Patent ID: 6254778
Filing Date: 2001-07-03
Classification: C02F,Y02W

Abstract:
A biological process for purifying waste water in order to produce an effluent with a low content of carbon and of oxygenated nitrogen compounds, the process comprising the steps:mixing the waste water in a biological reactor with activated sludge to denitrify the resulting mixture;introducing air into the mixture to form an anoxic sludge thereby directly oxidizing carbon present in the anoxic sludge and removing carbon therefrom, simultaneous with the denitrification;clarifying the anoxic sludge to separate it from a denitrified intermediate effluent;recycling the clarified anoxic sludge to the biological reactor;nitrifying the intermediate effluent to form a nitrified liquor;recycling a portion of the nitrified liquor into the anoxic sludge that is present in the biological reactor, thereby subjecting the anoxic sludge to oxygen present in nitrified compounds and consequently further removing carbon from the anoxic sludge, simultaneous with the denitrification;controlling a rate of removal of carbon as a function of the flow rate/pollution characteristics of the anoxic sludge;continuously measuring a redox potential of the anoxic sludge;continuously measuring a nitrate concentration of the intermediate effluent;adjusting an amount of air introduced into the anoxic sludge in accordance with the measured redox potential and measured nitrate concentration; andadjusting a recycling flow rate of the nitrified liquor in accordance with the measured redox potential and measured nitrate concentration; andproviding the remaining nitrified liquor as the final effluent.