Light Penetration and Wavelength Effect on Photosynthetic Bacteria Culture for Hydrogen Production

Abstract

The penetration of light into a photobioreactor and its relation to hydrogen production were analyzed using the photosynthetic bacterium, Rhodobacter sphaeroides. Two photo-bioreactor types were used to examine hydrogen evolution at various light penetration depths: the A-type was comprised of four compartments of bacterial suspension and the B-type consisted of two cell-immobilized gels. A large portion of the incident light energy was absorbed in the upper part of the reactor. In the first compartment (0–5 mm) of the A-type reactor, 69% of the incident light energy was absorbed; 21% was absorbed in the second (5–10 mm). About 75% of the incident light energy was entrapped in the front gel of the B-type reactor. The cells in the deep parts of both reactors showed higher light energy conversion efficiencies to hydrogen, although the light spectrum reaching the cells was altered and the intensity was low. Alteration of the light spectrum and light intensity upon passage of light through the reactor greatly affected hydrogen production. Excess light energy in the shallow region reduced the total efficiency of the reactor. Light reaching the deep part of the reactor (600–780 nm) could be used effectively for hydrogen production.