British Columbia Mine Reclamation Symposia

A literature review of constructed wetlands : a viable treatment system for acid mine drainage Attwater, C. J. 1995-12-31

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th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  A LITERATURE REVIEW OF CONSTRUCTED WETLANDS: A VIABLE TREATMENT SYSTEM FOR ACID MINE DRAINAGE  C. J. Attwater University of Northern British Columbia, P.O. Bag, 1950, Prince George, B.C., V2L 5P2 ABSTRACT Wetlands are marsh-like ecosystems exhibiting varying degrees of saturation throughout the year and usually contain a variety of aquatic plants. They have proven capabilities in treating wastewater with physical, chemical and biological processes. Wetlands, especially plant-dominated wetlands, have the capability to remove or convert large quantities of pollutants including suspended solids, metals or excess nutrients by filtration, sedimentation, plant uptake, microbial degradation and other processes. A constructed wetland (CW) is a man-made, engineered, marsh-like area designed and constructed to treat wastewater in the same manner as a natural wetland. It is a practical alternative to mechanical wastewater treatment and water quality requirements, especially in remote areas. Although the treatment of wastewater using CW has been in use for over 40 years, it is not a well-known technology outside of scientific and engineering circles. CW have advantages over mechanical wastewater treatment systems such as simplicity in operation and maintenance and relatively low capital and operating costs. The requirements for a larger land base and a lack of standardized design criteria are two disadvantages to mechanical systems.  Case studies from CW systems will illustrate that reductions in concentrations of various metals and sulphates and increased pH can be achieved when acid mine drainage is treated in a constructed wetland.  265  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  INTRODUCTION  Increased environmental awareness, environmental damage from past industrial practices and the continuing development of government environmental regulations have resulted in the need for natural resource based industries to develop more responsible environmental management systems. Planning and instituting environmentally sound management practices has become as important as planning the extraction of the resource. Wherever industry disturbs the natural environment, waste streams develop. Planning today involves setting out a clear and acceptable program of environmental management. This paper draws from the literature to discuss the Constructed Wetland, a wastewater treatment system that has the potential of reducing pollutants to levels that will meet existing standards for water quality prior to discharging to the environment. The background, development, classifications, functions, pollutant removal mechanisms and design considerations will be briefly reviewed. It will conclude by discussing 3 case studies and results obtained in treating acid mine drainage. Although most of the literature concerns itself with municipal wastewater treatment systems, the wetland treatment concept is applicable to mines. WETLANDS - WHAT ARE THEY? Wetlands have been described by Reed (1987, 207) as land where the water surface is near the ground surface long enough each year to maintain saturated soil conditions and the related vegetation. On the otherhand, Hammer et.al. (1989, 5) state that many types of wetlands are wet only after heavy rains or during one season of the year. At other times they may be very dry. Doku et.al. (1993, 28) quotes the definition that was adopted by the U.S. Fish and Wildlife Service in 1979: "Wetlands are transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification wetlands must have one or more of the following three attributes: (1) at least periodically, the land supports predominantly hydrophytes, (2) the substrate is predominantly undrained hydric soils, and (3) the substrate is non-soil and is saturated with water or covered by shallow water at some time during the growing season of each year." (Corwardinef.a/., 1979).  266  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  R.G. Wetzel, (1989) a student of wetlands for over 2 decades, declined to address the differences between natural and constructed wetlands. He commented that functionally, there should not be differences. Steiner et.al. (1988) state that:  "physical, chemical and biological processes occur in natural wetlands which are similar to those occurring and concentrated in conventional mechanical treatment plants. A constructed wetlands for wastewater treatment is designed to optimize these natural wetlands processes". (Steiner, 1988, 2).  