BMP testingWild, invasive and medicinal plantssingle study (4 samples)

Sedges (Carex spp.) — BMP: 4 studies, weighted mean 204 m³ CH₄/t VS

Sedges (Carex spp.) from wetlands are paludiculture biomass with high lignocellulose content; dry and wet digestion were studied for tufted sedge and lesser pond sedge.

CH₄ ≈ 52 % (estimate)

Published 5 August 2023Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Matt Lavin / Wikimedia Commons, licence CC BY-SA 2.0, source file; changes: cropping

Weighted mean: 204m³ CH₄/t VS
Range: 121–275m³ CH₄/t VS
Records: 4single study (4 samples)
Publications: 1source
Temperatures: —of 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 (204); 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
Czubaszek et al. (2021) · 1 DOI	121	—	Carex elata (CE), dry fermentation	end point (model curve)
Czubaszek et al. (2021) · 2 DOI	190	—	Carex elata (CE), wet fermentation	end point (model curve)
Czubaszek et al. (2021) · 3 DOI	228	—	Carex acutiformis + Carex elata (CA), dry fermentation	end point (model curve)
Czubaszek et al. (2021) · 4 DOI	275	—	Carex acutiformis + Carex elata (CA), wet fermentation	end point (model curve)
Weighted mean	204	arithmetic mean 204, SD 65

Process properties

fibrous
seasonal
variable composition
slowly degrading
editorial classification

Advantages

Methane potential in the database: weighted mean 204 m³ CH₄/t VS (median 209; range 121–275; 4 records from 1 sources).

Drawbacks and risks

Results differ several-fold between species and technology (wet vs dry digestion, Czubaszek 2021).

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

combines well
group: Animal excreta (slurry, manure, poultry litter)
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Dosing

No source-based dose limits; in the Czubaszek 2021 study sedges were processed as a mono-substrate (wet and dry digestion).

Practical requirements

Shred: shredding increases the surface available for degradation and speeds it up, but does not necessarily raise the final gas yield (FNR 2010, Ch. 3 “Triturado”).
Provide for removal of sand and heavy contaminants: sand is often strongly bound to organic matter and is released only in the digester, and sediments reduce its usable capacity, so a scraper or bottom drain is needed (FNR 2010, Ch. 3).

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

Sedges (Carex spp.) are grass-like wetland plants growing in wet meadows, fens and on the banks of waters. Tufted sedge (Carex elata) and lesser pond sedge (Carex acutiformis) are sometimes dominant in waterlogged habitats. In Poland and other European countries, biomass from these areas is considered in the context of paludiculture and the management of rewetted peatlands, where mowing can be a form of use without drainage.

Properties relevant to digestion

Sedge biomass is fibrous: it contains a lot of cellulose and hemicellulose as well as lignin, and few soluble sugars. Its composition depends on the mowing date, and material from late harvests is tougher, drier and poorer in nitrogen. Sedge leaves contain silica, which increases tool wear and may affect shredding systems. The high C/N ratio favours combining with slurry. Wetland biomass may be contaminated with soil, peat and organic residues.

How to read the spread of results

The set contains several records from a single study: tufted sedge and a mixture of both species, each in dry and in wet digestion. The temperature is not stated. Differences may result from the digestion technology (dry and wet), the species proportion, the mowing date, particle size and inoculum. A single study does not allow the effect of the method to be separated from the effect of the material, nor inter-laboratory variability to be assessed.

In biogas plant practice

Sedge biomass is an additive for co-digestion or dry digestion, after shredding and usually ensiling. Availability depends on the rules for peatland management: mowing in protected areas is restricted by nature conservation legislation and may require the consent of the conservation authorities. Material from wetland mowing has environmental value, but logistics (harvesting with equipment on wet ground) raise the costs. As agricultural biomass or green waste it has a different status depending on its origin.

It is worth remembering that the result for dry digestion is not directly comparable with that for wet digestion, because the conditions of mass transfer and the ammonia concentration are different, and in a batch test differences in the way water is introduced modify the availability of the substrate to microorganisms.

An additional factor is the content of minerals and silica in sedge biomass, which increases ash and lowers the result expressed per dry matter. When assessing profitability, one must therefore look at the entire harvesting chain and not only at the BMP result.

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

Czubaszek, R.; Wysocka-Czubaszek, A.; Wichtmann, W.; Banaszuk, P. (2021). Specific Methane Yield of Wetland Biomass in Dry and Wet Fermentation Technologies. Energies 14(24), 8373. DOI: 10.3390/en14248373 DOI

All sources of the site: bibliography.