Evaluation of conversion efficiency of light to hydrogen energy by Anabaena variabilis

Cyanobacteria provide an efficient system for producing H₂ from water using solar energy. The energy conversion efficiency can be defined by the ratio of H₂ produced to the light energy absorbed. An IR and opalescent plate method was used to measure the light energy absorbed. Since cyanobacteria absorb light in the visible range but not in the infrared range, the net amount of light energy absorbed by the cells can be estimated by measuring the IR and visible light intensities transmitted through the biochamber. A rectangular biochamber was used for measuring the conversion efficiency from light energy to H₂ energy. A quantum meter and radiometer were used to measure the light intensity transmitted through the chamber. Anabaena variabilis was cultured in a BG11 medium with 3.6 mM NaNO ₃ and the light intensity was 40-50 μ mol / m² / s in the growth phase and 120-140 μ mol / m² / s in the H₂ production phase. The maximum H₂ production was 50 ml for 40 h and cell density was 1.2 g/l. The H₂ production rate was 4.1 ml H₂ / g dry cell weight/h. Based on the light absorbed in the H₂ production phase, the energy conversion efficiency from light to H₂ was 1.5% on average and 3.9% at the maximum. Based on the light energy absorbed in the cell growth and H₂ production phases, the energy conversion efficiency was 1.1% on average.