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qualificationsQ U A L IF IC A T IO N S

Computational Fluid Dynamics

P R E F A C E / C O N T E N T S

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0207

19

Carollo Engineers is an environmental consulting firm with more than 1,050 employees in 44 offices throughout the United States. All of our work is performed in the areas of water and wastewater, resulting in a level of understanding of key project issues that few can match. Carollo strives to maintain the tradition of using sound and proven engineering principles while moving progressively forward to keep abreast of changing times and new technologies.

This is a specialty Statement of Qualifications (SOQ) for Carollo detailing some of our experience and expertise in the field of water treatment specific to this topic.

CONTENTS

Issues and Differentiators

Key Achievements

Testing and Optimization Capabilities

Publications

Company Profile

I s s u e s A n D D I f f e r e n t I A t o r s 1

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Water treatment requirements are evolving along with our understanding of environmental system needs and emerging contaminants of concern. As a leader in the development of new technologies for water and wastewater treatment, conveyance, and storage, Carollo has developed approaches to address these emerging issues. Simultaneously, existing infrastructure requires replacement or increased capacity. Many modeling tools are routinely employed in modern engineering practice to evaluate, predict, analyze, and design for replacement, expansion, and construction of new facilities. A powerful technique that Carollo has helped to pioneer in the water and wastewater industry — and has been using for almost two decades — is computational fluid dynamics (CFD). CFD is an advanced numerical modeling tool for solving 3-dimensional (3D) fluid and process problems. Enhanced by the ability to visually display results of flows and contaminants in complex geometries, this tool allows us to look inside the flow field and optimize process geometry.

The fluid flows encountered in the water and wastewater industry are turbulent, and in many cases, multiphase, which leads to uncertainty in designs. This uncertainty is traditionally addressed by using conservative safety factors. Given current resource limitations, there is a considerable incentive to reduce uncertainty and maximize capacity of existing and future water facilities. At Carollo, CFD is integrated into the design process to efficiently solve complex flow and process problems, leading to better understanding of system limitations and aiding in the development of innovative designs. This approach supplies the design engineer with a virtual laboratory for testing and optimization providing the ability to screen various design alternatives and converge on an optimal system design. In addition, this tool has often been applied to investigate performance problems at operating facilities, maximize the capacity, and lower operating costs.

Application of CFD models in the water and wastewater industry has become popular in recent years with better access to powerful desktop computers and readily available commercial CFD software packages. Carollo has devoted significant resources into developing

CFD shows the flow path through a closed vessel UV reactor.

Complex turbulent hydraulics

lead to flow conditions that can be difficult to

predict with other means during design.

Issues and 1

Issues and

r


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ddthe necessary tools to stay at the forefront of this technology and integrating knowledge gained from applied CFD research into our design process. Carollo’s commitment to incorporating conventional and innovative approaches to water and wastewater design goes hand-in-hand with in-house CFD modeling services we provide to our clients. Carollo has used CFD modeling on nearly 100 projects over the last two decades with over 50 of these projects occurring in the last five years.

A number of firms now offer general CFD services. However, they are usually not specialized in water and wastewater treatment processes, regulations, and construction methods. By keeping modeling services in-house, Carollo has integrated CFD modeling into the design process and developed custom tools specific to our industry. In this respect, Carollo’s approach to providing CFD services is distinctly different from many consulting firms. One crucial advantage to this approach is that we understand the strengths and limitations of CFD modeling as applied to water and wastewater treatment. We understand when CFD models can be successfully applied and when other approaches are more suitable. In-house modeling reduces contracting and communication requirements resulting in lower overall cost.

Another key element of providing CFD in-house is the ability to leverage our technical staff with backgrounds specific to a given project need. The key individuals in Carollo’s CFD group have expertise in hydraulic engineering, numerical modeling, water and wastewater design, and process engineering, allowing them to not only understand project goals, but also provide valuable input in the design process. Their experience brings the unique ability to integrate CFD modeling and process design experience to each project, making them an important part of the design team. Our CFD group has worked on multiple design as well as applied research projects within the Carollo Research Group, allowing integration of experience into each project to assist the design engineer. This experience, along with our knowledge of numerical modeling, minimizes errors in misapplication, reduces the time and cost required in the overall design phase, and results in a superior design.

Carollo has conducted many research studies that have included significant CFD components, leading to general application of CFD within the water and wastewater treatment design, including:

! American Water Works Association Research Foundation (AwwaRF) “Improving Clearwell Design for CT Compliance,” 1999.

! WaterRF (formerly AwwaRF) “Design and Performance Guidelines for UV Sensor Systems,” 2007.

Multiphase flow coupled flows have complex interactions.


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dd ! WaterRF “Optimization of UV Disinfection,” 2007.

! WaterRF “Computational Fluid Dynamics Based Models for Assessing UV Reactor Design and Installation,” 2009.

! WaterRF “Guidance Document for Testing Medium Pressure UV Inactivation of Viruses,” Ongoing.

! WaterRF “Develop Interim Factors for Credit with MP UV Systems,” Ongoing.

! WaterRF “Integrating Action Spectra and CFD Analysis for Optimizing Inactivation Credit of Regulated Pathogens in Medium Pressure UV Disinfection Systems,” Ongoing.

cfD DesIgn BenefItsIncorporating CFD into the design process enables our team to:

! Evaluate multiple design alternatives before construction, lowering the risk in application of innovative approaches and reducing the risk that important elements are overlooked.

! Diagnose deficiencies and evaluate operating strategies for existing systems providing optimized process efficiency while minimizing O&M costs.

! Evaluate process performance without physical modeling or pilot testing resulting in shorter design periods and lower design cost.

! Evaluate “black box” technologies reducing reliance on manufacturer claims, which allows for the selection of the best equipment to meet project needs.

! Assess cost saving or constructability changes proposed by contractors during construction.

CFD models have been used to improve the design and performance of most elements of a water treatment system from intake structures through the treatment train and finished water storage. At the base level, these models resolve flow field characteristics of single or multi-phase fluid systems. Additional process models can be integrated into the flow model for dissolved or particulate mass transport and

CFD modeling of clearwell tracer testing became a common application after “Improving Clearwell Design for

CT Compliance” was published.

