Microbial electrochemical septic tanks (MESTs): An alternative configuration with improved performance and minimal modifications on conventional septic systems

Abstract

Septic systems serve between 20% and 25% of households in the U.S. Malfunction of septic systems would deteriorate nearby air and water environment, e.g., causing eutrophication in inland lakes. This study attempted to improve the tank effluent by using microbial electrochemical septic tanks (MESTs), an alternative tank configuration to conventional septic tanks (CSTs). The performance was assessed by operating laboratory scale of 1L simulated MESTs for 171days at an average HRT of 8.3days. MESTs utilized inexpensive electrode material of stainless steel AISI 430, and were operated at small external voltage input (from 0.50V to 0.88V) and low energy consumption (0.26–37.1kWh/m3-treated sewage). Total phosphorus (P) removal efficiency was substantially improved by MESTs from 12.2% to 77.2%–98.7% at 25°C, and from 7.45% to 20.7%–93.9% at 15°C. Sulfide was completely removed from most MESTs effluents, while the CSTs generated sulfide concentrations of 0.17mM and 0.06mM at the respective two temperatures. Comparison of MESTs with other alternative systems like engineered ecosystems and membrane bioreactor showed its substantial effectiveness in P removal and its readiness to be incorporated in current septic systems. In conclusion, MESTs decreased the P load that enters the subsequent percolation field, and the adoption of MESTs would enhance the overall role of septic systems in sanitation and environmental protection.