Hydrochar composites for healthcare wastewater treatment: A review of synthesis approaches, mechanisms, and influencing factors

Healthcare wastewater (HWW) contains several emerging contaminants (ECs) that persist after treatment with conventional methods, underscoring the need for effective and sustainable alternatives. One promising technique is adsorption and catalytic degradation with hydrochar composites, which present an eco-friendly and cost-effective solution for HWW treatment. However, there are critical knowledge gaps on the efficiency of hydrochar composites, pivotal factors influencing the process, and underlying mechanisms. This study employs a semi-quantitative research approach to critically review existing literature on treating HWW using hydrochar composites. The review provides an overview of current research and pinpoints future research directions. Our review reveals that only a few studies have explored the application of hydrochar composites in eliminating ECs from HWW. The results demonstrate that hydrochar composites achieve an EC removal efficiency of >80 %. Notably, these composites remove ECs through simultaneous adsorption and advanced oxidation process mechanisms, with oxidation processes exhibiting dominance. Future research should emphasize enhancing the adsorptive and catalytic properties of hydrochar composites, exploring their reusability and environmental hazard, and investigating pilot-scale applications of this technology. The insights provided in this review are significant in mitigating the adverse health and environmental impacts resulting from the discharge of HWW into the ecosystem.