Abstract
Microalgae offer great potential as a third-generation biofuel feedstock, especially when grown on wastewater, as they have the dual application for wastewater treatment and as a biomass feedstock for biofuel production. The potential for growth on wastewater centrate was evaluated for forty microalgae strains from fresh (11), brackish (11), or saltwater (18) genera. Generally, freshwater strains were able to grow at high concentrations of centrate, with two strains, Neochloris pseudostigmata and N. conjuncta, demonstrating growth at up to 40% v/v centrate. Fourteen of eighteen salt water Dunaliella strains also demonstrated growth in centrate concentrations at or above 40% v/v. Lipid profiles of freshwater strains with high-centrate tolerance were determined using gas chromatography-mass spectrometry (GC-MS) and compared against those obtained on cells grown on defined maintenance media. The major lipid compounds were found to be palmitic (16:0), oleic (18:1), and linoleic (18:2) acids for all freshwater strains grown on either centrate or their respective maintenance medium. These results demonstrate the highly concentrated wastewater can be used to grow microalgae, which limits the need to dilute wastewater prior to algal production. In addition, the algae produced generate lipids suitable for biodiesel or green diesel production.
Highlights
The world’s demand for petroleum fuels continues to grow even as supplies dwindle
The brackish water Nannochloropsis strains had a lower centrate tolerance, with growth observed at a maximum of 14% v/v centrate for five strains and two strains unable to grow in the presence of any centrate
Forty microalgae species were screened for tolerance; two freshwater species were found to grow in up to 40% v/v centrate and multiple saltwater species could grow in up to 50% v/v centrate when supplemented with sea salt
Summary
There has been a strong push to develop alternative energy sources to help supplement or potentially replace fossil fuels. Wind turbines and photovoltaic technologies offer renewable sources of electric power; liquid fuels for the transportation sector make up more than 70% of the energy consumed in US (Forsberg, 2009). Biofuels have great potential to help fill this need, and there has been significant research in this area. First- and second-generation liquid biofuels, such as corn ethanol and soy biodiesel, have received considerable interest and resources in the last 20 years, and are considered technically mature. Third-generation biofuels, such as lignocellulosics and microalgae, not as technologically advanced, hold great promise as sustainable biofuels because they avoid the food versus fuel debate that has plagued corn and soy-based biofuels. As part of the Renewable Fuel Standard II, the US government has tapped the third-generation biofuels for 21 × 109 barrels/year of fuel by 2022, with 4 × 109 barrels/year of that coming from non-cellulosic
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