NITRATE REMOVAL EFFICIENCY WITHIN OVERLAND FLOW V OVERLAND FLOW-WETLAND TREATMENT OF SEWAGE EFFLUENT

Penn State University began routine treatment of up to 4 mgpd of its sewage effluent by spray irrigation (1983-present) following 12 years of research (1962-74). Effluent is applied at a 2-inch per week rate on a year around basis at two sites containing thick (>10 to 150 feet) residual soil overlying carbonate bedrock. Both forests and cropland receive effluent. Nitrate slowly increased in some groundwater monitoring wells eventually exceeding the 10 mg/L compliance limit. Possible contributing source areas of elevated nitrate included two areas of runoff and rapid winter infiltration. To determine if nitrate removal rates were inadequate, nitrogen was monitored in applied effluent and at runoff sites where flows range from <100 to 300 gpm above these two areas of rapid infiltration.

Renovation processes were expected during overland flow, interflow and deep percolation in one tributary together with possible wetland treatment in the second basin during winter. Nitrate in runoff varied from <1.0 to 3.0 mg/L for the basin that contained the four small natural wetlands, 3.0 to 8.0 mg/L for the overland and interflow dominated basin v 8.51 to 13.08 mg/L for the applied effluent and 20 to 30 mg/L nitrogen prior to modifications in the sewage treatment plant before the start of this study. Results of this investigation suggest that nitrogen removal processes are inadequate within interflow and overland flow sites during winter months under Pennsylvania's climate, whereas even small wetlands appear to provide beneficial results.