Environmental Dynamics International (EDI) is committed to providing a full spectrum of advanced lagoon technologies for application on wastewater treatment projects. EDI offers a full spectrum of treatment capabilities for lagoons including partial mix aerated lagoons, complete mix aerated lagoons, and advanced wastewater treatment systems with nutrient control i.e. nitrification denitrification and or phosphorus management. Under each of these different types of systems there are multiple levels of treatment that may be considered and specialized equipment and technology by EDI can be employed for maximum benefit to each project.

EDI supports the basic process capabilities for lagoons, with the latest technology, hardware plus offer advanced level treatment process considerations that can be used in conjunction with lagoons. These technologies may allow the existing infrastructure to be incorporated into the final lagoon solution. The infrastructure may offer pretreatment, and/or do polishing and advanced waste treatment of lagoon effluent for maximum performance. Lagoons can help control total system cost and take advantage of existing infrastructure for a substantial portion of the treatment process while maintaining easy to operate facilities for superior long-term performance.

An EDI aerated lagoon solution may be comprised of a single pond, a series of 2 or more ponds, or multiple zones within a single basin. These zones or ponds can be engineered for complete mix, partial mix, quiescent, and are generally capable of giving high degrees of BOD and suspended solids removals. For more advanced treatment including nutrient control, a number of ancillary systems and components can be incorporated into the design of EDI aerated lagoon pretreatment solutions. A description of the most common EDI lagoon process considerations are outlined below:

BASIC LAGOON PROCESSES
Complete Mix Lagoon

The complete mix (CM) lagoon is an aerobic treatment process maintaining all biological solids in suspension with aeration and mixing using diffused aeration. Influent sewage may be discharged directly into the CM lagoon preferably following fine screening to remove nuisance solids. Proper screening and/or grit removal is highly recommended to protect the aeration system and prevent unnecessary build-up of inert solids in the CM lagoon. Biological design of a traditional CM lagoon process is similar to a high F:M ratio (Low MLSS) activated sludge process without clarification or return MLSS. Note, CM basins maintain 100% solids in suspension and systems that allow settling while circulating liquid throughout the lagoon are actually partial mix lagoons. Energy levels for mixing in CM lagoons is generally considered 0.08 to 0.12 SCFM per ft2 floor area.

The CM process is effective in conversion of soluble C-BOD to biological solids that require solids management in a secondary process.  A significant removal of carbonaceous BOD can be economically effected when the CM lagoon is followed by effective solids separation.  Consistent nitrification in a CM lagoon requires long detention time to reduce the F:M ratio with long sludge age required. Lagoon nitrification has proven to be difficult when temperatures drop below 20˚C in the reactor. 

Complete Mix lagoons are usually 0.5 to 2 days detention. Typical BOD removal and oxygen demand in the CM lagoon is defined by biological reaction rates as published in US EPA design manual EPA-625/1-83-015, “Municipal Wastewater Stabilization Ponds”. Removals are based on first order kinetics which are dependent on mixing conditions and temperatures of the CM reactor. General design performance for complete mix lagoons are shown in graph 1.

 
Performance Curves Graph 1 Based on USEPA Design Manual Equations:

Equation 1 – BODeffluent = BODinlet [1 / (1 + kcm * t)]

                        kcm = Complete Mix Reaction Rate

                        kcm @ 20˚C = (2.5 day)-1 = 0.4 day

                        kcm @ design temp = k20 (Θ)T-20

Equation 2 – Θcm @ design temp = 1.085(T-20)

Equation 3 – kcm design temp = k20 (1.085)T-20

                                                                     = 0.4 (1.085)T-20
t = detention time in lagoon

Complete mix lagoons for municipal wastewaters may be mixing-limited. A mixing-limited condition occurs when more air is required to suspend all solids and maintain solids in suspension mixing versus the amount of air that is required to oxidize the C-BOD. Energy cost may be negatively impacted if blower and aeration requirements are designed around 100% mixing air flow requirements and the volume is greater than the process oxygen air requirements. One solution to this challenge is to employ a system that intermittently provides enough air to suspend solids in discreet zones while continuously supplying the air needed for biological oxidation of C-BOD. EDI has developed one such intermittent mixing solution, termed BioMizer™ (EnergySmart). Selection and programing of the BioMizer blower and/or valve sequencing is site specific and dependent on the characteristics of the biological solids.