THE CONSTRUCTED WETLAND - BACKGROUND/DEVELOPMENT Wetlands have received wastewater discharges in numerous situations in the past, but only recently have they been recognized as a potentially cost-efficient water treatment and purification system (Smith, 1989; Brix, 1993). The first work that specifically investigated treating wastewater in a wetland by Scirpus lacustris (bulrush) was initiated by K. Seidel in Germany in 1952 (Pride et.al, 1990; Gearheart, 1992). R. Kickuth continued this experimental work in Germany and in 1975 he monitored municipal wastewater discharged into a natural Phragmites (reed) marsh. During the 1970's, the National Science Foundation in the USA funded studies by John and Bob Kadlec at the University of Michigan and Odum and Ewel at the University of Florida in the use of natural wetlands for wastewater treatment (Bastian et.al, 1993). This led to a series of pilot studies and operational systems using constructed wetlands in both Canada and the U.S. The CW is an engineered and constructed complex of saturated substrates, emergent and submergent vegetation, animal life and open water that simulates natural wetlands for man's desired uses and benefits (Steiner et.al, 1988; Hammer et.al, 1989). CW are being used to treat acid mine drainage (Tomljanovitch e/.a/.,1988; Chen et.al, 1992; Tang, 1993; Davison, 1993), agricultural wastewater (Higgens et.al, 1993; Hammer et.al, 1993) and, among other applications, municipal wastewater (Steiner et.al, 1988; Watson, 1992).  267  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  CLASSIFICATION  A vegetative CW can be classified, in part, by the life form of the dominating plant. Three vegetative classifications are generally accepted: free floating, submergent and emergent (Brix, 1993). Free floating vegetation floats entirely, including root system, on the surface of the water. Both submergent and emergent vegetation are rooted in the substrate; the difference being emergent vegetation reaches above the water surface and submergent vegetation grows entirely below the surface although some of the leafy extremities may float on the surface. Watson (1992), has chosen to classify CW according to hydrology which consists of surface flow and subsurface flow (having horizontal flow patterns) and vertical (nonsaturated) filter flow. Regardless of varying classification combinations, an important advantage of the CW is the ability to control the hydraulics and thereby the loadings so that naturally occurring physical, chemical and biological processes are optimized for removal of target pollutants (Watson, 1992; Brix, 1993). Table 1 shows some common aquatic plants that have been tested for use in CW. Table 1 Wetland Species Tested for Use in Constructed Wetlands for Wastewater Treatment  adapted from Guntenspergen et.al. (1989, 74) and Doku et.al. (1994, 41)  268  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  FACTORS AFFECTING VEGETATIVE DIVERSITY There are many important factors that influence the selection of vegetation for a CW. Hammer (1991) discusses at length the strong influence that hydrology and substrate have on wetland vegetation. He states: "Water depths, frequency and duration of flooding and water chemistry are the most important factors determining the survival and growth of plants in a wetland system." (Hammer, 1991, 195) Depth influences gas exchange between the substrate and the atmosphere, light penetration for photosynthesis and the vegetation characteristics of the wetland. Different wetland plants are able to withstand varying degrees of flooding throughout the year depending on when and for how long. During dormant periods of the year, flooding may have little impact on vegetation but during active growth periods when oxygen demands are increased, extended flooding may cause stress or mortality (Hammer, 1991). Similarly, reduced flow through a wetland can cause mortality as well (Marble, 1991). Physical and chemical parameters of water such as pH, water clarity, dissolved nutrients, flow velocity, salt concentration and dissolved oxygen also affect the survival and growth of wetland plants (Hammer, 1991; Marble, 1991). For example, rooted aquatic plants with floating leaves (Nuphar spp., Brasenia spp., Ptomamogeton nodosus) can overcome physical light penetration limitations and in clear but fast flowing waters, plants with extensive root systems (Vallisneria spp.) are resistant to current disturbances (Hammer, 1991). Various species such as cordgrass (Spartind), wigeongrass (Ruppid) and some forms of bulrush (Scirpus acutus and S. fluviatilis) are tolerant of moderately to strongly saline conditions (Hammer, 1991; Marble, 1991). Most common substrates are suitable for wetland establishment. Hammer (1991) comments on two commonly found soil types: "Sandy loam and clay loam soils normally have adequate nutrients, provide good water and gas circulation and moderate texture to support new plants and to permit root or rhizome penetration." (Hammer, 1991, 204). "Clay and gravels may be so dense or hard that they inhibit root penetration, they may lack nutrients found in topsoil or they may be impermeable to water needed by roots." (Hammer, 1991, 204).  