BMP testingFruit, vegetables and their residues

Zucchini and vegetable marrow — BMP: 4 studies, weighted mean 309 m³ CH₄/t VS

Courgette and marrow (Cucurbita pepo) are very watery cucurbit vegetables; waste from cultivation and processing is readily fermentable, but has a low dry matter content.

CH₄ ≈ 52 % (estimate)

Published 22 October 2026Updated 29 October 20263 min readFeedstockData Editorial Team

Photo nociveglia from Appennino Emiliano, Italy / Wikimedia Commons, licence CC BY 2.0, source file; changes: cropping

Weighted mean: 309m³ CH₄/t VS
Range: 263–344m³ CH₄/t VS
Records: 4studies
Publications: 2sources
Temperatures: 35 °C, 38 °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 4 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 (309); 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

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Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Dubrovskis i Plume (2017) · 1	263	38 °C · mesophilic	Vegetable marrow biomass, bioreactor R11	end point (model curve)
Dubrovskis i Plume (2017) · 2	279	38 °C · mesophilic	Vegetable marrow biomass, bioreactor R12	end point (model curve)
Dubrovskis i Plume (2017) · 3	280	38 °C · mesophilic	Vegetable marrow biomass, bioreactor R10	end point (model curve)
Kouas et al. (2017) DOI	344	35 °C · mesophilic	zucchini	end point (model curve)
Weighted mean	309	arithmetic mean 292, SD 36

Process properties

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.

No published process studies

The literature we use does not describe the advantages or drawbacks of digesting this substrate beyond the BMP test results. Below are process characteristics assigned on the basis of the type of material — an editorial classification, not a study result.

easily degradable: sugars, starch, glycerol → fast hydrolysis and acidification (VFA), needs buffering
acidic: low pH of the substrate (silages, stillage, whey, fruit)
dilutes the feed (low DM): low dry matter, dilutes the feed
seasonal: seasonal availability — requires storage
poor in trace elements: poor in trace elements — mono-digestion requires supplementation
carbon-rich: high C/N → nitrogen deficiency; combine well with nitrogen-rich substrates
low in nitrogen: high C/N → nitrogen deficiency; combine well with nitrogen-rich substrates

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

combines well
substrates: nitrogen-rich — e.g. Pig slurry, Poultry manure, Waste activated sludge (secondary sludge), Chlorella vulgaris, Nannochloropsis salina
A nitrogen-rich co-substrate balances the low C/N of fruit and vegetable waste (Bouallagui et al. 2009).^[1]
combines well
substrates: high alkalinity (buffer) — e.g. Cattle manure, Pig slurry, Cattle slurry, Duck slurry, Rumen and digestive tract content
Co-digestion of easily degradable substrates with dairy slurry increased the methane yield relative to slurry alone.^[2]

Dosing

No source limits on the dose for this substrate.

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

Courgette and marrow are forms of cucurbits (Cucurbita pepo) grown as a vegetable. Waste arises on farms and in sorting plants: overgrown, misshapen, damaged or frost-damaged fruit. The compilation contains several records from several studies: records for marrow (replicates in reactors of a single study, at 38 °C) and for courgette (35 °C).

Properties relevant to digestion

The fruit contains a great deal of water and little dry matter, in which sugars predominate and the share of fibre and protein is small. They are therefore readily and quickly digestible, but the energy per unit of fresh mass is low. At a large dose rapid acidification is a threat, and the low level of nitrogen and trace elements argues for co-digestion with slurry. Overgrown fruit has harder seeds and skin, which require size reduction. Spoiled fruit may contain moulds and increase the microbiological load.

How to read the spread of results

Records for marrow come from a single study and describe replicates in separate reactors, so they are not independent observations. The record for courgette comes from another study and a different temperature. Differences may result from the variety, the ripeness of the fruit, the share of seeds and skin, moisture content, size reduction and the test parameters. From such a small amount of data the full variability cannot be assessed.

In biogas plant practice

Courgette and marrow are a seasonal substrate, most often useful as a local additive. Because of the low dry matter content, transporting it over longer distances is uneconomic. It requires size reduction and mixing with drier material, and the dose must be controlled through pH and volatile fatty acids. As agricultural waste it should be included in the scope of substrates of the installation. Yield is confirmed by a BMP test. For the energy balance, it is worth calculating the value per tonne of fresh matter, and not only per unit of volatile solids, because at very high moisture content the difference is fundamental and affects the profitability of accepting such deliveries. It is also good to establish with the farm whether the fruit was sprayed just before harvest, because residues of plant protection products can affect the digester microflora and the quality of the digestate.

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 = 0.245 d⁻¹ was assumed (median of rate constants k reported in the sources and/or fitted to the mean measured curves).

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.