The potential for the Anaerobic Digestion Process (AD) and the benefits of Biogas are massively undervalued
Discover mankind's sustainable renewable energy future here!
ANAEROBIC DIGESTION AND BIOGAS: SIMPLE FACT!
“Anaerobic digestion turns waste into wealth, transforming what we discard into energy and resources, and in doing so, it strikes at the heart of the sustainability challenge: closing the loop in the consumption cycle.”
Who are we?
This website is an independent venture, by guys who are simply fascinated by the subject (read our About Us).
We want to help more people see our vision for a vibrant low-carbon future, and become part of the AD technology movement.
You are very welcome to spend time on this website, and we hope that you will get involved by commenting, and maybe even joining our campaign for better AD awareness, as well.
Facts About the AD Process
for Techies
1. There are four key biological/ chemical reaction stages of anaerobic digestion:
- Hydrolysis
- Acidogenesis
- Acetogenesis
- Methanogenesis
2. Almost any organic matter can be digested anaerobically. Not all will produce enough biogas to be viable though.
3. Anaerobic digestion occurs in nature at all temperatures but below 10 degrees centigrade the rate of biogas production is so slow that running a biogas process is usually considered not viable, for any form of the biogas generation system.
4. There are two temperature ranges over which the many microorganisms that produce biogas work most efficiently. These are known as the:
Temperature ranges, with the optimum temperature usually considered to be at the top of the range.
5. The digester process is truly ancient:
- Fermentation for the production of alcohol was known to the Ancient Egyptians and is recorded as far back as 2,000 BC.
- The methane-producing stage of anaerobic digestion is performed by a type of microorganism known as archaea. It's not a bacteria. In fact, it comes from a distinctly different branch of the phylogenetic tree of life to bacteria.
Benefits of Anaerobic Digestion
a) Environmental Benefits
- Reduces carbon emissions and can contribute to national renewable energy targets. In some circumstances, it can be “carbon negative” removing more greenhouse gas than it creates
- Only biogas (with some carbon dioxide) is taken out, so valuable nutrients can be recycled back into the soil
- Digestate may also be used as natural fertiliser, as livestock bedding, as a feedstock for other biofuel production or for innovative fibre-based building-materials
- AD creates skilled ‘green’ jobs and contributes to growth in the local economy
- When used in conjunction with segregated municipal food waste collection, it reduces waste sent to landfill
- A digester sanitizes waste output providing a reduced public health hazard/ reduces pollution risk.
b) Benefits to Those That Own and Operate an Anaerobic Digestion Facility
- Landfill taxation costs are reduced, and transportation fuel costs can be less
- Owning an AD plant lends authority to the owner organisation’s green credentials
- Possible government incentive payments available
- Secures a reliable long-term waste disposal route for the plant owners' own waste
- Potential for truly profitable sales of digester outputs
- Make and use your own power and heat your home with CHP!
- Energy Cost Security: No more business-destroying energy cost price increases.
- Fertiliser Cost Security: Agricultural operators are protected against wild fluctuations in mineral fertiliser costs.
Is Anaerobic Digestion a Type of Composting?
Anaerobic digestion is a biological process similar to composting but without air. As in composting, micro-organisms break down organic matter into simpler smaller compounds and reduce its bulk or “mass”.
However, unlike composting, which overall always consumes energy, AD can be used to create energy. That is because it produces a gas known as biogas, just over half of which is methane. Everyone that lives in a developed nation and has cooked anything on a kitchen stove, using gas piped in from the street, has used methane and knows how cleanly it burns, and how wonderfully hot the flame is, because “natural gas” is pure methane.
In addition to biogas, the process also produces “digestate” a slurry or paste, which comprises a solid fibrous residue, and a liquid portion.
UK AD Sector is Healthy and Growing in 2024!
By April 2023, Europe had 1,322 biomethane-producing facilities. The EBA reported that 299 new plants were added between 2021 and 2023; approximately a 30% increase over the previous count in 2021.
According to the IEA Net Zero Emissions by 2050 Scenario, biogas output is expected to triple by 2030. They estimate that annual global growth in biogas output wis on the path to accelerate from 19% in 2017-2022 to 32% in 2023-2028.
According to estimates from the National Non-Food Crops Centre (NNFCC), as of 11th April 2022, the UK had 660 operational facilities, an increase from the previous year. This increase included 13 new biomethane to grid (BtG) and 8 new combined heat and power (CHP) plants. Additionally, there were 39 BtG projects planned or consented with a total cumulative biomethane capacity of 17,000 Nm³/hr.
Farm waste feedstocks, including manure, slurry, crops, and crop waste, were used to power most of them.
Food waste was the most common single feedstock, with the amount processed increasing by 20.4% from 4.08 million tonnes in April 2020 to 4.92 million tonnes in April 2021.
The Anaerobic Digestion Process Renaissance
Until the early 2000s, there had been a long period of cheap fossil-fuel sourced power. While power was so cheap before the pandemic, the anaerobic digestion process was largely ignored in the west. China and India and some other nations realized its value, especially to subsistence farmers and developed early versions. Many were the still popular buried, fixed dome, household and small community biogas digester systems which they invented. Ever larger numbers of these renewable energy plants are now being built and operated, so that in 2024 literally millions of people are benefiting from the “biogas renaissance”.
