July 2002
NSF 02/02/EPAWW399
Environmental Technology
Verification Report
Performance of Induction Mixers for
Disinfection of Wet Weather Flows
The Mastrrr Company
GAS MASTRRR Series 32
Submersible Chemical Induction
Mixers
Prepared by
NSF International
Under a Cooperative Agreement with
U.S. Environmental Protection Agency
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THE ENVIRONMENTAL TECHNOLOGY VERIFICATION
PROGRAM
*AM f\
ETV
SERA
U.S. Environmental Protection Agency NSF Into.natlona|
ETV Joint Verification Statement
TECHNOLOGY TYPE: Induction Mixer
APPLICATION: Disinfection of Wet Weather Flows
TECHNOLOGY NAME: GAS MASTRRR Series 32 Submersible Chemical Induction
Mixers
COMPANY: The Mastrrr Company
ADDRESS: 205 Laurel Friendswood, TX 77546
PHONE: (800) 299-6836 FAX: (800) 226-2659
WEB SITE: www.gasmastrrr.com EMAIL: mastrrr@c-com.net
The U.S. Environmental Protection Agency (EPA) has created the Environmental Technology
Verification (ETV) Program to facilitate the deployment of innovative or improved
environmental technologies through performance verification and dissemination of information.
The goal of the ETV program is to further environmental protection by substantially accelerating
the acceptance and use of improved and more cost-effective technologies. ETV seeks to achieve
this goal by providing high quality, peer reviewed data on technology performance to those
involved in the design, distribution, permitting, purchase, and use of environmental technologies.
ETV works in partnership with recognized standards and testing organizations; stakeholders
groups which consist of buyers, vendor organizations, and permitters; and with the full
participation of individual technology developers. The program evaluates the performance of
innovative technologies by developing test plans that are responsive to the needs of stakeholders,
conducting field or laboratory tests (as appropriate), collecting and analyzing data, and preparing
peer reviewed reports. All evaluations are conducted in accordance with rigorous quality
assurance protocols to ensure that data of known and adequate quality are generated and that the
results are defensible.
NSF International (NSF) in cooperation with the EPA operates the Wet-Weather Flow (WWF)
Technologies Program, a part of the Water Quality Protection Center, one of six Centers under
ETV. The WWF Program recently evaluated the performance of a chemical induction system
that can be used in the disinfection of wet weather flows such as combined sewer overflows and
sanitary sewer overflows. This verification statement provides a summary of the test results for
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the GAS MASTRRR Series 32 Submersible Chemical Induction Mixer manufactured by The
Mastrrr Company. Alden Research Laboratory, Inc, performed the verification testing as the
designated ETV Field Testing Organization, using the facilities of USGS's Conte Anadromous
Fish Research Center, Turners Falls, Massachusetts.
TECHNOLOGY DESCRIPTION
Induction mixers are mechanical mixers that can inject and disperse both gaseous and liquid
chemicals into potable water, process water or wastewater. Induction mixers can draw chemicals
from the point of chemical storage to the point of injection, and disperse the chemical into the
water. The dual functionality of the induction mixer essentially eliminates the need for a
separate injection system and diffuser system as commonly found in typical mixing installations.
The major components of an induction mixer are:
• A submersible motor with a propeller shaft,
• A uniquely shaped propeller, and
• A vacuum body surrounding the propeller shaft.
The submersible motor spins the propeller shaft and uniquely shaped propeller in excess of 3000
rpm. The rotation of the propeller causes a reduction in pressure in the vacuum body
surrounding the propeller shaft. This reduced pressure is used to draw chemical from the storage
location into the induction port. The chemical is then propelled outward by the rotating propeller
and mixed vigorously with the water.
Induction mixers have many applications, most of which include the transferring of a chemical
(either gaseous or liquid) into potable water, process water or wastewater. Induction mixers are
most commonly used for chemical disinfection of potable water or secondary treated wastewater.
Induction mixers are effective disinfection mixers because they provide a rapid and thorough
dispersion of disinfectant that greatly improves the reaction between the chemical disinfectant
and the water, which translates into chemical disinfectant and energy savings.
Recently, induction mixers have been used for the disinfection of wet-weather flows. However,
because wet-weather flows are typically characterized by fluctuating flow rates, the performance
of these mixers may vary as compared to their use for potable water or wastewater disinfection
applications where flows are relatively constant. The performance of an induction mixer can be
assessed by the following three parameters:
1. The size of the plume in which the chemical is transferred,
2. The uniformity of the chemical concentration within the plume, and
3. The rate at which the chemical reaches the extents of the plume.
These performance criteria are reported in this verification study in the following manner:
1. Isopleth diagrams showing the size of the plume into which the chemical can be
transferred,
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2. The uniformity of the chemical concentration within the plume as defined by the mix
factor, and
3. The rate at which the chemical reaches the extents of the plume as identified graphically
by the isopleth diagrams.
