Process for Aeration of Effluents in Equalizing and Reservoir Basins

The invention concerns a process for the aeration of industrial effluents in an equalizing and reservoir basin.

By known aeration processes with low oxygen supply, which are carried out in the reservoir and equalizing basins in order to prevent decay only a degradation of 10%, up to 20% at most, is reached automatically, whereas sludge is generated by excessive oxygen charging. This should be avoided because of the high cost of sludge disposal.

It is an object of this invention to disclose an aeration process that achieves higher degradation values without production of activated sludge. This is achieved by conducting the aeration in a way that flocculation is avoided and the bacteria remain as individuals.

The process according to this invention is characterized in that the aeration is carried out at a negative range of redox potential, preferably at -200 mV to -500 mV.

It was determined that after sufficient adaption time at strongly reduced aeration a biozoenose is formed which can consume up to 50% of the organic effluent waste load present when the formation of bacterium flakes usually occuring in the biological effluent purification is avoided, as the bacteria remain as individuals. A growth of pathogenic strains did not occur.

Furthermore, it was surprisingly found that under the conditions of the process the oxygen transfer values increase significantly. With a commercial aeration equipment, whose oxygen transfer performance, determined in pure water, was 20 kg O.sub.2 /hrs, performances of approximately 40 kg O.sub.2 /hrs were reached at equal current usage, at a water depth of 3 meters and a current consumption of 18 kW.

If one aerates a basin according to the procedure of this invention, the organic waste loads which are delivered to a subsequent biological treatment are significantly reduced. Therefore, the addition of oxygen which is much more costly in biological treatment is reduced and the production of excess sludge, whose disposal is 65-75% of the cost of a conventional activated sludge plant, is diminished.

In the procedure of the invention, the biomass adjusts the pH to the value of approximately 7 even if the pH values of the inflowing effluent vary between 4 and 11 during the day, averaging between 5 and 8.

The process according to the invention is therefore applicable also for the aeration of waste water with strongly varying pH-values.

After the already mentioned adaptation time with diminished aeration, the redox potential during continuous operation is kept at a constant value in the range between -200 to -500 mV, preferably in the range -200 mV to -300 mV. The nearer to the value of -200 mV the procedure is conducted, the more important it is to keep the redox potential at a constant value to avoid flocculation. (The redox potentials mentioned here are given in values from a measuring apparatus Fa. Ingold, Pt-4825-60.)

The concentration of the bacteriae is very low, about 200 to 300 mg/l. The formation of new biomass is low too, about 0,23 kg per kg COD degraded.

According to this invention the aeration is controlled in dependence from the deviation of the actual redox potential from the predetermined value.

It is advisable to use a computer, which, according to the predetermined set point of the redox potential, controls the on/off switch of the aerators. The computer is continuously fed with the actual value of the redox potential. Moreover, the aeration equipments are reversed in a certain sequence, when they are not in full speed, so that all parts of the basin are totally mixed.

As usual, the addition of minimum substances, if necessary, normally phosphate in industrial effluents, is done in such amounts that the losses of biomass which are caused by dilution are compensated. The addition can be controlled, too in dependence on the redox potential and/or the operating time of the aerators. In this case, too, it is advisable to use a computer.

The control is achieved in such a way that, if the redox potential drops under the predetermined set point even though the aeration equiment is fully used, the concentration of bacteria is lowered by diminuation of the minimum substance. The addition of minimum substance is increased when the efficiency of the aeration equipment drops too much when the redox potential is kept at the predetermined value.

Redox potential, intensity of aeration, minimum substance addition, and concentration of biomass influence each other and must be considered during the adjustment. In the procedure according to the invention, the redox potential is the primary reference value.