Proper application of BioMizer has been shown to reduce energy requirements for the mixing limited CM process by 25% to 70%!
The CM lagoon reactor will generally be part of a more complete treatment process which involves one or more of the following:
  • Head Works (screens, grit removal, etc.)
  • Secondary Clarification following CM lagoon
    • Sludge wasted to digester (lagoon or concrete)
    • Sludge may be returned to CM reactor for high rate active sludge performance
  • Partial Mix Aerated Lagoon (in series)
    • Provides solids retention and digestion i.e. solids management in partial mix
    • May be followed by a Quiescent Zone for effluent polishing.
  • Facultative lagoon (no aeration) for solids management and additional BOD removal.
  • Polishing biological process when cold weather nitrification/denitrification is achieved. Typical SMART process application.
  • A filtration system may be incorporated for advanced solids separation or with chemical dosage and filtration for phosphorous control
  • Disinfection

 

 
 
COMPLETE MIX LAGOON PERFORMANCE CHART
 
Picture1
 

Important note:  EDI is able to engineer CM lagoon designs to meet the immediate plant process needs while engineering for easy conversion to the IDEAL™ advanced treatment technology with future addition of decanters, BioReef™, and process control components. 

 

 
Partial Mix Lagoon

The Partial Mix (PM) lagoon is an enhanced facultative lagoon process using aeration to simultaneously remove BOD and suspended solids using low aeration energy levels which allow solids separation and solids digestion in the PM lagoon. Enhanced treatment is achieved by the aeration and circulation of the lagoon bulk liquid whereby soluble C-BOD is introduced to biosolids more efficiently than in a purely facultative flow-through lagoon. Note the difference between PM lagoons with energy levels much below 0.05 CFM/ft2 floor and Complete Mix lagoons which keep all biosolids in suspension at 0.08 to 0.12 SCFM/ft2 lagoon floor. Screening and grit removal are not required for PM lagoon systems but use of the screening pretreatment is recommended to help avoid nuisance floating materials maintain active lagoon volume and improve lagoon aesthetics.

PM lagoons are typically several days’ detention (generally more than 5 days). Aeration is only provided to maintain oxygen in the liquid portion of the lagoon, with air flow limited to the process oxygen demand from C-BOD removal and deposition plus nitrification in warm wastewater. C-BOD removal and solids settling and digestion is facilitated in the same reactor. Mixing (i.e., solids suspension) via aeration is not a factor in the design so a low- energy system is possible. Typical BOD removal and oxygen demand in the PM lagoon is defined by biological reaction rates as published in US EPA design manual EPA-625-83-015, “Municipal Wastewater Stabilization Ponds.” Removals are based on first order kinetics for detention times and temperature of the lagoon. General design performance for partial mix lagoons are shown in graph 2.

 
Performance Curves Graph 2 Based on USEPA Design Manual Equations:

Equation 4 – BODeffluent = BODeffluent = BODinlet [1 / (1 + kpm * t)]

                        kpm = Partial Mix Reaction Rate

                        kpm @ 20˚C = 0.276 day

Equation 5 – Θpm @ design temp = 1.036(T-20)

Equation 6 – kpm @ design temp = k20 (1.036)(T-20)

                                                          = 0.276 (1.036)(T-20)

                        t = detention time in lagoon

Considerable nitrogen is removed in PM reactors via assimilation by heterotrophic organisms typically up to 3% of C-BOD values. Very little autotrophic nitrification can be expected on a consistent basis unless lagoon temperature is maintained above 20°C, although nitrification may become established with the combination of a warm climate and long detention time. Additional treatment provisions must be employed if consistent high removals of nitrogen are desired and lagoon temperatures drop much below 20°C. Typically SMART™ nitrification reactors and/or flocculation and filtration are employed to reach advance treatment levels.

