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 9VAC25-790-910 - Biological nitrification

Current through Register Vol. 40, No. 24, July 15, 2024
A.
					 Biological nitrification is a process whereby autotrophic nitrifying bacteria
					 convert ammonia nitrogen to nitrate nitrogen. This process is capable of
					 removing most of the nitrogenous oxygen demand from domestic wastewater but
					 does not remove the nitrogen itself. Should nitrogen removal be required,
					 denitrification facilities must follow nitrification facilities. Although the
					 nitrification phenomenon has been observed for some time, unit process design
					 for optimum nitrification performances has only recently been employed.
If adequate performance data are not available, pilot
						plant evaluation for a particular application shall be completed prior to a
						full scale design proposal for upgrade of existing facilities. The recommended
						minimum or maximum design capacities are provided as guidelines and should be
						used if actual performance data or pilot plant evaluations do not provide
						sufficient design information.
B. Single stage design. Single stage systems
					 should be considered for cases where nitrification must be provided only during
					 periods when wastewater temperatures are above 13°C (55°F). For cases
					 where nitrification must be provided for prolonged periods of temperatures less
					 than 13°C, two stage activated sludge, biological nutrient removal, or
					 combinations with fixed film growth systems should be considered.
1. The reactor design shall prevent
					 short-circuiting. Plug flow basins should be used, with consideration given to
					 dividing the reactor into a series of compartments by installing dividers
					 across the basin width with ports through the dividers.
2. The aeration capacity shall be sized for
					 the peak ammonia load. Where data are not available on ammonia variation, a
					 peak hourly ammonia load (lbs/day) of 2.5 times the average load (lbs/day)
					 should be assumed. The aeration supply should have a capacity determined by the
					 following formula where automated blower controls linked to D.O. probes are
					 provided:
Aeration supply =
800 cu. ft. per total pounds of
								(BOD5 +NOD)
where: NOD =
4.6 x total Kjeldahl nitrogen (TKN)
BOD5 =
5 day BOD entering the aeration basin
The peak BOD5 and NOD must be used
						to ensure around-the-clock nitrification. The above air quantity should be
						doubled if automated blower controls are not provided. The design should
						maintain a D.O. concentration greater than 1.0 mg/l.
3. Aeration basin detention time should be
					 based upon pilot plant data on the specific wastewater involved. Proper control
					 of industrial discharges must be provided to minimize the possibility of
					 biological toxins upsetting the nitrification rates. The following minimum
					 criteria are suggested for municipal wastewaters free of significant industrial
					 wastes and which are subjected to primary settling prior to aeration.
a. Sludge age = 10 days or more and F/M =
					 0.25 or less
where: F/M = total daily lbs BOD5
						to aeration basin divided by average lbs active biomass in aeration
						tank.
b. Active biomass is
					 measured by the volatile portion of the suspended solids concentration within
					 the aeration basin (MLVSS).
4. Nitrification will destroy 7.2 lbs of
					 alkalinity per pound of NH3-N oxidized. If the wastewater is deficient in
					 alkalinity, alkaline feed and pH control must be provided. Sufficient
					 alkalinity should be provided to leave a residual of 30-50 mg/l after complete
					 nitrification.
5. The design of
					 final clarifiers will be similar to secondary clarifiers serving suspended
					 growth reactors. The basin shall be equipped with a surface skimming device. A
					 minimum biomass return rate of 25% and a maximum of 100% of the average daily
					 flow shall be provided.