Abstract: System and method are provided for treating materials in a liquid in a pool having a bottom, using at least one of a stirring device, a brushing device and a wiping device, and an automatic moving arrangement configured for moving any of these devices in the pool. The stirring device comprises at least one wing having a longitudinal axis and at least two bottom contacting elements spaced from each other along the longitudinal axis of the wing so that, when the wing is in such close proximity to the bottom of the pool that the contacting elements contact its bottom, the contact of the wing with the bottom is prevented by the contacting elements.

Abstract: A method of growing photosynthetic organisms comprising providing the organisms with flue gases from a fossil-fuel power plant, the gases being previously treated by desulfurization. The carbon dioxide (CO2) concentration of the flue gases may be increased over the CO2 concentration as released from the power plant. Also disclosed is a method for producing ? fatty acids and bio-fuels comprising growing microalgae by providing said microalgae with flue gases from a fossil-fuel power plant.