Intermittent operating characteristics of an ecological soil system with two-stage water distribution for wastewater treatment

Ecological soil systems (ESSs) are usually used to remove nitrogen from wastewater. Due to the poor denitrification performance of traditional ecological soil systems (ESSs), this study proposes a two-stage water distribution system to improve the nitrogen removal. The effects of different distribution ratios on the system treatment effect were studied in an intermittent operation mode. After determining the optimal distribution ratio and intermittent operation conditions, the dynamics of system inflow, outflow, and nitrogen removal were monitored. Theoretical analysis of the denitrification mechanism was carried out. The results showed that the optimum water distribution ratio was 2: 1, and a mean total nitrogen removal rate of 60.42% was achieved, which is 23.09% greater than that is typically achieved by the single-section ecological system. Under optimum distribution ratio conditions, the system also demonstrated effective removal of chemical oxygen demand (COD), total phosphorus (TP) and ammonia nitrogen ( NH 4 + ${\text{NH}}_4^{+}$ -N), allowing the effluent to satisfy China's urban sewage treatment plant level B emission standards.