Enhancing Methane Production from Olive Mill Wastewater Through Homogeneous Fenton Pretreatment Using Different Iron Sources

Large quantities of wastewater (OMW) are generated by the olive oil industry, requiring sustainable management to mitigate environmental impacts. The main goal of this work is to evaluate the possibility of using the homogeneous Fenton process as a pretreatment of OMW, as well as the iron (Fe (II) and Fe (III)) addition to improve the methane production through AD. The Fenton process achieved chemical oxygen demand (COD) and total phenolic compound (TPh) removals of 17–47% and 75–94%, respectively. However, methane production did not improve compared with untreated OMW, which yielded about 82 NmL CH4/ g CODi. The increase in H2S production from about 2 mL in raw OMW to more than 8 mL in treated OMW may justify the inhibition of AD. Supplementing AD with 2 mg/L of Fe (III) increased methane production by 65% and significantly reduced H2S due to FeS precipitation. The addition of 1 and 2 mg/L of Fe (II) also increased methane production by 82 and 59%, respectively, but no reduction in H2S was observed. Therefore, although the Fenton pretreatment effectively reduces recalcitrant organic matter, it does not necessarily enhance methane production. A balance must be achieved between improving OMW characteristics and minimizing adverse impacts on AD performance.