Up-Flow Anaerobic Sludge Blanket Reactors in Dye Removal: Mechanisms, Influence Factors, and Performance

Abstract

Society faces eco-environmental challenges when it comes to managing industrial wastewaters. In particular, textile effluents are one of the main threats to living being due to toxic dyes. Technologies used to remove dye compounds include physicochemical and membrane filtration processes. However, since current technologies have several limitations, including high investment and energy demand, researchers have investigated cheaper and eco-friendly alternatives. Among them, anaerobic processes have been an effective method to decolourise dye-containing effluents. In that direction, the up-flow anaerobic sludge blanket (UASB) technology stands out in terms of high cost-effectiveness. The authors reviewed the published literature on UASB reactors in dye compounds removal. Mechanisms, merits, demerits, and technical aspects of UASB reactors are introduced. Challenges and opportunities are discussed. The major points are 1) mechanisms of dye removal in UASB reactors comprise mainly dye adsorption onto sludge granules and azo bond cleavage (biodegradation), 2) dye structure and concentration, external organic carbon source, redox mediators, and bioreactor operating conditions play a key role in the treatment performance, 3) UASB technology exhibits high decolourisation rates. Removal efficiencies of chemical oxygen demand and colour lie within the range of 60–85% and 75–96%, respectively. However, anaerobic treatments may not be able to mineralise by-products of anaerobic metabolisms. Consequently, post-treatment of the anaerobically treated effluent is required, and 4) the energy production during the decolourisation process in UASB reactors is estimated at 22 kWh per m3 of treated wastewater. Bio-energy recovery can promote wastewater valorisation and decrease the economic burdens of dye-containing effluents treatment. Future studies should focus on optimising influence parameters of full-scale UASB reactors and biogas recovery from dye-containing wastewater treatment.