BMP testingEnergy crops and whole-crop plants (WCS)

Giant knotweed (incl. Igniscum) — BMP: 10 studies, weighted mean 192 m³ CH₄/t VS

Sakhalin knotweed (including the Igniscum variety) is a tall perennial grown as an energy crop, but one that raises reservations because of the invasiveness of related knotweeds.

rating: neutral CH₄ ≈ 53 % (estimate)

Published 4 July 2020Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Andrea Moro, Comune di Padova, Orto Botanico, Veneto, Italia / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean: 192m³ CH₄/t VS
Range: 146–270m³ CH₄/t VS
Records: 10studies
Publications: 3sources
Temperatures: 35 °C, 37 °C, 38 °Cof the test

Methane in biogas

≈52–54% 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 1.6 % 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

neutral — editorial rating for biogas plantsNo clear advantages — worth charging a fee for accepting it

Potential per tonne of fresh matter: moderate (34 m³ CH₄/t); no particular threats to stability. Handling costs: fibres, floating layer.

Why? Rating factors

Potential per tonne +1

+1potential 34 m³ CH₄/t fresh matter (BMP 192 × DM 19.4 % × VS 91.6 %)

Process stability 0

0no factors

Handling and costs −0.5

−0.5fibres, floating layer — shredding and intensive mixing

Total points: 0.5 · thresholds: ≥ 2.5 very good, ≥ 1 good, below — neutral; negative with cumulative process risk.

Editorial rating per the methodology · confidence of the rating: high · excluding market prices

Add to the co-digestion calculator CSV data

BMP curves from 10 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 (192); 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
Lehtomaki (2006) · 1	170	35 °C · mesophilic	Giant knotweed	end point (model curve)
Lehtomaki (2006) · 2	270	35 °C · mesophilic	Giant knotweed	end point (model curve)
Mast et al. (2014) · 1 DOI	146	37 °C · mesophilic	igniscum	end point (model curve)
Mast et al. (2014) · 2 DOI	148	37 °C · mesophilic	igniscum	end point (model curve)
Mast et al. (2014) · 3 DOI	150	37 °C · mesophilic	igniscum	end point (model curve)
Mast et al. (2014) · 4 DOI	158	37 °C · mesophilic	igniscum	end point (model curve)
Ruf i Emmerling (2018) · 1 DOI	190	38 °C · mesophilic	Giant knotweed · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Ruf i Emmerling (2018) · 2 DOI	192	38 °C · mesophilic	Giant knotweed · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Ruf i Emmerling (2018) · 3 DOI	220	38 °C · mesophilic	Giant knotweed · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Ruf i Emmerling (2018) · 4 DOI	222	38 °C · mesophilic	Giant knotweed · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Weighted mean	192	arithmetic mean 187, SD 41

Typical composition

Dry matter (DM): 19.4% (range 13–30.3)
Volatile solids (VS): 91.6 % DM (range 30.3–94)
Nitrogen: 1.6 % DM
C/N ratio: 32

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: CROPGEN D4, MY-D); dry matter: 10 determinations, volatile solids: 4 determinations.

Sources: Lehtomaki (2006); Mast et al. (2014); Ruf et al. (2018).

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
fibrous
editorial classification

Advantages

Methane potential in the database: weighted mean 192 m³ CH₄/t VS (median 180; range 146–270; 10 records from 3 sources).

Drawbacks and risks

Yield falls with a late harvest (Mast 2014).

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

combines well
group: Animal excreta (slurry, manure, poultry litter)
Co-digestion with excreta (slurry/solid manure) is the standard arrangement for plant biomass: they supply alkalinity and microflora.^[1][2]

Dosing

No source-based dose limits.

Sources of the process data

Mast, B.; Lemmer, A.; Oechsner, H.; Reinhardt-Hanisch, A.; Claupein, W.; Graeff-Hönninger, S. (2014) Methane yield potential of novel perennial biogas crops influenced by harvest date. Industrial Crops and Products 58, 194–203
Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
Lehtomaki, A. Viinikainen, T.A. Rintala, J.A (2006) Screening boreal energy crops and crop residues for methane biofuel production. Submitted to Biomass and Bioenergy
Hendriks, A.T.W.M.; Zeeman, G. (2009) Pretreatments to enhance the digestibility of lignocellulosic biomass. Bioresource Technology
Ruf, T.; Emmerling, C. (2018) Site-adapted production of bioenergy feedstocks on poorly drained cropland through the cultivation of perennial crops. A feasibility study on biomass yield and biochemical methane potential. Biomass and Bioenergy 119, 429–435

The co-digestion calculator will assess a specific mixture containing this substrate.

What it is and where it comes from

Sakhalin knotweed (Reynoutria sachalinensis, formerly Fallopia sachalinensis) originates from East Asia and forms tall, dense stands. The Igniscum variety is known from energy cropping in Germany, where it is meant to provide a high biomass yield for biogas. The compilation covers records from a Finnish study of Sakhalin knotweed and from a study of the Igniscum variety, obtained from different harvest dates.

Properties relevant to digestion

Knotweed biomass is green and succulent at an early stage, and becomes woody with time. The composition therefore depends on the harvest date: biomass harvested earlier is better digestible, later fibre dominates. The plant contains phenolic compounds and oxalates, the effect of which on the process at typical shares is a subject of research and should not be prejudged. Ensiling is possible, but requires adequate dry matter. Size reduction is essential, and the fibre readily forms a floating crust.

How to read the spread of results

The results cover two different groups: Sakhalin knotweed in general and the Igniscum variety tested at several harvest dates. The harvest date, plantation age, fertilisation, site and year affect the composition. In addition the test protocols differ (inoculum, substrate-to-inoculum ratio, temperature from 35 to 37 °C). The spread is therefore the resultant of plant and methodological differences.

In biogas plant practice

Knotweeds, including Sakhalin knotweed, appear on the national list of invasive alien species posing a threat to Poland (Regulation of the Council of Ministers of 9 December 2022, issued under the Act of 11 August 2021 on alien species), so their cultivation and the movement of material are subject to restrictions arising from these regulations. Before any decision on growing or accepting the biomass, the current regulations on alien species and the requirements for protection against spread must be checked. Technically the material requires size reduction and ensiling, and in the ration it behaves like other perennial tall plants. Cost-effectiveness should be assessed against other raw materials, and the decision should be based on a BMP test. For completeness it must be added that perennial tall herbaceous plants form permanent plantations, difficult to remove once established. The decision to grow is therefore a long-term one and should take into account not only the regulations but also the scenario for ending use of the plantation and protection against spread of the plant.

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 = 0.085 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.