BMP testingBioplastics and compostable packagingsingle study (6 samples)
Compostable coffee capsules — BMP: 6 studies, weighted mean 201 m³ CH₄/t VS
Compostable coffee capsules with grounds were tested in one study for three brands under mesophilic and thermophilic conditions; the result depends on the capsule material and the temperature.
Photo Reddalo / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping
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- Weighted mean
- 201m³ CH₄/t VS
- Range
- 67–355m³ CH₄/t VS
- Records
- 6single study (6 samples)
- Publications
- 1source
- Temperatures
- 38 °C, 58 °Cof the test
Methane in biogas
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.
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.
Add to the co-digestion calculator CSV data
BMP curves from 6 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 (201); 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 |
|---|---|---|---|---|
| Cazaudehore et al. (2021) · 1 DOI | 67 | 38 °C · mesophilic | Tintoretto · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment) | end point (model curve) |
| Cazaudehore et al. (2021) · 2 DOI | 92 | 38 °C · mesophilic | Launay · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment) | end point (model curve) |
| Cazaudehore et al. (2021) · 3 DOI | 127 | 38 °C · mesophilic | Beanarella · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment) | end point (model curve) |
| Cazaudehore et al. (2021) · 4 DOI | 257 | 58 °C · thermophilic | Tintoretto · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment) | end point (model curve) |
| Cazaudehore et al. (2021) · 5 DOI | 308 | 58 °C · thermophilic | Beanarella · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment) | end point (model curve) |
| Cazaudehore et al. (2021) · 6 DOI | 355 | 58 °C · thermophilic | Launay · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment) | end point (model curve) |
| Weighted mean | 201 | arithmetic mean 201, SD 121 | ||
Typical composition
- Dry matter (DM)
- 99.8% (range 99.7–99.8)
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: 0 determinations. Samples were tested dried/air-dry – the DM refers to the material in the test, not to fresh material.
Sources: Cazaudehore et al. (2021).
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
Advantages
- Methane potential in the Substraty.pl BMP set: weighted mean 201.0 m³ CH₄/t VS (SD 121.3; 6 records, 1 source).
- Thermophilic digestion of three commercial capsules ended in degradation after about 100 d (Cazaudehore et al. 2021).
Drawbacks and risks
- Under mesophilic conditions degradation was slow and incomplete after 100 d (Cazaudehore et al. 2021).
- Coffee grounds contain caffeine and polyphenols (Chen et al. 2008).
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
Dosing
No target share; the capsules require thermophilic conditions and a longer time.
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
- Benn, Zitomer (2018). Pretreatment and anaerobic co-digestion of selected PHB and PLA bioplastics. Front. Environ. Sci.
- Cazaudehore et al. (2021). Methane production and active microbial communities during anaerobic digestion of three commercial biodegradable coffee capsules under mesophilic and thermophilic conditions. Sci. Total Environ.
- Chen, Cheng, Creamer (2008). Inhibition of anaerobic digestion process: A review. Bioresour. Technol.
- 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
Compostable coffee capsules are single-use containers made of biodegradable material, filled with ground coffee and, after brewing, containing wet grounds. The samples tested come from three commercial brands. Aluminium capsules and those made of durable plastics, which are not suitable for digestion and do not belong to this group, are also on the market.
Properties relevant to digestion
The feed consists of two fractions: the biopolymer casing, usually based on biodegradable polymers and plant fibres, and the coffee grounds. The grounds contain cellulose, hemicelluloses and lignin, and also polyphenols and caffeine, which in large doses can inhibit microorganisms. The casing degrades depending on the polymer: aliphatic polyesters hydrolyse slowly at mesophilic temperature, and faster at thermophilic temperature. The whole capsule has a small area of contact with enzymes, so the risk is incomplete degradation and residues remaining in the digestate.
How to read the spread of results
The dataset covers a single source with three brands, tested under mesophilic and thermophilic conditions. The spread therefore reflects mainly differences between products and temperature, not between laboratories. The ratio of casing to grounds, which differs between capsules, the degree of size reduction before the test and the duration of the experiment all have an effect. For slowly degrading materials a test that is too short underestimates the result. Because there is a single source, the mean should not be regarded as typical for all capsules.
In biogas plant practice
Compostable capsules may reach a biogas plant together with catering waste or biowaste, but their share is small and irregular. Before digestion they require size reduction, and in mesophilic installations slower degradation of the casing must be expected. If the capsules come from catering, the rules on kitchen and catering waste apply, and for components of animal origin also the regulations on animal by-products. It is worth verifying the composition and making sure that the casing is genuinely biodegradable.
For the operator it is also important that coffee grounds usually have a high moisture content and spoil quickly, so longer storage before digestion worsens the quality of the raw material. For this reason capsules should be accepted as they arise and dosed in a small amount, best in a mixture with waste of higher content of readily available carbohydrates.
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.
Bibliography
- Cazaudehore, G.; Monlau, F.; Gassie, C.; Lallement, A.; Guyoneaud, R. (2021). Methane production and active microbial communities during anaerobic digestion of three commercial biodegradable coffee capsules under mesophilic and thermophilic conditions. Science of The Total Environment 784, 146972. DOI: 10.1016/j.scitotenv.2021.146972 DOI
All sources of the site: bibliography.
Other substrates in the group “Bioplastics and compostable packaging”
Starch-based bioplastics — BMP: 10 studies, weighted mean 266 m³ CH₄/t VS
266 m³ CH₄/t VS weighted mean from 10 studies
good — editorial rating for biogas plants≈52 %
Compostable bags — BMP: 8 studies, weighted mean 119 m³ CH₄/t VS
119 m³ CH₄/t VS weighted mean from 8 studies
neutral — editorial rating for biogas plants≈52 %
Cellulose-based films and packaging — BMP: 10 studies, weighted mean 355 m³ CH₄/t VS
355 m³ CH₄/t VS weighted mean from 10 studies
good — editorial rating for biogas plants≈51 %
PHA (polyhydroxyalkanoates) — BMP: 3 studies, weighted mean 341 m³ CH₄/t VS
341 m³ CH₄/t VS weighted mean from 3 studies
≈52 %