For maximum waste treatment levels PM lagoons are generally used as a part of a more robust treatment scheme and used in series with other processes:
  • Multiple PM reactors in series.
  • CM and PM in series.
  • IDEAL™ Bioreactor followed by PM.
  • PM Lagoons with polishing nitrification using SMART™ submerged rock filters, MBBR, polishing reactors or IFAS.
  • PM lagoon for side-stream sludge digestion and storage as part of an advanced lagoon process.
  • Filtration system for advanced solids separation or by chemical dosage and filtration for phosphorus control.
  • Disinfection contact basins and/or dichlorination basins.

Important Note: It is critical to understand the difference between the mixing (i.e., solids suspension) that occurs in a CM lagoon versus the water circulation that occurs in a PM lagoon. The CM lagoon can achieve a higher level of treatment in a smaller volume because of the efficient delivery of food to microorganisms and a much greater MLSS. PM lagoons may use less energy but may require greater pond volumes with larger footprints and are more limited in reaching high levels of BOD conversion and nitrification.

 

Partial Mix Lagoon Performance Chart

 
Picture2
 
 

QUIESCENT ZONE (LAGOON)

A Quiescent Zone (QZ) or lagoon may be employed as a final polishing or equalization step before discharge on continuous discharge lagoon treatment systems. The QZ is typically a short detention lagoon of 0.5 to 2 days to trap solids escaping a Partial Mix lagoon. The QZ is often created by inserting a baffle on one end of a larger pond. Short detention is preferred to prevent algae growth, which may result in an increase in BOD and TSS levels out of the QZ lagoon. Covers can be employed to prevent ultraviolet light from reaching the quiescent zone in order to severely deter or prevent algae growth.

The QZ, when paired with a traditional aerated lagoon treatment system, is primarily utilized as a means to flocculate and capture solids that do not settle out in the Partial Mix lagoon. When paired with batch-type advanced treatment lagoon processes, such as the IDEAL Bioreactor, the primary purpose of the QZ is to equalize effluent flow versus residual solids removal. When used as a post-treatment equalization basin the QZ may be either earthen or concrete. Normalized flow leaving the QZ or post-treatment equalization basin, is well-suited to minimize sizing of downstream treatment unit processes such as UV or chemical dosage and or filtration.

IDEAL™ – Advanced Waste Treatment Lagoon for Nitrification/Denitrification

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The IDEAL process incorporates long sludge age suspended growth biological process with the attached growth process features of BioReef. Operating mode is a modified SBR process with benefits and features as described below.

The Intermittently Decanted Extended Aeration Lagoon Solution incorporates EDI floating lateral aeration system with premium fine bubble diffusers, two chains of BioReef™ BioCurtain™, a decanter with flow control valves, process controls, with Storm Mode™, and a blower package and controls. See pg. 22 for schematic.

The reliable components of the IDEAL system provide easy, cost-effective operation while providing high levels of BOD, TSS, and ammonia removal. The IDEAL process is specifically engineered to minimize sludge management plus extremely high flow events can be handled routinely with minimum biomass loss. The IDEAL process also provides substantial total nitrogen reduction as part of the basic package delivering lowest energy cost as a basic process that can be easily expanded to accommodate strict total nitrogen or phosphorous limits.

The IDEAL Process removes BOD and ammonia up front where warmest carbon-rich influent wastewater is available to increase biological activity and drive nitrification plus denitrification for recovery of oxygen and alkalinity. Other processes look to the back of the plant for ammonia removal where BOD concentration is lowest and where temperature loss can be significant resulting in limited process performance or control.

The need for thermal covers is minimized by performing treatment in the first cell IDEAL Bioreactor where wastewater is warmest. Simple sludge management may be incorporated similar to a conventional aerated lagoon system. The IDEAL Bioreactor retains and maximizes biomass in the first cell for optimal treatment capability by using the entire surface of the bioreactor for clarification/solids separation, then a programmed decant of the treated effluent.

A unique advantage of the IDEAL process is the ability to allow high surge flows to pass through the system without having significant impact on biomass concentration or post- surge treatment capability. The IDEAL’s unique combination of suspended growth activated sludge plus attached growth biomass minimizes washout and/or system overload.

