Pig slurry treatment by a hybrid multi-stage unit system consisting of an ATAD and an EGSB followed by a SBR reactor

Experiments in a laboratory-scale hybrid multi-stage unit system (HMUS) for pig slurry treatment were conducted to demonstrate the feasibility of using autothermal thermophilic aerobic digestion (ATAD), coagulation and expanded granular sludge bed (EGSB) followed by sequencing batch reactor (SBR) system. Contaminants in pig slurry with high organic matter, nitrogen (N) and phosphorus (P) content were almost completely removed in the HMUS. Concentrations of volatile solids (VS) and chemical oxygen demand (COD) were 2.76 and 3.48% respectively, and they were reduced by about 98.9% by the process. The overall nitrogen reduction rates for total nitrogen and ammoniacal nitrogen were 97.9 and 98.3% respectively and were attained through NH3 gas emission, coagulated sludge disposal and nitrification–denitrification process. The overall phosphorus reduction rate for total phosphorous was 98.2% and this was also attained by coagulation and by the luxury-uptake sludge disposal in the HMUS. Faecal coliform density was reduced to <104 CFU g−1 total solids. The EGSB unit system produced biogas and CH4 in the range of 0.42–0.86 and 0.21–0.62 m3 kg−1 [VS removed], respectively. The biogas produced by the HMUS anaerobic digester contained 324 ± 37 ppm (v/v) [H2S].