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Oklahoma Administrative Code (Last Updated: March 11, 2021) |
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TITLE 252. Department of Environmental Quality |
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Chapter 656. Water Pollution Control Facility Construction Standards |
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Subchapter 16. Biological Treatment Standards |
SECTION 252:656-16-1. Suspended growth systems
Latest version.
- (a) General. Suspended growth wastewater treatment systems generally consist of one or more basins where incoming wastewater is mixed with mixed liquor suspended solids and aerated for a period of time. The mixed liquor suspended solids are then separated from the mixture where a portion is returned to the mixing basin and the remainder diverted to other units for additional treatment before beneficial re-use by land application or landfill disposal. The liquid after separation from the solid is discharged or diverted to other units for additional treatment before discharge. Suspended growth systems covered by these standards are commonly know as the Activated Sludge process including the Sequencing Batch Reactor ("SBR") process. The activated sludge process includes several modifications. The most common is the extended aeration process which includes the oxidation ditch and SBR variations. Submit a complete design analysis for all suspended growth systems to DEQ for review. Contact stabilization is not recommended as the only secondary treatment process, but may be considered where equalization of flow is provided or where other treatment units follow.(b) Primary treatment. The conventional activated sludge process must be preceded by primary treatment in the form of a primary clarifer(s) in accordance with 252:656-17. Provide equipment necessary to adequately remove sludge as it accumulates and transport it to sludge treatment facilities.(c) System Design. Submit a comprehensive discussion of all functional design calculations used to size activated sludge treatment facilities. Include the following:(1) influent wastewater characteristics,(2) temperature range of wastewater,(3) primary treatment of the waste,(4) hydraulic and organic loading applied to the aeration basin,(5) anticipated mixed liquor suspended solids level to be maintained in the aeration basin,(6) aeration time,(7) oxygen and mixing requirements for average and peak flows,(8) recirculation and sludge wasting,(9) degree of treatment anticipated, and(10) equation(s) used to compute treatment efficiency.(d) Aeration basins.(1) Capacities and permissible loadings. The minimum design criteria for activated sludge systems are listed in Appendix A, Design Tables.(2) Arrangement of aeration basins.(A) Basin dimensions. Design each unit to:(i) Maintain effective mixture and use of air.(ii) Prevent unaerated sections and noticeable channeling.(iii) Maintain velocities sufficient to prevent deposition of solids.(iv) Restrict short-circuiting through the tank.(B) Basin lining. Line earthen aeration basins with concrete, asphalt or equivalent material below the maximum water elevation. Do not use plastic liners in aeration tanks.(C) Number of units. Divide the total aeration basin volume into at least two units, capable of independent operation.(D) Inlets and outlets.(i) Controls. Provide inlet and outlet devices to control flow and maintain constant water level in all aeration basins. Design the system to allow for the maximum instantaneous hydraulic load with any single unit out of service.(ii) Channels. Design channels and pipes to maintain a velocity sufficient to hold solids in suspension or provide a mechanical means for suspending the solids. Provide for draining each channel when it is not being used.(E) Freeboard. Provide at least 18 inches of freeboard.(e) Aeration equipment.(1) Common elements. Aeration equipment must be capable of maintaining at least 2.0 mg/l of dissolved oxygen in the mixed liquor at all times and provide thorough mixing.(A) CBOD removal. Where data is not available, the design oxygen requirement for the activated sludge process is 1.1 lb O2/lb peak BOD applied to the aeration basins. For the extended aeration process, the requirement is 1.8 lb O2/lb peak BOD.(B) Nitrification. For nitrification the oxygen requirement for oxidizing ammonia must be added to the requirement for carbonaceous BOD removal. The nitrogen oxygen demand (NOD) shall be taken as 4.6 lb O2/lb NH3 at peak diurnal flow. Assure sufficient alkalinity to maintain pH as required by 252:656-16-3 (b)(3). If the alkalinity is not sufficient, then chemical addition must be required.(2) Diffused air systems.(A) Common elements. Normal air requirements for all activated sludge processes, except extended aeration, is 1,500 ft/lb peak BOD for aeration basin loading. For the extended aeration process the value is 2,000 ft/lb peak BOD loading.(B) Blowers. Design the blower system to account for temperature extremes ranging from 4 degrees F to 104 degrees F.(C) Multiple units. Provide multiple units with enough capacity to meet the maximum air demand with the largest unit out of service. The design must also allow the volume of air delivered to be varied in proportion to the load demand of the plant.(D) Diffusers. Systems must be capable of providing the diurnal peak oxygen demand or 200% of the design average oxygen demand, whichever is larger. Design air piping systems where the total head loss from blower outlet (or silencer outlet where used) to the diffuser inlet does not exceed 0.5 psi at average operating conditions. The spacing of diffusers must be in accordance with the oxygen requirements through the length of the channel or basin, and designed to allow spacing adjustment without major revisions to the air header piping. All plants using less than four aeration basins must be designed to incorporate removable diffusers that can be serviced and/or replaced without dewatering the basin.