 

Nitrate and Total Nitrogen Removal

Converting ammonia to nitrate is the first step in total nitrogen removal. Denitrification, or removing nitrate nitrogen is the second step necessary for total nitrogen removal. The IDEAL Process provides the benefit of both nitrification and denitrification as a natural function of the process and is easily expanded for total nitrogen and phosphorous control. Total nitrogen, nitrate and total phosphorous restrictions are on the horizon in almost all States and other systems may require expensive upgrades to achieve similar results. The IDEAL Process has shown an excellent ability to maintain performance during and after heavy wastewater surges that exceed design flow rates. IDEAL also easily adjusts to varying degrees of organic loading using a self -ballasting solids inventory with the combination suspended growth and attached growth process in the IDEAL Bioreactor providing excellent process stability.

EDI’s BioReef BioCurtain incorporates multiple chains of BioReef attached media that act as a biologically activated hydraulic curtain. The BioCurtain incorporates attached growth technology to increase biomass in the reactor, provide contact stabilization during the settling and decant phases, and acts as a hydraulic buffer to minimize short-circuiting potential within the complete mix IDEAL reactor.

The EDI engineered decanter and actuated valve assembly control effluent flow from the IDEAL Bioreactor. The decanter minimizes moving parts and reduces operator involvement. The IDEAL decanter and valve combination are engineered to minimize head loss between the IDEAL Bioreactor and downstream components; a crucial feature when upgrading an existing lagoon system. The provision of a Storm Mode™ operation of the decanter plus an emergency overflow provide fail safe operations should the decanter valve fail or lose electric power for an extended period.

The IDEAL Bioreactor has the advantage of utilizing EDI’s floating lateral system and premium fine bubble diffusers. The aeration technology applied to the IDEAL process combines an operator-centric focus with almost four decades of lagoon technology advancement. EDI heavy-duty polyethylene floating laterals stand up to environmental conditions and allow easy access even if the cell is insulated or covered. EDI fine bubble diffusers provide the optimum combination of aeration efficiency and mixing performance that are crucial in a complete mix lagoon environment.

 
                                     

Supplemental Lagoon Components

Blowers and Process Controls

EDI provides multiple control lagoon package choices to meet the needs of the owner and operator. A PLC-based control system is typically employed for maximum flexibility, reliability, and automation. This PLC option allows for easy future upgrade to advanced system process and blower control based on dissolved oxygen concentration, for maximum energy efficiency and total nitrogen removal. Expanded PLC interface can also deliver expanded data acquisition and reporting capabilities. Blower systems are available for multiple units for performance, turn down flexibility, and redundancy requirements. Sized to provide full range of process operation and economical energy management.

Motor starters and system controls are an integral part of any water resource reclamation system. EDI provides an ideal integration of controls and motor starters that ensure equipment longevity and owner satisfaction. Lifespan for blower equipment can be increased when the proper motor starters are used. Control systems can be equipped with upgrades including DO blower control, BioMizer lagoon aeration and mixing system, SCADA, and VFD technology for the ultimate in operator safety and convenience.

BioShade Algal Prevention Covers

There are several options available on the market for algae control and prevention. EDI’s BioShade eliminates the vast portion of ultraviolet light that enters the treatment lagoon and provides algae with the means to achieve photosynthetic growth. No UV, no algae. The BioShade cover is a floating, permeable lagoon cover that allows gas (from facultative lagoons or from aerobic lagoon aeration) to escape while allowing rainwater to pass through – thereby reducing or eliminating pooling on top of the cover.

BioInsulate Thermal Lagoon Covers for Heat Retainage

EDI’s modular cover system is comprised of a series of individual thermal panels that are encapsulated in a protective membrane sheath. The panels are available in a number of configurations and can provide insulation values up to R-30. The panel-type insulating cover is superior to other insulating cover options, such as particulate covers, due to their ability to resist environmental conditions (e.g., wind) and disturbance caused by treatment aeration systems.

Baffles and Lagoon Liners

EDI lagoon baffles provide for greater design flexibility by reshaping hydraulic flow in existing or new lagoons. Baffles are a way to address the potential for short-circuiting in a lagoon. They can also be used to create a series of small cells in series, rather than one large complete mix or partial mix basin, to increase the efficiency of the overall treatment process.