For this induction mixer verification study, different size induction mixers were operated and
these parameters measured at a hydraulic laboratory where clean water was used as a surrogate
to wet-weather flow and a tracer dye was used as a surrogate to the chemical disinfectant. Using
this controlled laboratory approach provided greater accuracy in measuring the size and
uniformity of the chemical plume created by the induction mixer. The objective of the study was
to verify the achievement of effective mixing within the designated parameters of the testing
program.
VERIFICATION TESTING DESCRIPTION
Test Facility
Testing was performed at the S.O. Conte Anadromous Fish Research Center (CAFRC), Turners
Falls, Massachusetts. The CAFRC is a hydraulic laboratory, consisting of three indoor flumes
(10 ft wide, 10 ft deep, and 104 ft in length) with a total capacity of 150 ft3/s. For this
verification study one of the three flumes was modified in size so that the induction mixers could
be tested at specified channel dimensions and flow velocities. Water was directed to the test
flume in the building via an inlet structure on the bank of the large canal on which the CAFRC is
located.
Each induction mixer was tested in a rectangular flume, incorporating a channel section 7 ft wide
with a water depth of 7 ft. To provide for a relatively uniform velocity distribution at the mixer,
the length of the flume upstream of the mixer was 20 ft, and the test channel entrance was
rounded to avoid flow separation. Upstream of the test channel entrance, the flow was guided by
a straight flume 10 ft wide and 32 ft long, with an upstream flow distributor. Downstream of the
mixer, the test flume was 28 ft long before expanding to the wider 10 ft flume width. Provisions
were made to accommodate installation of the mixer at the designated location in the test flume,
in accordance with instructions and mounting hardware from the manufacturer.
Methods and Procedures
The Mastrrr Company provided a 5 FTP, 10 FTP and 20 FTP induction mixer for verification
testing. Each induction mixer was installed in the test flume, and tested separately under nominal
flow velocities of 0.5 ft/s, 1.25 ft/s, and 3.0 ft/s. For each test, the flow velocity was held steady
at a water depth of 7 ft and the mixer was operated with a tracer dye as a surrogate for the
chemical disinfectant. A sampling rig was positioned at locations 5 ft, 10 ft, and 15 ft
downstream of the mixer to collect samples over the entire cross section of the flume. The size
and nature of the "chemical" plume was characterized by measuring the dye concentration over
the entire cross section of the flume. Figure VS-1 describes the test conditions under which
samples were collected during the verification testing.
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5 HP mixer operated at
0.5 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
10 HP mixer operated
at 0.5 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
20 HP mixer operated
at 0.5 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
5 HP mixer operated at
1.25 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
10 HP mixer operated
at 1.25 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
20 HP mixer operated
at 1.25 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
5 HP mixer operated at
3.0 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
10 HP mixer operated
at 3.0 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
20 HP mixer operated
at 3.0 ft/s and samples
taken at 5, 10 and 15 ft
downstream of mixer.
Figure VS-1: Operating Conditions for Induction Mixer Verification
Rhodamine WT tracer was used as the injection tracer. A stock injection solution of the tracer
was prepared by serial dilution of 20% commercial solution with distilled water. The injected
tracer rate and concentration were selected such that a mixed concentration at the sampling rig
location of approximately 10 ppb to 20 ppb was achieved.
The sampling rig had 25 withdrawal ports located equally spaced across the 7 ft x 7 ft cross-
section. Only one downstream position was sampled at a time, and provisions were made for
locating and moving the sampling rig so that only one sampling rig would be in the flume
channel at one time. Samples from the 25 suction tubes were drawn at approximately equal flow
rates for about 10 to 12 minutes. This continuous sampling time was adequate to produce a time
average or typical concentration reading. Each of the 25 samples was then analyzed for
concentration of tracer using a laboratory-calibrated fluorometer.
The tracer dye concentration at each of the 25 sampling ports throughout the cross section of the
flume allowed for the development of isopleth diagrams that were used to demonstrate the extent
and uniformity of the chemical plume. Figure VS-2 shows an example of a concentration
isopleth diagram.
