Seasonal effectiveness of a constructed wetland for processing milkhouse wastewater

Abstract

Constructed wetlands are gainign increased attention for treatment of nonpoint source pollution. Although constructed wetlands have been used for wastewater treatment in warm climates, their performance in cold climates has been questioned. A surface-flow wetland, designed to treat 2.65 m3d−1 of milkhouse wastewater, was constructed on the University of Connecticut’s Storrs campus in 1994. The purpose of the project was to determine the efficiency of the system to reduce nutrients, five-day biochemical oxygen demand (BOD5), bacteria, and total suspended solids and to reduce fecal coliform bacteria. During the first ten months of operation, outflow volume was 90% of inflow. Although the wetland was designed to process a BOD5 loading rate of 1500 mg/L, the average actual loading rate was 3000 mg/L. The overall percent mass retention of total suspended solids was 45% and for nutrients was 28%, 27%, 47%, and 6%, for total phosphorus, total Kjeldahl-N, nitrate-N, and ammonia-N, respectively. The percent reduction of fecal coliform and BOD5 was 31% and 28% respectively. Mass retention was significantly greater (p < 0.05) during the growing season than during plant senescence for total suspended solids, total phosphorus, total Kjeldahl, ammonia, and nitrate/nitrite nitrogen. Effluent ammonia nitrogen concentrations often exceeded influent values during the winter. Preliminary indications are that the treatment of the wastewater does not meet design standards, especially in the winter, probably due to overloading of BOD5.