Research from China shows how mixed farm waste can cut emissions

How co pyrolysis of straw and plastic works in practice

Pyrolysis is a thermal process that heats material in the absence of oxygen. Because there is no oxygen, the material does not combust. Instead, it breaks down into three main outputs.

The first output is biochar. Biochar is a stable, carbon rich solid that can be used as a soil improver. It locks up carbon for long periods when applied correctly.

The second output is syngas. This is a mix of gases that can be burned to provide heat for the process itself. In some systems it can also generate electricity.

The third output is bio oil. This can be refined further or used as a low grade fuel depending on quality.

In the Xinjiang studies, researchers focused on co pyrolysis. This means processing two waste types together in the same unit. The wastes were cotton straw and discarded plastic mulch film.

The optimal mix tested was one part plastic to four parts straw by mass. At this ratio, the behaviour of the materials during heating complemented each other.

Plastic releases volatile compounds when heated. These compounds promoted additional char formation from the biomass. As a result, the total biochar yield was higher than from straw alone.

This interaction matters. Plastic on its own produces very little biochar under pyrolysis. Straw produces biochar, but adding plastic increases output and improves overall carbon performance.

The studies assessed both centralised plants and mobile pyrolysis units that can be moved closer to farms. Transport distances turned out to be a key factor in emissions and cost.

What the published studies actually show

The core findings come from peer reviewed papers in journals including Agricultural Ecology and Environment and Waste Management. Life cycle assessment was used to compare different waste treatment routes.

According to the Agricultural Ecology and Environment study, co pyrolysis of all recyclable plastic mulch film with cotton straw in Xinjiang could produce around 224,000 tonnes of biochar each year.

This co processed material delivered a net greenhouse gas reduction of roughly 3.43 million tonnes of carbon dioxide equivalent. This figure already accounts for emissions from collection, processing, and operation.

Importantly, the plastic film on its own delivered negligible carbon reduction when pyrolysed without biomass. The benefit came from combining the two waste streams.

Cotton straw that remained after co pyrolysis could still be processed separately. The researchers estimate this could deliver a further 9.34 million tonnes of carbon dioxide equivalent reduction.

Combined, the theoretical total emissions avoidance across the region reached 12.77 million tonnes of carbon dioxide equivalent.

For context, the same research points out that standalone pyrolysis of cotton straw in Xinjiang could already reduce emissions by around 10.1 million tonnes of carbon dioxide equivalent. Adding plastic increases total benefits and solves another waste problem.

The Waste Management paper assessed the climate impact per kilogram of mixed waste treated. Mobile pyrolysis units achieved a global warming potential of minus 1.298 kilograms of carbon dioxide equivalent per kilogram of waste.

This represented a 70.79 percent emissions reduction compared with centralised waste combustion. It was also 38.82 percent lower than centralised pyrolysis systems.

Mobile units reduced transport emissions and avoided the need for large scale waste hauling. This had a direct effect on both carbon and operating cost.

Economic performance of mobile systems

The research did not stop at emissions. It also examined financial performance.

The Waste Management analysis modelled capital cost, operating cost, and revenue from biochar and energy recovery. It compared mobile pyrolysis units with larger fixed installations.

Mobile systems showed a strong internal rate of return of approximately 31 percent under the model assumptions. The net present value was estimated at 29.21 million US dollars.

These figures depended on local factors such as labour cost, fuel prices, and biochar demand. However, the direction of travel was clear. Cutting transport distance improved both climate and cash flow.

One quoted conclusion stated that mobile pyrolysis provides a promising option for recycling plastic mulch film residue due to its competitive economics and lower carbon footprint.

Another highlighted that co pyrolysis significantly enhances both biochar production and carbon reduction compared with pyrolysis of plastic mulch film alone.

These are research outcomes rather than guaranteed returns. Even so, they underline why interest in decentralised waste treatment is growing.

Why research from Xinjiang matters to UK businesses

At first glance, cotton farming in western China may feel remote from UK commercial life. Yet the underlying issues are familiar across many sectors.

UK agriculture also uses plastic films, bale wrap, and protective coverings. Disposal is regulated, costly, and increasingly scrutinised.

Food manufacturers, retailers, and textile firms face pressure to reduce supply chain emissions. Scope 3 reporting under frameworks such as the Greenhouse Gas Protocol brings farm waste into view.

Meanwhile, energy costs remain volatile. Waste treatment options that recover heat or power are therefore gaining attention.

The Xinjiang studies highlight a principle that translates well. Mixed waste streams do not always need separate treatment routes.

Processing organic and plastic residues together can improve outcomes if the chemistry works in your favour. That can mean better carbon results and better economics.

For UK SMEs, this matters most in three areas. Compliance risk, cost control, and tender requirements.

