Evaluation of Treatment Efficiency of Waste Stabilization Pond and Its Effluent Toxicity in Hawassa University, Southern Ethiopia

Abstract

Background: Waste stabilization pond is sanitation technology designed for the treatment of wastewater in order to reduce the carbon-containing organic matter and remove pathogens from wastewater and its effluent is expected to be used for fish production and irrigation. Hawassa University waste stabilization pond is frequently blocked with solid waste and discharging it’s effluent to nearby households and the environment. However, its efficiency and effluent toxicity were not clearly evaluated. The aim of this study was to evaluate the efficiency of waste stabilization pond and its effluent toxicity in Hawassa University, Southern Ethiopia. Methods: An experimental study was conducted at Hawassa University waste stabilization pond from March 1st and May 30th, 2017. Samples were collected by pre-cleaned plastic bottles using grab sampling techniques. Non-conservative parameters were performed on-site while conservative parameters were performed after transported to the Hawassa University chemistry laboratory. Three repeated experiments were performed. The mean value and removal percentage of each parameter of the waste stabilization pond were calculated. For acute toxicity, forty-two fry Tilapia young fishes were imported into six aquaria. The mortality and behavioral changes of the fishes were recorded according to toxicity protocol. Statistical Package for Social Sciences Version 21 was used for data analysis. Results: There is variables efficiency removal of wastewater treatment as indicated for total dissolved substance (14%), temperature (19%), manganese (20%), cadmium (96.90%), nitrate (73.77%) and copper (72.00%). The mean difference in effluent removals for total suspended solid, biological oxygen demand, nitrate, cadmium, chromium, and copper have a significant value between the inlet and outlet of the pond (p <0.05). The lethal concentration of fifty percent of the acute fish toxicity within 24 hours was 76%. All fishes in 100% effluent aquarium died within 24 hours. The lower observable adverse effect and non-observable adverse effect of the concentration were 60% and 40% of the effluent respectively. Conclusion: There is a significantly higher removal efficiency of the treatment pond on the inlet and outlet for nitrate, cadmium, and copper. While, the lower removal efficiency was obtained for total dissolved substance, temperature, and manganese. The pure effluent discharged from the pond caused a hundred percent fish mortality within a day. Therefore, the pond needs to redesign and upgrade to prevent the ecological health risk and to endure aquatic life like fish. Keywords: Bioassay; Fish toxicity; Heavy metals; Physicochemical