(E) Filters. Provide all blowers with air filters.(3) Mechanical aeration systems. The design requirements of a mechanical aeration system shall meet the following:(A) Maintain all mixed liquor suspended solids in suspension;(B) Meet maximum oxygen demand and maintain process performance with the largest unit out of service. A minimum of two units shall be provided;(C) Provide for varying the amount of oxygen transferred in proportion to the load demand on the plant; and(D) If depth of submersion is an important criteria, the aerators must be adjustable or the basin liquid levels must be easily controlled with regard to depth.(f) Sequencing batch reactor systems.(1) Reactor design. Provide at least three (3) reactors. Design each reactor to operate in a cyclic mode with sufficient time to fill, aerate, settle and remove the clarified liquid.(A) Organic loading shall be between 5 to 20 pounds of BOD per thousand cubic feet per day. Design the system using food to mass (F/M) ratios of 0.05 to 0.30. The total reactor volume must provide at least 18 hours of hydraulic detention time. Size the reactor volume on the hydraulic retention time and decant volume.(B) The design operating levels shall be 10 to 20 feet with at least two feet of freeboard.(C) Design for no more than four operating cycles per day per reactor at average design flow.(D) Sludge production depends on the mode of operation. For extended aeration mode (24 hours retention time), base sludge handling design on a minimum sludge production of 0.5 lbs. per lb. of BOD removed. For conventional activated sludge mode, or for systems using more than two cycles per day, base sludge production on 0.75 to 0.95 lbs. per lb. of BOD.(E) Base sludge storage requirements on a concentration of 8,000 mg/l with a specific gravity of 1.02 for the settled sludge. Base the calculated sludge volume on the liquid depth after decanting.(2) Aeration equipment. Aeration equipment must provide at least 1.4 lbs. of oxygen per lb. of BOD removed at a minimum residual dissolved oxygen level of 2.0 mg/l during the aeration period. Where nitrification is required, the aeration equipment shall have the capacity to provide an additional 4.6 lbs. of oxygen per lb. of ammonia nitrogen.(3) Decanter systems. Design the decanter system to draw effluent from 12 to 18 inches below the surface and to prohibit floating scum from entering the system during fill and aeration periods. The design must not create currents that pull solids from the settled zone at the lowest point in the cycle. The entrance velocities into the decanter shall not exceed 1.0 fps at the maximum design flow condition.(4) Scum management. Provide resuspension or removal equipment to control excessive scum build-up.(g) Oxidation ditches. An oxidation ditch may take any linear shape as long as it forms a closed circuit, and does not produce any eddies or dead spots.(1) Pretreatment. Bar screens and grit removal facilities are required. Primary settling is not necessary except for high strength waste.(2) Aeration basin.(A) The volume of the oxidation ditch must provide 18 to 24 hours hydraulic detention time at average dry weather flow. Organic loading may range from 12 to 15 pounds BOD per 1,000 ft/day.(B) Depth shall be at least 3 feet.(C) Freeboard shall be at least one foot at maximum water depths.(D) Aeration equipment shall maintain at least 1 fps velocity throughout the ditch.(E) Construct the ditch with reinforced concrete at least 4 inches thick for ditches up to 5 feet deep, and 6 inches thick where deeper.(F) Rotor weight shall not be supported directly by gear reduction or motor equipment. Protect motors, gear reduction equipment and bearings from inundation and rotor spray.(3) Rotor aerators.(A) Install at least two complete rotor units. Design the system so a single rotor can provide the average design oxygen demand and minimum velocity of 1 fps throughout the basin.(B) Place rotors before a long, straight ditch section.(C) Provide a method to control rotor submergence.(4) Miscellaneous.(A) Introduce raw sewage and returned sludge immediately upstream of the rotor that is farthest from the effluent control weir.(B) Provide elevated walkways for rotor maintenance.(h) Return sludge equipment.(1) Return rate. Design all return pumping systems for the capability to be operated at the following return rates:(A) Standard Rate:(i) 15% minimum to(ii) 75% maximum(B) Carbonaceous Stage of Separate Stage Nitrification:(i) 15% minimum to(ii) 75% maximum(C) Step Aeration:(i) 15% minimum to(ii) 75% maximum(D) Extended Aeration:(i) 50% minimum to(ii) 150% maximum(E) Nitrification Stage of Separate Stage Nitrification:(i) 50% minimum to(ii) 200% maximum.(2) Return pumps. Maintain the maximum return sludge requirement with the largest pump out of service. Provide a positive head on all pumps' suctions under all operating conditions. Provide a minimum pump's suction and discharge opening of at least 3 inches. Air lift systems shall be at least 3 inches in diameter. Further, air compressors shall be of sufficient capacity to supply design air requirements plus a 25% safety factor.(3) Return piping. Provide 4-inch discharge piping designed to maintain a minimum velocity of 2 fps at normal return rates. Provide mechanisms for observing, sampling and controlling return sludge flow from each clarifier.(i) Waste sludge facilities. Waste sludge control facilities shall have a maximum capacity of not less than 25 percent of the average rate of sewage flow and function satisfactorily at rates of 0.5 percent of average sewage flow or a minimum of 10 gpm, whichever is larger.(j) Measuring devices. Install a means to measure flow rates of raw sewage, primary effluent, waste sludge, return sludge, and air to each basin unit.