737 N NATURAL SYSTEMS FOR WASTEWATER TREATMENT INTRODUCTION In the continual search for a simple, reliable, and inexpen- sive wastewater treatment system, the natural systems are the latest discovery. They provide not only efficient methods of wastewater treatment, but also provide some indirect benefi- cial uses of the facility such as green space, wildlife habitat, and recreational areas. In the natural environment, physical, chemical, and bio- logical processes occur when water, soils, plants, microor- ganisms, and atmosphere interact. To utilize these processes, natural systems are designed. The processes involved in the natural systems include: sedimentation, filtration, gas transfer, adsorption, ion exchange, chemical precipitation, chemical oxidation and reduction, and biological conversions plus other unique processes such as photosynthesis, photooxidation, and aquatic plant uptake. 1 In natural systems, the processes occur at “natural” rates and tend to occur simultaneously in a single “ecosystem reactor” as opposed to mechanical sys- tems in which processes occur sequentially in separate reac- tors or tanks in accelerated rates as a result of energy input. Generally, a natural system might typically include pumps and piping for wastewater conveyance but would not depend on external energy sources exclusively to maintain the major treatment responses. 2 In this paper a general overview of natural systems for wastewater treatment is presented. The constructed wet- lands are becoming a viable wastewater treatment alterna- tive for small communities, individual homes, and rest areas. Therefore, in this paper, a great deal of information has been presented on site selection, design of physical facilities, per- formance expectations, hydraulic and organic loading rates, and cost of the constructed wetlands. TYPES OF NATURAL SYSTEMS Natural systems for effective wastewater treatment are divided into two major types: terrestrial, and aquatic systems. Both systems depend on physical and chemical responses as well as on the unique biological components. 2 Each of these systems are discussed below. Terrestrial Treatment Systems Land application is the sole terrestrial treatment system used to remove various constituents from the wastewater. It uti- lizes natural physical, chemical, and biological processes within the soil-plant-water matrix. The objectives of the land treatment system includes, irrigation, nutrient reuse, crop production, recharge of ground water and water reclamation for reuse. There are three basic methods of land application: (1) Slow-rate irrigation, (2) Rapid-infiltration–percolation, and (3) Overland flow. Each method can produce renovated water of different quality, can be adapted to different site conditions, and can satisfy different overall objectives. 3,4 Typical design features and performance expectations for Slow-rate irrigation Irrigation is the most widely used form of land treatment systems. It requires presence of vegetation as a major treatment component. The wastewater is applied either by sprinkling or by surface technologies. In this pro- cess surface runoff is not allowed. A large portion of water is lost by evapotranspiration whereas some water may reach the groundwater table. Groundwater quality criteria may be a lim- iting factor for the selection of the system. Some factors that are given consideration in design and selection of irrigation method are (1) availability of suitable site, (2) type of waste- water and pretreatment, (3) climatic conditions and storage needed, (4) soil type, and organic and hydraulic loading rates, (5) crop production, (6) distribution methods, (7) application cycle, and (8) ground and surface water pollution. 2,3,5 Rapid-infiltration – percolation In rapid-infiltration-percolation the wastewater percolates through the soil and treated effluent reaches the groundwater or underdrain systems. Plants are not used for evapotranspiration as in irrigation system. The objectives of rapid infiltration—percolation are (1) ground- water recharge, (2) natural treatment followed by withdrawal C014_001_r03.indd 737C014_001_r03.indd 737 11/18/2005 10:44:16 AM11/18/2005 10:44:16 AM © 2006 by Taylor & Francis Group, LLC the three basic terrestrial concepts are given in Table 1. 