Study on Operation Effect of Two-Stage MSL System for Rural Decentralized Sewage Treatment

To improve the removal efficiency of rural domestic sewage, a two-stage multi-soil-layer sewage treatment system with an “aeration section + non-aeration section” was designed, and its treatment performance was observed under different influent loads and aeration intensities. The experiment ran for a total of 150 days, and the results showed that the two-stage multi-soil-layer (MSL) system could effectively reduce the effluent concentration of sewage to meet discharge standards. Under the operating conditions of an influent hydraulic load of 1000 L·m−2·d−1 and an air–water ratio of 4:1, the final effluent average concentrations of COD, NH3-N, TN, and TP were 106.5 mg·L−1, 7.4 mg·L−1, 13.9 mg·L−1, 0.12 mg·L−1, and 18.6 mg·L−1, respectively, with average removal rates of 85.3%, 82%, 72.5%, 96%, and 85%. A longer hydraulic retention time and ideal anoxic conditions were ensured by designing a certain effluent height in the system. Adding aeration to the system allowed for a synchronous nitrification–denitrification reaction under reasonable influent loads, ultimately enabling the effluent to meet discharge standards.