Deproteination of chrome waste by washing and enzymatic hydrolysis

Abstract

Waste from the manufacture of chrome-tanned leathers (so-called shavings) can be processed (apart from alkaline or acid breakdown) by enzymatic hydrolysis employing alkaline proteases. Under mild reaction conditions, a soluble collagen hydrolyzate is formed and a solid fraction (so-called chrome cake) with high chromium content is formed after filtration. Further use of the chrome cake, e.g., tanning bath recycling, necessitates a maximum possible reduction in the protein fraction. This work performed deproteination of the chrome cake by decantation washing with water and enzymatic hydrolysis. Decantation washing of the chrome cake obtained after two-stage enzymatic hydrolysis of chrome-tanned shavings was performed six times with drinking water at laboratory temperature. A reduction in protein content occurs, as was proved by chemical analysis of chrome cakes prior to and after washing. Further deproteination of the chrome cake so washed (hence disposed of soluble part) was executed by means of additional enzymatic hydrolysis with ESPERASE and TRYPSIN. It was proved that further deproteination of chrome cake proceeded from this treatment even under very low concentrations of enzymes.