INTERMITTENT FILTRATION OF WASTEWATER - REMOVAL OF FECAL COLIFORMS AND FECAL STREPTOCOCCI

The effect of grain size, hydraulic dosing rate and distri- bution method were investigated. Two different natural sands and three different types of light weight aggregates were used. Intermitttent dosing rates from 20 to 80mm/day were applied to the filters by uniform pressure distribu-tion or point application by gravity dosing. Minimum reten-tion time was found to be a key parameter for predicting removal of bacteries in unsaturated aerobic filters. At minimum retention time lower than 50h there was a correla-tion of 0.96 between retention time and removal of fecal coliforms.