Enhanced Treatment of Anionic and Cationic Dyes in Wastewater through Live Bacteria Encapsulation Using Graphene Hydrogel

Organic dyes have been considered as persistent pollutants to the water environment and remain a challenge for industrial wastewater treatment. Here we integrated environmental biotechnology and adsorption technique into a highly porous, reactive hydrogel based material composed of live Shewanella xiamenensis BC01 encapsulated within reduced graphene oxide network (BC01-BGH). Because of the synergetic effects of adsorption and biodegradation, BC01-BGH showed exceptional decolorization performance of decomposing model anionic and cationic dyes, i.e., Congo red (CR) and methylene blue (MB), with efficiencies up to 99.8 and 97.3% in 55 h, respectively. Through a series of characterizations along the degradation process, we found that the hydrogel network provided universal adsorption to those dyes via joint electrostatic interaction, chemical interaction and pi-pi interaction with the assistance of the immobilized BC01, leading to the enhanced decolorization. The system did not require additional carbon sources and the resulting products, basically benzidine and anilines, were readily oxidized by ClO2 to a COD level below 60 mg/L. These results help bridge the knowledge gap of the bacteria encapsulation as a potential scale-up technology to clean up various dyes in wastewaters.