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: 3
Is there a preliminary estimate of the cost per unit biomass undergoing this harvesting, dewatering, and
drying process? The concern here is that the proposed process would prove to be utterly uneconomical.
Reviewer: 4
Overall Impression: 4
The researchers should begin by projecting the cost and energy consumption of these devices based on
other applications. Then estimate the needed decrease in cost/energy to make algae biofuels feasible. How
does that estimate compare with the best conceivable outcome from the research? This is an obvious
starting point for any applied research. Presumably this exercise was done at the proposal stage, but it still
needs to be shown to project reviewers. As it stands, these interesting technologies and the planned
research could make progress for various industrial and water treatment applications. It is unlikely they
will have a place in affordable algae biofuels production. Discuss this with one of the TEA teams and
look in the TEA literature.
Reviewer: 5
My impression is that the presenter had a technology that "he can make work"for this particular
application. Will this be an objective analysis? However, it appeared that some critical homework on
energy estimates on spin-tech units had not been performed at the outset. Results will be of very limited
applicability unless most of the tests use actual effluents from full-scale raceways.
Reviewer: 6
It appears to be a technology worth having a look at provided energy balances are executed.
Reviewer: 7
The project could benefit from definition of commercial performance criteria for various harvesting and
dewatering scenarios. Process specifications should include feed stream characteristics, separation
efficiency metrics, capacity requirements at scale, operating costs and capital cost. Characterization of
algae slurries at various states of de-watering may be useful, especially rheological analysis. High internal
moisture and high viscosities will be significant hurdles that can be partially defined by rheology.
Presenter Response
We appreciate the reviewer’s acknowledgement of the useful aspects of the project. We want to direct the
reviewer’s attention to the statement early on in the presentation that this is an “analytic evaluation of
cross flow filtration for harvesting/dewatering algae.” In that statement is the fact that there are a variety
of cross flow filtration configurations each with its own inherent advantages, disadvantages, and
limitations – thus the presentation of the levels of instantaneous face velocities in the presentation is an
attempt to justify the fact that once we understand the mechanistic aspects of the membrane fouling
caused by the presence of the algae, we will then be able to design an appropriate set of cross flow
membrane unit operations to accomplish the task. Something that the literature has virtually no references
that answer this basic question. At no time was it meant for the presentation to come across as a “machine
looking for a job”. The spinning membrane unit is only a single component in the entire system that will
be designed to dewater the algae to the economically viable level. Data for our preliminary cost estimates
for processing 12 M gal water/algae were obtained through discussions with industry leaders (Millipore,
Koch Membranes. Scenario 1) includes a floatation system and rotator system with 80% and 95%
recovery rates, respectively and a conservative assumption that filtration membranes will be replaced
every year. We anticipate an operational cost of $2.06 x 10E-5 per gallon for the filtration process or
$246.90. Scenario 2) includes same assumptions as above but without the rotary membrane and assuming
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