Comparative effects of selected indigenous bacterial treatments on the physicochemical characteristics of abattoir wastewater in Port Harcourt, Nigeria

Abattoir wastewater contains high concentrations of organic matter, nutrients, dissolved solids, and diverse microorganisms that may pose environmental and public health risks when discharged without adequate treatment. This study evaluated the bacteriological characteristics of abattoir wastewater and comparatively assessed the effects of selected indigenous bacterial isolates on its physicochemical characteristics. Wastewater samples were collected from selected abattoirs in Port Harcourt, Rivers State, Nigeria. Standard microbiological techniques were used for bacterial enumeration, isolation, characterization, and identification. The growth potential of the bacterial isolates in wastewater-supplemented mineral salt medium was assessed using optical density measurements. Selected Pseudomonas sp. and Bacillus sp. isolates, together with a separately formulated consortium of probable enteric bacteria, were evaluated under laboratory conditions for 21 days, with physicochemical parameters monitored at seven-day intervals. Mean total heterotrophic bacterial counts ranged from 6.33 × 106 to 1.60 × 107 CFU/mL, total coliform counts from 2.63 × 105 to 5.00 × 105 CFU/mL, and total faecal coliform counts from 5.00 × 103 to 1.73 × 104 CFU/mL. Total Pseudomonas counts ranged from 0 to 1.37 × 104 CFU/mL, Salmonella-Shigella counts from 8.33 × 103 to 2.80 × 104 CFU/mL, and total staphylococcal counts from 1.00 × 103 to 1.33 × 103 CFU/mL. Fifteen bacterial isolates representing ten probable bacterial taxa, including Bacillus, Pseudomonas, Escherichia, Klebsiella, Salmonella, Shigella, Staphylococcus, Serratia, Chromobacterium, and Micrococcus, were recovered. Pseudomonas sp. exhibited the highest growth response in the mineral salt medium (OD550 = 1.678). After 21 days of treatment, the consortium produced the greatest reductions in electrical conductivity, biochemical oxygen demand, nitrate, and phosphate, with reductions of 2.9%, 5.4%, 19.7%, and 31.5%, respectively, whereas Pseudomonas sp. produced the greatest reduction in total dissolved solids (26.7%). Temperature remained relatively stable throughout the treatment period, whereas pH showed a moderate increase. The findings demonstrate differential effects of the selected bacterial treatments on the physicochemical characteristics of abattoir wastewater. Although the consortium produced greater reductions in several parameters, its inclusion of probable Escherichia coli, Klebsiella sp., and Salmonella sp. limits its suitability for environmental application. The study highlights the potential of appropriately characterized indigenous bacterial isolates, particularly Pseudomonas sp. and Bacillus sp., for further laboratory-scale investigation of abattoir wastewater treatment and emphasizes the need to evaluate microbiological safety alongside treatment performance.