Engineering business solvents and hazardous waste reduction

Metal-finishing effluents are hazardous wastes and costly to dispose of. If you produce metal-finishing effluents you must comply with hazardous waste requirements. Therefore, it will save you money to reduce your use of chemicals, the amount of cleaning you need to do during processing and the volume of effluent.

Good purchasing and stock control are vital. Buying too much stock, or failing to rotate it, may result in waste. You should review your purchases and consider buying stock on a just-in-time basis. You should label containers clearly with the date of purchase and use-by date. Keep an inventory and make sure that old solutions are used before newer ones.

You should also train your staff about the need to reduce waste and to follow your procedures for achieving this. You could link bonus payments with water, chemical and waste disposal costs.

Keep detailed records of chemical and water use, the type, source and amount of aqueous effluent and solid waste, and of treatment, storage and disposal of effluents.

You should reduce drag-out from plating and other treatment baths. It has costly implications, including contamination of subsequent process baths, chemical waste, increased water needed to achieve adequate dilution ratios for rinsing, higher effluent treatment plant costs and additional filter cake and sludge generation.

You can reduce drag-out through:

• slower extraction of a workpiece from the solution
• adjusting the positioning of a workpiece to prevent the solution getting trapped in hollows
• extending drip time

Install drip boards between tanks to capture the run-off as workpieces move between rinse stages and dips. The boards should be tilted so run-off drains back into the tank. If you install an additional drip tank, one batch can drip while another is moved, before the solution is returned to the process bath. Drainage is more efficient when the layers of workpieces are staggered rather than hanging directly above one another.

You should also aim to use only the minimum amount of chemicals for cleaning. Use accurate thermostats, pH probes and measuring devices. Consider installing automatic dosing from larger to smaller containers, as this is safer and more accurate.

Use the minimum amount of water for cleaning as it creates effluent when mixed with chemicals. Pre-programmable water delivery systems ensure that only a specified volume of water is delivered at any one time. Install water meters and flow restrictors on process lines. Manually operated trigger hoses reduce waste by automatically cutting off the water once hand pressure on the trigger is released.

Spray and fog rinsing above the process bath are effective rinsing techniques and water efficient. Countercurrent rinsing uses a series of connected rinsing baths. Water from the bath with the lowest concentration of chemicals flows back into the previous rinse bath and then through the other baths in sequence. The volume of water used is significantly less than in traditional flow rinsing. This method is more effective as concentrations of drag-out chemicals in the rinse baths are kept low.