Processes

Natural Treatment and On-Site ProcessesReview by: Kevin D. White and Lawrence K. WangWater Environment Research, Vol. 72, No. 5, Literature Reviews [CD-ROM content] (2000)Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/29763097 .

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Natural Treatment and On-Site Processes

Kevin D. White and Lawrence K. Wang

Natural treatment systems are divided into several categories: land-treatment systems, wetland systems (both for stormwater treatment and wastewater treatment), aquatic systems (ponds and floating aquatic plant systems), and on-site and small community systems in this review.

LAND TREATMENT SYSTEMS

Sediment transport was studied in non-submerged overland flow over grass by Deletic (1999). Sediment concentration in runoff was found to decrease exponentially with distance and reaches a constant value. A simplified relationship between particle fall number, Nf, and the percentage of particles trapped in the grass was established. Munoz-Carpena et al.(1999) described a single event model to predict sediment transport in vegetative filter strips. The model links three submodels: a Petrov-Galerkin finite element kinematic wave overland flow submodel, a modified Green-Ampt infiltration submodel, and the University of Kentucky sediment filtration model. A set of 27 natural runoff events were used to test the model, with good predictive capability. A study of phosphorus storage on lands irrigated with treated sewage effluent for over 20 years found that P accumulation occured primarily in organic forms, both within the soil and as peat on its surface (Menzies et al., 1999). This finding throws into question the common

practice of predicting disposal scheme life on the basis of P adsorption curves.

WETLAND SYSTEMS

General. Gerba et al. (1999) evaluated a duckweed-covered pond, a subsurface flow wetland, and a surface flow wetland for the removal of indicator bacteria and pathogenic protozoa. Larger microorganisms {Giardia and Cryptosporidium) were best removed in the the

pond (sedimentation), while the best fecal coliform removal occurred in the subsurface flow wetlands (98%). These results suggest that combinations of ponds and wetlands work best to remove pathogenic organisms. A new mathematical model, using transport detention time, was

developed to describe BOD removal in wetlands by Chen et al. (1999). The model treats the wetland as a series of continuously stirred tank reactors and an nth-order ordinary differential

equation was derived based on mass balancing and convection/dispersion. The model is

compared to existing plug-flow models and is shown to be more accurate, particularly in transient conditions. Xue et al. (1999) quantified denitrification in constructed wetlands

receiving agricultural tile drainage. Nitrate disappearance rates in the water column ranged from 12 to 6.fmgNm"2 hf1.

Stormwater Wetlands. Hydrologie design considerations for stormwater treatment wetlands were described by Koob et al. (1999). Detention structure designs based on the time between events was encouraged to account for evaporation, infiltration, and treatment. Revitt et

Copyright ? 2000 by the Water Environment Federation. Water Environment Research, Volume 72, Number 5. Literature Review 2000.



al. (1999) discussed the use of constructed wetland systems to reduce the impacts of urban runoff on receiving stream quality. Sedimentation maintenance and an overflow mechanism to prevent sediment remobilization were described as key elements. A study of vegetative systems to treat

highway drainage was described by Ellis (1999). Various vegetative best management practices (BMPs) are identified with estimated pollutant removal efficiencies and a review of design procedures. Brown et al. (1999) presented an optimization scheme that sizes various stormwater

pollution control options, including stormwater treatment wetlands. As a case study, an

algorithm was developed and applied to a suburb in Australia to select the most effective

strategies for limited funds. A numerical simulation model for wetland removal of organic matter in stormwater was described by Shelley and Mudgett (1999). A mechanistic system dynamics approach was used to explore system behavior under reasonable ranges of environmental conditions and design parameters. Surface area was found to be key for

establishing biofilms that remove organic matter. Blackwell et al. (1999) investigated the effectiveness of riparian buffer systems to protect surface waters from diffuse agricultural pollution. The study concentrates on footslope seepage and overland flow, which are more effective for nitrate removal. The use of constructed wetlands to treat urban snowmelt from streets and snow disposal sites in Alaska was described by Jokela and Pinks (1999). A 5.7 ha wetland system is being used to treat runoff from snow disposal that contains suspended solids and metals. The system treats discharges from about 445 ha of residential, commercial, and industrial drainage.

