Full-scale practice of domestic wastewater source separation and collection in a semicentralized treatment system: a case study

Semicentralized supply and treatment systems (SCSTSs), which can realize water, nutrition, and energy recycling via separate water supply and discharge systems, have been developed for fast-growing urban areas. The world's first full-scale SCSTS was implemented in Qingdao in China. Greywater (GW) and blackwater (BW) are collected and treated separately, but the parallel setting of the BW and GW pipelines means that connection mistakes can easily occur. Taking Qingdao as an example, this article analyzes the occurrences of BW and GW pipeline misconnections and the changes in influent pollutants, to assess the feasibility of separating domestic sewage at the source. The misconnection rates were estimated by comparing the measured values with the theoretical values. The results show that cross-connections occurred in some buildings, and the average misconnection rates were 31.9%, 15.2%, 60.6%, and 0.2%, respectively, in hotels, residences, an office building, and a public building. The overall misconnection rate in the SCSTS was 27.9%. These findings suggest that measures should be taken to avoid or reduce misconnections. This study can provide a reference for the future design and construction of SCSTSs and has important practical significance for protecting the environment.