Study on the Decentralized Wastewater Treatment Plants in Khulna

Abstract

Khulna is the third largest city of Bangladesh and situated at the Southwest region of the country having 1.4 million populations living in 45.65 square kilometres area. It has been facing growing urban environmental problems due to daily generated wastewater. There is no sewerage network or any central treatment system in Khulna city. Conventional wastewater treatment plant needs large space for treating vast quantities of wastewater and also requires very high initial as well as operation and maintenance cost. This study is concerned about the two decentralized wastewater treatment (DEWAT) plants constructed at the Peoples Panchtola Colony' at Khalishpur in Khulna. DEWAT system may be defined as the collection treatment, and disposal or reuse of wastewater from individual homes, clusters of homes, isolated communities, industries or industrial facilities at or near the point of waste generation. It consists of septic tank, anaerobic baffled reactors (ABR), anaerobic filter bed baffled reactors (AFBBR), planted gravel filter (PGF) and polishing pond (PP). The specific objectives of this study were to (1) study the performance of two DEWAT plants regarding its technical and socio-economic acceptance by ordinary population in Panchtola Colony; (2) compare the performance of two DEWAT plants based on field and laboratory investigations; (3) identify the technical problems in the operation and maintenance of two DEWAT plants; and (4) recommend the modified DEWAT plants which will reduce construction cost and require small space above ground and low maintenance. To conduct necessary investigation both in field and laboratory, wastewater samples were collected from six different points such as in and out point of settler tank, middle of AFBBR, out of ABR, out of PGF, out of PP of two DEWAT plants at once a month for about one year. Different parameters such as BOD5, COD, pH, Nitrate, Phosphate, Temperature, Oil and Grease, Total Dissolve Solid (TDS), Faecal Coliform (FC), Dissolve Oxygen (DO), Total Suspended Solid (TSS), etc. were determined of the collected samples. The results show that the concentration of all harmful parameters were reduced significantly and lowered to an acceptable level. The results also indicate the effectiveness of ABR and AFBBR over the planted gravel filter considering the area required for PGF and the associated cost. The clogging is also a problem in the filter bed. Finally, it can be concluded that the modified DEWAT system can be practiced in low incoming developing countries as a mid-term solution to improve the sanitation condition.