Study on treatment performance of rural wastewater using the improved constructed rapid infiltration system-The influence of hydraulic loading cycle

Based on the conventional constructed rapid infiltration (CRI) system, the improved CRI system with non-saturated and saturated layers was constructed. The effects of three hydraulic loading cycles (3, 6 and 12h) on the treatment performance of rural domestic wastewater were investigated when corn cob was added as solid carbon source in the saturated layer, and the microbial mechanism was further elucidated. The results showed that the optimal hydraulic loading cycle of the improved CRI system was 6h. Under the optimal hydraulic loading cycle, the average effluent concentrations of chemical oxygen demand (COD), ammonia nitrogen, total nitrogen and total phosphorus were 5.40, 0.91, 5.59 and 0.47mg/L, respectively. The effluent water quality index meets the Discharge standard of pollutants for municipal wastewater treatment plant (GB 18918-2002) level A standard. The results of microbiological analyses implied that the removal of COD mainly occurred in the non-saturated layer of the system, and the Proteobacteria and Actinobacteria were the main functional microorganisms involved in the metabolism of organics. Nitrification also occurred in the non-saturated layer, and Nitrospirae was the main nitrifier. Functional microorganism Chloroflexi in the saturated layer could degrade corn cobs and provide sufficient carbon source for denitrification process, and carry high abundance of key functional genes for denitrification at the same time, facilitating the denitrification process in the saturated layer. This study can not only provide a basis for the resource utilization of agricultural wastes, but also provide technical support for the improved CRI system to strengthen the treatment of rural domestic wastewater. © 2024 Chinese Society for Environmental Sciences. All rights reserved.