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Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.

Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.

Protectakote Pty Ltd
Cleaner Production - Wastewater Reuse in Zinc Plating

Protectakote Pty Ltd has implemented a waste water recycling system at its Geelong facility which is saving it approximately $19,600 per annum and had a very attractive payback of 0.7 years, even without full qualification of all the benefits.

Background

Protectakote Pty Ltd (Protectakote) is a small metal plating and powder coating operation located in the Geelong region of Victoria. The company employs approximately 15 people.

The main operation involves cyanide-zinc plating of a range of metal components. High volume pieces, such as brackets, are processed in a barrel plating line. Larger pieces are processed using racks, or occasionally by hand. Components are finished with either a blue or gold chromate.

Zinc die cast components are also cleaned in a separate barrel line using an acid based cleaner followed by phosphate treatment.

The Process

Effluent from the two plating lines was discharged, via floor drains, to a central pit, where the pH was adjusted to a target value of 10. The effluent was then pumped to a series of holding tanks where it was held for approximately 24 hours to allow settling of the precipitated metals. The resultant sludge phase was then drained off through a manifold system fitted with a number of filter bags. The filtrate was discharged to sewer. The sludge filled filter bags were allowed to dry prior to disposal. The clarified effluent was also discharged to sewer.

Cleaner Production Initiative

The cleaner production initiative implemented by Protectakote involves reuse of treated effluent in a number of the rinsing processes.

In Stage 1 of the project, the clarified effluent from the settling tanks was gravity fed to a recycle tank and returned to the plating process.

In Stage 2 the filter bag system was replaced with a filter press. This allows the filtrate to also be collected and returned to the process.

The recycled effluent is not used in any of the final rinse stages because of concerns about the impact on final product quality. The amount of recycle effluent generated is therefore greater than demand and the excess is discharged to sewer.

Diagram of plating lines, showing recycled water

The process flows, including the inputs of recycled water, are shown in the following diagram.

The plating line

The plating line

 

There is no evidence of any problems due to the build up of elevated levels of impurities in the recycled water.

The success of the project has encouraged Protectakote to consider a third stage, which will involve polishing the effluent quality to enable its use in the final rinse stages. This would allow about 90% reuse of treated effluent.

Advantages of the Process

The development of the recycle system has seen the mains water consumption reduce from an average of 18.1 kilolitres per day (KL) to 8.0 KL per day for comparable production levels.

Wastewater settling tanks

Wastewater settling tanks

This has resulted in a direct saving of $3,100 per annum (pa) in water costs, despite a 33 % increase in the cost of mains water. Savings from reduced effluent discharge are expected, but are still subject to negotiation with the trade waste authority.

The economic performance of the project is summarised below.

 

Cost

Savings

Equipment and Installation

$12,400

 

Reduced water consumption

 

$3,100 pa

Reduced trade waste costs

 

yet to be realised

Reduced labour for sludge management

 

$15,000 pa

Consumables (filter bags)

 

$1,500 pa

Total

$12,400

$19,600 pa

Payback Period

0.7 years

Cleaner Production Incentive

The main incentive for the cleaner production initiative was the ongoing problems in complying with the zinc limit in the Trade Waste Agreement. Protectakote was facing increasing pressure from the trade waste authority to resolve this issue.

The successful establishment of the recycle water system has resulted in the following compliance benefits:

Barriers

The main barrier to implementing this system revolved around overcoming the high zinc levels in the final effluent, which exceeded the allowable trade waste limit. As total water consumption decreased the zinc concentration increased even though the mass load was unchanged.

Investigation indicated that the major source of zinc was the rinse overflow from the zinc casting barrel cleaning line. Historically this overflow had been directed to the holding tanks and was therefore not receiving any treatment. Re-routing of this stream to the treatment pit where the zinc precipitates out upon pH adjustment has overcome the problem. Zinc concentrations in the effluent are now typically less than 2 mg/l compared to the trade waste limit of 5 mg/l.

This particular problem took a long time to identify and overcome as it was initially thought that the high zinc would be coming from the zinc electroplating line.

Further Developments

Protectakote has continued to benefit from these initiatives. In early 2001, zinc concentrations in the effluent were at 0.6mg/l, well below the regulatory limit.

Contact

Neil Hornsey
Protectakote Pty Ltd
21 Lambert Avenue
NEWTOWN VIC 3220
Ph: (03) 5221 6438
Fax: (03) 5222 2692

Date of implementation: 1995
Date of further initiatives: Ongoing
Case study prepared: October 1997 by ACCP 
Date last modified: May 2001.
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Protectakote received a grant under the Cleaner Production Partnership Program to assist with installation of the waste water recycling system.