Okla. Admin. Code § 252:656-16-3

Current through Vol. 41, No. 19, June 17, 2024

Section 252:656-16-3 - Biological nutrient removal

(a)Purpose. Processes for nutrient removal in wastewater include conversion of ammonia and organic nitrogen to nitrate nitrogen (nitrification), the conversion of nitrate nitrogen to nitrogen gas (denitrification) and removal of phosphorus.

(b)Single stage (combined carbonaceous BOD removal and nitrification). Design processes according to the requirements of 252:656 and submit all design calculations. The following factors will have a significant impact on the nitrification process: ammonia and nitrite concentrations, BOD/TKN ratio, dissolved oxygen concentration, temperature, alkalinity and pH. The following steps shall be considered in the design of the suspended growth reactor and the resulting calculations submitted to DEQ for review. If actual kinetic coefficients cannot be obtained, textbook values may be used for design.

(1) Select an appropriate safety factor to handle peak, diurnal and transient loadings (a minimum safety factor of 2.0 applied to design mean cell residence time is required).

(2) Select the mixed liquor dissolved oxygen (DO) concentration. The minimum acceptable level is 2.0 mg/l. Determine the amount of oxygen required to satisfy the nitrogenous oxygen demand. Provide a minimum of 4.6 mg O2/mg N oxidized.

(3) Evaluate the requirement for pH control. Every mg/l of ammonium-nitrogen (NH4-N) oxidized will result in the destruction of 7.14 mg/l alkalinity.

(4) Estimate the maximum growth rate of nitrifying bacteria under the most adverse DO, pH and temperature conditions.

(5) Determine the design mean cell residence time with the safety factor (10-day is recommended).

(6) Predict the effluent nitrogen concentration.

(7) Determine the hydraulic retention time to achieve the necessary nitrogen concentration. A 10-hour retention time is needed to compensate for lower nitrification rates when wastewater temperatures are below 50 degrees F.

(c)Separate-stage nitrification. Design processes according to the requirements of 252:656 and submit all design calculations. Separate-stage suspended growth nitrification processes are similar in design to the activated sludge process. Show the process factors, considering the following:

(1) Experimentally measured nitrification rates are more appropriate than theoretical rates.

(2) Nitrification rates increase as the temperature increases.

(3) Nitrification rates increase as the BOD/TKN ratio decreases.

(4) Nitrification rates are affected by pH.

(5) Nitrification rates vary from 0.05 to 0.6 lbs. NH4-N oxidized per pound of MLVSS.

(d)Biological phosphorus removal.Design proprietary processes and submit all design calculations according to the manufacturer's recommendations or Wastewater Engineering: Treatment, Disposal & Reuse, Metcalf & Eddy, Inc. 4^th Edition (2003).

(e)Chemical phosphorus removal.

(1)Preliminary testing. Laboratory, pilot, or full scale studies of various chemical feed systems and treatment processes are recommended for existing plant facilities to determine the achievable performance level, cost-effective design criteria, and ranges of required chemical dosages.

(2)System flexibility. Systems shall be designed with sufficient flexibility to allow for several operational adjustments in chemical feed location, chemical feed rates, and for feeding alternate chemical compounds.

(3)Dosage. The design chemical dosage shall include the amount needed to react with the phosphorus in the wastewater, the amount required to drive the chemical reaction to the desired state of completion, and the amount required due to inefficiencies in mixing or dispersion. Excessive chemical dosage should be avoided.

(4)Chemical feed points. Selection of chemical feed points shall include consideration of the chemicals used in the process, necessary reaction times between chemical and polyelectrolyte additions, and the wastewater treatment processes and components utilized. Flexibility in feed locations shall be provided to optimize chemical usage.

(5)Flash mixing. Each chemical must be mixed rapidly and uniformly with the flow stream. Where separate mixing basins are provided, they shall be equipped with mechanical mixing devices. The detention period shall be at least 30 seconds.

(6)Flocculation. The particle size of the precipitate formed by chemical treatment may be very small. Consideration shall be given in the process design to the addition of synthetic polyelectrolytes to aid settling. The flocculation equipment shall be adjustable in order to obtain optimum floc growth, control deposition of solids, and prevent floc destruction.

(7)Liquid-solids separation. The velocity through pipes or conduits from flocculation basins to settling basins shall not exceed 1.5 feet per second in order to minimize floc destruction. Entrance works to settling basins shall also be designed to minimize floc shear.

(8)Sludge handling. For design of the sludge handling system, special consideration shall be given to the type and volume of sludge generated in the phosphorus removal process.

(9)Filtration. Effluent filtration shall be provided where effluent phosphorus concentrations of 1 mg/l or less must be achieved.

Okla. Admin. Code § 252:656-16-3

Added at 23 Ok Reg 937, eff 6-15-06; Added at 28 Ok Reg 1282, eff 7-1-11