Acid Mine Drainage Wetlands. A constructed wetland system, in combination with

spoil amendment, was used to reclamate an ironstone spoil heap in Scotland (Heal and Salt, 1999). Vegetation (trees) were planted in spoil amended with dried sewage sludge, limestone, and peat. The wetland system has been found to remove 33% of the acidity in runoff and between 20% and 40% of metal inputs. Iron and manganese concentrations leaving the site have increased, however, even after passing through the wetland system. A wetland system to treat acidic spoil heap drainage was also investigated by Jarvis and Younger (1999). Using waste manures and composts as substrate, the wetland was found to reduced iron and aluminum

concentrations, and lowered acidity. Groudev et al. (1999) investigated the use of a lab-scaled anaerobic cell and constructed wetland to remove heavy metals, radioactive elements, arsenic, and sulphates from copper mine tailings. The anaerobic cell contained manures, compost, and sawdust; and was found to be effective for adsorbing metal pollutants. Anaerobic cell effluents, high in soluble organic mattter, were effectively treated in the wetland system to levels

appropriate for reuse in agricultural or industrial areas. Two populations of woolgrass (Scirpus cyperinus) were investigated to determine population level differences in aboveground and

belowground growth response to acid mine drainage (Demchik and Garbutt, 1999). Results showed some differences in growth, suggesting that there is potential for selecting specific genotypes for increased performance in the presence of acid mine drainage.

Free Water Surface-Constructed Wetlands. Gearheart (1999) assessed the capability of a constructed wetland and UV disinfection to achieve current California Reuse Standards for

public use irrigation. Removal of key constituents, along with the cost of the system, is

compared to the results and costs of other reuse treatment alternatives. Performance data were

incorporated into a decision support model. Phosphorus removal from agricultural wastewater was studied by Serodes and Normand (1999), using a 4-cell surface-flow wetland system. Ortho-P removal was found to be about 50%, while total P removal averaged 63%. Phosphorus




gradients were noted both horizontally and vertically. Bolton and Greenway (1999) investigated the potential for constructed Melaleuca wetlands to provide buffering of sewage spills. The

system was loaded with primary settled sewage and was found to be excellent for TSS, BOD, and turbidity. Nitrogen removal was dependent on loading rate. A conceptual model for

emergency buffering of sewages spills was presented. The treatability of dairy lagoon effluent in a lab-scale constructed wetland was investigated by Benham and Mote (1999). Ten scaled wetland systems were used to examine several design and operational variables-loading rate and attachment sites (vegetated, inert, and none). A model was developed that included microbial attachment site parameters and reaction rate constants. Sakadevan and Bavor (1999) studied the influence of hydraulic loading, retention time, water column depth, and P-loading on phosphorus and nitrogen removal. Results showed that low hydraulic loading and longer retention times enhanced the removal of both nitrogen and phosphorus in wetland systems. A nitrogen balance for a pond/wetland system was developed by Lund (1999). Using a mass balance approach, it was found that over 60% of the nitrogen was lost from the system, via denitrification. Based on this study, wetland systems were enhanced to meet nitrogen discharge requirements rather that traditional in-plant treatment improvements.

Subsurface Flow-Constructed Wetlands. An overall strategy for sustainable wastewater treatment for small communities, using wetlands was described by Griffin and Upton (1999). A long-implemented policy is reviewed in terms of appropriateness, performance, and

sustainability. Odor and stormwater issues are also discussed. Griffin et al. (1999) also

investigated nitrogen removal in systems consisting of rotating biological contactors, subsurface flow reed beds, and employing recycle. Total nitrogen levels were maintained below 10 mg/L. Summertime low oxygen conditions in the wetland was found to allow sulfate reducing conditions and odors. The distribution of nutrients and heavy metals in a constructed wetland was investigated by Obarska-Pempkowiak and Klimkowska (1999). Most nutrients and metals were removed in the inlet areas of the wetland. Metal removal was primarily by adsoption to

particulate matter. Distribution of elements in biomass was found to be insignificant. Maschinski et al. (1999) evaluated the efficiency of a small-scale subsurface-flow wetland

system treating domestic wastewater using native southwestern U.S. plants. The treatment

system was operated at an elevation of 2350 m and was found to remove TKN and TP by 84% and 73% respectively. Fecal coliform removal achieved recreational full-body contact standards

(200 cfu/100 mL) in 14 out of 15 months of operation. A pilot-scale wetland system was used to study the treatment of lignite pyrolysis wastewater that contained ammonia and organic components of large molecular size (Wiessner et al., 1999). Results indicated that nitrogen removal was effective, but that only a limited removal capacity for low molecular and large

molecular organic components was seen. Consequently, the decolorization and removal of total

organics decreased over time. Various phosphate-removing substrates for subsurface-flow

wetlands were investigated by Drizo et al. (1999). Bauxite, shale, burnt oil shale, limestone, zeolite, light expanded clay aggregates, and fly ash were characterized by pH, cation exchange capacity, hydraulic conductivity, porosity, specific surface area, particle size distribution, and

phosphate adsorption capacity. Fly ash and shale were found to have the highest P-adsorption values, with shale having the best, overall characteristics for use in wetland systems. Lee et al.

