BMP testingBy-products of the agri-food industry

Spent coffee grounds — BMP: 18 studies, weighted mean 262 m³ CH₄/t VS

Spent coffee grounds are used coffee from catering and the instant coffee industry, containing fat, lignin and caffeine; they digest well after size reduction and in a small share.

rating: neutral CH₄ ≈ 65 % (estimate)

Published 8 November 2024Updated 29 October 20263 min readFeedstockData Editorial Team

Photo ПростоУчастник / Wikimedia Commons, licence CC0 1.0, source file; changes: cropping

Weighted mean: 262m³ CH₄/t VS
Range: 110–413m³ CH₄/t VS
Records: 18studies
Publications: 3sources
Temperatures: 37 °C, 38 °C, 58 °Cof the test

Methane in biogas

≈60–68% CH₄

High methane content · ≈ 6.5 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 2.8 % DM × 6.25); 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: moderate (40 m³ CH₄/t); process risk: fats, inhibitors, foaming. Handling costs: fibres, floating layer.

Why? Rating factors

Potential per tonne +1

+1potential 40 m³ CH₄/t fresh matter (BMP 262 × DM 16 % × VS 95.7 %)

Process stability −1.75

−1fats: risk of accumulation of long-chain fatty acids (LCFA), flotation and overloading
−0.5inhibitors: natural or residues (e.g. limonene, polyphenols, antibiotics, metals)
−0.25foaming: tendency to form foam in the digester

Handling and costs −0.5

−0.5fibres, floating layer — shredding and intensive mixing

Total points: −1.25 · 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 18 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 (262); 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.

Show the remaining records in the legend (6)

Records and sources

Download CSV

Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Cazaudehore et al. (2021) · 1 DOI	294	38 °C · mesophilic	spent coffee · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Cazaudehore et al. (2021) · 2 DOI	301	58 °C · thermophilic	spent coffee · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Dias et al. (2023) · 1 DOI	127	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 2 DOI	217	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 3 DOI	252	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 4 DOI	266	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 5 DOI	311	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 6 DOI	320	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 7 DOI	322	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 8 DOI	329	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 9 DOI	336	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 10 DOI	338	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 11 DOI	350	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 12 DOI	362	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 13 DOI	370	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Dias et al. (2023) · 14 DOI	413	37 °C · mesophilic	industrial spent coffee ground	end point (model curve)
Velasquez-Pinas et al. (2023) · 1 DOI	110	37 °C · mesophilic	ground coffee waste	end point (model curve)
Velasquez-Pinas et al. (2023) · 2 DOI	251	37 °C · mesophilic	dischard coffee	end point (model curve)
Weighted mean	262	arithmetic mean 293, SD 79

Typical composition

Dry matter (DM): 16% (range 6.3–97.2)
Volatile solids (VS): 95.7 % DM (range 95.1–96.3)
Nitrogen: 2.8 % DM
C/N ratio: 17.5

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: MY-D); dry matter: 9 determinations, volatile solids: 2 determinations. C/N was calculated as the ratio of C and N content (% DM) from the same source. 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: Cazaudehore et al. (2021); Dias et al. (2023); Velasquez-Pinas 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

fat-rich
fibrous
contains inhibitors
tendency to foam
editorial classification

Advantages

Methane potential in the Substraty.pl BMP set: weighted mean 262.0 m³ CH₄/t VS (SD 79.2; 18 records, 3 sources).
Spent coffee grounds have been studied for digestion as coffee waste (Lane 1983).
They contain fat, which raises the potential (Lane 1983; Long et al. 2012).

Drawbacks and risks

Fat may give LCFA at high loading (Long et al. 2012).
Caffeine and polyphenols may inhibit (Chen et al. 2008).
They mould quickly and require rapid use.

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 supplies N and alkalinity, balancing the high C/N of the material.^[1][2]
caution
substrates: fat-rich — e.g. Food waste, Primary sludge, Sunflower seeds, Olive pomace / olive mill solid waste, Slaughterhouse waste (cattle, pigs, poultry)
Grounds + oil/fat: two sources of LCFA.^[3]

Dosing

No source threshold. Low/medium dose, shredded; the share is limited by fat and inhibitors.

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

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

Spent coffee grounds are the residue after brewing coffee or extracting instant coffee. They arise in cafes, restaurants and offices, and on a large scale in plants producing instant coffee. In biogas plants they appear as a component of kitchen (catering) waste or as a separate, homogeneous batch from industry. Owing to the growth of coffee culture, the stream in Poland is noticeable, but dispersed.

Properties relevant to digestion

Spent coffee is a material containing fat (a few per cent of dry matter), hemicellulose (mannans, galactans), cellulose, lignin and protein. Thanks to the lipid content the gas potential is high, but the risk is the accumulation of long-chain fatty acids (LCFA) at a high load. The grounds also contain caffeine, tannins and polyphenols, which can affect microorganisms, although at typical shares they do not block the process. The fibrous structure includes a fraction that is hard to degrade, so degradation is slower than for sugars. Fresh grounds are moist and quickly go mouldy.

How to read the spread of results

The dataset contains several records from several sources, including mesophilic (37-38 °C) and thermophilic (approx. 58 °C) studies. The spread results from the origin of the grounds (brewed coffee, industrial extract), the species and degree of roasting of the beans, whether the grounds were defatted, and also from size reduction, drying of the samples, the test conditions and the inoculum. In one study industrial grounds were tested under different test conditions, which in itself creates variability.

In biogas plant practice

Spent coffee grounds are used as an additive in co-digestion in a small share, best with slurry or sludge, which bring buffering and trace elements. Dosing should be stable, because a sudden increase in the lipid load can disturb the process. Fresh grounds are not stored for long. Catering waste requires compliance with the regulations on kitchen waste and, if it is mixed with products of animal origin, also with veterinary regulations.

For a full assessment of a batch it is worth checking the fat and dry matter content, because grounds from the instant coffee industry, after extraction with hot water, have a different composition from grounds from espresso machines in cafes, which contain more residual fat and are moister.

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.