BMP testingEnergy crops and whole-crop plants (WCS)

Hemp, stalks and whole plant — BMP: 3 studies, weighted mean 242 m³ CH₄/t VS

Fibre hemp as a whole plant or stems is a lignocellulosic biomass of high yield. The compilation is based on several studies with different forms of the material.

CH₄ ≈ 52 % (estimate)

Published 4 April 2021Updated 29 October 20263 min readFeedstockData Editorial Team

Photo D-Kuru / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean: 242m³ CH₄/t VS
Range: 163–289m³ CH₄/t VS
Records: 3studies
Publications: 3sources
Temperatures: 36 °C, 37 °Cof the test

Methane in biogas

≈51–54% CH₄

Medium methane content · ≈ 5.2 kWh/m³ of biogas

estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (carbohydrate-dominated (no protein or fat characteristics)) and the yields of compound groups according to FNR.

How we calculate it and what the zones mean

Rating for biogas plants

not rated — editorial rating for biogas plants

Not rated: the dry matter in the data refers to a sample dried for the test, not to the material as delivered. We calculate the rating when the dry matter and volatile solids of the material are known.

Editorial rating per the methodology

Add to the co-digestion calculator CSV data

BMP curves from 3 studies

Weighted mean Individual records

Dashed lines are a model curve (first-order kinetics, B(t) = B₀·(1 − e^−kt)); the end point comes from the publication. All curves are model curves.

Cumulative methane production over the test [m³ CH₄/t VS]. The thick line is the weighted mean of all records (242); dots mark the end values given in the publications. Point at the chart to read values; click a legend item to hide or show a record.

Records and sources

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Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Kaiser (2007)	163	37 °C · mesophilic	Cannabis silage	end point (model curve)
Luna-delRisco et al. (2011)	289	36 °C · mesophilic	hemp	end point (model curve)
Matassa et al. (2020) DOI	275	—	Stalks	end point (model curve)
Weighted mean	242	arithmetic mean 242, SD 69

Typical composition

Dry matter (DM): 60.2% (range 28.3–92)
Volatile solids (VS): 90.5 % DM (range 86.7–94.3)

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: MY-D); dry matter: 2 determinations, volatile solids: 2 determinations. The DM range includes fresh samples as well as samples partly dried or dried before the test – for fresh material the lower part of the range applies, ideally your own measurement.

Sources: Kaiser (2007); Luna-delRisco et al. (2011).

The composition of the raw material varies between batches — for plant calculations use an analysis of your own sample. The calculator inserts typical values automatically.

Process properties

seasonal
fibrous
slowly degrading
editorial classification

Advantages

Methane potential in the database: weighted mean 242 m³ CH₄/t VS (median 275; range 163-289; 3 records from 3 sources).
Hemp fibres have the highest BMP among the fractions (422 ± 20 m³ CH₄/t VS according to Matassa 2020); hurds lower (239 ± 10).

Drawbacks and risks

The hurds require treatment: alkaline treatment or grinding gave +15.9% (Matassa 2020).
The leaf and inflorescence fraction caused long-lasting inhibition of methanogenesis and gave a BMP many times lower than the fibre; NaOH treatment improved it (Matassa 2020).

Co-digestion — what to combine it with, what to watch out for

combines well
group: Animal excreta (slurry, manure, poultry litter)
Co-digestion with excreta (slurry/solid manure) is the standard arrangement for plant biomass: they supply alkalinity and microflora.^[1][2]

Dosing

No source dose limits; Matassa 2020 suggests treating the fractions separately (fibre, hurds, leaves, inflorescences).

Introduce gradually, starting with a small dose and monitoring the process (e.g. FOS/TAC, pH, gas composition).

Practical requirements

Shred: shredding increases the surface available for degradation and speeds it up, but does not necessarily raise the final gas yield (FNR 2010, Ch. 3 “Triturado”).

Sources of the process data

The co-digestion calculator will assess a specific mixture containing this substrate.

What it is and where it comes from

Fibre hemp is varieties of common hemp grown for fibre, seed and biomass, with a low THC content. The plants are tall and give a high dry matter yield. After the fibre is extracted, woody shives remain, and in the context of biogas the whole plant is also considered. The compilation contains several records: silage from whole plants, dried plant and stems, coming from different studies.

Properties relevant to digestion

Hemp stems consist of bast fibres of high cellulose content and a woody core with a large share of lignin. Whole plants at an earlier stage are more readily digestible than at maturity. A high fibre content causes slow hydrolysis and a tendency to form scum, and long fibres may wrap around agitators. Size reduction is therefore crucial. For a biogas plant, the regulations on hemp cultivation are also important, including the use of authorised varieties only.

How to read the spread of results

The records concern different forms of the material: silage from whole plants, dried plant and stems alone, and therefore different fractions of differing digestibility. In addition, the variety, harvest date, degree of maturity, size reduction, treatment (for stems pretreatment is often applied; only material without it is included here) and test parameters have an effect. One of the studies does not state the temperature. The records do not exhaust the variability of the material.

In biogas plant practice

Hemp is a niche crop, more linked to the fibre and seed market than to biogas. Use in a biogas plant makes sense mainly for waste after processing or for biomass from crops aimed at multiple uses. Before feeding it must be thoroughly size-reduced and scum formation controlled. Cultivation requires compliance with the regulations on varieties authorised for cultivation and on notifications, which should be checked in current legislation. Your own BMP test is recommended because of the small number of records. Even if hemp is grown for other reasons, for example for fibre, it must be remembered that biomass harvested late is very fibrous and can cause technical difficulties, so before making a decision it is good to carry out a small-scale trial.

Methodology in brief

BMP is the amount of methane obtained from volatile solids (VS) in a batch test, given in m³ CH₄ per tonne of VS (numerically the same as NmL CH₄/g VS in the publications) and converted to normal conditions (0 °C, 101.325 kPa). The weighted mean gives each publication a total weight of 1, split equally between its results for the substrate — a paper testing twenty varieties does not outweigh a paper with a single sample. In inter-laboratory programmes the unit is the laboratory (total weight 1), and within it the weight of a test grows with the number of bottles (replicates). Results after pretreatment (e.g. thermal, chemical, enzymatic) are shown separately and are not included in the mean.

Solid lines are curves measured in the tests. Where a publication gives only the final result, we draw a first-order kinetic model, B(t) = B₀·(1 − e^−kt): only the end point comes from the publication, and the shape of the curve serves purely as visualisation — do not read the production on a particular day from it. For this substrate k = 0.085 d⁻¹ was assumed (median of rate constants k reported in the sources and/or fitted to the mean measured curves).

The statistics describe the spread of published results — a descriptive compilation, not a meta-analysis or a guarantee of plant yield.

Full methodology and correction policy

Bibliography

All sources of the site: bibliography.