# Biological Methods in Biodiesel Production and Their Environmental Impact
## 3 Production of Biodiesel by Biological Transesterification Process
For example, the authors of [34] studied, inter alia, the influence of the type of carrier (LifetechTM ECR1061M, LifetechTM ECR8804M, LifetechTM ECR8806M, LifetechTM ECR1090M, and LifetechTM ECR1030M) and the type of lipase (from: _Rhizomucor miehie, Thermomyces lamuginosus, Candida antarctica_, and the ultra-phospholipase of _Lecitase antarctica_), and the ultra-phospholipase reactions of _Lecitase_ oil and the phospholipase reactions. Their performances were compared with commercial biocatalysts (TL-IM, RM-IM, Novozyme 435). It was found that some of the tested systems (enzyme-carrier) showed better performance than commercial biocatalysts. This may be related to better diffusion of the substrate into the active center of the enzyme. Enzyme-catalyzed transesterification has one more advantage: free fatty acids contained in oils do not constitute an obstacle in the process and can be completely converted to methyl esters [8]. Work is also carried out on replacing alcohols with other compounds that are acyl acceptors in order to increase the effectiveness of the transesterification process (elimination of the inhibition effect). The authors of [35] investigated the possibility of transesterification of five different oils during lipase-catalyzed transesterification, with methyl acetate as an acyl acceptor. They stated that under optimal reaction conditions,tested fats (plant oils and animal fats) led to high yields of methyl ester on the level from 91% (for soybean oil) to 98% (for cotton-seed oil). The use of lipases can reduce the cost, due to easier separation of product and glycerol, lack of side reactions, and reduced wastewater treatment [36]. The lipase-catalyzed process enables to use low-quality oils containing high free fatty acid content as a substrate. In Table 1, the transesterification methods are compared using different types of catalysts. The main benefits of using an enzyme catalyst include lowering the reaction temperature, the possibility of using a lower quality raw material (containing free fatty acids), eliminating the dangers of soap formation, increasing the efficiency of the reaction, and no difficulties in the process of glycerin recovery and ester purification. The use of enzymatic catalysts that eliminate the disadvantages of inorganic processes listed in Table 1 requires a lot of research to solve technological problems that limit their profitability [38]. As shown in [39], the product of transesterification using the biocatalytic approach can be much cleaner and less energy-demanding in comparison with chemical catalysts. It has been shown that the biocatalysis could be comparable with the conventional catalysis reaction in the production of biodiesel, taking into account the reaction rate and conversion. The technology of biological production is constantly being developed, which is caused by the increase of biofuels' demand. This is reflected in the number of published new solutions of biodiesel production. For the last 20 years, these solutions have generally been related to: reactors (55%), raw materials (21%), catalysts (9%), pre-treatment (13%), and testing methods (2%) [40]. In the field of biodiesel production through lipase catalysis, the changes are mainly aimed at: raw materials' quality, enzymes, process parameters, acyl acceptors, solvents, and reactor systems. The raw materials' selection is very important because their cost represents nearly 80% of the biodiesel production cost. In that area, research is underway to change food feedstocks into non-food and waste ones [41; 42]. As feedstocks, different types of non-edible oil raw materials have been investigated, such as: Jatropha seeds, _Calophyllum inophyllum_, tobacco, rubber, mahua, Cotton seeds, Karanja seeds, Castor seeds, _Cynara carduculus_ L. seeds oil factory wastes, industrial by-products rich in fatty acids (palm oil sludge, waste cooking oils), animal fats, spent coffee grounds, and municipal sludge [43; 44; 45; 46].