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BMP testingStraws and crop residues

Cotton stalks — BMP: 2 studies, weighted mean 82 m³ CH₄/t VS

Cotton stalks are a woody residue left after fibre harvest in tropical and subtropical crops. Not available in Poland; in the dataset they are described by two studies from Turkey and China.

CH₄ ≈ 51 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo USDA NRCS Texas / Wikimedia Commons, public domain, source file; changes: cropping

Weighted mean
82m³ CH₄/t VS
Range
71–94m³ CH₄/t VS
Records
2studies
Publications
2sources
Temperatures
37 °Cof the test

Methane in biogas

Low methane content · ≈ 5.1 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 0.5 % 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

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 2 studies

Weighted mean Individual records

BMP curves: Cotton stalksCumulative methane production over time for 2 records and the weighted mean of 82 m³ CH₄/t VS. 2 of the curves are model curves (first-order kinetics).0255075100051015202530time [d]m³ CH₄/t VSÖZBAYRAM i İNCE (2021): 71 m³ CH₄/t VS (model curve)Zhang et al. (2018): 94 m³ CH₄/t VS (model curve)mean82

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 (82); 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
ÖZBAYRAM i İNCE (2021) DOI7137 °C · mesophiliccotton stalkend point (model curve)
Zhang et al. (2018) DOI94—Cotton stalk (Gossypium herbaceum)end point (model curve)
Weighted mean82arithmetic mean 82, SD 16

Typical composition

Volatile solids (VS)
96.9 % DM (range 96.9–96.9)
Nitrogen
0.5 % DM
C/N ratio
96.8

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: BCBPD); dry matter: 0 determinations, volatile solids: 1 determination. C/N was calculated as the ratio of C and N content (% DM) from the same source. No DM in the sources – the calculator has to ask for a value.

Sources: Zhang 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

  • fibrous
  • slowly degrading
  • carbon-rich
  • low in nitrogen
  • seasonal
  • editorial classification

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.

Advantages

  • Methane potential in the database: weighted mean 82 m³ CH₄/t VS (median 82; range 71-94; 2 records from 2 sources).

Drawbacks and risks

  • Heavily lignified lignocellulosic material requires pretreatment to increase the availability of cellulose (Hendriks 2009).
  • Spread of results in the database: standard deviation 16 at a mean of 82 m³ CH₄/t VS (2 records from 2 sources).

Dosing

No source dose limits; this is not an attractive digestion substrate without pretreatment.

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”).

Sources of the process data

  1. ÖZBAYRAM, E.G.; İNCE, O. (2021) Comparative Assessment of Biogas Production Potential of the Most Abundant Agro-residues in Turkey. Deu Muhendislik Fakultesi Fen ve Muhendislik 23(68), 547–555
  2. Zhang, H.; Khalid, H.; Li, W.; He, Y.; Liu, G.; Chen, C. (2018) Employing response surface methodology (RSM) to improve methane production from cotton stalk. Environmental Science and Pollution Research 25(8), 7618–7624
  3. Dahunsi, S. (2019) Mechanical pretreatment of lignocelluloses for enhanced biogas production: Methane yield prediction from biomass structural components. Bioresource Technology 280, 18–26
  4. Hendriks, A.T.W.M.; Zeeman, G. (2009) Pretreatments to enhance the digestibility of lignocellulosic biomass. Bioresource Technology
  5. Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
  6. FNR (2010). Guía sobre el Biogás – Desde la producción hasta el uso (hiszp. wydanie „Leitfaden Biogas”, GIZ 2013)

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

What it is and where it comes from

Cotton stalks are the woody shoots of cotton plants left after the fibre is harvested. They arise in large quantities in cotton-growing countries, including in Asia and the Mediterranean region. They are usually removed from the field because they hinder subsequent operations, and are used as fuel or burned in the field. Methane fermentation is being considered as an alternative. The material does not occur in Poland, so it is of mainly comparative interest.

Properties relevant to digestion

Cotton stalks are stiff and woody, with a high content of lignin and cellulose and a low content of protein. This results in slow decomposition and a high C/N ratio. The raw material is dry once it has dried out in the field, but before digestion it requires very thorough size reduction, because coarse fragments hardly degrade within a typical retention time. For this reason pretreatment is often described in the literature, but the records in this dataset concern material without it. Pesticide residues are also possible, as these are sometimes applied intensively in cotton growing.

How to read the spread of results

The dataset contains several records from several different studies: including a record from Turkey, carried out in the AMPTS II system at a specified inoculum-to-substrate ratio, and a record from China, with no temperature stated. They differ not only in the material, but also in the gas measurement method, sample preparation, inoculum and test duration. The cotton species, plant age and growing conditions also have an effect. With so little data, the spread does not describe the full variability and cannot be transferred to other regions.

In biogas plant practice

For Polish biogas plants, cotton stalks are not a practical substrate. In cotton-growing countries their use after shredding, in a mixture with animal manure, is being considered, the greatest limitation being the cost of obtaining and shredding them, as well as competition from combustion. Anyone considering their use should run their own BMP test on material from the specific source and take the content of mineral impurities into account. For the same reason, no conclusions should be drawn about possible results for other woody plant residues, such as maize or reed stalks, because each of these materials has a different structure and a different course of decomposition.

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 = 0.136 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. ÖZBAYRAM, E.G.; İNCE, O. (2021). Comparative Assessment of Biogas Production Potential of the Most Abundant Agro-residues in Turkey. Deu Muhendislik Fakultesi Fen ve Muhendislik 23(68), 547–555. DOI: 10.21205/deufmd.2021236817 DOI
  2. Zhang, H.; Khalid, H.; Li, W.; He, Y.; Liu, G.; Chen, C. (2018). Employing response surface methodology (RSM) to improve methane production from cotton stalk. Environmental Science and Pollution Research 25(8), 7618–7624. DOI: 10.1007/s11356-017-0682-y DOI

All sources of the site: bibliography.

Other substrates in the group “Straws and crop residues”