(1999) studied the effects of low temperature on ammonia removals in constructed wetlands. From 5?C to 23?C nitrification rates only varied by 20%. Reduced nitrification was correlated to




low oxygen conditions.

AQUATIC SYSTEMS

Ponds. Mara and Pearson (1999) discuss the effectiveness of combining a waste stabilization pond with a wastewater storage and treatment reservoir to produce safe effluents for

crop irrigation. During irrigation season, the waste stabilization pond was used for restricted

irrigation and the wastewater storage and treatment reservoir was used for unrestricted irrigation. This system provides an internal return rate of 58% and was financially feasible. As the levels of dissolved oxygen in waste stabilization ponds increased, the inactivation of both enterococci and F-RNA phages increased, as studied by Davies-Colley et al. (1999). The increased inactivation of enterococci and F-RNA phages was also dependant upon light-absorbing pondwater constituents. The natural disinfection in waste stabilization ponds was mostly dependant on its

exposure to sunlight. Coliform removal in maturation and facultative ponds was studied by Von

Sperling (1999). Two flow regimes were investigated: CSTR and dispersed flow. Both models

yielded similar removal efficiency values. It is concluded that for any given removal efficiency, a shallow pond (due to its larger Kb) requires less surface area than a deep pond, even though the

deeper pond has a higher detention time. Ghosh et al. (1999) explored the combination of a UASB reactor followed by two ponds for the treatment of domestic wastewater. The second

pond served as a maturation pond and was stocked with common carp and silver carp. This

system achieved 30-35% organic pollutant removal, 30-80% nutrient reduction, and 97-99% fecal coliform reduction. The performance of a full-scale aerated lagoon was evaluated by Surampalli et al. (1999). The objective was to evaluate the lagoon's efficiency under varied

temperature conditions. BOD5, TSS, and ammonia-N were assessed. Results showed that

nitrification rates increased with increasing temperatures and the 5-day BOD and suspended solids limits were met according to the National Pollutant Discharge Elimination System. Also, nitrifying bacteria were found to be diminished in winter, which resulted in reduced nitrification rates.

Floating Aquatic Plant Systems. The use of a hyacinth wetland system following a stabilization pond was found to be highly effective at pathogen removal (Fujioka et al, 1999). This scheme, in conjunction with coagulation, filtration, and UV disinfection was found to reduce fecal coliform by 99.99% and produce effluent that meets and unrestricted reuse standard of <1 fecal coliform/100 mL. Several indicator microorganisms were monitored. Zhu et al.

(1999) studied the accumulation of trace elements by water hyacinths and found that cadmium, chromium, selenium, and copper were best accumulated. Bioconcentration factors of 2150 for cadmium, 1823 for chromium, and 595 for copper showed that hyacinths are a promising candidate for phyto remediation of wastewaters containing cadmium, chromium, copper, and selenium. A macrophyte raft-lagoon system was studied by Perkins and Hunter (1999) in West Yorkshire, England. This report indicates the need for more focused research on the dynamics of

sanitary indicator bacteria in macrophyte systems for determining the suitability of water for recreational and public-supply purposes. Pradeep and Garde (1999) investigated the stratification in 4 laboratory scale models of hyacinth ponds of varying depth over a 4-month

period. Stratification of hyacinth ponds was found to be unsubstantiated because: 1) a 90% reduction of radiation prevented the growth of algae and thus increased the dissolved oxygen content, 2) no thermal or density stratification was found, 3) influent and effluent streams located at different levels produced secondary circulation which prevented stratification, and 4) it




was concluded that unstratified water hyacinth ponds promote uniform treatment. Van der Steen et al. (1999) evaluated the treatment of stabilization pond effluent through duckweed ponds to reduce algae concentration. Suspended solids concentrations were found to increase and

pathogen removal was poor. Tarn and Wong (1999) conducted experiments to determine the

capacity of mangrove soils in purifying synthetic wastewater containing pollutant concentrations 4 times of that found in local municipal sewage and of two salinities. Results of this study indicated that mangrove soils can retain pollutants. However, its efficiency was affected by salinity. An innovative treatment system for mine/mill wastewater was studied by Erten-Unal and Wixson (1999). A tailings pond was followed by a series of artificially constructed

