In order to produce the vast amounts of fuel needed by the United States, and the rest of the world, there will be a demand for massive quantities of biomass to be grown. This could be problematic when using terrestrial biomass, since in most cases, growing plants would re­quire a switch from using land for food sources to energy sources. An alternative source of biomass, however, is available in the form of aquatic and marine species of biomass such as kelps, algae, and other types of water borne plants or bacteria. Aquatic and marine biomass (excluding bacteria) are typically plant-like in that they are autotrophic organisms that con­tain photosynthetic pigmentation, can utilize inorganic carbon for biomass development, and express molecular oxygen as a byproduct. However, these organisms do not suffer from the inherent liability of requiring fertile soil to grow, minimizing competition with the food supply chain. Also, as microscopic organisms, they do not require abundance of land to de­velop root systems and large floral brush in order to absorb sunlight and nutrients, and therefore, a much more effective utilization of space. With rapid growth rates that can typi­cally double in concentration in less than a day, it is possible to have daily harvests, creating a steady and abundant supply of biomass for harvesting. As such, marine and aquatic bio­mass can be a useful alternative source of biomass that can be used to produce a wide range of biofuels for commercial use, while avoiding several of the more common pitfalls associat­ed with more traditional sources of terrestrial biomass, and thus, will be the biomass focus of discussion for the remainder of this article.

Primarily, growth of algae for the production of oils and energy conversion has focused on microalgae, including species of diatoms and cyanobacteria (as opposed to macroalgae, such as seaweed), although some bacterial species (such as Clostridium sp.) have been demonstrat­ed for production of biologically derived hydrogen and methane [4]. To date, there have been numerous studies of algae and other water based biomass in order to identify strong candidates for biomass accumulation rates as well as lipid content for production of biodie­sel. Some strains are summarized for these characteristics in Table 2. There is also a wealth of microbial biomass resources available as a by-product of industrial activities such as sew­age treatment, brewing industries and food processing that could provide biomass or nu­trients for further microbial biomass growth [5, 6]. With this concept, it is feasible to use algae as a means for tertiary wastewater treatment in order to utilize trace nutrients such as phosphorous — and nitrogen-containing compounds, or can be used at industrial processes as a way to absorb carbon dioxide by entraining algal cultures to gaseous exhaust streams.

Growth of aquatic and marine biomass is not without challenges though. Maximum growth rates of the microorganisms typically occur under very specific conditions, and any variance on these conditions can cause substantial delays in biomass development. Also, open pond algal systems (which are common for algae production due to their ease of construction and inexpense) are susceptible to contamination from various airborne microorganisms that can decrease overall productivity. And of prime concern, is the ability to separate algae from water, which due to their very dilute nature, can be expensive and inefficient. Several meth­ods are used to do this, such as flocculation with chemicals (such as hydroxides or alum) or electric fields, filtration, centrifugation, or thermal drying, but each of these methods is not without bulky equipment, expensive materials, or long processing times.