Straightforward comparisons can be made on the impact of different types of equipment in the

flow stream.

The model allows us to test conditions that may be difficult to or undesirable to conduct

in the field.

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reaction kinetics to predict the overall process performance of a given system. This approach allows operators and engineers to look inside the “black box” to gain an understanding of the critical factors that influence process efficiency. Examples of CFD application to water treatment, conveyance, and storage facilities are provided in the table above.

Component Benefits of CFD Applications

Water Intake Facilities ! Improved water quality from stratified reservoirs ! sedimentation management ! site minimization ! Aquatic organism exclusion or management

Pump Station ! Verification/improvement of pump intake hydraulics to meet Hydraulic Institute standards

Flow Distribution ! optimized designs for flow-splitting

Coagulation/Flocculation ! Improved mixing ! Improved flocculation formation

Sedimentation ! reduced flow short-circuiting and velocity gradients ! Improved solids capture

Chemical Disinfection ! Location of chemical feed ! Improved t10/t ratios ! Location of monitors ! reduced DBP formation

UV Disinfection ! Balanced flow split ! Improved flow distribution ! Dose verification with uVXPt

Water Storage ! Improved reservoir mixing ! reduced DBP formation

CFD-Enhanced Design Benefits for Drinking Water Facilities

Chemical mixing modeling helps locate system monitors to optimize dosing.

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CFD can also be applied to improve many components of a wastewater system from collection facilities through the treatment process to reuse or discharge the environment. Examples of CFD applications to wastewater conveyance and treatment facilities are provided in the table above.

Component Benefits of CFD Applications

Collection System ! Improved surge storage operation ! sewer junction flow splitting optimization ! Head loss evaluation of unique facilities

Headworks ! Improved screen channel balance ! Improved screen flow distribution ! Improved grit separation

Pump Station ! Verification/improvement of pump intake hydraulics to meet Hydraulic Institute standards

Flow Distribution ! optimized designs for flow-splitting

Primary and Secondary Sedimentation

! Improved inlet energy dissipation ! reduced flow short circuiting and velocity gradients ! Improved solids capture

Activated Sludge Processes

! solids Mixing optimization ! oxygen transfer Improvement ! Improved reactor Design for Biological Processes

Chemical Disinfection ! Improved t10/t ratios ! reduced DBP formation

UV Disinfection ! optimized dosing strategy ! reduced power usage

Effluent Discharge ! Improved Discharge facilities for receiving Water Mixing Zone

Digester ! Mixing optimization

Dissolved Air Flotation ! Minimized short circuiting

CFD-Enhanced Design Benefits for Wastewater Facilities

Mixer size and location tested to verify solids were well mixed.

K e y A c H I e V e M e n t s 6

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The project profiles on the following pages present highlights of Carollo’s key achievements in CFD modeling of Water and Wastewater Treatment and Conveyance. These examples illustrate our ability to:

! Implement innovative technologies to improve process design and performance.

! Integrate engineering and research to achieve practical solutions tailored to specific client needs.

! Involve project participants early in the process to “demystify” advanced technology and fully understand each other’s needs.

! Offer advanced solutions that are practical, affordable, and reliable.

We would be happy to provide client references that can attest to the quality and responsiveness of Carollo’s services.

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The City of Los Angeles filter plant UV treatment system at the Van Norman complex was the second largest UV facility in the world at the time of design. Fourteen 48-inch diameter UV reactors were located in parallel downstream from the filter plant with a capacity of up to 600 mgd. CFD modeling was used to throughout the design process to evaluate and optimize the hydraulics of the facility.

The reactors are located in parallel along a common deadend flow distribution channel. This configuration can lead to a non-uniform flow split along the various paths due to the complex losses associated with dividing flow. The channel design for the filter plant UV facility was refined using CFD modeling to develop a design that minimized headlosses with passive flow splitting. The final layout included an outside tapered wall to minimize excavation and concrete costs while also reducing conflicts with existing buried utilities. The primary baffle is parallel to the reactors and a stub wall is included to improve the flow distribution at most downstream reactors.

The design has a good flow split for the range of cases modeled. The system will have online flow monitoring and the ability to modulate valves to adjust the flow split if needed for situations where the flow reaches the maximum validated flow. Models showed that separating offline reactors improves the flow split and reactor hydraulics for all scenarios and should be part of control algorithm.

Los AngeLes DepArtment of WAter AnD poWer, CALiforniA

Van norman complex uV treatment of Drinking WaterH

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The initial flow distribution baffling led to jetting and large velocity field variations in the reactor piping.

The final inlet design helped balance flow and create similar velocity fields for all reactors.

The model was used to develop a deflector that improved the flow

distribution to the last reactor.

CFD modeling throughout the design process to evaluate and optimize the hydraulics of

the facility.

Model used to design a passive flow split to save system energy.

The footprint was minimized to reduce construction costs.

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Aged equipment was replaced in the eight 195-foot diameter activated sludge secondary clarifiers at the Dallas Water Utilities (DWU) Central Wastewater Treatment Plant (CWWTP). While DWU needed the design schedule to be expedited, they considered this rehabilitation as an opportunity to improve the performance of the clarifiers without major structural modifications to the existing basins or to the below-grade piping. The activated sludge secondary clarifiers had been identified as the limiting factor, directly reducing plant capacity. Optimum settling in the clarifiers is vital to clarifier efficiency and will deliver more concentrated solids in both the return and waste streams and minimize the volume of water returned or wasted.

Due to the minimal floor slope of the existing clarifiers, only hydraulic-style sludge collectors were considered, including draft tube, vertical riser pipe, and hydraulic header. While the incremental efficiency gain of the hydraulic header collectors is an improvement, it does not improve the settling characteristics in the clarifier. In order to identify settling improvements, the center column, inlet well, and flocculation well were modeled using 3D hydrodynamic CFD modeling, which has proven to accurately mimic conditions in clarifiers during full-scale testing.

