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Wednesday August 2 2023

What are the disadvantages of biogas?

We’ve written previously about the advantages of biogas but, it’s also important to consider if there are any disadvantages.

Biogas is growing in popularity as it’s an environmentally friendly source of fuel, heat and power and can also help to tackle waste. Biogas does have a wide range of advantages but, in this blog, we’ll look at what are the limitations of biogas, if there are any issues with biogas and what are the key concerns around biogas.

The reality is that the advantages easily outweigh any disadvantages of biogas but this will explore the key challenges surrounding the production of biogas.

Producing biogas feedstock

One of the key concerns for biogas production is maintaining the supply of organic waste that is needed for the anaerobic digestion process.

The material placed into the digestion chamber to produce biogas is a hot topic. The organic waste can vary from pure energy crops and processed sewage through to food, industrial and animal waste.

As biogas production is a valuable way of tackling waste, there is considerable pressure to cut the use of energy crops, which also take valuable space away from food crops.

However, using waste products can present challenges. For one, anaerobic digester operators need to consistent and contaminant-free feed stock so the microorganisms at the heart of biogas production are kept in top health. Maintaining this quality can be difficult with something a varied as food waste.

Secondly, with a growing demand for food waste and an increasing number of anaerobic digestion plants, competition for quality feedstock is rising and some have concerns about maintaining a regular supply to meet the demands for energy.

Cost of building a biogas plant

Biogas plants can vary significantly in size and range from simple on farm digesters that primarily use animal waste through to large-scale commercial plants that consume a variety of feedstocks and are producing 1,000m3 to 2,000m3 of biogas per hour.

Run properly, the return on investment on these plants can be significant and there are Government schemes designed to reward and incentivise biogas producers further. However, the initial cost of building a biogas plant  can be significant.

In terms of the cost of a biogas plant, a small plant treating slurries and manure that includes a simple digester and a combined heat and power (CHP) unit could cost around £750,000 to £1m. A larger commercial plant capable of producing 1,000m3 of biogas per hour will cost considerably more and will require an investment of around £15m.

While these are big numbers, the return on biogas is even greater. Properly run, biogas operators can potentially see a return on their investment in as little as five years and, under the current Government Green Gas Scheme, anaerobic digestion plants are expected to operate for  15 years.

Effect of temperature on biogas production

The biological process inside an anaerobic digester is complex and carefully balanced. The microorganisms that consume the waste and produce biogas need to kept in perfect conditions to maximise their potential.

One of the key factors in creating an ideal environment for bacteria and maximising biogas production is temperature. The majority of anaerobic digesters need to operate between 35oC and 40 oC and ideally need to be around 37 oC.

This bacteria can be very sensitive to temperature changes and thermal shocks will have an impact on the amount of biogas being produced.

This means biogas producers need to think about being able to heat or even cool their digesters. For many, heating isn’t an issue as they will have CHP units attached and this can be used to heat the digestate. For cooling, many look to heat exchangers and pump the slurry through them to help regulate temperatures.

With record temperatures becoming more and more frequent, it is another key consideration for anaerobic digestion plant operators.

How do you transport biogas?

As we’ve said, biogas production is growing in popularity but, as these plants are a great way to tackle organic waste while producing valuable fertilisers, a large number of them are situated on farms or in rural locations.

While this brings benefits to rural communities, it can present a challenge in getting the resulting biogas to the end consumer.

If the biogas is being compressed into the national gas network, it will require infrastructure to connect to the grid. If the biogas is being upgraded to biomethane, so it can be used as a fuel, it will then have to be transported in insulated tanker trucks and this will mean an adequate road network is connected to the anaerobic digestion plant and upgrading unit.

Biomethane as an alternative fuel is also becoming increasingly attractive so the ability to transport it quickly and effectively needs to be considered.

Biogas and methane emissions

Biogas is primarily made up of methane and this is one of the most dangerous greenhouse gases. If there is leak of methane from an anaerobic digester, this potent gas can contribute to climate change and could pose a potential hazard to people working around the plant.

However, this risk is minimal and the biogas production process makes huge contributions to the cutting of greenhouse gas emissions.

If organic waste was left to decompose in landfill or manure lagoons, it will continue to produce methane and this will all escape into the atmosphere. If the organic waste is fed into a digester, all of the methane is captured and when the resulting biogas is burned, all of the harmful methane is converted into CO2.

Another key benefit of diverting animal manure and food waste from landfill is that it helps to protect the environment and water sources from harmful pollutants that can run-off from the decomposing material.

In the long-term, biogas could even become a viable alternative to mined natural gas as a fuel for heating, cooking and powering our homes and may even be a valuable alternative fuel to diesel and petrol, further strengthening its environmental credentials.

Overall, biogas offers a wealth of advantages and little in the way of disadvantages. When the performance of an anaerobic digester is optimised it can divert tonnes of waste from landfill, will capture and convert thousands of cubic metres of harmful methane gas, it can provide a genuine and valuable alternative source of energy and, most importantly, offers a solid return on investment.

If you have any questions about the advantages of biogas or want to discuss any concerns you have around the disadvantages of biogas production, speak to one of the Birch Solutions team at enquiries@birchsolutions.co.uk