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Challenging move to bio-power

With EU targets in place to generate more energy from renewable sources, a Government commitment to a “huge increase” in energy from waste (EfW) via anaerobic digestion (AD) and ongoing targets to cut the amount of waste sent to landfill, will using more bioplastic packaging be part of the solution or will it just serve to confuse matters?

According to the National Non Food Crops Centre (NNFCC), the national centre for renewable materials and technologies in the UK, there is significant potential to boost the energy output from AD plants if bioplastic food packaging is treated in the AD waste stream.

Speaking at an event organised by the Westminster Food & Nutrition Forum this summer, NNFCC chief executive Jeremy Tomkinson explained that, as a result of retailers and food manufacturers trying to reduce the amount of packaging they generate by lightweighting it, more complex packaging formats, made up of different layers of different types of plastic polymers, are increasingly being put on the market.

These are typically found in applications such as fresh produce packaging, soup pouches and so on. But while these mean that less material is used overall, such packaging formats are difficult to recycle because of the mix of materials used.

Energy targets

Tomkinson argues that using biodegradable plastic for these applications could contribute to renewable energy targets, if the biomethane generated by the bioplastics is captured in the AD process. He says this could also eliminate the need to separate out the hard-to-recycle packaging – usually film packaging and food trays – that is otherwise a contaminant to AD processes. 

The NNFCC has done some research with Southampton University that tested biodegradable films in the AD process and measured the biomethane generated from the film. This is expected to be published by the end of the year.

“For every 1% of film that we can change to biodegradable and put through AD, we could generate 5GWh of energy. Given what we know, and the energy scenarios going forward, this combined thrust has got to be a positive way forward”

NNFCC polymers and materials manager John Williams, who has been working on the project, explains that the work stemmed from the fact that front-end de-packaging systems on AD plants would never be able to capture and remove every piece of plastic that finds its way into a food waste collection system.

“Some of the lightweight flexible packaging is also difficult to separate and find an economic value for, and is not recycled at the moment,” he says. “And if you do have de-packaging units, can they take out the rigids, the cans and so on as well as the food-contaminated materials? You will have some contamination in AD if you are not careful, so the idea was to look at the bioplastics side of things.”

The first phase of the project looked at the bioplastic film materials already on the market, used for packaging organic ranges and salads, as well as caddy liners. Williams says the results have been “really encouraging”.

The organisation calculates that more than of 270 million cubic metres of biogas a year could be generated if all film packaging was treated in this way. In a “more realistic scenario” of only 10% EU market penetration, Tomkinson says this is enough to generate 54GWh of power a year.

“For every 1% of film that we can change to biodegradable and put through AD, we could generate 5GWh of energy. Given what we know, and the energy scenarios going forward, this combined thrust has got to be a positive way forward,” he says.

While Tomkinson acknowledges that the UK has an established system in place for PET bottle recycling, he argues that there is an opportunity to convert the post-consumer plastic films and food trays not currently recycled into renewable bioplastics, in order to benefit from this energy output at the end of life. He puts forward the case for such a move.

“One, we are using a renewable resource, not mining a petrochemical. Two, it is providing us with additional shelf life and extended properties in the material. And three, it is now starting to roll out into a range of products.”

Williams points out that while there is still a lot of work to do, and bioplastics are a relatively small part of the market, the bioplastics sector is growing fastest in the packaging sector.

Tomkinson says there are also technical benefits to putting bioplastics into AD systems: “Foodstuffs contain, by virtue, a lot of protein. Proteins are very good for digestate, but they are not that good for energy generation. We don’t want nitrogen‐containing gases like ammonia being generated in AD plants.

“What bioplastics are, predominantly, is carbohydrates with a high carbon to nitrogen ratio. So these actually complement one another. We want the nitrogen to remain in the digestate they use back on the field as a fertiliser, and these bioplastics to raise the carbon to nitrogen ratio that we need in digesters to maximise energetic output.”

In the NNFCC’s research, most biodegradable films achieved maximum gas yields in around 14 days, which Tomkinson says demonstrates compatibility in AD plants. So why should we do this?

“We have huge targets for 2020 in the Renewable Energy Directive to meet for biofuel, biopower, bioelectricity and bioheat. AD is a fantastic means in which we can dispose of food waste and generate this energy,” he explains.

Based on data from WRAP, the NNFCC calculates that for every seven million tonnes of food waste generated by households, about a quarter of a million tonnes is packaging, not an insignificant amount. It estimates that this household packaging waste can generate around 89 million cubic metres of biogas.

