FAQ
This document compiles the most frequently asked questions from our users, with the aim of providing quick access to essential information.
What is biomethane?
Biomethane is a gas that is generally produced from biogas derived from anaerobic digestion, following cleaning and purification (upgrading) to remove carbon dioxide (CO₂), hydrogen sulphide (H₂S), water vapour, siloxanes and other impurities. At the end of this treatment, biomethane has a methane (CH₄) concentration of between 92–97%, achieving compositional and thermodynamic characteristics similar to those of natural gas. By reducing impurities to residual levels, biomethane meets the regulatory requirements for injection into the natural gas grid and for use in conventional combustion equipment, as well as being suitable for use as a vehicle fuel. Because it is produced from biomass, biomethane is considered a renewable energy source.
How does biomethane differ from natural gas? And from biogas?
Natural gas is a fossil fuel composed mainly of methane (CH₄, 85–98%), with smaller amounts of ethane (C₂H₆), propane (C₃H₈), carbon dioxide (CO₂), nitrogen (N₂), and other light hydrocarbons and inert gases.
Biogas is a gas of biological origin produced by the anaerobic digestion of organic substrates, such as manure, food-waste, wastewater treatment sludges or agricultural residues. Its typical composition includes 50–65% methane (CH₄) and 35–50% carbon dioxide (CO₂), as well as small amounts of hydrogen sulfide (H₂S), water vapour, siloxanes, ammonia (NH₃) and other volatile compounds. Due to its high CO₂ content and the presence of corrosive or toxic impurities, biogas does not meet the necessary requirements for direct injection into the natural gas grid, requiring prior purification treatment.
Biomethane is produced from biogas following cleaning and purification, in a process known as upgrading, which removes CO₂ and contaminants to residual levels. With a methane (CH4) content of between 92–97%, biomethane has properties similar to those of natural gas and can be injected into the gas grid or used as a renewable fuel. Being derived from biomass, it is a renewable alternative to fossil natural gas.
Does the production of biomethane in Anaerobic Digestion plants cause unpleasant odours in the surrounding area?
Yes. During the handling of organic substrates (manure, sludge, biodegradable waste) and during the biogas production — before upgrading — odour emissions may occur, particularly from sulfur compounds (such as H₂S), nitrogen compounds (amines, ammonia) and other volatile organic compounds. However, proper containment systems, air treatment (biofilters, chemical scrubbers, activated carbon filters) and the adoption of good operational practices can significantly reduce, or even eliminate, these odours in practice.
Does the use of biomethane in the industry, transport or after injection into the Public Gas Grid (RPG) cause bad odors?
No. Biomethane is odourless following the purification (upgrading) process, during which odorous compounds such as H₂S, ammonia, siloxanes and other volatile organic compounds are removed. For distribution in the grid, biomethane is artificially odourised, just like natural gas, solely to enable the rapid detection of any leaks. It is also important to note that, as methane is a gas with a high global warming potential, the operation and use of biomethane follow strict practices to prevent leaks and atmospheric emissions.
What are the main feedstocks used in biomethane production?
According to the Biomethane Action Plan (PAB 2024–2040), the most relevant raw materials for biomethane production in Portugal stem directly from five identified strategic sub-sectors, on the basis of which the national production potential has been estimated. These sub-sectors provide the waste streams with the greatest availability, stability and technical and economic viability for anaerobic digestion. Namely:
- Municipal solid waste (MSW): this includes the organic fraction of municipal waste collected separately or treated in organic waste treatment facilities. This is one of the pillars of the first phase of PAB 2024-2040 development, due to the significant production already existing in municipal waste management systems. This sub-sector includes out-of-date packaged food obtained from the food retail sector (hypermarkets, supermarkets, food retailers) and food waste obtained from the HORECA sector (restaurants, hotels, etc.) via direct collection.
- Wastewater and sludges from wastewater treatment plants (WWTP): these sludges have high organic loads and are already commonly treated by anaerobic digestion, offering significant potential for conversion into biomethane.
- Agricultural residues and plant by-products: these include crop residues, agricultural processing waste and other organic materials from farming activities, considered essential for increasing the availability of organic matter for anaerobic digestion.
- Livestock waste: identified as having one of the greatest growth potentials for the 2026–2040 period, the livestock sector provides large volumes of manure and slurry with a high organic load, making it one of the main raw materials for scaling up biomethane production.
- Agro industrial by-products and effluents: these include effluents and organic waste from the agri-food industries (e.g. dairy, animal slaughter, fruit and vegetable processing, beverages, amongst others). These effluents have high organic matter content and are considered strategic in boosting national biomethane production.
What are the first steps to licensing a new biomethane production plant?
