Closing the loop

In the past, manufacturers have, of necessity, focused on their product. Any waste which arose from the organisation’s activities was simply considered to be a necessary by-product which had to be disposed of at the lowest cost. Manufacturers did not regard the way their product was used or the final fate of that product when it came to the end of its useful life as being their responsibility.

This can be summed up in the following diagram:

In terms of material flow, this is known as an ‘open loop’.

A more modern approach, which acknowledges the true environmental cost of the manufacturing process, is described as a ‘closed loop‘ in the activities of an organisation. Here wastes are either recovered or sold as useable by-products, and the product is re-used or recovered at the end of its useful life.

Looking at waste materials in this way is more efficient in the long term and can bring about significant savings.

Taking some steps, such as careful attention to detail when examining efficiency, may not require re-design of the product or of the process which produces it. Minimising the quantities of material taken for quality tests and buying in raw materials in quantities which fit production requirements can provide quick and easy savings.

One example of a successful attention to detail is a company which produced a filter cake from a metal cleaning process. The filter cake had a high water content and water was removed from the cake via a vacuum drum. The wet filter cake was passed over the rotating drum which was covered in fine filter cloth whilst a vacuum was applied in the centre of the drum. Water was sucked through the cloth whilst the solid material stuck to the outside of the cloth. The dried cloth was scraped from the drum by a fixed blade. However, even after this process, the cake still had a water content of over 70 percent.

The high water content of the waste made it expensive to transport, because of its weight, and difficult to dispose of, because of landfill site operators’ reluctance to import water into their sites.

In a waste minimisation survey, it was found that, due to staff shortages, the system which produced the filter cake was run intermittently. The equipment was designed to run continually, and stopping and starting the process caused a marked loss of efficiency.

Rescheduling staff rotors and giving the waste processing plant a higher priority allowed the equipment to be run continually and, therefore, more efficiently.

In the longer term, however, it was acknowledged that replacing the vacuum drum system with another technology, such as a centrifuge or a filter press, would be a more efficient option.

Segregating wastes so that recoverable and non-recoverable materials are held separately makes recovery a more viable option.

Segregation needs an initial organisational effort. It also requires regular education and information of the workforce to ensure that the right material continues to end up in the right bin. Cross contamination may result in inefficiently ‘segregated’ materials being rejected by the recyclers.