Performance Evaluation Of The Pagla Sewage Treatment Plant

The Pagla Sewage Treatment Plant (PSTP) was first started in 1968 with 4 facultative lagoons which were further renovated in 1977 to serve about 500,000 citizens in Dhaka city. The present PSTP had been rehabilitated in 1992 by JICA to treat a capacity of 120,000 m3/day. The plant is located 8 km away at the south-east portion of Dhaka city and about 1 km north of the Buriganga. The plant has been designed considering influent BOD5 of 200 mg/l and effluent BOD5 of 50 mg/l which indicates that PSTP is designed to treat domestic wastewater. The laboratory test results of Pagla Sewage Treatment Plant were collected from the office situated within the premise of the plant. The PSTP is a multi stage treatment plant in which BOD5 and SS is measured at inlet, outlet at primary sedimentation tank and outlet of lagoons. Generally, in PSTP SS data is recorded in every alternate day while BOD5 is generally recorded twice a week. From all the available data it is obtained that average influent BOD5 is 398 mg/l and effluent BOD5 is 79.31 mg/l which is greater than design value(influent 200 mg/l and effluent 50 mg/l). Also SS has the same efficiency as that of BOD5. Also yearly variations for BOD5 have been obtained. From 1999 and onwards high concentration of BOD5 and SS indicates strong evidence of industrial wastes entering PSTP. Seasonal variation in concentration of BOD5 and SS is also pronounced. In dry season high concentration is observed and in wet season relatively low concentration is obtained. From the obtained data correlation between BOD5 and SS can be obtained well at inlet. But correlation between BOD5 and SS is rather poor at outlet. Also correlation between different months shows good relationship both for BOD5 and SS. For the improvement of the performance of Pagla Sewage Treatment Plant immediate cleaning of the lagoon is recommended. It is also necessary to record the data in user friendly interface in computer format and also improvement of laboratory facilities for constant effective supervision. Moreover, the reasons for high BOD5 concentration should be identified by closely monitoring the influent characteristics. In case of industrial discharge mixing into city sewerage network it must comply with Environment Quality Standards. Finally, considering the performance of PSTP the option for constructing more sewage treatment plant should be seriously in contention.