Organic stabilisation and nitrogen removal in a membrane separation bioreactor for domestic wastewater treatment

Abstract

Organic stabilization and nitrogen removal wore investigated using a hollow fibre membrane separation bioreactor of 62 I volume. The process employed was direct solid-liquid separation by the hollow fibre membrane inside an activated sludge aeration tank. By providing highly turbulent conditions within the separation zone and incorporating a 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 auction. A high degree of organic stabilisation was obtained in the system without sludge wastage except for sampling purposes. Continuous and intermittent aeration modes were investigated. Average effluent COD concentrations of 20.8 and 16.5 mg/I were observed during continuous and intermittent aeration, respectively. The degree of nitrification depended on the DO concentration of the mixed liquor during the aerating period. Introduction of intermittent aeration enhanced total nitrogen removal up to 80% or more by simultaneous nitrification and denitrification, resulting in an average value of 4.9 mg/I of total nitrogen in the effluent. Increasing the DO in the aerating period from 1.5 – 2 mg/I to 4 – 5 mg/I increased nitrogen removal to more than 90%. Rejection of 4 – 6 log virus concentration by a gel layer formed on the membrane surface was also observed.