Engineering business solvents and hazardous waste reduction

You can save money and recover materials by treating and reusing metal-finishing effluents (liquid waste).

Polluted effluents can damage the bacterial beds at sewage treatment works, contaminate sewage sludges and lead to pollution of watercourses. You must ensure that your metal-finishing effluents are dealt with appropriately to comply with the conditions of your trade effluent consent and to prevent water pollution incidents.

You can treat your effluents on site to a safe level, or pay a waste-disposal business to remove them.

You could use the following recovery methods:

• Extending drip time after processing allows solutions to drain and be returned to the process bath. Doubling the drip time from 15 seconds to 30 seconds can increase the amount of electrolyte returned to the plating solution by up to 50 per cent.
• Ion exchange can be used for the treatment of cyanide plating baths, nickel, copper, tin and zinc, and aluminium anodising rinse waters. Ion exchange can recover metals and clean water for recycling.
• Electrochemical recovery allows metal to be recovered in powder or solid form. The metal can then be melted down, reused as a soluble anode or regenerated as a concentrated process solution. Electrochemical recovery is a cost-effective method for recovering precious metals from rinsewater and exhausted plating baths. It also reduces the amount of metal sludge requiring disposal.
• An evaporation unit with a pump and evaporative panels of up to 1,000 square metres can recover more than 96 per cent of drag-out chemicals.
• Reverse osmosis uses a semi-permeable membrane to separate water from dissolved salts. This generates water and a concentrated liquid consisting of metals and salts. The liquid can be drawn off for further treatment or returned to the process baths.
• Ultrafiltration can be used to filter out molecules from a contaminated wastewater stream. It is useful for a final cleaning of water before recycling back to the process.