Improvement of domestic wastewater quality by subsurface flow constructed wetlands

Eight subsurface-flow wetlands in Texas, which represented different households and effluent quality and quantity, were evaluated to assess wastewater-quality improvement. All of the constructed wetlands consisted of lined gravel beds supporting aquatic plants. Analysis of the data revealed that the quality of influent varied among locations over the whole sampling period. On average, the BOD of the wetland effluents was below 20 mg/ml, and good reductions were achieved for ammonium nitrogen, phosphorus, total suspended solids, and volatile suspended solids. Populations of total and fecal coliforms were reduced by 90 99%. When chlorination was applied at one of the wetland sites, fecal coliform populations were reduced to less than 2 colony-forming units/100 ml.