Effects of treated agro-industrial effluents on physical and chemical characteristics of the receiving stream Wawa in south-eastern Côte d'Ivoire

Abstract

In this research we examined the impact of effluents from an agro-industrial plant on River Wawa. Water quality was assessed by monitoring monthly during a year. Eleven parameters were retained: temperature, conductivity, dissolved oxygen, turbidity, pH, chemical oxygen demand, nitrates, nitrites, ammonia, orthophosphates and organic pollution index. Except temperature and ammonia which didn’t differ among sites, chemical oxygen demand and organic pollution index were significantly (p < 0.00001) higher at reference sites upstream the discharge point of effluents than sites located downstream. On the contrary, values of the other variables were significantly (p < 0.05) higher at sites receiving the effluents. These results certainly support the hypothesis that the rejected effluents have a negative influence on the water quality downstream the discharge point. However, results suggest a decrease of the parameters content at the second site more distant from the discharge point, maybe due to the self-purifier capacity of the receiving stream. Ecological impacts not being all immediate, this wastewater could have a negative impact on the species living in the receiving stream in long term, either by bio-accumulation or by bio-magnification. It would be interesting to undertake complementary studies of bio-accumulation or bio-magnification on fauna.

Keywords: Water pollution, industrial wastewater, wastewater discharge, water quality, pollution prevention