Performance Evaluation of Overland Flow Wastewater Treatment System under Winter and Summer Conditions

Abstract

A study was conducted to evaluate the effects of seasonal variations, summer and winter conditions, on the performance of an existing and successfully operated overland flow wastewater treatment system in the Midwest. The effect of design parameters, such as hydraulic and organic loading rates, and the seasonal temperature effects on performance were investigated. The overland flow system studied consists of an aerated lagoon, two conventional lagoons, and an overland flow area. The overland flow area is divided into six groups of terraces and the terraces are constructed at a slope of 2% with slope length of 341.3 m (1,120 ft). The influent and effluent samples were analyzed for biological oxygen demand (BOD 5), suspended solids (SS), pH, and temperature. The effluent samples were also analyzed for ammonia nitrogen. The results of the study indicate that the overland flow system provided excellent treatment of municipal wastewater. The average removal for BOD 5 and SS were 89% and 85%, respectively, in warm weather. During cold weather the percent removals for these parameters were 81% and 69%, respectively. The effluent ammonia-nitrogen was 1.2 and 2.9 mg/L, respectively, for summer and winter, which indicates significant ammonia nitrification, especially in summer months. Regardless of seasonal conditions, the effluent BOD 5 and SS for the system met the National Pollutant Discharge Elimination System effluent permit requirements throughout the year.