OMICRON™ tertiary filtration

  • Solids removal by direct filtration
  • Chemical feed + filtration for phosphorous ESS removal

Aerobic Digester

Earthen basin digesters can be a very effective and economical solution for sludge stabilization. Typical digester installations may be incorporated in any treatment plant with biological treatment and clarifier or separate solids wasting capability. Earthen digesters can be aerated and mixed with typical lagoon aeration/mixing equipment with floating laterals and suspended diffusers favored to allow ease of operation and maintenance.

EDI total lagoon solutions typically include earthen basin digesters when using a complete mix reactor with clarifier (extended aeration). The IDEAL advanced waste treatment process is another process that typically uses aerobic digester as part of the total solution.  

Disinfection

Total lagoon solutions may incorporate a final process step of disinfection. The EDI total solutions routinely incorporate UV disinfection or a chlorine disinfection system for maximum polishing. Note: EDI supplies premium quality disinfection systems manufactured by technology leaders to support total lagoon solutions.

BioMizer™ bioreactor mixing with sequencing solutions

A powerful tool for enhanced mixing in low intensity systems. Using BioMizer sequencing and control systems lagoons or other bio reactors can generally operate at energy levels for process oxygen. Systems that are mixing limited can have zones of aeration, plus programed sequence operation to complete mix basins 2–3 times the normal size based on 0.8 – 0.12 SCFM of air for continuous diffused operation. The major energy savings and process control by EDI offers smaller systems the opportunity to upgrade with full complete mix and not need extra energy above process oxygen. BioMizer control systems are by EDI and can be applied to almost any lagoon.  

Biomzer technology is an innovative concept emphasizing use of high efficiency diffuser systems properly engineered and controlled to provide aeration/mixing to optimize municipal and industrial wastewater treatment. Biomizer systems utilize high efficiency EDI tube, disc, or panel assemblies with integrated control for aeration and mixing of the biological reactor. Biological treatment systems are sized for use of fine bubble and high efficiency aeration designs. Biological systems may be mixing limited with optimized fine bubble diffuser efficiency i.e. air for oxygen supply is less than accepted air or energy levels to maintain all solids in suspension requiring additional mixing considerations:

Options to provide supplemental or enhanced mixing to the bioreactor include:

  • Over oxygenating and over aerating to achieve mixing.
    • Aeration wastes energy and excess D.O. may not allow
    • BNR process to function.
  • Use coarse bubble diffusers
    • Not desirable in most cases as uses about 2 times the energy of fine bubble
  • Aerate with high efficiency diffusers then add mechanical mixers to suspend/mix reactor solids
    • Excellent for oxidation ditch process.
    • Not preferred for conventional active sludge.
  • Use EDI BioMizer™ with highest efficiency diffusers for low aeration energy.
    • Create multiple aeration zones in reactor then sequence aeration air volume into each zone in a programmed sequence.
      • All air required to supply process oxygen supplied all the time.
      • Air supplied in programmed sequence to operate aeration zones.
      • Air always provides process oxygen while being switched between aeration zones in the reactor.
      • Sequencing generally between 2 to 4 zones.
      • Aeration switched between zones with frequency to prevent most solids from settling while aeration is active in alternating zones.
  • BioMizer controller (PLC) used to sequence operation of aeration zones.
  • Duration of operation per zone to assure full complete mix and uniform suspension of solids (MLSS).
  • Frequency of sequencing to control DO per zone and to manage solids.
  • Typical BioMizer ½ to ⅓ the energy of mixing limited systems aeration technology.

In addition to optimizing energy consumption for biological reactor mixing, BioMizer technology can also be used to create aerobic/anoxic zones in a continuous sequencing reactor for biological control of nutrients. BioMizer sequencing for nutrient control can produce full nitrification with substantial denitrification in BioMizer – N configuration. Coupled with anerobic zones the BNR capabilities of the process can be expanded for bio-P removal.

