Enzymatic hydrolysis of waste fats, oils and greases (FOGs) : Status, prospective, and process intensification alternatives

The increasing global generation of waste fats, oils, and greases (FOGs) is resulting in a cascade of economic, environmental, and public health issues as mismanagement is a common practice worldwide. Hence industrial exploitation and valorization is required towards a circular economy within the oleochemical industry. FOGs suitable for further oleochemical exploitation include used cooking oils, trap greases, mill effluents, rendering fats, spent earths from filtration and bleaching, deodorization distillates, soapstocks, and sewage sludges, among others. However main challenge for FOGs harnessing are their heterogeneity and the high content of impurities, acidity, and water. Alternatively, waste FOGs could be subjected to complete hydrolysis to recover free fatty acids (FFAs), which are widely used oleochemical feedstocks. Different catalysts have been explored for this process, however, lipases are of particular interest because they are able to work on low-quality feedstocks under milder operating conditions. This paper reviews most recent investigations on the enzymatic hydrolysis of waste FOGs, describing main processes characteristics, operating conditions, challenges, current attempts to improve enzymes performance, the use of combined chemical processes to improve feedstock utilization, and the implementation of intensified processing technologies. Potential for industrial implementation and future research possibilities in the process intensification field are identified.