Bags of potential

With food waste collections by local authorities on the increase, what type of bin liner should they be encouraging their residents to use? Deputy Editor Andrea Height from Material Recycling Week finds out

Paper sack or compostable bio-plastic sack? Which material is best suited to collecting food waste from households and which is easiest for organics recyclers to handle once the material has been collected?

According to paper sack supplier Ecosack, paper sacks are increasing in popularity, and the company’s sales figures have been on the up during the past year. Sales manager Peter Crawley says this is because the company is taking a more proactive approach to promoting the benefits that paper offers.

“Paper sends the right environmental message. Our paper sacks are a natural product and, unlike some bio-plastics, do not rely on valuable food crops. They are fully compostable and biodegradable, add structure to the compost and use less energy during the
manufacturing process,” he says. “And the sacks are made from waste: the shavings from trees used in the timber industry.”

Crawley adds that because paper breathes, it will dry out if it gets wet and this helps to prevent liquid collecting in the bags, reduces the volume collected in the bags and helps smells to dissipate. “And paper doesn’t get confused with plastic, whereas bio-plastics do get confused with ordinary plastic bags,” he adds.

But Crawley does admit that “cornstarch did steal a march on us”, and several of the high-profile food waste trials conducted in the UK involved using these cornstarch or bio-plastic caddy liners.

One council that has opted to use paper rather than bio-plastic sacks is the London Borough of Bexley, which is using them for its mixed garden and kitchen waste collections. Waste and recycling adviser Terry Wallis explains why it chose paper: “It is really down to the crews so that, when they look into the bin, it is easier for them to check that it is just paper. They Bags of potential With food waste collections by local authorities on the increase, what type of bin liner should they be encouraging their residents to use? Andrea Height finds out haven’t got time to check whether a bag is plastic or compostable plastic. If we stick to paper only, it resolves these issues.” In addition, Wallis says that using paper sacks is easier for the general public to understand.

The downside to paper sacks is that they are more bulky to store and transport than their bio-plastic counterparts, which come in rolls. This is a point picked up by Novamont, which manufactures several grades of its bio-plastic raw material, Mater-Bi. This is sold to companies such as BioBag, which convert it into caddy liners.

Popularity of bio-plastic sacks

Novamont UK co-ordinator Tony Breton says that bio-plastic sacks are lighter than paper, so involve less carbon emissions when transporting and distributing. He says the reason that bio-plastic sacks are popular for food waste collections “is due to reasons already outlined by WRAP: they keep everything clean and hygienic, and collection crews like them because they enclose the wetter food stuffs and don’t stick to the caddies when they empty them. And because the bags tie up, it is easy for crews to carry several at once before going back to the vehicle”.

The main reason Breton says that local authorities and composters like bio-plastic sacks is because of the higher capture rates they achieve, because people are more likely to put wet food scrapings into a lined caddy than a non-lined caddy. He says that when caddy liners are used for separate food waste collections, it is easier for collection crews to check the kerbside caddies and confirm that bio-plastic liners have been used. But with mixed food and garden waste collections,he concedes that such liners are not as popular, because it becomes more difficult to identify whether a liner is compostable or just plastic if it has been put into a wheelie bin along with loose garden waste.

Organics recycler Agrivert’s sales and marketing director Harry Waters says that both paper and cornstarch sacks are not a problem for composters “as long as you get good composting conditions”. He says that if conditions are too dry, card will not deteriorate while if temperatures are not hot enough, cornstarch will not deteriorate. Agrivert has run several trials which have enabled it to identified clearly the conditions under which these materials will and will not compost.

“The difficulty is that if you say to someone ‘put your material in biodegradable bags’, you will find the amount of non-biodegradable material will increase significantly as well,” he adds. The other potential downside of using bio-plastic sacks for green waste, he adds, is that they can increase litter contamination around the composting site: when they
go through shredders, fragments can get caught by the wind and blow around.

Waters adds that, for a reprocessor, the best way to collect is by using a bin, but he acknowledges that this is not always possible.

On the other hand, Greenview Environmental chief executive John Jardine says: “My feeling is that paper is better. We take compostable sacks and we will continue to do so. But from a purely practical standpoint, from what we have seen of it, paper is easier to deal with.”

That said, he is confident that improvements will be made in the bio-plastics sector as the market evolves. His concern is that the public will use normal plastic carrier bags if they run out of bio-plastic liners, and says that wrapping food waste in newspaper is best.

Where bio-plastic sacks seem to pose more of a problem at the processing stage is within anaerobic digestion (AD) treatment, particularly wet systems, rather than in-vessel composting (IVC). BiogenGreenfinch designs, constructs and operates anaerobic digestors. In a letter to Ecosack last month, BiogenGreenfinch research scientist Becky Arnold outlined the company’s position on biodegradable/ compostable packaging in AD.

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