Sampling and measurements
A simplified summary of measurements and their frequency is outlined in the table below. See each corresponding section for more details.
Once for each production batch, on a single representative sample of biochar
H/Corg and organic carbon content (full description here)
Three times per production batch
Biochar moisture content (if measuring biochar amount via mass) (full description here)
Once per year, or anytime biomass feedstock changes
Methane emissions, on three kilns representative of all other kilns in the same production batch (full description here)
Environmental pollutants of biochar, on one composite sample mixing biochar from each kiln run (full description here)
Dry bulk density of biochar, on at least one sample from each kiln (i.e. 20 different kilns, 20 bulk density measurements) (if measuring biochar amount via volume) (full description here)
Each kiln run
Moisture content and type of biomass input (full description here)
Mass or volume of fresh biochar produced (full description here)
Temperature curve measured in each kiln using real-time sensors, proving pyrolysis has occurred (full description here)
Sampling records (proof of setting aside a small sub-sample of biochar, to be combined with sub-samples from all other kiln runs in the same production batch) (full description here)
All biochar used
Proof of eligible, durable biochar end use, with names and GPS coordinates of spreading locations, among other information (full description here)
Once per year
Production batch
A production batch is the biochar produced across multiple kilns of the same technology type, with the same singular biomass feedstock type and storage conditions, quenching approach, and pyrolysis temperature curve.
It is assumed that all biochar from the same production batch has the same characteristics. The definition of production batch is used to group the following measurements: H/Corg, organic carbon content, bulk density and methane emissions.
A production batch is valid for a maximum of 6 months or 75 tonnes of biochar, whichever comes first. After this period or mass threshold, the biochar is considered part of a new production batch, even if conditions remain unchanged. This means that after 6 months, the production batch ID resets, a new batch is created, and new monitoring requirements apply, regardless of whether 75 tonnes have been produced or if feedstock or pyrolysis conditions have changed.
For the purpose of defining a singular biomass feedstock, wood pruning from different species may be combined as long as all leaves are removed.
Biochar sampling procedure
Kiln operators and kiln supervisors shall follow the general biochar sampling procedure outlined below:
Mixing the site's biochar, once per production batch
The Site Composite Biochar Pile shall be ground and thoroughly mixed by the kiln operator to ensure homogeneity. Once per production batch, a representative sample of biochar is then taken from this mixed site-level pile. This is called the Annual Site Composite Sample. Kiln supervisors shall take a sample from this pile at each site to conduct bulk density measurements.
Taking a representative sample
The Production Batch Composite Biochar Pile is thoroughly mixed by the kiln supervisor, and a representative sample— the Project Representative Sample— is taken and sent to an accredited laboratory for measurement of organic carbon content, H/C ratio, and environmental pollutants.
Specific protocols within this approach may vary depending on the project type and the kiln size. The recommended approach is detailed below, but Project Developers may propose their own approach if it:
is detailed in the PDD and in Sampling Records;
ensures one homogenized and representative composite sample per production batch;
describes the amount and frequency of samples and composite samples.
The VVB and the Rainbow Certification team must validate the rigor and representativeness of the proposed sampling approach.
Sampling each kiln run for Site Composite Biochar Pile: Set aside 3 liters from each kiln run, by taking a 1 liter sample from different spots in the pile. Continuously add these 3-liter samples to the Site Composite Biochar Pile throughout the production batch.
Mixing for Annual Site Composite Sample: Grind the biochar shall to a size of <3 mm.
Mix the ground sample by shoveling the pile three times from one pile to another. A sub-sample of 1.5 liters shall be taken from 15 spots in the mixed pile. The 15 sub-samples are re-combined, and then mixed by shoveling the pile three times from one pile to another. From the mixed pile of the combined sub-samples, 15 subsamples of 150 ml each should be taken at 15 different spots in the pile and combined. The remaining biochar in the Site Composite Biochar Pile may be used in a permanent end use and credited.
Mixing for Production Batch Composite Biochar Pile: Combine all Annual Site Composite Samples into one pile. Shovel the pile three times from one pile to another. A sub-sample of 1.5 liters shall be taken from 15 spots in the mixed pile. The 15 sub-samples are re-combined, and then mixed by shoveling the pile three times from one pile to another.
Taking a representative sample: From the mixed pile of the combined sub-samples, 15 subsamples of 150 ml each should be taken at 15 different spots in the pile and combined. This final sample is the Project Representative Sample, and shall be sent to an accredited laboratory for measurement of organic carbon content, H/C ratio and environmental pollutants.
Maintain a Retention sample: Keep the remaining biochar in the Production Batch Composite Biochar Pile in a protected area, separate from all other Production Batch Composite Biochar Piles, and to be used as the retention sample. Retention samples must be stored for a minimum of two years.
Records shall be uploaded to dMRV at each step, and track the date and time, location, the kiln ID/QR code, the production batch ID/QR code, and visual proof of the steps taken.
Moisture content of biomass
The moisture content of the biomass must be below 15% (w/w) for every kiln run. This shall be measured using handheld moisture sensors, with results uploaded as photographic evidence to the dMRV platform.
A minimum of 15 measurements must be taken for each kiln run, regardless of biomass volume. The mean moisture content must not exceed 15%, and no individual measurement shall exceed 25%.
Measurements must be taken from evenly distributed spots across the biomass pile, covering its width and depth.
Kiln operators must document photographic evidence of each sensor measurement result in the dMRV platform.
