Reviewer Comments - EERE

2011 Algae Platform Review – Reviewer Comments
Reviewer Comments are direct transcripts of commentary and material provided by the Platform’s
Review Panel. They have not been edited or altered by the Biomass Program.
Reviewer: 2 Criteria Score: 7
This project is considering the process of anaerobic digestion to change residual biomass to biogass
(methane and carbon dioxide) and to recycle CO2 to cultures. Three species (Nannochloropsis, Chlorella,
Phaeodactylum) are being used. This is good, because these algae are different biochemically while being
good biofuels' targets. The PI promised to share data and the project's overall approach seems sound.
Reviewer: 3 Criteria Score: 7
Biogas production will be optimized for three algal species, best conditions will be scaled up, nutrient
recycle will be explored, and results will inform TE and LCA models
Reviewer: 4 Criteria Score: 6
See Overall Impressions text.
Reviewer: 5 Criteria Score: 4
The goal is to characterize the digestion potential of extracted algal biomass and the nutrient value of the
digested effluent. Unfortunately, the approach is includes the use of lab-grown algal cultures rather than
biomass grown in pilot- or full scale systems. This seems both unnecessarily slow and potentially
irrelevant (if the experiments need to be repeated to test biomass from full-scale systems).
Reviewer: 6 Criteria Score: 5
They are doing the "right" thing in terms of the subject area, and simply address each unit operation
(growth, harvesting, dewatering, extraction....) but without new hypothesis to be tested, in the context of
the long literature history out there. Also, AD of defatted microalgae biomass will not produce much
methane (relative to CO2) unless one has added in carbon.
Reviewer: 7 Criteria Score: 5
It is highly desirable to define some specific quantitative goals based on economic and process
perfromance criteria. Sourcing of biomass from a partner is a strong positive.
Presenter Response
We have chosen the three strains of microalgae for our studies (Nannochloropsis sp., Chlorella vulgaris
UTEX395, and Phaeodactylum tricornutum) based on careful consideration. These strains sample the
extremes of genetic diversity among eukaryotic microalgae being utilized for algal biofuels development.
They are industrially relevant, but are also some of the best understood biochemically and
physiologically. This provides several advantages; for example, our own work on the analysis of the cell
wall composition of UTEX395 will be useful in designing enzymatic approaches to pretreatment. We
have obtained Nannochloropsis from a commercial source (Seambiotic). Unfortunately, we are currently
unaware of industrial sources for the other two strains. In-house cultivation allows us more control over
growth conditions and will generate sufficient biomass for the studies. Of course, we would be very
interested to hear of possible commercial sources for large quantities of biomass from these or related
species. The criticism regarding a lack of hypothesis and context is noted, and perhaps this was a failure
of the presentation. A number of technoeconomic (TE) modeling efforts, including NREL’s, have made
assumptions about the efficiency of anaerobic digestion on oil-extracted algae. Essentially, the hypothesis
that we are testing is whether those assumptions are reasonable. Andy Aden’s presentation, which
preceded this one, covered analysis of the cost of algal lipids based on scenarios that include anaerobic
digestion of algal residues after oil extraction. Inputs to the model (with current base case assumptions in
parentheses) include efficiency of carbon conversion to biogas (65%), methane content of the biogas
(40%), digester retention time (10 days), nitrogen recycle fraction (75%) and phosphorous recycle
fraction (50%). Base case assumptions are based primarily on Weissman and Goebel (1996), and are just
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