Ditch the cars, install solar panels, and recycle packaging—businesses across the UK are looking to improve their impact on the environment and society. However, one area that can be forgotten is food waste. Anaerobic digestion is a technology that composts food waste while also producing renewable energy and avoiding carbon emissions. It can significantly reduce greenhouse gas emissions and manage organic waste.
With environmental, social, and governance (ESG) reporting high on the agenda, exploring ways to reduce food waste is now more important than ever.
Let’s explore how the anaerobic digestion process can provide significant environmental and economic benefits for your business.
What is Anaerobic Digestion?
Anaerobic digestion is the process where microorganisms convert organic waste like plant and animal materials into useful products in the absence of air. Picture a bustling microscopic city where microorganisms are hard at work. They break down biodegradable material without oxygen, going through four stages:
- Hydrolysis
- Acidogenesis
- Acetogenesis
- Methanogenesis
These stages produce biogas, liquid digestate, and solid digestate.
This process isn’t just confined to sophisticated anaerobic digestion facilities; it naturally occurs in swamps and landfills. However, commercial anaerobic digestion captures the biogas and digestate to convert it into renewable energy and recycled products. We’ll explore this later in the blog.
How does Anaerobic Digestion Work?
Anaerobic simply means in the absence of oxygen. Anaerobic digestion converts organic matter, from food waste to slurry and manure, crops and crop residues, into renewable energy. Complex bacterial cultures digest the waste in a sealed, oxygen-free tank called an aerobic digester.
Let’s look at the steps of the anaerobic digestion process:
Step 1: Organic matter arrives. Biodegradable organic materials, such as solid animal manure, biowaste and food waste, are delivered to an anaerobic digestion facility.
Step 2: Anaerobic digester. Any contaminants are removed, and the organic matter is heated to 70°C before being fed into the anaerobic digester.
Step 3: Biogas production. Bacteria break down the organic material to produce biogas and a liquid fertiliser called digestate.
Step 4: Nutrient-rich fertiliser. The digestate is used on farmland as a soil improver, removing the need for petrochemical fertilisers.
Step 5: Renewable energy. Biogas is either upgraded into renewable natural gas and injected into the natural gas distribution system or burnt to create renewable electricity for the National Grid.
Anaerobic digestion could play a significant part in helping your business move towards net zero and meet ESG goals.
The Commercial Importance of Anaerobic Digestion
Waste and Resources Action Programme (WRAP) recorded in a 2020 report that the UK produces around 9.5 million tonnes of food waste, every year, much of which goes to landfill. Farms in the UK generate around 100 million tonnes of manure and slurry, which filters into water supplies, causing significant pollution. Yet, a tonne of organic material filtered through an aerobic digester could produce 300-kilowatt hours of energy.
Let’s explore how anaerobic digestion could have serious economic benefits for your business by producing renewable energy and reducing carbon emissions.
The Scale and Scope of Commercial Anaerobic Digestion
The UK has seen a significant rise in the adoption of anaerobic digestion technology, reflecting its growing impact on communities and industries. In April 2021, over 600 operational anaerobic digestion plants (excluding water treatment facilities) were listed in the UK. The agricultural, commercial, and industrial sectors are the primary industries generating clean, renewable energy from organic waste.
Large Scale Industries Generate Heat and Power
Below are examples of well-known companies embracing anaerobic digestion in the UK.
Coco-Cola
In the UK, Coca-Cola has used anaerobic digestion to treat liquid waste since 1989. The anaerobic digestion facility is used to reduce the strength of wastewater by 90 per cent and produce biogas to be collected and used in biogas boilers on site.
Poundbury
Rainbarrow Farm in Poundbury is the home of the UK’s first biomethane-to-grid anaerobic digestion plant. The anaerobic digestion facility produces enough renewable gas to generate heat for 7,500 houses mid-winter and 100,000 houses mid-summer. The digestate is sold as a soil improver, blooming amazing!
Carbon Dioxide (CO2) is one of the other gases produced during anaerobic digestion. The food and drink industry uses high-quality, renewably sourced CO2.
AstraZeneca
AstraZeneca has worked with partners to establish the UK’s first unsubsidised industrial-scale supply of biomethane gas. Once the anaerobic digestion facility is operational in 2025, the partnership will reduce emissions by an estimated 20,000 tonnes of CO2 equivalent and supply 100-gigawatt hours per year.
The Technology Powering Commercial Anaerobic Digestion
It can be confusing at first to understand the various technologies available for anaerobic digesters. At Waste Mission, we can explain this in more detail, and our responsive team of experts can become an extension of your business, taking care of your food waste so you can stay focused on your core operations.
At the big picture level, the digester can be wet or dry, mesophilic or thermophilic, and single or multistage.
The type of anaerobic digester will depend on the heating system being used.
- The Mesophilic system operates at the optimum temperature for bacteria, around 35°C. Functioning at a lower heat, this digester is more stable and less expensive, but the process is slower.
- The Thermophilic system – operates around 55°C, providing a faster reaction. This digester is more expensive, and the microorganisms are more sensitive to change.
