Characteristics of rural agritainment sewage in Sichuan, China

Characteristics of rural domestic wastewater with source separation

Rural domestic wastewater (RDW), one of the non-point pollution sources, has become a significant object related to sanitation improvement and water pollution control in Taihu Lake Basin, China. Current research on RDW characteristics and management with source separation is limited. In this study, a source-separated investigation into the characteristics of RDW was conducted, and the management suggestions were proposed. The results showed that the average RDW production coefficient was 94.1 ± 31.6 (range: 71.8-143.0) liters per capita (person) per day. Household-level wastewater generation peaked two or three times daily, and the synchronous fluctuation could cause hydraulic loading shocks to treatment facilities. The population equivalents of chemical oxygen demand, ammonium nitrogen (NH₄⁺-N), total nitrogen (TN), and total phosphorus (TP) in RDW were 78.7, 3.7, 4.12, and 0.8 g/(cap·d), respectively. Blackwater from water closet source accounted for 30.4% of the total wastewater amount, contributing 93.0%, 81.7%, and 67.3% to loads of NH₄⁺-N, TN, and TP, respectively. Graywater from the other sources with low nutrient-related pollutant concentrations and loads, accounting for 69.6% of the total wastewater amount, was a considerable alternative water resource. The quantitative and qualitative characteristics indicated that GW and BW had the potential of being reused in relation to water and nutrients, respectively.

Characteristics of Internal Ammonium Loading from Long-Term Polluted Sediments by Rural Domestic Wastewater

Given long-term decentralized and centralized rural domestic wastewater (RDW) discharge, nitrogen is continuously depositing in sediments. RDW discharge is assumed to be an important source of ammonium in surface water; however, the effect of long-term RDW discharge on nitrogen pollution in sediments remains unknown. Batch incubations were conducted to investigate the characteristics of internal ammonium loading from long-term polluted sediments by RDW discharge. Four sediments were demonstrated to be heavily polluted by long-term RDW discharge, with total nitrogen (TN) values of 5350, 8080, 2730, and 2000 mg·kg^-1, respectively. The internal ammonium release from sediment was a slow and long process, and the risk of ammonium release from sediment during the dry season was significantly greater than that during the wet season. Though all selected sediments were heavily polluted by long-term RDW discharge, the relative contribution of internal ammonium loading from sediments was generally lower than that of external pollution. Hence, dredging is not suggested for RDW-polluted sediments except in response to an emergency. The excessive ammonium in the selected catchment was mainly from untreated and centralized black water in RDW. Centralized black waters in rural communities are highlighted to be separately treated or reused to maintain ammonium content at a safe level.