Cleaner processing: a sulphide—free approach for depilation of skins

Abstract

The conventional unhairing process in leather making utilises large amount of lime and sodium sulphide which is hazardous and poses serious waste disposal concerns. Under acidic conditions, sodium sulphide liberates significant quantities of hydrogen sulphide which causes frequent fatal accidents. Further, the conventional unhairing process involves destruction of the hair leading to increased levels of biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS) and total suspended solids (TSS) in the effluent. A safe approach is needed to overcome such environmental and health problems through an eco-benign process. The present study deals with a clean technology in which the keratinous body is detached from the dermis using enzymes produced from Bacillus crolab MTCC 5468 by solid state fermentation (SSF) as an alternative to noxious chemicals. Complete unhairing of skin could be achieved with an enzyme concentration of 1.2 % (w/w). The bio-chemical parameters of the spent liquor of the enzymatic process were environmentally favourable when compared with conventional method. The study indicates that the enzymatic unhairing is a safe process which could be used effectively in leather processing to alleviate pollution and health problems.

Evaluation of the Bacillus cereus Strain 1-p Protease for the Unhairing of Goatskins during Leather Production

“…Although various factors affecting the enzymatic unhairing have been investigated and are well established, the effect of the enzyme dilution has not been extensively studied and documented. Nonetheless, as an increase in dilu-tion generally lowers the concentration of enzyme molecules present in a specific volume, these findings correspond to those reported from the use of a protease extract from Bacillus crolab MTCC 5468 to unhair goatskins where the unhairing activity and efficiency increased with the increase in enzyme concentration, thus a complete unhairing was achieved faster [7].…”

“…This can also be attributed to the enhanced absorption of tanning chemicals following the adequate splitting of collagen fibres. Similar observations on the appearance and fullness of the enzymeunhaired leather have previously been reported [7]. The 'fibres splitting' effect of the enzyme processing also influences the uptake of colour and dye material, thus giving the leather the observed deeper and more uniform colour [14].…”

“…The enzyme-unhaired leather was of good quality characterized by uniform colour, smooth grain, appreciable flexibility and a good appearance without any scud. This general observation has been attributed to the enhanced uptake of processing chemicals following the sufficient opening up of the fibre matrix as documented by previous research on enzymatic unhairing that reported similar results [7,12,13,18,47]. The general appearance of the conventionally and enzymatically treated goatskin leathers had a clear and clean grain without any foreign materials, but the enzyme-unhaired leathers were rated higher for the smooth feel, the gloss of the grain surface, a good handle, colour evenness and the general fullness of the leather structure.…”

“…This stage is thus associated with major environmental pollution. In the conventional unhairing technique, hides and skins are exposed to an extreme chemical treatment using lime and sodium sulphide that breakdown the hair and epidermal structures to remove them from the hide/skin [7]. As a result, this processing stage releases volumes of solid wastes in the form of broken epidermal structures and hair [8].…”

“…Enzymes have been used in food, textile, detergents and soaps, bioactive peptides, agricultural, cosmetic, beverage, pharmaceutical and leather industries, among others [10]. Microbial enzymes have been mostly employed in tanneries for rehydration, hair removal, bating and removal of fats [7]. The application of enzymes for unhairing eliminates the use of the toxic sodium sulphide and can facilitate recovery of quality hair and fats which significantly lowers the pollution load in the effluent [10].…”