The result of this design is an inlet well arrangement with target baffles for energy dissipation custom designed and optimized for these large clarifiers. Using CFD modeling allowed DWU to implement an energy dissipating inlet arrangement that did not require proprietary technologies and without allowing each manufacturer to bid a unique configuration. The inlet well designed using CFD modeling leveled the playing field for bidders and resulted in the installed arrangement matching the modeled configuration, thus ensuring DWU that the performance of the clarifiers meets its expectations. By using the unexpected failure of equipment as an opportunity to improve performance, DWU was able to do more than simply react and replace equipment. They were able to improve the clarifiers within their budget and schedule and have set the stage for process performance at the plant for the next 20 years and beyond.

DALLAs WAter UtiLities, texAs

central Wastewater treatment Plant secondary clarifier rehabilitation

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The model illustrates a that tradition inlet improvement would still lead to turbulent

conditions within the floc well.

A modified inlet was developed with the CFD model and installed, which dissipated inlet energy and led to more rapid sedimentation.

The original clarifier inlet led to turbulent conditions within the floc well.

Carollo’s sedimentation model used to develop an improved inlet

for a unique clarifier design.

The model predictions of operations were accurate.

Recommended improvements increased clarifier capacity after

installation.


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As part of a plant rehabilitation and upgrade, a new headworks screen system and influent pump station are being built for the San Leandro Water Pollution Control Plant. The new headworks will handle up to 27.5 mgd through three screen channels and parallel self-cleaning trench wet wells. A CFD model was used to investigate the screen channel and pump intake hydraulics.

The site layout required bend just upstream from the screen channels. The model was used to evaluate flow split between the screen channels and flow distribution approaching the screens.

Several tests were done to improve the geometry of the influent channel and provide better flow distribution to the screens.

The model was also used to evaluate the pump intake hydraulics. One of the parallel self-cleaning trench wet wells was modeled in detail with the three submersible pumps. The model was used to develop geometric modifications to the wet well geometry that reduced formation of vortices that could enter the pump and improve the pump intake hydraulics. A pump down test was performed with the model to simulate the self-cleaning cycle, which showed that the geometry promoted good sweeping of the wet well floor.

sAn LeAnDro WAter poLLUtion ControL pLAnt, CALiforniA

Headworks screening and Influent Pump stationH

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This shows an overview of the complete system

modeled.

Evaluated and improved approach conditions to influent

screens.

Developed wet well modifications to improve pump intake

hydraulics.

Modeled a self cleaning pump down cycle.

The model shows different velocities at the water surface during a self-cleaning cycle.

Sub-surface vortices were identified that could impact pump perforance.

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A CFD model was used to evaluate the primary clarifier influent channel hydraulics at the Central Marin Sanitation Agency’s WWTP. There were five primary clarifiers at the facility, located along a common influent channel, identical across the centerline. Two additional primary clarifiers were added to the system to increase the capacity; however, the site dictated that the new clarifiers be located on one side by extending the influent channel to their location. Gates at the entrance to the clarifiers will be used to adjust the flow split to a relatively uniform distribution between all of the clarifiers.

As the flow conditions through the system are complex, the losses are difficult to explicitly quantify. A 3D CFD model of the system was developed to evaluate the flow split between the primary clarifiers. Modeling focused on a peak wet weather flow of 125 mgd and the flow rate monitored through each clarifier. The target flow was 17.8 mgd, but the flow distribution initially ranged from 4.7 to 37.1 mgd.

The flow path to clarifier 5 is the least obstructed, leading to the highest flow. There was initially more flow toward the new clarifiers than their design flow. Jetting through the center slot hits the wall, rolls, and turns 90 degrees to parallel the chamber walls, leading to high-velocity flow past the clarifier 3 gates in both directions and causing it be starved for flow. Headloss can be high for this type of dividing flow situation where a portion of high-velocity flow past an opening needs to pass through the opening.

The gates were adjusted in the model until the flow split was relatively uniform. The flow split ranged from 15.9 to 19.0 mgd between the clarifiers within a reasonable gate-operating range. The gates provided sufficient headlosses at the clarifier inlets to balance the complex losses along the flow paths through the distribution channels, which included contraction/expansion losses accounting for the approach flow direction and complex dividing flow losses. The CFD model demonstrated that the flow could be uniformly distributed between the clarifiers during peak flow condition by adjusting the gate openings for each clarifier.

CentrAL mArin sAnitAtion AgenCy, CALiforniA

WWtP cfD Modeling to Manage flow split Between Primary clarifiers

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Adjusting clarifier inlet gates balances flow between all seven clarifiers.

High-velocity flow past the clarifier 3 entrances reduce flow to the clarifier.

CFD model to evaluate the primary clarifier influent channel

hydraulics.

The model was used to identify flow split due to complex

hydraulic losses.

The model demonstrated that the flow split could be balanced

within the operating range of existing equipment.


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A 1-million gallon (MG) clearwell located below a filter gallery provides chlorine disinfection at the Dakin Yew Water Treatment Plant (WTP). Redwood boards located between roof support columns create a serpentine path through the clearwell. The hydraulic residence time is 2 hours at a typical operating flow of 11 mgd. The clearwell operates without trouble; however, the residual sampler is located in an area outside of the primary flow path, leading to slightly unrepresentative measurements. A CFD model was used to develop baffling changes to improve residual measurements.

The model was used to simulate slug dose tracer tests by injecting the tracer at the chlorine diffuser location and then tracking it for two hydraulic residence times. The concentration at the outlet and total volume in the clearwell were monitored to develop a residence time curve and the characteristic T10. The initial configuration had a T10 of 0.52, typical for the geometry. For this study, geometric changes should not decrease the T10 from the initial clearwell geometry.

Based on the initial results, several outlet baffles arrangements were tested in the model to eliminate any flow circulation near the outlet. The final baffle design better flushed out the corner where the monitor sensor is located. The model shows a slightly improved T10 of 0.54. The changes were incorporated in the clearwell, and the sensor now reads very consistently, ensuring the proper chlorine dose is being used.

City of BeLLinghAm, WAshington

Dakin yew Water treatment Plant clearwell Baffle configuration Investigation

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5E-05 100

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Outlet FractionPercent Recovered

The residence time distribution is typical for this type of layout.

Model to simulate slug dose tracer tests by injecting the

tracer.

Model used to develop baffle improvements to aid in dose

monitoring.

Outlet baffles arrangements tested to eliminate any flow circulation near the outlet.

