was demonstrated as a fermentation substrate. Gracilaria salicornia also has been shown to be a suitable substrate for microbial fermentation to ethanol (Wang et al., 2011).

2.3.5.6 Microalgae or Macroalgae Harvested for Whole-Biomass Processing

Interest is increasing in whole-biomass conversion for processing of terrestrial biomass (Marker et al., 2010; Wright et al., 2010). Pyrolysis of whole biomass yields an upgradeable biocrude. A recent review (Anex et al., 2010) shows that these routes have cost advantages relative to other biomass conversion technologies. The material produced potentially can be used in an existing refinery, saving capital relative to other options.

Several forms of pyrolysis have been explored. Hydropyrolysis is reported to be appropriate for use in processing of algal biomass (Marker et al., 2012). The low aromatic content in algal biomass (because of the absence of lignin) is said to make algal biomass a particularly good feedstock for hydropyrolysis.

The development of two pilot-scale alternatives has been reported, both producing fossil fuel-compatible materials (Hatcher, 2011). These synthetic crudes are stated to be compatible with existing refineries. In one of the processes, fertilizer is a coproduct.

Insufficient documentation is available for a detailed mass and energy balance of the processes. It can be presumed that the detailed studies on terrestrial biomass will yield similar results when algae are the feedstock. That is, whole-cell processing provides a potentially viable means of producing drop-in replacement fuels, taking advantage of existing refinery infrastructure to reduce risk and costs.

2.3.6 Fuel Products and Coproducts

The processes described above make many potential fuel components. Table 2-7 summarizes some of the dominant inputs and outputs for the technologies described.

2.3.7 Status of Algal Biofuel Production

Algal biofuel production is rapidly evolving, and as such, any status report is outdated at the moment of its completion. There are currently no operating algal biofuel production facilities that are comparable in scale to the average capacity of about 13.5 million gallons (51 million liters) per year for U.S. biodiesel refineries, much less rivaling the largest at about 100 million gallons (378 million liters) per year (NBB, 2012). Many projects are still in the research and development phase and exact production numbers are difficult to obtain.

2.4 CONCLUSIONS

An integrated coordination of biological (for example, algal strain selection and development of algae cultivation) and engineering processes (for example, reactor design, harvesting and dewatering methods, and processing) is needed to realize the potential of algal biofuels. However, the domestication of algae poses a special challenge as investigation into key biological and ecological aspects of algal biofuel production has lagged far behind the progress in feedstock processing design, system engineering, and life-cycle analyses over the past few decades. Nonetheless, increased core understanding of algae and their potential for improvements is fundamental to accelerating the entire algal biofuel enterprise. Relative to the vast and diverse spectrum of potentially available organisms, only a narrow range of currently cultivated microalgal strains are considered for commercial production



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