Particle size analysis for improved sedimentation and filtration in waste water treatment

Size distributions of particle mass, chemical oxygen demand (COD) and phosp horus at four municipal waste ;water treatment plants were investigated by fractionation of samples through 0.1-8.0 mu m polycarbonate filters and 32- 125 mu m sieves, respectively. Particle size analysis of primary and second ary effluents at each plant showed significantly different size distributio n functions. These distribution functions remained constant with respect to time under dry weather conditions so they can be considered as characteris tic patterns for each sample location. Advanced treatment by deep bed filtr ation can be improved by taking into consideration the distribution pattern in the secondary effluents. In raw sewage and primary effluents 45-90% of COD and 35-80% of phosphorus were associated with suspended solids. In the secondary effluents particulate COD drops to 14-45% but particulate phospho rus increases to 55-80%. Conclusions are drawn for a better design of advan ced contaminant reduction in connection with suspended solids removal proce sses. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.