Some tracer passes the outlet initially.

The additional baffles arrangements eliminate any flow circulation and better

direct flow at the outlet.

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A new CO2 injection system is being added for pH control at the City of Manhattan WTP, where flow from four sedimentation basins is combined into a single pipe. The length of piping required to achieve a uniform mixture of water and CO2 needed to be identified to locate a monitoring equipment and minimize the overall distance required for complete mixing. A CFD model was used to study flow in the system to optimize the location of the CO2 diffusers and configuration of influent piping.

The model showed that the initial configuration took over 50 pipe diameters to achieve complete mixing through the cross section. The location and orientation of the diffusers were adjusted to improve mixing. The configuration of the four influent pipes were adjusted based on the interaction of the various fluid streams when combined. The final configuration resulted in more rapid mixing of the CO2, with the mixture close to uniform in approximately 30 pipe diameters.

City of mAnhAttAn WAter treAtment pLAnt, KAnsAs

carbon Dioxide (co2) Diffuser AnalysisH

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One of the sedimentation basins upstream from the CO2 injection system.

[Left] CO2 mixing into the flow stream. [Right] Flow path of combing fluid streams and mixing of CO2 into the water.

Optimized configuration of inlet piping and diffusers to

promote rapid mixing.

CFD model showed required length of downstream piping to

achieve uniform mix.

Model results were used to locate monitoring sensor.


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A CFD model study evaluated the jet aeration and mixing system of a sequencing batch reactor (SBR) system at the Blacks Ford Regional Water Reclamation Facility (BFRWRF) in Jacksonville. Inadequate mixing in the SBR system during unaerated pumped mix cycles may be inhibiting the ability of the facility to remove nitrogen. Additionally, the jet mixing system was thought to be an inefficient system for mixing and aeration as compared to other modes of mixing and aeration such as diffused aeration with mechanical mixers.

Field tests were conducted to establish solids concentration profiles under normal operating conditions. CFD simulations were made of the field test conditions using customized functions to simulate suspended solids settling and transport as a scalar within the tank. The model confirmed that air would produce good mixing. The solids concentration profile at different times after initiation of a pumped mixing cycle showed that the pumping could not keep the solids well mixed, which caused a vertical gradient to develop.

Following qualitative calibration, the model was used to study operational changes to improve mixing using higher nozzle velocities. Increasing the jet velocity from 8 to 9.9 fps reduced solids separation in the tank, but did not eliminate it. Increasing the jet velocity to 11.5 fps eliminated all clear water separation and produced relatively well-mixed conditions in the tank, but did not eliminate solids separation entirely. Increasing the jet velocity to 13 fps produced relatively complete mixing, since these options would require a significant increase in pumping horsepower, other mixing options were recommended. Improving the mixing system should provide more efficient denitrification within a given anoxic cycle time and may aid in a better settling sludge. Furthermore, more efficient denitrification might allow the anoxic cycle times to be reduced, and consequently the aeration cycle times to be lengthened, thereby providing better nitrification during cold weather conditions.

In a follow-up investigation, Carollo simulated the influence of density currents on solids mixing. These studies found that if the fluid was considered neutral density (no influence of solids concentration on fluid density), the model over-predicted the degree of mixing that had been seen in the calibrated tests. These follow-up studies showed the importance of simulating density gradients in tests on activated sludge mixing.

JACKsonviLLe eLeCtriC AUthority, fLoriDA

Blacks ford regional Water reclamation facility sequencing Batch reactor Mixing

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Solids were uniformly mixed during air mixing phase.

The model showed solids stratification during jet mixing as observed during

field testing.

Modeled two mixing cycles of an SBR, jet mixing and air

mixing.

Solids concentration profiles compared well with

field measurements.

Model used to estimate mixing energy needed to fully mix tank

during jet mixing phase.

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UV is used for disinfection at the Chambers Creek Regional WWTP. A new UV system has been designed to accommodate future peak flows up to 80 mgd and provide better reliability and redundancy. The new system will be constructed within an existing basin, formerly used as a chlorine contactor, downstream of the secondary clarifiers, and have seven parallel channels.

Balancing and distributing flow is commonly done with baffling or other flow control devices such as weirs, all of which increase system head loss. The proposed system is being retrofit into a hydraulic profile with limited head available for flow splitting and redistributing the flow profile. CFD modeling was used to evaluate modifications that would improve the passive flow split and flow distribution while minimizing headloss.

Initial modeling showed that the passive flow split could range in the channels between 61 and 117 percent of the design flow, and that the channel flow distribution could be non-uniform approaching the UV banks. The key details of the final design developed with the CFD model included a flow distribution baffle wall to balance the flow between seven UV channels, channel flow distribution baffle plates, the UV lamps, the delta wing baffles, and the outlet weirs. The channel water level is controlled with finger weirs, providing a very long total crest length that conveys a wide range of flows within a relatively narrow range of depths.

The modeled flow split with the final design is summarized for four scenarios in the table below. Channel flows ranged from 13.2 to 13.5 mgd for the first three 80-mgd scenarios, and 10.2 to 10.3 mgd for fourth 41.1-mgd scenario. The baffle headloss calculated by the CFD model was 4.1 inches at 13.4 mgd. The headloss across each lamp bank was 0.3 inches. Overall, the system design appears to provide good hydraulic conditions for the horizontal UV system proposed.

pierCe CoUnty pUBLiC WorKs AnD UtiLities, WAshington

chambers creek regional WWtPH

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ScenarioModeled UV Flow (mgd)

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

1 13.5 13.4 13.4 13.4 13.4 Off-line 13.4

2 13.5 Off-line 13.4 13.3 13.3 13.3 13.2

3 Off-line 13.4 13.4 13.4 13.3 13.3 13.2

4 10.3 10.2 10.3 Off-line Off-line Off-line 10.3

Velocity magnitude at sections through the UV channels shows the channel

baffle distributes flows approaching the UV banks in the channels.

Velocity magnitude at a horizontal section through the complete system shows

uniform velocity through the UV channels.

Existing tank utilized for new UV system, saving on

piping, space, etc.

Model used to design low headloss improvements to

balance flow.

In-channel flow distribution baffle performance was verified.


