Activated carbon modified with nano manganese dioxide triggered electron transport pathway changes for boosted anaerobic treatment of dyeing wastewater

Herein, an expanded granular sludge bed (EGSB) reactor with activated carbon (AC)-nano manganese dioxide (MnO₂) added was employed for azo dye wastewater treatment to investigate its effectiveness at decolorizing of azo dyes and removing COD. The results showed that the treatment of azo dye wastewater with the AC-MnO₂ modified EGSB reactor gave an 83% average decolorization efficiency, which was more efficient than the pure AC modified EGSB reactor. Moreover, the COD removal and changes in the intermediate products were controlled by AC-MnO₂. Additionally, there was a sharp increase in the sludge conductivity, while there was a significant decrease in the coenzyme F₄₂₀ concentration with long-term operation. Moreover, electrochemical analysis showed that the addition of AC-MnO₂ can enhance electron transfer in anaerobic system. The AC-MnO₂ can act as redox mediator; in the presence of the Mn⁴⁺/Mn²⁺ cycle, accelerating the electron transfer between the microbial cells and dyes, thereby promoting the decolorization of azo dyes. This caused a decrease in the methanogenic activity. Furthermore, high-throughput sequencing showed that the relative abundances of Pseudomonas and Desulfovibrio were significantly high among the acidogenic bacteria community, while Methanobacterium and Methanosaeta had very low abundances from among the methanogenic archaea community.