Sewage Treatment : The Operation
Denitrification occurs when oxygen levels are depleted and nitrate becomes the primary oxygen source for microorganisms.
The process is performed under anoxic conditions, when the dissolved oxygen concentration is less than 0.5 mg/L, ideally less than 0.2.
When bacteria break apart nitrate (NO3-) to gain the oxygen (O2), the nitrate is reduced to nitrous oxide (N2 O), and, in turn, nitrogen gas (N2).
For the process to proceed, the bacteria needs a carbon source. This can be obtained from carbon within the waste or a small amount of primary effluent can be added. Alternatively, an external source of carbon can be provided (Methanol).
After leaving the anoxic tank, the wastewater is aerated for
10 to 15 minutes to drive off the Nitrogen gas and add oxygen to the wastewater before sedimentation
The Air Stripping Process
The process consist of converting the amm liquid in air
The gaseous phasehase NH3NH4+ exist and together the inequilibrium aqueousand the p dominance of any one is dependent on pH and Temperature. A pH of >11 is required for complete conversion to NH3
Lime is used to raise the pH to >11
Stripping-gasificationofismostdeefficiently done using a counter current spray tower.
Design Parameters are:
2000-6000m3 of air / m3 wastewater
Tower Depths > 7.5 m
HRL- 4640L/min/m2 of tower
Advantages and Disadvantages of the air Stripping
Air strippingemosteconomicalismeans thofremoving nitrogen, however, as temperature approaches freezing the efficiency drops significantly.
Noise pollution by roaring fans.
Air pollution by odor caused by release of
Additionimecause softeninglof WW of alkalinity.
The precipitation of calcium carbonate on the packed media therefore requires continuous cleaning.