BMP testingFruit, vegetables and their residues

Cauliflower — BMP: 2 studies, weighted mean 274 m³ CH₄/t VS

Cauliflower (whole plant or florets) is a watery vegetable waste, readily fermentable and rich in sulphur compounds, which in the biogas can raise the H₂S level.

CH₄ ≈ 59 % (estimate)

Published 28 February 2020Updated 29 October 20263 min readFeedstockData Editorial Team

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

Weighted mean: 274m³ CH₄/t VS
Range: 250–299m³ CH₄/t VS
Records: 2studies
Publications: 2sources
Temperatures: 35 °Cof the test

Methane in biogas

≈56–62% CH₄

Medium methane content · ≈ 5.9 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 6.1 % 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 2 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 (274); 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. (2017) DOI	250	—	Cauliflower (Brassica oleracea var. Botrytis) – Whole	end point (model curve)
Kouas et al. (2017) DOI	299	35 °C · mesophilic	cauliflower	end point (model curve)
Weighted mean	274	arithmetic mean 274, SD 35

Typical composition

Volatile solids (VS): 90.2 % DM (range 90.2–90.2)
Nitrogen: 6.1 % DM
C/N ratio: 6.8

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. (2017).

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
variable composition: high variability of composition between batches

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]

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

Cauliflower (Brassica oleracea var. botrytis) is grown in Poland in the open field, and waste batches arise in sorting plants, packing houses and frozen food processing plants, and as surpluses that are not worth harvesting or selling. This description concerns the fruit of this plant in the culinary sense, i.e. florets (inflorescences), or possibly the whole plant. The outer leaves and stems that remain in the field or in the packing house are described separately as crop residues.

Properties relevant to digestion

Cauliflower is a material that is almost entirely water, with a small dry matter content. Its components are simple sugars, starch in small amounts, pectins, protein and fibre, and lignin is present in a small amount. Like all brassicas, it contains glucosinolates and other sulphur compounds, which during digestion convert, among other things, into hydrogen sulphide (H₂S). For installations without biological desulphurisation, this means the need to control the H₂S concentration in the biogas, particularly when the share of brassicas in the feed rises. The material undergoes rapid hydrolysis, so with large portions it can lead to a temporary rise in fatty acids.

How to read the spread of results

The dataset contains few records from several different sources, so it is not possible to speak of reliable statistics. Differences may result from the variety, the stage of maturity, whether florets or the whole plant were tested, and from size reduction, moisture content and the inoculum used. One of the studies does not state the test temperature, the other was carried out under mesophilic conditions. Because the material is very watery, the error in measuring dry matter and volatile solids is of great importance for the result expressed per unit of VS.

In biogas plant practice

Cauliflower works as a supplement to the feed in season, if it is available in batches. It should be size-reduced, and dosing adapted to the capacity of the desulphurisation system. Because of its high water content it has a low energy density per tonne of fresh matter, so long-distance transport rarely pays. Storage is difficult: the material quickly spoils and gives off unpleasant odours, so it is usually introduced into the digester within a day or two. Plant waste from processing and trade is treated as waste, so its acceptance requires appropriate authorisations of the installation.

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.