Saskia John

Methane production from glycolate excreting algae as a new concept in the production of biofuels.

It is the aim of the present work to introduce a new concept for methane production by the interaction of a glycolate-excreting alga (Chlamydomonas reinhardtii) and methanogenic microbes operating in separate compartments within one photobioreactor. This approach requires a minimum number of metabolic steps to convert light energy to methane thereby reducing the energetic and financial costs of biomass formation, harvest and refinement. In this feasibility study it is shown that the physiological limitations for sustained glycolate production can be circumvented by the use of C. reinhardtii mutants whose carbon concentrating mechanisms or glycolate dehydrogenase are suppressed. The results also demonstrate that methanogenic microbes are able to thrive on glycolate as single carbon source for a long time period, delivering biogas composed of CO(2)/methane with only very minor contamination.

Model fundamentals for the design of three-phase loop reactors

Loop reactors under multi phase operation are distinguished by low-maintenance and usually economically and ecologically advantageous operating conditions and thus have abroad spectrum of applications in chemical as well as biotechnological industries. Nevertheless, the design of these reactors is currently based on in accurate physical and mathematical models. The interactions found in three-phase flows, which can result, e.g., in both an increase and a decrease in gas-void fraction due to an increase in solids-void fraction, have been explained phenomeno logically in recent experiments and a reschematically shown in Fig. 1.

Improved model for the calculation of homogeneous gas-liquid flows

The research project presented below gives a detailed explanation of the phenomenon of an increased relative velocity between gas and liquid phase in bubbly flows. It points out the conditions under which classical models for the description of two-phase flows tend to predict higher gas hold-ups than those determined experimentally, and explains the underlying physical relations. The cause for the increased relative velocity is an interactive effect of the bubble wakes on the shapes and trajectories of other bubbles. The experimental facilities of this research project which allowed the simultaneous observation of integral and local effects under a broad range of operating conditions are described in detail. p]A model for the calculation of the relative velocity in homogeneous bubbly two-phase flows is presented. It overcomes deficiencies of classical models which do not consider the mutual effects of swarm turbulence, gashold-up,bubble shape and size on the relative velocity. Based on observations of the shape and trajectories of single bubbles under swarm conditions ane xtension to the model, which includes further parameters of the liquid phase, is proposed.