“The energy contained in that is about 0.93TWh, which is about 2% of the heat target alone,” Tomkinson says.  (See table below)

Biomethane potential of UK food waste and primary food packaging

 Tonnes a yearVolatile solids %Biomethane cu mGas energy contentAs proportion of 49 TWh RES heat target %As proportion of 117 TWh RES electricity %

Correct waste streams

Of course, all these calculations about the amount of energy such packaging could generate via AD is subject to the public putting their bioplastics in the correct waste stream, and indentifying which packaging materials are bioplastics in the first place. That is something that Industry Council for Packaging and the Environment (Incpen) director Jane Bickerstaffe thinks is unlikely to happen.

“How would you explain that to the public? It might work for back-of-store retail operations, where you are informing a smaller number of people, but I can’t see how that information [that bioplastics should go in the AD waste stream] would be got over to the public.

“The messaging would be horrendous. You would be saying the bag for your peas goes in this bin and the bag for your carrots in this other one. I just can’t see a future in it.”

She adds that retailers experienced this type of confusion when introducing biodegradable bags on certain ranges, with consumers confused over whether materials were home compostable or compostable only in a commercial facility.

“The best thing to do is not say anything to the public about it, so that it can go to EfW plants via the municipal waste stream,” she says. “AD is interesting but it is only suitable for things that biodegrade, while EfW is suitable for everything.”

Williams admits that educating the public about such a move “is a concern”, but adds that labelling systems, such as the seedling logo used to depict compostable materials, are now getting more widely known. “If you only went for the 100% option, you would never do anything,” he adds.

Calorific values

He agrees that plastics going into EfW via the residual waste stream would offer a high calorific value, but adds that burning petro-plastics would also generate greenhouse gases, whereas with bioplastics you will get the energy without the emissions.

Recoup, the UK organisation dedicated to supporting plastics recycling, raises concerns about such a move but does agree that post-consumer films are best kept out of the recycling stream. 

Director Stuart Foster says: “We do strongly advocate that this fraction is not collected through existing kerbside and bring recyclables collection systems because it can cause contamination of other recyclables and serious processing issues. At the same time, we need to adhere to the general rule that no plastic items should be transferred into a bioplastic alternative where current or planned recycling options are in place.

“The worst-case scenario would be a combination of plastic film and bioplastic film arising from post-consumer sources. That would render the mix completely unrecyclable by plastic reprocessors and, I suspect, unrecoverable through AD.”

But AD operator BiogenGreenfinch is more positive about the idea. Technology director Michael Chesshire says the concept of moving food packaging such as trays and films into biodegradable formats “must be the way to go”. While he admits that the early days of such a shift would be challenging, he says there would be long-term benefits in such a move.

He admits there have been a number of issues for AD operators around accepting biodegradable packaging, but these are starting to be overcome. “If there is a big move to biodegradable packaging, we could develop the right technology,” he says.



The view from Novamont

Novamont manufactures several grades of its bioplastic raw material Mater-Bi, used to package foodstuffs such as Sainsbury’s So Organic range. UK co-ordinator Tony Breton feels that NNFCC chief executive Jeremy Tomkinson raises some salient points.

“Flexible film, in particular flexible film used for packaging fresh produce, is often contaminated with residues of its contents or even unopened – as found in some of the recent WRAP studies on food waste. So for it to be recycled traditionally, it will need to be separated from other plastics and washed,” he says.

“And because of the in life performance requirements, these packaging products are typically made up of several layers of different materials and plastics which essentially render the final pack unrecyclable, even if there was no contamination from the original contents.

“However, while Tomkinson is correct in saying the de-packaging step could be avoided, for the time being there is still a need for pre- and/or post-treatment of materials going into or coming out of an AD process to ensure the right quality of feedstock and end product. Also, depending on the original packaging, such as steel cans or glass, a de-packaging step is needed. In dry batch systems, virtually no pre-treatment is needed – just post-refining.

“During the past 20 years, Novamont has, and continues to, invest heavily in research to develop biodegradable products with specific mechanical and technical properties to their traditional counterparts, and many of these products can now be found in the marketplace,” Breton continues.

“We also work closely with a number of AD and composting plants across the EU. This work is ongoing, and the benefits of using Mater-Bi products to collect organic waste are being realised at these plants through increased feedstocks and substantially reduced contaminants in the final product.

“Our internal research to date would agree in general with the statements made by Tomkinson in terms of gas yield.”

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