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CentrAL ArKAnsAs WAter, ArKAnsAs

ozark Point WtP flocculation and sedimentation Basin Hydraulics

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The flocculation-sedimentation basins were evaluated at the Ozark Point WTP. During the last treatment upgrade, an old tank was divided into two halves by an inlet channel through the middle. Each side includes a similar flocculation and sedimentation zone. Flow is distributed by baffles and weirs from the inlet channel to the two sides. The flocculation zone contained eight 2-blade propeller mixers, with flow continuing to the sedimentation basin through an underflow baffle.

The CFD model showed the influent momentum continued towards the opposite wall within the flocculation zone leading to higher flows toward the far side of the sedimentation zone. This effect slightly decreases the hydraulic efficiency of the sedimentation zone as particles on the higher velocity side have less time to settle before flow exits the weirs. A tracer test was performed for each side of the basin to characterize the hydraulic efficiency. The T10 on the right was 0.43 and was 0.54 on the left. It appeared that the slightly shorter flocculation zone on the left, coupled with the sludge trough downstream from the underflow baffle helped better distribution flow across the sedimentation zone leading to higher hydraulic efficiently than observed on the right side of the system.

The variation between the halves of the system and overall low T10 indicate that the hydraulic efficiency could be improved somewhat. Modifications in the flow distribution channel and/or changes in the underflow baffle could improve the flow distribution across the width of the sedimentation zone making all flow paths approximately the same length. A limited number of baffling improvements that would be easy to implement were tested on the right half of the system. The best option improved the T10 to 0.5, a 7-percent improvement in hydraulic efficiency.

Inlet geometry coupled with basin configuration led to short

circuiting in the basin.

The model was used to evaluate improvements and showed that

simple baffle changes could increase the hydraulic efficiency

by 7 percent.

Baffles and weirs along the inlet channel distribute flow to each side of the system.

The right side of the sedimentation basin.

The CFD model included all of the key

details in the system.

The velocity was higher

along one side of the sedimentation zone

leading to short-circuiting.

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K E Y A C H I E V E M E N T S 16

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The use of UV disinfection for drinking water treatment is increasing as a result of the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and Stage 2 Disinfection/Disinfection Byproducts Rule. In order for utilities to receive inactivation credits for UV under the LT2ESWTR, systems must first be validated using costly biodosimetry methods under the specific design configuration and operating conditions planned for full-scale treatment. CFD is a modeling tool that has been shown to successfully determine relative differences in UV reactor performance as the model provides detailed information on flow-field characteristics that can aid in identifying hydraulic-based reasons for variations in reactor performance.

In many cases, utilities will be retrofitting UV systems into existing treatment processes, so they will be limited in their available inlet/outlet configurations and may not be able to achieve optimal configurations. Thus, a tool is needed to assess hydraulic impacts on UV disinfection performance and evaluate alternative configurations early in the design process. Moreover, a better understanding of the effects of inlet/outlet hydraulic configurations on UV disinfection performance will result in more pragmatic design recommendations with potential to significantly reduce capital costs in future UV installations.

The goal of this work was to evaluate whether CFD-based models could be used to accurately model the hydraulics, UV intensity distribution, and reduction equivalent dose (RED) in commercial UV reactors with different reactor and piping configurations. In particular, the primary objective was to demonstrate whether CFD-based models could be used to compare the performance of installed UV disinfection systems relative to validated systems with different piping configurations (potentially caused by retrofits or space limitations at the installed site).

Three different commercial reactors, some with multiple piping and baffling arrangements, were simulated for the validation configurations. The results of the modeling showed that CFD-based simulations were able to capture the salient trends measured as a function of different flow rates, UV transmittances, and lamp power. In addition, the use of different pipe sizes and the comparison of runs with and without a baffle plate showed notable impacts on the measured RED in the validation tests. The simulated performance of these different reactors and configurations showed good matches between simulated and measured data for a wide range of operating conditions.

WATER RESEARCH FOUNDATION, COLORADO

UV Reactor Design Assessment and InstallationH

I G

H L

I G

H T

S

One of the reactor geometries modeled, including an S-bend, baffle

plate, and a six-lamp reactor.

CFD models showed a good match in predicting headlosses.

The UV dose models showed a good match in RED.

The work has led to improved application of CFD modeling to

UV facility design.

K E Y A C H I E V E M E N T S 17

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A confined gas mixing system is used in two 2-MG municipal mesophilic digesters. Recycled digester gas is injected into four draft tubes located in the quadrants of the digesters. The digester lids are floating with levels varying by 8 feet, changing the elevation of the lances in the draft tubes during operation. Over time, the system performance had been affected by reduced gas flow rates and gas lance functionality. Temperature profiles and tracer testing had been undertaken to evaluate the reduction in system performance due to these factors, but tests were inconclusive. Therefore, a CFD model was used to further investigate the performance of the mixers for a range of gas injections rates, operating levels, and the impact of gas lance plugging. The aim of the model was to evaluate impacts of the process operating conditions including the lance location and lance plugging.

The model was run with the digester lid at the maximum and minimum levels (maximum and minimum sludge depths) for 5 air flows ranging from 100-cubic feet per minute (cfm) to 500 cfm with all lances operating. A second condition was modeled to evaluate the operation with plugged lance heads with an air flow was 400 cfm.

For all runs made, the flow rate into the draft tube was monitored. The CFD modeling showed that the flow through the draft tube

mixer was 45 percent higher at the low sludge depth as compared to the high sludge depth. This was due to the lower position of the lances within the draft tube at low sludge levels. Further, plugged lances showed a more significant reduction of flow at high sludge levels, as compared to low sludge levels.

Several conclusions can be drawn from the study. The rating curve developed can allow operators of this system to optimize the gas injection rate at different sludge levels to improve mixing. Second, plugging of the lance head will decrease the digester mixing for a given gas flow. Finally, the mixing would probably be more uniform if the lances were always located at the same elevation within the draft tube, which could be achieved by either attaching the draft tube to the floating lid, or the lances independent of the lid.

KING COUNTY DEPARTMENT OF NATURAL RESOURCES AND PARKS, WASHINGTON

West Point Treatment Plant CFD Model of Sludge Digester Gas Mixing System

H I

G H

L I

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T S

The velocity at a section through the draft tube for the 400 cfm run at high sludge depth showed low

velocity, but good circulation.

