Does commingling result in a higher recycling rate, as MRW asked in the Big Question last week? The first response is whether this is the right question
Does commingling result in a higher recycling rate, as MRW asked in the Big Question last week? The first response is whether this is the right question.
A resource-efficient system might not be one with the highest percentage recycling rate if the amount of waste disposed of is lower. Perhaps the question should be “is more always better?”
Many councils have seen reduced waste arisings from the introduction of separate food waste collections. Behavioural change has resulted in less wasted food. The amount of packaging is also reduced.
Also important is the focus on collection rather than materials reprocessed. Nothing is recycled at a MRF; the volumes recycled by the reprocessors receiving the materials and the material losses incurred are the key.
In the paper industry, the relationship between contraries ‘in’ and residual ‘out’ is normally about double. A relatively clean batch of 100 tonnes with, say, two tonnes of contraries will result in four tonnes of waste. Most MRF mixed paper loads struggle to achieve contrary rates below 2%.
For most exported paper, the processing losses will be higher unless they are re-sorted before entering the mill. US exporters are open in acknowledging that this happens to materials from there - the US is not a signatory to the Basel Convention, which precludes the practice. It is generally accepted that the quality of paper derived from US MRF operators is better than that from the UK.
Claims that commingling is cheaper are not usually based on like-for-like analysis. Where analysis does exist, the opposite is found. Pro-curements that have tested different systems normally result in lower costs for kerbside sort options.
As a practitioner who is also involved in running a MRF, I have modelled almost every solution and the results are mostly the same - kerb-side sort is optimal for price.
The Welsh Government report that backs its collection blueprint placed a number on the difference at around 25%, assuming all systems were designed for high diversion. In my experience, 25% is about right and the cost saving is more than enough to cover the cost of any system changes.
A striking feature of recycling system changes is the fact that very few have been tested in like-for-like procurements. Kerbside sort systems are the most likely to be subject to a competition between systems and are most likely to win. But commingled single stream is most unlikely to be tested against alternatives and is also most often operated by direct services working for councils.
What is optimal for kerbside sort will not be the same as for commingled systems. For example, weekly separate food waste and weekly kerbside sort do work well, but alternate weekly is optimal for commingled systems. No kerbside sort system offered less frequently than once weekly will perform well, and all systems benefit from a reduction in the frequency of refuse collections and smaller refuse bins.
Waste management design needs to be rooted in the resource efficiency debate, not the percentage debate. Lots of systems are seeing reductions in captures from materials such as newspaper, for example, because of changes in how we consume.
As long as we capture a high proportion of what has been consumed, and it is delivered at a quality that ensures reprocessing losses are minimal, why should we worry that less is being consumed and that our percentage recycling rate could be a fraction higher?
Andy Bond, Development director, GB, Bryson Recycling