Biomethane is produced by upgrading biogas: removing carbon dioxide and unwanted contaminants to obtain a methane-rich gas suitable for its intended use. At an anaerobic digestion plant, the complete production process begins with organic feedstocks and ends with gas-quality checks and delivery to a gas network or another user.
The sequence is:
Feedstock preparation → anaerobic digestion → biogas collection → cleaning → upgrading → quality assurance → delivery or use.
The digester produces raw biogas. The upgrading equipment produces biomethane. Understanding that distinction helps explain why a methane digester alone is not a complete biomethane production plant.
Biomethane Production from Organic Waste
Animal manure, food waste, suitable agricultural residues and sewage sludge can provide feedstocks for anaerobic digestion. The material available at a site helps determine the plant’s design and operating requirements.
Producing renewable gas is only part of the project. Feedstock supply, waste handling, digestate management and the route to market must work together. The US Environmental Protection Agency explains that digestion produces both biogas and digestate, and that several organic materials can be combined through co-digestion. Source: EPA, How Does Anaerobic Digestion Work?
The Biomethane Production Process, Step by Step
1. Receive and prepare the feedstock
The plant receives organic material and prepares it for the chosen digestion system. Preparation requirements vary with the material: a slurry and packaged food waste do not present the same handling needs.
For a project assessment, identify the expected feedstock quantity, composition and variability before choosing equipment. A production forecast should state its assumptions rather than promise a fixed gas output from every tonne of waste.
2. Produce raw biogas through anaerobic digestion
Microorganisms break down organic matter in a sealed reactor without oxygen. The resulting gas contains methane, carbon dioxide and smaller quantities of other compounds. Digestate remains after digestion and requires appropriate handling.
For the upstream process in more detail, see our biogas production process guide.
3. Collect and clean the gas
Collected biogas needs treatment appropriate to the downstream equipment and final application. Moisture and contaminants such as hydrogen sulphide must be considered. Cleaning and upgrading are related stages, but removing contaminants alone does not necessarily produce gas suitable for injection into a network.
4. Upgrade biogas to biomethane
Upgrading removes much of the carbon dioxide to increase the methane concentration. Commercial approaches include membrane separation, water scrubbing, pressure swing adsorption and solvent absorption.
This article explains where upgrading fits into production. For a practical explanation, read how upgrading biogas to biomethane works. To compare equipment options, see our biogas upgrading technologies guide.
Existing illustration credited to Viaspace; image retained without modification.
5. Confirm quality and arrange delivery
The required product specification depends on the destination. A project needs to establish the relevant gas-quality, pressure, monitoring and delivery requirements before selecting its equipment.
Biomethane can supply compatible natural-gas applications. Routes include gas-network injection and vehicle fuel, with compression or further processing as appropriate. This does not mean every plant can connect to an existing gas main without additional equipment or arrangements.
Biogas vs Biomethane
Biogas is the mixed gas produced during digestion. Biomethane is the methane-rich product obtained after upgrading. They are successive products in the same production chain, rather than interchangeable names for untreated digester gas.
For a fuller comparison of composition and applications, see biomethane vs biogas.
Other Production Routes
Collected landfill gas can also be upgraded. Another route uses solid biomass gasification followed by gas cleaning and methanation. These routes require different equipment and should not be described as identical to digestion-based production. Source: IEA, An Introduction to Biogas and Biomethane, 2020
What Determines Output and Cost?
A useful project estimate separates raw biogas production from saleable biomethane output. Ask the supplier to explain feedstock assumptions, gas composition, methane recovery, energy consumption, operating availability and the final product specification.
Compare the complete project rather than the upgrader’s purchase price alone. Feedstock reception, digestion, gas treatment, delivery and digestate handling all contribute to the overall operation.
Is Biomethane Automatically Carbon Neutral?
Renewable origin does not establish that a project has zero emissions. Assessment should consider the feedstock, the alternative waste-management practice, energy use and methane losses across the system. Avoid applying a single emissions-saving claim to every production route. Source: IEA, Sustainable Supply Potential and Costs, 2020
Frequently Asked Questions
Is biomethane produced directly in a digester?
The digester produces raw biogas. Cleaning and upgrading then produce biomethane suitable for the chosen application.
Is biomethane chemically different from fossil methane?
The methane molecule is the same: CH₄. The source differs, while the composition and specification of the supplied gas still matter.
What is biomethane used for?
It can replace fossil natural gas in suitable heating, industrial and vehicle-fuel applications, subject to the required gas quality and compatible equipment.
Must every plant store its biomethane?
The delivery arrangement determines the storage needs. Do not assume that a project supplying a network has the same storage requirements as one supplying vehicle fuel.
Where should a new project start?
Start with the available feedstock and intended gas customer. Those choices inform the digestion system, upgrading equipment, product specification and delivery infrastructure.
