Virginia Administrative Code › Title 9 - ENVIRONMENT › Agency 25 - STATE WATER CONTROL BOARD › Chapter 790 - VIRGINIA POLLUTANT DISCHARGE ELIMINATION SYSTEM (VPDES) PERMIT REGULATION › Part III - Manual of Practice for Sewerage Systems and Treatment Works › Article 10 - Nutrient Control › Section 9VAC25-790-920 - Ammonia stripping

Current through Register Vol. 40, No. 24, July 15, 2024
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.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.