269  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  The selection of aquatic plants for planting in a CW is not only dependent on the factors briefly discussed above. Planners should ensure that species endemic to their region are selected. This can be accomplished by observing naturally occurring wetlands in the vicinity. Hammer (1991) suggests that once the objectives of constructing a wetland are established, species must be selected that will achieve those objectives keeping in mind that water depth and/or flooding duration is the most important controlling factor for species survival. A selection of wetland plants with accompanying environmental requirements is presented in Table 2.  Table 2 Environmental Requirements of Selected Herbaceous Plants  FUNCTIONS  Doku et.al. (1993) briefly describe wetlands as affording natural shoreline protection, flood reduction and control, providing geochemical sinks or traps for substances including carbon, sulphur from acid rain and heavy metals, wildlife food and habitat and recreational pursuits. They also note that wetlands provide water quality improvement by;  270  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  "providing effective free treatment for many types of water pollution, removing or converting large quantities of pollutants from point sources and non-point sources including organic matter, suspended solids, metals and excess nutrients by natural filtration, sedimentation and other processes". (Doku et.ai, 1993, 44) Studies over the years have shown that wetlands are able to provide high levels of wastewater treatment (Bastian et.al., 1989). They have a very significant role in the natural cycling of organic and inorganic materials and they support an abundance of macro- and microscopic vegetation which converts inorganic chemicals into the organic materials required as food for both animals and man (Bastian et.al., 1993). Pretreatment prior to wastewater entering a CW is usually necessary to remove coarse and heavy solids (Steiner et.al., 1991). The literature primarily discusses CW as efficient secondary (Gersberg et.al., 1983; Pride et.al., 1990) or tertiary (Brix, 1993; Tettleton et.al., 1993) treatment systems and polishers for both municipal and industrial wastewaters (Watson et.al., 1986; Reed et.al., 1992 ).  REMOVAL MECHANISMS CW have a number of removal mechanisms in aquatic plant or macrophyte-based treatment systems. Table 3 lists a number of removal mechanisms described by Watson et.al., (1989, 321), Brix (1993, 11) and Tang (1993, 257).  Table 3 Removal Mechanisms in Macrophyte-Based Wastewater Treatment Systems  271  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  Suspended solids are removed rapidly from wastewater at the inlet zone of a CW by both sedimentation and filtration (Watson et.al., 1988) and by autoflocculation and sedimentation as the solids reach open spaces and move between the plants (Gearheart, 1992). Watson (1992) suggests: "that solids can be managed much better in other facilities prior to the wetlands, preserving the wetlands for removal of soluble pollutants and colloidal solids not easily removed in conventional facilities". (Watson, 1992, 11) Bavor et.al. (1993) concur that effective pre-settling is vital for maintaining good hydraulic conductivity. Sedimentation build-up at the inlets to CW can shorten the useful life of the system and cause internal pollutant loading (Watson, 1992).  DESIGN CONSIDERATIONS Prior to establishing a constructed wetland for wastewater treatment, a number of considerations must be evaluated. Brodie (1989) notes some of the considerations in selecting a site: 1.  Clearly define the wastewater management objectives and the regulatory considerations  2.  Collect sufficient data to develop the preliminary design of a wetland system  3.  Investigate the environmental and social conditions and sensitivities to predict any adverse effects and provide mitigation and,  4.  