738 NATURAL SYSTEMS FOR WASTEWATER TREATMENT by pumping or under-drain systems for recovery of treated water, (3) natural treatment with groundwater moving verti- cally and laterally in the soil, and (4) recharging a surface water source. 5 Overland flow In the overland flow system, the wastewater is applied over the upper reaches of the sloped terraces and allowed to flow overland and is collected at the toe of the slopes. The collected effluent can be either reused or discharged into a receiving water. Biochemical oxidation, sedimentation, fil- tration and chemical adsorption are the primary mechanisms for removal of the contaminants. Nitrogen removal is achieved through denitrification. Plant uptake of nitrogen and phospho- rus are significant if crop harvesting is practiced. 3,5 Aquatic Treatment Systems Aquatic system utilize lagoons and ponds, and wetlands. The lagoons and ponds depend on microbial life, and lower plants and animals, while wetlands support the growth of rooted plants. Both pond systems and wetlands are discussed below. Pond Systems Within the aquatic systems, pond systems are the most widely accepted ones. Basically pond systems can be of three types based on oxygen requirement. These are aerobic, anaerobic and facultative pond systems. In all cases the major treatment responses are due to the biological components. 2,7 In most of the pond systems both performance and final water quality are dependent on the algae present in the system. Algae are func- tionally beneficial, providing oxygen to support other biologi- cal responses, and the algae-carbonate reactions are the basis for the effective nitrogen removal in the ponds. However, algae can be difficult to remove from the effluent. As a result, the stringent limits for suspended solids in the effluent can not be met. The design features and performance expectations for Aerobic ponds Aerobic ponds, also called high rate aero- bic ponds, maintain dissolved oxygen (DO) throughout their entire depth. They are usually 30 to 45 cm deep, allowing light to penetrate to the full depth. 3 Mixing is often pro- vided to expose all algae to sunlight and to avoid deposi- tion. As a result, formation of anaerobic sludge layer can be reduced. Oxygen is provided by photosynthesis and surface reaeration. Because of the presence of sufficient dissolved oxygen, aerobic bacteria can stabilize the waste. Detention time is short, usually 3 to 5 days. Aerobic ponds are lim- ited to warm sunny climate and are used infrequently in the United States. 2,7 TABLE 1 Design features and expected performance for terrestrial treatment units Typical criteria Concepts Treatment goals Climate needs Vegetation Area, b ha Organic loading, kg BOD 5 /ha.d Hydraulic loading, m/year Effluent characteristics, mg/L Slow rate Secondary, or AWT a Warmer season Yes 23–280 — 0.5–6 BOD Ͻ2 TSS Ͻ1 TN Ͻ3 c TP Ͻ0.1 c FC 0 d Rapid infiltration Secondary, or AWT, or groundwater recharge None No 3–23 45–180 6–125 BOD 5 TSS 2 TN 10 TP Ͻ1 e FC 10 Overland flow Secondary, nitrogen removal Warmer season Yes 6–40 Ͻ95 3–20 BOD 10 TSS 10 f TN Ͻ10 TP Ͻ6 a Advanced wastewater treatment. b For design flow of 3800 m 3 /d. c Total nitrogen removal depends on type of crop and management. d FC ϭ Fecal coliform, number per 100 ml. e Measured in immediate vicinity of basin, increased removal with longer travel distance. f Total suspended solids depends in part on type of wastewater applied. Source: Adopted in part from Refs. 2, 3, 5, and 6. C014_001_r03.indd 738C014_001_r03.indd 738 11/18/2005 10:44:16 AM11/18/2005 10:44:16 AM © 2006 by Taylor & Francis Group, LLC natural aquatic treatment units are summarized in Table 2. NATURAL SYSTEMS FOR WASTEWATER TREATMENT 739 Anaerobic ponds Anaerobic ponds receive