Development of a Laboratory Scale Drainage Wastewater Treatment Plant for Khulna Municipality

Abstract

Cities in developing countries are experiencing unparalleled growth and rapidly increasing water supply and sanitation coverage that will continue to release growing volumes of wastewater. Wastewater is increasingly being used for irrigation in urban and peri-urban agriculture, and even in distant rural areas downstream of the very large cities. The present study was conducted to analyse municipal wastewater quality parameters of the existing drainage outlets over Mayur River around Khulna city and to develop a laboratory scale treatment plant for safe disposal and prevent environmental pollutions. To fulfil the purpose of the research, wastewater samples from three municipal drain outlets were collected and analysed for selecting treatment system and the evaluation of effluent’s suitability for irrigation use as well as safe disposal into surface water bodies. From the analysis of physico-chemical characteristics of wastewater, it can be seen that pH, EC, BOD, COD, alkalinity, hardness, chloride, nitrate and sulfate values were not fully satisfy the irrigation standard limit as the wastewater was highly polluted. The BOD and COD concentration of wastewater sample were varied from 57-226 mg/l and 320-435 mg/l respectively and the total coliform ranged from 70000-98050 N/100ml. Chloride and hardness values were of high range as the collected samples were heavily polluted by organic matter and microorganisms. Therefore, a laboratory scale treatment technology has been developed for the treatment of this wastewater. Treatment technologies adopted are primary sedimentation followed by aeration, chemical precipitation and filtration. In treated wastewater BOD5, COD and TDS were found to be in the range of 40-115 mg/l, 160-256 mg/l and 1356-1500 mg/l respectively. These test results suggest that the performance of the developed treatment plant was not adequate to fulfil the acceptable limit (ECR'97) for safe disposal into surface water bodies. Based on preliminary treatment results, some modifications of developed laboratory scale treatment plant were done by activated sludge process followed by granular media filtration. As a result, the final BOD, COD and TDS concentration of effluents were found 1.38-1.78 mg/l, 32-128 mg/l and 590-1667 mg/l respectively which satisfy ECR'97 standard limits for safe disposal into inland water bodies. Comparing with national (ECR'97) and international (FAO'85) wastewater quality standards, the effluents of modified treatment plant may be reused for irrigation purposes that would be able to meet the increasing water demand for the farmers and can be safely disposed into the surrounding water bodies of Khulna city.