Abstract
A series of biochars and activated carbons (ACs) was prepared combining carbonization and physical or chemical activation of cheap and abundant residues of the olive oil industry. These materials were used as Fe-support to develop low-cost catalysts for the heterogeneous Fenton-like oxidation of simulated olive mill wastewater (OMW), the highly pollutant effluent generated by this agroindustry. Commercial ACs were also used as reference. All catalysts prepared were extensively characterized and results related with their performances in the catalytic wet peroxide oxidation (CWPO). Results showed a linear relationship of the textural properties of the catalysts with the adsorptive and catalytic performance, as well as the preferential adsorption and degradation of some phenolic compounds (caffeic and gallic acids) by specific interactions with the catalysts’ surface. Despite the best performance of catalysts developed using commercial supports, those prepared from agro-industrial residues present some advantages, including a smaller catalyst deactivation by iron leaching. CWPO results show that catalysts from physically activated olive stones are the most promising materials, reaching total organic carbon and toxicity reductions of 35% and 60%, respectively, as well an efficient use of H2O2, comparable with those obtained using commercial supports. This approach showed that the optimized treatment of this type of residues will allow their integration in the circular economic process of the olive oil production.
Highlights
Pollution of water bodies and scarcity of clean water is an increasing worldwide issue related to population growth, excessive urbanization and industrialization, as well as climate changes
The olive oil sector is important for countries in the Mediterranean region, where ~3.3 million metric tons of olive oil were extracted in the 2018 campaign, according to the International Olive Oil Council (IOOC) [3]
The carbonization process was simulated by Thermogravimetric analysis (TGA) in order to fit experimental conditions of samples’ preparation
Summary
Pollution of water bodies and scarcity of clean water is an increasing worldwide issue related to population growth, excessive urbanization and industrialization, as well as climate changes. According to the Food and Agriculture Organization Corporate Statistical Database (FAOSTAT) on crops around the globe, the water footprint of olive oil’s processing industry can reach 14,500 m3 per ton of oil extracted [2]. Depending on the olive oil extraction process employed, the amount of wastewater generated may be as high as 50% of the total water inputs. The volume and intrinsic characteristics of olive mill wastewaters (OMW) strongly varies according to the extraction process employed, olive variety, climate conditions, cultivation practices, and storage. Phenolic compounds of olive’s stones and pulp are important thanks to their greater solubility in water than oil, leading to the high concentration (2–15% w/w) observed in such effluents [4,5]. It has been reported that phenolic compounds, along with some organic acids such as the acetic and formic acids, are responsible for OMW’s phytotoxic and antibacterial effect [6,7]
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