Best Biogas Digester Plant in 2025

Axelis

3 years ago

Biogas definitions
Materials suitable for biogas production
Types of biogas systems
- Wet biogas system
- Dry biogas system
Types of small scale biogas digesters
- Fixed dome plants
- Floating drum plants
- Low-cost polyethlene tube digester
- Balloon plant
Various stages of biogas production
- Collection, transport and processing of biogas feed-stocks.
- Biogas production, upgrading and injection into the gas network.
- Biogas distribution logistics.
- Emissions from biogas use. tank to wheel, TTW.
Steps used in biogas production.
- Hydrolysis
- Acidification
- Methane formation
Importance of biogas.
- Waste treatment benefits
- Energy benefits
- Environmental benefits
- Economical benefits
Advantages and disadvantages of using biogas
How to efficiently Service and Maintain biogas digester
Benefits of rigorous / regular maintenance of biogas plant
How to stop biogas from smelling
How to minimize risks and ensure safety during every step of your biogas project
- Plant design
- Project construction
- Biogas plant commissioning
- Biogas plant operation
Summary

1. Biogas Definitions

Biogas has been defined in various different ways;

Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a renewable energy source. (Wikipedia)
A type of biofuel naturally produced from the decomposition of organic matter when exposed to an environment without oxygen they free a blend of gases. (youmatter)
A renewable biofuel naturally produced by the breakdown of decomposition of organic matter, such as food scraps and animal waste, when exposed to an environment without oxygen.
Any gas fuel derived from the decay of organic matter, as the mixture of methane and carbon dioxide produced by the bacterial decomposition of sewage, manure, garbage, or plant crops.(dictionary.com)
Biogas is a gaseous mixture generated during anaerobic digestion processes using waste water, solid waste (e.g. at landfills), organic waste, and other sources of biomass. (climate technology centre & network)

NB;

In summary from the above definitions biogas is;

A mixture of gasses i.e carbon dioxide, methane and hydrogen oxide.
Biogas is a biofuel/gasfuel
Biogas is a mixture of methane and carbondixide
Biogas is a renewable fuel.

All the definitions are in agreement that biogas is derived, produced or generated from decomposed waste materials, organic matter, waste water, and solid waste or plant crops. In absence of oxygen.

Biogas is produced through the processing of various types of organic waste such as food waste, human waste, sewage, paper waste, manure, green waste, biodegradable plastic, and slaughterhouse.

Biogas production also helps in the easy disposal of organic wastes and is eco-friendly because combustion of biogas does not cause much pollution. It has high calorific value and is a non-polluting renewable source of energy

Biogas production starts from the arrival of feed-stocks at the biogas plant. A diverse range of solid as well as sludge-like feed-stocks can be used.

2. Materials Suitable for Biogas Production

Biodegradable waste from enterprises and industrial facilities e.g. surplus lactose.
Spoiled food from shops, homes, hotels and institutions.
Bio-waste generated by consumers
Sludge from wastewater treatment plants
Manure and field biomass from agriculture

3. Types Of Biogas Systems

There are two types of biogas systems depending on the moisture content of the feed-stocks;

Wet biogas system– it’s the most common digester style. A wet digester or low solids AD system generally processes feedstock with less than 15 percent solids content
Dry biogas system – Dry digesters keep the substrates in a stackable form and remain in a pile during the digestion process. Food waste is mixed with green wastes such as yard debris for structure and porosity and is put into a long, rectangular vessel in a stack. The vessel is then sealed tight and warmed.

4. Types Of Small Scale Biogas Digesters

The table below gives a first comparison of the different types of biogas;

Factors	Fixed done	Floating drum	Tabular design	Plastic container
Gas storage	Internal Gas storage up to 20 m³ (large)	Internal Gas storage drum size (small)	Internal eventually external plastic bags	Internal Gas storage drum sizes (small)
Gas pressure	Between 60 and 120 mbar	Upto 20 mbar	Low, around 2 mbar	Low around 2mbar
Skills of contractor	High; masonry, plumbing	High; masonry, plumbing, welding	Medium; plumbing	Low; plumbing
Availability of Material	yes	Yes	yes	Yes
Durability	Very high >20 years	High; drum is weakness	Medium; Depending on chosen liner	medium
Agitation	Self agitated by Biogas pressure	Manual steering	Not possible; plug flow type	Evtl Manual steering
Sizing	6 to 124 m³ digester vol	Up to 20 m³	Combination possible	Up to 6 m³ digester vol
Methane emission	High	Medium	Low	Medium

FIXED DOME– A fixed-dome plant comprises of a closed, dome-shaped digester with an immovable/ fixed rigid gas-holder and a displacement pit, also named ‘compensation tank’. Gas pressure increases with the volume of gas stored, i.e. with the height difference between the two slurry levels.

