Puro.earth Biomass Sourcing Criteria: a dynamic standard for biomass-based CDR 

Biomass lies at the heart of engineered carbon dioxide removal. Biochar and bioenergy with carbon capture and storage (BECCS) are the two largest CDR pathways at scale today, and both depend entirely on the sustainability of what goes into the process. Biomass is a finite resource, and its use for CDR must not conflict with ecosystem functions, food systems, or other human needs.  

As CDR continues to scale, the Puro.earth Biomass Sourcing Criteria (BSC) was designed to address this. Here, we set out to explain this framework in detail. 

Why a standalone framework 

Before the BSC existed, biomass requirements were embedded within individual methodologies. As the range of feedstocks and biomass-based CDR pathways grew, it became more efficient to keep all biomass rules within one document.  

The BSC, first published in 2024 alongside the Puro.earth Geologically Stored Carbon (GSC) Edition 2024 methodology, was designed from the outset as a cross-methodology tool – a single, coherent framework sitting as a layer across all of our latest biomass-based methodologies, with each methodology then able to add pathway-specific requirements on top. 

The BSC is a set of criteria – risk-based, socio-ecological in focus, and pragmatic in application – that must be met and enforced. It builds on existing international biomass sustainability frameworks, including recognised voluntary certification programmes and national and international regulations, but it does not treat any of them as a blanket pass.   

The spirit here aligns closely with what you find in some national and international regulations, which state that certification and third-party verification schemes can support due diligence but cannot substitute for it. The operator remains responsible for demonstrating compliance, and certification information must itself be assessed for relevance, audit quality and governance.  

We adopt the same principle: for example, a supplier can use an FSC Sustainable Forest Management certificate as evidence toward meeting one or several of our criteria, but the certificate is not itself a direct approval of eligibility. The supplier must still justify how the evidence available meets the BSC’s specific requirements. 

Biomass is not one thing 

The BSC recognises 16 distinct feedstock categories – from forest biomass and agricultural residues to food waste, municipal sludge, animal waste, aquatic biomass, and conservation landscape management material. Each carries different socio-ecological risks and different traceability challenges, and the BSC treats them accordingly. 

For each category, three elements are defined: the traceability information that must be documented and reported for every delivery; the sustainability criteria that must be evidenced; and the evidence options available to demonstrate them.  

For lower-risk waste-derived feedstocks – sorted food waste, green waste, animal waste – the requirements centre on demonstrating that the material is what it claims to be, that it comes from where it is said to come from, and that it has not been deliberately produced for CDR purposes.  

For higher-risk categories, the bar is substantially higher. For forest biomass, suppliers must demonstrate legal operations, safe working conditions, systematic regeneration of harvested areas, maintenance of carbon stocks and soil quality, protection of water resources and biodiversity, avoidance of primary forests and high-value ecosystems, and respect for the rights of indigenous communities.  

For agricultural biomass, comparable requirements apply alongside additional criteria covering food and feed competition and environmentally sound cultivation. The requirements scale with the risk – this is the fundamental design principle of the BSC. 

Under the Puro Standard, rules on biomass operate in two layers. The first is the BSC itself, setting baseline requirements for biomass sourcing across all pathways. The second layer is the individual methodology, which adds pathway-specific requirements on top. Biochar, for example, has strict rules on hazardous biomass and impurity contamination – because biochar quality and carbon quantification are directly affected by contaminants – while the same feedstock might be acceptable in a BECCS facility authorised to process it under local regulation. The two layers work together. 

How it works in practice 

Demonstrating compliance with Puro’s Biomass Sourcing Criteria (BSC) is a two-step exercise.  

At the Production Facility Audit, the Supplier presents a demonstration plan showing how compliance will be evidenced for each biomass source and applicable criterion; this plan is reviewed and validated by the auditor. At subsequent Output Audits, the Supplier then collects and presents the evidence defined in that validated plan. The first step – the Production Facility Audit – is therefore the more detailed and time-consuming one, but it is performed to establish a robust and repeatable compliance approach. Once this has been validated, the Output Audit process should be more streamlined and focused on execution. 

Step 1. Validation of the demonstration plan 

At the Production Facility Audit, compliance should be demonstrated against each individual criterion, whereby for each of these, the Supplier should identify which evidence option is being relied on and explain how that evidence addresses the criterion. 

