Process development for hydrogen production with Chlamydomonas reinhardtii based on growth and product formation kinetics.

Certain strains of microalgae are long known to produce hydrogen under anaerobic conditions. In Chlamydomonas reinhardtii the oxygen-sensitive hydrogenase enzyme recombines electrons from the chloroplast electron transport chain with protons to form molecular hydrogen directly inside the chloroplast. A sustained hydrogen production can be obtained under low sulfur conditions in C. reinhardtii, reducing the net oxygen evolution by reducing the photosystem II activity and thereby overcoming the inhibition of the hydrogenases. The development of specially adapted hydrogen production strains led to higher yields and optimized biological process preconditions. So far sustainable hydrogen production required a complete exchange of the growth medium to establish sulfur-deprived conditions after biomass growth. In this work we demonstrate the transition from the biomass growth phase to the hydrogen production phase in a single batch culture only by exact dosage of sulfur. This eliminates the elaborate and energy intensive solid-liquid separation step and establishes a process strategy to proceed further versus large scale production. This strategy has been applied to determine light dependent biomass growth and hydrogen production kinetics to assess the potential of H2 production with C. reinhardtii as a basis for scale up and further process optimization.

Harvesting fresh water and marine algae by magnetic separation: screening of separation parameters and high gradient magnetic filtration.

In this study, the focus is on magnetic separation of fresh water algae Chlamydomonas reinhardtii and Chlorella vulgaris as well as marine algae Phaeodactylum tricornutum and Nannochloropsis salina by means of silica-coated magnetic particles. Due to their small size and low biomass concentrations, harvesting algae by conventional methods is often inefficient and cost-consuming. Magnetic separation is a powerful tool to capture algae by adsorption to submicron-sized magnetic particles. Hereby, separation efficiency depends on parameters such as particle concentration, pH and medium composition. Separation efficiencies of >95% were obtained for all algae while maximum particle loads of 30 and 77 g/g were measured for C. reinhardtii and P. tricornutum at pH 8 and 12, respectively. This study highlights the potential of silica-coated magnetic particles for the removal of fresh water and marine algae by high gradient magnetic filtration and provides critical discussion on future improvements.

Developments and perspectives of photobioreactors for biofuel production.

The production of biofuels from microalgae requires efficient photobioreactors in order to meet the tight constraints of energy efficiency and economic profitability. Current cultivation systems are designed for high-value products rather than for mass production of cheap energy carriers. Future bioreactors will imply innovative solutions in terms of energy efficiency, light and gas transfer or attainable biomass concentration to lower the energy demand and cut down production costs. A new generation of highly developed reactor designs demonstrates the enormous potential of photobioreactors. However, a net energy production with microalgae remains challenging. Therefore, it is essential to review all aspects and production steps for optimization potential. This includes a custom process design according to production organism, desired product and production site. Moreover, the potential of microalgae to synthesize valuable products additionally to the energetic use can be integrated into a production concept as well as waste streams for carbon supply or temperature control.