ORGANIC STABILIZATION AND NITROGEN REMOVAL IN MEMBRANE SEPARATION BIOREACTOR FOR DOMESTIC WASTE-WATER TREATMENT

In this study, organic stabilization and nitrogen removal were investigated using a household type hollow fiber membrane separation bioreactor of 62 l volume. The process employed direct solid-liquid separation by hollow fiber membrane inside an activated sludge aeration tank. By providing highly turbulent conditions within the separation zone in conjunction with jet aerating installation inside the membrane module, sludge accumulation on the membrane surface and inside the module can be reduced. Permeate flux obtained after 330 days of operation was 0.2 m/d under intermittent suction. High degree of organic stabilization was obtained in the system by operation without sludge wastage except for sampling purposes. Continuous and intermittent aeration modes were investigated in the study. The average effluent COD concentration of 20.8 and 16.5 mg/l were observed during continuous and intermittent aerating application respectively. Degree of nitrification depended upon DO concentration of mixed liquor during aeration period. Introduction of intermittent aeration enhanced total nitrogen removal up to 80% or more by simultaneous nitrification and denitrification, resulting in average of 4.9 mg/l of total nitrogen in the effluent. Increase in DO in aeration period from 1.5-2 mg/l to 4-5 mg/l improved percentage of nitrogen removal to more than 90%. Rejection of 4-6 log virus concentration by gel layer formed on the membrane surface was also observed.