characteristics for processing biomass to fuels, ensuring that coproducts from lipid-extracted algae are safe for use, and minimizing downstream effects of water-soluble toxins. Human and Animal Pathogens in Algal Cultivation Systems

Cultivated Spirulina, Chlorella, and Haematococcus have been used to produce foodgrade products, and the presence of pathogens has not been a concern. However, algal production systems are diverse communities that may contain pathogens particularly if municipal wastewater, wastewater from concentrated animal feeding operations (CAFOs), biosolids (sewage sludge), or manures are used as water or nutrient supplies. Although the algal cultivation systems using wastewater are similar to the thousands of algal wastewater ponds in the United States, different occupational exposures might arise because the algal biomass being handled in algal biofuel production is larger in quantity (that is, higher sludge mass in algae cultivation for fuels than in algal wastewater pond) and higher in concentration (from harvesting and drying before processing to fuels). The density and probability of particular pathogens in wastewater is related to the level of treatment, with greater pathogen numbers and diversity in primary treated sewage than secondary treatment. Primary treatment is the sedimentation of solids, secondary treatment is the removal of suspended and dissolved organic materials, and tertiary treatment is the removal of inorganic constituents such as nitrogen and phosphorus. Biosolids (sewage sludge), for example, may include bacterial, viral, protozoan, or helminth pathogens (EPA, 2011b). In a study of mesophilic anaerobic digested biosolids from 18 locations in the United States, Clostridium perfringens, Shigella, Campylobacter, Salmonella, enteric viruses, and adenoviruses were detected, but Ascaris and Escherichia coli 0157:H7 were not. The original wastewater would be expected to contain at least these species. In another study of treated wastewater and biosolids in Michigan, adenovirus, enterovirus, and norovirus were detected in 100, 70, and 10 percent of samples, respectively (Simmons and Xagoraraki, 2011). The taxonomic identities and abundances of pathogens in biosolids (and by extension, wastewater) are determined by the incidence of infection within the wastewater-generating community and the particular wastewater treatment process used (Straub, 1993; EPA, 2011b). Survival of some pathogens from biosolids in soil has been studied (Zerzghi et al., 2009), but the survival of human and animal pathogens in algal biofuel cultures is only beginning to be investigated.

Where pathogens are present in algal cultures, there could be occupational health effects or environmental effects (if release occurs). The presence of fecal coliforms or other pathogens would limit the options for coproducts.

5.10.2 Comparison of Pathways

The key difference in pathways is that photobioreactors are less likely to be colonized by toxin-producing strains than open ponds (Table 5-11).

5.10.3 Opportunities for Mitigation

Selecting strains known not to produce toxins will mitigate toxin concerns in closed systems and aid in mitigating toxin concerns for open systems, though toxins could be

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