A septic tank‐UASB combined system for domestic wastewater treatment: a pilot test

A 250 L and a 550 L pilot scale Up‐Flow Anaerobic Sludge Blanket (UASB) reactors having different reactor height were fed septic tank effluents and operated at ambient temperatures of 0°C to 30°C. Both UASB reactors were fed intermittently at least 8 times per Hydraulic Retention Time (HRT) and the performance was monitored at 4d and 1d HRT. The removal efficiencies of Total Suspended Solid (TSS) and Total Chemical Oxygen Demand (COD_t) were about 59–68% and 54–59%, respectively, for both reactors at both HRT. The TSS and CODt removal efficiencies of Septic tank – UASB combined system were above 80% for both HRTs tested. The average biogas yields were almost same at 4d and 1d HRT, representing 31(±3)% of influent CODt. The nitrogen and phosphorous removal efficiency was an average 20–30%. The tested system can become a suitable low cost yet effective option.