For categories with only a few sustainability criteria, one piece of evidence may be sufficient. For more complex categories – including Category G (Forest Biomass), Category I (Non-food agricultural crop), Category J (Food agricultural crop), and Category M (Palm oil biomass and derivatives) – several pieces of evidence may be needed to cover all applicable criteria. 

For Category G, a FSC or PEFC certificate may cover many of the sustainability criteria, but it should not simply be cited as a blanket demonstration of compliance. The relevant standard, scope and claim should be checked against the BSC criteria. The type of FSC evidence also matters: FSC 100%, FSC Controlled Wood, and an FSC Chain of Custody (CoC) certificate provide different levels and types of assurance; a CoC certificate alone does not demonstrate that the biomass itself carries a qualifying sustainability claim. 

At the Production Facility Audit, the Supplier shall therefore: 

1. Identify the applicable BSC criteria for each biomass source used; 

2. Map each criterion to the relevant evidence option – such as certification, regulation, permits, management plans, declarations or other supporting documentation – and explain how the selected evidence demonstrates compliance; 

3. Identify any gaps that require additional evidence; and 

4. Based on the above, define which evidence and traceability records will be collected and presented at Output Audits. 

Where certification is used, the Supplier should be able to indicate which part of the relevant standard addresses the specific BSC criteria.   

Some criteria may require separate evidence even where a recognised certification is in place. For example, FSC 100% certified wood will typically not by itself demonstrate compliance with Puro’s material-use criterion for forest biomass, which requires evidence that the biomass is not suitable for long-lived wood products. This may need to be demonstrated through biomass specifications, supplier documentation, purchase or delivery records, intake records, or processing records. Other certification schemes with broader biomass-sustainability requirements, such as the Sustainable Biomass Program (SBP) certification, may address this type of criterion more directly, depending on the applicable scope and claim. 

Step 2. Verification of the records 

At the second step – the Output Audits – the Supplier shall provide the evidence and traceability records defined in the validated demonstration plan, covering the biomass used during the reporting period. The purpose is not to redesign the compliance approach at each audit, but to apply the previously validated approach consistently and demonstrate that the required evidence has been collected. Naturally, if biomass sourcing changes between audits – for example through a new source, feedstock type, certification status, or evidence pathway – the relevant information can be updated and re-validated efficiently as part of the Output Audit. 

Transparency and the public record 

The BSC is a publicly available, versioned document that makes Puro.earth’s requirements visible to suppliers, buyers, researchers and civil society. Independent Facility and Output Audit reports for every certified facility are publicly available on the Puro Registry. Puro.earth receives and archives the relevant traceability and sustainability records submitted by suppliers as part of the audit process. During the audit process, auditors also often request and access further primary evidence as needed, whether inspected on site or received directly from biomass providers or record holders.  

Suppliers may choose to go further by publishing evidence openly on their Puro.earth supplier listing or websites, rather than making it available only to auditors. We actively encourage this additional transparency where feasible, while recognising that contractual obligations, liability considerations, confidentiality requirements, and commercially sensitive partner information may limit what can be disclosed publicly. Where full disclosure is not possible – because records are commercially sensitive or are regulatory documents normally reserved for authorities and auditors – suppliers can still publish selected excerpts with accompanying context, for example to illustrate how their chain of custody operates without revealing confidential details. Steps like this build trust across the sector, and Puro.earth is keen to support suppliers who take them. 

A living standard 

The BSC is updated at least every two years, or sooner when the science or operational experience demands it. Version 1.0 was published in 2024 alongside the GSC Edition 2024 update; v1.1 followed in June 2025 alongside the Biochar Edition 2025 public consultation; with slightly amended versions published in November 2025 (v1.2) and September 2026 (v1.3). What drives the next evolution includes new feedstock types, accumulated operational experience, emerging market expectations and scientific advances. 

Biomass sustainability is not a challenge unique to the CDR sector – it is a challenge for any sector that depends on biomass in its supply chain, but also an opportunity to show what a sustainably managed practice can look like. The BSC is Puro.earth’s contribution to raising the bar. It will continue to evolve, while remaining globally applicable and pragmatic, and building on established biomass sustainability frameworks rather than reinventing them.