Carlile Bros. Pty Ltd is a joint venture partner in the Bowron lambskin crust tannery located at Bendigo, in regional Victoria. The tannery processes green and salted lamb skins to produce crust tanned skins, which are further processed in tanneries in New South Wales and New Zealand.
The green or salt preserved skins are processed in wooden vats where the skins are soaked, washed, fleshed, scoured and tanned with a synthetic tanning agents. Each vat has a capacity of 50 skins. After draining, the skins are then dried, ready for further processing.
Cleaner Production Initiative
The main cleaner production initiatives involved were:
- the installation of a centrifuge to spin dry skins between the washing and tanning stages;
- installation of a system to collect and recycle tanning liquors; and
- evaluation of specific chemicals used in the tanning process.
An essential prerequisite to identifying these cleaner production initiatives was the undertaking of a rigorous mass balance and analysis program over every process operation in the tannery. This was essential to obtaining valuable and precise data on the various sources of effluent, and allowed the identification of a number of cleaner production options.
Key findings from the mass balance analysis were:
- tanning liquors were not being fully recycled and up to 50 per cent of some tanning chemicals were being discharged to the effluent;
- there was excessive water use on the baffling and fleshing machines, which could be reduced by installation of automatic controls;
- a high concentration of boron in the final effluent could be reduced by the selection of alternative chemicals; and
- the effluent quality was sensitive to the concentration of tanning solution.
One of the main reasons for the relatively low rate of tanning liquor recycling was that additional water was entering tanning solutions. As a result, excess tanning solution had to be dumped from the tanning baths at the end of each cycle. The minimisation of this water input was given a high priority.
One of the more significant inputs of water into the tanning solutions was water carryover from the skin washing process. In the existing process the skins were left to drip dry between the washing and tanning stages.
This proved to be an ineffective method of removing excess water from the skins and in fact was adding approximately 5 litres of water per skin to the tanning solution.The installation of a centrifuge to spin dry the skins after washing has reduced the carryover volume by 30 per cent.
After tanning, the skins are left to air dry in a specified area. All excess tanning solution that drains from the skins is collected and returned to the tanning baths.