Microcosm Wetlands for Wastewater Treatment with Different Hydraulic Loading Rates and Macrophytes (original) (raw)

2002, Journal of Environment Quality

Constructed wetlands (CW) usually require large land areas for ties. Applying any traditional wastewater treatment treating wastewater. This study evaluated the feasibility of applying system to purify these reservoirs would be expensive. CW with less land requirement by operating a group of microcosm wetlands at a hydraulic retention time (HRT) of less than 4 d in In addition, the annual water temperature in southern southern Taiwan. An artificial wastewater, simulating municipal waste-Taiwan ranges from 20 to 32ЊC and under such warm water containing 200 mg L Ϫ1 of chemical oxygen demand (COD), weather conditions treating the polluted water with a 20 mg L Ϫ1 of NH ؉ 4-N (AN), and 20 mg L Ϫ1 of PO 3Ϫ 4-P (OP), was the wetland system becomes a reasonable option. inflow source. Three emergent plants [reed, Phragmites australis In our initial study, we found that a CW system effec-(Cav.) Trin. ex Steud.; water primrose, Ludwigia octovalvis (Jacq.) tively removed nutrients from highly polluted river wa-P.H. Raven; and dayflower, Commelina communis L.] and two floatter (Jing et al., 2001). Removal efficiencies for organics, ing plants [water spinach, Ipomoea aquatica Forssk.; and water letammonia nitrogen (AN), and orthophosphate (OP) tuce, Pistia stratiotes L.] plants were tested. The planted systems were influenced by the health and growth rate of the showed more nutrient removal than unplanted systems; however, macrophytes. The presence of the macrophytes enthe type of macrophytes in CW did not make a major difference in treatment. At the HRTs of 2 to 4 d, the planted system maintained hances several functions in the CW system: assisting greater than 72, 80, and 46% removal for COD, AN, and OP, respecsolids sedimentation, reducing algae production, providtively. For AN and OP removal, the highest efficiencies occurred at ing surface area for microbial growth, improving nutrithe HRT of 3 d, whereas maximum removal rates for AN and OP ent uptake, and releasing oxygen (Brix, 1997). Comoccurred at the HRT of 2 d. Both removal rates and efficiencies were monly used macrophytes in CW systems in the United reduced drastically at the HRT of 1 d. Removals of COD, OP, and States are bulrushes (Scirpus spp.), cattails (Typha spp.), AN followed first-order reactions within the HRTs of 1 to 4 d. The and water hyacinth [Eichhornia crassipes (Mart.) Solms] efficient removals of these constituents obtained with HRT between (Brown and Reed, 1994). However, it was necessary to 2 and 4 d indicated the possibility of using a CW system for wasteidentify domestic macrophytes for potential use in our water treatment with less land requirement. CW system. The treatment efficiency of pollutants in a CW system is usually improved by decreasing the hydraulic loading: Abbreviations: AN, ammonia nitrogen; CCE, surface-covered control experimental system; COD, chemical oxygen demand; CW, constructed wetlands; CW-Co, constructed wetlands planted with day-Shuh-Ren Jing, Ying-Feng Lin, and Der-Yuan Lee, Department of flower; CW-Ip, constructed wetlands planted with water spinach; CW-Environmental Engineering and Health, and Tze-Wen Wang, Depart-Lu, constructed wetlands planted with water primrose; CW-Ph, conment of Pharmacy, Chia