WASTE WATER ELIMINATION
Parr Paints solved its waste water problem by optimising cleaning processes and reusing the collected wash water in the next batch of product. The purchase cost ($800) of an off the shelf high pressure wash unit was more than offset by the $3000 pa savings in waste disposal and improved labour efficiency.
Parr Paints Pty. Ltd. (Parr Paints) is a small family owned business that manufactures paints and textile coatings (latex adhesive). The company was started in 1971 and currently employs eight people.
Water based house paint accounts for about 80% of production, while solvent based paint accounts for the remaining 20%. The main water based paint is white acrylic suitable for tinting at the point of retail sale. Coloured acrylic paints (browns, reds and blacks) are also produced.
Waste water is generated from the clean out of the new blending tanks after each batch. The main types of waste water are:
- Wash water from white acrylic paint manufacture which is reused as make up water in the next production run;
- waste water from coloured acrylics which is also stored for reuse in the next production run. However because of the lower demand for these colours it is usually six months or so between production runs, by which time the wash water has "gone off" due to degradation and bacterial activity. It therefore requires disposal;
- Wash water from the latex adhesive which was collected for disposal; and
- wash solvent from solvent based paints is collected for reuse.
The wash water from coloured acrylic paints and the latex was stored in 205 litre drums and spare vats pending pick up by a waste disposal company.
Cleaning of the latex blending tank was done using a low (mains) pressure hose and generated approximately 200 litres of wash water for each 800 litre batch. Approximately 800 litres of latex wash water was generated per month.
The company had made attempts to re-use the wash water in the next batch, but found that the ammonia and latex in the wash water caused the thickener to form lumps and impacted on product quality
ADD SET VOLUME WATER
ADD FINAL VOLUME
pH ADJUSTMENT WITH AMMONIA
Paint Pigment Ball Mill
Cleaner Production Initiative
The cleaner production initiative implemented by Parr Paints appears very simple in hindsight - changing the tank washing process to a high pressure system which has reduced wash water generation by 75%. More importantly this has allowed reuse of the latex wash water as make up water for the next latex batch, thereby eliminating a complete waste stream.
Parr Paints had previously focused on trying to treat the latex wash water so that it could be reused. However the wash water always "went off" before it was treated to a degree that would allow reuse.
An examination of the latex tank cleaning operation indicated that the use of a nozzle on a mains pressure hose was relatively ineffective. Because of this the operator also had to scrape down latex adhering to the tank walls.
Parr Paints decided to optimise the cleaning process first and then look at the process chemistry. Optimising the cleaning process by changing to an "off the shelf" low volume/high pressure cleaning unit reduced cleaning water requirements from 200 litres to approximately 40-50 litres. It was then found that this wash water could be totally reused in the next batch without any adverse impacts on product quality.
Advantages of The Process
The main advantage has been the elimination of the major source of waste water and the associated cost savings. The high pressure system has also decreased the time required for cleaning.
The direct cost savings are summarised in the following table:
Cost of High Pressure Unit
Savings in Waste Disposal
Cleaner Production Incentive
There were a number of incentives for Parr Paints to address its waste water problem;
- as the production of latex adhesive increased the company could see that the associated problems of waste water handling and disposal, as well as raw water costs, were going to increase
- storage of all the waste water created compliance problems and Parr Paints had previously been instructed by the EPA to reduce on-site waste storage and to ensure all waste was stored in appropriately bundled areas.
Latex Blending Tank
The most significant barrier was concerns about the latex chemistry and the effect that the reuse of wash water would have on product quality. The thickener used in the latex is activated by ammonia and it was found that the residual ammonia in the wash water would form lumps when initial attempts were made to reuse it. Although the product was filtered to remove these lumps there was an adverse impact on product quality.
After consideration of the blending process it was realised that there was an opportunity to reduce the volume of wash water and use all of this as top up water for the next batch. As the top up water was added after the thickener the problem of lumping was overcome.
Involving the operator in the identification of the opportunity to reduce wash water was a key success factor.
Mr Howard Parr
Parr Paints Pty. Ltd.
38 Strong Avenue
Thomastown Vic 3074
Ph: 03-9460 7166
Fax: 03-9462 2636
Case Study Prepared By:
ACCP June 1998
Parr Paints received assistance under the Victorian Environment Protection Authority’s Cleaner Production Partnership Program for the reuse of latex wash water.