Aerobic thermophilic and anaerobic mesophilic treatment of swine waste

Laboratory experiments were conducted to investigate two-stage aerobic ther mophilic and anaerobic mesophilic treatment of swine waste. The two-stage s ystem included a 1-day sludge retention time (SRT) aerobic thermophilic rea ctor operating at 62 degrees C and with 1.0 mg dissolved oxygen/l, followed by a 5, 9, and 14-day SRT anaerobic mesophilic digester operating at 37 de grees C. A single stage anaerobic mesophilic digester operating at 6, 10, a nd 15-day SRT and 37 degrees C was used as the control. Feed swine waste sl urry average composition included total solids (TS) = 4.3%; volatile solids (VS) = 67% of TS; supernatant chemical oxygen demand (COD) = 14,330 mg/l; fecal coliform density = 7.2 x 10(8) MPN/g TS; pH = 7.1; and alkalinity = 2 700 mg CaCO3/l. Two-stage system operating at 6, 10, and 15-day system SRT reduced VS by 46, 54, and 61%, respectively, and was significantly better t han the control at each SRT. Supernatant COD reduction by the two-stage sys tem (56-67%) was significantly better than that obtained in the control (44 -60%). Fecal coliform density was reduced to < 10(3) MPN/g TS at all SRT by the two-stage system, whereas, the control did not reduce the fecal colifo rm density below 10(5) MPN/g TS at all SRT. The two-stage system anaerobic digester produced 0.56-0.64 m(3) CH4/kg VS destroyed compared to lower leve ls of 0.47-0.51 m(3) CH4/kg VS destroyed by the control, both operating at 6, 10, and 15-day system SRT. The methane gas production by the two-stage s ystem of 0.26, 0.32, and 0.39 m(3)/kg VS fed at 6, 10, and IS-day system SR T, respectively, was significantly higher than that by the control system ( 0.17, 0.22, and 0.25 m(3)/kg VS fed at 6, 10, and 15-day SRT, respectively) . The biogas produced by the two-stage system anaerobic digester contained 353-387 ppm (v/v) H2S content compared to 569-609 ppm (v/v) H2S content in the biogas from the control anaerobic digester. The time-to-filter values o f the product sludge from the two-stage system (245, 197, and 158 s at 6, 1 0, and 15-day system SRT, respectively) were about 50% lower than those of the product sludge from the control (355, 295, and 250 s at 6, 10, and 15-d ay system SRT, respectively), indicating better dewaterability of the two-s tage system product sludge. (C) 2000 Elsevier Science Ltd. All rights reser ved.