Harnessing thermally treated drinking water sludge: a sustainable approach for the removal of crystal violet and congo red from wastewater

This study investigates the utilization of thermally treated drinking water treatment sludge (DWTS) as an eco-friendly adsorbent for the removal of Congo Red (CR) and Crystal Violet (CV) dyes from wastewater, aligning with circular economy principles. The research evaluates the adsorption performance of DWTS by analyzing various factors, including pH, contact time, adsorbent dosage and initial dye concentration. Kinetic and isotherm studies were conducted to elucidate the performance of the adsorbent and investigate the adsorption mass transfer mechanisms. Characterization of the DWTS adsorbent was performed using Energy Dispersive Spectrometry (EDS), Scanning Electron Microscopy (SEM), Zeta potential, point of zero charge, Brunauer-Emmett-Teller (BET), and Fourier Transform Infrared Spectroscopy (FTIR) analysis. The results revealed that the optimal conditions for dye removal were established at 120 min, 2 g adsorbent dosage, 50 mg/L dye concentration, pH5 and pH9, achieving 94.3% and 86.9% for CR and CV, respectively. The dye adsorption equilibrium data fitted well to the Langmuir isotherm model with monolayer maximum adsorption capacity of 21.368 and 10.1419 mg/g for CR and CV dye, respectively. In addition, the kinetic studies showed rapid sorption dynamics following a First-order kinetic model. Moreover, the intra particle diffusion and Elovich models exhibited high correlation coefficient values indicating a contribution of physical and chemical adsorption process. These findings suggest that DWTS is a cost-effective and viable alternative for dye removal in wastewater treatment, with implications for sustainable waste management practices. Additionally, recommendations for the safe disposal of spent adsorbents are discussed, highlighting potential applications in construction materials.