Virginia Law

Ammonia stripping is the chemical-physical process by which dissolved ammonias are converted to gaseous ammonia and removed from the wastewater by changes in the surface tension of the air-water interface. The removal of ammonia nitrogen in treated effluent is the objective of this treatment unit operation.

1. Ammonia stripping typically involves the addition of lime to treated effluent (secondary or advanced treatment), followed by agitation in the presence of air. Wastewater effluent with an adjusted pH of 10 or more is usually allowed to flow downward through special media. The ammonia gas which develops is stripped out by the passing contact with outside air. These ammonia stripping towers become inoperable at temperatures below freezing (32°F or 0°C wet bulb). Therefore, before consideration can be given to ammonia stripping the minimum air temperature must be determined and provisions made to prevent freezing.

2. For effective conversion of ammonium to ammonia gas the system pH must be maintained at a minimum of 10.5 on a continuous basis. The elevation of the pH of the wastewater for conversion of the ammonium to ammonia should be selected from the ammonia solubility curve versus pH.

Ammonia stripping units may be of countercurrent operation or utilize cross flow air movements. Minimization of scale formation may be obtained by countercurrent operation.

3. The loading applied to the stripping reactor should not exceed 1,250 pounds of wastewater ammonia per hour per square foot of cross-sectional media area. The gas-liquid ratio shall normally be in the range of two to four expressed in terms of pounds per square foot per hour of air, divided by pounds per square foot per hour of wastewater.

4. The reactor media shall be (i) resistant to continuous loading of high pH liquid; (ii) consist of material which can be readily cleaned of scale deposits; and (iii) structurally sound. Facilities shall be provided for media cleaning, consisting of either manual means, or high pressure jets of water, or other approved means. Provisions shall be made for treatment of washdown waters and scale removed from the packing media.

5. In areas where reliability is questionable due to physical restraints of the system, a back-up system for nitrogen removal shall be required. Duplicate pumping units are required where pumping is employed to apply or remove the liquid.

6. Facilities shall be provided for post-pH adjustment.

7. Considerations shall be given to remote locations for stripping reactors in relation to bodies of water. Each proposal shall include sufficient information to substantiate expected plume dispersion areas and, if necessary, removal of ammonia gas from the plume.