such a heavy organic loading that there is no aerobic zone. They are usually 2.5 to 5 m in depth and have detention time of 20 to 50 days. 2,3 The principal biological reactions occurring are acid formation and methane production. Anaerobic ponds are usually used for treatment of strong industrial and agri- cultural wastes, or as a pretreatment step where an industry is a significant contributor to a municipal system. They do not have wide application to the treatment of municipal wastewater. Facultative ponds It is the most common type of pond unit. These ponds are usually 1.2 to 2.5 m (4 to 8 ft) in depth with an aerobic layer overlaying an anaerobic layer, which often contains sludge deposits. The usual detention time is 5 to 30 days. 2 Anaerobic fermentation occurs in the lower layer, and aerobic stabilization occurs in the upper layer. The key to facultative operation is oxygen produc- tion by photosynthetic algae and surface reaeration. The algae cells are necessary for oxygen production, but their presence in the final effluent represents one of the most serious performance problems associated with the facultative ponds. 7 Wetland Treatment Systems The wetlands are inundated land areas in which water table is at or above the ground surface (usually 0.6 m or more). This water table stands long enough time each year to main- tain saturated soil conditions and also to support the growth of related vegetation. The vegetation provides surface for attachment of bacteria films, and aids in the filtration and adsorption of wastewater constituents. Vegetation also trans- locate oxygen from leaves to the root systems to support a wide range of aerobic and facultative bacteria and controls the growth of algae by restricting the penetration of sunlight. 9 The unique ability of wetland plants to translocate oxygen to support a wide range of bacteria in the wetlands is shown and constructed wetlands. Both natural and constructed wet- lands have been used for wastewater treatment, although the use of natural wetlands is generally limited to the polishing or further treatment of secondary or advanced wastewater treated effluent. 2 Natural wetlands From a regulatory standpoint, natural wetlands are usually considered as part of the receiving waters. Consequently discharges to natural wetlands, in most cases, must meet applicable regulatory requirements, which typically stipulate secondary or advanced wastewater treat- ment. 10 Furthermore, the principal objective when discharg- ing to natural wetlands should be enhancement of existing habitat. Modification of existing wetlands to improve treat- ment capability is often very disruptive to the natural ecosys- tem and, in general, should not be attempted. 10,11 Constructed wetlands Constructed wetlands offer all of the treatment capabilities of the natural wetlands but with- out the constraints associated with discharging to a natural ecosystem. Additionally, the constructed wetland treatment units are not restricted to the special requirements on influ- ent quality. They can ensure much more reliable control over the hydraulic regime in the system and therefore per- form more reliably than the natural wetlands. 10 Two types of constructed wetlands have been developed for wastewater treatment (1) free water surface (FWS) systems, and (2) sub- surface flow system (SF). The schematic flow diagrams of eral description of both types of systems is provided below. The basic design considerations such as (a) site selection, (b) plants types, (c) physical facilities, (d) hydrologic fac- tors, (e) organic loading factors, and (f) performance expec- tations, that are presented under a separate section entitled Basic Design Considerations of Constructed Wetlands. Free water surface (FWS) wetlands The free water surface wetlands typically consist of a basin or channels with some type of barrier to prevent seepage, soil to support the root systems TABLE 2 Design features and expected performance for pond treatment units Parameter Aerobic (High