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6 -
5 -
J 4-
i
3 -
Ss 2^
1 -
TEST: 1
HP: 5
Flume Velocity (ft/s): 0.55
Sampling Location (ft): 5
Max. Normalized
Concentration: 2.14
Normalized Sample
Standard Deviation: 0.69
Mix Factor: 0.47
-3-2-10 1 23
DISTANCE FROM FLUME CENTERLINE, FT
Figure VS-2: Example of Normalized Concentration Distribution Isopleth Diagram
The isopleth diagrams were prepared for each test condition using normalized concentration
values. The measured tracer concentration at each cross-section was normalized by dividing the
measured concentration by the uniform concentration (Cu) (where Cu is the tracer concentration),
if the tracer was equally dispersed throughout the cross-section of the flume. Thus, a normalized
concentration of 1.0 means that the theoretical targeted concentration has been achieved. The
performance of the induction mixers was interpreted from these isopleth diagrams.
VERIFICATION OF PERFORMANCE
The mixers produced a roughly circular plume with higher concentrations in the center. Smaller
plume areas and higher peak concentrations were observed under the higher flow velocity
conditions. In other words, as the energy imparted by the mixer became smaller in relation to the
kinetic energy of the flow in the flume (related to flow velocity), the level of mixing observed
also lessened. At the lowest flume velocity (0.5 ft/s), the tracer concentrations were more evenly
distributed across the flume cross-section and approached a uniform mix, as the plume was able
to spread rapidly.
The normalized concentration values and the corresponding isopleth diagrams were used to
generate the numerical performance indicators for each of the induction mixers. These indicators
are described below and the results are presented in Table VS-1.
A mix factor, F, was calculated for each test using the isopleth diagram. The mix factor indicates
the percentage of the total cross-sectional flume channel area that experienced a theoretical
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complete mix (i.e. equal dye concentration throughout the entire cross-sectional area). By
definition, a mix factor of 1 (or 100%) indicates that complete theoretical mixing has occurred.
The mix factor provides insight into the area affected by a concentration of chemical greater than
the theoretical uniform concentration. In general, the channel area affected by the mixer
increased as horsepower increased and decreased as flow velocity increased. For example, as
presented in Table VS-1, at 10 ft downstream of the mixer and a flume velocity of 1.25 ft/s the 5
HP mixer affected 35% of the channel area whereas the 20 HP mixer affected 51%.
Additionally, when considering the 5 HP mixer at the 10-ft downstream sampling location, the
area affected at a flume velocity of 0.5 ft/s was 48% as compared to only 32% at 3.0 ft/s.
The maximum (peak) normalized concentration is the highest concentration of tracer dye
observed within the plume, which generally occurred in the center of the channel, closest to the
point of injection. The maximum normalized concentration is an indicator of the uniformity of
the plume concentrations produced by the mixer. This factor is important because it is possible to
have two sets of plume data with similar mix factors but with substantially different maximum
concentrations. For example, the 5 HP mixer at the 3.0 ft/s flume velocity at the 10-ft and 15-ft
downstream sampling location had approximately equal mix factors of 0.30. With no further
information, this could lead to an erroneous conclusion that the plume does not spread as it
moves downstream away from the mixer. The maximum normalized concentrations from the two
sets of data, however, reveal that the plume is in fact continuing to disperse as it moves
downstream, with the maximum value decreasing from 8.52 times to 6.66 times the theoretical
average as it moves from 10 ft downstream to 15 ft downstream.
The standard deviation of the normalized dye concentrations at each sampling location
characterizes the uniformity of plume concentrations produced by the mixer. The standard
deviation is the mathematical expression of the variation of chemical concentration around the
average concentration. More uniform mixing is represented by smaller standard deviations. A
standard deviation of 0.0 would represent complete uniformity of mixing. Similar to the mix
factor trend, uniformity of the chemical concentration within the plume increased as mixer HP
increased and decreased as the flow velocity increased.
Table VS-1 below provides a summary of the mix factor, maximum normalized concentration,
and standard deviation for the three induction mixers at each of the three flume velocity
conditions.
