Bio-lubricant from the olive mill waste through a new biocatalyst immobilized on ZnFe2O4

Given the growing global demand for energy, the depletion of fossil fuel reserves, and increasing environmental concerns, bio-lubricants are more and more a promising alternative to conventional mineral oil-based lubricants. Bio-lubricants have several advantages over mineral lubricants, such as (i) high biodegradability, (ii) low toxicity, and (iii) little impact on human health and environment. On the other hand, the use of vegetable oils for the synthesis of bio-lubricants is expensive, representing the raw material about 70-80% of the total cost of production. In this respect, olive mill wastes (OMW) can represent a promising alternative to vegetable oils. In particular, they contain a large number of carbohydrates, organic acids, lipid and mineral nutrients, as well as a high content of phenols and other natural antioxidant compounds that could be considered as a potential source of natural products with high added value. Olive oil-producing countries, like Italy, generate a significant amount of effluents from mills, which are among the most damaging agro-industrial emissions with a powerful pollution capacity. Indeed, because of the high pollution load, these effluents are exceptionally toxic to the entire soil-air-water ecosystem and to the living organisms that inhabit it. Traditionally, processes of transesterification-esterification favored by acid/basic catalysts are used for bio-lubricants production. Enzymatic catalyst has different advantages over the traditional ones, such as (i) high selectivity, (ii) ability to handle significant variations in quantity, (iii) moderate process conditions, (iv) it is "eco-friendly," etc...On the other hand, free enzymes have poor stability and their cost has encouraged the use of immobilization techniques to facilitate separation, recovery, and improve their activity.