BMP testingWild, invasive and medicinal plants

Herbs and herbal industry wastes (lemon balm, alder buckthorn, mint, andrographis, catnip, figwort) — BMP: 6 studies, mean 144 m³ CH₄/t VS

Herbal plants and herbal waste (lemon balm, buckthorn, mint, andrographis, catnip, leprosy plant) are six materials from several studies, rich in secondary compounds.

CH₄ ≈ 59 % (estimate)

Published 21 August 2020Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Donald Hobern from Copenhagen, Denmark / Wikimedia Commons, licence CC BY 2.0, source file; changes: cropping

Weighted mean: 144m³ CH₄/t VS
Range: 82–197m³ CH₄/t VS
Records: 6studies
Publications: 2sources
Temperatures: 38 °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 5.2 % 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 6 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 (144); 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
Yan et al. (2017) · 1 DOI	82	—	Schizonepeta (Nepeta cataria)	end point (model curve)
Yan et al. (2017) · 2 DOI	118	—	Common andrographis (Andrographis paniculata)	end point (model curve)
Yan et al. (2017) · 3 DOI	131	—	Mint (Mentha haplocalyx)	end point (model curve)
Yan et al. (2017) · 4 DOI	184	—	Summer radish (Scrophularia ningpoensis)	end point (model curve)
Czubaszek (2019) · 1 DOI	122	38 °C · mesophilic	Alder buckthorn (Frangula alnus) waste	end point (model curve)
Czubaszek (2019) · 2 DOI	197	38 °C · mesophilic	Lemon balm (Melissa officinalis) waste	end point (model curve)
Weighted mean	144	arithmetic mean 139, SD 44

Typical composition

Volatile solids (VS): 76.1 % DM (range 69.2–86.8)
Nitrogen: 5.2 % DM
C/N ratio: 7.3

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: 4 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. (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

seasonal
variable composition
fibrous
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 database: weighted mean 144 m³ CH₄/t VS (median 127; range 82–197; 6 records from 2 sources).

Drawbacks and risks

Spread of results in the database: standard deviation 44 at a mean of 139 m³ CH₄/t VS (6 records from 2 sources).

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

combines well
group: Animal excreta (slurry, manure, poultry litter)
Slurry dilutes and buffers the effect of secondary compounds.^[1]

Dosing

No source-based dose limits; in Czubaszek 2019 lemon balm and buckthorn waste was tested under BMP conditions — this is not evidence of a dose limit.

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

Herb growing and the herbal industry generate waste in the form of plant residues after cutting, sieving, drying and extraction (herbal teas, medicinal preparations). The dataset brings together two wastes from the herbal industry in Poland (lemon balm and buckthorn bark) and four medicinal plants from a Chinese study: catnip, Andrographis paniculata, mint and leprosy plant. These plants differ in structure and chemical composition, so the set does not describe a single raw material.

Properties relevant to digestion

Herbal plants contain secondary compounds: essential oils, flavonoids, tannins, alkaloids and glycosides, which have antimicrobial activity. At high concentrations they can limit microbial activity, whereas waste after extraction is sometimes partly free of them. Buckthorn bark is woody and contains anthraquinones. The leaves of herbs such as lemon balm and mint are more readily degradable than bark and stems. The material is usually dry, and its quality depends on the processing technology.

How to read the spread of results

Several records come from several studies and describe six different plants; the differences result from the species, the part of the plant (leaves, bark, stems), whether the waste had been subjected to extraction, and the test conditions. For some records the temperature is not given in the compilation. The degree of grinding, moisture, adaptation of the inoculum to secondary compounds and the length of the test also have an effect. Transferring values between species is not justified.

In biogas plant practice

Herbal waste can appear as an additional stream in regions with herb processing. It should be size-reduced and fed gradually while monitoring pH and microbial activity. Material with a high content of oils or anthraquinones can lower yield, so it is worth running a BMP test on your own batch. Waste from herbal production is waste within the meaning of the waste act and is subject to the appropriate records.

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 = 0.134 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.