Study on the nitrogen removal effect of novel ecological concrete in drainage ditches of coastal saline-alkali farmland

ABSTRACT

Farm drainage ditches play a crucial role in effectively removing nitrogen nutrients from agricultural wastewater. However, traditional earthen ditches have limitations in treating nonpoint source pollution, and insufficient attention has been paid to their application in the coastal saline-alkali soil region. To address this gap, we developed ecological drainage ditches using self-formulated ecological concrete and systematically evaluated their nitrogen removal performance under the conditions characteristic of coastal saline-alkali environments. Batch experiments were conducted to investigate the influences of hydraulic retention time, water level, influent pollutant concentration, and salinity on nitrogen removal efficiency. The results demonstrated that, after 120 h of treatment, the NH4+-N concentration decreased to 0.31 mg/L at a low water depth of 8 cm, whereas the NO3−-N concentration reached 1.03 mg/L at a medium water depth of 15 cm. Under low influent pollutant loading (total nitrogen concentration of 20 mg/L), the maximum total nitrogen removal rate reached 84.88%. Orthogonal experimental analysis further identified water level as the predominant factor governing nitrogen removal performance. Compared with traditional earthen drainage ditches, the ecological concrete drainage ditches exhibited substantially higher nitrogen removal efficiency, highlighting their potential as a sustainable solution for agricultural nonpoint source pollution control in coastal saline-alkali regions.