A STUDY ON VARIOUS PARAMETERS AFFECTING HYDROGEN PRODUCTION OF Cyanothece 51142

The key parameters that affect Cyanothece 51142 growth kinetics were investigated and optimised. These include the light intensity, temperature, nitrogen source and growth condition – photoautotrophic and photoheterotrophic. The Cyanothece 51142 strain was shown to grow effectively using 10% volume CO2 volume air 1 – 10% CO2 and 71% N2 within the supplied gas mixture - as its carbon and nitrogen sources respectively. Even under continuous illumination, the cyanobacterium maintained its periodically alternating growth, pH and pO2 profiles, confirming light-independence of the metabolic shift behaviour. The cyanobacterial growth rate at least doubled when CO2 was replaced by glycerol or nitrate salt was supplied instead of N2. In the presence of glycerol or nitrate, the oscillating behaviour of cells no longer exists, suggesting their inhibitive nature. However, as soon as a cyanobacterial culture has consumed all of these substrates, it reinstates a diurnal cycle. With increasing light intensity, from 23 to 320 μmol/m2/s1, the photoautotrophic specific growth rate of Cyanothece 51142 strains consistently increases with no sign of photoinhibition, while there was little effect on the final biomass concentration of the culture, beyond 92 μmol/m2/s. The latter is most likely due to the significant light attenuation, induced by the dense culture. The transition from photo limitation into a saturation regime was determined to be at an average irradiance of 347 μmol/m2/s. In terms of temperature, the optimal value to cultivate Cyanothece 51142 under photoautotrophic growth conditions was found to be 350C and clear evidence of photoinhibition was detectable at 400C.