An Engineering Failure Analysis of a Biological Treatment Plant in Nigeria

Waste stabilization ponds (WSP) have been found useful and applicable in most parts of the world. Their application has been found in the treatment of industrial, commercial, institutional, and domestic wastewaters. Failures of WSP have not been reported until recently. This then calls for engineering analysis of failed ponds to prevent the recurrence of these ugly events. This paper presents results of an engineering failure analysis conducted on a waste stabilization pond at Obafemi Awolowo University, Ile-Ife, Nigeria. The ponds receive wastewater from selected student halls and academic buildings by gravity as a result of the topography of the campus. The ponds were visited, and influent and effluent qualities of the ponds were determined. Adequacy of the design parameters and structural behavior were studied and compared with the standard code. The study revealed that some of the engineering parameters were higher than the upper limit recommended by the standard code. Solids had accumulated in the ponds, resulting in anaerobic conditions in the ponds, generating hydrogen sulfide and acids as end products. Production of these acids corroded the sewers, cracked some manholes, and dislocated pipes (sewers). Accumulation of solid also led to sludge formation and thus reduced effective depth, length, and breadth of the ponds and made detention time below the specified range in the standard environmental pollution control code. It was concluded that the failure of the ponds can be attributed to partial adherence to the standard code in terms of vegetation, flood control mechanism, high biochemical oxygen demand and suspended loadings, and flow rate, as well as to low detention; all originated from improper maintenance.