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Production of biofuels from aquatic species involves four steps, all of which must be completed at very low cost to achieve profitability. These steps are listed briefly below: Feedstock: Our experience indicates that the only practical way to grow aquatic species cheaply enough is with outdoor ponds or inexpensive troughs. Depending on the climate, the water may have to be heated in winter. If wastewater solids or other waste streams are used as the feedstock, the solids should ideally be concentrated or "thickened" to at least 10% solids for the most economical operation. See Feedstocks for more detail. Harvesting: If the biomass is grown as a crop, part of the process of species selection is to pick species (or genera) which are easy to harvest. This also tends to favor species which produce larger forms, as opposed to very small unicellular species which are generally harvested by expensive processes such as centrifugation. Fuel production: In the Genifuel process, fuel is produced by catalytic wet gasification. Renewable natural gas is the product gas, but carbon dioxide and various other chemicals are also produced. The output gas (containing mostly methane and carbon dioxide) may be used directly as a medium-BTU fuel (app. 620 BTU/cubic foot), or may be further processed to remove carbon dioxide and water vapor to produce pipeline-quality natural gas (app. 1020 BTU/cubic foot). Nutrients: All
photosynthetic organisms require carbon, usually in the
form of carbon dioxide. CO2
can be obtained from the atmosphere but
growth is faster if CO2
concentrations in the water are higher than they would
be with normal atmospheric exchange. In the Genifuel process, CO2
released in the gasifier is captured in the condensed
water and recycled back to the growth ponds,
accelerating biomass growth and nearly eliminating emissions.
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