Microbial solid-electrolyte electrosynthesis of electrolyte-free hydrogen peroxide coupled with far-UVC for enhanced...

Microbial electrosynthesis of H₂O₂ offers a sustainable alternative to the energy- and resource-intensive anthraquinone process, yet existing systems rely on liquid electrolytes that introduce impurities and require downstream purification. Here, we develop a microbial solid-electrolyte electrosynthesis (MSE) system for the production of an electrolyte-free H₂O₂ solution using porous solid electrolytes (SE). Replacing conventional liquid electrolytes with SE creates a solid-phase ion-conductive interface that facilitates H⁺ transport between the bioanode and cathode, thereby obviating the need for supporting liquid electrolytes. By modulating the ultrapure-water elution flow rate, the MSE system continuously produced an electrolyte-free H₂O₂ solution at concentrations up to 342.2 mg L⁻¹, representing the first demonstration of SE-based H₂O₂ electrosynthesis driven by bioanode-derived electrons. An overall electron recovery of approximately 54 % was achieved from COD removal to H₂O₂ formation. Furthermore, coupling MSE-derived H₂O₂ with far-UVC (222 nm) irradiation established a hybrid MSE-UV₂₂₂ process that achieved complete removal of 1 mg L⁻¹ carbamazepine over three consecutive cycles at a UV₂₂₂-unit hydraulic retention time (HRT) of 2 h. Quenching assays combined with electron spin resonance (ESR) spectroscopy confirmed the formation of •OH, •O₂^-, and ¹O₂, with •OH dominating the oxidation pathway. Complete removal of 16 representative micropollutants was achieved in both tap water and WWTP secondary effluent, highlighting the hybrid process's applicability across diverse water matrices. This work demonstrates a laboratory-scale, SE-enabled microbial strategy for wastewater energy valorization, upgrading low-grade chemical energy stored in wastewater organics into high value electrolyte-free H₂O₂ solution via bioelectricity and enabling its direct coupling with far-UVC irradiation for sustainable water purification.