Clay-biomass composite for treatment of real dyestuff wastewater

Dye wastewater from the textile industry is known to contain a variety of toxic, persistent, and non-biodegradable pollutants, which, if discharged untreated, can severely impact the environment. Effective pre-treatment of such effluents is therefore essential. In this study, a kaolinite-moringa seedcake composite was evaluated for its ability to remove colour and chemical oxygen demand (COD) from actual dyestuff wastewater. Both batch and fixed-bed column experiments were conducted to assess the effect of key operational parameters. The results from batch experiments highlighted that wastewater pH, adsorbent dosage, and contact time significantly influenced removal efficiency. Optimal removal was achieved at pH 2, with a composite dosage of 2 g/L and a contact time of 60 min, yielding 45.7% colour removal and 31.9% COD reduction. To further understand the sorption behaviour, kinetic and isotherm models were employed. The pseudo-second-order model and the Freundlich isotherm provided the best fit, indicating that the process is controlled primarily by chemisorption and multilayer adsorption on a heterogeneous surface. A maximum adsorption capacity of 675.3 mg/g for COD removal was obtained by Langmuir isotherm model. In column studies, both bed depth and flow rate were found to influence removal performance. The data from these continuous flow tests were analysed using several mathematical models. Among them, the Clark and Bed Depth Service Time (BDST) models showed strong agreement with experimental results, whereas the Thomas and Yoon-Nelson models exhibited limited predictive accuracy. Overall, the findings affirm that the kaolinite-moringa seedcake composite is an effective, low-cost, and environmentally sustainable adsorbent for real dye wastewater treatment.