The Application of Microwaves in Sulfate Radical-based Advanced Oxidation Processes for Environmental Remediation: A Review

The generation of sulfate radicals is a key factor to limit the catalytic activities of sulfate radical-based advanced oxidation processes (SR-AOPs). Microwave irradiation is a specific method to heat solutions via thermal and nonthermal effects, and has attracted an increasing amount of attention in recent years. Herein, we focus on the application of microwaves in SR-AOPs that called SR-MAOPs in environmental remediation, including wastewater, landfill leachate, biological waste sludge and soil, etc. treatment. Various systems including homogeneous and heterogeneous SR-MAOPs were reviewed. In wastewater treatment, not only the dyes and pharmaceutical and personal care products (PPCPs) were considered, the application in actual water matrices was also summarized. In addition, the function of remediation for organic-contaminated soil, landfill leachate and biological waste sludge were assessed using SR-MAOPs. In addition to evaluating the degradation efficiency of various organic pollutants from environment, the dewaterability is another key to treat biological waste sludge. The SR-MAOPs could break up hydrogen bonds and inactivate and denature complex biological molecules via microwave effects to achieve the dewatering of microorganisms in sludge. Furthermore, the COD of the sludge increased to a high level after microwave irradiation of sludge, which means that biopolymers released from microbial cells into the solution. Then, the released COD could be well treated by the SR-MAOPs. Based on the summary, we reveal that SR-MAOPs are potential technologies for environmental remediation, especially for systems with complicated organic compounds.