Assessing rainfall infiltration dynamics and effluent assimilation capacity for land application of treated wastewater

Sustainable wastewater management through land application requires balancing effluent loading rates with soil assimilation capacity. Excess hydraulic loading can overwhelm natural drainage, causing surface ponding and runoff. This study aimed to evaluate rainfall infiltration dynamics and effluent assimilation potential for a proposed treated effluent irrigation site in Chun'an County, China. The Green-Ampt model was used to simulate infiltration under different rainfall scenarios. Key parameters including hydraulic conductivity, wetting front suction, and initial water content were obtained from in-situ testing and soil sampling. Results showed the soil matrix has adequate capacity to assimilate effluent under normal conditions. However, surface water logging and runoff risks emerge during moderate (8.6 mm/h) and intense (39.85 mm/h) rainfall events. Simulations indicated increasing matric suction to 68 cm by planting vegetation could avoid ponding for 24-h extreme events. Monitoring, warning systems, and adaptive management are recommended to utilize natural drainage capacity while preventing hazards from intense rainfall exceeding 2.1 cm/h. Outcomes provide guidance for integrating effluent irrigation planning with climate resilience strategies. • Utilized Green-Ampt model to assess soil infiltration and effluent assimilation. • Identified critical rainfall intensities triggering surface water accumulation. • Developed climate-resilient guidelines for sustainable effluent irrigation practices.