Potential of Alum Sludge from Katosi Drinking Water Treatment Plant for Reduction of Phosphorus in Wastewater Treatment Plant Effluent in Uganda

Abstract

In response to the global surge in wastewater production due to population growth and economic development, improving wastewater treatment is crucial. The presence of excess nutrients, particularly phosphorus (P), in wastewater effluent poses a significant threat of eutrophication. This study, therefore, set out to assess the potential of reusing alum sludge from the Katosi Drinking Water Treatment Plant (KDWTP) as a phosphorus adsorbent in wastewater effluent, aiming at finding a more sustainable and effective alum sludge disposal solution while reducing environmental and health risks associated with P-contamination. Effluent samples were analysed for total phosphorus, temperature, pH, and turbidity. Alum sludge was characterized using a variety of methods (pH, moisture content, FTIR, XRF, and SEM analyses). Phosphorus reduction was evaluated using alum sludge granules (ASG) prepared by binding oven-dried alum sludge with Carboxymethyl cellulose (CMC) in batch experiments. The effect of varying contact time and ASG masses on phosphorus reduction was investigated. The adsorption behaviour was described by the Langmuir and Freundlich models, and statistical tests were used to determine model suitability and group differences. The alum sludge exhibited favourable characteristics for phosphorus adsorption, with a maximum adsorption capacity of 0.3 mg/g. The highest reduction, 86 %, was achieved at 24 hours of contact at an ASG mass of 9 g. The Langmuir isotherm model, with a coefficient of determination, R², of 0.743, provided the best fit for total phosphorus adsorption onto ASG, demonstrating the potential of reusing alum sludge from the Katosi Drinking Water Treatment Plant for phosphorus reduction in wastewater effluent in Uganda. Further field testing, pilot studies, and exploration of granulation techniques are recommended for real-world applications.