Water Treatment in Aerospace

Surface finishing in the aerospace industry is typified by the need to process low volume numbers of high value parts through a wide range of treatment processes including:-

	Electroless nickel		Sulphuric acid anodising
	Cadmium plating		Phosphating
	Chromic acid anodising		Chromating

Many of these process chemistries are difficult to treat and contain extremely

hazardous compounds, some of which may not even be licensed for discharge.

Due to the number of process stations, most are followed by a single rinse stage and the requirement for high quality finishing means that large volumes of water are often used for rinsing. The result is a high volume of rinse water being discharged to drain with little addition of process waste.

Demineralised water is often favoured for rinsing post finishing processes and guarantees a high quality finish free of stains. It can have other benefits as well, including ensuring silica free water for rinse post anodising seal.

Increasing water costs, reduction in discharge consent levels and in some cases the need to prevent discharge at all has led many aerospace companies to consider water recovery within their finishing areas.

First it is necessary to consider the mass balance of the various contaminants so that a suitable plant can be adequately sized. Often there is a need to segregate waste streams that may be hazardous or difficult to treat if combined.

Ion exchange in the form of a demineraliser is most often used for recirculation of the rinse water. Many contaminants present in the rinse water are fouling to an ion exchange resin and may be difficult to remove through regeneration. EWS (UK) Ltd demineralisers for water recovery are designed to accommodate for these compounds, offering excellent inter-regeneration capacity and the facility for additional maintenance associated with this type of application.

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