Rate) Aerobic–anaerobic (Facultative) Anaerobic Detention time, days 5–20 10–30 20–50 Water depth, m 0.3–1 1–2 2.5–5 BOD 5 loading, kg/ha.d 40–120 15–120 200–500 Soluble BOD 5 removal, percent 90–97 85–95 80–95 Overall BOD 5 removal, percent 40–80 70–90 60–90 Algae concentration, mg/L 100–200 20–80 0–5 Effluent TSS, mg/L 100–250 a 40–100 a 70–120 a a TSS is high because of algae. Effluent quality can be improved significantly if algae is removed. Source: Adopted in part from Refs. 3, 4 and 8. C014_001_r03.indd 739C014_001_r03.indd 739 11/18/2005 10:44:16 AM11/18/2005 10:44:16 AM © 2006 by Taylor & Francis Group, LLC both types of system have been shown in Figure 2. A gen- in Figure 1. Wetlands can be of two types: natural wetlands 740 NATURAL SYSTEMS FOR WASTEWATER TREATMENT of the emergent vegetations, and water through the system at a relatively shallow depth. 2,9 The water surface in FWS wet- lands is exposed to the atmosphere, and the intended flow path through the system is horizontal. Pretreated wastewater is applied continuously to such systems, and treatment occurs as the water flows slowly through the stems and roots of emergent vegetation. Free water surface systems may also be designed with the objective of creating new wildlife habitats or enhanc- schematic flow diagram of free water surface wetlands. Subsurface flow (SF) wetlands The subsurface flow wet- lands also consist of a basin or channel with a barrier to pre- vent seepage. The basin or channel is filled to a suitable depth with a porous media. Rock or gravel are the most commonly used media types. The media also supports the root systems of the emergent vegetation. The design of these systems assumes that the water level in the bed will remain below the top of the rock or gravel media. The flow path through the operational systems is usually horizontal. 12 The schematic flow diagram of submerged flow wetlands is provided in Figure 2(b). Comparing the two types of constructed wetland sys- tems, the SF type of wetlands offer several advantages over FWS type. If the water surface is maintained below the media surface there is little risk of odors, public exposure, or insect vectors. In addition, it is believed that the media provides larger available surface area for attached growth organisms. As a result, the treatment response may be faster, and smaller surface area may be needed for the same waste- water conditions. 2,10 Furthermore, the subsurface position of the water, and the accumulated plant debris on the surface of the SF bed, offer great thermal protection in cold climates as compared to the FWS type. 14 The reported disadvantage of the SF type system however, is clogging of the media possible overflow. Basic Design Considerations of Constructed Wetlands Constructed wetlands are relatively recent development, and are gaining popularity for treatment of wastewater from small communities, and residential and commercial areas. In this section the basic design information and economics of constructed wetlands are compared. Site selection A constructed wetland can be constructed almost anywhere. In selecting a site for a free water surface wetland the underlying soil permeability must be consid- ered. The most desirable soil permeability is 10E-6 to 10E-7 m/s. 10 Sandy clay and silty clay loams can be suitable when compacted. Sandy soils are too permeable to support wetland vegetation unless there is an impermeable restricting layer in the soil profile that result in a perched high ground water table. Highly permeable soils can be used for wastewater flows by forming narrow trenches and lining the trench walls and bottoms with clay or an artificial liner. In heavy clay soils, addition of peat moss or top soil will improve soil per- meability and accelerate initial plant growth. Plants Although natural wetlands typically contain a wide diversity of plant life, there is no need to attempt to reproduce the natural diversity in a constructed wetland. Such attempts in the past have shown that eventually cattails alone or in combination with either reeds or bulrushes will dominate FIGURE 1 An enlarged root hair of wetland plants. C014_001_r03.indd 740C014_001_r03.indd 740 11/18/2005 10:44:17 AM11/18/2005 10:44:17 AM © 2006 by Taylor & Francis Group, LLC ing nearby existing natural wetlands. Figure 2(a) provides a NATURAL SYSTEMS FOR WASTEWATER TREATMENT 741 in a wastewater system owing to the high nutrient levels. 