Relationships of activated sludge characteristics to fouling rate and critical flux in membrane bioreactors for wastewater treatment.

The objectives of this study were to examine the effects of activated sludge characteristics on fouling rate (FR), and to discern whether there is a correlation between FR and critical flux. The activated sludge samples were collected from pilot scale submerged membrane bioreactor plants operated under different process conditions. Their characteristics were assessed by analyzing mixed liquor suspended solids, mixed liquor volatile suspended solids, time to filter, diluted sludge volume index, colloidal total organic carbon, and bound and soluble extracellular polymeric substances including carbohydrate, proteins and humic substances. The fouling potential of these samples was measured in terms of FR and critical flux. Results confirmed that colloidal particles were key constituents responsible for short-term fouling. The soluble carbohydrates were identified as the most important soluble extracellular polymeric substances component responsible for short-term fouling potential. Furthermore, an excellent correlation was observed between critical flux and FR suggesting that the colloidal total organic carbon measurement could be used to predict not only critical flux but also FR.