The present paper is aimed at describing a “closed cycle” power plant schematic (SOFT, Solar Oxygen Fuel Turbine) with macroalgae (seaweed) cultivation in a pond, combustion of its organic matter in a fluidized bed boiler of Rankine cycle and return of the combustion products to the pond to feed algae. The oxygen used for combustion is released to atmosphere in photosynthesis. As a renewable fuel for combustion after drying the seaweed Ulva lactuca is selected. Its growth rate from many experiments (in literature) is 0.1 – 0.2 1/day, heating value of dry weight is 19 MJ/kg, optimal concentration in salty water 1: 1000. Energy efficiency is less than in photovoltaics but energy expenditures to construct the pond as solar energy receiver are much less, it gives some economic benefits. The present paper highlights the interest of immediate combustion of the dried biomass fuel without converting it in liquid transportation fuel. The latter is the cause of additional technological problems and energy losses.

This study assessed the role of picocyanobacterial photosynthesis in the induction of calcite precipitation. It aimed at establishing whether photosynthetic uptake of bicarbonate by Synechoccoccus cells leads to calcite nucleation. The precipitation of calcite was initiated by addition of previously washed cyanobacterial cells of Synechococcus strain PCC 7942 to solutions of calcium carbonate at different saturation levels with respect to calcite. Precipitation experiments were performed under controlled laboratory conditions in two set-ups: one in which photosynthesis was inhibited using a herbicide called Diuron and the other one in which photosynthesis was taking place. During the experiments, a pH meter monitored the pH and ion selective electrodes monitored concentrations of carbonate and calcium ions. The morphology of the precipitated crystals was analysed using Scanning Electron Microscopy. When the kinetics of calcium carbonate nucleation by the Synechococcus cells were compared for the two sets of experiments, there were very little differences. In fact, the induction times for precipitation reactions with photosynthesis were shorter due to the uptake of carbon dioxide. It is therefore ‘ concluded that photosynthesis does not directly influence the nucleationof calcite at the surface of Synechococcus cells with sufficient supply of carbon dioxide, i.e. cells took up carbon dioxide and not bicarbonate.The microscopic observations, however, provided some evidence that picocyanobacterial cell walls act as a template for calcite nucleation.