A biological reactor for growing a biological mass has a tank with an interior for growing the biological mass, a plate movable in a substantially vertical direction and an interior of the tank, and a valve means provided with the plate and configured so that in a lower position of the plate the valve means are open, so that during displacement of the plate upwardly and downwardly, a solution in the interior of the tank is thoroughly fixed, while an upper position of the plate, the valve means are closed and the plate during movement downwardly provides a collection of a concentrated solution to be removed from the tank.