Jul 1, 2012
Journal name not available for this finding
The green alga Chlamydomonas reinhardtii has the ability to produce molecular hydrogen (H2) through the biophotolysis of water under anaerobic conditions. The aim of this thesis was to improve our understanding of the growth and H2 production of Chlamydomonas reinhardtii in order to develop a continuous and practical biophotolytic H2 production process. A novel flat-plate photobioreactor was designed to facilitate green algal growth and H2 production at the laboratory scale and to measure key process parameters under controlled conditions. Membrane Inlet Mass Spectrometry was developed to measure H2 production rates in situ. In order to achieve effective H2 production, it was necessary to grow dense and healthy Chlamydomonas reinhardtii cultures. Favourable algal growth conditions included a temperature of 25°C, continuous illumination at 5-100 W·m-2 and photomixotrophic growth conditions. Optimum photoautotrophic growth was measured at a carbon dioxide concentration of 11%. Photosaturation of Chlamydomonas reinhardtii occurred at 273 W·m-2 and photoinhibition at 600 W·m-2. A reactor-independent nutrient control technique was developed by optimising the sulphate and acetate concentrations in the Chlamydomonas reinhardtii growth medium. It enabled a fully grown algal culture to spontaneously achieve anaerobic H2 production. A maximum H2 production rate of 1.52 mlH2·l-1·h-1 and a H2 yield of 119.8 mlH2·l-1 were measured. The sulphur dilution technique proved effective at encouraging cyclic H2 production, resulting in alternating Chlamydomonas reinhardtii recovery and H2 production stages. Chlamydomonas reinhardtii cultures produced H2 at an average rate as high as 0.4 mlH2·l-1·h-1 under a series of consecutive 95% dilutions. These complementary approaches have demonstrated that engineering advances can lead to improvements in the scalability and affordability of biophotolytic H2 production, giving increased confidence that H2 can fulfil its potential as a sustainable fuel of the future.