2 The emergent plants most frequently found in the waste- water wetlands include cattails, reeds, rushes, bulrushes and sedges. Some of the major environmental requirements of Physical facilities The constructed wetlands behave typ- ically like a plug flow reactor. Constructed wetlands offer significant potential for optimizing performance through selection of proper system configuration, including aspect ratios, compartmentalization, and location of alternate and multiple discharge sites. The aspect ratio, defined as the ratio of length to width, typically varies from 4:1 to 10:1. However, based on research data developed on experimental constructed wetlands, the aspect ratios approaching 1:1 may be acceptable. 13 Several alternative flow diagrams and configurations of constructed Hydrologic factors The performance of the constructed wet- lands system is dependent on the system hydrology as well as many other factors such as precipitation, infiltration, evapotrans- piration, hydraulic loading rate, and water depth. These factors affect the removal of organics, nutrients, and trace elements not only by altering the detention time but also by either con- centrating or diluting the wastewater. 9,10 For a constructed wetland, the water balance can be expressed by Eq. (1) [d V /d t ] ϭ Q i − Q e ϩ P − ET (1) where, Q i ϭ influent wastewater flow, m 3 /d Q e ϭ effluent wastewater flow, m 3 /d P ϭ precipitation, m 3 /d ET ϭ evapotranspiration, m 3 /d [d V /d t ] ϭ change in volume of water per unit time, m 3 /d t ϭ time, d Influent Lined Basin Soil Media Effluent Water surface Wetland Plants Influent Lined Basin Soil Media Effluent Water surface Wetland Plants (a) (b) FIGURE 2 Schematic flow diagrams of constructed wetland systems, (a) Free water surface, (b) Subsurface flow. 13 C014_001_r03.indd 741C014_001_r03.indd 741 11/18/2005 10:44:18 AM11/18/2005 10:44:18 AM © 2006 by Taylor & Francis Group, LLC these plants are given in Table 3. wetlands are provided in Figure 3. 742 NATURAL SYSTEMS FOR WASTEWATER TREATMENT Inf. Effl. Influent Effluent RecycleRecycle Recycle Inf. Eff. (a) (b) (d)(c) FIGURE 3 Alternate flow diagram and configurations of constructed wetlands: (a) Plug flow with recycle; (b) Step feed with recycle; (c) Step feed in wrap around pond; (d) Peripheral feed with center drawoff. TABLE 3 Emergent aquatic plants for constructed wetlands Common name (Scientific name) Temperature, °C Maximum salinity tolerance, ppt b Optimum pHSurvival Desirable a Cattail (Typha spp.) 10–30 12–24 30 4–10 Common reed (Phragmites communis) 12–33 10–30 45 2–8 Rush (Juncus spp.) 16–26 — 20 5–7.5 Bulrush (Scirpus spp.) 16–27 — 20 4–9 Sedge (Carex spp.) 14–32 — — 5–7.5 a Temperature range for seed germination: roots and rhizomes can survive in frozen soils. b ppt ϭ parts per thousands. Source: Adopted in part from Ref. 15. C014_001_r03.indd 742C014_001_r03.indd 742 11/18/2005 10:44:18 AM11/18/2005 10:44:18 AM © 2006 by Taylor & Francis Group, LLC NATURAL SYSTEMS FOR WASTEWATER TREATMENT 743 Hydraulic loading rate for FWS system is closely tied to the hydrologic factors and conditions specific to the site. Typical hydraulic loading rate of 198 m 3 /d.ha (21,000 gpd/acre) is considered sufficient for optimum treatment efficiency. BOD 5 loading rates There are two goals for organic load control in the constructed wetlands. The first is the provision of carbon source for denitrifying bacteria. The second goal is to prevent overloading of the oxygen transfer ability of the emergent plants. High organic loading, if not properly dis- tributed, will cause anaerobic conditions, and plants die off. The maximum organic loading rate for both type of systems (FWS and SF) should not exceed 112 kg BOD 5 /ha.d. 2,9,10 Performance expectations Constructed wetland systems can significantly remove the biochemical oxygen demand (BOD), total suspended solids (TSS), nitrogen and phos- phorus, as well as metals, trace organics and pathogens The basic treatment mechanisms include sedimentation, chemi- cal precipitation, adsorption, microbial decomposition, as well as uptake by vegetation. Removal of BOD 5 , TSS, nitrogen, phosphorus, heavy metals and toxic organics have been reported. 