Sewage Treatment : The Operation

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

The Operation

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.