Professor of chemical engineering Peter Pfromm, one of the authors of the study about algae biodiesel production. (Photo: K-State/Stock File/FIS)
Algae biodiesel production impractical: study
Wednesday, April 13, 2011, 23:50 (GMT + 9)
Kansas State University researchers have cautioned that making petroleum diesel completely eco-friendly would both defy the laws of physics and be excessively expensive.
A K-State interdisciplinary team including professor of chemical engineering Peter Pfromm analysed algae diesel production. Its first algae-related nonprofit study, "Sustainability of algae derived biodiesel: A mass balance approach," was published in Bioresource Technology.
The team applied a carbon mass balance to measure the sustainability of algae diesel production and determined that mass conservation and especially a closed carbon mass balance must be maintained for the production and consumption system to be sustainable, Pfromm said.
Then, the researchers created a mass flowchart with carbon as a tracer and followed it through the algae diesel system, checking for use of non-sustainable resources like oil and gas and ensured CO2 was not released into the atmosphere. Such a facility creates biomass mainly from CO2, and this carbon flow must be balanced out to obtain sustainability, Pfromm said.
"The inflow must equal the outflow if we want to be sustainable," he explained. "Without this, our production cycle won't last for decades ─ or even centuries ─ and will instead deplete resources that can't be renewed and degrade our planet."
The study focused on the science and technology of algae biodiesel and showed that technically, producing algae-based biodiesel sustainably will not eliminate dependence on petroleum diesel. Under the most optimistic conditions, the amount of algae diesel produced per day paled in comparison to the ideal quantities of 200-500g per sqm of open pond per day because not enough sunlight comes through the atmosphere to support these figures, Pfromm told.
Using a more realistic number of 50g per sqm per day, the team found it would take 11 sqmi of open ponds making 14,000 tonnes of algae daily to replace 50 million gal of petroleum diesel per annum ─ just 0.1 per cent of the US yearly diesel consumption.
"The end result is the yield isn't that high because we can either stress the algae to produce more oil or let them reproduce very efficiently ─ not both," Pfromm said.
Economics will be tackled in a follow-up study.
"Once money is involved, technological sustainability becomes theoretical because nobody is going to use the technology or science unless there's an incentive," Pfromm said. "For investors and most of the industrial world, the incentive is going to come with a dollar sign. But if it takes 20 years before anyone starts making a buck in profit, no one's going to back it."
While open ponds are the cheapest containment unit for the endeavor, a facility spanning 11 sqmi in size is expensive, Pfromm noted, and the ponds are susceptible to algae-eating organisms or microorganisms spread by the wind; various other aspects of these facilities also have a steep overhead.
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By Natalia Real