**4. Olive Mill Wastewater Treatment**

As reported above, OMWW is the waste of olive oil production characterized by high organic content and phytotoxic features mainly due to the presence of phenols, which are responsible for the olive oil's antimicrobial and antioxidant qualities. This makes waste biodegradation difficult in conventional treatment facilities (e.g., anaerobic digestion processes) that generally use microorganisms for waste biodegradation.

According to these premises, the OMWW treatment has faced several traditional approaches, which can be categorized as: disposal, physicochemical, biological, and advanced oxidation methods. Figure 4 schematizes their potentialities and weakness.

**Figure 4.** Main advantages/disadvantages of the standard technologies used for OMWW treatment.

As can be observed, all the mentioned technologies have specific advantages, but also cost problems. Therefore, some alternatives are currently the object of hard work by the research community. Among all the possibilities, one emerging and valid strategy is the OMWW steam reforming (OMWWSR), which permits valorization of wastes, producing green H2, following the circular economy perspective [32]. It is a promising strategy in the view of the future projections of the H2 market demand recently published by the International Energy Agency [56–58]. This method is described as having a high potential because of the environmental attractiveness of H2, which is able to reduce CO2 emissions in the atmosphere [56]. In this way, OMWWSR could contribute to air pollution reduction and, at the same time, valorize the waste from the olive oil industry [32]. However, this process still deserves to be properly studied and optimized because of some drawbacks affecting the catalyst formulation (e.g., low stability, deactivation, coke poisoning) [32].

The following paragraphs provide an accurate description of each traditional technology.
