Publications

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Algae can be cultivated in open or closed bioreactors. Open bioreactors are defined as any reactor that is exposed to the environment. These reactors can take many different forms, but most conform to one of the following broad categories: shallow lagoons and ponds, inclined cascade systems, circular central pivot ponds, mixed ponds, and raceway ponds (Borowitzka and Moheimani 2013). While these ponds are configured differently in terms of their construction, lining, means of propulsion/ mixing, and intensity of management, they all share the common element of being fully exposed to the external environment. Research on how to successfully cultivate microalgae using open systems was initiated in the late 1940s and early 1950s in the United States, Germany, and Japan (Cook 1950; Gummert et al. 1953; Mituya et al. 1953). While significant progress has been made over the intervening decades, the open pond systems still face serious challenges that stem from being exposed to unpredictable and uncontrollable meteorological conditions, suboptimal mixing within the culture, and exposure to many forms of contamination. These problems limit productivity, nutrient utilization efficiency, and performance stability. Despite these challenges, open ponds continue to be used and developed primarily because they are cheaper and easier to scale, build, and operate when compared to closed photobioreactors (Sheehan et al. 1998; Waltz 2009).

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The following trade study was done to answer the following task from the Sandia JPL Collaboration for Europa Lander Statement of Work: Survey SNL capabilities for modeling the transport and survivability of biological organisms in extremely hot, cold, and high radiation environments.

The following trade study was done to answer the following task from the Sandia JPL Collaboration for Europa Lander Statement of Work: Perform a trade study to assess the feasibility of other sterilization/decontamination methods for reducing forward biological contamination on S/C and assess their suitability for PP applications

One of the major challenges to achieving high rates of long-term production in microalgal mass cultures is the elimination or reduction of the impact of biocontamination and culture losses (i.e., crashes) in production systems. Although there are both biotic and abiotic root causes of mass culture crashes, infection by deleterious organisms is the most important and least understood. In general, the diversity of pathogens, parasites, predators, and competing algal species (or weed species) has not been well characterized. Lost production days due to pond crashes can significantly lower annual production yields. In addition, depending on the 184scale and type of system, days to weeks of production can be lost while the system is disinfected and new inoculum and the growth medium is prepared. Depending on the design and operation of the production facility, there is a risk of spread or persistence of contamination and successive crashes. Despite a paucity of publically available data on the economic impact of biocontaminants on the nascent algae biomass industry, the consensus is that they constitute an economic barrier to commercialization (Davis et al. 2012; Gao et al. 2012). Some insight into the potential magnitude of the financial impact may be gained from the aquaculture-for-food industry, which loses several billion U.S. dollars annually (Subasinghe et al. 2001; FAO 2010) due to bacterial and fungal infections (Defoirdt et al. 2004; Ding and Ma 2005; Ramaiah 2006).

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Productivity of algal mass culture can be severely reduced by contaminating organisms. It is, therefore, important to identify contaminants, determine their effect on productivity and, ultimately, develop countermeasures against such contamination. In the present study we utilized microbiome analysis by second-generation sequencing of small subunit rRNA genes to characterize the predator and pathogen burden of open raceway cultures of Nannochloropsis salina. Samples were analyzed from replicate raceways before and after crashes. In one culture cycle, we identified two algivorous species, the rotifer Brachionus and gastrotrich Chaetonotus, the presence of which may have contributed to the loss of algal biomass. In the second culture cycle, the raceways were treated with hypochlorite in an unsuccessful attempt to interdict the crash. Our analyses were shown to be an effective strategy for the identification of the biological contaminants and the characterization of intervention strategies.