Utilization of cyanobacteria in photobioreactors for orthophosphate removal from water.

The effectiveness of photosynthetic free-living and polyurethane foam (PU) immobilized Anabaena variabilis cells for removal of orthophosphate (P) from water in batch cultures and in a photobioreactor was studied. Immobilization in PU foams was found to have a positive effect on P uptake by cyanobacteria in batch cultures. The efficiency of P uptake by immobilized cells was higher than by free-living cells. A laboratory scale photobioreactor was constructed for removal of P from water by the immobilized cyanobacteria. The photobioreactor was designed so that the growth medium (water) from a reservoir was pumped through a photobioreactor column with immobilized cyanobacteria and back to the reservoir. This created a closed system in which it was possible to measure P uptake. No leakage of cells into the photobioreactor medium reservoir was observed during the operation. The immobilized cells incorporated into a photobioreactor column removed P continuously for about 15 d. No measurable uptake was demonstrated after this period. Orthophosphate uptake efficiency of 88-92% was achieved by the photobioreactor.

Spiral tubular bioreactors for hydrogen production by photosynthetic microorganisms : design and operation.

Spiral tubular bioreactors were constructed out of transparent PVC tubing for H2 production applications. Both a cyanobacterial Anabaena variabilis mutant that lacks uptake hydrogenase activity and the photosynthetic bacterium Rhodobacter sp. CBS were tested in the bioreactors. Continuous H2 photoproduction at an average rate of 19 mL min-2.h-1 was observed using the A. variabilis mutant under an air atmosphere (without argon sparging or application of a partial vacuum). The cyanobacterial photobioreactor was run continuously for over one month with an average efficiency of light energy conversion to H2 of 1.4%. Another H2-producing approach employed a unique type of activity found in a strain of photosynthetic bacteria that shifts CO (and H2O) into H2 (and CO2) in darkness. Continuous dark H2 production by Rhodobacter sp. CBS from CO (in anticipation of using synthesis gas as the future substrate) at rates up to 140 mL . g cdw-1 . h-1 was observed in a bubble-train bioreactor for more than 10 d.

The potential applications of cyanobacterial photosynthesis for clean technologies.

Natural photosynthesis may be adapted to advantage in the development of clean energy technologies. Efficient biocatalysts that can be used in solar energy conversion technologies are the cyanobacteria. Photobioreactors incorporating cyanobacteria have been used to demonstrate (a) the production of hydrogen gas, (b) the assimilation of CO2 with the production of algal biomass, (c) the excretion of ammonium, and (d) the removal of nitrate and phosphate from contaminated waters.