meandering biotreatment channels and a polishing lagoon. The abundance of aquatic plants promoted the removal of heavy metals and sedimentation. This study confirms that the new

system provides good treatment for removal of heavy metals and results in compliance with state and federal regulatory guidelines. Abissy and Mandi (1999) assessed wastewater purification efficiency of Typha and Juncus, two higher aquatic plants. Organic load was reduced in both

systems. COD and TSS removal efficiencies were 91% and 73%, respectively for Typha and 92% and 76%, respectively for Juncus. It was also found that these helophytes maintained

porosity sufficiently within the system to allow water percolation for treatment; where as the control system with no plants, clogged in the winter months.

Solar Aquatic Systems. Sinton et al. (1999) compared sunlight inactivation rates of somatic coliphages, F-RNA, and fecal coliforms during 7 summer and 3 winter survival

experiments. Dark inactivation rates were lower in winter and higher in the summer. For F

RNA, winter inactivation rates were lowest, but highest for fecal coliforms. The summer inactivation rates found, from greatest to least, were as follows: fecal coliforms, F-RNA phages and somatic coliphages. Spectral cutoff wavelengths (50% light transmission) were also

investigated. Longer solar wavelengths, which are predominant in seawater, have higher inactivation rates for F-RNA phages and fecal coliforms than somatic coliphages. Sinton et al.

(1999) suggested the use of somatic coliphages as fecal and, possibly viral indicators, in marine waters. Particulate suspensions of Ti02 irradiated with solar light were investigated by Malato et al. (1999) to catalyze the oxidation of organic contaminants. Organic anions might be added to enhance the organic degradation rate. This study was designed to focus on solar photocatalysts. The results showed that peroxydisulphate, the organic anion, enhances the photocatlytic mineraliztion of agricultural rinsates the most effectively.

ON-SITE AND SMALL-COMMUNITY SYSTEMS

Septic Tank Systems. A septic tank system includes both the buried septic tank and subsurface soil absorption field. The septic tank provides separation of solids and flotable materials from the wastewater, an anaerobic environment for partial decomposition of organic carbon, while the soil absorption field realizes the complete degradation of organic carbon and nitrification. The produced nitrate leaches through the septic tank system due to the lack of external organic carbon. In situ septic tank effluent denitrification using a sulfur-limestone

autotrophic denitrification (SLAD) process system was attempted by Shan (1998), Zhang and

Lampe (1999) and Zhang and Shan (1999). It was observed by Zhang and Shan (1999) that

significant nitrification occured in the sand layer, while significant denitrification occurred in the




sulfur-limestone layer. The SLAD system is effective in denitrification, while production of sulfate and hardness and existence of sulfide in effluent may be limiting factors in its application.

Wolfe (1999) described the history of wastewater collection and treatment from the

Mesopotamian Empire in 3500BC to year 2000, and presented a comprehensive sanitation

technology from primitive cesspools to advanced denitrification process.

The feasibility of using a septic tank as a heat source for geothermal heat pumps was discussed

by Hanegan and DenBraven (1999). There was no evidence of the septic tank freezing up or

failing to properly function. The use of the septic tank on a full-time basis was suggested. There was a need to have the septic tank surrounded on all side by a large amount of soil and insulated from the ground surface. Lenox Institute of Water Technology (1999) documented the

U.S. Patents in the area of septic tank technology from 1969 to 1999. Urban legends regarding the environmental aspects of plumbing and septic tans were examined by Morse (1999). Legends included the common belief that detergents might cause pipe backup and septic tanks needed to be pumped every few years. Often, other factors contributed to pipe back up, and

septic tanks should be checked for sludge buildup before pumping. Doom and Likes (1999) conducted a study to estimate global and country-specific methane emissions from open sewers and on-site wastewater treatment systems, including latrines and septic tanks. This study used an emission factor that expresses methane emissions in terms of COD reduction. The nitrogen cycle effects in these systems to qualify ammonia and nitrous oxide emissions from these

systems was also discussed. It was concluded that these systems were likely to contribute

significant quantities of ammonia and nitrous oxide to the atmosphere. Water Environment Federation (1997) provided a principle reference source for those associated with the specialized task of managing and treating septage. This manual of practice is comprised of the collective

experiences and innovations of many individuals involved with the applications of the best

principles and practices for treatment and disposal of septage. Hedstrom and Hanaeus (1999) presented information on a study which investigated the concept of on-site treatment of sludge from septic tanks with respect to dewatering and nutrients.

