Study On Membrane Bioreactors For Domestic Wastewater Treatment And Retarding Membrane Fouling By Pre-coating With Ferric Salt

Membrane fouling is a critical problem in membrane technology application, whichlimits the development of membrane bioreactors for wastewater treatment. It is theimportant task for environmental engineers to work out on efficiency ways to mitigatethe membrane fouling. Many literatures have been published in which severalmethods can be used to mitigate the membrane fouling, most of them are physicalcleaning, chemical cleaning or changing the characteristics of the membrane surface.Pre-coating method used for microfiltration membranes with ferric salt to mitigate themembrane-fouling rate was not reported. In this paper, a study on the membranepre-coating with ferric salt was carried out.The surface of membrane A was pre-coated with ferric hydrate colloid and themembrane B was without any pretreatment. The two membrane bioreactors ran fortreatment of domestic wastewater for 254 days in same condition. It was found thatthe decline of membrane flux of the two membranes was with different pattern. Themembrane A kept to be stable for long time and the flux of membrane B was droppedtoo quickly to continue running, it had to be cleaned by tap water. All results ofexperiment showed obviously that during experiments the membrane A waspreferable compared with the membrane B to resist membrane fouling. The flux ofmembrane A was recovered to 99.17%, 112.35% and 158.86% after cleaned by tapwater, 10% hydrochloric acid and 0.5% hypochlorite sodium respectively. At sameconditions, the flux of membrane B was recovered to 95.88%, 108.13% and 138.14%.The effluent from two membrane bioreactors was monitored. Average values ofturbidity, chemical oxygen demand (CODCr) and ammonia nitrogen in effluent fromMBR A were 0.2 NTU, 16.32 mg/L and 5.89 mg/L respectively; those of MBR Bwere 0.3 NTU, 18.44 mg/L and 7.62 mg/L respectively. Comprehensive analysisshows that both effluents meet the related standard issued by the state on reuse waterqualities.The result of comparative experiment showed that pre-coating with ferric salt atmembrane surface is a new method to increase the membrane capability in resistingfouling. It is an efficient and economical method to mitigate the membrane fouling.