CFD model used to investigate the performance of the mixers.

Two-phase liquid-gas model.

Developed rating curve for system that would be difficult to

measure.

Provided better operational guidance for plant.

Modeled tank geometry and key features.


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City of Longmont, CoLorADo

clarifier Inlet evaluationH

I G

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I G

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S

Carollo performed field testing and CFD modeling of the secondary clarifier tanks at the City of Longmont, WWTP. The existing radial flow circular tanks have four simple port openings in the vertical inlet pipe at the center of the clarifier. Based on previous work at a number of sites around the country, Carollo felt that improvements could be made to these inlets to increase plant capacity and performance. A series of alternative inlet configurations were investigated using a model that had been calibrated to the existing configuration by solids profile testing in the existing tanks.

The four different inlet configurations included:

1. Target baffles over the existing inlet ports.

2. A 45-degree tangential inlet.

3. A concentric tub inlet.

4. A fully baffled inlet.

The concentric tub and fully baffled inlets showed the best sedimentation performance, while the tangential inlet showed the poorest. The tangential inlet directs mixed liquor flow from an inlet well into the main clarifier tank volume in a spiral pattern. Conventional wisdom concerning the tangential inlet is that, by inducing a spiral pattern in the tank, settling is facilitated by providing a longer flow path for sludge particles. The modeling has shown, however, that the tangential inlet produces higher velocities over a larger part of the tank than inlets that more effectively dissipate inlet energy. Rather than improving clarifier performance, the modeling showed that the spiral flow pattern slows settling.

As part of this work, Carollo performed the first independent CFD evaluation of the concentric tub inlet, which has been used in several Carollo design projects: Metro District, Denver, CO; Clark County, Las Vegas, NV; and the North San Mateo Sanitation District, Daly City, CA.

Model verified full-scale failure condition.

Improved inlet increased tank capacity, delaying the need for

additional tank.

Independent model verification of the concentric tub inlet for

capacity improvement.

The existing configuration was in failure at 10 mgd.

Model mesh used for the concentric tub inlet.

The concentric tub inlet produced a sludge blanket level 2 feet lower than the tangential inlet and 4 feet lower than the

existing inlet at 10 mgd.

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t e s t I n g A n D o P t I M I Z A t I o n c A P A B I L I t I e s 19

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cAroLLo seDIMentAtIon AnD MIXIng MoDeL cALIBrAtIonCarollo has developed a custom sedimentation and solids transport model for use in CFD that incorporates industry standard sedimentation parameters. This custom model allows the effects

of solids concentration gradients on fluid density and viscosity to be incorporated into the CFD analysis. However, since every wastewater is slightly different, the model needs to be calibrated to a given utility’s specific wastewater characteristics. Carollo has solids settling velocity columns to establish field settling parameters and an optical solids probe to measure solids concentration profiles at specific locations. These data allow us to calibrate the CFD model with test data for a given facility and to verify the CFD model application for different conditions.

DesKtoP eVALuAtIonsuVXPt - cfD-Based uV system Performance Modeling softwareCarollo has developed UVXPT, a software package for modeling UV system dose delivery. CFD provides a detailed description of microbe trajectories through UV reactors that takes into account short-circuiting and eddy zones. Dose delivery is calculated by integrating

I I j 'JE~ J J ~ and Optimization Capabilities

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t e s t I n g A n D o P t I M I Z A t I o n c A P A B I L I t I e s 20

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ddthe UV intensity experienced by the microbes over time as they follow the predicted trajectories through the UV reactor. UV intensity fields are modeled either for monochromatic low-pressure or for polychromatic medium-pressure UV lamps. UV intensity sensor measurements are also modeled to allow simulation of a UV reactor’s dose monitoring system.

Carollo uses UVXPT in the design and implementation of UV systems for drinking water, wastewater, and reclaimed wastewater applications including:

! Optimizing UV reactor inlet/outlet and baffle design for enhanced dose delivery and reduced headloss.

! Scaling validation data as a function of flow rate, water UV transmittance, and reactor size.

! Comparing hydraulic conditions obtained with an installation to those conditions used with validation.

! Evaluating UV reactor designs.

UVXPT compared validation and installation hydraulics to support regulatory approval for

East Bay MUD.

P u B L I c A t I o n s 21

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seLect cfD PuBLIcAtIons - Peer-reVIeWeD ! Ho, C.K., Khalsa, S.S., Wright, H.B., and Wicklein, E. “Computational Fluid Dynamics Based Models

for Assessing UV Reactor Design and Installation.” Water Research Foundation: Denver, CO. 2011.

! Samstag, R. “Process Models.” Chap. 2 in Water Environment Federation, Information Technology in Water and Wastewater Utilities. Water Environmental Federation Manual of Practice No. 33. 2011.

! Wright, H., Hart, C., and Wicklein, E. “Mercury Release and Control with UV Disinfection.” Drinking Water Research 18(6): 9-13. October - December 2008.

! Khan, L.A., Wicklein, E.A., Rashid, M., Ebner, L.L., and Richards, L.A. “Case Study of an Application of a Computational Fluid Dynamics Model to the Forebay of the Dalles Dam, Oregon.” Journal of Hydraulic Engineering 134(5): 509-519. 2008.

! Khan, L.A., Wicklein, E.A., and Teixeira, E.C. “Validation of a Three-Dimensional Computational Fluid Dynamics Model of a Contact Tank.” Journal of Hydraulic Engineering 132(7): 741-746. 2006.

! Khan, L.A., Wicklein, E.A., and Rashid M. “A 3D CFD Model Analysis of the Hydraulics of an Outfall Structure at a Power Plant.” Journal of Hydroinformatics 7(4): 283-290. 2005.

! Khan, L.A., Wicklein, E.A., Rashid, M., Ebner, L.L., and Richards, N.A. “Computational Fluid Dynamic Modeling of Turbine Intake Hydraulics at a Hydropower Plant.” Journal of Hydraulic Research 42(1): 71-80. 2004.

seLect cfD PuBLIcAtIons - otHer reVIeWeD ! Wicklein, E.A. and Wright, H.B. “Velocity Profiles: What Do They Mean For UV Dose Delivery?”

