BMP testingAlgae and aquatic plants

Chlorella kessleri — BMP: 2 studies, weighted mean 193 m³ CH₄/t VS

Chlorella kessleri (now Parachlorella kessleri) is a green freshwater alga with a rigid wall, the treatment of which affects the availability of the cells for digestion.

CH₄ ≈ 58 % (estimate)

Published 13 May 2020Updated 29 October 20263 min readFeedstockData Editorial Team

Illustration: FeedstockData (AI, Google Gemini)

Weighted mean: 193m³ CH₄/t VS
Range: 168–218m³ CH₄/t VS
Records: 2studies
Publications: 2sources
Temperatures: 38 °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 2 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 (193); 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

Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Jankowska et al. (2017) DOI	168	38 °C · mesophilic	(orig.: “Chlorella kessleri”): value quoted in a literature review · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Mussgnug et al. (2010) DOI	218	38 °C · mesophilic	Chlorella kessleri	end point (model curve)
Weighted mean	193	arithmetic mean 193, SD 35

Process properties

protein-rich
nitrogen-rich
dilutes the feed (low DM)
slowly degrading
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 193 (range 168-218) m³ CH₄/t VS, 2 records from 2 studies (weighted mean 193).

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))

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

Chlorella kessleri, now referred to as Parachlorella kessleri, is a unicellular green freshwater alga. It is studied as a source of lipids, protein and biomass for biofuels, and in laboratory studies it is grown in photobioreactors or tanks. It is not a commercial substrate for biogas plants, and the BMP data come from scientific papers, of which one value is quoted in a review.

Properties relevant to digestion

Chlorella cells have a rigid cell wall with layers built of polysaccharides, and in some strains also of a resistant biopolymer of the algaenan type. Such a wall limits access of enzymes to the interior of the cell, so disruption of the cells (mechanical, thermal or enzymatic) usually improves the digestion result. Protein predominates in the dry matter, followed by carbohydrates and lipids, and the proportions depend on the growing conditions. A low C/N ratio means a risk of ammonia, particularly when digesting algal biomass alone at a high load. The ash content can be elevated in cultures in mineral media.

How to read the spread of results

Records coming from different sources differ in the strain and the method of cultivation, and also in the form of the sample: fresh suspension, centrifuged or dried biomass. The composition of algae depends strongly on the growth phase and on the presence of nitrogen in the medium: nitrogen-deficient cultures contain more lipids and starch and less protein, which increases the methane potential. Disruption of the cell wall, temperature, test duration and adaptation of the inoculum also have an effect. Values quoted in reviews do not always have a full description of conditions.

In biogas plant practice

Chlorella kessleri is not used in agricultural biogas plants. It has practical significance for concepts in which algal biomass is obtained as a by-product of wastewater treatment or of a biorefinery. In such a case it is worth digesting it together with a substrate of low nitrogen content (for example straw, or waste rich in carbohydrates) in order to balance the C/N ratio. Cell disruption improves conversion, but increases the energy cost. Legal requirements depend on the origin of the biomass, including whether it arose in a wastewater treatment plant.

For plant designers it is also important that the cost of producing algal biomass is many times higher than the cost of typical agricultural substrates. Methane fermentation therefore makes sense mainly as a way of utilising residues or biomass from wastewater treatment, not as an end in itself.

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.