Analysis of Compensation Point of Light Using Plane-Type Photosynthetic Bioreactor

Abstract

Five cylindrical, plane-type, photosynthetic bioreactors of different depths (1, 3, 5, 10, and 20 cm) were used to examine the effect of reactor depth with agitation on hydrogen production using Rhodobacter sphaeroides RV and artificial waste water. This batch test was performed with simulated solar energy using halogen lamps. The irradiation pattern was a sine curve of light_12h/dark_12h cycle with a peak value of 1 kW/m². Investigation of the effects of depth showed that the rate of hydrogen production decreased and organic acid concentration increased as reactor depth increased. This was probably due to the increasing effect of the dark zone. Under dark conditions and with strong agitation of the gas/liquid phase in the 1-cm deep reactor, the uptake rate of hydrogen was 100 mL H₂/g dry cell weight/day. Hydrogen production and uptake were occurring and balancing in the photosynthetic bioreactor. The light compensation point using a plane-type photosynthetic bioreactor with agitation was about 102 MJ/m³ culture/day. Thus, an important factor to be considered for scaling-up photosynthetic bioreactors is the penetration of light into the cell culture and the absence of a dark zone in the reactor.