Load limit of a UASB fed septic tank-treated domestic wastewater

Performance of a 250 L pilot-scale up-flow anaerobic sludge blanket (UASB) reactor, operated at ambient temperatures, fed septic tank effluents intermittently, was monitored for hydraulic retention time (HRT) from 18 h to 4 h. The total suspended solids (TSS), total chemical oxygen demand (COD_T), dissolved chemical oxygen demand (CODdis) and suspended chemical oxygen demand (CODss) removal efficiencies ranged from 20 to 63%, 15 to 56%, 8 to 35% and 22 to 72%, respectively, for the HRT range tested. Above 60% TSS and 47% COD_T removal were obtained in the combined septic tank and UASB process. The process established stable UASB treatment at HRT ≥ 6 h, indicating a hydraulic load design limit. The tested septic tank–UASB combined system can be a low-cost and effective on-site sanitation solution.