2,17 The performance of many well known con- structed wetlands in terms of BOD 5 , TSS, ammonia nitrogen Mosquito control and plant harvesting are the two opera- tional considerations associated with constructed wetlands for wastewater treatment. Mosquito problems may occur when wetland treatment systems are overloaded organically and anaerobic conditions develop. Biological control agents such as mosquitofish ( Gambusia affins ) die either from oxygen starvation or hydrogen sulfide toxicity, allowing mosquito larvae to mature into adults. Strategies used to control mos- quito populations include effective pretreatment to reduce total organic loading; stepfeeding of the influent wastewater stream with effective influent distribution and effluent recy- cle; vegetation management; natural controls, principally mosquitofish, in conjunction with the above techniques; and application of approved and environmentally safe chemical control agents. The usefulness of plant harvesting in wetland treatment systems depends on several factors, including climate, plant species, and the specific wastewater objectives. Plant harvest- ing can affect treatment performance of wetlands by altering the effect that plants have on the aquatic environment. Further, because harvesting reduces congestion at the water surface, control of mosquito larvae using fish is enhanced. It has been reported in the literature that a total of 29,000 kg/ha dry weight of harvestable biomass of Phragmites shoots can be harvested for single harvesting in a year. Higher yield is achievable with multiple harvesting. The BOD 5 , TSS, nitrogen and phosphorus removal effi- ciencies of constructed wetlands are discussed below. BOD 5 Removal in FWS wetlands In the free water surface constructed wetlands the soluble BOD 5 removal is due to microbial growth attached to plant root, stems, and leaf litter that has fallen into the water. BOD 5 removal is generally expressed by a first order reaction kinetic (Eq. 2). 2,3,10 [ C e / C o ] ϭ exp(− K T t ) (2) where, C e ϭ effluent BOD 5 , mg/L C o ϭ influent BOD 5 , mg/L K T ϭ reaction rate constant, d −1 t ϭ hydraulic retention time, d. BOD 5 Removal in SF wetlands The major oxygen source for the subsurface components (soil, gravel, rock, and other media, in trenches or beds) is the oxygen transmitted by the vegetation to the root zone. In most cases, there is very little direct atmospheric reaeration as water surface remains below the surface of the media. 17 Removal of BOD 5 is expressed by Equation (3). This is also a first order equation and can be rearranged to calculate the area required for the subsurface flow system. log( C e / C o ) ϭ −[ A s K t d e]/ Q (3) where, C e ϭ effluent BOD 5 , mg/L C o ϭ influent BOD 5 , mg/L K t ϭ reaction rate constant, d −1 Q ϭ flow rate through the system, m 3 /d d ϭ depth of submergence, m e ϭ porosity of the bed, A s ϭ surface area of the system, m 2 . Suspended solids removal Suspended solids removal is very effective in both types of constructed wetlands. Most of the removal occurs within few meters beyond the inlet. Control dispersion of the inlet flow will enhance removal near the inlet zone. Proper dispersion of solids can be achieved by low inlet velocities, even cross sectional load- ings, and uniform flow without stagnation. 