Evaluation of the Performance of Decentralised Wastewater Treatment Systems in Peri-Urban Areas of Kaduna, Kaduna State

This study evaluates the technical performance and operational condition of decentralised wastewater treatment systems installed in peri-urban communities on the outskirts of Kaduna, Kaduna State, North West Nigeria. Peri-urban expansion in Kaduna has proceeded faster than the extension of centralised sewerage, and decentralised systems including septic tank and soak pit combinations and small package biodigesters have been installed as interim solutions in twenty newly developed residential schemes. Performance assessment was conducted through on-site inspection using a structured protocol, influent and effluent sampling for biological oxygen demand, total suspended solids, faecal coliform, and nutrient parameters, and structural integrity assessment. Findings show that only 35 percent of inspected systems are operating within intended performance parameters. The most common failure modes include soak pit saturation from inadequate percolation capacity, lack of regular desludging, structural cracking of septic tank walls allowing short-circuit of untreated sewage, and absence of any effluent quality monitoring by the Kaduna State Water and Sewerage Corporation. Systems installed under supervised community WASH projects perform significantly better than those installed informally. Effluent quality from non-functional systems contributes to groundwater contamination and surface runoff pollution. The study identifies absence of a post-installation maintenance support system as the primary performance driver. Recommendations include a WASH department-operated mobile desludging service and annual system inspection programme for peri-urban Kaduna. Keywords: decentralised wastewater, septic tank, peri-urban sanitation, Kaduna, treatment performance.