Obtain legal access to the site". (Brodie, 1989, 308)  He further suggests four categories that are of equal importance in siting a CW; land use/general considerations, hydrology, geology and environmental/regulatory considerations. Bastian et.al.(\9&9), Wieder et.al.(1989) and Choate et.al. (1990) provide both advantages and disadvantages of constructed wetland systems in Table 4. Since each CW is a unique entity there are no standardized or "cookbook" designs that are applicable in given situations. A CW must be established to treat the specific contaminants on a site-by-site basis. Cost-effectiveness of CW is very site specific and only technology that has a chance of performing acceptably should be used. (Steiner et al, 1993).  272  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  Table 4 Advantages and Disadvantages of Constructed Wetlands for Wastewater Treatment  adapted from: Bastian et.al., 1989, 268; Wieder et.al., 1989, 300/303 and Choate et.al., 1990,1  CASE STUDIES The results of three case studies are presented where CW or CW test systems proved beneficial in removing sulphates and heavy metals from mine drainage. An extensive review of the available literature will provide more detailed and varied information than can be presented in this paper.  At the Big Five Tunnel near Idaho Springs, Colorado, the important process for raising pH and removing metals was found to be bacterial sulphate reduction followed by precipitation of metal sulphides. The following results were achieved: (EPA/540/SR-93/523, 1) • pH was raised from 2.9 to 6.5. • Dissolved Al, Cu, Zn, Cd, Ni and Pb concentrations were reduced by 98% or more. • Iron removal was seasonal with 99% removal in the summer. • Mn reduction was relatively poor unless the pH of the effluent was raised above 7 • Biotoxicity to fathead minnows and Ceriodaphnia was reduced by factors of 4 to 20.  Eger (1994) discusses aerobic and anaerobic reactions occurring in test systems constructed in Minnesota and presents the following results. Table 5 illustrates Nickel removal in the wetland treatment cells. The mean input Nickel concentration was 0.66 mg/L (range 0.11-2.1 mg/L).  273  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  Table 5 Nickel Removal in Wetland Treatment Cells, 1989-1990  (Eger, 1994,251) Table 6 illustrates water quality results from sulphate reduction treatment. Table 6 Water Quality Results, Sulphate Reduction Treatment, 1990-1991  Average Concentrations1 , mg/L  1 2 3 NA  by titration; recent data indicates that these values are low since metal precipitation is not instantaneous and neutralization reactions were not complete when acidity was measured. 10 kg. horse manure to 1 kg. sawdust, wet weight basis 2 barrels municipal compost followed by 1 barrel sawdust Not applicable (Eger, 1994, 253)  274  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  A study at a PB/Zn mine at Shaoguan, Guangdong Province, China utilizeed a Typha latifolia dominated wetland flowing into a stabilization pond. Input levels of Pb and Zn were measured at 1.6 mg/L and 1.9 mg/L respectively. Water samples were collected every 10 days from January, 1985 to June, 1988. The results indicated an 87% reduction in Pb and a 95% reduction in Zn at the discharge end of the system. An 88% reduction in Cd was also noted over the same sampling period. (Lan et a/., 1992). The results from the case studies have been briefly noted to provide examples of the effectiveness of CW in treating mine drainage. I urge those of you who want more detailed information on the case studies presented to obtain complete copies of the papers referenced. Review of the literature has determined that a constructed wetland is an effective method of treating wastewater. Natural wetlands have physical, chemical and biological processes that occur in conventional mechanical wastewater treatment systems. Functionally, a constructed wetland should not perform any differently than a natural wetland but the opportunity is created to make it operate more effectively and efficiently. I have provided references in excess of those cited in the paper should you wish to further explore this technology for treating acid mine drainage. REFERENCES Bastian, R.K., P.E. Shanaghan and B.P. Thompson. 1989. "Use of Wetlands for Municipal Wastewater Treatment and Disposal" in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural. D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI. Bastian, R.K. and D.A. Hammer. 1993. "The Use of Constructed Wetlands for Wastewater Treatment and Recycling", in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Bavor, H.J. and T.J. Schulz. 