The phosphate behavior in two well-characterized, oxidizing septic system plumes was monitored by Robertson and Harman (1999) for extended periods of two to four years after

decommissioning of the tile beds. Their results showed that rapid and reversible sorption reactions dominated the phosphate behavior in the ground water zone at these sites. The frontal

part of the phosphate plume was observed to continue its advance during the decommissioned

period. A synoptic survey of septic indicators in streams and springs at Monte Sano Mountain, Madison County, Alabama in January 1998 was completed by McPherson and Mooty (1999) in

cooperation with the City of Huntsville, Alabama. Recent heavy commercial and residential

development has required the construction of wastewater treatment methods in communities outside the reach of existing municipal sewage treatment systems. Water Engineering &

Management (2000) described a special effort by the developers and community officials to solve wastewater issues and drinking water problems in Santa Cruz, Bolivia. In a demonstration

system, effluent bypassed the old seepage pit and flowed from the septic tank into the chambers where it infiltrated into the soil. The modular plastic leaching chamber offered twice the infiltration capacity in the same space as a 24-inch stone and pipe septic leach field installation. Burnham (1999) developed and tested a model for predicting contaminant transport in leaching beds. Burnham's model may prevent groundwater pollution from bacteria and nitrate transport




in and through the septic tank leaching beds. The New Jersey Pinelands area is characterized by sandy soil, underlain by a water-table aquifer. The Pinelands Commission allowed the use of subsurface pressure dosing septic systems as an alternative to standard septic systems. No

significant difference in nitrogen removal was found between the subsurface pressure dosing septic system and the standard septic system. Sixty residential wells in Palm Bay, Florida were tested by Arnade (1999) for fecal coliforms, nitrates, and phosphates to determine if season has a

significant effect on the correlation between well contamination and septic tank distance. Ground water samples collected at all distances of septic tanks during the wet season contained twice as many fecal coliforms and higher concentrations of nitrates and phosphates compared with samples collected during the dry season.

Chen (1999) completed a dissertation entitled, "Transformations and Transport of Fixed

Nitrogen from Septic Tanks in Soil Absorption Systems and Underlying Aquifers". Chen's environmental transport models were developed to predict groundwater pollution. Improved septic tank and soil absorption systems were suggested. Griffin et al. (1999) conducted a detailed survey to determine the concentration of microbial fecal indicators and the presence of human pathogenic microorganisms. A total of 19 sites, including 17 canal sites and 2 near-shore water sites, were assayed for human pathogenic microorganisms. Results indicated that the canals and near-shore waters throughout the Florida Keys were impacted by human fecal contaminants from septic tanks. Exposure to canal waters through recreation and work may be

contributing to human health risks.

Small Treatment Systems. The temperature changes affecting the performance of trickle-bed biofilters was studied by Chungsying et al. (1999). Treatment of benzene, toluene, ethylbenzene and o-xylene (BTEX) vapors was the focus of the study. A temperature range of 25-35?C was determined to be most effective when utilizing the trickle-bed biofilter. Philippi et al. (1999) reported an experiment involving the use of a combined septic tank and root zone wetland system for treating domestic sewage from 66 people. The experiments were carried out in the Agriculture Secretary's Training Center, Santa Catarina State, Brazil. Outstanding performances were observed and documented. Krofta and Wang (1999) compiled a technical

report for introduction of conventional and innovative technologies for treatment of household wastes, septage and septic tank effluents. A compact dissolved air flotation (DAF) clarifier is feasible for treating the septic tank effluents, while an ozone process (Oxyozone Process) is feasible for treating the septage and biosolids. Vanderholm et al. (1999) introduced the state-of the-art methodologies and technologies for management of livestock wastes. A giant septic tank (or septic building) and a lagoon connected in series are feasible for treatment of liquid livestock wastes.

Decentralized Treatment. Zeeman and Lettinga (1999) described a decentralized wastewater treatment that employed an anaerobic treatment unit in combination with vegetable, fruit, and yard waste. A model was developed to evaluate hydraulic retention time, temperature, and solids retention time. Attitudes towards the sustainability of traditional and decentralized wastewater systems was discussed by Hedberg (1999). Urban development and environmental

sustainability are discussed, showing that there exists a strong driving force and interest in

changing existing systems.




Kevin D. White is an associate professor of civil engineering at the University of South Alabama. Lawrence K. Wang is dean and professor, Lenox Institute of Water Technology.

Correspondence should be addressed to Kevin D. White, Department of Civil Engineering, University of South Alabama, Mobile, AL 36688.

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