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Graphic element Research > Growth > Research themes > Products & processes > Clean technologies feature: Effluent-free production cleans up plating industry
Graphic element Clean technologies feature: Effluent-free production cleans up plating industry
    09-08-2002
 

Ensuring the involvement of small- and medium-sized enterprises (SMEs) in clean technology actions figures high on the Commission agenda. Methodologies applied to environmental management systems in larger companies, often reflected in government schemes and standards, are not always wholly appropriate – nor affordable – for SMEs. GROWTH therefore encourages SME participation in its funded projects. Typical is the need to treat the several hundred thousand cubic metres of liquid effluent release into the environment on a daily basis by metal plating and surface treatment plants across Europe, many of them SMEs.

Studies by the French Ministry of the Environment in 1994 suggest that liquid effluent release from such plants is responsible for 40% of the toxic heavy metal contamination in natural water. The waste also contains nitrates, adding to those from agricultural sources – and thus making it impossible in some areas to keep levels below the 50-mg/l ‘safe’ limit stipulated by the EU for drinking water. In order to protect the health of citizens and achieve the ultimate goal of sustainable development, current physico-chemical methods of effluent treatment must be replaced by cleaner and more effective technologies.

Finding affordable solutions to these contamination problems is crucial for an industry that employs more than half a million people in Europe. In addition to around 10,000 workshops of significant size (20+ employees), there are up to 20,000 more small craft shops with less than five people. The latter are often heavier polluters than their larger counterparts, but do not have the means to invest in costly counter-measures.

Adopting a pragmatic approach
The TOZELIWA project set out to tackle this problem by developing a selection of techniques to clean up waste streams as well as to limit pollution in the first place. Its consortium has therefore adopted a very pragmatic approach in the drive to eliminate liquid discharges by developing a group of techniques for cleaning workshop effluents. In addition, it aims to limit pollution at source, by maximising the recycling of useful plating bath constituents.

Techniques are being targeted at the requirements of a broad spectrum of specific surface treatment processes, and will be designed either as replacements for, or supplements to, existing water purification systems.

Launched in February 2001, the three-year initiative is exploring an array of possible techniques. The most appropriate candidates will then be selected for further development and testing in pilot trials conducted on the sites of workshops in three Member States. The results should be suitable for early application in new installations, or for longer-term adoption by existing workshops. They could equally be of interest in other water-consuming industries, such as tanning, textiles and paper.

Working in combination
Evaporation under partial pressure, and membrane techniques such as ultrafiltration, are already used to some extent to separate the constituents of treatment and rinse water baths for subsequent concentration or regeneration. TOZELIWA partners are investigating combinations of evaporation and nanofiltration or reverse osmosis as methods of eliminating degradation products prior to recycling. Electrolytic reclamation of cadmium, zinc and copper, as previously developed by co-ordinator Protection des Métaux, will also be used as a supplement to evaporation in cleaning up certain exhausted baths.

Early indications are that evaporation plus nanofiltration alone will enable rinse water to be recycled, without the added cost of subsequent deionisation by resins.

At the same time, participants are liaising with two other European Commission funded projects – Recy-chrom (also in the GROWTH programme) and Rechrome (under CRAFT ) – studying the use of electrodialysis and electro electrodialysis for the recovery of chromium. Industry experience to date indicates that the equipment lacks robustness, but electrodialysis could be useful for the separation of undesirable orthophosphite in electroless nickel baths.

Obtaining technology enhancements
Evaporation is one of the most economical options for cleaning dynamic rinses and exhausted baths. Here, the problem of impurities is less critical because regeneration by means of ion-exchange resins will provide water of suitable quality for return to the processes.

However, currently available evaporators designed to recover the constituents of treatment baths and static rinses are not suitable for such applications, which will involve on-site treatment of large volumes of liquid. A further task for the project is therefore to adapt existing devices to a wider range of effluents, including corrosive mixtures. Italian partner LED is evaluating various materials to find a suitably resistant construction.

In addition, TOZELIWA will explore an interesting improvement based on the use of textile support for ion exchange resins, which promises higher throughput and a substantial increase in efficiency.

For larger-scale operators, such as integrated automotive platers, traditional techniques still have many years ahead of them. But Jacques Halut of Protection des Métaux is confident that the project will confirm the ability of SME plating shops to run without discharging any liquid waste, without cleaning up the liquid effluents by means of a physico-chemical water-treatment plant, and by using only waste-reduction technologies that do not themselves consume chemicals.

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