Decision model to optimize wastewater treatment in the built environment

Water resource conservation and consumption is an integral component of future sustainable development given the increase in global population and subsequent growth in population density. Concern for both water quantity and quality will continue to grow globally as the competition for the resource is increased. Much attention is given to the supply side of the hydrologic cycle in built environment research and little is dedicated to buildings’ wastewater save for quality studies conducted at the centralized treatment facilities. A review of life cycle assessment studies of centralized wastewater treatment facilities, rural septic systems, and constructed wetlands revealed common indicators of ecological performance and maintenance and infrastructure constraints. Typically, indicators are plotted to determine the relationship, and a framework is established to select appropriate systems given a desired outcome. Life cycle assessment data from literature and case studies combined with optimization techniques creates a multivariate tool to assist utilities, municipalities, developers with decisions concerning wastewater handling and treatment. A decision model is created to determine the optimum wastewater treatment approach among the three alternative systems given population densities and land area constraints. The decision model is spreadsheet based, with an interface to change variables and determine the systems that achieve the minimum ecological impact. The decision model uses linear programming and selects for the wastewater treatment system combination with the least environmental impact given available land area and population. The results indicate the process is region and geographic specific. Capital and maintenance costs are not included, and should be included in a final analysis prior to implementation. Future studies could include empirical inputs of integrated constructed wetland performance over an extended period.