Advantages:

There are no moving or rusting parts involved.
Its design is compact hence saves space and is well insulated.
It’s a Source of employment during construction for both locals and skilled people.
Has a long life span if well constructed and fixed.
The underground construction saves space and protects the digester from temperature changes.
Low initial and construction costs and long useful life-span;

Disadvantages:

Masonry gas-holders require special sealants and high technical skills for gas-tight construction
Gas leaks occur quite frequently
Fluctuating gas pressure complicates gas utilization
Amount of gas produced is not immediately visible.
Fixed dome plants need exact planning of levels.
Excavation can be difficult and expensive in bedrock.
Constructed and supervised by highly experienced biogas technicians.

FLOATING-DRUM PLANTS– Floating-drum plants consist of an underground digester (cylindrical or dome-shaped) and a moving gas-holder. Floating-drum plants consist of an underground digester (cylindrical or dome-shaped) and a moving gas-holder. The gas-holder floats either directly on the fermentation slurry or in a water jacket of its own.

They are chiefly used for digesting animal and human feces on a continuous-feed mode of operation.

They are used most frequently by small to middle-sized farms (digester size: 5-15m³) or in institutions and larger agro-industrial estates (digester size: 20-100m³).

The floating-drum must not touch the outer walls. It must not tilt, otherwise the coating will be damaged or it will get stuck.

Disadvantages:

The steel drum is relatively expensive and maintenance-intensive.
Removing rust and painting has to be carried out regularly.
The life-time of the drum is short (up to 15 years while in tropical regions about 5years
The gas-holder gets “stuck” If fibrous substrates are used in the resultant floating scum.

Advantages

The floating gas drum can be replaced by a balloon above the digester.
Readily available materials are used to construct the digester.

LOW – COST POLYETHYLENE TUBE DIGESTER- The tubular polyethylene film is bended at each end around a 6 inch PVC drainpipe and is wound with rubber strap of recycled tire-tubes. With this system a hermetic isolated tank is obtained.

Advantages

Easy to solve the technical problems arising in the polyethylene tube digester.
Economically, it saves the producer costs of buying liquid gas, firewood and chemical fertilizers. Low cost biodigester.
It helps minimize health hazards such air pollution
Reduces environmental threats, due to decrease in use of chemical fertilizers and organic waste exposures.
There is also reduced deforestation from firewood use for energy purposes.

Disadvantages

Has a short lifespan meaning the biodigester is not long lasting.
There is no reliable back up support.
PTDs suffer from effects of variable temperatures.
The bio digesters can only function properly and last a little longer if the farmer takes good care of the digester.

BALLOON PLANTS– A balloon plant consists of a heat-sealed plastic or rubber bag (balloon), combining digester and gas-holder. The gas is stored in the upper part of the balloon. The inlet and outlet are attached directly to the skin of the balloon. Gas pressure can be increased by placing weights on the balloon. The useful life-span does usually not exceed 2-5 years. Safety valves are placed to regulate gas pressure.

Advantages

Standardized prefabrication at low cost
low construction sophistication
Ease of transportation
Shallow installation suitable for use in areas with a high groundwater table
High temperature digesters in warm climates
Uncomplicated cleaning
Emptying and maintenance

Disadvantages

Low gas pressure may require gas pumps
scum cannot be removed during operation

5. Various Stages Of Biogas Production

Biogas is produced using well-established technology in a process involving several stages:

Collection, transport and processing of biogas feed-stocks– Raw materials or Feedstocks used in biogas production are delivered to biogas plants and the emissions put into account. Biowaste is crushed into smaller pieces and slurrified to prepare it for the anaerobic digestion process. Slurrifying means adding liquid to the biowaste to make it easier to process Feedstock processing and odor control also is put to consideration in this stage.
Biogas production, upgrading and injection into the gas network- s regards biogas production and upgrading, emissions from heat and electricity consumed at biogas plants, emissions from the production of chemicals used in the biogas process and emissions related to water consumption and wastewater treatment are taken into account
Biogas distribution logistics– Emissions related to biogas transmission in the gas pipeline network consist of methane emissions and carbon dioxide emissions from compressor stations and transmission pipelines. Containers are also used for biogas transport.
Emissions from biogas use (tank to wheel, TTW)- In the final stage, the gas is purified (upgraded) by removing impurities and carbon dioxide.

6. Steps Used in Biogas Production

Hydrolysis

It involves the conversion of polymeric organic matter (e.g., polysaccharides, lipids, proteins) to monomers (e.g., sugars, fatty acids, amino acids) by hydrolysis secreted to the environment by microorganisms.

Acidification

Acidification increased biogas and carbon dioxide production in five cases, increased methane production and reduced nitrogen production in four cases, and reduced methane content in biogas in four of five cases.

Methane formation

In practice this means that microbes feed on the organic matter, such as proteins, carbohydrates and lipids, and their digestion turns these into methane and carbon dioxide.

