BMP testingFats, oils and animal by-products

Used cooking oil — BMP: 2 studies, weighted mean 730 m³ CH₄/t VS

Used vegetable oil from catering is a waste, high-energy lipid. It requires careful dosing owing to fatty acid inhibition and contaminants from frying.

rating: neutral CH₄ ≈ 63 % (estimate)

Published 11 April 2021Updated 29 October 20263 min readFeedstockData Editorial Team

Illustration: FeedstockData (AI, Google Gemini)

Weighted mean: 730m³ CH₄/t VS
Range: 648–811m³ CH₄/t VS
Records: 2studies
Publications: 2sources
Temperatures: 35 °C, 37 °Cof the test

Methane in biogas

≈59–68% CH₄

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

neutral — editorial rating for biogas plantsNo clear advantages — worth charging a fee for accepting it

Potential per tonne of fresh matter: very high (727 m³ CH₄/t); process risk: fats, foaming. Handling costs: ABP cat. 3, physical contaminants (packaging, plastics), fibres, floating layer.

Why? Rating factors

Potential per tonne +3

+3potential 727 m³ CH₄/t fresh matter (BMP 730 × DM 99.6 % × VS 100 %)

Process stability −1.25

−1fats: risk of accumulation of long-chain fatty acids (LCFA), flotation and overloading
−0.25foaming: tendency to form foam in the digester

Handling and costs −2.5

−1ABP cat. 3: pasteurisation at 70 °C / 60 min
−1physical contaminants (packaging, plastics) — depackaging and separation
−0.5fibres, floating layer — shredding and intensive mixing

Total points: −0.75 · 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

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 (730); 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

Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Labatut et al. (2011) DOI	648	35 °C · mesophilic	Used vegetable oil	end point (model curve)
Li et al. (2013) DOI	811	37 °C · mesophilic	Used vegetable oil	end point (model curve)
Weighted mean	730	arithmetic mean 730, SD 115

Typical composition

Dry matter (DM): 99.6% (range 99.6–99.6)
Volatile solids (VS): 100 % DM (range 99.9–100)

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: MY-D); dry matter: 1 determination, volatile solids: 2 determinations. Samples were tested dried/air-dry – the DM refers to the material in the test, not to fresh material.

Sources: Labatut et al. (2011); Li et al. (2013).

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

fat-rich
tendency to foam
forms a floating layer
physical contaminants
ABP cat. 3
variable composition
editorial classification

Advantages

Methane potential in the Substraty.pl BMP dataset: weighted mean 729.8 m³ CH₄/t VS (SD 114.9; 2 records, 2 sources).
Used cooking oil from catering is a lipid concentrate of high methane potential (Long et al. 2012).
Co-digested with sewage sludge under thermophilic conditions it gave a positive effect at a controlled dose (Silvestre et al. 2014).

Drawbacks and risks

Contains free fatty acids, degradation products and food residues, which intensify inhibition and foaming (Long et al. 2012; Chen et al. 2008).
Excess lipids affect the dewatering properties of the digestate (Silvestre et al. 2014).
Separates out and thickens at low temperature (Long et al. 2012).

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

combines well
substrates: high alkalinity (buffer) — e.g. Cattle manure, Pig slurry, Cattle slurry, Duck slurry, Rumen and digestive tract content
Slurry stabilises pH and dilutes LCFA.^[1]
avoid
substrates: fat-rich — e.g. Food waste, Spent coffee grounds, Primary sludge, Sunflower seeds, Olive pomace / olive mill solid waste
Used oil + other fats: LCFA accumulation.^[2]

Dosing

No source-based percentage for this oil. As for oils: start low, as a guide do not exceed 2% of the mixture (Pitk et al. 2014, technical fat). Shared limit with other lipids.

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

Practical requirements

ABP cat. 3 (Art. 10 of Reg. 1069/2009; admitted to biogas plants by Art. 14): hygienisation before the digester in a mandatory unit: shredding to a maximum of 12 mm, temperature throughout the mass of at least 70 °C for at least 60 min without interruption (Reg. 142/2011, Annex V Ch. I Section 1 and Ch. III Section 1); the installation requires approval by the competent authority (Art. 24(1)(g) of Reg. 1069/2009).
Do not feed hygienised substrate into the digester hot (FNR 2010, Ch. 3: hygienisation).

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

Used vegetable oil (UCO, used cooking oil) arises after frying in catering, mass-catering establishments and the food industry. It is collected by specialised companies and usually directed to biofuel production or other uses, so it reaches biogas plants less often. The compilation covers several records from several publications, all under mesophilic conditions.

Properties relevant to digestion

Used oil consists mainly of triglycerides, but after repeated heating it also contains degradation products, free fatty acids, polymers and food residues. Free fatty acids and long-chain fatty acids released in hydrolysis inhibit methanogenesis and cause flotation of the biomass and foaming. The material has a very low water and protein content and a high share of organic matter, which means a concentration of energy. It requires good mixing, because it tends to separate and form a layer on the surface. At low temperatures it thickens, so it is harder to pump.

How to read the spread of results

The compilation has few records, so it does not capture the full variability. Differences between batches of used oil result from the type of oil used for frying, the number of frying cycles, contaminants and the water content. In a BMP test the substrate-to-inoculum ratio is particularly important, because overloading with lipids understates the result and delays gas production. The method of emulsifying the sample, the adaptation of the inoculum to fats and the test length also have an effect.

In biogas plant practice

Used oil can be an additive that improves the biogas yield, but only in a small, gradually increased share, with control of volatile fatty acids, pH and foaming. A heated tank and filtration of solid contaminants are needed. Its origin in catering means that waste regulations and possibly animal by-product regulations apply, and suppliers and the installation must meet documentation requirements. Owing to competition from the biofuel industry, availability and price may change, so the balance must be calculated for a specific contract. When purchasing or accepting used oil, it is worth asking the supplier about the share of water, food residues and any additives, and with each new batch observing the digester's reaction during the first days, before the dose is raised to the target level.

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

All sources of the site: bibliography.