The aerobic treatment of silage effluent: Effluent characterization and fermentation

Analyses were made to characterize silage effluent and identify its major constituents, both in the raw state and during treatment processes. Determinations of volatile fatty acids (VFA) and lactic acid in silage effluent were made using a modified high performance liquid chromatography (HPLC) method. Other analyses made included biochemical oxygen demand (BOD5), permanganate value (PV), dry matter (d.m.) (TS), suspended solids (SS), pH, carbohydrate, total and ammoniacal nitrogen, total- and ortho-phosphate and microbial counts. In exploratory studies diluted silage effluent with a BOD, value of 8000 mg/l and a pH of 4.5 was treated aerobically in an upflow laboratory-scale glass fermenter with glass packings and concurrent forced aeration. Each fermentation lasted for 14 d but was virtually over in half that time. The satisfaction of the oxygen demand and the kinetics of the process were studied. The results indicated a 91-93% decrease in BOD5, down to 400-700 mg/l, and an increase in pH to 9, so that the final effluent was much less environmentally harmful to watercourses. (C) 1995 Silsoe Research Institute