10 Nitrogen removal Nitrogen removal is very effective in both the free water surface and submerged flow constructed wetlands, and the nitrification/denitrification is the major path of nitrogen removal. Total nitrogen removals of up to 79 percent are reported at nitrogen loading rates of (based on elemental N) up to 44 kg/(ha.day) [39 lb/(acre.day)], in a variety of constructed wetlands. If plant harvesting is prac- ticed, a higher rate of nitrogen removal can be expected. 9,20 Phosphorus removal Phosphorus removal in many wet- lands is not very effective because of the limited contact opportunities between the wastewater and the soil. The exceptions are in the submerged bed design when proper soils are selected as the medium for the system. 21 A signifi- cant clay content and the presence of iron, and aluminum will enhance the potential for phosphorus removal. 9,20,21 C014_001_r03.indd 743C014_001_r03.indd 743 11/18/2005 10:44:18 AM11/18/2005 10:44:18 AM © 2006 by Taylor & Francis Group, LLC and total phosphorus is summarized in Table 4. 744 NATURAL SYSTEMS FOR WASTEWATER TREATMENT TABLE 4 Performances of some well known constructed wetlands System name Location Type Record (years) Area (ha) Flow (m 3 /d) BOD 5 (mg/L) TSS (mg/L) NH 3 -N (mg/L) TP (mg/L) IN OUT IN OUT IN OUT IN OUT Lakeland FL FWS 2 498 26978 3 2.5 4 3.5 0.90 0.36 9.46 4.07 Reedy Creek FL FWS 11.2 35.24 12058 5.3 1.9 8.9 2.4 2.98 0.72 1.4 1.78 Reedy Creek FL FWS 11.2 5.87 2423 5.8 1.6 10.9 2.4 3.29 0.12 1.8 0.79 Ironbridge FL FWS 1 486 34254 4.8 2.1 10.5 65.9 3.99 0.94 0.53 0.11 Apalachicola FL FWS 3 63.7 3936 15.2 1.1 107 8 3.62 0.09 3 0.21 Fort Deposit AL FWS 0.67 6 628 29.9 5.4 78.7 10.4 13.59 1 — — West Jackson MS FWS 0.5 8.91 1953 21.6 10.5 65.9 24.5 2.69 0.19 5.13 3.56 Leaf River 1 MS FWS 1.2 0.13 225 15.8 14 54.8 30.1 9.91 7.21 8.91 8.16 Leaf River 2 MS FWS 1.2 0.13 254 15.8 15.7 54.8 34.9 9.91 6.33 8.91 8.19 Leaf River 3 MS FWS 1.2 0.13 220 15.8 13.9 54.8 25.5 9.91 6.79 8.91 5.9 Cobalt Canada FWS 1 0.10 49 20.7 4.6 36.2 28 2.95 1.04 1.68 0.77 Pembroke KY FWS 0.75 1.48 188 67.4 9.4 91.9 8.2 13.8 3.35 6.03 3.16 Central Slough SC FWS 4 32 5372 16.3 6.5 27.7 14.8 7.49 1.38 4.09 1.46 Gustine 1A CA FWS 1 0.39 163 130 49.8 73.5 39.6 17.4 16.1 — — Gustin 2A CA FWS 1 0.39 174 151 44.8 99.8 33.8 18 23.2 — — Philips School AL SFS 2 0.20 58.7 15.3 1 63.7 2 11 1.7 6 0.3 Kingston TN SFS 0.7 0.93 76 56 9 83 3 22 16 3.4 2.1 Denham Sprg. LA SFS 1.5 2.10 2548 28.2 10.5 53 17 11 4.33 — — Monterey VA SFS 1.1 0.023 83 38 15 32 7 9.33 8.67 — — Source: Adopted in part from Ref. 13. C014_001_r03.indd 744C014_001_r03.indd 744 11/18/2005 10:44:18 AM11/18/2005 10:44:18 AM © 2006 by Taylor & Francis Group, LLC NATURAL SYSTEMS FOR WASTEWATER TREATMENT 745 Cost Cost is often a significant factor in selecting the type of treatment system for a particular application. Unfortunately, the availability of reliable cost data for wetland treatment systems is limited. The cost of wetland treatment systems varies depending on wastewater characteristics, the type of wetland system, and the type of bottom preparation required. Subsurface flow systems are generally more expensive than free water surface systems. It has been reported that the Tennesee Valley Authority (TVA) wetland construc- tion costs ranged from $3.58/m 2 to $32.03/m 2 . 22 Estimates are that the construction, operation, and maintenance costs of constructed wetland systems are quite competitive with other wastewater treatment options. REFERENCES 1. Mitsch, W.J. and J.G. Gosselink, Wetlands, Van Nostrand and Reinhold Company, New York, 1993. 2. Reed, S.C., E.J. Middlebrooks, and R.W. Crites, Natural Systems for Waste Management and Treatment, McGraw-Hill, Inc., New York, NY, 1988. 3. Qasim, S.R., Wastewater Treatment Plants: Planning, Design, and Operation, Technomic Publishing Company, Inc. PA, 1994. 4. Middlibrooks, E.J., C.H. Middlebrooks, J.H. Reynolds, G.Z. Watters, S.C. Reed, and D.B. George, Wastewater Stabilization Lagoon Design, Performance and Upgrading, Macmillan Book Co., New York, 1982. 5. US Environmental Protection Agency, Process Design Manual for Land Treatment of Municipal Wastewater, Office of Water Program Operation, EPA/COE/USDA, EPA 625/1-77-008, October 1977. 