The science of recycling

An industrial engineer at Purdue University has developed a computer model to help recycling plants process raw materials from the millions of computers and other electronic items more economically.

The number of personal computers that become obsolete in the US every year is expected to rise steadily, from an estimated 41.9 million this year to 61.3 million by 2007, according to the US National Safety Council’s Environmental Health Centre.

Julie Ann Stuart, an assistant professor of industrial engineering at Purdue University, believes recycling plants will face a significant challenge trying to manage the surging flow of high-tech junk if recycling is made mandatory.

Certain electronic components contain dangerous pollutants, including mercury, lead and cadmium, making it important to recycle discarded computers so they are not simply left in landfills. Some of the electronic products received by recycling plants are still useful and can be repaired, while others are cannibalised for parts. The remaining junk is processed and, in some instances, reprocessed to extract and purify the metal, plastic and glass it contains.

This reprocessing involves repeating various steps such as grinding, shredding and separating materials. However, at a certain point it becomes too expensive to continue purifying the bulk materials.

There hasn’t until now been no analytical tool to help recycling plants reprocess the bulk materials more economically. Stuart has created just such a tool. Her ‘discrete reprocessing model’ can be used to determine the threshold at which it becomes unprofitable to continue purifying bulk materials.

‘Our model allows us to find the pricing threshold for reprocessing,’ said Stuart. ‘So, if the price of copper fluctuates, it helps us find how low the value could be to justify reprocessing.’

‘We are the first to look at the reprocessing decision,’ said Stuart, noting that recyclers have relied more on instinct than analytical tools. ‘There has been no formal way to decide questions like: When do you process something more than once? What level of purity do you want?’

US law does not commonly require recycling electronic hardware, although the state of Massachusetts has enacted America’s first ban on dumping computer screens, television sets and other glass picture tubes at landfills.

However, similar policies could become more common in the future, drastically increasing the flow of electronic products to recycling plants and causing their inventories to rise sharply.

Complicating matters is the fact that most recycling centres are small-scale operations and would be ill equipped to handle surging demands on service.

‘A contributing factor to the closing of some recycling companies has been excessive material handling and inventory,’ concluded Stuart.