BMP testingBy-products of the agri-food industrysingle study (3 samples)

Coffee husk — BMP: 3 studies, weighted mean 152 m³ CH₄/t VS

Coffee husk is a dry, lignocellulosic waste from the dry processing of coffee cherries; in the dataset it was tested at three temperatures: 21, 30 and 37 °C.

CH₄ ≈ 52 % (estimate)

Published 8 June 2021Updated 29 October 20263 min readFeedstockData Editorial Team

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

Weighted mean: 152m³ CH₄/t VS
Range: 140–159m³ CH₄/t VS
Records: 3single study (3 samples)
Publications: 1source
Temperatures: 21 °C, 30 °C, 37 °Cof the test

Methane in biogas

≈51–54% CH₄

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.

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 3 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 (152); 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
Chala et al. (2019) · 1 DOI	140	21 °C · psychrophilic	Coffee husk, 21 C	end point (model curve)
Chala et al. (2019) · 2 DOI	157	30 °C · mesophilic	Coffee husk, 30 C	end point (model curve)
Chala et al. (2019) · 3 DOI	159	37 °C · mesophilic	Coffee husk, 37 C	end point (model curve)
Weighted mean	152	arithmetic mean 152, SD 11

Process properties

fibrous
slowly degrading
contains inhibitors
seasonal
high dry matter
editorial classification

Low confidence: the description is based on general characteristics of the substrate group, not on studies of this material. Treat it as a hint to be verified.

Advantages

Methane potential in the Substraty.pl BMP set: weighted mean 152.0 m³ CH₄/t VS (SD 10.6; 3 records, 1 source).
Dry material, easy to store; contains residual sugars and protein (Hendriks and Zeeman 2009).

Drawbacks and risks

Caffeine and tannins at a high concentration inhibit microorganisms (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
Slurry supplies N and alkalinity, balancing the high C/N of the material.^[1][2]

Dosing

No source threshold; low share, combine with slurry.

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

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

What it is and where it comes from

Coffee husk arises in the dry processing method, in which whole coffee cherries are dried and the fruit covering is then removed mechanically. It is one of the largest waste streams in coffee-growing countries such as Brazil or Ethiopia. In Poland coffee is imported as beans, so husk does not occur in significant quantities.

Properties relevant to digestion

The husk is a dry lignocellulosic material: it contains cellulose, hemicellulose and lignin, as well as protein, residual sugars, caffeine and tannins. Polyphenols can inhibit microorganisms to some extent, but at typical shares they do not block the process. The structure is fibrous, so hydrolysis is slower than in the pulp and mucilage. The risk of acidification is moderate, and the C/N ratio is relatively high. The material stores well if it is dry.

How to read the spread of results

The dataset contains several records from a single study, carried out at temperatures of 21, 30 and 37 °C. The results are close to one another, which means that within the range studied temperature had little effect on the final result, although it may have affected the rate. The lack of an independent source makes it impossible to assess variability between laboratories. The coffee variety, the degree of comminution, the content of pulp residues, moisture and the inoculum also have an effect.

In biogas plant practice

On coffee farms the husk is sometimes used as fuel, compost or, after treatment, feed, so it competes with biogas. If it goes into the digester, it should be shredded and its share moderate, together with manure or sludge. A low temperature in a hot climate without heating is a realistic scenario for simple installations, which adds practical value to the results at 21 and 30 °C. For installations in Poland the material is of comparative interest only.

On coffee farms, combining the husk with pulp and mucilage, which ferment faster, and with manure is often a good solution. The husk then contributes structure and extends the gas potential, and the sugar fractions ensure a quick start to the process, provided the whole is dosed evenly.

In producing countries the husk is also sometimes sold locally as fuel, which affects its price and availability for biogas installations.

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

Chala, B.; Oechsner, H.; Müller, J. (2019). Introducing Temperature as Variable Parameter into Kinetic Models for Anaerobic Fermentation of Coffee Husk, Pulp and Mucilage. Applied Sciences 9(3), 412. DOI: 10.3390/app9030412 DOI

All sources of the site: bibliography.