

= biochemical oxygen demand at time t, mg/LL = ultimate BOD, mg/Lk = deoxygenation

rate constants, day-1

The carbonaceous oxygen demand curve can be expressed mathematically as:

If the sample is unneeded, the relationship is:

PDDBOD 21 −=

33

K2

= K1

x θ(T2

-T1

)

Where •

K2

= reaction rate constant at temperature T2

, per day•

K1

= reaction rate constant at temperature T1

, per day •

θ =

temperature coefficient = 1.047

Water type

K, per day (base 10)Tap water 0.04Surface water

0.04 –

0.1

Raw sewage

0.15 –

0.30Well-treated sewage

0.05 –

0.10

The reaction rate are temperature dependent:

34

Example 1-1: A seeded BOD analysis was conducted on a food-processing wastewater sample. Ten ml portions were used in preparing the 300-ml bottles to determine the DO of the aged, settled wastewater seed at 20ºC. The seeded sample BOD bottles contained 2.7 ml of food-processing wastewater and 1.0 ml of seed wastewater. The results of this series of test bottles are listed below.

Seed Tests Sample TestsTime B1 B2 D1 D2(days) (mg/l) (mg/l) (mg/l) (mg/l)0 7.8 - 8.1 -1.0 7.8 6.9 8.1 5.62.0 7.8 6.6 8.1 4.33.0 7.8 6.3 8.1 3.64.0 7.8 5.8 8.1 3.05.0 7.8 5.7 8.1 2.56.0 7.8 5.3 8.1 2.07.0 7.8 5.4 8.1 1.8

(1) Calculate BOD5 at 20ºC(2) Calculate BOD10

at 20ºC if assuming a k of 0.15

(3) Calculate BOD5

at 30ºC

35

COD (Chemical oxygen demand)

COD to measure the oxygen equivalent of the organic material in wastewater that can be fully oxidized chemicallyThe basis for the COD test nearly all organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions.COD determination potassium permanganate (KMnO4) was used for years potassium dichromate (K2Cr2O7) becomes the most effective oxidant now (it is relatively cheap, easy to purify, and is able to nearly completely oxidize almost all organic compounds) need about 2.5 h to complete a COD test

Cn

Ha

Ob

Nc

+ d Cr2

O72−

+ (8d+c) H+

n CO2

+ [(a + 8d −

3c)/2] H2

O + c NH4+

+ 2d Cr3+

where d = 2n/3 + a/6 −

c/2

36

Relationships between BOD and COD

COD > BOD? or COD = BODultimate

?

Many organic substances which are difficult to oxidize biologically (e.g., lignin) can be oxidized chemicallyInorganic substances that are oxidized by the dichromate increase the apparent organic content of the sample high COD values may occur because of the presence of inorganic substances with which the dichromate can reactCertain organic substances may be toxic to the microorganisms used in the BOD test

37

TOC (Total organic carbon)

To determine the total organic carbon in an aqueous sample an indicator of water quality or cleanliness

Measurement TOC = total carbon (TC) –inorganic carbon (IC) done instrmentally

It takes only 5 to 10 min to complete

BOD/COD ≥ 0.5 easily treated by biological means (biodegradable organic)BOD/COD ≤ 0.3 have some toxic compounds or acclimated microorganisms may required in its stabilization (non-biodegradable organic)

38

Interrelationships between BOD, COD and TOC

Type of wastewater BOB/COD BOD/TOC

Untreated 0.3-0.8 1.2-2.0

After primary settling 0.4-0.6 0.8-1.2

Final effluent 0.1-0.3 0.2-0.5

(Tchobanoglous

et al., Wastewater Engineering, 2003)

Comparison of ratios of various parameters used to characterize wastewater

39

(4) Biological characteristicsOrganisms in surface water and wastewater

bacteria, fungi, algae, protozoa, plants and animals, and viruses

Pathogenic organisms in water and wastewater pathogen = specific agent causing disease (special concerns!) can be classified into four broad categories

viruses obligate, intracellular parasites that replicate only in living hosts’ cellsbacteria microscopic single-celled organisms that use soluble food and are capable of self-reproduction without sunlightprotozoa intestinal parasites that replicate in the hosthelminths intestinal worms that do not multiply in the

human host 40

(Shanahan, Water and Wastewater Treatment Engineering, 2005)

41

(Viessman

et al., Water supply and pollution control, 2009)42

Coliform bacteria testing

Coliform group of bacteria aerobic and facultative anaerobic, nonspore-forming, Gram’s-stain negative rods that ferment lactose with gas production within 48 hr of incubation at 35ºCthe more popular technique for total coliform

bacteria testing fermentation tube technique based on gas production during the

fermentation of lauryl tryptose broth, which contains beef extract, peptone (protein derivatives), and lactose (milk sugar)

43

(Viessman

et al., Water supply and pollution control, 2009)

Diagram of the coliform

bacteria testing44

(5) Water quality standardsFederal standardsGuidelines for Canadian Drinking Water QualityCanadian Water Quality Guidelines for the Protection of Aquatic Life Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses Guidelines for Canadian Recreational Water

Standards in Newfoundland and LabradorGuidelines for Canadian Drinking Water QualityStandards for Bacteriological Quality of Drinking Water Standards for Chemical and Physical Monitoring of Drinking Water

45

Guidelines for Canadian Drinking Water Quality (Health Canada, 2008, http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/2010-sum_guide-res_recom/index-eng.php#a14)

(Health Canada, Guidelines for Canadian Drinking Water Quality, 2008) 46

(Health Canada, Guidelines for Canadian Drinking Water Quality, 2008)

MAC maximum acceptable concentration

Substances in conc.greater than the MAC drinking water is either capable of producing deleterious health effects or is aesthetically objectionable

47

(Viessman

et al., Water supply and pollution control, 2009)

US EPA

48

Guidelines for Drinking Water Quality from US EPA

(Viessman

et al., Water supply and pollution control, 2009)

Continued

US EPA

49

Water-qualityConstituent

Units Canada U.S. EPA European Union

World Health Organization

E. coli Number/ 100ml

0 Detected in < 5% of samples

0 0

Arsenic μg/l 10 10 10 10Copper mg/l 1 1.3 2 2Lead μg/l 10 15 10 10TTHM μg/l 100 100 100 200/100/100/60aChloride μg/l 250 250 250 250Iron μg/l 300 300 200 No guidelineBenzene μg/l 5 5 4 4Carbon tetrachloride

μg/l 5 5 4 4

a Chloroform/bromoform/dibromodichloromethane/bromodichlorodimethane

Comparison of standards

50