ENERGY FROM WASTE
How to better digest packaged food waste
De-packaging equipment is one of the most important components of an AD plant when it comes to processing food waste, argues Shaun Flynn
other parts of Europe; in fact the levels can be up to 20% by weight of plastic, card, glass and cans. Similar food waste in Germany for example has packaging contamination of around 5-10%.
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Supermarket waste generally contains the most packaging contamination – this is due to a number of factors. Firstly, food manufacturers are competing for shelf space and there- fore making their product more attractive to the eye than competitors, this often results in higher levels of packaging. If you consider the packaging on some well known brands where there is a tin foil tray inside a plastic try inside a cel- lophane wrapper inside a card box.
Secondly, most supermarkets backhaul out-of-date food waste back to distribution centres, this involves placing the out-of-date stock into as many as three plastic bags in some cases. The reality at some waste producer sites is segregated waste streams quite often end up contaminated with items such as stones, batteries, concrete blocks and other general waste. This has been the experience at a Monsal-built AD facility in Cumbernauld, Scotland.
Controlling contamination
When the food waste is delivered to an AD plant it requires some form of mechanical treatment to remove the packag- ing and other contamination prior to the anaerobic digestion process. The de-packaging equipment is one of the most important components of an AD facility; an insufficient facility will lead to downstream issues within the digestion process.
Most food waste de-packaging systems have been devel- oped in Europe to deal with lower levels of packaging contamination, and this has led to issues at some UK AD plants. The high levels of packaging can cause de-packaging equipment to have blockages and for screens to be blinded leading to downtime of the equipment, as well as carryover of the packaging into digesters and even into the final diges- tate product which will affect the operator obtaining the PAS110 accreditation.
Despite all these issues in dealing with the UK’s contami- nated food waste, Monsal has installed its fully automated
32 Local Authority Waste & Recycling April 2011
naerobic digestion plants being built in the UK to treat food waste are all facing the same challenge when it comes to dealing with the waste. The levels of packaging are proving to be far higher than those seen in
separation technology at a 30,000 tonne AD food waste plant in Cumbernauld, Scotland within the past 12 months. The separation technology can achieve high levels of organic removal where conventional waste processing plants with manual or semi-automatic screening/sorting can only achieve low separation of organic components. The plant now deals with over 20 different waste streams from supermarkets and food processors, of which some can contain as much as 20% packaging by weight. The plant has been able to treat all waste delivered to the site, as the Monsal separation equipment has the capacity to process the most difficult of contaminated food wastes. In an ideal world food waste would be de-packaged at source and arrive at anaerobic digestion facilities with no contamination. In reality this is unlikely to ever happen, so the UK needs to adopt more advanced separation technology to deal with higher levels of contamination in food waste.
Shaun Flynn is waste business development manager at Monsal
Monsal’s separation equipment has the capacity to process difficult contaminated food waste
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