BMP testingFruit, vegetables and their residues

Cucumbers — BMP: 3 studies, weighted mean 313 m³ CH₄/t VS

Cucumbers (fruit) are one of the most watery vegetable wastes, with a low dry matter content; they digest readily but have a low energy density.

CH₄ ≈ 55 % (estimate)

Published 4 June 2022Updated 29 October 20263 min readFeedstockData Editorial Team

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

Weighted mean: 313m³ CH₄/t VS
Range: 242–349m³ CH₄/t VS
Records: 3studies
Publications: 3sources
Temperatures: 38 °Cof the test

Methane in biogas

≈54–57% CH₄

Medium methane content · ≈ 5.5 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 3.4 % DM × 6.25)) 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 (313); 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
Yan et al. (2021) DOI	242	—	Cucumber (Cucumis sativus) – Whole	end point (model curve)
Aybek et al. (2017) DOI	349	—	Cucumber	end point (model curve)
Shin et al. (2011) DOI	348	38 °C · mesophilic	Cucumber	end point (model curve)
Weighted mean	313	arithmetic mean 313, SD 62

Typical composition

Volatile solids (VS): 89.8 % DM (range 89.8–89.8)
Nitrogen: 3.4 % DM
C/N ratio: 13.4

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: BCBPD); dry matter: 0 determinations, volatile solids: 1 determination. C/N was calculated as the ratio of C and N content (% DM) from the same source. No DM in the sources – the calculator has to ask for a value.

Sources: Yan 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

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

Cucumbers (Cucumis sativus) are one of the staple vegetables grown in Poland, both in the field and under cover. The waste arises at sorting plants (crooked, overgrown, damaged fruit), on greenhouse farms and in processing, especially in the production of pickled cucumbers. Discarded greenhouse fruit appears in season in large batches of uniform material.

Properties relevant to digestion

Cucumber contains more than ninety per cent water, so the dry matter is very low. Soluble sugars, pectins and protein dominate the dry matter, and lignin occurs almost exclusively in the seeds and skin. The material hydrolyses quickly, but because of the low dry matter content the organic load on the digester is small relative to the volume. Cucumbers contain cucurbitacins, which give the bitter taste, but these are not a significant inhibitor at typical doses. Waste from processing may contain salt, vinegar and spices from the brine, which changes the conditions in the digester and must be taken into account.

How to read the spread of results

The dataset contains several records from several sources, including records without a stated temperature and mesophilic records. They describe market fruit, discarded greenhouse fruit and a general sample. Maturity matters a great deal, because overgrown cucumbers have more seeds and a thicker skin. Differences may also result from the variety, size reduction and dry matter determinations, where at 95% water the measurement error is relatively large. The inoculum and the substrate-to-inoculum ratio complete the picture.

In biogas plant practice

Cucumbers are an addition with a low energy value per tonne, so they are cost-effective mainly when they arise on site or within a short distance. After size reduction they can be introduced together with slurry or silage, which supplies dry matter and structure. The dilution of the feed by a large share of water should be monitored so as not to shorten the retention time. Storage without cooling quickly leads to spoilage and odours. Waste from processing and trade counts as waste, whereas own crop residues may be treated as agricultural products.

With very watery wastes it pays to determine the dry matter of each delivery and to convert the dose to organic load rather than to fresh matter, because only in this way can batches of different moisture be compared and biogas production planned.

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.