Fenton-primed microbubble-enhanced cold plasma oxidation for food processing wastewater treatment

Cold plasma is a promising electrified approach for wastewater treatment, but its performance in complex food-processing effluents is limited by matrix scavenging, foaming, and restricted plasma-liquid interactions. Here, we demonstrate a Fenton-integrated microbubble-enhanced cold plasma activation (MB-CPA) process for the purification of tofu-processing wastewater. Fenton pre-oxidation served as a priming step, reducing chemical oxygen demand (COD) by 32% and separation of suspended particles by 35%. The organic and protein-rich wastewater formed a persistent foamy suspension that intensified shielding, which was strategically destabilized by adding an antifoaming agent, restoring gas-liquid contact. In the subsequent MB-CPA stage, we varied the plasma discharge configurations, dual-needle corona discharge (56 W) versus dielectric barrier discharge (DBD, 100 W), to quantify their impact under identical microbubble-mediated gas delivery. Under corona discharge, MB-CPA reduced COD by 14.7%, decreased fat emulsions by 80%, and reduced total suspended solids by 53%. Switching to DBD increased mineralization efficiency by 2.3-fold relative to corona discharge, indicating that spatially extended plasma generation in DBD enhances oxidative treatment in quenching-prone wastewater matrices. Beyond pollutant removal, the treated effluent contained 372.8 μ M reactive nitrogen species and promoted plant growth, suggesting potential for nutrient valorization. Overall, the dual-stage strategy of Fenton priming and MB-CPA polishing demonstrates the potential of plasma-enabled oxidation to food-processing wastewater.