Oxygen: Dosing arrangement and typical dosing rates
- When oxygen is dosed to sewer, it is utilized for both sulfide and COD oxidation. Oxygen dosing requirement can be estimated as follows:
It is assumed that the end product of sulfide oxidation is sulfate and the oxygen uptake rate of sewer biofilm (OUR) is constant throughout the sewer length.
- With the injection of pure oxygen, maximum level of DO that could be achieved is only 30-40 mg/L (depending upon the pressure) as not all the oxygen supplied gets dissolved in the wastewater. When the oxygen is dosed at the wet-well of a rising main, then the DO will be depleted in few hundred meters of the pipe, and there will be no protection against the sulfide produced in the remaining anaerobic portion of the sewer pipe. In order to avoid this, the point of injection (POI) should be “reasonably” close to the points where sulfide control is required (Point of Control – POC). An injection site should be selected such that:
- there would be an adequate hydraulic retention time (HRT) between POI and the POC to enable the full oxidation of any sulfide present at the POI before it reaches the POC, and that
- aerobic conditions are maintained between the two points with minimum requirement of oxygen. There should be no high points between POI and POC, as otherwise air pockets rich in oxygen and hydrogen sulfide would format such locations causing corrosion of pipes.
- Typical oxygen dosing rate: 15.9-91.5 kg O2/ML of wastewater (exact dosing rate depends upon the pressure, type of injection and oxygen transfer efficiency).
Further information can be obtained as follows:
Final Report – ARC Linkage Project on Sewer Biotransformation
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