1993. "Sustainable Suspended Solids and Nutrient Removal in Large-Scale, Solid Matrix Constructed Wetlands Systems", in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Brix, H. 1993. "Wastewater Treatment in Constructed Wetlands: System Design, Removal Processes and Treatment Performance", in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Brodie, G.A. 1989. "Selection and Evaluation of Sites for Constructed Wastewater Treatment Wetlands", in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural, D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI.  275  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  Chen, C.L.G., C. Lan, L. Li and M.H. Wong. 1990. "Use of Cattails in Treating Wastewater from a Pb/Zn Mine". Prepared for presentation at the Use of Constructed Wetlands in Water Pollution Conference, Cambridge, U.K. Choate, K.D., J.T. Watson and G.R. Steiner. 1990. "Demonstration of Constructed Wetlands for Treatment of Municipal Wastewaters". Monitoring report for the period March 1988 to October, 1988, Tennessee Valley Authority, River Basins Operation, Chattanooga, TN. Cowardin, L.M., V. Carter, F.C. Golet and E.T. Laroe. 1979. Classification of Wetlands and Deepwater Habitats of the United States. U.S. Fish and Wildlife Service Pub. FWS/OBS-79/31. Washington, B.C., 103p. Davido, R.L. and T.E. Conway. 1989. "Nitrification and De-nitrification at the Iselin Marsh/Pond/Marsh Meadow Facility", in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural, D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI. Davison, J. 1993. "Successful Acid Mine Drainage and Heavy Metal Site Bioremediation", in Constructed Wetlands for Water Quality Improvement, G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. DeBusk, T.A., P.S. Burgoon and K.R. Reddy. 1989. "Secondary Treatment of Domestic Wastewater Using Floating and Emergent Macrophytes" in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural, D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI. Doku, I. A., and G.W. Heinke. 1993. "The Potential for Use of Wetlands for Wastewater in the Northwest Territories". Report to the Department of Municipal and Community Affairs, Government of the Northwest Territories. Eger, P. 1994. "Wetland Treatment for Trace Metal Removal from Mine Drainage: The Importance of Aerobic and Anaerobic Processes" in Water Science Technology. Vol. 29, No. 4, pp. 249-256, IAWQ, Great Britain. Feierabend, J.S. 1989. "Wetlands: The Lifeblood of Wildlife", in Constructed Wetlands for Wastewater Treatment: Municipal, Industrial and Agricultural, D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI. Gearheart, R.A. 1992. "Use of Constructed Wetlands to Treat Domestic Wastewater, City of Arcata, California", in Water Science Technology. Vol. 26, No. 7-8, pp. 1625-1637, IAWPRC., Great Britain. Gersberg, R.M., B.V. Elkins and G.R. Goldman. 1983. "Nitrogen Removal in Artificial Wetlands", Water Resources. Vol. 17, No. 9, pp. 1009-1014, Pergamon Press, Great Britain. Guntenspergen, G.R., F. Stearns and J.A. Kadlec. 1989. "Wetland Vegetation", in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural. D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI.  276  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  Hammer, D.A. and R.K. Bastian. 1989. "Wetland Ecosystems: Natural Water Purifiers ?", in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural, D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI. Hammer, D.A. 1992. Creating Freshwater Wetlands. Chapter 10, pp. 195-226, Lewis Publishers, Chelsea, MI. Hammer, D.A., B.P. Pullin, T.A. McCaskey, J. Eason and V.W.E. Payne. 1993. "Treating Livestock Wastewaters with Constructed Wetlands", in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Higgens, M.J., C.A. Rock, R. Bouchard and B. Wengnezynek. 1993. "Controlling Agricultural Run-off by the Use of Constructed Wetlands", in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Jenssen, P.D., T. Maehlum and T. Krogstad. 1993. "Potential Use of Constructed Wetlands for Wastewater Treatment in Northern Environments", Water Science Technology. Vol. 28, No. 10, pp. 149-157, (Publisher not noted). Marble, A.D. 1991. A Guide to Wetland Functional Design. 222 p., Lewis Publishers, Boca Raton, FLA. Pride, R.E., J.S. Nohrstedt and L.D. Benefield. 1990. "Utilization of Created Wetlands to Upgrade Small Municipal Wastewater Treatment Systems", Water. Air and Soil Pollution. 50: 371-385, Kluwer Academic Publishers, Netherlands. Reed, S.C. 1987. "Wetlands as Effluent Treatment Systems" in Appropriate Wastewater Management Technologies for Rural Areas Under Adverse Conditions. D.H. Waller and A.R. Townsend, Eds., Tech Press, Halifax, N.S. Reed, S.C. and D.S. Brown. 