Magnetic Dolochar-Mediated Aerobic Granulation: A Sustainable Strategy for Efficient Organic Matter and Nutrients Removal from Rice Mill Wastewater

Aerobic granulation (AG) is a novel and emerging technology, but long granulation periods and stability issues in the system have been major drawbacks. Magnetic material and inert carbonaceous matter have been shown to play an important role in granule cultivation and treatment. The synergistic advantages of both have been achieved by combining them into a dolochar-Fe3O4 composite. The current study focuses on incorporating this composite for granule cultivation and for treating simulated rice mill effluents. Its addition improved granule morphology, increased secretion of extracellular polymeric substances, and increased the PN/PS ratio. Simultaneously, the stability of the granule was enhanced. Average chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) removal efficiencies were achieved at 95%, 70%, and 65%, respectively, which is found to be increased by 12%, 16%, and 15%, respectively; thus, increased performance was observed. Microbial community analysis revealed that higher TN and TP removal was due to the microorganisms responsible for heterotrophic nitrification-aerobic denitrification (HN-AD) and denitrifying phosphorus-accumulating organisms (DPAOs). Overall, the present study highlights the potential of utilizing dolochar-Fe3O4 composite to enhance granular formation, stability, and performance of the treatment.