Oxygen: Major limitations

  • The oxygen transfer to sewage is limited due to low solubility of oxygen. As a result, it would be almost impossible to keep the entire sewer pipe aerobic, especially in the case of long pipes.
  • The oxygen injection is effective in controlling sulfide production during periods when oxygen is present. In addition to preventing sulfide from formation, any sulfide present would be oxidized. However, oxygen injection has no long-lasting inhibitory or effect on the SRB activities.
  • Oxygen injection enhances SRB activities in the downstream sections of sewers. This is due to the re-generation of sulfate (from sulfide) at sites where oxygen is injected so that more downstream sewer biofilms are exposed to sulfate, which enhances the growth of SRB.
  • The available oxygen would be quickly consumed in sewer and during long quiescent periods, the anaerobic conditions favourable for sulfide production would be quickly established in the system, thereby negating any positive effect achieved by oxygen injection.
  • High VFA consumption is another main concern as this would create a limitation of carbon source for downstream nutrient removal plant.
  • Its effectiveness and efficiency are highly sensitive to the injection locations. The selection of the injection sites and the determination of the dosage profiles could be a difficult task, particularly for large, complex networks.

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