Application of Extracellular Polymeric Substances Extracted from Wastewater Sludge for Reactive Dye Removal

This study aimed to investigate the adsorption of three commercial reactive dyes using extracellular polymeric substances (EPS) extracted from the waste sludge of a beer wastewater treatment plant in Hanoi, Vietnam. EPS was extracted from sludge by the HCHO-NaOH method and was characterized by measuring kaolin flocculation activity, dry weight, chemical composition, and functional groups. Adsorption of dyes on EPS was conducted by Jartest at different pH values, contact times, and EPS dosages. The EPS was composed of 25% sludge by weight. The FTIR analysis showed the presence of amine and carboxyl groups in the EPS structure. The removal efficiencies of reactive dyes were high at pH values below 6, a contact time of 30 to 60 min, and EPS dosage of 200 - 250 mg/L. At optimum condition, removal efficiencies of 85%, 99%, and 99% were obtained for Reactive Yellow 176 (RY 176), Reactive Blue 21 (RB 21), and Reactive Red 241 (RR 241), respectively. The adsorption process could be described by both Langmuir and Freundlich models. The maximum dye adsorption capacities for RY 176, RB 21, and RR 241 were 0.50 g/g, 0.72 g/g, and 0.95 g/g, respectively. It is concluded that EPS in wastewater sludge could be utilized as an effective adsorbent for dye removal, thereby enhancing the value of sludge in wastewater treatment.