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Combine wastewater treatment with biofuel production

| By Mary Page Bailey

Algae Systems LLC (Daphne, Ala.; has inaugurated a demonstration plant that integrates municipal wastewater treatment with the cultivation of biofuel-producing algae. Pretreated and disinfected municipal wastewater is passed to Algae Systems offshore floating-bag photobioreactors (PBRs), which are located in a bay off of Daphnes coast. There, the oxygen, nitrogen and phosphorous from the wastewater, along with atmospheric CO2, are mixed with and consumed by freshwater algae. This algae is then processed into what the company calls bio-crude, via hydrothermal liquefaction (HTL) — a high-temperature, high-pressure process that decomposes the biomass. The bio-crude can be converted to a variety of valuable end products. In laboratory trials, the company has shown that its algae-based bio-crude can be upgraded to diesel fuel. The company’s proprietary HTL process eliminates an energy-intensive drying step, since a partially dewatered algae slurry, rather than moisture-free biomass can be fed to the process.

Algae Systems PBRs provide a closed system where algae can flourish at a moderate ambient temperature. The bags rise and sink with the tide and the waves provide mixing. The algae that grows within the PBRs is a native, non-invasive freshwater species, so in the event of a release, it will not disrupt the bays ecosystem.

The demonstration plants PBRs presently reside on one-half acre of bay, but the company is planning to double that area in the coming months. The current wastewater-treatment capacity of the site is up to 40,000 gal/d.