6. Sanks, R.L. and T. Asano (Eds.), Land Treatment and Disposal of Municipal and Industrial Wastewater, Ann Arbor Science Publisher, Ann Arbor, Mich. 1976. 7. Metcalf and Eddy, Inc., Wastewater Engineering: Treatment, Disposal and Reuse, McGraw-Hill, Inc., New York, NY, 1991. 8. Bastian, R.K. and S.C. Reed (Eds.), Aquaculture Systems for Waste- water Treatment: Seminar Proceedings and Engineering Assessment, US Environmental Protection Agency, Office of Water Program Opera- tions, Municipal Construction Division, EPA 430/9-80-006, Washing- ton, D.C. 20460, September 1979. 9. Hammer, D.A., Constructed Wetlands for Wastewater Treatment, Lewis Publishers, Ann Arbor, Michigan, 1989. 10. Water Pollution Control Federation, Natural Systems for Wastewater Treatment, Manual of Practice No. FD-16, Water Pollution Control Federation, 1990. 11. Dinges, R., Natural Systems for Water Pollution Control, Van Nostrand and Reinhold Company, New York, 1982. 12. Reed, S.C., Constructed Wetlands for Industrial Wastewaters, Presented at Purdue Industrial Waste Conference, May 10, 1993, Purdue University, West Lafayette, IN. 13. Moshiri, G.A., Constructed Wetlands for Water Quality Improvement, Lewis Publishers, Florida, 1993. 14. US Environmental Protection Agency, Subsurface Flow Constructed Wetlands Conference, Proceeding of a conference at University of Texas at El Paso, August 16 and 17, El Paso Texas, 1993. 15. Stephenson, M., G. Turner, P. Pope, J. Colt, A. Knight, and G. Tcho- banoglous, The Use and Potential of Aquatic Species for Wastewater Treatment, Appendix A, The Environmental Requirements of Aquatic Plants, Publication No. 65, California State Water Resources Control Board, Sacramento, California, 1980. 16. Tchobanoglous, G., Aquatic Plant Systems for Wastewater Treatment: Engineering Considerations, in Aquatic Plants for Water Treatment and Resource Recovery. K.R. Reedy and W.H. Smiths, Eds. Magnolia Pub- lishing, Orlando, FL, 1987, pp. 27–48. 17. US Environmental Protection Agency, Subsurface Flow Constructed Wetlands for Wastewater Treatment — A Technology Assessment, Office of Water, EPA 832R-93-001, July 1993. 18. Cueto, A.J., Development of Criteria for the Design and Construction of Engineered Aquatic Treatment Units in Texas, Chapter 9, Constructed Wetlands for Water Quality Improvements, G.A. Moshiri, Lewis Pub- lishers, FL 1993, pp. 99–105. 19. Hammer, D.A., B.P. Pullin, and J.T. Watson, Constructed Wetlands for Livestock Waste Treatment, National Nonpoint Conference, St. Louis, MO, April 1989. 20. US Environmental Protection Agency, Design Manual on Constructed Wetlands and Aquatic Plant Systems for Municipal Wastewater Treat- ment, Office of Research and Development, Center for Environmental Research Information, Cincinnati, OH, September 1988. 21. Brix, H., Treatment of Wastewater in the Rhizosphere of Wetland Plants—The Root-Zone Method, Water Science Technology, Vol. 19, 1987, pp. 107–118. 22. Brodie, G.A., D.A. Hammer, and D.A. Tomljanovich, Constructed Wetlands for Acid Drainage Control in the Tennessee Valley, in Mine Drainage and Surface Mine Reclamation, Bureau of Mines Information Circular 9183, 1988, pp. 325–331. MOHAMMED S. KAMAL SYED R. QASIM The University of Texas at Arlington C014_001_r03.indd 745C014_001_r03.indd 745 11/18/2005 10:44:18 AM11/18/2005 10:44:18 AM © 2006 by Taylor & Francis Group, LLC . facilities, per- formance expectations, hydraulic and organic loading rates, and cost of the constructed wetlands. TYPES OF NATURAL SYSTEMS Natural systems for effective wastewater treatment. Table 1. 738 NATURAL SYSTEMS FOR WASTEWATER TREATMENT by pumping or under-drain systems for recovery of treated water, (3) natural treatment with groundwater moving verti- cally and laterally. bacteria in the wetlands is shown and constructed wetlands. Both natural and constructed wet- lands have been used for wastewater treatment, although the use of natural wetlands is generally