There are two main types of anaerobic digesters on the UK market: single-stage and multi-stage. Single-stage digesters are cheaper and easier to maintain, as all the processes are carried out in the same place. Multi-stage digesters are more complicated to operate but can provide optimal conditions for each stage of the process.
A New Generation of Biogas Technology
Wet anaerobic digestion is the more traditional form of anaerobic digester technology. The process is time-consuming, and the high water consumption can make it difficult for regions where water is scarce.
Engineering progress has recently allowed solid-state anaerobic digestion to adapt to dry materials. This means materials like municipal solid, food and garden waste can now be processed through anaerobic digestion.
Solid-state anaerobic digestion can handle dry, stackable biomass with a high percentage of solids. The facility consists of gas-tight chambers called fermenter boxes that are loaded and unloaded with solid biomass. Liquid digestate produced during the digestion is recirculated and sprinkled on the dry biomass to ensure continuity and stability.
Co-Digestion Techniques
Co-digestion techniques are developing to enhance biogas production. For example, the co-digestion of food waste and poultry litter in combination with goat manure has been shown to produce a higher yield of biogas than other substrate combinations.
Combined Heat and Power Systems
Combined heat and power systems are employed in anaerobic digestion facilities to maximise energy utilisation efficiency. These units contribute to reducing dependency on national grid electrical power, leading to lower electrical bills for the site. Combined heat and power units are powered by methane generated from the anaerobic digestion process.
Imagine a farm-based anaerobic digestion system fuelling combined heat and power units or farm equipment; it’s a beautiful synergy of waste management and energy production.
Environmental and Economic Benefits of Biogas
Once captured, biogas can be utilised into valuable products, bringing incredible economic benefits to businesses and reducing detrimental environmental effects. But first, it has to be purified.
Biogas typically comprises 60 per cent methane and 40 per cent CO2, along with traces of other contaminants. The purification process involves removing impurities, including hydrogen sulfide, siloxanes, and moisture, through technologies such as particle filtration and liquid/gas coalescence methods.
Purifying biogas is an essential process. Left untreated, it can cause serious maintenance issues, such as corrosion, abrasion, and degradation of biogas-related machinery and equipment, leading to unexpected repairs and energy production inefficiencies.
But once treated, biogas can be used to produce an incredible array of products:
Vehicle fuel from biogas.
Biogas can be converted into biomethane that meets the quality standards for vehicle fuels. Using biogas as a valuable fuel can significantly reduce CO2 emissions compared to conventional fossil fuels. In the UK, biomethane fuel stations supply a significant portion of vehicles, and by 2025, biomethane could fuel approximately 10% of the UK’s high-mileage heavy goods vehicles (HGV) fleet.
One example to explore is McCulla Transport. They reduce carbon emissions by fuelling their CNG trucks with biomethane from leftover food at their biogas plant.
Renewable natural gas from biogas.
Methane produced during anaerobic digestion can be upgraded to biomethane. Once upgraded, biomethane can be injected into the natural gas distribution system to serve as an energy source. In the UK, initiatives like the Non-Domestic Renewable Heat Incentive and the Green Gas Support Scheme support biomethane production and injection into the natural gas grid.
Biogas into biohydrogen.
Biogas is converted into biohydrogen, useful in fuel cells for clean energy production. In the iron and steel industry, biohydrogen is used to achieve harmful emissions by taking more CO2 out of the atmosphere than adding to it compared to traditional fossil-fuel-intense steelmaking routes.
Bioplastics from biogas.
Biogas can also be processed to produce bioplastics, replacing petroleum-derived plastics. A 2023 study found that bioplastics are fully biodegradable within two years and degrade between 50 per cent and 70 per cent in the soil within the first 120 days.
The Benefits of Digestate
It’s incredible to note that every tonne of food waste recycled through anaerobic digestion rather than taken to landfill prevents up to 1 tonne of CO2 from entering the atmosphere. However, valuable byproducts of anaerobic digestion can also be a source of cost-saving and potential revenue. Digestate is one of them.
Digestate is the leftover material after the digestion process. Digestate is considered waste if left untreated and must meet waste management controls. However, if treated, digestate can be used as a bio-fertiliser.
Digestate can be created into three varieties:
- Solid digestate. A more fibrous matter, providing moisture retention and organic content for soils.
- Liquid digestate. A sludge-like matter provides nutrients for plant growth and protects soil from erosion.
- Whole digestate. Combining the liquid and solid digestate creates a sludge form, which is good for a wide range of agricultural uses.
Summary
At Waste Mission, we believe it’s our responsibility to help build a future that’s a few shades greener. We love that anaerobic digestion has incredible environmental and economic benefits for a wide range of industries. We have already seen many customers divert 100% of their organic waste from landfills and reap financial benefits.
By adopting anaerobic digestion technologies into your business, you could:
- Reduce waste tonnage and landfill costs
- Reduce operational costs within your business
- Increase environmental awareness across your business
- Create a renewable form of energy
- Invest in environmentally friendly processes
- Boost your environmental credentials
Our team excel at making complex waste streams simple from a single point of contact. Contact our team today to find out how your company can simply and efficiently adopt anaerobic digestion technologies into your business.