Published in the Proceedings of Water Quality Technology, Toronto, Canada. November 4-8, 2012.

! Nopens, I., Batstone, D., Griborio, A., Samstag, R., Wicklein, E., and Wicks, J. “Computational Fluid Dynamics (CFD): What is Good CFD-Modeling Practice and What Can Be the Added Value of CFD Models to WWTP Modeling?” Proceedings of the 85th Annual Water Environment Federation Technical Exhibition and Conference, New Orleans, LA. September 29 - October 3, 2012.

! Samstag, R.W., Wicklein, E.A., Reardon, R.D., Leetch, R.J., Parks, R.M., and Groff, C.D. “Field and CFD Analysis of Jet Aeration and Mixing.” Proceedings of the 85th Annual Water Environment Federation Technical Exhibition and Conference, New Orleans, LA. September 29 - October 3, 2012.

! Samstag, R.W., Wicklein, E.A., and Lee, B. “Computational Analysis of Activated Sludge Lamella Sedimentation.” Proceedings of the International Water Association World Water Congress & Exhibition, Busan, Korea. September 16-21, 2012.

! Samstag, R., Zhou, S., Chan, R., Royer, C., and Brown, K. “Comprehensive Evaluation of Secondary Sedimentation Performance.” Proceedings of the Water Environment Federation 82nd Annual Technical Conference and Exposition, New Orleans, LA. 2010.

! Wright, H., Wicklein, E., and Ho, C. “CFD-Based UV Dose Models Provide Accurate Predictions of UV Reactor Performance.” Proceedings of the American Water Works Association Water Quality

f


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Technology Conference, Savannah, GA, November 14-18, 2010.

! Samstag R. and Griborio, A. “Calibration and validation of CFD Models – Case Study: CFD Modelling of Secondary Clafirers.” Second International Water Association/Water Environment Federation Wastewater Treatment Modeling Seminar, Mont-Sainte-Anne, Quebec, Canada. March 28-30, 2010.

! Wicklein, E. and Samstag, R. “Comparing Commercial and Transport CFD Models for Secondary Sedimentation.” Proceedings of the 82nd Annual Water Environment Federation Technical Exhibition and Conference, Orlando FL. October 11-15, 2009.

! Ho, C., Khalsa, S., Wright, H., and Wicklein, E. “Modeling UV Disinfection Using Integrated Computational Fluid Dynamics and Discrete Ordinates Radiation Models.” Published in the Proceedings of Water Environment Federation Disinfection, Atlanta, GA. February 28th - March 3, 2009.

! Ho, C., Khalsa, S., Wicklein, E., and Wright, H. “Important Factors for Computational Modeling of UV Disinfection Systems.” Proceedings of the Water Quality Technology Conference, Cincinnati, OH. November 16-20, 2008.

! Wicklein, E., Wright, H., and Ho, C. “Computational Fluid Dynamics Modeling of UV Reactor Validation Tests.” Proceedings of the Water Quality Technology Conference, Cincinnati, OH. November 16-20, 2008.

! Virgadamo, O., Marks, K., Wicklein, E., Salveson, A., Glotzbach, K., and O'Brien, A. “Improving the Design of UV Disinfection Systems Using CFD Modeling.” Proceedings of the 81st Annual Water Environment Federation Technical Exhibition and Conference, San Diego, CA. October 13-17, 2008.

! Wicklein, E., Dent, E., Matson, B., Bateman, L., and Smyth, G. “Use of Collection System Modeling to Evaluate CSO Control Strategies.” Paper presented at the Pacific Northwest Clean Water Association Conference, Kennewick, WA. September 21-24, 2008.

! Wicklein, E., Virgadamo, O., and Salveson, A. “Optimizing UV Disinfection System Hydraulics Using CFD Modeling.” Paper presented at the Pacific Northwest Clean Water Association Conference, Kennewick, WA. September 21-24, 2008.

! Khan, L. and Wicklein, E. “Optimization of a Clearwell Design by Using a 3D CFD Model.” Proceedings of the World Environmental and Water Resources Congress, Honolulu, HI. May 12–16, 2008.

! Wicklein, E., Schuyler, A., McClellan, J., McKee, J., and Nestegard, D. “CFD Analysis of Passive Chemical Injection and Mixing Systems.” Paper presented at the Pacific Northwest Section American Water Works Association Conference, Vancouver, WA. April 30 - May 2, 2008.

! Wicklein, E., Kildare, B., and Chan, R. “CFD Modeling of Flow Splitting Between Treatment Components in WWTPs.” Paper presented at the California Water Environment Association Conference, Sacramento, CA. April 13-16, 2008.

! Wicklein, E. “Using Computational Fluid Dynamic Modeling to Evaluate and Improve Disinfection CT.” Workshop 1B: Demystifying the CT Calculation Process, Florida Section American Water Works Association Conference, Orlando, FL. November 11-15, 2007.

! Wicklein, E., Hadler, K., Yildiz, S., Peterson, B., and Kohler, R. “Cleaning and Disinfection Demonstration Study to Help with Conversion of a Wastewater Force Main to Reclaimed Water Distribution Service.” Proceedings of the 80st Annual Water Environment Federation Technical Exhibition and Conference, San Diego, CA. October 13-17, 2007.

! Wicklein, E.A., Sweeney, C., Senon, C., Hattersley, D., Schultz, B., and Naef, R. “Computational Fluid Dynamics Modeling of a Proposed Influent Pump Station.” Proceedings of the 79th Annual Water


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Environment Federation Technical Exhibition and Conference, Dallas, TX. October 22-25, 2006.

! Wicklein, E.A., Sweeney, C., Thompson, D., and Fischer, S. “Design of a New Juvenile Fish Collection Screen System at the Cowlitz Falls Project.” Proceedings of the Hydrovision 2006 Conference, Portland, OR. July 31-August 4, 2006.

! Khan, L.A., Wicklein, E.A., and Rashid, M. “A 3D CFD Model Investigation of an Outfall Reservoir Hydraulics for Repowering a Power Plant.” Proceedings of the 2006 World Environmental and Water Resources Congress, Omaha, NE. May 21-25, 2006.

