SOLAR HYDROGEN PROJECT Biophotolytic Hydrogen Production

1. SOLAR HYDROGEN PROJECT Biophotolytic Hydrogen Production B. Tamburic*, K. Hellgardt, G. C. Maitland, F. W. Zemichael Department of Chemical Engineering, Imperial College London, SW7 2AZ, UK *bojan.tamburic@ic.ac.uk • Why Solar Hydrogen? • With the decline in reserves and increasing concern over fossil fuel use, there is a demand for an alternative energy carrier that is CLEAN, RENEWABLE and AVAILABLE • HYDROGEN can be the solution – but only if it is produced by a SUSTAINABLE process • Aim is to generate carbon-free hydrogenusing unlimited resources – SUNLIGHT and WATER • Imperial College project, funded at £4.2M by EPSRC • Unique multidisciplinary approach from genetic engineering to reactor and system design Scientific Background • The green alga Chlamydomonas reinhardtii has the ability to photosynthetically produce molecular hydrogen under anaerobic conditions (Fig.1) : • Photons are absorbed within the chloroplasts of C.reinhardtii • This facilitates photochemical oxidation of water by photosystem II (PSII) proteins • The hydrogenase (H2ase) enzyme catalyses the process of proton and electron recombination to produce H2 • Hydrogenase activity is inhibited in the presence of O2 • Sulphur deprivation of C.reinhardtii reduces photosynthetic O2 production below the level of respiratory O2 consumption, thus creating an anaerobic environment and leading to sustained H2 production (Fig.4) Fig.1 Photosynthetic electron transport chain during anaerobic H2 production in C.reinhardtii H2 Production Photobioreactor Design • Measurement • Products identified using injection mass spectrometry • Gas phase H2 production measured by water displacement • Dissolved oxygen/hydrogen content measured with reversible Clark electrode • Dissolved gas extracted using a H2-permeable membrane and analysed with a mass spectrometer • Algal Growth • Control the light intensity, pH, agitation and temperature of the system (Fig.2) • Minimise the risk of contamination by using filters and sterilisation procedures • Measure optical density of culture Fig.2 AquaMedic® culture reactors facilitate C.reinhardtii growth • Sulphur deprivation • Cycle the algal growth medium by: • Extracting algal cells by centrifugation/ultrafiltration • Heavily diluting the growing culture with a sulphur-replete medium • Controlling sulphur content through better understanding of process kinetics (Fig.3) Fig.4 H2 production commences once anaerobic conditions have been established • Optimisation • Increase H2 production rate (Fig.4) by: • Controlling light intensity and algal optical density • Improving light penetration • Preventing H2 diffusion leaks Fig.3 Sartorius® photobioreactor used to investigate growth and H2 production kinetics Conclusion This project links genetic approaches to reactor design and engineering, demonstrating the power of using an integrated, cross-disciplinary approach to address the challenge of carbon-free H2 production. Improvements in H2 production efficiency and bioreactor design may allow hydrogen to fulfil its potential as the sustainable fuel of the future.