Performance Assessment of Coagulation and Ceramic Filtration of Tannery Effluent Using Hydroxyapatite/Kaolin-Based Materials

Abstract

Tannery effluent remains a pressing environmental concern due to its complex composition and presence of hazardous contaminants. In this study, an approach employing chemical coagulation followed by filtration using hydroxyapatite (HAp)/kaolin-based ceramic materials was applied to treat tannery effluent. Aluminium sulphate served as primary coagulant and was introduced to the effluent at varying concentrations (75, 150, 225, 300, 375, 450, 525, and 600 mg/L). Samples were subjected to rapid mixing (10 mins), slow mixing (30 mins), and allowed to settle for 24 hrs. Post-coagulation, supernatant was filtered using three types of ceramic filters fabricated from: (i) pure kaolin, (ii) kaolin combined with HAp, and (iii) kaolin blended with HAp and starch. The performance of each filter was evaluated based on chromium removal efficiency and turbidity reduction. The kaolin, kaolin + HAp, and kaolin + HAp + starch filters achieved chromium removal efficiencies of 75.75%, 81.36%, and 84.03%, respectively. The optimum chromium removal (84.03% at pH 6.93, temperature of 24.9°C, with a corresponding turbidity reduction of 45.44%) was obtained using the kaolin + HAp + Starch filter. However, the treated effluent still exceeded regulatory limits for chromium in effluent, as established by required standards at 1 mg/L and U.S. Environmental Protection Agency (EPA) at 0.02 mg/L. The kaolin/HAp/starch filter, which demonstrated an optimal flow rate of 29.17 mL/h, gave the most effective contaminant removal. These findings suggest that while HAp/kaolin-based ceramic filters show considerable promise for chromium removal in tannery wastewater, their performance must be further enhanced.