Dual water distribution network design under triple-bottom-line objectives

Rapid urban growth has stressed limited supplies of high-quality water sources and water shortage has become a major issue in worldwide. Today, sustainable water supply to meet growing demand is a significant concern for water utilities. Developing additional high-quality sources is not necessarily available; it may be costly to convey water from sources that are usually located far from users or there may be legal battles over water rights. A well-proven source that does not have significant conveyance costs and that does not pose water right conflicts is wastewater reclamation for nonpotable uses. A few studies have been completed for the design of reclaimed water distribution through a parallel pipe system. In earlier works, however, attention has mainly focused on the recycling of effluent for large users, such as golf courses, parks, and schools with the objective of minimizing economic cost. As reclaimed water takes on a larger role in many communities' water supply, the questions of how and what water to deliver to consumers must be addressed. To that end, this study presents a multi-objective optimization algorithm for designing dual-water distribution systems that recyce effluents for local residential nonpotable uses. Triple-bottom-line objectives are posed, as well as economic costs for pipe and pump installation and operation, environmental costs represented by greenhouse gas production, and system reliability against mechanical failure representing social cost. Under the premise that the systems will be constructed in a new community, thorough comparisons are made between a conventional single system and three alternative dual systems. The resulting problems are mixed integer problems and solved using a genetic algorithm (GA) linked to a hydraulic simulation model. Applications begin to demonstrate water deliver trade-offs and can guide policy decisions on appropriate system types taking a fuller picture of system costs and effects.