Preparation and application of unhairing enzyme using solid wastes from the leather industry—an attempt toward internalization of solid wastes within the leather industry

Abstract

Usage of the animal fleshing waste as the source of carbon and nitrogen for animal skin unhairing protease (EC 3.4.21) production along with agro-industrial wastes like wheat bran has been investigated. Thermal hydrolysis of delimed fleshing waste for 3 h yielded a fleshing hydrolysate (FH) having a protein content of 20.86 mg/mL and total solids of 46,600 ppm. The FH was lyophilized and spray dried to obtain fleshing hydrolysate powder (FHP) to be used along with wheat bran and rice bran for protease production. The carbon, nitrogen, hydrogen, and sulfur contents of the FHP were found to be 40.1, 13.8, 5.4, and 0.2%. The control solid-state fermented (SSF) medium without FHP showed a maximum activity of only 550 U/g. A maximum protease activity of 956 U/g was obtained by using 6% FHP (taken based on the combined total weight of wheat bran and rice bran) after 96 h of fermentation, resulting in a 1.7-fold increase in the protease activity. The total cost of producing 1 kg of FHP and the cost of producing 1000 kU of protease using FHP along with wheat bran and rice bran were found to be USD 24.62 and USD 2.08, respectively; 25% of SSF protease along with 40% water was found to be capable of unhairing the sheepskins in 7 h eliminating the hazardous conventional lime sulfide unhairing system. Thus, the leather industry's solid waste internalized for the production of unhairing enzyme resulted in a sustainable solution for pollution problems. Graphical abstract ᅟ.

Overview of the Leather Industry and Pollution Impact

“…Exposure of the animal skin to this protease achieved its complete dehairing in 7 hours of treatment, with 25 wt% of enzymes. Pollution parameters showed a reduction of 79.6 wt% of COD and 67.7 wt% of BOD (Ramesh, Muralidharan, and Palanivel 2018).…”

“…Fleshings and wet-blue shavings, have been studied as auxiliaries in protease production for hair removal applications. Ramesh, Muralidharan, and Palanivel (2018) evaluated the use of fleshings as an additional source of carbon and nitrogen to increase the protease activity in the dehairing process. The enzyme exhibits its maximum activity (956 U/g) using 6 wt% of fleshing hydrolysate powder, at pH9.…”

“…The exposure of skin to enzymatic techniques not only showed a clear reduction in pollution load but also demanded less time to complete the process, which translates to a drop in the energy cost when compared to the standard method. Even though enzyme production is not economical (Ramesh, Muralidharan, and Palanivel 2018), the exploitation of the generated wastes throughout their life cycle by reusing solid leather wastes, reduce the hazardous environmental impact, and encourages responsible consumption and production (United Nations 2016). Furthermore, the use of enzymes allows hair recovering for further applications, contrary to the oxidative method, which destroys the hair (Andrioli, Petry, and Gutterres 2015) and brings a new concern: the hydrogen peroxide poisoning (Watt, Proudfoot, and Vale 2004).…”

“…For each metric ton of tanned hide, between 190 to 380kg of waste are released to effluents (Tahiri 2009). According to Ramesh, Muralidharan, and Palanivel (2018), fleshings contribute to a one-third volume of the solid wastes, generated in the leather tanning process. Moreover, the presence of these solid wastes conduces to a sludge problem and blockage of waste collection systems (Covington 2011;Kanagaraj et al 2015).…”

Multilayer Structure Ammoniated Collagen Fibers for Fast Adsorption of Anionic Dyes

“…In the tanning industry, the utilization rate of raw leather is low, only 30–50% of them can be converted into useable leather, and the rest is mainly in the form of waste leather shavings. − Therefore, a large amount of waste leather shavings is produced every year. At present, except for a small part of the waste leather shavings used to produce recycled leather and to prepare gelatin, most of the remaining shavings are treated as garbage, which causes a very serious waste of resources.…”