Enhanced p-nitrophenol removal via electrochemical activation of peroxymonosulfate (PMS) with biochar in a flow-through reactor: Mechanistic insights and optimization

The utilization of biochar for peroxymonosulfate (PMS) activation has gained attention due to its functional groups and porous structure. Nonetheless, its practical application is limited by challenges in regulating reaction rates and the short catalyst lifespan due to natural organic matter (NOM) and anions. Furthermore, most studies have focused on batch-type experiments. To address these limitations, this study introduced a combined electrolysis (E) and biochar (BC) system for PMS activation in a flow-through reactor to remediate dissolved p-nitrophenol (p-NP) as a model pollutant. It is hypothesized that the E-BC-PMS system enhances degradation through three mechanisms: (1) simultaneous activation of PMS by biochar and electrochemical reactions, (2) adsorption of contaminants onto biochar, and (3) formation of diverse reactive species. The E-BC-PMS system removed 99.9 % of p-NP and showed the highest removal rate constant (0.497 min⁻¹) suggesting a synergistic effect compared to individual PMS (1.1 %), BC (1.6 %), or E (48.8 %) systems. Moreover, the E-BC system utilizing PMS exhibited 3.7 and 4.5 times higher p-NP degradation rate constants than peroxodisulfate or hydrogen peroxide, respectively. Mechanistic investigations using scavenger tests, electron paramagnetic resonance, and x-ray photoelectron spectrometry revealed that non-radical (electron transfer and ¹O₂) and radical (O₂^•- and •OH) pathways contributed to p-NP degradation. Overall, the E-BC-PMS system activates PMS through the electrochemical, functional groups, and alkaline activation. These findings suggest that the E-BC-PMS system is highly effective for p-NP removal and presents a promising strategy for groundwater remediation applications.