BMP testingAlgae and aquatic plants

Scenedesmus obliquus — BMP: 5 studies, weighted mean 207 m³ CH₄/t VS

Scenedesmus obliquus (Tetradesmus obliquus) is a freshwater green alga with a cell wall containing resistant algaenan; results depend on cell disruption, temperature and cultivation.

CH₄ ≈ 58 % (estimate)

Published 26 March 2020Updated 29 October 20263 min readFeedstockData Editorial Team

Illustration: FeedstockData (AI, Google Gemini)

Weighted mean: 207m³ CH₄/t VS
Range: 35–332m³ CH₄/t VS
Records: 5studies
Publications: 3sources
Temperatures: 33 °C, 38 °C, 54 °Cof the test

Methane in biogas

≈55–62% CH₄

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 5 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 (207); 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

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Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Fermoso et al. (2016) DOI	332	—	Scenedesmus obliquus	end point (model curve)
Jankowska et al. (2017) · 1 DOI	35	38 °C · mesophilic	(orig.: “Scenedesmus obliquus”): value quoted in a literature review · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Jankowska et al. (2017) · 2 DOI	130	33 °C · mesophilic	(orig.: “Scenedesmus obliquus”): value quoted in a literature review	end point (model curve)
Jankowska et al. (2017) · 3 DOI	170	54 °C · thermophilic	(orig.: “Scenedesmus obliquus”): value quoted in a literature review	end point (model curve)
Mussgnug et al. (2010) DOI	178	38 °C · mesophilic	Scenedesmus obliquus	end point (model curve)
Weighted mean	207	arithmetic mean 169, SD 107

Process properties

protein-rich
nitrogen-rich
dilutes the feed (low DM)
slowly degrading
variable composition
editorial classification

Advantages

Methane yield in the compendium: median 170 (range 35–332) m³ CH₄/t VS, 5 records from 3 papers (weighted mean 207).

Drawbacks and risks

Scenedesmus obliquus digested inefficiently (approx. half the biogas obtained from Chlamydomonas reinhardtii) (Mussgnug et al. (2010))
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))

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

combines well
substrates: carbon-rich — e.g. Wheat straw, Maize silage (whole crop), Cereal straw (unspecified), Willow (short rotation), Cardboard and paperboard
The low C/N of algal sludge was balanced by the addition of paper: 50-60% VS of paper increased the rate of methane production, optimum C/N 20-25.^[1][2]
caution
substrates: nitrogen-rich — e.g. Pig slurry, Poultry manure, Waste activated sludge (secondary sludge), Chlorella vulgaris, Nannochloropsis salina
Algal protein releases ammonia; additional nitrogen sources increase the risk of ammonia inhibition.^[2][3]

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

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

What it is and where it comes from

Scenedesmus obliquus, now also classified in the genera Acutodesmus or Tetradesmus, is a unicellular green alga forming colonies of several cells. It occurs in fresh waters and is widely used in research on wastewater treatment and biofuels. It is cultivated in ponds and photobioreactors. It is not used as a biogas plant substrate, and the values come from laboratory studies and a review.

Properties relevant to digestion

The cell wall of Scenedesmus contains a layer of a resistant algaenan-type biopolymer, which greatly hinders hydrolysis. Without cell disruption, conversion is therefore low, and pretreatment (thermal, mechanical, enzymatic) improves the result. The biomass has a relatively high protein content, so the C/N ratio is low and there is a risk of ammonia. The content of lipids and starch varies with cultivation conditions. At thermophilic temperature hydrolysis proceeds faster, but sensitivity to ammonia also increases.

How to read the spread of results

The records include tests at several temperatures, including thermophilic, and samples with different preparation. The results depend on the strain, cultivation conditions, growth phase, cell disruption, the substrate-to-inoculum ratio, test length and inoculum adaptation. Some records are quoted from a review, without a full description of the conditions, which limits comparability. With a small number of records the spread is wide, and low values often correspond to intact cells or unfavourable conditions.

In biogas plant practice

Scenedesmus obliquus is not a biogas plant substrate. When it arises as biomass at a wastewater treatment plant or biorefinery, its digestion requires cell disruption and combination with substrates of higher C/N. The nitrogen load should be limited to avoid ammonia accumulation. The cost of cultivating and concentrating the biomass remains an economic barrier. The legal status depends on the origin of the biomass and the permits of the plant.

It is worth adding that, owing to changes in classification, the same organism is described in the literature under different names (Scenedesmus, Acutodesmus, Tetradesmus obliquus), which makes it harder to search for data. These names have been gathered in one entry so that the results are not scattered between synonyms.

If the biomass comes from a treatment plant, its composition also changes with the time of year and with illumination, which is a further source of variability.

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

All sources of the site: bibliography.