A novel bioflocculant extracted from excess-activated sludge for dye-containing wastewater treatment

Abstract

Textile dyes are a major environmental concern related to the textile industry field due to their chemical complexity that hampers biodegradability and constraints conventional wastewater treatment. In this context, this work presents a bioflocculant produced from textile industry excess-activated sludge capable of precipitating azo dyes. The alkaline hydrolysis employed on dried activated sludge was optimized and the produced bioflocculant was characterized in terms of chemical composition, SEM-EDX, TEM, XRF, AAS, and TGA. The resulting flocculant presented 27 % protein, 12 % carbohydrate, and 12 % lipid contents, with hydroxyl and aliphatic CH functional groups. The chemical structure of dyes, the pH, and the respective zeta potential of the flocculating medium were taken into consideration during assays to conclude the flocculation mechanism. Flocculation assays resulted in color removal outcomes of 91 and 100 % for reactive and disperse dyes, respectively, at pH 5, and the OECD 301A biodegradability test confirmed the low presence of cellular debris after treatment. The activity of the bioflocculant was evaluated with a commercial naphthalene-based dispersant and the results were compared to color removal promoted by polyaluminum chloride (PAC). This work shows the feasibility of the low-cost activated sludge as a bioflocculant source and its potential in clarifying wastewater with azo dyes.