Hydrogen production by Anabaena variabilis PK84 under simulated outdoor conditions

Hydrogen production by autotrophic, vanadium-grown cells of Anabaena variab ilis PK84, a cyanobacterial mutant impaired in the utilization of molecular hydrogen, has been studied under simulated outdoor conditions. The cyanoba cterium was cultivated in an automated helical tubular photobioreactor (4.3 5 L) under air containing 2% CO2, with alternating 12-h light (36 degrees C ) and 12-h dark (14 degrees to 30 degrees C) periods. A. variabilis steadil y produced H-2 directly in the photobioreactor during continuous cultivatio n for 2.5 months. The maximum H-2 production by the continuously aerated cu lture under light of 332 mu E . s(-1) . m(-2) was 230 mL per 12-h light per iod per photobioreactor and was observed at a growth density corresponding to 3.6 to 4.6 mu g Chl a . mL(-1) (1.2 to 1.6 mg dry weight mL(-1)). Replac ement of air with an argon atmosphere enhanced H-2 evolution by a factor of 2. This stimulatory effect was caused mainly by N-2 deprivation in the cel l suspension. A short-term decrease of the CO2 concentration in the air sup pressed H-2 evolution. Anoxygenic conditions over the dark periods had a ne gative effect on H-2 production. The peculiarity of hydrogen production and some physiological characteristics of A. variabilis PK84 during cultivatio n in the photobioreactor under a light-dark regime are investigated. (C) 20 00 John Wiley & Sons, Inc.