Development of Chitosan-Bentonite Composite Membranes for Heavy Metal Ion Removal from Industrial Effluents in Onitsha, Anambra State

Industrial activities in Onitsha, South East Nigeria, generate effluents containing cadmium, lead, and chromium at concentrations that threaten the Niger River ecosystem and the health of communities relying on the river for water and food. This study develops composite membranes from chitosan extracted from crab shells obtained from Onitsha fish markets and bentonite clay sourced from Edo State for the removal of cadmium, lead, and chromium ions from industrial effluents. Composite membranes were fabricated by casting chitosan-bentonite suspensions at bentonite loadings of 5, 10, 15, and 20 wt% on glass plates and crosslinked with glutaraldehyde. Membranes were characterised for morphology, tensile strength, water uptake, swelling behaviour, and ion exchange capacity. Filtration performance was evaluated in a dead-end membrane cell at transmembrane pressures of 2 to 8 bar using synthetic effluent containing 50 mg/L of each target metal ion, and by dynamic experiments using actual Onitsha industrial effluent samples. The 15 wt% bentonite composite membrane achieved 94.7%, 92.1%, and 88.6% rejection for lead, cadmium, and chromium ions respectively at 6 bar. Lead and cadmium rejection exceeded NESREA discharge limits after a single pass. Membrane regeneration using 0.1 M HNO3 solution recovered 97.3% of adsorption capacity over five cycles. The study presents a scalable, low-cost membrane fabrication route using locally sourced materials for industrial effluent treatment in South East Nigeria. Keywords: chitosan-bentonite membrane, heavy metal removal, lead, cadmium, Anambra State