Aerobic Mesophilic and Thermophilic Treatment of Piggery Wastes at Short Retention Times

Abstract

ABSTRACT Aseries of intermittently fed 1.5 L digesters were used in this laboratory study to compare the effectiveness of aerobic treatment at temperatures of approximately 54 C, 46 C and 38 C. A positive level of dissolved oxygen was maintained during waste treatment while the retention time averaged about 1 day. The pH of un-treated effluents (total solids approximate 22 g/L) ranged from 7.4 to 7.8 while the pH in the treated ef-fluents averaged 7.0 at 54 C and 8.1 at 38 C. The mean 5 day biological oxygen demand (BOD5) of the un-treated wastes ranged from 7.8 to 9.8 g/L. Reductions in BOD5 were of the order 52 percent, 12 percent and 20 percent at 54 C, 46 C and 38 C respectively. Approx-imately 36 percent, 21 percent and 9 percent of volatile solids were oxidised during treatment, increasing with increasing temperature. The ABOD5/AVS ratios were 1.3, 0.3 and 0.8 for treatments at 38 C, 46 C and 54 C respectively. The numbers of faecal coliforms and faecal streptococci declined markedly during ther-mophilic treatment (T90 = 1.5 h) but were unaffected by treatment at either of the other lower temperatures.