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BMP testingAlgae and aquatic plants

Dunaliella salina — BMP: 3 studies, weighted mean 221 m³ CH₄/t VS

Dunaliella salina is a halophilic green alga without a rigid cell wall; it brings a lot of salt into the digester, which can inhibit methanogenic microorganisms.

CH₄ ≈ 58 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo Terry J. McGenity i in. / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean
221m³ CH₄/t VS
Range
63–323m³ CH₄/t VS
Records
3studies
Publications
3sources
Temperatures
38 °Cof the test

Methane in biogas

Medium methane content · ≈ 5.8 kWh/m³ of biogas

estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (protein-rich (process classification)) 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

BMP curves: Dunaliella salinaCumulative methane production over time for 3 records and the weighted mean of 221 m³ CH₄/t VS. 3 of the curves are model curves (first-order kinetics).01002003004000510152025303540time [d]m³ CH₄/t VSFermoso et al. (2016): 63 m³ CH₄/t VS (model curve)Mussgnug et al. (2010): 323 m³ CH₄/t VS (model curve)Roberts et al. (2019): 276 m³ CH₄/t VS (model curve)mean221

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 (221); 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
Fermoso et al. (2016) DOI63—Dunaliella salinaend point (model curve)
Mussgnug et al. (2010) DOI32338 °C · mesophilicDunaliella salinaend point (model curve)
Roberts et al. (2019) DOI27638 °C · mesophilicDunaliella sp.end point (model curve)
Weighted mean221arithmetic mean 221, SD 139

Typical composition

Volatile solids (VS)
50.4 % DM (range 50.4–50.4)

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: MY-D); dry matter: 0 determinations, volatile solids: 1 determination. No DM in the sources – the calculator has to ask for a value.

Sources: Roberts et al. (2019).

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

  • protein-rich
  • nitrogen-rich
  • saline
  • dilutes the feed (low DM)
  • variable composition
  • 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 yield in the compendium: median 276 (range 63-323) m³ CH₄/t VS, 3 records from 3 studies (weighted mean 221).

Drawbacks and risks

  • The high protein content of the cells causes release of ammonia, which can be toxic to the process (Sialve et al. (2009); Rajagopal et al. (2013))
  • The presence of sodium in marine species may impair digester operation (Sialve et al. (2009))

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).

Practical requirements

  • Do not dry the biomass before feeding: drying lowered biogas production to about 80% (Mussgnug et al. (2010))
  • Monitor ammonia (high protein) and, for marine species, sodium (Sialve et al. (2009))

Sources of the process data

  1. Anaerobic co-digestion of algal sludge and waste paper to produce methane
  2. Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable
  3. A critical review on inhibition of anaerobic digestion process by excess ammonia
  4. Screening of biomethane production potential from dominant microalgae
  5. Microalgae as substrates for fermentative biogas production in a combined biorefinery concept
  6. Semi-continuous anaerobic digestion of the marine micro-algal species I. galbana and D. salina grown under low and high sulphate conditions

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

What it is and where it comes from

Dunaliella salina is a unicellular green alga living in waters of very high salinity, for example in salt lakes and brines. It is grown commercially mainly to obtain beta-carotene. In the dataset, one study concerned samples described as Dunaliella sp., but the title of the publication indicated D. salina, so the records were assigned to that species. Algal biomass after carotenoid extraction may be a by-product.

Properties relevant to digestion

Dunaliella cells have no rigid cell wall, only an elastic envelope, so after death they are readily accessible to enzymes. The composition of the biomass depends on the growing conditions: under salt and light stress the content of carotenoids and glycerol, which is readily assimilable, rises. The main problem is salt: the biomass comes from a medium with a high concentration of sodium chloride, and sodium ions at a high concentration inhibit many microorganisms, including methanogenic archaea. In addition, protein may release ammonia. Adaptation of the inoculum to salinity improves results.

How to read the spread of results

The records come from different studies and may have concerned biomass grown at different salinities and at different stages of processing. The salinity of the sample, its washing before the test, the growth phase and the presence of glycerol and carotenoids must be taken into account, because they affect the result. In addition, temperature, the substrate-to-inoculum ratio and adaptation of the bacteria to salt are significant. With a small number of records the spread does not describe the full variability of the species.

In biogas plant practice

Dunaliella salina is not a biogas plant substrate. If it arises as a residue after carotenoid extraction, the key factor is the salt concentration in the suspension: it may require dilution or mixing with other substrates. An installation working with waste of high salinity needs an inoculum adapted to salt, or operation at a lower load. Legal requirements depend on the origin and status of the biomass and on the installation's permits.

It is worth noting that high salinity is also an advantage in another sense: cultivation in salt water limits the risk of contamination by other organisms. However, this does not solve the problem of salt in the digester, which must be solved at the stage of biomass preparation.

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

  1. Fermoso, F.G.; Beltran, C.; Jimenez, A.; Fernández, M.J.; Rincón, B.; Borja, R.; Jeison, D. (2016). Screening of biomethane production potential from dominant microalgae. Journal of Environmental Science and Health, Part A 51(12), 1062–1067. DOI: 10.1080/10934529.2016.1198627 DOI
  2. Mussgnug, J.; Klassen, V.; Schlüter, A.; Kruse, O. (2010). Microalgae as substrates for fermentative biogas production in a combined biorefinery concept. Journal of Biotechnology 150(1), 51–56. DOI: 10.1016/j.jbiotec.2010.07.030 DOI
  3. Roberts, K.P.; Heaven, S.; Banks, C.J. (2019). Semi-continuous anaerobic digestion of the marine micro-algal species I. galbana and D. salina grown under low and high sulphate conditions. Algal Research 41, 101564. DOI: 10.1016/j.algal.2019.101564 DOI

All sources of the site: bibliography.

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