Environmental and Economic Approach to Assess a Horizontal Sub-Surface Flow Wetland in Developing Area

Many urbanized areas in tropical climate regions are coping with water contamination due to inadequate sewage collection, particularly in communities that inhabit marginal land of rapid-growth. Relying on large-scale Waste-Water Treatment Plants -WWTPs and implementation of traditional sewage collection infrastructures have proven limited success to cope with the mentioned problem. Alternatives based on Nature-based Solutions - NbS, have the potential to deliver des-centralized treatment as well as additional socio-environmental benefits for the improvement of urban poor conditions. This research focused on modelling cost-efficiency and environmental performance of Nb-S implemented in fast-growing urban areas of the developing countries. A Horizontal Sub-Surface Flow Constructed Wetland - HSSF-CW is proposed to perform as complementary cost-effective decentralized treatment of local sewage. P-K-C* model is applied as sizing approach of the system for a 60% minimum removal of Biological Oxygen Demand - BOD in the influent. Cost-Benefit Analysis (CBA) has been used to analyse the feasibility of the CW proposal with environmental performance of CW modelled through shadow prices methodology. Shadow prices of contaminants, i.e. phosphorus, nitrogen and BOD, act as a proxy of environmental benefit in monetary units, allowing to include the environmental performance of CW into CBA. This new method combines both P-K-C* sizing approach and environmental performance through shadow prices to enhance best allocation of resources for water treatment.