Benefits of an integrated water and nutrient reuse system for urban areas in semi-arid developing countries

Urban areas of developing countries face the challenge to implement adequate water and sanitation infrastructures while using natural and financial resources sustainably. The objective of this study was to identify benefits and challenges of different nutrient and water reuse systems. For this, we evaluated and compared four systems; (1a) the local conventional water and sanitation system, (2a) a novel water and nutrient reuse system connecting sanitation, advanced wastewater treatment and nutrient-rich water reuse for the irrigation of human food crops, (1b) the local conventional water and sanitation system adapted for water reuse and (2b) the novel water and nutrient reuse system adapted to be low-tech. Our case study, a town in Namibia, exemplifies the typical problems of urban areas in developing countries. We compared the four systems using ecological, economic, societal, institutional, political, and technical criteria, via multi-decision criteria analysis with the Analytic Hierarchy Process (AHP). Our results indicate that the novel water and nutrient reuse system (2a) scores highest with environmental and societal criteria when weighting all evaluation criteria equally. Its challenges lay especially in the economic criteria. Nonetheless, for our case study, an urban area in a developing country, the novel water and nutrient reuse system (2a) is a viable sanitation, wastewater and irrigation infrastructure for using fewer resources, being economically feasible, institutionally and politically practical and technically sound. However, the preference for a particular water and sanitation infrastructure also depends on which criteria the decision-maker is willing to assign the highest weight to. The presented methodology helps decision-makers and engineers with complex decision-making by evaluating numerous criteria in order to have proper information on the benefits and challenges of water and sanitation systems.