How to generate energy from raw material
NRM
Environment
Europe is aiming to become the first climate-neutral continent by 2050. To do this, ambitious measures are being taken to help businesses and people seamlessly transition to sustainable practices. These include the generation and use of renewable energy. Renewable energy represented nearly 20% of energy consumed in 2019 in Europe, helping to reduce carbon emissions and dependency on fossil fuels.
Anaerobic digestion (AD) plants use feedstock or raw material to produce biogas, which can be converted into energy. This is undertaken by microorganisms in the feedstock under anaerobic conditions. Not only is this a greener way of generating electricity, but it also provides a new sustainable way to handle waste instead of sending it to landfill. Another benefit is that the engine, which feeds the biogas, generates heat as well as electricity. The heat, which is needed to keep the biology inside the feedstock at a warm 37°C, is pumped back into the plant itself, saving on costs on extra heat for the cyclical process.
Read on to find out more about what feedstock is, why it needs to be tested, and the process of testing material for its suitability as feedstock for energy generation.
What is feedstock and why does it need to be tested?
Feedstock is the material used in AD. Suitable feedstock for a digester includes any biodegradable animal matter or food and drink waste, processing residues, agricultural residues, crops, and sewage sludge. Producers get paid for the amount of biogas that they generate, and so available feedstocks are assessed for their biogas potential. They can then use the results to make informed commercial decisions to ultimately maximise their revenue.
The yield of biogas will vary according to volatile matter content and its concentrations of protein, carbohydrates, and fats. If there is an issue that kills the biology inside the feedstock, the producer will have to start from scratch—a costly process leading to wastage and loss of profit. So, it is important that the contamination levels of any feedstocks are measured to check nothing will have a detrimental effect to the microorganisms, inhibiting the generation of biogas.
The testing process
There are three steps for testing the suitability of feedstock for AD: the feedstock itself; the health of the digester; and the quality of digestate (the end product). Each step is very important, as they directly affect how much profit can be generated from the feedstock.
- The feedstock
The feedstock must be tested to ensure that it does not contain any contaminants that will inhibit the AD process. This will determine the potential biogas generated from the feedstock. There are three different service options:
- Theoretical biogas, gas yield, and methane concentration, which can be produced by a feedstock calculated from the levels of protein, oil, and total solids in the sample
- Bullet Biomethane Potential, which uses NIR to predict gas yield of a feedstock against a library of substrates
- Biogas Potential (BGP) and Biomethane Potential (BMP), which simulates digestion of substrate in reactors under mesophilic conditions, and volumes of gas produced over time are recorded.
- Health of the digester
To generate the most methane and biogas, we need to maintain a healthy digester. This is like feeding yourself a balanced diet: to stay healthy, you require enough carbohydrates for energy, protein for muscle building, and vegetables for micronutrients and water content. It is the same with feedstock. Microorganisms live inside the AD plant, and so we need to feed them a balanced diet (i.e. the feedstock) for effective energy generation.
So, while the feedstock is processing or digesting, the health of the digestion process is monitored. The Volatile Fatty Acids (VFAs) that are produced are tested, as well as the FOS/TAC ratio. These indicate the stability of the digester, and ensures it is running correctly. Additives can then be used to optimise the process and ultimately produce more biogas and a higher quality digestate. It is extremely important to produce VFA and FOS/TAC analysis results quickly, as if found to be unhealthy, the process is costly to correct.
- Quality of the digestate
In addition to biogas, another material is produced. The spent digester material is called digestate. This has fertiliser qualities and is a benefit to agriculture—a huge interest to NRM as the UK’s largest independent provider of agronomic and environmental waste analysis for land-based industries.
How we determine the quality of the digestate depends on what the farmer wants from it. This could be: high levels of ammoniacal nitrogen, which is the leachable nitrogen that is readily available to the crops to improve crop yield; any organic potential to generate digestible materials; or high levels of trace metals, such as magnesium, which help the crops thrive.
Waste plants following the AD protocol look to produce a certified product, not a waste stream. To do this, they must pass certain operational and chemical analysis procedures: namely, the PAS110.
The PAS110 accreditation provides a set of quality criteria that need to be achieved to demonstrate a digestate producer is generating safe and beneficial digestate. If there are no contaminants found in the digestate (such as metals, pathogens, or plastics) and it has a low residual biogas potential, it can be used safely as soil improver. Valuable levels of NPK provide a fertiliser quality demanded by farmers. Other non-PAS110 tests analyse energy crop or agriculture sludges (onsite farm waste) for its suitability as manure and slurry feedstock.
NRM: environmental testing services to the renewables sector
As one of only two laboratories in the UK approved by REAL to test to PAS110 regulations, NRM offers a year-round service for producers looking to test the suitability of feedstock for the AD process. For more information on our services, read our AD brochure, or to speak to a member of our team request a callback.
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