Integrated physicochemical and microbiological evaluation of industrial wastewater treatment and its impact on a receiving river in Gondar City, Ethiopia

Abstract

Industrial wastewater from brewery and malt-processing industries can adversely affect aquatic ecosystems and public health when inadequately treated before discharge. This study evaluated the physicochemical and microbiological performance of the Dashen Brewery oxidation pond treatment system and its impact on the receiving Shinta River in Gondar City, Ethiopia. Wastewater and river-water samples were collected from treatment units and upstream and downstream river locations and analyzed using standard methods. Raw wastewater contained elevated concentrations of organic matter, suspended solids, nutrients, and microbial contaminants. The oxidation pond achieved high removal efficiencies for BOD₅ (94.69%), nitrate (90.0%), nitrite (87.5%), silica (72.97%), and phosphorus (52.72%), while moderate reductions were observed for COD (41.21%), phosphate (51.57%), turbidity (43.76%), color (43.51%), and ammonia (26.47%). However, conductivity and total dissolved solids showed limited removal. Several physicochemical and microbiological parameters in the treated effluent remained above recommended discharge limits, and Salmonella spp. and Shigella spp. were detected after treatment. Downstream river sites exhibited increased pollutant and microbial concentrations with lower dissolved oxygen than upstream sites. These findings indicate that the existing oxidation pond system provides only partial treatment, emphasizing the need for treatment optimization, polishing, disinfection, and routine monitoring to protect receiving water bodies.