Bench-top to Raceway Scale Cultivation of Geothermal Microalgal Consortia
AuthorBywaters, Kathryn Faye
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Studies have highlighted the potential, and also the challenges, associated with culturing microalgae for commercial/industrial purposes. The potential for high production rates for microalgae have been demonstrated; challenges have also been recognized such as, economic feasibility and environmental controls. The focus of most algal based culturing has been on unialgal strains, even though maintaining unialgal stains during mass culturing is challenging. The potential of algal consortia, a possible alternative to unialgal strains, for production purposes has yet to be established. Studies are necessary that investigate the potential of consortia. Three lines of inquiry were conducted on microalgal consortia investigating production capabilities.The first study investigated growing native microalgal consortia for biomass production, in association with geothermal resources - which has the potential to mitigate the negative impacts of seasonally low temperatures. This study assessed community composition, growth rates, biomass and neutral lipid production of microalgal consortia obtained from geothermal hot springs in the Great Basin/Nevada area, that were cultured under different thermal and light conditions. Biomass production (368 to 3246 mg C L-1 d-1) was within the upper limits of those reported for individual strains, and production of neutral lipids was increased with secondary treatment - all results demonstrate a potential of culturing and manipulating microalgal consortia for biomass-based energy production and perhaps even for biofuels.The second study investigated the relation between microalgae and cyanobacteria consortia in tailored geothermal media from a cost verses benefit perspective (cost of nutrient additions verses the biomass yields). The biomass yields and stability of community composition were evaluated for geothermal, microaglal consortia cultured in various media (five different standard algal culturing media, just nitrogen and/or phosphorus addition, as well as basal geothermal water). Nutrient inputs averaged $32.09 per gram of ash free dry mass (AFDM); with the most cost effective being $1.16 per gram of AFDM. The third study looked at biomass production rates from a laboratory-to-field scale and the potential effects of environmental fluctuation on production (i.e. temperature and light). Production was evaluated as AFDM, carbon, and chlorophyll a (chla). The effects of temperature were evaluated at the field scale (5000 L raceway pond) by heated (8 - 29% increase in water temperature) verses non-heated raceway, in an attempt to mitigate the negative impacts of seasonal and diurnal temperature fluctuations. A 72-75% increase in production was seen when the raceway that was heated verses non-heated.