Wastewater Treatment by a Prototype Slow Rate Land Treatment System

摘要

Six slow rate land treatment prototypes, three containing a Windsor sandy loam and three containing Charlton silt loam, were studied from June 1974-May 1980. The systems were spray irrigated with either primary or secondary wastewater at application rates ranging from 2.5 cm/wk to 15 cm/wk. Application schedules were also varied. The performance of forage grasses was studied to determine the yield and nutrient uptake under the various application regimes. The results indicate that, on a mass basis, an average of 91% of the nitrogen (N) applied could be attributed to either plant uptake or percolation of soluble N, mainly nitrate. Nitrate concentrations in the percolate were found to correlate with N loading rate. An N loading rate of 800 kg/ha resulted in a mean concentration of about 10 mg/L of NO3-N in the percolate. Plant uptake of N was linearly related to N loading rate at loading rates less than 800 kg/ha. In this range, plant uptake accounted for about 60% of the N applied. Mean phosphorus (P) concentrations in the percolate were found to range from 0.03 to 0.07 mg/L P and depended only slightly on application rate. Removal of P averaged greater than 99% for all application regimes. Water balance measurements indicate that evapotranspiration exceeded pan evaporation by a factor ranging from 0.86 to 1.17 over a 6-year period. Treatment of biochemical oxygen demand (BODs), suspended solids, total organic carbon (TOC), and fecal coliform were excellent. Residual levels of BODs, suspended solids, and TOC in the percolate averaged 1.3, 1.2 and 1.8 mg/L, respectively.