Sludge Cake Derived Biochar for Irrigation Water Recovery in a Sequencing Batch Granular Sludge Reactors

Abstract

Aerobic granular sludge is a sustainable, viable substitute to improve industrial effluent treatment capabilities, lessen environmental impact, and significantly contribute to industrial sustainability. Hence, the efficacy of granular sequencing batch reactors (GSBR1 and GSBR2) operating side by side with and without the inclusion of waste‐derived biochar, respectively, for COD and NH 4 + ‐N removal was assessed. The synthesized biochar was used in the GSBR2 for contaminant removal. Process optimization was carried out through the application of response surface methodology. Cycle duration of 0.25–0.75 day and an industrial effluent concentration of 50%–100% were utilized as the independent variables. Results demonstrated that biochar as a biosorbent and nucleation carrier led to the production of more substantial and stable aerobic granules. Biochar speeds up granulation, lessens the compression carried on by inter‐particle collisions, and appears to have no negative influence on the granule bacterial community structure. The bacterial proliferation inside the granules caused a considerable rise in granule size. At 0.25 day cycle time and 100% industrial effluent, process results showed a considerable reduction of COD (62.8%, 94.1%) and NH 4 + ‐N (51.5%, 65.37%) for the GSBR1 and GSBR2 systems, respectively. Analyzing the kinetic models revealed that the Grau model performed better in estimating the rate of substrate removal with R 2 values in the range of (0.9608–0.9865) and (0.9575–0.9612) for COD and NH 4 + ‐N, respectively. Microbial community studies revealed that the microbiome diversity and adaptation supported aerobic granules' long‐term stability even at 75 days. Additionally, granule size and density were demonstrated, and the outcomes showed that the valorization of industrial effluent could be accomplished using an aerobic granulation mechanism employing biochar. The current results demonstrated that biochar application in GSBR as a biosorbent and nucleation carrier is a viable option to enhance organic matter and nutrient removal from industrial effluent, thereby making the water suitable for irrigation practices. It is also a solution to hazardous sludge wastes that could foster the transition toward sustainable and circular economy processes.