Multicriteria Assessment of Various Onsite Wastewater Treatment Options for Nigeria

Abstract

Eight onsite wastewater treatment systems (OWTS) were evaluated for suitability of application in Nigeria for efficient treatment and disposal of domestic wastewater, using analytic network process (ANP). Ten location related risks were used as criteria in the decision making process. Expert views were used to obtain pairwise comparison matrices of the OWTSs with respect to the criteria. Saaty’s Super Decision Software was used to complete the ranking process. The order of ranking obtained was as follows: septic tank with absorption field (0.1502) > septic tank with soakaway (0.142) > composting toilet (0.128) > septic tank with sand filter (0.125) > septic tank with constructed wetland (0.12) > septic tank with holding tank (0.12) > septic tank with mound system (0.118) > septic tank with recirculating sand filter (0.096). However, when the costs and life spans of these systems were incorporated into the ranks, and considering other factors, the septic tank with absorption field stood out as the best option. A simple sensitivity analysis shows that depth to water table, proximity to drinking water, susceptibility to flooding and proximity to large roots have the highest influence on the ranks of OWTSs.