VHSP Pty Ltd undertakes chrome tanning of cattle hides. Approximately 85 per cent of hides are received as green hides from abattoirs, with the remainder being salt-preserved hides. The VHSP tanning plant was built in the late 1980s using the Sirolime process developed by CSIRO.
The hides are ‘fleshed’ to remove adhering fat and flesh, which would otherwise compromise the tanning process. These fleshings are sent to a rendering plant to produce tallow for soap manufacture. The hides are tanned in large rotating drums. The tanned hides, known as wet-blue hides, are then passed through rollers (sammyer machine) to remove excess tanning liquor before packing for export.
Tanning is undertaken to stabilise a protein in the skin (collagen) and hence stop the skin from degrading. The tanning operation traditionally produces effluent which is high in total dissolved solids (TDS), suspended solids (SS) and biochemical oxygen demand (BOD), plus salt, chrome, nitrogen, ammonia and sulphur compounds.
Conventional wet-blue tanning involves four operations which are undertaken in large rotating drums.
These stages are:
- hair removal, by dissolving in a solution of sulphide and lime at pH 12-12.5;
- washing and deliming to pH 9 using ammonium salts and carbon dioxide;
- enzyme treatment and pickling (formic and sulphuric acid); and
- tanning with a chrome salt to produce wet-blue hides.