Patent EA-000912-B1 (EA)
Title: Controlling wastewater treatment by monitoring oxygen utilisation rates
Inventor: GORONSZY MERVYN CHARLES
IPC: C02F3/00
Filed: 1996-06-21
Abstract: 1. A method of treating waste material forming at least a part of a biomass comprising a single activated sludge in a variable depth bioreactor using controlled intermittent and successive aeration sequencing and liquid decantation to for the biological removal of the organic carbon, nitrogen and phosphorus components from wastewater admitted the bioreactor, opened to the atmosphere, characterized in that said bioreactor having at least two interconnected zones in series connection, wherein at least a part of the treated contents of the second zone of the reactor is transferred to the first zone for admixture with incoming influent waste simultaneously with an aeration sequence of operation of the last or second zone and continuously monitoring dissolved oxygen concentration in the biomass of the second zone at a location such that at least that part of the biomass in that location is in motion, whereby a mixture of biomass, wastewater and dissolved oxygen are introduced in the second reactor the single sensor or probe means is used to cause operation of oxygen input means during input into and aeration of the wastewater in the second reactor zone in order to operate to a set protocol of successively increasing dissolved oxygen concentration from zero to about 2.5 mg/L with the detection of the dissolved oxygen utilization rate of that biomass in the second zone, in discrete predetermined adjustable time increments to optimise the retention of adsorbed organic substance in the second and final zone of the reactor having a potential oxygen uptake rate, being in excess of about three times the measured uptake rate of the single sludge biosolids adjunctively with the introduction of air into the first zone of the reactor to partially limit the release of phosphate. 2. A method according to claim 1, characterized in that the method removes up to 40 percent of the design depth of the variable depth reactor during the decantation step at a rate that does not cause removal of settled solids from within a settled sludge layer in the reactor. 3. A method according to claim 1 or 2, characterized in that the net fluid oxidation reduction potential of the combined liquid stream passing through the initial reaction zone obtains a value less than -150 mV as compared to a hydrogen reference electrode.  4. A method according to claims 1 to 3, characterized in that up to 40 percent of the total bioreactor volume is introduced into the first zone during the time equivalent to the cycle time less the liquid removal air-on/off time sequence.  5. A method according to claims 1 to 4, characterized in that the cyclic air-on time exposure of the biomass and the amount of recycled treated waste admixed with the influent wastewater is sufficient to yield the -150 mv oxidation reduction potential in a time of less than 80 minutes. 6. A method according to claims 1 to 5, characterized in that the oxidation reduction potential of segregated sludge in the second or last reaction zone falls substantially less than -150 mV within 90 minutes into the air-off sequence.  7. A method according to claims 1 to 6, characterized in that the biomass remains in motion for up to 10 minutes after interruption of the supply of air or oxygen.  8. A method according to claims 1 to 7, characterized in that the values of dissolved oxygen concentration are automatically in situ sensed and monitored substantially continuously but not less than at intervals of 10 to 20 seconds during the total air-on and air-off sequences of each cycle. 9. A method according to claims 1 to 8, characterized in that the use of the cycles of operation are managed by the measurement of the oxygen utilisation rate in order to adjust it to appropriate values to provide for the satisfaction of reactor stoichiometric oxygen demand which permits a single air supply to alternately service one or more zones of the bioreactor.  10. A method according to claims 1 to 9, characterized in that the TKN loading on the activated sludge is up to about 0.01 kg TKN/kgMLSS/M<2>/d for typical domestic sewage applications. 11. A method according to claims 1 to 10, characterized in that the total phosphorus loading of activated sludge solids is up to about 0.002 kg Phosphorus/kgMLSS/m<2>/d for typical domestic sewage applications. 12. A method according to claims 1 to 11, characterized in that the dissolved oxygen concentration in the second or final reactor zone is controlled to less than 0.7 mg/L (average) for 75 percent of the air-on time and to between 2 and 3 mg/L for the remaining air-on time period. 