Application of an autocatalytic fenton process for the pre-treatment of an oily sludge: A sustainable approach for valorisation of refinery wastes

Introduction Nowadays, the refinery industry generates huge amounts of hazardous wastes during the petroleum refining processes (especially oily sludge) (Hu et al., 2013). The environmental risks associated with the inadequate disposal of these wastes makes necessary the development of technologies to treat and valorize them properly within the framework of circular economy and sustainability. Oily sludge is usually composed of three different phases: oily, aqueous, and solid. The oily phase presents a high percentage of carbon content, due to the presence of petroleum hydrocarbons (PHC). The solid phase contains organic and inorganic material, with a high concentration of metals (principally iron), and the aqueous phase evidences the presence of nutrients (ammonia and phosphate) and low organic carbon concentration. According to this composition, different valorization strategies can be addressed (Jerez et al., 2021). Fenton oxidation treatment is a well-known advanced oxidation process for the removal of harnessing pollutants, especially those which are difficult to degrade by microorganisms (Pourehie and Saien, 2020). Fenton oxidation treatment shows lower energy requirements, reaction time and operational costs, as compared to other oxidation processes. The process consists in the decomposition of H2O2 into •OH radicals, in the presence of an iron catalyst, performing the non-selective oxidation of organic compounds, such as PHC present in refinery oily sludge, in more biodegradable compounds (Sivagami et al., 2019). According to the characterization results of the oily sludge, an assessment of autocatalytic Fenton oxidation treatment has been performed in this work. The oily sludge presents a high concentration of iron which makes unnecessary the addition of a catalyst to promote Fenton reactions. The purpose of this pre-treatment is the decrease in the concentration of solids, and consequently a reduction of volume, of the sludge, generating a biodegradable aqueous effluent with higher loading of soluble carbon.