There's no Net Zero without Biogas AD: ending waste, delivering the circular economy, tackling the climate crisis.

Basic Anaerobic Digestion – How Does Anaerobic Digestion Work?

Anaerobic digestion (AD) is in-truth an unhelpful name for the basic age-old natural process that produces renewable energy as heat and biogas, and natural crop fertilizer. That is basic anaerobic digestion, and how the AD (or fermentation) process works.

Some even think it is a human stomach complaint! Read on and we will dispel any misconceptions you may hold!
Updated September 2019: The original article was posted on 23 August 2012

It works by applying fermentation (very like as used in the food and drink industry) to waste and almost any generally non-woody biomass and optimising the production of the useful gas which is largely methane.

The following video is a very popular video which explains how AD works:


A common challenge faced by many is getting to grips in their mind what the Anaerobic Digestion Basics of how it works.

Anaerobic Digestion Basics – How It Works for Farms and Businesses

Here are 5 essential points about anaerobic digestion to help you succeed at understanding the anaerobic digestion basics:

1. What is Anaerobic Digestion?

Anaerobic digestion is a natural biological process that occurs when bacteria break down biodegradable material in the absence of oxygen, which creates biogas, a mixture of mainly methane and carbon dioxide with small quantities of other gases such as hydrogen sulphide.

The biogas can be burned to create heat, used to generate electricity, or used as automobile fuel.

Why should you want to do that? Well, you may need the energy to use it in your business, or at home to cook food, for example, or you may wish to make a profit from selling the energy.

That can be very important now that the price of energy tends to keep rising and can rise quite rapidly over short time periods.

With your own biogas plant you not only have a secure source of power at a known cost, but you also gain in waste management especially as a farm owner because the process converts waste to a natural fertilizer.

2. What is the Most Undervalued Benefit of Anaerobic Digestion

The by-product of anaerobic digestion which is the solid/liquid residue called digestate but in reality is a wonderful natural crop fertilizer , is most undervalued.

Some wonder whether making fertilizer from waste could spread disease. However, digestate used as a fertilizer is not a health risk, when created according to good practice. Where necessary, it is sanitized by pasteurization before being used.

As time goes on this benefit will become more significant because the cost of alternative (carbonaceous chemical sourced) fertilizer keeps rising. Not only that:

  • the fibrous portion of digestate helps improve soil quality, and reduce erosion when spread on land
  • the micro-organisms in the digestate tend to invigorate growth by becoming established in so many of our soils which have been depleted of helpful microbes by many years of chemical fertilizer application.

3. What is the Big Advantage of the Renewable Energy from Anaerobic Digestion (AD)

Energy produced from digester biogas is categorized as “green energy” or “renewable energy“.

Organic waste or mixed municipal waste when processed in anaerobic digesters (AD plants) contributes to sustainable and renewable energy targets set by regional and national governments, electrical utilities, and large businesses, right across North America and Europe.

Now that that many jurisdictions have set mandatory RPS (renewable portfolio targets), AD projects are becoming increasingly attractive as one of a portfolio of green energy sources that can contribute to the goal.

To ensure that enough AD plants are built, tax breaks are increasingly being given to AD plant owners.

This is mainly because administrations are projecting forward to the future higher compliance targets to which they have been committed and see the need to kick-start the development of the industry.

“Always available energy when its needed”

Another reason why that this is advisable is that biogas is always available energy. Unlike solar or wind energy it can be easily stored and used at night and in cold weather.

The technology produces energy, no matter what the wind speed is, day and night, to make power and provide heat.

This is something which most other alternative renewable energy production methods are very poor at achieving.

4. Producing Biogas Can Help Raise Company Reputations in the Age of the Civil Society

In a generation where carbon trading and carbon neutral are current hot buzzwords, anaerobic digestion is looking like an exciting new prospect to many stakeholders. By running an AD plant within a business to manage organic waste, it shows to society that your business is a responsible one using sustainable practices and looking to continue to trade in the long-term.

Nations like the UK are already setting targets for “Net Zero 2050” programs enshrined in national law. These programs require carbon emissions to be reduced to a net value of zero by 2050.

Other types of carbon emission reductions such as through solar and wind energy are valuable, but don’t assist agriculture or the transport sector to decarbonize and cease carbon emissions in anything like the same direct way that the AD process can.

And why may this be important?

Well, the answer is that in a number of countries the owner of an alternative energy plant which provides waste to energy (WTE) can offset their AD Plant’s carbon benefits against the need to pay taxes through RHI rebates.

Might there be another reason?

There is, and that reason lies in the fact that more and more companies see the possession of an anaerobic digestion WTE plant within the organisation as a way to be able to publicize their own good “green” credentials. Long-term institutional investors (e.g. pension funds) need the reassurance of in-house AD capability. In house AD within a business positively demonstrates that any company is sincere about decarbonizing. These institutional investors are more likely to invest in companies they can see are going to adapt and survive while being required to achieve net zero carbon emissions by 2050.

5. Other Plus Factors

Very many Anaerobic Digestion Plants use the principle to generate heat and light, fuel and solid by-products like soil-improvement fiber.

The raw materials that are fed can be food waste, waste from pharmaceutical or paper industry and animal wastes, will all produce methane and carbon dioxide.

Traces of nitrogen, carbon monoxide, hydrogen, oxygen and other gases also get produced.

Typically, the anaerobic digestion produces 50-80% of methane and 20-50% of carbon dioxide. It may be possible to separate the CO2 out and to sell that profitably as well.

Just what is probably the main plus factor with this?

Well. As energy prices rise it becomes more profitable to sell unwanted power. What other reasons would there be in favour of this?

This power could still be available even if the country in which the Anaerobic Digestion Plant exists goes to war with oilfields no longer producing, or shipping is blocked from international ocean routes.

A number of military establishments (e.g. the RAF in the UK, and the US Air-Force and Army) operate their own anaerobic digestion

Uncover some ways to understand biogas plant basics by visiting this: Click here to check this out .

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