BMP testingAlgae and aquatic plants

Water hyacinth — BMP: 3 studies, weighted mean 191 m³ CH₄/t VS

Water hyacinth (Eichhornia crassipes) is a floating invasive plant of very high moisture content; its methane potential depends on the lignin content of the tissues.

CH₄ ≈ 52 % (estimate)

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

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

Weighted mean: 191m³ CH₄/t VS
Range: 178–213m³ CH₄/t VS
Records: 3studies
Publications: 2sources
Temperatures: 35 °Cof 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 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 (191); 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
Ahou et al. (2021) DOI	178	—	Water hyacinth (Benin)	end point (model curve)
Chynoweth et al. (1993) · 1 DOI	196	35 °C · mesophilic	Water hyacinth (high lignin)	end point (model curve)
Chynoweth et al. (1993) · 2 DOI	213	35 °C · mesophilic	Water hyacinth (low lignin)	end point (model curve)
Weighted mean	191	arithmetic mean 196, SD 18

Process properties

dilutes the feed (low DM)
seasonal
variable composition
contains inhibitors
editorial classification

Advantages

Methane yield in the compendium: median 196 (range 178-213) m³ CH₄/t VS, 3 records from 2 studies (weighted mean 191).
Water hyacinth is a nitrogen-rich plant; co-digestion with sheep waste has been studied (Ahou et al. (2021); Patil et al. (2014))

Drawbacks and risks

The transport of heavy metals during hyacinth digestion has been the subject of separate studies: for plants from polluted waters, monitor metals (Ilangovan and Noyola (1990))
Co-digestion with cassava peel gave less methane than the sum of the mono-digestions of the two substrates (Ahou et al. (2021))
Aquatic plants with a high lignocellulose share have a lower methane potential than easily degradable substrates (Labatut et al. (2011))
Theoretical methods overestimated methane yields if biodegradability was not taken into account: a plan based on composition requires confirmation by a BMP test (Labatut et al. (2011))

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

combines well
group: Animal excreta (slurry, manure, poultry litter)
Co-digestion of hyacinth with sheep waste has been studied.^[1]
caution
Cassava peels
The mixture with hyacinth gave less methane than the sum of the mono-digestions.^[2]

Dosing

The sources do not give a safe share of this substrate in the feed.

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

Water hyacinth (Eichhornia crassipes, now also Pontederia crassipes) is a free-floating aquatic plant native to South America, which has spread across tropical and subtropical water bodies worldwide. It forms dense mats that restrict navigation, the inflow of light and oxygen, and hinder fishing and the operation of hydroelectric plants. In Poland it does not persist, because it does not tolerate frost, and in the European Union it is on the list of invasive alien species of Union concern (Regulation (EU) No 1143/2014), which entails, among other things, a ban on its import, transport, keeping and release into the environment.

Properties relevant to digestion

Fresh biomass consists of over 90% water, and the dry matter is mainly cellulose, hemicelluloses, protein and ash. The lignin content is moderate and differs between leaves, petioles and roots. The plant absorbs heavy metals and nutrients from the water, so biomass from polluted water bodies may contain elevated amounts of metals. The large water content hinders transport and dosing, and the breakdown of proteins releases ammonia, although usually in amounts that do not dominate in mixtures.

How to read the spread of results

The dataset contains several records from several sources, including some distinguished as biomass of higher and lower lignin content. Such a difference shows the main factor of variability: the age of the plant, the season, the availability of nutrients in the water and the share of the individual organs affect the composition. In addition there are size reduction, the method of preservation (fresh, dried, ensiled), temperature and the substrate-to-inoculum ratio. With a small number of records the spread does not allow a typical range for the whole species to be determined.

In biogas plant practice

Water hyacinth is considered as a substrate mainly in countries where it is a serious environmental problem, and its harvesting is linked to the clearing of water bodies. In European conditions it is not available. Where it occurs, before digestion it is worth size-reducing it, dewatering it (pressing) or mixing it with drier substrates. The heavy metal content and the effect on the digestate should be checked. Legal requirements include the regulations on invasive species, which may restrict the movement of live plants.

It is also worth remembering that floating plants such as hyacinth grow very fast, so under favourable conditions the biomass can be harvested several times a year. This is one of the reasons why it is sometimes seen as a potential energy source, despite its low dry matter.

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 = 0.102 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.