Supplemental Dissolved Oxygen
Hydrogen peroxide has been used to reduce BOD and COD in refinery wastewaters for many years.
This includes:
- Supply of Supplemental Dissolved Oxygen (DO) when biological treatment systems experience temporary overloads or equipment failure.
- Predigestion of wastewaters which contain moderate to high levels of compounds that are toxic, inhibitory or recalcitrant to biological treatment.
As indicated by these examples, H2O2 can be used as a stand-alone treatment or as an enhancement to existing physical or biological treatment processes, depending on the situation.
Supplemental Oxygen Source
The BOD/COD removal efficiency of aerobic biological treatment processes depends on a number of factors including (but not limited to): Influent BOD/COD loading, F:M ratio, temperature, nutrient levels and dissolved oxygen (DO) concentrations. Many biological treatment facilities use H2O2 to supplement DO levels when oxygen limited conditions in aeration basins result in poor BOD/COD removal. These conditions can be brought about by unexpected peaks in influent BOD/COD loading; seasonal variations in BOD/COD loading; and hot weather – which reduces the efficiency of oxygen transfer by mechanical aeration equipment (i.e., O2 solubility decreases as temperature increases). These conditions may or may not be accompanied by filamentous bulking.
When H2O2 is used to supplement DO, it is metered directly into the aeration basin of a biological treatment system to provide an immediate source of dissolved oxygen. The conversion of H2O2 to DO in an activated sludge mixed liquor proceeds according to the following reaction:
| Catalase Enzyme: 2 H2O2 → O2 + 2 H2O |
Catalase enzyme is a natural decomposition catalyst for H2O2, and is found in all activated sludge mixed liquors, being produced by most aerobic organisms. Because this enzymatic decomposition of H2O2 is very rapid, the oxygen supplied by H2O2 is immediately available for uptake by the aerobic organisms.
The above reaction shows that two parts of H2O2 will yield one part of dissolved oxygen. Therefore, the amount of H2O2 required to oxygenate the wastewater is surprisingly small. In actual practice, the requirement may be higher due to side reactions with oxidizable compounds.
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