7. Importance Of Biogas

Biogas systems protect our air, water, and soil by recycling organic waste into renewable energy and soil products. Biogas is beneficial in the following categories;

Waste treatment benefits
Natural waste treatment process
Mature technology
Smaller physical footprint (vs. composting)
Reduces volume of waste for transport, land application, (vs. not using digestion)
Very efficient decomposition
Complete biogas capture
Nutrient recovery and recycling
Energy benefits
Net-energy producing process
Multiple existing biogas end-use applications, including; heat-only, electric-only, combined heat & power, pipeline quality biomethane and transportation fuel.
Baseload/dispatchable energy source(vs. intermittent wind and solar)
Distributed generation (which means lower transmission / transportation costs and higher reliability)
Direct replacement for non-renewable fossil fuel
Environmental Benefits
Dramatic odor reduction
Reduced pathogen levels
Reduced greenhouse gas emissions
Platform for reducing nutrient runoff
Increased crop yield
Economic Benefits
Jobs (temporary/construction and permanent)
Turns cost item (i.e., waste treatment) into revenue-generating opportunity
Can operate in conjunction with composting operations
Improves rural infrastructure and diversifies rural income streams
Digestate produced by the system can replace synthetic fertilizer or bedding purchase

8. Advantages & Disadvantages of Using Biogas

Advantages

Biogas is Eco-Friendly.
Biogas Generation Reduces Soil and Water Pollution.
Biogas Generation Produces Organic Fertilizer.
It’s A Simple and Low-Cost Technology That Encourages A Circular Economy.
Healthy Cooking Alternative for Developing Areas.

Disadvantages

Little Technological Advancement. An unfortunate disadvantage of biogas today is that the systems used in the production of biogas are not efficient.
Contains Impurities.
Effect of Temperature on Biogas Production.
Less Suitable For Dense Metropolitan Areas.
Flammable
Highly toxic
Potentially explosive

HOW TO EFFICIENTLY SERVICE AND MAINTAIN BIOGAS DIGESTER

9. How to Efficiently Service and Maintain Biogas Digester

Maintaining a biogas plant involves;

Doing minor repairs to the equipment,
Changing its oil as needed,
Removing debris from organic matter that falls to the bottom of the tank,
Solving problems in the process
Removing debris from organic matter that falls to the bottom of the tank
Breaking and removal of any scum formed at the top of the slurry.
Leakage test trouble shooting along the gas line.
Inspection of any clogged/blocked joints at the utilization point
Check the air blower on monthly basis.

10. Benefits Of a Rigorous / Regular Maintenance Of Biogas Plant

Among other things, the advantages include:

Prevention of technical failures or problems in the process
Increase in the life cycle of the equipment
Prevention of accidents and safer plant environment
Optimization of a plant operation or of biogas production.

11. How To Stop Biogas From Smelling

The method comprises the following steps:

(1) Firstly coarsely filtering through a mechanical grid, separating biogas residues from biogas slurry and introducing the biogas slurry into a reaction tank.

(2) Adding ferrate into the reaction tank and performing oxidation and deodorization;

(3) Introducing the biogas.

12. How To Minimize Risks and Ensure Safety During Every Step Of Your Biogas Project

The operator and the plant designer have to take certain measures at every step of a project. The goal is to ensure safety and minimize risks.

1. Plant design

This step is particularly important to ensure the safety of the biogas plant. The operator and the plant designer have to pay attention to:

The norms, guidelines and all other codes that apply to biogas plants
The classification of explosion zones, since the electric system installed on the biogas must be suited according to the risks of explosion
Avoiding confined space
Potential risks that can happen during the operation of the plant

2. Project construction

Make sure to plan the project rigorously
Hire an onsite expert to insure the workers apply the health and safety measures that are established

3. Biogas plant commissioning

Commissioning of a biogas plant can be the most dangerous step of a project.

Accidents that can happen include:

Structural failure rarely happens when the tank is being filled or the high-pressure pipes are being tested
Accidental hydraulic discharge during the pre-operation test of the pumps and valves
Lack of calibration of the health and safety equipment
Higher risks of explosion when the air inlets are opened and the air reach biogas

4. Biogas plant operation

During this step, a lot of accidents and incidents happen. To avoid them, the operator must:

Train every operator of the plant for the work in confined space, portable gas detection, process and equipment use
Apply strict procedures for equipment locking
Regularly verify health and safety equipment to make sure they are calibrated and offer precise measurements
Do a visual screening of all equipment to detect leaks and verify the state of equipment
Make sure all workers apply health measures to avoid pathogen diseases
Train all plant workers for basic firefighting skills and CPR

13. Summary

The biogas production process is the same for all types of biogas, and it leverages chemical reactions that are 100% natural. By placing biomass (organic waste) in a digester, you enable bacteria to break down the organic elements and turn them into biogas, which can then be used to generate energy.

It’s a zero-waste process that reduces the amount of waste that ends in landfills while permitting you to produce cleaner energy than by using fossil-fuel sources.

The process can occur at a large scale in industrial plants, but it can also be adapted for domestic usage, so you can easily have a small biogas station and produce energy for your house’s needs.