Study of highly furfural-containing refinery wastewater streams using a conventional homogeneous Fenton process

Abstract

The conventional Fenton process has been evaluated to treat highly furfural-containing wastewater of 76 g/L at an initial pH of 3. Streams of these features can be accidentally generated after solvent extraction operations in petrol refineries, which leads to significant concern for downstream wastewater treatment facilities. The influence of temperature, initial hydrogen peroxide, and iron catalyst concentrations was investigated. Intensive oxidizing conditions (64 g/L of hydrogen peroxide initial concentration, temperatures higher than 50 °C, or catalyst concentration -FeSO4- higher than 1.26 g/L) produce a higher concentration of carbonyl intermediate compounds, that promote the subsequent generation of complex molecules hardly biodegradable (humins). In contrast, treating a diluted furfural stream (ca. 3 g/L) from a refinery using a temperature of 60 °C and a hydrogen peroxide concentration of 5.7 g/L did not evidence the formation of humins. In these conditions, the oxidation of furfural preferentially proceeds by oxidation of furfural to furoic acid and 2(5H)-furanone, further opening of the furan ring and subsequent oxidation until readily biodegradable acetic and formic acids. When working with highly concentrated wastewater streams, milder oxidizing conditions are required, such as low temperature (20–40 °C), low hydrogen peroxide (< 38 g/L) and a H2O2/Fe2+ mass ratio lower than 109 to prevent the formation of non-biodegradable humins. A remarkable furfural removal (> 99%) and low depletion of total carbon were achieved with highly furfural concentrated effluents (76 g/L of furfural) at 40 °C and a low concentration of hydrogen peroxide (38 g/L).