As the world looks for sustainable energy sources that can propel the shift away from fossil fuels, Anaerobic Digestion is increasingly gaining focus as an answer, potentially the answer.
It is a process by which plant and animal waste in the form of slurry, manure, crop residue and so on are converted by microorganisms, in the absence of air, into valuable products. Biogas is a by-product of this, consisting of 40% carbon dioxide and 60% methane.
The gas is clean and energy-efficient, can be distributed through the same network of pipes and used for the same heating and cooking purposes as regular gas. And unlike regular gas, biogas comes from renewable sources.
‘Renewable sources’ includes organic waste, which, as we know, are unlike underground gas reserves that cannot be replaced once depleted. Biogas also has its by-product, a methane-rich fertiliser, that can boost farmland yields or be sold for profit.
Finally, Anaerobic Digestion involves minimal greenhouse gas emissions. It can be used directly as a heat or power source or purified to produce biomethane, which has applications as a vehicle fuel and as part of the public natural gas grid.
Anaerobic Digestion in the UK: An overview
In 2020, the overall energy produced from Anaerobic Digestion in the UK was 1021 thousand tonnes of oil equivalent, almost the same as the 2019 production of 1015 thousand tonnes.
A significant contribution was from electricity, which accounted for 953 thousand tonnes up from 947 thousand tonnes in 2019.
The most rapid increase in energy production from AD occurred between 2009 and 2016, supported by an increased interest in alternative energy sources and important schemes like Renewables Obligation (RO).
However, the growth rate declined after March 2017 when RO was shut down. Another scheme that contributed to growth is the Renewable Heat Initiative (RHI), providing monetary incentives to support renewable heat production for non-domestic purposes.
Biomethane production flourished under the RHI scheme, with 95 registered producers by the end of 2020 producing a total of over 13470 GWh of heat from Anaerobic Digestion between 2011 and 2020.
There are two ways in which biomethane can be used. Most of it goes into the mains gas grid, which accounted for 3.96 GWh and 23% of the overall heat generated under non-domestic RHI two years ago in 2020. It has indeed proven to be a much better alternative to fossil fuels.
A much smaller quantity comes from the heat generated directly from biogas combustion, either through a biogas boiler or a combined heat and power (CHP) system. This accounted for 8% of the heat generated under non-domestic RHI in 2020.
Anaerobic Digestion in agriculture
Agriculture has also shifted to accommodate the growing need for energy produced from Anaerobic Digestion. In 2019-2020 there were 579 operational AD plants in the UK, of which 481 were farm-fed.
And of the feedstocks used for these plants during the same period, 34% (about 4.7 million tonnes) came from crops. It is important to note that most of this (about 4.2 million tonnes) came from crops grown primarily for AD.
Among the most suitable crops for feedstocks (and thus for Anaerobic Digestion) are grass, maise and oilseeds.
The same data shows that the area of maize cultivated for AD was about 75 thousand hectares in June 2020, accounting for 34% of the total maize cultivation area in 2020 and going up 12% from the cultivated area in 2019.
Research continues on the cultivation of oilseeds and their impact, as well as other possible candidates for feedstock contribution and what that would mean for agriculture in general.
As we advance, we can expect further developments as more AD plants currently under development commence operations.
Food waste and Anaerobic Digestion
Around 16 million tonnes of post-farmgate food and drink happens annually in the UK. Around half of this waste comes from households, while the rest comes from retail, hospitality, manufacturer and public sector.
The thing is, large quantities of this food are avoidable (i.e. could have been eaten at some point). However, this waste’s production, distribution, and disposal generate significant greenhouse gas emissions.
Thankfully, Anaerobic Digestion is the best solution to the food waste disposal problem and a fundamental step towards being environmentally accountable:
1. Valuable fertiliser
Digestate is the semi-solid residue left behind after the digestion process. An excellent fertiliser, it is rich in nutrients and easier for plants to process than raw manure. Plus, it is more sustainable than chemical fertilisers.
2. On-site energy generation
Biogas reduces the food producer’s dependency on fossil fuels, which results in saved costs and less air pollution. It also helps capture methane gas which would otherwise have escaped into the atmosphere and contributed to global warming.
3. Improved hygiene
Food waste can cause contamination and poor hygiene problems on business premises. Anaerobic Digestion reduces the need for waste to accumulate as even smaller quantities can be fed to the digester.
Wrapping it up
Anaerobic Digestion is considered the best option for food waste management in the UK. And given its contributions to the UK, we are not surprised that it is. But to leverage it fully, one needs to have the proper technological support.
We are currently developing compact Anaerobic Digestion systems that businesses can use to convert food waste into renewable energy. If you want to know more about our innovative technologies in detail, get in touch with us.