Physico-chemical Characterization of the Tchoga River Waters Receiving Effluents from the Bidabanga Slaughterhouse, Katana, DRC

Abstract

This study evaluates the impact of organic waste from cattle slaughter on the physicochemical quality, ecological status, and organic pollution of the Tchoga River. Nine sampling campaigns were conducted between November 2024 and October 2025 at three stations along a longitudinal gradient: upstream near the Bidabanga slaughterhouse, midstream, and downstream at Mugeri. The assessment combined twelve physicochemical parameters, benthic macroinvertebrate inventories, and the organic pollution index (OPI) to characterize ecological conditions. Results show elevated conductivity, total dissolved solids, chlorides, total hardness, and suspended solids upstream, reflecting significant organic loading from slaughterhouse effluents. Downstream, water quality improves gradually, with higher dissolved oxygen and pollutant dilution, while bicarbonate, calcium, and magnesium remain relatively stable. Despite this partial recovery, OPI values remain below 3 at all sites, indicating moderate organic pollution without a significant longitudinal gradient (p > 0.05), suggesting limited self-purification and diffuse anthropogenic pressures across the basin. Seasonal trends reveal greater degradation during the rainy season due to runoff mobilizing organic matter and nutrients, with slight improvement in the dry season. Dissolved oxygen is strongly negatively correlated with nitrate concentrations (r = −0.80), indicating active nitrification. Macroinvertebrate richness increases from upstream to downstream (12–16 taxa), reflecting partial ecological recovery. Overall, the findings highlight persistent ecological degradation of the Tchoga River and underscore the urgent need for sustainable slaughterhouse waste management and watershed restoration to preserve water quality and ecosystem health.