Experiment on start-up phase of new modified septic tanks treating domestic sewage

Three on-site septic tanks, namely ABR-septic tank(R1), YDT-carrier-septic tank(R2) and traditional septic tank(R3), were operated in parallel over a three-month period under the hydraulic retention times (HRT) of 36 hours at sewage temperature of 14~29°C. The achieved CODtot removal efficiencies in R1 and R2 increased by 30.5% and 9.2%, respectively, compared with R3 at the stage of 24°C, while the value reduced to 10. 9% and 9% in the phase of 16°C. The achieved removal efficiencies of TN and NH₄⁺-N arrived at 5%~30%, and the value of TP was negligible, with approximately 5%. R1 achieved a better specific methane production rate as compared to R2 and R3. The two modified septic tanks improve biochemical characters and attain better removal efficiency for domestic sewage. The results provide a technical support and a theoretical basis for the modification of septic tank.