Adsorption study of isotherms, kinetics modelling, and thermodynamics of immobilized Candida rugosa lipase on metal oxide for esterification of waste cooking oil

The problem regarding improper disposal of waste cooking oil (WCO) can be solved via biotransformation of WCO to value added product using lipases as a biocatalyst. Thus, immobilization method was proposed for the recyclability of the biocatalyst. However, a comprehensive discussion on adsorption study is limited for lipase immobilization. In this study, Candida rugosa lipase (CRL) was immobilized on modified metal oxide (Mg2+/ Al2O3) and the support was improved by addition of activating agent (L-lysine/Mg2+/Al2O3). Subsequently, the biocatalysts were used for esterification of WCO in the presence of methanol. Maximum adsorption capacity for the support was improved after addition of L-lysine resulting in 0.262 mg protein/g of support. The equilibrium adsorption data for both systems were fitted to the Redlich Peterson isotherm model while the kinetics study was most fitted with Elovich model, and the adsorption process were influenced by intraparticle and film diffusion mechanisms. Thermodynamic analysis explained that the adsorption process of CRL/L-lysine/Mg2+/Al2O3 was more spontaneous and stronger as compared to CRL/Mg2+/Al2O3. Furthermore, CRL/L-Lysine/Mg2+/Al2O3 exhibited its potential in esterification of WCO by converting 62.95% of free fatty acid (FFA), while CRL/Mg2+/ Al2O3 converted lower FFA (53.62%). This study offers a fundamental understanding on designing an effective immobilization system by addition of activating agent to develop a good biocatalyst for biotransformation of WCO.