Recommended Design Criteria for Aerated Ponds...
Supplement to Engineer's Report, Plans and Specifications...
Refer to Chapter IV, Section A for applicable requirements.
Basis of Pond Design...
1. Detention Time : The aerated stabilization pond(s) shall be designed to meet the effluent requirements as described in the discharge permit. The minimum detention time for the pond(s) is determined by the following formula :

t = E / [ 2.3 K_T (100 - E) ]

Where :
t= detention time, days
E= percent of 5-day BOD to be removed in aerated pond
K_T = reaction coefficient per day ( base 10 ) in aerated pond assuming a complete mixed system. For complete treatment of normal domestic sewage, the K_T value may be assumed to be 0.20 1 / day at 20 ^OC or 0.08 1 / day at 0 ^OC. The rate of biological oxidation in an aerated pond as represented by the value of the reaction coefficient K_T is affected by temperatures other than 20 ^OC shall be according to the following formula :

K_T = ( K₂₀ ) [ 1.047 ^{( T - 20 )} ]

Where :
K_T = Reaction coefficient at temperature T ^OC in aerated pond
K₂₀ = Reaction coefficient at temperature 20 ^OC
T = Temperature in aerated pond, ^OC

For wastewater with a 5-day BOD to the pond of 150 to 300 mg/l, the K₂₀ value will be assumed to be 0.20 per day. For wastewater with a 5-day BOD to the pond greater than 301 mg/l, the reaction rate coefficient must be determined by a pilot plant study for various conditions which might be encountered in the aerated ponds. The detention time should be based on the rate of metabolism during the coldest period of the year, when the oxygen demand rate is at its lowest. Aeration equipment should be sized according to the oxygen and mixing requirements based on peak 24-hour summer loadings. The configuration of the aerated ponds should be such that the detention time is maintained between approximately 5 and 10 days in warm weather and between approximately 8 and 20 days in cold weather. Due consideration shall be given to possible future expansion and/or additional sources of wastes when the original land acquisition is made. Suitable land should be available at the site for increasing the size of the original construction.

2. Industrial Wastes : Consideration shall be given to the type and possible effects of industrial wastes on the treatment process.

3. Multiple Units : There should be a minimum of two aerated ponds for a total aerated system. It is recommended that they be designed to permit both series and parallel operation. This allows maximum operational capability to achieve the desired effluent quality.

4. Pre or Post Treatment : Where aerated ponds are to be used in conjunction with conventional treatment works, the Department will, upon request, review and recommend BOD loading limits for the pond after due consideration of the efficiency of other treatment units.

5. Shape : Refer to Chapter IV, Section B-5, for applicable requirements.
Pond Location...
Refer to Chapter IV, Section C for applicable requirements other than :

1. Distance from Habitation : An aerated pond system should be at least 750 feet and if used with a conventional pond system should be at least one-quarter mile or as far as practicable from habitation or any area which is likely to be developed within a reasonable future period.
Pond Construction Details...
Embankments and Dikes : Refer to Chapter IV, Section D for applicable requirements other than :

a. Embankment slopes shall be provided with bank stabilization and liner. Embankment slopes may be as steep as two horizontal to one vertical (2:1).
b. Embankment slopes should not be flatter than four horizontal to one vertical (4:1) on the inside.
c. The maximum liquid pond depth shall not exceed 20 feet. The minimum normal liquid depth will depend upon the aeration equipment to be used with the pond depth but generally should not be less than 10 feet. Normally, the better mixing action will occur in depths of 12-15 feet. For economical reasons, diffuser systems should be used on the bottom of ponds with 15-20 foot depths.
Pond Bottom...
Refer to Chapter IV, Section E for applicable requirements other than :

1. Adequate concrete pads shall be provided under mechanical surface aerators to prevent bottom scour.

2. Consideration should be given to providing some additional detention time and storage capacity for sludge accumulation over a period of 10 to 20 years. The maximum sludge storage depth should not be greater than 6 feet. This sludge storage capacity could be held to a minimum if the bottom was concrete lined with a hopper type sump for cleaning purposes. It may be assumed that the sludge will compact to about 6 percent dry solids.
Influent Lines...
Refer to Chapter IV, Section F for applicable requirements other than :

1. A comminutor or manually cleaned bar screen should be provided upstream from the influent line conveying raw sewage or waste into an aerated pond system. Screening or comminution will be required to prevent damage to mechanical surface aerators.

2. Influent lines should discharge under water and provisions provided for adequate distribution to the pond of the incoming flow. Normally, the influent should be discharged under mechanical aerators, near the aeration grid or other diffusers where air diffusion systems are used. When diffused air tubing is used in the ponds, they must be installed at 90 degrees to the direction of the plug flow of the influent.

3. Recirculation should be considered when wastewater has a high sulfate content or contains waste of high BOD.

4. The inlet pipe may go directly through the dike and end at the toe of the inner slope with concrete or riprap placed in front of and around the pipe to prevent erosion of pond bottom and dike slope.
Control Structures and Interconnecting Piping...
Refer to Chapter IV, Section G for applicable requirements other than :

1. In a multiple cell facility with a diffused air aeration system and summerged air headers, consideration must be given to arranging the overflow structure and piping to allow for independently draining each cell down to or below the level of the air header.

