An innovative design of septic tank for wastewater treatment and its performance evaluation: An applicable model for developing countries

摘要

A study was carried out to evaluate the treatment efficiency of modified model of septic tank (ST) for the treatment of domestic wastewater.The objective was to explore the possibility of increasing the removal efficiency,at household level,thereby reducing cost and treatment burden on city level treatment plants.For this purpose,a bench scale model of ST was prepared and operated continuously for 78 days at different detention times i.e.,48,24 and 12 h and at two reactor temperatures viz.15 ℃ and 25 ℃.Domestic wastewater was fed to the bench scale ST without pre-settling.Research was conducted under two different arrangements.Firstly,by installing baffles in the bench scale ST (called Run-1 setup),and secondly by installing perforated plates between the baffles (called Run-2 setup).Results demonstrated that Run-2 setup is better than Run-1 setup.Temperature significantly affects the efficiency.Detention time of 24 h was found feasible.Run-2 setup demonstrated a percentage BOD removal of 45％ with effluent BOD of 113 mg· L-1 at 15 ℃ and 85％ removal with effluent BOD of 31 mg·L-1 at 25 ℃ It is concluded that ifa modified design of ST using Run-2 setup is provided at household level,the effluent coming out of the house will meet the National Environmental Quality Standards (NEQS) when reactor temperature is close to 25 ℃.Development authorities are suggested to change their by-laws and make modified ST mandatory for all households.This may significantly reduce the cost and footprint of city level wastewater treatment plants being planned.