! Wicklein, E.A. and Rashid, M. “Use of Computational Fluid Dynamic Modeling to Evaluate Pump Intake Performance and Develop Design Modifications.” Proceedings of the 2006 World Environmental and Water Resources Congress, Omaha, NE. May 21-25, 2006.

! Samstag, R., Narayanan, B., Hagstrom, J.P., Bridges, T.G., and Bahl, A. “Hydraulic Characteristics of Activated Sludge Aeration Tanks.” Paper presented at the Water Environment Federation 77th Annual Technical Conference and Exposition, Washington, D.C. October, 2005.

! Wicklein, E.A., Allaben, C., and Rashid, M. “Optimizing Cooling Tower Pump Intakes Using Computational Fluid Dynamics Models.” Proceedings of the 2002 Industrial Water Conference, Orlando, FL. December 10-12, 2002.

! Wicklein, E.A. “Use of Computational Fluid Dynamics and Physical Models to Improve Suction Pipe Hydraulics.” Paper presented at the Pacific Northwest Pollution Control Association 69th Annual Conference, Yakima, WA. October 20-23, 2002.

! Khan, L.A., Wicklein, E.A., Rashid, M., Ebner, L., and Richards, N. “Analyses of Forebay Hydraulics of The Dalles Dam, Oregon for Different Spill Scenarios.” Paper presented at the Hydrovision Conference, Portland, OR. July 29-August 2, 2002.

! Wicklein, E.A., Khan, L.A., Rashid, M., Deering, M., and Nece, R. “A Three-Dimensional Computational Fluid Dynamics Model of the Forebay of Howard Hanson Dam, Washington.” Paper presented at the Hydrovision 2002 Conference, Portland, OR. July 29-August 2, 2002.

! Wicklein, E.A. and Khan, L.A. “Using Computational Fluid Dynamic Models to Optimize Site Specific Clearwells.” Proceedings of the 2001 American Water Resources Conference, Albuquerque, NM. November 12-15, 2001.

C O M P A N Y P R O F I L E 24

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WATER AND WASTEWATER EXPERTSCarollo is an environmental engineering firm specializing in the planning, design, and construction of water and wastewater facilities and infrastructure. Carollo’s reputation is based upon client service, a continual commitment to quality, and technical leadership.

During our 86-year history, Carollo has successfully completed more than 25,000 projects for public sector clients. Carollo is currently ranked within Engineering News Record's (ENR) top 500 design firms. More importantly, ENR’s annual Source Book ranks Carollo among the top 10 firms for water and wastewater treatment plant design. Unlike many of our competitors, Carollo provides only water and wastewater engineering services.

With our focus on water and wastewater, we recruit nationwide and hire technical staff who have the extensive background and training specific to this field. For that reason, the quality and professional standing of our core group of water and wastewater professionals equals or exceeds that provided by some of the largest engineering firms in the U.S.

ResourcesCarollo’s staff numbers more than 1,050 employees, including

more than 500 registered engineers. We are a full-service water and wastewater

engineering company with the experience and qualified

professionals to successfully manage projects of any size. Our staff includes civil, sanitary, electrical, environmental,

mechanical, chemical, structural, instrumentation, and corrosion control engineers, as well as

architects, planners, and specialists in other areas. These individuals perform work solely on water and wastewater related facilities.

Carollo is currently

ranked within Engineering

News Record's top 500 design

firms . . . ENR's annual Source

Book ranks Carollo among the

top 10 firms for water

and wastewater treatment

plant design.

Carollo has engineered water and wastewater projects

across the country.

C O M P A N Y P R O F I L E 25

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Carollo’s state-of-the-art computer network allows us to effectively

communicate between offices and interface with almost any engineering

software on the market today.

MANAGEMENT PHILOSOPHYCarollo’s management philosophy and the success of our company are founded on simple precepts:

! Seek out, hire, and hold onto the best people in the business. Carollo aggressively recruits the top candidates from the leading engineering schools across the country. We train and mentor these engineers to become the next generation of leaders for Carollo and the industry. This long-term commitment to developing excellent engineers has resulted in a depth of talent

unmatched by other consulting firms.

! Specialize in the planning, design, and construction management of water and wastewater

projects. This is our business. Our success hinges solely upon our ability to provide responsive service to our municipal clients.

! Commit our principals to an active role in every project. This provides our clients with top management interest, clear accountability, responsiveness, and talent—and helps to ensure that the necessary staff and resources are committed to each assignment.

! Focus on client service. Carollo knows the value of listening to our clients and recognizes that successful projects result from the combined expertise of our staff and the client’s staff. This commitment to understanding client needs and valuing their input is one of the cornerstones of Carollo’s success.

FORMULA FOR SUCCESSMuch of our success as an industry leader is based on our ability to offer advanced solutions that are practical, affordable, and reliable. We strive to maximize the use of existing infrastructure whenever possible, promote environmental conservation, and make the best technologies available at a competitive cost.

A major factor in maintaining Carollo's ability to integrate new technology is the Carollo Research Group (CRG). The relationship between our design engineers and the CRG is unique in the industry and serves as a company-wide resource for evaluating water quality and treatability data, performing pilot studies, developing design criteria, tailoring design solutions to water quality issues, and addressing regulatory compliance concerns.

Our firm takes pride in the large number of clients with whom we have maintained continuing working relationships. We have worked with some clients for more than 80 years — a clear indication of the quality of our work, our control of costs, and our ability to meet schedules. This dedication to quality has resulted in a long list of successful projects and satisfied clients.

Our client list includes the following:

! City of Phoenix, AZ

! East Bay Municipal Utility District, Oakland, CA

! Metropolitan Water District of Southern California

! Sacramento Regional County Sanitation District, CA

! City of San Diego, CA

! City and County of San Francisco, CA

! City of Sacramento, CA

! Miami-Dade County, FL

! Palm Beach County, FL

! Denver Water Department, CO

! Metro WWRD, CO

! Kansas City, MO

! Clark County WRD, NV

! Southern Nevada Water Authority, NV

! City of Arlington, TX

! City of Austin, TX

! Upper Trinity Regional Water District, TX

! King County, WA

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