BMP testingFruit, vegetables and their residues

Peppers (fruit) — BMP: 5 studies, weighted mean 329 m³ CH₄/t VS

Sweet and hot peppers (fruit) are a watery vegetable waste with low lignin; chilli pepper contains capsaicinoids, which may matter at a high share.

CH₄ ≈ 54 % (estimate)

Published 26 July 2022Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Nikodem Nijaki / Wikimedia Commons, licence CC BY-SA 3.0, source file; changes: cropping

Weighted mean: 329m³ CH₄/t VS
Range: 250–354m³ CH₄/t VS
Records: 5studies
Publications: 3sources
Temperatures: 38 °Cof the test

Methane in biogas

≈52–55% CH₄

Medium methane content · ≈ 5.3 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 2.2 % 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 5 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 (329); 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) · 1 DOI	250	—	Bell pepper (Capsicum annuum) – Whole	end point (model curve)
Yan et al. (2021) · 2 DOI	286	—	Red chili (Capsicum cultivars) – Whole	end point (model curve)
Yan et al. (2021) · 3 DOI	346	—	Bell pepper (Capsicum annuum var. Grossum) – Whole	end point (model curve)
Aybek et al. (2017) DOI	339	—	Pepper	end point (model curve)
Shin et al. (2011) DOI	354	38 °C · mesophilic	Paprika	end point (model curve)
Weighted mean	329	arithmetic mean 315, SD 45

Typical composition

Volatile solids (VS): 91.5 % DM (range 82–92.1)
Nitrogen: 2.2 % DM
C/N ratio: 22.2

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: 3 determinations. 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

Pepper (Capsicum annuum) is grown in Poland under cover and in the field, and its waste arises at sorting plants, processing plants (frozen products, purées, sauces), in trade and on greenhouse farms. A separate group is hot pepper (chilli), the waste of which appears in the production of spices and sauces.

Properties relevant to digestion

Pepper fruits contain about ninety per cent water, and the dry matter consists of simple sugars, pectins, protein and fibre; the seeds and husks contribute a more poorly degradable fraction containing lignin. The fat content is small, but the seeds contain oil. The material hydrolyses relatively quickly, so doses should be spread over time. Hot pepper contains capsaicinoids, which at high concentrations can inhibit the activity of some microorganisms, but in typical co-digestion, at a small share, their effect is limited.

How to read the spread of results

The dataset contains several records from several sources, mostly without a stated test temperature. They describe sweet pepper, hot pepper and market waste, so part of the spread results from varietal differences and the share of seeds. Maturity and condition of the fruit, degree of size reduction, the way the sample is prepared and the inoculum further differentiate the results. For a watery material the accuracy of the volatile solids determination is of great importance.

In biogas plant practice

Pepper is a seasonal supplement to the feed, especially in greenhouse-growing regions. After size reduction it can be dosed together with slurry, while monitoring pH and volatile acids. Storage in warm conditions leads to rapid spoilage, and waste from hot varieties can cause respiratory irritation in workers during handling, which requires observing safety rules. Waste from trade and processing is subject to the waste rules.

Because of the small scale of the stream, pepper is rarely the main component of the feed; it usually enters the digester in a mixture of other vegetable wastes, which further dilutes any effect of capsaicinoids and evens out variability in deliveries.

It is worth remembering that waste from pepper processing (e.g. seed cores with stalks after mechanical processing) has a different composition from whole fruit: more seeds and fibre, less pulp. Such batches behave more slowly and require a longer retention time.

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.