Environmental compliance around waste handling tightens steadily. Being able to show that waste goes to a lower carbon treatment route reduces regulatory exposure.

From a cost view, landfill and incineration fees remain high. Any alternative that cuts haulage and gate fees merits attention.

Finally, many public sector and large private contracts now assess waste and carbon performance. Suppliers that understand and manage these issues have an advantage.

Carbon accounting and biochar implications

Biochar plays a central role in the reported emissions savings. It is considered a form of carbon sequestration when applied correctly.

In simple terms, carbon from plants is converted into a stable form that stays in soil for decades or longer. This prevents it returning quickly to the atmosphere.

The UK government recognises biochar as a potential greenhouse gas removal method. Ongoing work sits under the Department for Energy Security and Net Zero.

According to guidance discussed by the Department for Energy Security and Net Zero, durable removals could play a role in meeting net zero targets.

However, accounting rules are strict. Not all biochar qualifies. Feedstock, processing method, and end use all matter.

The Xinjiang studies used full life cycle assessment. They included emissions from collection, processing, and application.

UK businesses considering biochar claims must do the same. Over simplified calculations risk greenwashing accusations and commercial damage.

The Carbon Trust provides clear advice on measurement boundaries and evidence expectations. Their guidance on carbon footprinting remains a useful reference.

For many firms, the value of biochar may sit less in credits and more in practical benefits such as soil health or waste cost reduction.

Limits and cautions in applying the findings

It is important to be realistic. Results from Xinjiang cannot be copied directly into a UK business plan.

Feedstock volumes differ. Cotton straw is abundant and concentrated in that region. UK residues are more fragmented.

Regulatory conditions also differ. Planning permission, waste permits, and environmental controls are stricter and costlier in the UK.

Markets for biochar are still developing. Demand varies by region and use case.

Plastic types matter too. Mulch film is relatively uniform. UK agricultural plastics include a mix of polymers and contamination levels.

That said, the core lesson stands. Treating waste streams together can open options not available when they are handled in isolation.

For firms involved in waste management, farming, or manufacturing, these studies offer evidence worth examining rather than dismissing.

How SMEs should interpret this research

From our work with UK SMEs, three practical questions tend to follow studies like this.

First, is there a comparable waste problem in your operation or supply chain. Many firms underestimate the volume and cost of low value waste.

Second, are current disposal routes creating hidden carbon exposure. Landfill and long distance transport carry emissions that show up in reporting.

Third, could collaborative solutions work better than isolated action. Shared facilities or service contracts can change the economics.

Co pyrolysis may not be the answer in most UK cases today. However, the principle of integrated waste treatment is very relevant.

We often see clients focus narrowly on recycling rates rather than whole life impact. This research underlines why that approach can miss opportunities.

Understanding how materials interact under different treatment methods allows better commercial decisions.

For businesses selling into larger supply chains, demonstrating awareness of these options strengthens conversations with customers and auditors.

SBS Insights

At SBS, we rarely advise clients to chase experimental technology. What we do recommend is informed positioning.

Research such as this helps frame realistic discussions with waste contractors, landlords, and customers.

If you handle organic residue and plastic waste, it is worth asking providers how they treat each stream and why.

Many UK SMEs accept standard disposal routes without scrutiny. That can lock in unnecessary cost and carbon.

Where mobile or decentralised treatment options exist, the transport savings alone can matter.

From a reporting view, clear evidence of lower carbon waste treatment reduces risk under scope 3 disclosures.

It also prepares you for tenders that ask detailed questions about waste fate and emissions.

We see this most often in food processing, construction materials, and manufacturing.

Our work on SBS support for carbon reporting compliance often highlights waste as an early area for improvement.

Similarly, our guidance on sustainable procurement requirements shows how disposal choices affect supplier scores.

The key is not copying Xinjiang, but learning from it.

Sources and further reading

Readers who want to explore the evidence base can refer to the original studies and related guidance.

The Agricultural Ecology and Environment paper is accessible via the Maxapress platform and details the co pyrolysis modelling.

The Waste Management life cycle assessment was published online in July 2024 and explores mobile pyrolysis economics.

UK context on carbon accounting and removals can be found through the Carbon Trust guidance on carbon footprinting.

Policy direction on greenhouse gas removals is outlined by the Department for Energy Security and Net Zero.

For businesses assessing farm waste and plastics, the Waste and Resources Action Programme also provides practical UK focused material.

As with all emerging options, careful due diligence is essential.

Need help managing your waste-related carbon emissions?

At SBS, we help UK businesses understand and reduce their environmental footprint across all operations, including waste management. From carbon accounting to identifying lower-impact disposal routes, we provide practical support grounded in recognised standards.

Contact us to discuss how we can support your sustainability journey.