Development of recycling techniques and zero discharge through the implementation of ionic membrane in effluents from the tanning sector.
Industrial wastewater can contain high concentration of salts leading to high conductivity. Water reuse is only possible under certain conditions and it is dependent on the industrial water requirements of any given process. The tanning sector is a suitable sector for water reuse provided the correct conditions are met (the sector consume 50 m3 of water per leather ton and 40% of leather weight in salt).
The project consists in tanning leather with reused water of different quality coming from: ground water (GW), biological treatment (BT), Reverse osmosis (RO) and electrodialysis (ED). From a quality (physiochemical point of view), all currents can be used in a tannery.
On the other hand other electric techniques such as bipolar electrodialysis (BED) can also be used in order to obtain 2 outputs - one basic, the other acidic. The acidic effluent can be used in pickling operation within the tannery, while the basic effluent is suitable for soaking and liming operations.
Both ED and BED have similar electricity and membrane replacement costs to RO, but both avoid costs associated with chemical consumption and sludge management resulting in an overall reduction in running costs when compared to RO.
Membranes, chemicals, electricity supply, analytic equipment
Cost avoided: 1,50 - 2,75 €/cubic meter of industrial water
Evidence of success
The test show that water recycling using these techniques is possible, although the reuse is only possible in specific conditions, depending on the industrial requirements.
With regards to the leather propierties, from a physicochemical point of view (Tear strength, tensile strenght, elongation at break and grain burst) results were satifactory for all samples treated that had been produced using recycled water, highlighting that recycled water can be used in the tanning sector.
From a aesthetic point of view, the leather after tanning, looks different when is treated with "fresh" water or with "recycled" water although
the following preferences were established:
Drawbacks should be avoided including a final rinse of deionised water.
Potential for learning or transfer
The project has proved that is possible to use the waste water as a raw material in the tanning sector. In areas of water scarcity waste water treatment plants are a good source to obtain water for industry requirements.
Further investigation is needed in order to reach the standard of aesthetics required for leather. The investigation can be also adressed to identify ions more suitable for tanning.