Engineering business solvents and hazardous waste reduction

Reducing solvent use in - or even eliminating it from - your metal-finishing operations will save you money on materials, waste treatment and disposal. Reusing or recycling solvents can also benefit your business.

The following changes in working methods will help you reduce solvent use:

• eliminate cleaning between processes where appropriate
• use alternative measures to keep components, materials and machinery clean - eg when preparing surfaces, use mechanical methods such as brushing, blasting and tumbling to remove dirt or grease
• avoid excessive cleaning by spinning off excess oil prior to degreasing
• install time controllers, alarms and idling cut-outs to schedule cleaning
• ask your component suppliers if they could use less protective greasing in shipping and so reduce your need to clean
• use stock rotation to ensure you use materials before they reach expiry date
• mix only sufficient paint for the job
• schedule colour coatings and products that require the same series of different coatings in batches to minimise the need to clean equipment

Opt for methods which do not involve solvents, such as:

• powder coatings or high-solid, water-based paints
• electrodeposition and autodeposition dipping - which use water-based coatings
• aqueous (water-based) cleaning systems for surface cleaning
• biocleaners - these remove oils, greases, paints and solvents from components

You should choose processes which are appropriate to the task, such as:

• Barrelling - used where only a low quality finish is needed. Items are loaded into a barrel, which is immersed in a bath of coating material and rotated to ensure adequate coverage. The barrel is then withdrawn and allowed to drain.
• Flow coating - suited to large or oddly shaped parts that are difficult or impossible to dip coat. As in dipping, excess coating material is allowed to drain and is collected for reuse.
• Electrostatic spraying and hot spraying - two techniques to help achieve high coating efficiencies.
• An appropriate paint delivery system that will minimise wastage - eg gravity cup feed systems.
• High volume low pressure spray guns - these are efficient, but spray painting can be wasteful. Spray gun and paint manufacturers offer training courses for operators.

Metal finishing solvent reuse

Reusing materials from the cleaning process reduces waste. For example, you may be able to reuse water used to cool trichloroethylene (trike) for rinsing and dry blast media for mechanical cleaning.

In waste plants, reuse can optimise performance, eg using spent alkaline cleaners to adjust the pH of acidic wastewaters prior to treatment, or recovering spent solvent and using treated cleaning water on site.

Solvent recovery machines heat waste, boil off solvent and collect the cooled vapours, which can be used to clean spray guns. You can also recover and recycle solvent in waste on site by distilling the sump contents in the degreaser.

Metal finishing solvent disposal

If further solvent recovery is not possible, you should follow the correct procedure for disposal, including:

• separating, packaging and labelling all spent solvents
• allowing only trained personnel to handle and store spent solvent
• adopting correct handling procedures
• documenting and recording movements of both spent solvent for reclaim and final waste