 

OPERATING SEQUENCE

Typical 2 Zone BioMizer Reactor

Zone A = 50%

Zone B = 50%

total-lagoon-solutions
Phase I

Zone A – Under aeration

  • Time of aeration programmable.
  • Air volume to satisfy plant total oxygen demand goes entirely into Zone A.
  • Energy level in Zone A greater than 0.12 (2.05 Nm3/m²) CFM/ft2 per ASCE and WPCF M.O.P.
  • DO level increases during aeration

Zone B – No air

  • Off cycle programmable.
  • DO concentration drops as bio activity continues with no air.
  • Minor solids settling or trending toward floor.
Phase I-II

Valve B opens to allow air to zone B prior to valve A closing i.e., both valves open for a short time to prevent blowers from discharging against closed valves.

Phase II

Zone A – No air

  • Off cycle programmable.
  • DO concentration drops as bio activity continues with no air.
  • Minor solids settling or trending toward floor.

Zone B – Under aeration

  • Time of aeration programmable.
  • Air volume to satisfy total oxygen demand goes entirely into Zone B.
  • Solids re-suspended and complete mix during cycle operation of Zone B with energy level in excess of 0.12 CFM/ft2 (2.05 Nm3/m2)
  • DO level increases during aeration
Phase II-III

Valve A opens to allow air to zone A prior to valve B closing i.e., both valves open for a short time.

Phase III

Repeat programmable sequencing.

  • Primary Screens
    • Primary screens have been demonstrated to offer several benefits for long term performance in most lagoon systems. Removal of rags and other significant gross solids delivers reduced maintenance and minimizes nuisance conditions in almost all lagoon applications. For partial mix lagoons where settling and sludge management are engineered as part of lagoon volume and operation, the screens minimize nuisance conditions but are not critical to process performance. For higher rate lagoon systems of complete mix (with or without clarifiers) and IDEAL advanced treatment reactors screening is definitely recommended.
    • EDI lagoon solutions will include premium screening equipment or systems from quality manufacturers working as partners with EDI for total system performance. 
    • General design  considerations for aerated lagoons.
  • BioSweep- Enhanced lagoon aeration
    • Enhanced lagoon aeration with Biosweep operation
      • Maximum lagoon coverage
      • Maximum suspension of solids at low energy levels
      • Minimizes cellular pumpage between laterals
      • Two-hose diffuser mount keep diffusers level at all times
      • Handles variable liquid levels
      • Superior 0, transfer efficiency

BiosweepTM

Tether Tension Controls Movement and Coverage
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EDI ADDITIONAL SUPPORT PROGRAMS

Complete lagoon solutions from EDI not only simplify the design and provision of lagoon upgrades.  They also allow for worry-free communication and coordination, because EDI can provide installation, start-up, and maintenance or service contracts for your lagoon system.

Aeration Works Installation

EDI Aeration Works division was created to give contractors and operators of aeration systems a source for fast, reliable installation and maintenance. The EDI Aeration Works group is made up of experienced installers and field service professionals. Aeration Works personnel are experts at the installation and maintenance of aeration systems with process and operational optimization objectives.

Aeration Works (AW) expert installers are faster and more thorough than someone new to installing in-basin components of EDI aeration systems. AW experts know what tools are needed, how to perform installations quickly, and how to ensure it is done exactly to manufacturer’s specifications. Utilizing Aeration Works’ expertise for system installation ensures the job is done right.

Benefits of planning for Aeration Works installation include:

  • Mechanical warranty against defects and workmanship increases from 2 to 5 years.
  • Eliminates inspection requirements for validation of process warranty.
  • Project completed more quickly with seamless communication and familiarity between installation crew and manufacturer.
  • Decreased contractor administrative duties (inspection scheduling, inventory, subcontractor scheduling, etc.)
  • Single-point responsibility should any future issues arise.

Preventative Maintenance Program

For maintenance or preventative maintenance, the Aeration Works group has the experience to evaluate the degree of work needed then properly refurbish a system for maximum long-term performance. When construction crews or contractors have already been selected, Aeration Works can also provide supervision to assure the work is done to manufacturer's specification.

