Treating wastewater from non-destructive testing

Liquid penetrant testing is a non-destructive technique that is widely used in aircraft manufacturing and maintenance. However, it produces brightly coloured wastewater which cannot be discharged until the distinctive colour has been stripped. Desotec's mobile activated carbon filtration solutions are used by several customers in the European aerospace industry to treat such wastewater, allowing it to be discharged or even reused.

The problem

At our client’s aircraft factory in Poland, parts are soaked in a fluorescent penetrant liquid, then placed under a UV light to highlight any microcracks. After their safety inspection, these parts must be washed of the penetrant liquid before they can be assembled, repaired or discarded.

Wastewater from the cleaning process contains organic pollutants, which turn it a fluorescent yellow colour. It is not harmful, but it looks too alarming to be discharged.

Therefore, the wastewateris stored in tanks ready for treatment.

Prior to Desotec's involvement, the contractor which carries out non-destructive testing for this client was also supplying activated carbon filters to treat the wastewater. However, the set-up was unable to remove all the colour, and the filters themselves were beginning to smell.

So the client contacted Desotec to ask if we could supply a different type of carbon for its existing filters.

The solution

We determined that the fault lay not so much in the type of carbon, but in the inefficient design of the filtration system.

The existing filters were unsuited to the flowrate, and had become overgrown with biofilm. This was preventing them from working satisfactorily, and causing the odour.

We took samples of wastewater and carried out lab tests using our own filters. This resulted in completely clear water, even when examined under UV light.

A pilot test at the client’s site confirmed our solution was viable. In fact, the client realised the water was now clear enough to be reused for cleaning rather than discharged, thus closing the loop and boosting sustainability.

We were contracted to supply four MOBICON 1000 or 2000 filters, suitable for the low flow rate of a few cubic metres per hour.

The results

Desotec's system has now been in place at this site for several years, and the client remains satisfied with the results.

The filters are continuing to produce clear wastewater, and there is no formation of biofilm or associated smell.

Other aerospace companies have also taken note of the set-up when visiting the factory, including the client’s own customers, who have been impressed by the clear wastewater during audits. Some have now contacted Desotec to replicate the solution at their own sites, which is simple for us to do.

A further key advantage of Desotec's model is that no carbon is handled at the client’s site, keeping conditions dust-free and pristine – something that is essential in a highly controlled aircraft manufacturing environment. Desotec's filters are mobile, so when the carbon becomes saturated, we simply transport the old closed unit away and exchange it for a new one in a quick process that does not require any downtime.

All waste carbon is then taken to our facilities in Belgium for analysis, safe handling, and treatment. In this client’s case, the waste carbon can be reactivated, thus improving sustainability and reducing costs.

In Desotec's furnaces, all molecules that were adsorbed onto the carbon at our customers’ sites are desorbed and fully destroyed in accordance with national and European legislation. The entire installation and its emissions are under continuous online monitoring, guaranteeing that only harmless water vapour exits the chimney.