Anaerobic Digestion (AD) is not a new technology, and many will have heard of or even experienced the benefits if they are working within a water or wastewater environment. In fact, most of the hundreds of AD plants operating in the UK are managed by those in the water sector.
This is mainly due to the complex nature of operating a plant and the experience required to use the by-products and ensure sustainable and efficient operation, both safely and effectively.
Let's begin with a quick summary of Anaerobic Digestion for those with limited knowledge. It encompasses an array of processes used for industrial, agricultural, and domestic purposes to break down biodegradable waste using microorganisms in the absence of oxygen, to produce valuable by-products such as fuel and fertiliser.
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Interest in AD saw a substantial surge between 2009 and 2016 as the private sector responded to heat and electricity incentives. Investment stabilised in 2020, due to the pandemic, but commercial interest in AD plants is on the increase once again.
There are a variety of reasons for adopting the technology in specific sectors, notably the food and beverage, pharmaceutical, and agricultural sectors, where it is more likely to deliver the return on investment by helping to de-carbonise their operations, as detailed below.
A transitional technology to assist with de-carbonise operations
The key target product from the AD process is biogas (which is mostly methane). As the microorganisms digest the biomass – which includes organic matter such as manure, crop residue, food waste, municipal solid waste, paper, or wastewater – biogas is produced and the amount of organic matter left behind is reduced.
Biogas has a variety of uses within the operations of many plants, for example, as a fuel used to power machinery or industrial vehicles. In the current absence of any commercially viable electric heavy goods vehicles, this could reduce the carbon requirements of fleet operations considerably.
HGV manufacturers, such as Volvo and Scania, offer biogas-fuelled trucks and fuel retailers are building a network of biogas refuelling stations to support long distance logistics operations.
Depending on the size of the plant, excess biogas can be compressed, transported, and utilised in other areas of operations to reduce the reliance on carbon-heavy alternatives. There has been an increase in the supply of biogas back to the grid.
The process is complex as the gas needs to comply with grid standards for calorific value. The equipment for achieving this is costly and is therefore contingent upon a large excess of biomethane from the site in order to generate a return on investment.
One example of this type of operation is in cheese production, where site owners are finding that conversion of whey concentrate by AD into biomethane for use in the gas grid is commercially more attractive than its sale as a food additive or animal feed.
An interesting example of transitional decarbonisation are the whisky distilleries in Scotland, which are increasingly investing in anaerobic digestion to provide fuel for steam generation. Due to the location of many of these sites, the electricity grid infrastructure is currently incapable of supporting steam boilers of the size required. While renewable electricity may be an option for the future, AD represents the best current route towards net zero for the manufacture of this desirable product.
In addition to the biogas, the digestate produced in the AD process also has commercial benefits. It is often asked if the digestate is compost. The answer is no, but they have some similarities. Compost is produced in aerobic (with air) decomposition processes, whereas digestate is produced without air, anaerobic.
However, both make excellent organic fertiliser, which can be used as feedstock for the reactor to support plant operations or sold to local purchasers as an additional revenue stream.
Whilst AD carries many benefits in de-carboning business operations in terms of reducing reliance on fossil fuels and dramatically reducing operating costs, particularly where there is a high and consistent output of organic waste and a high demand for energy – Anaerobic Digestion will not be suitable for every business so it is important to fully understand the variables and value for your specific business.
Understanding the variables in Anaerobic Digestion
Anaerobic Digestion is a complex process with many variables that businesses must consider achieving the success required to mitigate the investment. Investing in Anaerobic Digestion is a costly undertaking, and many companies who have done so because they felt it was the right thing to do have found themselves coming unstuck. What are the variables, and what should we consider ensuring your business investment sees a sufficient return?
- 24-hour operation: The chemical and biological processes within an AD plant operate 24 hours a day and 365 days a year, and typically require qualified personnel to spend extended hours on site with cover for silent hours, weekends, and holidays. Management of health, safety and environmental risks typically require a considerable amount of above-site specialist support, particularly in the first year of operation.
- Understanding your Waste Stream: Firstly, do you know the characteristics of your waste stream, and do you have sufficient knowledge of the consistency and volume of the waste to facilitate a 24/7 operation?
- Growing Feed: Could your business grow, purchase or obtain digestible material to feed the plant in periods of reduced waste products, or if your operation doesn't supply sufficient feed? Although this approach is most common in agriculture, businesses have considered growing energy crops on unutilised land.
- Digestate: Do you have a use for or a market for the digestate?
- Biogas: Do you have the facilities and understanding to store and handle the methane with sufficient space to allow for explosive atmosphere zoning?
- Financial: The financial risk profile is different from other potential investments and funders need to have the right risk appetite to invest in such a project.
Collaboration is the key to Anaerobic Digestion success
With the complexities around the processes, the variables, and the high capital outlay, it is understandable that many businesses collaborate with a specialist Anaerobic Digestion partner for their plant to reduce some of the operational and financial risks.
An experienced partner will offer various benefits to your organisation and ascertain the true long-term value of the investment, or indeed identify if it is unlikely to deliver value versus the capital outlay.
Predominantly, an effective collaborative partner will discuss your requirements and expectations of your plant and will advise on what is achievable based on your operational output. As an expert, they can advise whether your waste stream is sufficient for the plant or if it may need to be supplemented by growing or obtaining feed from an outside source.
A successful partner will offer advice and guidance on managing your outputs – storing the biogas or finding a suitable partner to purchase the digestate. Most importantly, they will have access to highly trained and extremely proficient professionals who will ensure you can maintain the plant's consistent operations all year round, ensuring no break in processes that could significantly impact output.
If I were to advise on a suitable partner, consider how open, honest, and transparent they are. AD requires flexibility. No site is the same, and the suggested operation should be bespoke to your business. To use a cliché, one size does not fit all.
Most importantly, if you think Anaerobic Digestion may be the transitional solution to the de-carbonising of your site, with assets – such as boilers – using biogas instead of fossil fuels whilst critical infrastructure is adapted for better sustainable operation, suggest your operations management, energy or sustainability teams seek a partner's advice at the earliest possible stage to help you build a plan that works for your site and delivers against your sustainability goals.
Looking to the future, or for those already operating and AD plant, enlisting a partner who can monitor, review, improve and suggest next-stage advancements will enable you to continue to reap the financial and environmental rewards for many years to come.
