Preparation of saline-tolerant electroactive granular sludge and its application in treating saline azo-dye wastewater

Saline azo dye wastewater is challenging traditional biological treatment processes. In this study, an electroactive granular sludge (E-AGS) was prepared by using a Shewanella Biologically Augmented saline SBR reactor, and its ability to treat saline azo dye wastewater was verified. The simulated wastewater contained 3 % NaCl, 50 mg/L NH 4 + -N, and 500 mg/L COD. After adding Shewanella , the removal rate of COD and TN increased by about 20 %, and the operational stability of the system in response to seasonal temperature changes was improved. After running for 350 days, larger particle size and higher electron transfer activity granular sludge were formed relatively quickly, with a relative increase of 150 % in MLVSS. In the SBR reactor, the nitrogen transformation function genes represented by AmoC were significantly up-regulated, and the abundance of Shewanella was also significantly increased. Furthermore, the treatment capacity of E-AGS for two types of azo dye wastewater, amaranth and reactive black 5, was tested at 50 mg/L initial dye concentration. Compared to the control group, E-AGS exhibited about four times higher decolourization efficiency, better pollution treatment performance, and electron transfer activity. The EEM and 2D-COS results show that E-AGS exhibits higher structural stability and environmental responsiveness in wastewater treatment through EPS. This study reveals the feasibility of using Shewanella bacteria to enhance the activated sludge process and form electroactive granular sludge. It provides a new perspective for developing and transforming activated sludge processes. • Shewanella enhanced SBR system performance and stability and prepared E-AGS. • E-AGS reactor improved 15 % COD and 20 % TN removal compared to control. • E-AGS removed 91 % reactive black 5 and 100 % amaranth in 48 h for decolourization. • E-AGS has a robust EPS structure for quick environmental adaptation.