Amount of biochar produced
Project Developers shall choose one of the two following methods for measuring the amount of biochar produced: volume or mass. The same measurement approach shall be used for all biochar, across all kilns, for a given project.
Biochar volume
If biochar volume is tracked as the main indicator of biochar production and use, Project Developers shall establish a standardized container (with fixed size and material) for use across all project sites. Kiln operators must record the number of containers filled with biochar and applied to permanent end uses.
For example, a project might use a 1 m3 nylon bag as the standard container. Kiln operators could report that a kiln run produced 2 full bags, with 1 bag applied on day 1 and the second bag applied on day 2.
Volume of biochar must be converted to mass of biochar, because laboratory measurements of organic carbon content and are provided on a dry w/w% basis (i.e. in kg carbon/kg dry biochar). Biochar volume is converted to dry mass using bulk density measurements.
Bulk density measurements in distant accredited independent laboratories are not appropriate, because the biochar sample received at the lab is expected to be unrepresentative of biochar as produced and spread, due to damage during the shipping.
Onsite measurements are required for bulk density and shall be conducted by the kiln supervisor as part of their annual site visit. They shall collect a representative sample from the Site Composite Biochar Pile at each site during their visit.
Kiln supervisors shall take and prepare the biochar sample following these steps:
Take a mixture of biochar sampled from the bottom, middle, and top of the pile of biochar, already set aside by the kiln operator for sampling.
Transport the biochar from the kiln operator’s site to the location with measurement equipment, taking measures to protect the biochar from breaking during transport.
Keep biochar samples from each site separate.
Dry the biochar in a ventilated oven at at least 110°C for a minimum duration of overnight.
Kiln supervisors shall conduct and report bulk density measurements as follows:
Use containers of a standard and predefined volume size.
Use scales with proven calibration and high accuracy (e.g., digital readings; if non-digital, values rounded down).
Conduct measurements separately for each site (samples from different sites shall not be mixed, and measurements shall not be taken on composite samples).
Outliers may be excluded from the bulk density dataset (defined as any individual measurement that is 3 standard deviations above or below the mean of the dataset).
The final bulk density value used for GHG quantification of each production batch shall be the mean minus one standard deviation of all measurements within that batch.
Photos shall be uploaded to dMRV at each step. Project Developers shall prove that scales are well- calibrated at least once per year.
The VVB shall review all records related to biochar drying and bulk density measurements to ensure that:
Drying: biochar was sufficiently dried prior to measurement.
Transport and handling: the biochar sample used for bulk density measurement is similar to, and representative of, the biochar initially sampled, and has not been excessively damaged during transport or handling.
Representative subsample: the biochar sample used for bulk density measurement has a bulk density consistent with the larger biochar retention sample pile from which it was taken.
This method is deemed higher uncertainty than the biochar mass measurements described below, and will incur a higher uncertainty discount factor of at least 9%, instead of 6% used for projects measuring biochar mass directly.
Biochar mass
If biochar mass is used as the main indicator of biochar production and use, Project Developers shall provide kiln operators with accurate and calibrated measurement scales. The biochar output of all kiln runs shall be weighed upon completion of pyrolysis. Biochar mass may be measured either before quenching (bone dry) or after quenching (wet).
If biochar is weighed before quenching, the recorded mass reflects the dry mass of biochar produced and may be used directly to calculate carbon removals.
If biochar is weighed after quenching, the moisture content of the biochar must be measured and accounted for. Moisture content must be measured on 3 separate samples for every biochar production batch.
Moisture measurements shall be conducted using one of the following methods:
By the kiln supervisor, following the approach described above for bulk density. Measurements must begin on the same day the biochar is produced and weighed. Photos shall be uploaded to dMRV at each step, including time stamps showing that biochar is produced, weighed and dried on the same day.
By sending biochar samples to an accredited independent laboratory for moisture content measurement. Samples shall be sent on the same day the biochar is produced and weighed, and must be protected to minimize moisture loss, including at a minimum wrapping the biochar in three layers of sealed plastic bags. Photos shall be uploaded to dMRV at each step, including time stamps showing that biochar is produced, weighed and dried on the same day, and including photographic evidence of sealing the biochar sample.
Project Developers shall prove that scales are well-calibrated at least once per year.
Methane emissions
Methane emissions shall be measured with a calibrated sensor anytime biomass feedstock changes, or annually, if biomass feedstock does not change. Methane emissions shall be measured on three runs of three separate kilns of the same technology type and using the same feedstock, operated by different kiln operators (if there are more than three different kiln operators in the project).
Methane emissions shall be reported in kg CH4/kg biochar, and the mean value of the replicate runs shall be used for GHG quantification of all biochar produced in that year with the same biomass feedstock.
This value shall be considered representative of all other kiln runs as long as the following conditions are met:
The kiln type is the same
The biomass input type remains the same
Biomass moisture content requirements are met (all below 15% average, no measurement above 25%)
Photos of the measurement process must be uploaded to dMRV.
Methane emission measurements must be taken by a measurement organization accredited with either ASTM D7036, ISO 17025, or approved by state or regional authority, or for the use of portable equipment proof of calibration and a reputable independent instrument provider.
Accredited labs
Biochar measurements such as proximate and elemental analysis shall be performed by laboratories with at least one quality assurance accreditation, such as:
ISO/IEC 17025
CEN/TS 17225-1
ISO 10694
Unaccredited laboratories from academic settings shall be evaluated on a case by case basis by the VVB and the Rainbow Certification Team.
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