Mass transfer mechanisms and decolorization kinetics of the mixed azo dyes

Abstract

The treatment of dye-contaminated wastewater using granular sludge was evaluated to ensure an effective design process for biogranulation technology. The investigation of dye-contaminated wastewater treatment in a sequencing batch reactor (SBR) aimed to understand the decolorization of mixed azo dyes (MAD) mediated by aerobic granular sludge (AGS) and magnetic-activated carbon aerobic granular sludge (MACAGS). The applicability of Generalized Fulazzaky equations was expanded to predict the mechanisms and kinetics of global, external, and internal mass transfer. The performance of SBR in decolorizing MAD with AGS and MACAGS reached 65.04% and 82.32% efficiency, respectively, exhibiting an increased efficiency of 17.28% (82.32-65.04%) with the presence of magnetic-activated carbon (MAC) in the formation of AGS. A trend in the variation of the internal mass transfer factor was similar to that of the global mass transfer factor and was far higher than that of the external mass transfer factor, indicating that the rate-limiting step of MAD decolorization was dependent on the resistance of external mass transfer. An analysis of the decolorization efficiency based on the internal mass transfer factor provided new insights into the role of MAC in enhancing the SBR performance, contributing to the advanced treatment of dye-contaminated wastewater.