Waste-to-Resource Approach for Industrial Wastewater Treatment, a Sustainable Removal of Organic Pollutants, Nutrients, and Heavy Metals from Paint Effluent Using Biomass-Derived Sawdust and Periwinkle Shell Biochars

Paint industry effluents contain elevated concentrations of suspended solids, dissolved substances, nutrients, organic pollutants, and toxic heavy metals, posing significant environmental and public health risks. This study investigated the treatment of paint wastewater using Oven-ashed low-cost waste-derived adsorbents prepared from sawdust and periwinkle shell biomass in both unmodified and modified forms. Sawdust and periwinkle shells collected from Abakaliki, Ebonyi State, Nigeria, were processed through washing, drying, grinding, sieving, and controlled thermal treatment and characterized using FTIR to produce unmodified sawdust char (USD), modified sawdust char (MSD), unmodified periwinkle shell char (UPC), and modified periwinkle shell char (MPC). Batch adsorption experiments were conducted at adsorbent dosages of 100–400 mg and contact times ranging from 1hr to overnight equilibrium. Treatment efficiency was evaluated using physicochemical, nutrient, and heavy metal analyses. Data were generated in triplicate and expressed as mean ± standard deviation, while statistical significance was assessed using ANOVA (p < 0.05). The results showed that contaminant removal increased with adsorbent dosage and contact time, with modified periwinkle shell char exhibiting the highest overall performance. Under optimum adsorption conditions, turbidity decreased by approximately 28–31%, TDS by 16–18%, EC by 12–14%, total hardness by 6–8%, COD by 7–10%, and BOD by 18–33%, while dissolved oxygen increased by approximately 40–47%. Nutrient reduction efficiencies ranged from 6–17% for sulphate, 21–28% for phosphate, 13–23% for nitrate, and 8–10% for chloride. Heavy metal adsorption demonstrated substantial removal efficiencies, with As (79–88%), Pb (85–95%), Cr (82–91%), Cd (88–96%), Zn (80–87%), and Cu (84–92%) removed under optimum treatment conditions. The improved adsorption performance was attributed to increased surface area, pore development, electrostatic attraction, ion exchange, mineral precipitation, and surface complexation mechanisms. Overall, periwinkle shell-derived adsorbents showed better treatment efficiency than sawdust-derived adsorbents, while modification further enhanced pollutant removal. The findings demonstrate that agricultural and marine wastes can be transformed into efficient and environmentally sustainable adsorbents for paint wastewater remediation and provide a practical low-cost alternative to commercial treatment materials.

Keywords: Paint effluent, adsorption, biochar, sawdust char, periwinkle shell char, heavy metals, wastewater treatment, nutrient removal, circular economy.