Study on the treatment of tannery solid wastes of Bangladesh for their potential utilisation

Abstract

The tannery solid waste namely chrome shaving dust has been characterized and subjected to biochemical treatment using proteolytic enzyme and mild alkalis. In this study full chrome (chrome content 3.42 % and low chrome (chrome content 1.37 %) from cow wet blue leather have been used as raw materials for collagen protein extraction. MgO and CaO have been used for mild alkaline medium where trypsin, pepsin and proteinase K have been used as proteolytic enzymes. Several methods have been developed for the hydrolysis of chrome shaving dust after optimization of pH, types of alkalis and their dosages, variation of enzymes and their dosages and the amalgamation of enzymes. A three step hydrolysis process has been developed in all hydrolysis methods for the maximum recovery of collagen hydrolysate. The collagen hydrolysate has been extracted through vacuum filtration and preserved at 4 ºC in an incubator. The prepared collagen hydrolysates by different methods have been analyzed for various physical and chemical parameters. MgO has been found to be better than CaO during hydrolysis since all the samples treated with MgO has given more protein yield. Trypsin enzyme has been found to be suitable for collagen hydrolysis compared to pepsin and proeinase K but the amalgamation of trypsin with proteinase K has given highest protein yield. The quality of collagen hydrolysate produced from the treatment of MgO is also better than that of CaO. Low chrome shaving dust has given more protein yield than that of full chrome shaving dust with the similar treatment. After complete hydrolysis, the chrome cake has been treated with sulfuric acid to separate the chromium present in chrome cake. The percentage of chrome recovery was 94.32% and 96.36% in samples 4 and 5 respectively. All the samples have shown the characteristics protein peak during FTIR analysis. The collagen hydrolysates have been characterized by amide A and B bands, associated with NH stretching modes. The characteristics amide I, II and III bands have proved that the collagen was in hydrolyzed form. All collagen hydrolysates have been analyzed for the determination of chromium by atomic absorption spectrophotometer and trace amount of chromium (<4.5 ppm) was found in most of the samples while some samples contained below detection level of chromium (0.1 ppm). Ca and Mg content of collagen hydrolysate have also been determined by atomic absorption spectrophotometer and 1165 and 1033 ppm was found respectively. The protein content of the samples have been determined by BUCHI Kjeldhal instrument and found more protein yield in trypsin and MgO treated samples, amalgamated trypsin with proteinase K and MgO treated samples and low chrome shaving dust samples with similar treatment. This biochemical method of producing collagen hydrolysate is environmentally friendly since there was no toxic chemical used in this method. Therefore, this approach of “waste to resource or wealth” will not only release the burden of disposal of tannery solid wastes but also produce valuable protein products which can be utilized in poultry feed, fertilizer and leather processing.