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Designing a 5.2 or 6.5 *MGD Water Treatment Plant using Top Entering Mixers for Flash or Rapid Mixing and Flocculation:

33,000Anoxic Denitrification Mixing System.  Click Larger Image

TANK DESIGN RETENTION TIMES (at MAXIMUM FLOW RATE) PARAMETERS:  

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Flash/Rapid Mixer Tank: 40 Seconds.

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Primary Floc Chamber: 15 Minutes.

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Secondary Floc Chamber: 15 Minutes.

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Maximum Design Flow: 2.6 MGD (24 hour basis).

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See example - Maximum Design Flow: 5.2 MGD (24 hour basis).

Waste and Water Treatment systems can involve numerous units of operation, which are dependent upon the source of water and it's specific treatment requirements.  As an example, prior to discharging waste water to a stream may require a neutralization or a chlorination step prior to aeration.  Other downstream applications might involve separation equipment such as a centrifuge or a water filtration system.  Each go beyond the scope of this discussion, which will focus on Flash or Rapid Mixing and Flocculation using Top Entering Mixers. 

  1. FLASH OR RAPID MIXING
  2. FLOCCULATION or FLOC MIXING

33,931 & 26,798 Gallon Anoxic or DeNitrification Mixing Systems for Waste Treatment:

Base Mixer (Priced):

Anoxic Denitrification Mixing Information
Anoxic Mixing System Engineering Specifications

In designing a mixer for an anoxic mixing system, otherwise known as DeNitrification.  The mixing application is generally defined by the percent by weight solids.  Anoxic DeNitrification mixing typically operates at relatively low percent weight by solid concentrations.  Please reference Sludge Mixing for these higher solids rates.  The following mixer design generally applies applications of this type.    

Anoxic -DeNitrification is a biological process that utilize bacteria and other micro-organisms to absorb or break down organic matter and organic compounds by oxidizing them.  This is typically referred to as Biological or Biochemical Oxygen Demand (BOD).  DeNitrification involve facultative bacteria that use organic carbon in the waste stream as both a carbon and energy source.  Nitrate is used as an electron acceptor in energy metabolism.  Bacteria first reduces ammonia & nitrates to nitrites, which then evolves to inert nitrogen gas, which requires venting.  The DeNitrification process is covered to minimize oxygen absorption from the atmosphere.  Anoxic basins can both precede and follow stages of aerobic treatment.  

Attached is a typical 33,931 & 26,798 gallon anoxic mix tanks optimized for your consideration.  Anoxic tanks are constructed either using concrete basins, ponds, or various other tank configurations.  

Design Basis:

  1. Maximum Specific Gravity = 1.06
  2. Viscosity Range = 400 centipoise maximum.
  3. 33,931 Gallon Concrete Tank: 18' x 18' x 16' SS, Flat Bottom, SWD=14'.
  4. 26,798 Gallon Concrete Tank: 16' x 16' x 15' SS, Flat Bottom, SWD=14'.
  5. A vertical-on-tank-centerline mounting arrangement is used.
  6. No in-tank anti-swirl baffles are required. 
  7. 316D Stainless Steel mixer wetted parts with 316 Stainless Steel hardware.
  8. 230/460 Volt Power source.
  9. Mixer support bridge supplied by others.
  10. For larger basins, multiple mixer can be used subdividing the basin.  Example: A 36' x 36' x 16' tall basin can be subdivided into four (4) equal mix tanks.

Three Primary Equipment Design Options:
   1. All non-stainless components coated with two-part corrosion resistant epoxy paint.
   2.  A Non-Painted Mixer available in two configurations.  In lieu of investing cost into paint & its related labor, a marginal cost adder is invested into all corrosion resistant materials that is suitable for 95% plus of all mixing applications which includes stainless couplings & exposed hardware:
     Option A - Only the motor is provided with that manufacturers commercial grade paint.
     Option B - Use an all stainless steel wash down duty motor.

This mixers advantages are significant:

  1. Lowest continuous energy cost using both lower horsepower's & speeds. Maximum high flow capability impellers combined with lower horsepower, higher torque mixers maximize the available utility of the design.
  2. After investing in both paint & its labor, it is inevitable that surface damage during installation will occur.  In time, exposed surfaces due to flaking & peeling is also inevitable causing sites for corrosion.  Chalking & discoloration is also common.  A corrosion resistant non-painted mixer is a better overall long term investment.  
  3. Time & manpower costs are always an issue.  Contractors can be costly, lifting equipment is expensive, internal work teams must be scheduled & prioritized causing costly system delays & reacting to emergencies is always an expensive proposition.  Although installations typically include on-site erection equipment & labor force, downtime is another mater.  Maintenance & operators prefer designs that feature light weight one-man gearboxes as future servicing will be required.  In many cases, the removable motor assembly divides the assembly into two light weight components.  Being able to handle the servicing yourself gives autonomy within a system resulting in immeasurable benefits.  
  4. Model AQPX is a pedestal mounted mixer option locating the agitator shaft coupling above mounting surface which allows you to hang the shaft & impeller in place.  The lightweight one-man gearbox & motor component assemblies can then be easily removed for servicing.
  5. These are NOT throw-away-mixers.  The have a projected life of 11+ years {24 hour per day service life}.  These mixers are designed to be dusted off, repaired or rebuilt, and put right back into service.    
  6. Easy access lube points and oil servicing located above the mixers mounting surface.  External viewable Site glass to easily observe oil levels. 
  7. Equipped with flexible motor coupling to absorb inherent shock loads to protect the overall service life our super quiet gearing.  The motor coupling allows for quick removable, retrofit (new motor replacement) & reinstallation. 
  8. Engineering Mixer Specification.

Complete design for 5.2 or 6.5 *MGD Water Treatment mixing application. Includes engineering specifications, complete mixer pricing, tank drawing, mixer mounting orientation for waste water treatment systems.

 

Note: *MDG - Millions Gallons per 24 hours Day.  

01.30.12 

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