In the western nations during the first half of the 20th century, AD had been popular among the water boards, and municipal corporations for the safe disposal of sewage sludge, but almost all of those digesters had, by then, been replaced by incinerators.
Energy was so cheap that even those running those incinerator plants failed to truly realize that they were using energy, to destroy energy!
That was an expensive waste, which is now being put right as globally large numbers of sewage sludge incinerators are being shut-down and replaced with biogas plants. The latest of these can be so efficient in making power that they can produce electricity to run the entire wastewater treatment works (sewage works) solely using the sludge from the works as their bio-fuel!
These are just two examples of many, of the way that the anaerobic digestion and biogas industry is now growing at the smallest community level and at huge wastewater treatment facilities.
The word is out now, and even if fluctuating natural gas and oil prices reduce in the coming year, expect to see more and more biogas plants wherever you go!
The new UK trend will be for new food waste AD facilities ahead of food waste curbside collection to all English districts by 2025.
Types of Anaerobic Digestion Plants – From the Smallest to the Largest
DIY and Micro-Anaerobic Digestion Systems
Users:
Individuals and educational establishments
Type: Desk-scale, laboratory and yard digesters
Equipment:
-bottle and flask reactors – balloons and car type inner tubes
More Info:
Watch YouTube videos for demos.
Household and Community Biogas Plants
Users: Households and community groups Type: Fixed dome and “Arti” Equipment: -stone built buried chambers -arched dome, floating drum More Info: YouTube videos, “Arti” website etc.
On-Farm and Central Biogas Plants
Users: Farm businesses, co-operatives etc. Type: Usually wet-process Equipment: -circular tank reactors – biogas holders – flexible dbl. membrane covers More Info: US Agstar, UK WRAP websites etc.
Large Waste & Commercial Anaerobic Digestion Facilities
Users:
Public bodies, large waste companies.
Type: WasteWater Sludge Treatment Facilities, Large Farms, MBT Plants, Food Waste
Equipment:
-Wet & Dry AD Processes – Various
More Info:
Here and on our blogsite.
Types of Anaerobic Digestion Process
Wet AD Process (Most Common)
>Users:
All.
Feed Type:
All organic wastes, and crop residues.
Features:
-Wet & Dry feeds are mixed with water and pumped. -Large tanks. look like typical AD Plants
– Opportunities for CHP
Dry AD Process (Popularity Rising)
Users:
Not for DIY'ers or most farmers.
Feed Type: Fibrous low water content Feed Materials.
Features:
-Material handled as a solid -Not pumped. -Inoculum spray introduces micro-organisms.
More Info:
Other Anaerobic Digestion Processes
- Low-Temperature AD
- High-Temperature Bio Thermic
- Two-Stage AD Digester
- UASB Digesters for Water Treatment
- Plug Flow Digestion Systems
- Semi Plug Flow Systems
- Facultative Bio-treatment
- Microbial Fuel Cell Systems
Reasons for Building an AD Facility – Other Than for Energy
For Water Treatment
- Although Wastewater Treatment Plants, which treat foul sewage, are routinely aerobic processes, some are anaerobic, especially in South America.
- Upflow Anaerobic Sludge Blanket (UASB) digester systems use the process and are primarily used for water treatment.
For Odour Abatement
- Large intensive livestock farms that are situated close to housing may be able to obtain permission to extend their operations only if they install an AD plant to reduce the odour of “muck spreading”.
- Digestion of manure substantially reduces muck-spreading odours, especially if ground injection of digestate, is used.
To Reduce Risk of Water Pollution (1)
- High-intensity livestock farms in high rainfall areas, and nitrate sensitive zones, may experience a particularly high risk of river pollution and prosecution from nitrate contaminated run-off when heavy rain occurs soon after spreading manure.
- Plant and soil uptake of the nutrients, from the digestate from a biogas plant, can be more rapid and reduce watercourse pollution risks.
To Reduce Risk of Water Pollution (2)
- The quality of the seawater at Blue Flag bathing beaches was shown to be impaired after heavy summer rainstorm events, in an estuarine environment.
- Installation of farm biogas plants to digest all livestock farm cattle slurry, reduced the faecal indicator organism counts on nearby beaches, avoiding damage to local tourism.
3 Top AD Plant Add-Ons and Upgrades
A Hydrolysis Stage
“Hard to digest” feed materials can benefit greatly by including a hydrolysis stage in which the substrate is subjected to high temperature and pressure, before digestion. Hydrolysis breaks up intact cells allowing the digestion micro-organisms to carry out a much more complete digestion/ higher gas yields/ reduced retention times and greater plant throughput.
Upgrade Biogas to Biomethane
- There is a lot of talk about creating added value for the raw biogas from anaerobic digesters, by “upgrading“.
- Upgrading is the process of removing carbon dioxide and other impurities from biogas and compressing it.
- It produces biomethane – a highly sought after product. It is sold as Renewable CNG (Compressed Natural Gas – a substitute for Liquefied Natural Gas) as a vehicle fuel, or injected into the regional natural gas grid distribution network.
Improved Biogas Reactor Mixing and Avoidance of “Hard Crust”
(Applies to Wet AD Processes Only)
- Many early digesters benefit from improved reactor mixing, which avoids “dead zones” within the digester tank.
- Some mixing systems can also break-up any tendency for a crust to form on the reactor surface.
- Higher biogas volumes may repay the cost of installation quite rapidly.
