Upgrading of secondary clarifiers by inclined plate settlers

Secondary sedimentation is one of the most commonly used unit operations in wastewater treatment plants. It is customarily designed to achieve solids separation from biologically treated effluent through clarification of biol ogical solids and thickening of sludge. As treatment plants receive increas ingly high wastewater flow, conventional sedimentation tanks suffer from ov erloading problems which result in poor performance. Inclined plate settler s, a form of tube settlers, may have good potential in upgrading sedimentat ion tanks. This study was conducted to examine the possibility of applying inclined plate settlers in secondary sedimentation in order to upgrade conv entional rectangular sedimentation tanks and improve their performance. Exp eriments were carried out at Al-Awir sewage treatment plant in Dubai using a pilot-scale inclined plate settler which received a mixed liquor stream f rom the high-rate activated sludge aeration tank. The results showed that i nclined plate settlers perform slightly better than conventional type settl ers during normal operation of plants, but during peak flows the inclined p late settlers showed much better performance than conventional settlers. Th e inclined plate settlers are less affected by overloading in comparison to conventional settlers. The solids removal efficiency increased as the hydr aulic residence time was increased or as the surface loading rate was decre ased. Application of these plates will not cause any interruption of daily operation of treatment plants and could be achieved at minimal cost when co mpared with other methods such as addition of chemicals, application of dee p tanks, ... etc. The study revealed that SS is a better parameter than TS, BOD, COD to evaluate the performance of sedimentation tanks. A statistical model was formulated to describe tank performance and design parameters we re obtained based on the experimental results. (C) 1999 Published by Elsevi er Science Ltd on behalf of the IAWQ. All rights reserved.