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BMP testingFruit, vegetables and their residues

Tropical tubers (sweet potato, Chinese yam) — BMP: 2 studies, weighted mean 280 m³ CH₄/t VS

The tropical tubers in the dataset are sweet potatoes and Chinese yam; starchy roots from several studies are characterised by high degradability and low lignin content.

rating: goodCH₄ ≈ 52 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo Llez / Wikimedia Commons, licence CC BY-SA 3.0, source file; changes: cropping

Weighted mean
280m³ CH₄/t VS
Range
214–345m³ CH₄/t VS
Records
2studies
Publications
2sources
Temperatures
37 °Cof the test

Methane in biogas

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 (protein from total nitrogen (N 1.3 % 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

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

Potential per tonne of fresh matter: high (95 m³ CH₄/t); process risk: acidification. No additional handling requirements.

Why? Rating factors

Potential per tonne +2

  • +2potential 95 m³ CH₄/t fresh matter (BMP 280 × DM 35.5 % × VS 95.4 %)

Process stability −0.5

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

Handling and costs 0

  • 0no factors

Total points: 1.5 · thresholds: ≥ 2.5 very good, ≥ 1 good, below — neutral; negative with cumulative process risk.

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

Add to the co-digestion calculator CSV data

BMP curves from 2 studies

Weighted mean Individual records

BMP curves: Tropical tubers (sweet potato, Chinese yam)Cumulative methane production over time for 2 records and the weighted mean of 280 m³ CH₄/t VS. 2 of the curves are model curves (first-order kinetics).0100200300400051015202530time [d]m³ CH₄/t VSYan et al. (2021): 214 m³ CH₄/t VS (model curve)Ge et al. (2014): 345 m³ CH₄/t VS (model curve)mean280

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 (280); 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
SourceBMP
m³ CH₄/t VS		TemperatureSampleCurve
Yan et al. (2021) DOI214—Chinese yam (Dioscorea polystachya) – Wholeend point (model curve)
Ge et al. (2014) DOI34537 °C · mesophilicsweet Potatoend point (model curve)
Weighted mean280arithmetic mean 280, SD 93

Typical composition

Dry matter (DM)
35.5% (range 35.5–35.5)
Volatile solids (VS)
95.4 % DM (range 93.1–97.6)
Nitrogen
1.3 % DM
C/N ratio
34.9

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: BCBPD, MY-D); dry matter: 1 determination, volatile solids: 2 determinations. C/N was calculated as the ratio of C and N content (% DM) from the same source. DM from a single determination – indicative value.

Sources: Yan et al. (2021); Ge et al. (2014).

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

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.

No published process studies

The literature we use does not describe the advantages or drawbacks of digesting this substrate beyond the BMP test results. Below are process characteristics assigned on the basis of the type of material — an editorial classification, not a study result.

easily degradable
sugars, starch, glycerol → fast hydrolysis and acidification (VFA), needs buffering
carbon-rich
high C/N → nitrogen deficiency; combine well with nitrogen-rich substrates
low in nitrogen
high C/N → nitrogen deficiency; combine well with nitrogen-rich substrates
poor in trace elements
poor in trace elements — mono-digestion requires supplementation
seasonal
seasonal availability — requires storage

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

Dosing

No source limits on the dose for this substrate.

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

Sources of the process data

  1. Improvement of fruit and vegetable waste anaerobic digestion performance and stability with co-substrates addition
  2. Biochemical methane potential and biodegradability of complex organic substrates
  3. Compositional components and methane production potential of typical vegetable wastes
  4. Biogas energy production from tropical biomass wastes by anaerobic digestion
  5. Lab-scale anaerobic digestion of cassava peels: the first step of energy recovery from cassava waste and water hyacinth
  6. Effects of size and thermophilic pre-hydrolysis of banana peel during anaerobic digestion, and biomethanation potential of key tropical fruit wastes
  7. Effect of particle size on biogas generation from biomass residues

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

What it is and where it comes from

Sweet potatoes (Ipomoea batatas) and Chinese yam (Dioscorea polystachya) are plants grown for their tubers, eaten as vegetables or processed. In a biogas plant they may appear as waste from processing or sorting, or as a product that does not meet commercial standards. In Poland these are niche crops and imported goods, so this is rather an occasional stream.

Properties relevant to digestion

Tubers contain mainly starch and sugars and little lignin and fibre, so they hydrolyse readily. A high rate of degradation means a risk of sudden fatty acid production, so dosing should be gradual. Raw tubers have a compact structure, but the soft tissues size-reduce well. The protein content is moderate, which reduces the risk of excess ammonia.

How to read the spread of results

The entry describes two different species from several studies, so the differences do not result from measurement error. The results are affected by the variety (starch content), the degree of ripeness, the share of peel, size reduction, the test conditions and the method of conversion to volatile solids. In one record the temperature is not stated in the compilation, which makes it harder to assess comparability.

In biogas plant practice

Tropical tubers rarely form a regular stream. If waste does appear, it is used as an energy additive to the mix, in the same way as potatoes. Size reduction, pH control and a gradual increase in dose must be remembered. Spoiled tubers may be contaminated with soil, which increases the amount of sediment in the tank.

From a planning perspective, it is worth remembering that tubers have a high feed and food value, so using them as an energy substrate generally concerns only waste or batches that do not meet quality standards. A small number of records is too few to determine a typical value for the whole group, so in practice a BMP test on the specific batch and monitoring of the rate of digester acidification are needed.

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 = 0.245 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

  1. Yan, H.; Cai, F.; Wang, L.; Chen, C.; Liu, G. (2021). Compositional components and methane production potential of typical vegetable wastes. Environmental Science and Pollution Research 28(38), 54177–54186. DOI: 10.1007/s11356-021-15798-y DOI
  2. Ge, X.; Matsumoto, T.; Keith, L.; Li, Y. (2014). Biogas energy production from tropical biomass wastes by anaerobic digestion. Bioresource Technology 169, 38–44. DOI: 10.1016/j.biortech.2014.06.067 DOI

All sources of the site: bibliography.

Other substrates in the group “Fruit, vegetables and their residues”