Wastewater is treated and purified into the secondary water resource of city using water with low quality by using water resource, middle water reusing and developing circular washing water, which has the comprehensive benefits of development resource, saving water and environment protection. 水资源化、中水回用、开发循环冲洗水,将污水处理、净化为城市低水质用水的第二水源,具有开源、节流与环境保护的综合效益。