Abstract: A continuous process by which waste water containing low to high concentrations of organic constituents and total nitrogen is biologically purified to such an extent that the organic constituents are minimized, the content of total nitrogen is completely nitrified, if it exceeds the assimilation demand, and the nitrate formed is reduced by aerating the waste water or exposing it to oxygen while not exceeding a preselected redox potential. In the subject process, the expenditure on the oxygen introduction and the expenditure on the denitrification are minimized. Further, the amount of excess sludge produced is extremely small.

Abstract: The invention concerns a process for the aeration of industrial and commercial effluents in equalizing and reservoir basins before the effluent is cleaned in a conventional biological treatment plant. The aeration is conducted at a low redox potential, favorably attained by controlling the rate of aeration in dependence on the redox potential, as the set point and thereby keeping the redox potential at a constant value. Furthermore the addition of minimum substances, if necessary, can be conducted in dependence on the redox potential and the intensity of the aeration.