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Monday February 27 2023

Anaerobic digestion – biology and benefits

With a degree in Biomedical Science, Birch Solutions’ senior biologist Danielle Stead works to enhance and improve the performance of anaerobic digester plants across the UK with a range of laboratory and consultancy services that keep the complex biological processes optimised. In this blog she looks at the anaerobic biological process itself and the key considerations for plant operators …

I’ve been in the anaerobic digestion industry for more than six years now but I’m also a keen farmer and this means I understand the challenges anaerobic digestion plant operators face and what support and advice they need to make sure they are getting the most out of their systems.

In my role with Birch Solutions, I run the Birch BioLab and that means I take care of all of the biological testing and analysis as we collect samples from our own plants and from the customers who we help to maximise the efficiency of their own plants.

This means we are analysing the full anaerobic digestion process, troubleshooting any issues and, most importantly, providing diagnosis and advice to make sure their plants are fulfilling their potential.

What is the biology of anaerobic digestion?

Anaerobic digestion is a process in which microorganisms or bacteria break down a range of organic matter, such as food waste, energy crops or animal manure, in an atmosphere without oxygen. 

The bacteria give off a rich mix of gases while they consume the waste, primarily methane and CO2, and this rises to the top of the digestion chamber where it can be collected. The solid remains of the waste left by the bacteria then sinks to the bottom of the digester and is then extracted and makes a valuable, nutrient-rich fertiliser to be used on fields.

This is a complex and carefully-balanced process and a number of factors must be closely-monitored to make sure the bacteria are kept in top condition and able to produce the maximum amount of gas.

Very few anaerobic digesters are alike, they come in a variety of shapes and sizes and each needs a precise mix of nutrients, this is where I come in. Maximising the potential of the process can be quite an art but we test, measure and analyse to ensure the bacteria are in perfect conditions and we can add a range of ingredients and additives to maintain the optimum environment.

In many ways, anaerobic digesters are essentially a huge stomach. It requires regular feeding and a healthy-balanced diet to maintain optimum health. Like a stomach, you also need to prepare food carefully and make sure you have a recipe the bacteria will love.

How do you improve anaerobic digestion?

Digester health is set within specific parameters and it’s crucial you maintain it within these to keep the performance optimised.

An anaerobic digester is alive and you need to keep it in top health. If you don’t, you won’t be getting the gas you need and you’ll be losing out on potential revenue or even risking a complete failure of the biological process.

It’s like an athlete, you have to keep it in top condition to ensure it performs and that means you need bespoke solutions for your digester. I work to create a range of advice and guidance for customers and run a variety of specific tests to ensure we understand fully what is going on in the digester, the state of the biological process and the performance of the bacteria.

By gathering these valuable and measurable insights, we are then able to provide expert advice and the inputs you need to maintain a happy and healthy digester that is capable of performing to its full potential and delivering a profit.

Most common mistakes with anaerobic digesters

The biggest mistake people make with anaerobic digesters is not monitoring the health. People often don’t realise just how crucial it is to closely monitor what is going on inside the digester and how much gas is being produced. Often, people think you just put the food in and then you can walk away and wait for it to produce gas.

However, the reality is that, if you’re not closely monitoring the digester, it doesn’t take long for things to go horrendously wrong. If your digester fails and the bacterial colony collapses, it can cost hundreds of thousands of pound to repopulate.

If you fail to monitor the digester, you risk a big loss in revenue. On the flip side, if your digester is performing well and is being cared for, it will make you more money.

The key is to perform regular tests and monitor all of the key processes in the digester so you can catch any issues before they become a major problem.

How do you maintain an anaerobic digester?

One of the most important maintenance measures you can take is to undertake monthly or quarterly trace element tests so you can be sure the microorganisms in the digester are getting what they need. Depending on the feedstock, digesters can often be deficient in key nutrients like iron or selenium, which are key for the bacteria, and a test will identify this issue early on.

If we know there is a problem, we can then provide advice on the supplements you need address any imbalance.

Where possible, we also like to have remote access systems for the digester so we can get a full overview of the process to monitor for any issues and we can also keep an eye on gas analysis this way, which provides key insights into the health of the digester too.

Another key part of the services we provide is analysing the feed stock for the digester. It’s important any feed stock is vetted and critiqued, especially with food waste, to ensure it has the calorific value you need to produce the gas and is also contaminant free.

Plastic can be a significant issue with food and green waste and we recommend you make sure you get a robust waste agreement that meets your specific needs and requirements. This way, you have the right to reject anything that fails to meet these standards and you aren’t then burdened with the cost of dealing with the fallout.

Testing of the feed stock is going to become increasingly important as Government incentives drive more and more anaerobic digestion plant operators to increase their use of waste. Pure feed stocks like energy crops are consistent and predictable but food waste, in particular, will have a huge range of different ingredients – and potentially a lot of contaminants – so careful analysis will be key to maintain the health of the biological process.

Anaerobic digesters are on the rise. They are becoming increasingly important as nations work to build better energy security by diversifying their power generation mix.

Biogas has a key role to play in the future but, to truly fulfil it’s potential, we need to make sure digesters are running at their maximum capacity. To do that, we need to ensure careful monitoring and regular testing is taking place.

If you have any questions about the biology of anaerobic digesters or would like to know more about the different tests and monitoring solutions, get in touch with me at dstead@birchsolutions.co.uk