Assessment of Pollution Reduction in the Tannery Pre-tanning Processes Through the Use of Enzymes

Abstract

The process of transforming hides/skins into leather has been categorized as one of the most environmentally detrimental industries globally. Because of elevated pollution levels linked to the leather manufacturing sector, there has been a concerted search for clean technology options that could replace or reduce the hazardous chemicals used in tanneries. Application of enzymes has been suggested but has not been fully adopted in Kenya and there have been complaints about the poor performance of enzymes available in the market. In order to address these problems, a study was conducted to assess the potential of enzymes in reduction of pollution in the tannery pre-tanning processes. Commercial beamhouse enzymes in Kenyan market and special formulations of enzymes prepared by mixing different enzymes (lipase, amylase, keratinase and protease) were assessed for their effectiveness in different pre-tanning processes. Their potential in reducing pollution and improving leather quality was also evaluated and compared with the conventional method. To determine the potential of enzymes on pollution reduction, several parameters were measured on the tannery effluent: biochemical and chemical oxygen demand, total and suspended solids. The quality of produced leathers was also determined by organoleptic tests, tearing strength, tensile strength, shrinkage temperature and flexing endurance. SPSS Statistical Software was used for data analysis and T-test and ANOVA analysis were performed to identify the means that were statistically significant (p≤ 0.05). Microbate, micro enzyme-P, microbate elbate and microenzyme elbate enzymes were found to be the only commercial enzymes in the Kenyan market used by the tanners specifically in the bating process. Assessment of protease activity of these bating enzymes from five local tanneries showed that Microbate elbate -AHITI had 11,341.2 ± 68.05 (U/g), Microbate- Ewaso Nyiro had

21,321.33± 54.64 (U/g), Microenzyme elbate- LIK had 23,883.6 ± 97.10 (U/g), Microbate-Yetu leather had 24,137.4 ± 65.25 (U/g) and Micro enzyme P-Sagana had 24,717.6 ± 109.84 (U/g). The majority of the other evaluated variables (fat content, protein, suspended and total solids) to compare the efficiency of these enzymes in various pre-tanning techniques revealed no significant difference (p> 0.05). The commercial enzymes were only effective in the bating process only. In the case of various combinations, the utilization of a blend of keratinase and lipase enzymes (KL) was chosen for the soaking process, leading to a clean pelt with a weight gain of 68.3% and a residual fat content of 8.40%. The most effective combination for unhairing process was found to be a formulation containing keratinase, protease, and lipase enzymes (KPL), resulting in a completely unhaired pelt with a residual fat content of 6.4%. Additionally, the lipase enzyme was employed for degreasing purposes. Goatskins and cattle hides were processed using the selected formulations. In most of the physio-chemical parameters analysed on the effluent from processing leather, the enzymatic method had lower values compared to the conventional method. The enzymatic method was highly effective in pollution reduction in the unhairing process with a percentage reduction of total solids (48.89%), suspended solids (66.73%), biochemical oxygen demand (52.1%), chemical oxygen demand (80.96%) and sulphide (100%) for goatskins and total solids (74.26), suspended solids (73.52), biochemical oxygen demand (49.79%), chemical oxygen demand (80.01%) and sulphide (100%) for cattle hides. On the assessment of the organoleptic properties, both conventional and enzymatic tanned leather had a rating of more than 8. Elongation, shrinkage temperature, tearing and tensile strength of enzymatic processed goat leather was found to be 67.24 %, >100oC, 17.12 N and 30.17 mpa

respectively while that of conventional process was found to be 66.5%, >100 oC, 29.25 N and 26.7 mpa. A comparison of these properties in cattle leather also revealed the same results where enzymatic method had higher values. For enzymatic method of cattle leather the shrinkage temperature was > 100 0C, tearing strength (79.54 N), tensile strength (23.91 mpa) and elongation (68.62 %) while that of the conventional method was shrinkage temperature > 100 0C, tearing strength (81.44 N), tensile strength (16.2 mpa) and elongation (66.29 %). In addition, both cattle and goat leather processed by enzymatic and conventional methods met most of the minimum requirement for shoe uppers such as tearing strength 50 N, tensile strength 15 mpa, percentage elongation > 30%, shrinkage temperature > 100 0C and flexing endurance > 50, 000 flexes. In conclusion, use of enzymes can replace some of chemicals used in the tannery, reduce pollution and produce quality leathers that meet the requirement for making different leather products. Therefore, it was recommended that the special formulations should be adopted for use in the tanneries to significantly reduce the pollution.