The installation of a new biomethane production plant with main Economic Activity Code (CAE) 35210 (gas production) involves four stages:
- Application for Prior Registration with the Directorate-General for Energy and Geology (DGEG) in accordance with Decree-Law No. 62/2020 and Joint Order of the Portuguese Environmental Agency (APA) and DGEG No. 1/2026.
The application for prior registration may be rejected within 30 days in the following cases:- Failure to comply with the legal and regulatory requirements for carrying out the activity; or
- Lack of technical conditions; or
- Failure to submit the documents listed in Annex VI to Decree-Law No. 62/2020, or to pay the security deposit, where applicable.
- If the 30-day period expires without the registration having been refused, the developer must initiate the environmental licensing process on the SILiAmb platform, managed by APA.
- In parallel with the environmental licensing process, the developer must initiate the urban licensing process with the respective City Council.
- Once steps 1–3 have been completed, DGEG enters the mandatory sectoral licensing decisions in the preliminary register and notifies APA of the entry in the exploratory register.
However, each case is unique, and it is recommended that you consult the “Licensing” subsection on this Portal and the documents contained therein.
For details, please consult the “Licensing” subsection on the Portal.
I am planning to invest in a biomethane production plant and would like to know if I am entitled to feed my gas into the Public Gas Grid (RPG)?
Yes, this right is explicitly stated in Article 71 of Decree-Law No. 62/2020, which defines the rights of holders of prior registration for the production of gases from renewable sources (including biomethane).
If you invest in a biomethane production plant, you are entitled to feed your gas into the RPG provided you have obtained prior registration with DGEG and meet the technical conditions, and provided you bear the costs of connecting to the network, in accordance with Article 72 of the same Decree-Law.
I am a biogas producer and I want to convert my plant to biomethane and feed it into the Public Gas Grid (RPG). Do I have to pay the cost of connecting to theRPG?
Yes. Current legislation stipulates that the costs of connecting renewable gas projects to the RPG are borne entirely by the producers. However, the Energy Services Regulatory Authority (ERSE) has already indicated that the model is set to evolve, proposing a cost-sharing arrangement between producers and network operators to accelerate the integration of biomethane into the national gas system.
What do I need to do to prove that the biomethane I produce is sustainable?
The produced biomethane must comply with the sustainability and greenhouse gas (GHG) emission reduction criteria set out in Decree-Law No. 84/2022, which transposes the Renewable Energy Directive (Directive (EU) 2018/2001, commonly referred to as REDII), into national law. Directive (EU) 2023/2413 (REDIII) introduced amendments to REDII, strengthening the sustainability requirements. These amendments will be reflected in the transposition of REDIII into national legislation.
Sustainability must be ensured throughout the entire value chain, from the origin of the raw materials to the production of biomethane. Demonstration of compliance with sustainability and GHG reduction criteria must be provided exclusively through certification issued under a voluntary scheme recognised by the European Commission for this purpose. Thus, as a link in the biomethane production value chain, the production unit must be certified in accordance with the procedures of one of these voluntary schemes and be subject to periodic audits under that certification.
LNEG, through the coordination of the Sustainability Criteria Entity (ECS), is responsible for verifying compliance with sustainability criteria and GHG emission reduction targets. To this end, the entity must be provided with evidence that the produced biomethane meets the aforementioned criteria.
For more information: ecs@lneg.pt
How can I obtain Guarantees of Origin (GOs) for the biomethane I produce?
Guarantees of Origin (GOs) are electronic documents that certify the origin of the energy consumed, including electricity, heat, biomethane and other renewable or low-carbon gases. The issuance of GOs for biomethane in Portugal is carried out by the Guarantees of Origin Issuing Entity (EEGO) and follows the procedure below:
- Opening an account and registering production facilities in the EEGO System;
- Audit and monitoring: for the purpose of verifying production and metering systems, EEGO carries out an initial audit and a periodic audit every two years;
- Monthly submission of Production Declarations: production data are declared monthly in the EEGO System and subsequently validated by EEGO.
- Issuance of GOs: following validation, GOs are issued and recorded in the relevant account;
- GO lifecycle: GOs may be freely transferred within the national and European (AIB) areas for 12 months from the end of the production period and may be cancelled up to 18 months thereafter.
For more information: http://eego.ren.pt or eego@ren.pt
Will I need to replace my natural gas oven or water heater to use biomethane?
Using biomethane in domestic appliances originally designed for natural gas does not require any technical modifications to the appliances (ovens, water heaters, boilers or heaters). They are fully compatible, due to the physical, chemical, thermodynamic and regulatory similarities between the two gases.
Is it just as safe to use piped natural gas as it is to use piped biomethane?
Domestic natural gas appliances are designed to operate within a range of physical and chemical properties defined by regulations. As biomethane, like natural gas, has methane as its dominant component, is distributed at regulated pressure, is odourised in the same way, and there are no changes in combustion regimes—namely in the air-fuel mixture or flame stability—it is just as safe to use biomethane as natural gas.
