BMP testingEnergy crops and whole-crop plants (WCS)

Beet roots (sugar/fodder beet) — BMP: 4 studies, weighted mean 397 m³ CH₄/t VS

Sugar beet and fodder beet roots are a substrate rich in readily available sugars, degrading quickly. They require care in dosing and removal of soil.

rating: good CH₄ ≈ 52 % (estimate)

Published 14 February 2025Updated 29 October 20263 min readFeedstockData Editorial Team

Photo kallerna / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean: 397m³ CH₄/t VS
Range: 300–450m³ CH₄/t VS
Records: 4studies
Publications: 2sources
Temperatures: 37 °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

good — editorial rating for biogas plantsStable, usually accepted without a fee

Potential per tonne of fresh matter: high (81 m³ CH₄/t); process risk: acidification. Handling costs: sand, stones, shells.

Why? Rating factors

Potential per tonne +2

+2potential 81 m³ CH₄/t fresh matter (BMP 397 × DM 21.1 % × VS 96.7 %)

Process stability −0.5

−0.5acidification: rapid degradation / acidic pH, risk of VFA accumulation, needs buffering

Handling and costs −0.5

−0.5sand, stones, shells — sediment in the digester

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

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

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 (397); 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 (2004)	450	37 °C · mesophilic	Sugar beet (beet)	end point (model curve)
Kaiser (2007) · 1	300	37 °C · mesophilic	Beets fresh	end point (model curve)
Kaiser (2007) · 2	355	37 °C · mesophilic	Beets fresh	end point (model curve)
Kaiser (2007) · 3	376	37 °C · mesophilic	Beets fresh	end point (model curve)
Weighted mean	397	arithmetic mean 370, SD 62

Typical composition

Dry matter (DM): 21.1% (range 18.1–22.8)
Volatile solids (VS): 96.7 % DM (range 73.2–97.7)

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: CROPGEN D4, MY-D); dry matter: 4 determinations, volatile solids: 3 determinations.

Sources: Lehtomaki (2004); Kaiser (2007).

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

easily degradable
sand and sediment
seasonal
high dry matter
carbon-rich
editorial classification

Advantages

Methane potential in the database: weighted mean 397 m³ CH₄/t VS (median 365; range 300-450; 4 records from 2 sources).

Drawbacks and risks

Rapid hydrolysis of easily degradable carbohydrates may acidify the reactor; alkalinity from slurry is needed (Chen 2008: VFA accumulation as an indicator of overload).
Spread of results in the database: standard deviation 62 at a mean of 370 m³ CH₄/t VS (4 records from 2 sources).

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

combines well
substrates: high alkalinity (buffer) — e.g. Cattle manure, Pig slurry, Cattle slurry, Duck slurry, Rumen and digestive tract content
Slurry buffers acidification from rapidly degradable roots.^[1][2]
caution
Beet leaves and tops
Beet roots and leaves together accumulate an easily degradable load.^[3][1]

Dosing

No source dose limits; overload with an easily degradable load is described in the review by Chen 2008.

Introduce gradually, starting with a small dose and monitoring the process (e.g. FOS/TAC, pH, gas composition).

Practical requirements

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).
Ensiling makes it possible to store seasonal biomass; properly ensiled plants (in the study maize, sorghum, forage rye, triticale) can be stored for up to a year without loss of methane production (Herrmann et al. 2011).

Sources of the process data

Chen, Y.; Cheng, J.J.; Creamer, K.S. (2008) Inhibition of anaerobic digestion process: A review. Bioresource Technology
Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
Kaiser, F.L. (2007) Einfluss der stofflichen Zusammensetzung auf die Verdaulichkeit nachwachsender Rohstoffe beim anaeroben Abbau in Biogasreaktoren. Dissertation, Technische Universität München, Wissenschaftszentrum Weihenstephan
Lehtomaki, A. Chistensson, K. and Bjornsson, L (2004) Pilot Scale two-stage anaerobic digestion of energy crops. Proceedings Anaerobic Digestion Conference 1763-1766
FNR (2010). Guía sobre el Biogás – Desde la producción hasta el uso (hiszp. wydanie „Leitfaden Biogas”, GIZ 2013)
Herrmann et al. (2011). Effects of ensiling, silage additives and storage period on methane formation of biogas crops. Bioresour. Technol.

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

What it is and where it comes from

Sugar beet is grown mainly for sugar mills, and fodder beet for animal feeding. The roots are a store of sucrose, and after harvest they can be ensiled or fed to a biogas plant fresh. In Germany and some other countries, beet is used as an energy substrate. The compilation contains several records from several studies, for fresh beet and sugar beet roots, under mesophilic conditions.

Properties relevant to digestion

Beet roots contain a lot of simple sugars and little protein and fibre, so they are very readily digestible. The advantage is rapid biogas production, the drawback the risk of overloading: too large a dose causes rapid acid production, a fall in pH and inhibition of methanogenesis. Fresh beet requires washing or separation of soil, because sand settles in the digester. Ensiling allows storage, but involves losses of sugars and leachate. The low content of nitrogen and trace elements suggests combining them with slurry or another buffering material.

How to read the spread of results

The records come from several studies in which fresh beet and sugar beet roots were used. The result depends on the variety, the sugar content, the degree of soiling, the form of the material (fresh, ensiled, size-reduced) and the method of sample preparation. Because the substrate is very rapidly fermentable, the substrate-to-inoculum ratio and buffering are particularly important in BMP tests, because too high a load lowers the result. Test length and inoculum quality also play a part.

In biogas plant practice

Beet is a seasonal substrate, available from autumn. Using it requires equipment for washing and size reduction and control of the dose over time. It is safer to feed it in a small share of the mix, with monitoring of pH and volatile fatty acids. Because of competition with the sugar industry and its feed value, profitability depends on local prices. A BMP test on your own batch is recommended. On farms with access to cheap beet, it is worth considering ensiling it with drier material, for example with straw or grass silage. Such a mixture limits juice leachate and stabilises the material until it is used in the biogas 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.