« BackNews: What Is Anaerobic Digestion?

What Is Anaerobic Digestion?

When it comes to the circular economy, anaerobic digestion (AD) has an awful lot to offer, turning waste organic material into green energy and natural biofertilisers.

It works by breaking down organic matter such as manure in the absence of oxygen, with biogas generated as a byproduct by the bacteria involved in the process. This biogas is predominantly made of methane, which is the main component of natural gas, with the non-methane components removed so the resulting methane can be used for energy.

Not all organic matter is created equal, however, and some breaks down a lot more easily than others. The amount of biogas produced depends on how digestible this matter is, with codigestion taking place when AD is used to break down a variety of different types of waste in one digester.

Waste that can be used in codigestion with manure includes the likes of fats, oil and grease, energy crops, food byproducts, waste from cafe or restaurant food and crop residues.

Coproducts that arise as a result of the AD process include digested solids that can be used for the likes of livestock bedding or biodegradable planting pots and soil amendments. It’s also possible that effluent solids can be used in building materials such as particle and deck boards. Liquid effluent from digesters can be used as fertilisers.

The resulting biogas created during AD is typically used to generate electricity, but it can also be used in boilers or heaters instead of propane. Thermal energy is also a byproduct of the AD process and this can be recovered to heat nearby buildings or the digesters themselves.

There are all sorts of benefits associated with AD, particularly where dealing with food waste is concerned.

A recent report from the Waste and Resources Action Programme (WRAP), reported on by the Guardian, revealed that although total food waste in the UK has been reduced by the evailent of seven per cent per person in the last three years, more must still be done to reduce the 4.5 million tonnes of food waste created annually.

The majority of food waste ends up in landfill, where it’s left to rot and emit methane - but by sending it off to an AD plant, it can be used to generate clean energy and biofertilisers for farmland, helping to drive down greenhouse gas emissions significantly.

The AD process can also help reduce reliance on fossil fuels, thereby reducing carbon emissions even further. The methane-rich biogas produced is used to produce heat and electricity, so no methane is released into the atmosphere.

There is also the opportunity to drive down energy costs because biogas can be used to generate electricity and provide fuel for vehicles - so it’s a win-win for all.

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