Use of MBR to sustain active biomass for treatment of low organic load grey water

The aim of this study was to test the local small-scale treatment of grey water (mainly shower water) of a sports centre to be reused for recreational irrigation. Due to the low organic load which limits the growth and aggregation of biomass, a membrane bioreactor (MBR) was selected for this purpose. A pilot-scale system was operated and studied for more than 1 year in the conduct of this task. The MBR process proved to be a very efficient biological treatment stage, producing superior effluents with low BOD₅, NH₄ ⁺ and TSS. Detergents and COD were degraded efficiently and the effluents did not contain total coliforms and faecal coliforms. Due to the low organic load, biomass accumulation was very slow and the system could reach and function at relatively low mixed liquid suspended solid (MLSS) levels. The MBR ultrafiltration module thus was able to produce a steady permeate flux for more than 1 year just with air scouring and without membrane backwash or chemical regenerating. Another important advantage was the minimal requirement for excess sludge wastage.