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Nannochloropsis oculata — BMP: 3 studies, weighted mean 240 m³ CH₄/t VS

Nannochloropsis oculata is a marine microalga grown for lipids and omega-3 acids; its resistant cell wall requires disruption in order to increase conversion.

CH₄ ≈ 58 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo CSIRO, CSIRO / Wikimedia Commons, licence CC BY 3.0, source file; changes: cropping

Weighted mean
240m³ CH₄/t VS
Range
210–290m³ CH₄/t VS
Records
3studies
Publications
2sources
Temperatures
37 °C, 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: Nannochloropsis oculataCumulative methane production over time for 3 records and the weighted mean of 240 m³ CH₄/t VS. 3 of the curves are model curves (first-order kinetics).01002003004000510152025303540time [d]m³ CH₄/t VSJankowska et al. (2017) · 1: 210 m³ CH₄/t VS (model curve)Jankowska et al. (2017) · 2: 290 m³ CH₄/t VS (model curve)Roberts et al. (2019): 231 m³ CH₄/t VS (model curve)mean240

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 (240); 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
Jankowska et al. (2017) · 1 DOI21037 °C · mesophilic(orig.: “Nanochloropsis oculata”): value quoted in a literature reviewend point (model curve)
Jankowska et al. (2017) · 2 DOI29037 °C · mesophilic(orig.: “Nanochloropsis oculata”): value quoted in a literature review · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)end point (model curve)
Roberts et al. (2019) DOI23138 °C · mesophilicN. occulataend point (model curve)
Weighted mean240arithmetic mean 244, SD 42

Typical composition

Volatile solids (VS)
80.3 % DM (range 80.3–80.3)

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 231 (range 210–290) m³ CH₄/t VS, 3 records from 2 papers (weighted mean 240).

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. Biogas from microalgae: Review on microalgae's cultivation, harvesting and pretreatment for anaerobic digestion
  5. Semi-continuous anaerobic digestion of the marine micro-algal species I. galbana and D. salina grown under low and high sulphate conditions
  6. Microalgae as substrates for fermentative biogas production in a combined biorefinery concept

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

What it is and where it comes from

Nannochloropsis oculata is a unicellular marine microalga, widely grown as live feed for fish and crustacean larvae and studied as a source of lipids and omega-3 fatty acids. It is cultivated in tanks and photobioreactors at marine salinity. It is not a biogas plant substrate, and the BMP results come from laboratory studies, including a review.

Properties relevant to digestion

The cells have a wall containing a resistant biopolymer (algaenan) and cellulose, which means that without cell disruption conversion is limited. The biomass is rich in lipids, and lipids have a high methane potential, but long-chain fatty acids at high concentration inhibit acetogenic bacteria and archaea. Protein contributes nitrogen and an ammonia risk. The marine origin means that the biomass may contain salt from the culture medium, which at a large share in the mixture inhibits methanogenesis. The lipid content depends strongly on the growing conditions.

How to read the spread of results

The records concern biomass of differing degrees of processing and come from different studies. The result is affected by the strain, the growing conditions (light; nitrogen deficiency increases the lipid share), the growth phase, salt washing, the form of the sample (fresh, freeze-dried, after cell disruption), temperature and the substrate-to-inoculum ratio. Some records are values cited in a review, with a simplified description of conditions, so they cannot be regarded as fully comparable.

In biogas plant practice

Nannochloropsis oculata is not used in biogas plants. As a residue after processing (e.g. after lipid extraction) it can be an interesting substrate for a biorefinery. If the biomass goes into the digester, the important points are desalination or dilution, cell disruption and moderate loading because of ammonia and LCFA. Legal requirements depend on the origin and status of the biomass.

It should be added that this species is cultivated on an industrial scale mainly in aquaculture, so the availability of biomass as a waste is limited. Real use in digestion is limited to residues after processing and to laboratory-scale research.

From the operator's point of view it is also important that algal biomass usually occurs as a dilute suspension, and its thickening requires energy.

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. Jankowska, E.; Sahu, A.K.; Oleskowicz-Popiel, P. (2017). Biogas from microalgae: Review on microalgae's cultivation, harvesting and pretreatment for anaerobic digestion. Renewable and Sustainable Energy Reviews 75, 692–709. DOI: 10.1016/j.rser.2016.11.045 DOI
  2. 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.

Other substrates in the group “Algae and aquatic plants”