An application of advanced hair-save processes in leather industry as the reason of formation of keratinous waste: few peculiarities of its utilisation

Detection and kinetic simulation of animal hair/wool wastes pyrolysis toward high-efficiency and sustainable management

Large quantities of solid wastes are produced each year in the leather industry. The considerable wastes generated exhibit tremendous application potential in terms of renewable energy sources and functional materials. Among them, animal hair/wool wastes possess high carbon content, which can be used sustainably and efficiently by using pyrolysis. Herein, the pyrolysis process of hair/wool wastes was investigated using TG-IR and Py-GC/MS, while the pyrolysis kinetic and thermodynamic were analyzed using "model-free" methods. The results showed that the hair/wool waste pyrolysis process can be divided into three stages: dehydration, devolatilization, and carbonization. The volatile products were mainly phenols (7.42%) and heterocyclic compounds (21.26%), which can be directly used as bio-energy (bio-gases and bio-oil) or converted to other useful chemical products. The kinetic parameters (E_a and A) calculated using the Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Kissinger methods indicated the complexity of the decomposition reactions, which was also confirmed by thermodynamic (ΔH, ΔG, and ΔS) calculation. Some suggestions have also been provided for the preparation of functional biochar with heteroatoms (i.e., N, O, and S) doping. These results not only provide a guide for designing the pyrolysis of hair/wool wastes but can also help develop a potential method to convert the hair/wool wastes into bioenergy to achieve sustainable development of the leather industry.

Heterologous expression and purification of keratinase from Actinomadura viridilutea DZ50: feather biodegradation and animal hide dehairing bioprocesses

The keratin-degrading bacterium Actinomadura viridilutea DZ50 secretes a keratinase (KERDZ) with potential industrial interest. Here, the kerDZ gene was extracellularly expressed in Escherichia coli BL21(DE3)pLysS using pTrc99A vector. The recombinant enzyme (rKERDZ) was purified and biochemically characterized. Results showed that the native and recombinant keratinases have similar biochemical characteristics. The conventional dehairing with lime and sodium sulfide degrades the hair to the extent that it cannot be recovered. Thus, these chemical processes become a major contributor to wastewater problem and create a lot of environmental concern. The complete dehairing was achieved with 2000 U/mL rKERDZ for 10 h at 40 °C. In fact, keratinase assisted dehairing entirely degraded chicken feather (45 mg) and removed wool/hair from rabbit, sheep, goat, or bovine' hides (1.6 kg) while preserving the collagen structure. The enzymatic process is the eco-friendly option that reduces biological (BOD) (50%) and chemical (COD) oxygen demands (60%) in leather processing. Consequently, the enzymatic hair removal process could solve the problem of post-treatments encountering the traditional leather processing. The enzymatic (rKERDZ) dehaired leather was analyzed by scanning electron microscopic (SEM) studies, which revealed similar fiber orientation and compactness compared with control sample. Those properties support that the rKERDZ enzyme-mediated process is greener to some extent than the traditional one.