A maintenance plan allows facility operators to outsource scheduled maintenance of their aeration systems to EDI Aeration Works group. When this program is chosen as part of a new IDEAL Process sale, the mechanical warranty of the aeration system is extended as long as a service agreement is in place. Aeration Works can inspect any existing aeration or treatment system and a preventative maintenance program can be developed. 

The benefits of a preventative maintenance plan include:

  • Minimizing unscheduled outages
  • Easy budgeting with a single annual expense to cover all parts and labor
  • Increased energy efficiency and savings
  • Decreased operating costs

Infinity Program

This program incorporates the mechanical warranty and services of the Preventative Maintenance Program but goes one step further by guaranteeing the performance of the aeration system.  Under this program, EDI maintains the physical condition of the membranes through preventative maintenance procedures and will periodically measure the performance of the membrane.  Aeration Works will replace or adjust the equipment to ensure the aeration system operates within a predetermined performance envelope.

 
General Design Considerations for Aerated Lagoons

Aerated lagoons have unique physical characteristics to be considered when selecting process equipment to use in a lagoon design. Items for consideration in general application of aeration technologies include:

Is the bottom level?

If bottom of lagoon is not level it is difficult to deploy a floor mounted diffuser system effectively. Floor mounted units at higher elevations receive a disproportionate amount of air with poor air distribution across the lagoon. For systems with uneven floors best performance may require floating systems.

  • Floating laterals with suspended diffusers. All units same depth from floating air supply pipe (lateral).
  • Surface aerators which float on surface. (see comparison surface aerator with diffuser systems)

Sludge Deposits

With sludge deposits selection of aeration is similar to non-level floor and floating diffuser systems or floating surface aerators to be considered as advantageous.

Earth Floor

Systems must be able to operate without erosion of earth floor and remain level for long term operation.

  • Surface aerators to be reviewed for erosion below units. Some designs require vortex erosion pads below the units with adequate base area and weight.
  • Diffuser systems are generally low intensity aeration allowing either floor mounted or suspended (floating lateral) units.
Lined Lagoons

Systems must operate without damage to liners.

  • Floor mounted systems must have broad bases for support and prevent puncturing liners.
  • Surface aerators must have vortex protection in many basins. Vortex from aerators can easily suck liner off floor, into aerator and cause major system failures.
  • Suspended diffusers generally never touch liner and low intensity aeration at any unit is best liner protection.
Oxygen Transfer

All systems need to be reviewed on basis of energy efficiency. High efficiency diffuser systems generally saved 30% - 50% energy over surface aeration (see diffuser/surface aeration analysis). For diffuser systems clean water transfer data may be available but generally must be adjusted down from test data generally developed for concrete aeration basins i.e. activated sludge testing. Low energy per unit of lagoon volume reduces most published clean water test data! See clean water testing protocol and analysis.

Variable Water Levels

Systems on the floor of the lagoon must be designed for aeration and mixing at the lowest water level. Blowers must have motors sized for maximum water level. As a result, floating aeration systems generally preferred to always operate at constant diffuser submergence and constant design blower pressure. Surface aerators also accommodate variable water levels better than floor mounted diffusers but only allow limited variation in levels.

Access for Maintenance
  • Floating diffuser systems have 100% components accessible from surface for maintenance.
  • Surface aerators are also suitable for access but subject to limitations (see comparison of diffusers to surface aeration system).
  • Floor mounted diffusers and piping more difficult to access.
Empty Basins or Basins that Liquid Level Very Low i.e. Less Than 2 – 5 ft.

Care must be employed when water levels are reduced, or basins are empty for extended operating periods:

  • All components must be suitable for exposure to sunlight. Generally stainless-steel coarse bubble diffuser systems are preferred.
  • Surface aerators must be shut down to protect basin or basin liner as water level is lowered.
  • When some water can be maintained over diffuser units full protection of UV and full choice of diffuser types may be available.
Aeration Distribution

Generally multiple energy input points will benefit basin process performance.

  • Floating diffuser systems generally best suited for distribution of aeration and mixing. See comparison with surface aerators.
  • Surface aerators suitable when proper type units with proper energy levels and proper spacing.
  • Floor mounted diffuser systems generally more difficult to cover large basins and or maintain uniform air distribution. (see analysis of floor mounted diffuser systems).