Heterogeneous Fenton oxidation assisted by zero-valent iron for on-demand pretreatment of extreme furfural spills

Accidental discharges of highly concentrated furfural can severely inhibit biological wastewater treatment in refineries. This study assesses an on-demand pretreatment based on heterogeneous Fenton oxidation assisted by zero-valent iron (ZVI) shavings to mitigate extreme shock loads in real refinery wastewater (ca. 75 g/L furfural). Experiments were conducted at 60–80 °C and at natural pH, evaluating the effects of temperature, H 2 O 2 dosage, and ZVI loading, and quantifying furfural removal and improvements in biodegradability and toxicity by respirometry. At 80 °C, hydrogen peroxide alone achieved substantial furfural conversion (70%), confirming that thermal peroxide decomposition provides the primary oxidative driving force. The presence of ZVI further accelerated conversion (up to 97%) and shifted product selectivity toward short-chain carboxylic acids (mainly formic acid), while iron leaching remained negligible (< 0.1 mg/L). Although TOC removal was moderate (4–14%), the treated effluent showed a substantial increase in biodegradability and a marked reduction in toxicity, enabling safe downstream integration into activated sludge systems. A preliminary techno-economic assessment, framed within an event-based operating scenario, confirms the industrial feasibility of the approach when applied as an emergency mitigation measure, with an OPEX of 181 k€/y. Overall, the findings demonstrate the feasibility of a rapid, simple and industrially relevant pretreatment strategy for emergency mitigation of extreme furfural releases prior to biological wastewater treatment.