A simple anaerobic and filtration combined system for domestic wastewater treatment

Abstract

Anaerobic treatment of domestic wastewater can only partially treat the effluent and still contains concentration of organic matter, suspended solids, nutrients and pathogens beyond the recommended safe limit. This study aims to observe the effect of sand filter as a low cost post treatment solution. A 250 L pilot scale upflow anaerobic sludge blanket (UASB) reactor was fed septic tank effluent and operated at an average ambient temperature of 19 °C. The reactor was fed intermittently at 6 h hydraulic retention time and the performance was monitored. The UASB effluent was filtered in a 1 m³ sand filter unit. The removal efficiencies of Total Suspended Solid, Chemical Oxygen Demand and Faecal Coliform for combined system were 93%, 87% and 93%, respectively. However, the top layer of the sand in the filter needs to be replaced in every two to three months to maintain acceptable filtration capacity performance. The tested combined anaerobic and filtration system was sufficient to treat effluents from a typical Nepalese family and the result could be useful to design and develop a suitable compact, low cost onsite sanitation system in developing countries like Nepal. The result should encourage investigating on the establishment of a safe route of sand replacement and handling as well as alternative low cost filtration media in order to avoid frequent replacement of the sand.