13. A method according to claims 1 to 12, characterized in that it further comprises: microbially treating the wastewater in the activated sludge process in the presence of a micro-organism population acclimated to the wastewater contaminants and their concentrations in the wastewater and including nitrifying micro-organisms capable of converting ammonia nitrogen to at least nitrite nitrogen and facultative micro-organisms capable of denitrifying nitrite and optionally nitrifying organisms capable of converting nitrite to nitrate nitrogen and facultative micro-organisms capable of reducing nitrate to nitrite nitrogen to nitrogen gas and phosphorus removal micro-organisms capable of biologically removing available soluble phosphorus.  14. A method according to claims 1 to 13, characterized in that the mixed liquor solids concentration in the second reactor is sensed and recorded at the moment that the air supply to that reactor is terminated and the oxygen uptake rate is sensed, recovered and analysed following termination of the process oxygen supply and the liquid level at the time of closure of the influent valve to the reactor (plus two minutes). 15. A method according to claim 14, characterized in that the sensed process values are processed and used to determine the waste sludge pumping time, the duration of the air-on sequence for the next cycle, the mass flow rate of air for the next cycle, adjustment of the dissolved oxygen concentration set-points, such that the process conditions are sufficient to maintain the set-point oxygen uptake rate in the principal reactor determined at the end of the previous aeration sequence.  16. A method according to claims 1 to 15, characterized in that a pH correction is made to the influent wastewaters.  17. A method according to claims 1 to 16, characterized in that the set-point oxygen uptake rate is experimentally determined. 18. A method according to claim 17, characterized in that the oxygen uptake rate or measured potential oxygen uptake rate in the initial admixture reactor is at least 20 mgO2/gVSS/hr. 19. An apparatus for growing and maintaining a culture of mixed autotrophic, heterotrophic and facultative micro-organisms for the biological removal of the organic carbon, nitrogen and phosphorus components from wastewater comprising a variable depth operated bioreactor with cycling aeration, characterized in that said reactor comprises a partition separating it at least for the first and second zones which are interconnected to transfer liquid from one zone into another at least at the air intake step, an aerator for selective treatment of biomass at repeated steps during air-on and air-off sequences comprising diffused aeration grids for forming air bubbles to secure uniform agitation and transfer of oxygen, at least, in the final zone, said grids are located at floor of the reactor, and a means for directing air flow into the reactor for transfer the oxygen in the reactor, wherein said first zone is provided with an inlet for incoming influent waste, the apparatus is also provided with a valve to close waste water flow incoming into the first zone, a valve or a pump for removing liquid/solid material from last hydraulic zone into the remote location from the reactor, conduit or pipe through which part of the liquid/solid material from the last zone into the first zone having an input, a valve for closing incoming influent waste and the air flow into the reactor, a movable water overflow for reducing an amount of clarified lye forming on the surface retained in the last zone upon cessation of air-on sequence to the predetermined lower level, using a motor-driven decanting unit comprising a horizontal water gage container with an overflow with a fencing against flowing solids, including foam, said container is connected via a drainage pipe with a rotating shaft of a drum with seals to retain liquid and outlet pipes with an air gate valve, a sensor or a probe means able to measure the rate of change of dissolved oxygen concentration in the reactor in combination with calculation of the oxygen utilisation rate in biomass wherein said rate of change of dissolved oxygen concentration is measured by an oxygen detection means of dissolved oxygen is located in biomass at a location such that at least part of biomass is in motion at the time of taking the measurement, a means for analysing uptake rates of change of dissolved oxygen concentration at the end of each of air-on supply in the last zone, a means for automatic regulation of operating time of each full cycle of the successive cycle, a means for controlling and regulating following cessation of air-on sequence in successive cycles in the last zone. 20. An apparatus according to claim 19, characterized in that the last zone of the reactor is provided with diffused aeration grids for transfer of dissolved oxygen, said grids located at or towards the floor or base of the reactor. 21. An apparatus according to claim 19 or 20, characterized in that the bioreactor is provided with at least one air supply downcomer having at least one motor operated control valve which is alternately opened for a set program of air-on operation in a cycle and then closed. 22. An apparatus according to claim 21, characterized in that during the aeration sequence, all motor operated control valves are operated in unison, or a f