An eco-friendly approach of biodiesel production from tannery fleshing wastes by crude neutral protease enzyme

Abstract

A new approach for extracting fat from tannery fleshing wastes (TFW) was established by hydrolyzing in water using a crude neutral protease enzyme. The bacterial strain for protease preparation was isolated from the waste dumping site of Institute of Leather Engineering and Technology of the University of Dhaka. The crude enzyme thus obtained was found highly active at 55 °C and pH 8.0, with a substrate concentration of 2%. Several reaction parameters, such as enzyme concentration, hydrolysis temperature and duration, were optimized using response surface methodology (RSM). The detailed analysis data by RSM showed 31.33% enzyme to dry weight of fleshing, 2.874 h of hydrolysis, and at 65.23 °C temperature to be the optimum for maximum theoretical fat yield of 38.46%. The laboratory experiments under optimum conditions resulted 34.9% fat yield with an error of 10.17%. The fleshing fat was transesterified in methanol into biodiesel using a recyclable magnetic nano catalyst with a 98% conversion and glycerol as a byproduct. The FT-IR spectroscopic results demonstrated an absorption of CO stretching at 1740 cm−1 for α, β-unsaturated esters in the biodiesel and its fatty acid ethyl ester. The 1H-NMR spectroscopy revealed a singlet peak of methoxy protons at 3.65 ppm and a triplet at 2.26–2.30 ppm for α-CH2 protons that confirmed the presence of unsaturated fatty acids with a carbonyl hydrogen double bond peak at 2.00–2.01 ppm. The GC-MS data of the biodiesel comprises of ethyl E−11-hexa-decanoate, ethyl myristate, palmitate, stearate, and decanoate. The results of various fuel parameters of the biodiesel were measured and compared with standard biodiesel EN14214 which revealed that it has comparable fuel properties to the standard. The higher calorific value (38.5 MJ kg−1) and flash point (152 °C) of the biodiesel than the standard, indicating its high potential and ease of storage stability than standard biodiesel.