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BMP testingFats, oils and animal by-products

Vegetable oil (rapeseed, sunflower) — BMP: 4 studies, weighted mean 777 m³ CH₄/t VS

Vegetable oil (rapeseed, sunflower) has a very high energy potential, but is a strong risk of inhibition and foaming. In biogas plants it is used only occasionally and in small doses.

CH₄ ≈ 63 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

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

Weighted mean
777m³ CH₄/t VS
Range
540–940m³ CH₄/t VS
Records
4studies
Publications
2sources
Temperatures
35 °Cof the test

Methane in biogas

High methane content · ≈ 6.3 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); fat-rich (process classification)) 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: no dry matter or volatile solids in the data. 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 4 studies

Weighted mean Individual records

BMP curves: Vegetable oil (rapeseed, sunflower)Cumulative methane production over time for 4 records and the weighted mean of 777 m³ CH₄/t VS. 4 of the curves are model curves (first-order kinetics).025050075010000510152025303540time [d]m³ CH₄/t VSChynoweth et al. (1993): 940 m³ CH₄/t VS (model curve)Kouas et al. (2017) · 1: 540 m³ CH₄/t VS (model curve)Kouas et al. (2017) · 2: 611 m³ CH₄/t VS (model curve)Kouas et al. (2017) · 3: 691 m³ CH₄/t VS (model curve)mean777

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 (777); 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
Chynoweth et al. (1993) DOI94035 °C · mesophilicVegetable oilend point (model curve)
Kouas et al. (2017) · 1 DOI54035 °C · mesophilicoilend point (model curve)
Kouas et al. (2017) · 2 DOI61135 °C · mesophilicoilend point (model curve)
Kouas et al. (2017) · 3 DOI69135 °C · mesophilicsunflower oilend point (model curve)
Weighted mean777arithmetic mean 696, SD 174

Process properties

  • fat-rich
  • tendency to foam
  • forms a floating layer
  • easily degradable
  • editorial classification

Advantages

  • Methane potential in the Substraty.pl BMP dataset: weighted mean 777.0 m³ CH₄/t VS (SD 174.3; 4 records, 2 sources).
  • Pure lipid without water and protein - maximum energy concentration in the mix (Long et al. 2012).
  • In co-digestion with slurry, lipids are described as increasing yield if the dose is limited (Long et al. 2012).

Drawbacks and risks

  • Triacylglycerols give glycerol (readily fermentable) and LCFA - the latter inhibits methanogenesis and leads to biomass flotation and foaming (Long et al. 2012).
  • Separates out and forms a layer on the surface - without good mixing an indicator of local overloading (Long et al. 2012).
  • Unsaturated acids (oleic, linoleic) are more strongly inhibitory than saturated ones (Elsamadony et al. 2021).

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

Dosing

No source-based percentage for pure oil. In a study with technical fat and slurry, floating granules formed above 2% of the mixture (Pitk et al. 2014); take this as an upper guide and start an order of magnitude lower.

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

Sources of the process data

  1. Pitk et al. (2014). Mesophilic co-digestion of dairy manure and lipid rich solid slaughterhouse wastes. Bioresour. Technol.
  2. Creamer et al. (2010). Stable thermophilic anaerobic digestion of dissolved air flotation (DAF) sludge by co-digestion with swine manure. Bioresour. Technol.
  3. Fountoulakis, Petousi, Manios (2010). Co-digestion of sewage sludge with glycerol to boost biogas production. Waste Manag.
  4. Elsamadony et al. (2021). Advances towards understanding long chain fatty acids-induced inhibition and overcoming strategies for efficient anaerobic digestion process. Water Res.
  5. Long et al. (2012). Anaerobic co-digestion of fat, oil, and grease (FOG): A review of gas production and process limitations. Process Saf. Environ. Prot.

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

What it is and where it comes from

Vegetable oil is a liquid fat produced mainly from rapeseed and sunflower seeds. The compilation includes records for rapeseed oil, sunflower oil (including edible oil) and oil designated generally as vegetable. Pure oil is a product with commercial value, so as a biogas plant substrate it occurs mainly in studies or as a possible waste requiring no processing when the product range changes.

Properties relevant to digestion

Oil consists of triglycerides, which break down into glycerol and long-chain fatty acids (LCFA). Glycerol is readily fermentable, whereas LCFA, especially unsaturated ones, can inhibit methanogenesis, adsorb onto biomass and cause it to float and foam. The dose must therefore be very cautious, gradual and distributed within the mixture. Oil has practically no water or protein and a very high share of organic matter, so it is a concentrated material. It requires good mixing, because it separates as a layer on the surface.

How to read the spread of results

The records concern different oils (rapeseed, sunflower, edible) and come from several studies, including one from 1993. With a pure lipid the result is sensitive to the substrate-to-inoculum ratio: too high a dose in the test causes inhibition and underestimated results, while too low a dose gives a result that mainly reflects the method. Adaptation of the inoculum to fats, the way the oil is emulsified, the length of the test and the conversion to volatile solids also have an effect. The results from different studies are therefore not a simple measure of the material alone.

In biogas plant practice

Vegetable oil is not a standard biogas plant substrate. If it is nevertheless present, it should be at a minimal share of the feed, with monitoring of the volatile fatty acid concentration, pH and the tendency to foam. It requires a heated tank, good mixing and dosing in small portions. The commercial value of the oil usually exceeds the benefit of digesting it, so fatty wastes such as used oil or fats from separators are more realistic. Legal requirements depend on the origin and classification of the material, so they should be checked before use. When testing your own batch, it is recommended to run several BMP tests at different substrate-to-inoculum ratios to establish the threshold at which inhibition appears, and only then to plan the dose at the plant.

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 = 0.091 d−1 was assumed (no kinetic data for the group – the median of all available rate constants k (93 values) was used).

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. Chynoweth, D.; Turick, C.; Owens, J.; Jerger, D.; Peck, M. (1993). Biochemical methane potential of biomass and waste feedstocks. Biomass and Bioenergy 5(1), 95–111. DOI: 10.1016/0961-9534(93)90010-2 DOI
  2. Kouas, M.; Torrijos, M.; Sousbie, P.; Steyer, J.P.; Sayadi, S.; Harmand, J. (2017). Robust assessment of both biochemical methane potential and degradation kinetics of solid residues in successive batches. Waste Management 70, 59–70. DOI: 10.1016/j.wasman.2017.09.001 DOI

All sources of the site: bibliography.

Other substrates in the group “Fats, oils and animal by-products”