## 1 Introduction  
Fossil fuels such as coal, natural gas, and petroleum have been extensively used as raw materials for synthesizing several fuels and chemicals. However, these non-renewable materials have caused a variety of damaging effects to the environment, such as global warming from greenhouse gas (GHG) emissions, land contamination, and air/water pollution [1]. In the last few decades, renewable materials have gained much attention worldwide as promising substitutes for petroleum-based materials, given their environmental benefitsand sustainable properties [1; 2]. In fact, many government and environmental organizations have imposed strict regulations that seek to reduce GHG emissions in several countries, by replacing traditional petroleum-based materials with renewable-based materials [2; 3]. There are a wide variety of renewable materials for producing biofuels and other valuable products for chemical industries, e.g., different types of agricultural crops, wood, microorganisms, animal manure, human sewage, and agricultural waste [3]. Of these different renewable materials, triacylglycerlycerols (TAGs), such as vegetable and microbial oils, animal fats, waste oils (cooking oils, yellow or brown greases, and sludge or soapstock from refining vegetable oils), and their derivatives (FFAs), have proven to be promising raw materials for producing valuable industrial products [4; 5]. Specifically, waste oils, including used cooking oils, have been used as eco-friendly and economic options given their low prices relative to edible vegetable oils, and their use in minimizing environmental problems, given that they can be directly disposed of in natural settings [6; 7]. In some instances, the direct use of oleaginous feedstocks, including waste oils, is not recommended, due to the presence of reactive \(\beta\)-hydrogen atoms in the glycerol moiety, and double bonds in unsaturated fatty acids, thus resulting in low thermal and oxidative stabilities [8; 9; 10; 11]. In this context, technological advancements have been extensively applied to process them to promote their use in oleochemical industries e.g., chemical modifications to exploit their functional groups [6]. The main chemical modification strategies employed are hydrolysis, esterification, transesterification, hydrogenation, epoxidation and ring-opening reactions [5; 9; 10; 11; 12; 13; 14]. Interestingly, these different strategies have also been commonly combined to introduce functional groups into their chemical structures to expand their versatility and application in chemical industries [5; 11; 13; 14]. In this field, bio-based epoxidized materials from different oleaginous feedstocks have been widely used as lubricants, plasticizers, acid scavengers, stabilizers, recycled asphalt pavement materials, coatings, and corrosion inhibitors [11; 13; 15; 16; 17; 18; 19]. They can also be transformed into several value-added raw chemical materials for producing biopolymers/bioplastics, including polyols/polyurethanes, estolides, and surfactants via epoxy ring-opening reactions [11; 20; 21; 22; 23; 24; 25]. Thus, the main objective of this study is to produce and characterize epoxidized monokalyl esters (EMAE) from USCO and fused oil via a three-step chemozymatic approach. This process first involves a complete hydrolysis of the waste oil to produce FFA, followed by the esterification of the produced FFA with fused oil, and epoxidation of the produced monoalkyl esters (MAE) in situ, generating performic acid from the reaction of formic acid and hydrogen peroxide. In this study, several lipase preparations with different specificities were used to produce FFA via the hydrolysis of ester bonds of waste oil (USCO), e.g., lipase from _Candida rugosa_ (CRL), a non-specific lipase [26]; lipase from _Thermomyces lanuginosus_ expressed in _Aspergillus oryzae_ (Eversa(r) Transform 2.0--ET2.0--_sn_-1,3 specific) [27]; _Candida_ sp. (CALA--_sn_-2 specific) [28]; _Rhizopus jaanicus_ (RJL--_sn_-1,3 specific) [29]; and _Aspergillus niger_ (ANL--_sn_-1,3 specific) [29].