Treatment of domestic wastewater using modified septic tank

Abstract

The treatment of domestic wastewater using conventional, single-baffle, two-baffle, and packed-type septic tanks was the main theme of the present study. The septic tanks were fed continuously with domestic wastewater at three hydraulic retention times (HRTs), ranging from 24 to 72 h. The average characteristics of raw domestic sewage investigated in this study in terms of chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS) were 960, 450, and 295 mg/l, respectively. The product quality of the treated domestic wastewater by the four types of septic tanks in terms of physicochemical and biological characteristics proved to be satisfactory. Comparison wise, better results were obtained using the packed-type septic tank for primary treatment. The average removal of pollutants for each type of septic tank in terms of COD, BOD, and TSS improved in direct proportion to HRT. The fecal coliform removal values were affected by the type of the septic tank and the HRT. The highest percentage removal reached only one log. The accumulated sludge volume and weight were found to be dependent on the septic tank type and HRT. The average percentage of sludge volatile organic matters was almost equal. At each HRT, the due time for tank desludging was observed to be in order of conventional > single-baffle > packed-type > two-baffle septic tank. Based on the achieved results, either the two-baffle or the packed-type septic tank is considered to be a viable solution for the on-site decentralized treatment of high-strength domestic wastewater, especially at rural communities.