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BMP testingStraws and crop residues

Rapeseed straw — BMP: 2 studies, weighted mean 241 m³ CH₄/t VS

Oilseed rape straw is a lignified, hard-to-degrade residue left after rapeseed threshing. In the dataset it rests on a small number of records, so its description should be treated as indicative.

rating: goodCH₄ ≈ 53 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo Richard Humphrey / Wikimedia Commons, licence CC BY-SA 2.0, source file; changes: cropping

Weighted mean
241m³ CH₄/t VS
Range
240–241m³ CH₄/t VS
Records
2studies
Publications
2sources
Temperatures
35 °C, 38 °Cof the test

Methane in biogas

Medium methane content · ≈ 5.3 kWh/m³ of biogas

estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (protein from total nitrogen (N 1.5 % DM × 6.25)) and the yields of compound groups according to FNR.

How we calculate it and what the zones mean

Rating for biogas plants

good — editorial rating for biogas plantsStable, usually accepted without a fee

Potential per tonne of fresh matter: very high (170 m³ CH₄/t); no particular threats to stability. Handling costs: fibres, floating layer, slow degradation.

Why? Rating factors

Potential per tonne +3

  • +3potential 170 m³ CH₄/t fresh matter (BMP 241 × DM 81 % × VS 87 %)

Process stability 0

  • 0no factors

Handling and costs −1

  • −0.5fibres, floating layer — shredding and intensive mixing
  • −0.5slow degradation — long retention time

Total points: 2 · thresholds: ≥ 2.5 very good, ≥ 1 good, below — neutral; negative with cumulative process risk.

Editorial rating per the methodology · confidence of the rating: medium · excluding market prices

Add to the co-digestion calculator CSV data

BMP curves from 2 studies

Weighted mean Individual records

BMP curves: Rapeseed strawCumulative methane production over time for 2 records and the weighted mean of 241 m³ CH₄/t VS. 2 of the curves are model curves (first-order kinetics).0100200300051015202530time [d]m³ CH₄/t VSLehtomaki (2006): 240 m³ CH₄/t VS (model curve)Lallement et al. (2023): 241 m³ CH₄/t VS (model curve)mean241

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 (241); 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

Download CSV
SourceBMP
m³ CH₄/t VS		TemperatureSampleCurve
Lehtomaki (2006)24035 °C · mesophilicStraw of rapeseedsend point (model curve)
Lallement et al. (2023) DOI24138 °C · mesophilicstraw rapeseed wasteend point (model curve)
Weighted mean241arithmetic mean 241, SD 1

Typical composition

Dry matter (DM)
81% (range 71.9–90)
Volatile solids (VS)
87 % DM (range 87–87)
Nitrogen
1.5 % DM
C/N ratio
29.4

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: CROPGEN D4, MY-D); dry matter: 2 determinations, volatile solids: 1 determination. C/N was calculated as the ratio of C and N content (% DM) from the same source.

Sources: Lehtomaki (2006); Lallement et al. (2023).

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

  • fibrous
  • slowly degrading
  • carbon-rich
  • seasonal
  • forms a floating layer
  • editorial classification

Advantages

  • Methane potential in the database: weighted mean 241 m³ CH₄/t VS (median 241; range 240–241; 2 records from 2 sources).

Drawbacks and risks

  • Lignin; long HRT; floating crust (review by Hendriks 2009).

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

Dosing

No source-based dose limits; like other straws.

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

  1. Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
  2. Lehtomaki, A. Viinikainen, T.A. Rintala, J.A (2006) Screening boreal energy crops and crop residues for methane biofuel production. Submitted to Biomass and Bioenergy
  3. Dahunsi, S. (2019) Mechanical pretreatment of lignocelluloses for enhanced biogas production: Methane yield prediction from biomass structural components. Bioresource Technology 280, 18–26
  4. Hendriks, A.T.W.M.; Zeeman, G. (2009) Pretreatments to enhance the digestibility of lignocellulosic biomass. Bioresource Technology
  5. Lallement, A.; Peyrelasse, C.; Lagnet, C.; Barakat, A.; Schraauwers, B.; Maunas, S.; Monlau, F. (2023) A Detailed Database of the Chemical Properties and Methane Potential of Biomasses Covering a Large Range of Common Agricultural Biogas Plant Feedstocks. Waste 1(1), 195–227
  6. FNR (2010). Guía sobre el Biogás – Desde la producción hasta el uso (hiszp. wydanie „Leitfaden Biogas”, GIZ 2013)

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

What it is and where it comes from

Oilseed rape straw is the residue left after the threshing of rapeseed, one of the most important oil crops in Poland. It consists of thick, lignified stalks, remnants of pods and small elements of branching. On farms it is usually chopped and ploughed in, because it is stiff and of little use as bedding or fodder. The dataset rests on a small number of records from several publications, carried out under mesophilic conditions.

Properties relevant to digestion

Oilseed rape straw is a typical lignocellulosic material: it has a lot of lignin and cellulose, little protein and a very high C to N ratio. The stalks are hard and stiff, so without thorough chopping they wet poorly and form a loose structure in the digester that is prone to floating. Biological degradation is slow, and the dry matter content is high. Compared with green biomass, such as grasses or silages, straw contributes few readily available compounds, and its main role in a mixture may be to contribute structure and dry matter. Because of its composition it requires nitrogen supplementation, for example from slurry.

How to read the spread of results

With a small number of records, a full picture of variability cannot be given. Actual differences between batches arise from the oilseed rape variety (winter, spring), the timing and technique of harvest, moisture and the share of pods, which are more easily digestible than the stalks. The chopping of the sample is of great importance: finely milled straw behaves differently in the test from straw cut into pieces several centimetres long. Added to this are the test parameters: inoculum, substrate-to-inoculum ratio, incubation time and temperature. The records in this dataset concern material without pretreatment.

In biogas plant practice

Oilseed rape straw is not a typical substrate of agricultural biogas plants. When it is considered, thorough chopping is necessary and the dose limited to a small share, so as not to impair mixing or create scum. Because after ploughing-in the straw replenishes the soil with organic matter, collecting it carries an agronomic cost that must be set against the energy gain. Storage should take place in dry conditions. Before contracting a batch it is worth carrying out a BMP test, because data from the literature describe only a fraction of the possible materials and conditions.

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 = 0.136 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

  1. Lehtomaki, A. Viinikainen, T.A. Rintala, J.A (2006). Screening boreal energy crops and crop residues for methane biofuel production. Submitted to Biomass and Bioenergy.
  2. Lallement, A.; Peyrelasse, C.; Lagnet, C.; Barakat, A.; Schraauwers, B.; Maunas, S.; Monlau, F. (2023). A Detailed Database of the Chemical Properties and Methane Potential of Biomasses Covering a Large Range of Common Agricultural Biogas Plant Feedstocks. Waste 1(1), 195–227. DOI: 10.3390/waste1010014 DOI

All sources of the site: bibliography.

Other substrates in the group “Straws and crop residues”