Anaerobic on-site treatment of kitchen waste in combination with black water in UASB-septic tanks at low temperatures

Anaerobic on-site treatment of a mixture of black water and kitchen waste (BWKW) was studied using two-phased upflow anaerobic sludge blanket (UASB) septic tanks at the low temperatures of 20 and 10 °C. Black water (BW) was also treated alone as reference. The two-phased UASB-septic tanks removed over 95% of total suspended solids (TSS) and 90% of total chemical oxygen demand (CODt) from both BWKW (effluent CODt 171–199 mg/l) and BW (effluent CODt 92–100 mg/l). Also, little dissolved COD (CODdis) was left in the final effluents (BW 48–70 mg/l; BWKW 110–113 mg/l). Part of total nitrogen (Ntot) was removed (BW 18% and BWKW 40%) and especially at 20 °C ammonification was efficient. A two-phased process was required to obtain the high removals with BWKW at 10 °C, while with BW a single-phased process may have sufficed even at 10 °C. BWKW also produced more methane than BW alone. Sludge in phases 1 of BW and BWKW treatment was not completely stabilised after 198 d of operation.