1992. "Constructed Wetland Designs - the First Generation", Water Environment Research. Vol. 64, No. 6, pp. 776-781, Washington, D.C. Rogers, K.H., P.P. Breen and A.J. Chick. 1993. "Hydraulics, Root Distribution and Phosphorous Removal in Experimental Wetland Systems", Water Science Technology. Vol. 28, No. 10, pp. 587-590, IAWQ., Great Britain. Smith, A.J. 1989. "Wastewaters: A Perspective", in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural. D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI. Steiner, G.R. and R.J. Freeman Jr. 1988. "Configuration and Substrate Design Considerations for Constructed Wetlands Wastewater Treatment". Prepared for the International Conference on Constructed Wetlands for Wastewater Treatment, Chattanooga, TN. Steiner, G.R., J.T. Watson and D.A. Hammer. 1988. "Constructed Wetlands for Wastewater Treatment". Prepared for presentation at the Mississippi Water Resources Conference, Jackson, MS.  277  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  Steiner, G.R., J.T. Watson and K.D. Choate. 1991. "General Design, Construction and Operation Guidelines for Small Constructed Wetlands Wastewater Treatment Systems". Prepared for the International Symposium on Constructed Wetlands for Water Quality Improvement, Pensacola, FLA. Steiner, G.R. and J.T. Watson. 1993. "General Design, Construction, and Operation Guidelines: Constructed Wetlands Wastewater Treatment Systems for Small Users Including Individual Residences", Second Edition. Technical Report Series, TVA/WM-93/10, Resource Group, Water Management Branch, Tennessee Valley Authority, Charranooga, TN. Tang, S. 1993. "Experimental Study of a Constructed Wetland for Treatment of Acidic Wastewater for an Iron Mine in China", Ecological Engineering. Vol. 2, pp. 253-259. Elsevier Science Publishers B.V., Amsterdam. Tchobanoglous, G. 1993. "Constructed Wetlands and Aquatic Plant Systems: Research, Design, Operational and Monitoring Issues" in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Tettleton, R.P., F.G. Howell and R.P. Reaves. 1993. "Performance of a Constructed Marsh in Tertiary Treatment of Bleach Kraft Pulp Mill Effluent: Results of a 2 Year Pilot Project", in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Tomljanovich, D.A., G.A. Brodie and D.A. Hammer. 1988. "Constructed Wetlands for Treating Drainage at TVA Facilities". Progress report to Tennessee Valley Authority, Knoxville, Tennessee. United States Environmental Protection Agency. 1993. "Emerging Technology Summary - Handbook for Constructed Wetlands Receiving Acid Mine Drainage", EPA/540/SR-93/523, National Technical Information Service, Springfield, VA. Viessman, W., Jr., and M.J. Hammer. 1992. Water Supply and Pollution Control. Chapter 8, pp. 255-294, 5th. Edition, Harper Collins, College Publishers, New York, N.Y. Watson, J.T., F.D. Diodato and M. Lauch. 1986. "Design and Performance of the Artificial Wetlands Wastewater Treatment Plant at Iselin, Pennsylvania". Prepared for presentation at the Conference for Research and Application of Aquatic Plants for Water Treatment and Resource Recovery, Orlando, FLA. Watson, J.T., S.C. Reed, R.H. Kadlec, R.L. Knight and A.E. Whitehouse. 1988. "Performance Expectations and Loading Rates for Constructed Wetlands". Prepared for the International Conference on Constructed Wetlands for Wastewater Treatment, Chattanooga, TN. Watson, J.T., K.D. Choate and G.R. Steiner. 1990. "Performance of Constructed Wetland Treatment Systems at Benton, Hardin and Pembroke, Kentucky During the Early Vegetation Establishment Phase". Prepared for the Conference on the Use of Constructed Wetlands in Water Pollution Control, Cambridge, England, TVA, Chattanooga, TN. Watson, J.T. 1992. "Constructed Wetlands for Municipal Wastewater Treatment: State of the Art". Presented at the Symposium des Eaux Usees par les Plants: Perspectives D'Avenir aux Quebec, P.Q.  278  th  Proceedings of the 19 Annual British Columbia Mine Reclamation Symposium in Dawson Creek, BC, 1995. The Technical and Research Committee on Reclamation  Wetzel, R.G. 1993. "Constructed Wetlands: Scientific Foundations are Critical" in Constructed Wetlands for Water Quality Improvement. G.A. Moshiri, Ed. Lewis Publishers, Boca Raton, FLA. Wieder, R.K., G. Tchobanoglous and R.W. Tuttle. 1989. "Preliminary Considerations Regarding Constructed Wetlands for Wastewater Treatment" in Constructed Wetlands for Wastewater Treatment: Municipal. Industrial and Agricultural. D.A. Hammer, Ed. Lewis Publishing, Chelsea, MI.  279  

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