2. Effluent from the first cell should be withdrawn from an underflow baffle. Effluents from interconnecting cells may be discharged at or near the surface without baffling to reduce the potential for algal growth.
Aeration Equipment...
1. Dissolved Oxygen Requirements : Oxygen requirements generally will depend on the BOD loading, the degree of treatment and the concentration of suspended solids to be maintained. Aeration equipment shall be capable of maintaining a minimum dissolved oxygen level of 2 mg/l in the ponds at all times. Suitable protection from the weather and elements shall be provided for electrical controls.

2. Required Capacity of Aeration Equipment : In designing aeration equipment, the a' factor in the following equation should be at least 1.5 and possibly 2, to provide sufficient aeration capacity during critical periods of the year :

R= ( a^' ) ( L )

Where :
R = Pounds of oxygen required per day
L = Pounds of 5-day BOD removed per day
a^' = Ratio between oxygen utilized and BOD removed

3. Emergency Operation : Spare aeration units shall be provided to allow the system to be fully operational in event a unit is out of service. Aeration units should be provided with an emergency power supply.

4. Mixing : A bottom velocity of at least 0.3 ft/sec. should be created by the aeration equipment throughout the pond.

5. Diffused Aeration :

a. If fine bubble diffusers (flexible tubing diffused aeration equipment) are used, allow a transfer rate of 0.75 pounds of oxygen per horsepower-hour.
b. If a large bubble diffusers (horizontal type) are used, allow a transfer rate of 1.2 pounds of oxygen per horsepower-hour. If large bubble diffusers (vertical tubular- type) are used, allow a transfer rate of 0.7 pounds of oxygen per horsepower-hour.
c. The specified capacity of blowers or air compressors, particularly centrifugal blowers, should take into account the possibility that the air intake temperature may reach 104 degrees F (40 degrees C) or higher and also that the pressure may be less than normal.
d. The specified capacity of the motor drive should take into account that the intake air temperature may be as low as -22 degrees F (-30 degrees C) or lower, which may require over-sizing of the motor or a means of reducing the rate of air delivery so as to prevent overheating and damage to the motor.
e. The blowers shall be provided in multiple units, so arranged and in such capacities as to meet the maximum air demand with the single largest unit out of service. The design should also provide for varying the volume of air delivered in proportion to the demand resulting from the variable loadings in the ponds.
f. Air intakes and blowers shall be designed to minimize noise.
g. The piping and air diffuser system shall be capable of delivering 200 percent of the design average oxygen demand. The spacing of the diffusers should be in accordance with oxygenation requirements throughout the length of each pond.
h. Individual assemblies or units of diffusers shall be equipped with control valves, preferably with indicator markings for throttling, or for complete shut off. The air diffusion piping and diffuser system shall be designed to deliver normal air requirements with minimal uniform pressure losses. The air diffusion system should be of non-corrosive material.
i. Air piping systems should be designed such that the total head loss from blower or silencer outlet to the diffuser inlet does not exceed 0.5 psi at average operating conditions.
j. Air filters shall be provided in numbers, arrangements, and capacities to furnish at all times an air supply sufficiently free from dust to prevent clogging of the diffuser system. In diffused air systems, the greatest percentage of air should be provided in the first pond. Connections for gassing facilities to control sealing should be provided at frequent intervals along the air header pipes.

Mechanical Aeration : ( a ) If surface aerators are used, allow a transfer rate of 1.5 pounds of oxygen per horsepower-hour. ( b ) The mechanism and drive unit shall be designed for the expected conditions in the aeration ponds in terms of the proven performance of the equipment. ( c ) The raw sewage should be discharged immediately below the aerators in the first cell so as to minimize freezing during winter. ( d ) Consideration shall be given to protecting the mechanisms from freezing. Floating surface aerators are not acceptable except for installations in operation from April to November. ( e ) Installations of multiple individual aerators shall be so designed as to meet the maximum oxygen demand with the largest unit in each pond out of service. ( f ) The design should also provide for varying the amount of oxygen transferred in proportion to the demand represented by the load on the pond. ( g ) Fix-mounted aerator units should have adjustable baseplates or other methods for varying the submergence of the rotor. Where practical, bridge-mounted platforms with handrails should be provided for maintenance.
Settling Pond...
A 5 to 7 day detention time settling pond shall be constructed following the second or last aerated pond. Other methods of treatment may be considered by the Department where adequate documentation is provided. The settling pond must meet the requirements for slope, bank erosion protection and water tightness for the aerated pond. The outlet structure should be baffled with an overflow rate not to exceed 800 gpd/sq.ft.
Disinfection...
Equipment for disinfection of the effluent when required shall be provided as outlined in Chapter 90 of the Recommended Standards for Sewage Works, 1978 or the latest edition.
Miscellaneous...
Refer to Chapter IV, Section H for applicable requirements other than :

1. Flow Measurement : A flow recorder and totalizer shall be provided on the influent line at the pond. A weir should be provided at the out-fall of the pond system to allow periodic measurement of the flow of effluent. Flow measurement equipment shall be protected from the weather and flow conditions.

2. Housing : The design should provide a service building to house laboratory, mechanical, control, and maintenance equipment with chemical storage facilities.