Continuous Hydrogen Production by Rhodobacter sphaeroides O.U.001

Abstract

This paper describes hydrogen gas production by Rhodobacter sphaeroides O.U.001 using a column photobioreactor in batch and continuous operation. The effect of substrates on the hydrogen production rate was investigated in batch-type photobioreactor experiments. Substrate concentrations (L-malic acid and sodium glutamate) were measured by using high-pressure liquid chromatography. The gas produced was analyzed by gas chromatography.

In order to achieve prolonged and stable hydrogen production, pH, cell, and substrate concentrations (L-malic acid and sodium glutamate) were maintained within a certain range by periodically diluting the culture with fresh feed. Optimum conditions obtained in a previous study (150-mL volume) were applied to a photobioreactor having an inner volume of 400 mL. Light and dark period cycles were applied to simulate outdoor conditions. After every 100 h, the feed containing 100 mL of fresh medium replaced the same volume of culture removed. In some experiments, after every 100 h, 100 mL of growth medium and 30 mL culture grown overnight (fresh inoculation) replaced the same volume of culture removed. In operations without fresh inoculation to the medium, hydrogen evolution ceased after 25 days; however, by adding fresh medium, 3.6 L of gas was evolved in 70 days.

In conclusion, the L-malic acid to sodium glutamate concentration ratio and cell concentration are important factors affecting the hydrogen production rate. In this regard, the amount of feed and time intervals of the dilution must be optimized for a continuous system.