The method for the mass cultivation of planktonic algae/bacteria mixed culture in open, flat round basins (1) for biomass production and/or sewage cleaning, comprises obtaining periodically floating components for the cultivation of algae bacteria mixed cultivations over a central overflow (8), extracting the deposited fractions over a lower removal point (9) on height of the funnel bottom (2), obtaining the algae-bacteria fraction over a middle sampling point lying between the upper and the lower sampling points and then recycling in the peripheral of the basin without the surplus biomass. The method for the mass cultivation of planktonic algae/bacteria mixed culture in open, flat round basins (1) for biomass production and/or sewage cleaning, comprises obtaining periodically floating components for the cultivation of planktonic algae bacteria mixed cultivations over a central overflow (8), extracting the deposited fractions over a lower removal point (9) on height of the funnel bottom (2), obtaining the planktonic algae-bacteria fraction over a middle sampling point lying between the upper and the lower sampling points and then recycling in the peripheral of the basin without the produced surplus biomass. The basins are provided with shield chamber mechanisms (3) under peripheral supply of nutritive solutions and a central discharge funnel with three sampling points. The fermented residue or digested sludge from local or industrial anaerobic treatment plants are peripherally supplied to the algae basins and then the biomass fraction is reached in central funnels, from which it is removed and then led back into the anaerobic treatment plant. The plankton surplus amount is washed to the preparation for the usage in the anaerobic treatment plant into a fermented residue fraction. The clear water fraction is washed by the fermenting residue of a putrefying plant and then the fermenting residue is promoted back to putrefying plant. The sedimentable algae biomass is flu
