Comprehensive Utilization of Rainwater and Domestic Sewage in Ecological Residential Quarters

In new built ecological residential quarters, the overall green ratio usually exceeds 30%. The scale of public facilities and road area are larger than those in ordinary residential quarters. So water consumption for greening, roads, waterscape and other facilities is enormous, which causes much burden to residents and real estate companies. Tap water is commonly the sole water resource for these usages. However, the growing price of tap water overloads this burden. New water resources must be found. Rainwater and domestic sewage may be two alternatives. They are compared in aspects of technology complexity, investment, operation cost and reliability. Rainwater can be easily treated. Unit operation cost for rainwater treatment is about 1/4 of tap water. But initial investment on rainwater collection system and reservoir is large because the scale of rainwater reuse is decided by unpotable water demand on the most unfavorable condition. The treatment facilities for domestic sewage reclamation are more complicated, but sewage capacity and quality is relatively more stable. Sewage reuse can save 1/2 of daily costs compared with tap water usage. Therefore in periods with plenty of rainfall, rainwater is the first substitute for tap water in ecological residential quarters. Rainwater collection system and reservior should be designed and installed appropriately. Sewage is a reliable water resource except tap water in periods with insufficient rainfall. But it should be treated thoroughly. When the reclaimed water is used as waterscape supplement, the sewage needs deep treatment to remove nitrogen and phosphorus effectively in case of algae propagation. Comprehensive utilization of rainwater and sewage is suggested. It can not only save investment and costs, but also enhance water supply reliability and residential environment level. The implementation of this integrated water reuse needs the support of policies and strategies.