Slow Sand Filtration of Secondary Sewage Effluent: Effect of Sand Bed Depth on Filter Performance

Abstract

Slow sand filtration (SSF) is a simple technique for drinking water purification and may be adapted for wastewater stabilization but only a few studies have been done towards this direction. This study aimed at the evaluation of the effect of sand bed depth on SSF performance by comparing data from sewage effluent filtered through sand beds of varying depths (0.5, 0.7 and 1.0) m. Removal efficiency was determined in terms of selected bacteriological indicators such as coliforms, faecal Streptococcus, total bacterial counts and physicochemical parameters such as biochemical oxygen demand, conductivity, pH, Total Suspended Solids and nutrients. Results of this study indicated significant differences in levels of all physicochemical parameters except phosphates in effluents filtered through the three sand bed depths whereby removal efficiency of these parameters was found to be better at 0.7 m. However, removal of bacteria was not significantly affected by sand bed depth.