Direct observations of membrane scale in membrane bioreactor for wastewater treatment application

초록

The formation of inorganic fouling on MF membrane was investigated in membrane bioreactor (MBR) treating industrial wastewater. Membrane autopsy works using microscopic techniques and surface analysis were carried out at the completion of pilot-scale operation to analyze foulant materials extensively. Scaling occurred on the membrane surface significantly in the MBR treating calcium-rich wastewater (LSI > 2.0). Our experiments showed that the coverage of the membrane surface by the inorganic fouling consisted mostly of calcium while the internal fouling within membrane pores due to the scale formation was almost negligible. Most of calcium was rejected on the MF membrane surface as calcium carbonate scale formation (> 90 % as rejection). The sequence sodium hypochlorite-citric acid for the removal of membrane scale was more effective than the sequence citric acid-sodium hypochlorite. It appeared that the structure of organic compounds combined with calcium became loose by the addition of the sodium hypochlorite. As a result, the calcium could be released easily from the membrane by applying citric acid solution subsequently. Keywords Membrane bioreactor, scaling, membrane autopsy, calcium carbonate