BACTERIAL REMOVAL FROM SECONDARY SEWAGE EFFLUENT BY A COMBINED DOWNFLOW FLOATING MEDIUM FLOCCULATOR PREFILTER AND SAND FILTER/

semi pilot-scale study conducted with the combined downflow floating m edium flocculator/prefilter and sand filter indicated that, it is an e ffective filter system for removing bacteria from the secondary sewage effluent. Since the filter system can remove more than 99% faecal col iform and faecal streptococci from the secondary sewage effluent, the chlorine dose required to achieve the effluent discharge standard of 2 00 cfU/100 mL will be significantly reduced. It was found out that a s uitable alum dose of 35 mg/L obtained from jar test was found to be an optimum dose for the filter system. The results also indicated that t here was no significant effect of filtration velocity on bacterial rem oval.