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Table VS-1 Summary of Numerical Performance Indicators
5 ft downstream of
Mixer
5 HP
10 HP
20 HP
10 ft downstream of
Mixer
5 HP
10 HP
20 HP
15 ft downstream of
Mixer
5 HP
10 HP
20 HP
Flume Velocity 0.5 ft/s
Mix Factor, F
Maximum Normalized
Concentration
Standard Deviation
0.47
2.13
0.69
0.57
1.49
0.30
0.46
1.79
0.28
0.48
1.68
0.47
0.56
1.28
0.17
0.49
1.41
0.20
0.54
1.47
0.33
0.43
1.16
0.11
0.52
1.25
0.20
Flume Velocity 1.25 ft/s
Mix Factor, F
Maximum Normalized
Concentration
Standard Deviation
0.32
6.55
1.84
0.44
3.02
1.04
0.52
2.82
0.76
0.35
4.47
1.51
0.43
2.39
0.74
0.51
2.16
0.53
0.39
3.66
1.22
0.46
2.13
0.61
0.52
1.96
0.42
Flume Velocity 3.0 ft/s
Mix Factor, F
Maximum Normalized
Concentration
Standard Deviation
0.17
13.34
2.61
0.23
12.00
2.41
0.32
7.73
2.11
0.28
8.52
2.08
0.33
7.11
2.02
0.36
5.01
1.51
0.32
6.66
2.00
0.33
4.88
1.56
0.38
3.73
1.20
Mean velocity gradient (G) is a measure of mixing intensity and has become an industry standard
for representing the fluid dynamics of mixing. The G number gives an indication of turbulence
as it relates to head loss, which in turn relates to mixing, and is a therefore a parameter of
disinfection efficiency. The mean velocity gradient for a typical well-designed diffuser grid
system is on the order of 200-500/sec. Research indicates that a G number between 700 and
1,000/sec may be appropriate for disinfection (White, 1992). For the purposes of the verification
testing, the mean velocity gradient is used to gauge whether a particular sized induction mixer at
a particular velocity is capable of providing mixing adequate for disinfection.
In order to calculate the mean velocity gradient, a minimum affected volume of process water
must be calculated. The method used to define the affected volume in the open channel during
verification testing was to define the downstream boundary of the channel length beyond which
the mix factor ceased to improve by more than five percent. This criterion was made on the
assumption that the energy imparted by the mixer had a less significant role in mixing than the
energy imparted by the kinetic energy of the flowing process water.
By determining the smallest size mixer that results in sufficient mixing, an appropriate ratio of
horsepower to flow (MGD) can be established. The following criteria were used to assess if
sufficient mixing was provided for disinfection of wet-weather flow process water for the
purposes of verification testing:
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• The standard deviation for the mixing zone was less than 0.5, and consequently the
maximum normalized concentration of the tracer was not significantly more than twice
the normalized mixer concentration, which suggested the energy imparted by the mixer
dispersed disinfectant effectively across the cross-sectional area;
• The mix factor ceased to improve by more than five percent, which suggested the energy
imparted by the mixer dispersed disinfectant more aggressively than the kinetic energy of
the flow of process water, which defines an affected volume of disinfected water from
which to calculate the mean velocity gradient; and,
• The mean velocity gradient (G) is close to, if not greater than, 700/sec within the
minimum established volume of water, which can assist in determining an appropriately
sized motor for a particular application.
The following is a summary of the verification tests in which a sufficient mixing criteria was
achieved, and the correlating power to process water volume ratio:
• The 5 HP mixer marginally failed to provide sufficient mixing at a flume velocity of 0.5
ft/s within the 7 ft x 7 ft open channel. The actual diameter of the plume where superior
mixing was observed was 6 ft. The 5 HP unit failed to provide sufficient mixing at flume
velocities greater than 0.5 ft/s. This equates to a horsepower to MOD ratio of 0.50.
• The 10 HP mixer provided sufficient mixing at flume velocities of 0.5 ft/s within the 7 ft
x 7 ft open channel, and marginally failed to provide sufficient mixing at 1.25 ft/s. The
10 HP unit did not provide sufficient mixing at flume velocities greater than 1.25 ft/s.
This equates to a horsepower to MGD ratio of 0.46.
• The 20 HP mixer provided sufficient mixing at flume velocities of 0.5 and 1.2 ft/s within
the 7 ft x 7ft open channel. This equates to a horsepower to MGD ratio of 0.53.
In summary, the data suggest that a mixer sizing criteria of between 0.46 and 0.53 HP/MGD
resulted in mixing sufficient for disinfection for mixing applications in the 7 ft x 7 ft open
channel with flow velocities between 0.5 and 3.0 ft/s. The data also indicated a break point at a
flow velocity 1.25 ft/s, where at higher velocities the influence of higher horsepower on the size
of the mixing zone volume has diminishing returns. It is clear that flow velocity significantly
influences the ability of the mixers to effectively disperse tracer. Therefore, expected range of
flow velocities must be considered when selecting an appropriately sized mixer during the design
of open channel mixing facilities.
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Original Signed by
E. Timothy Oppelt
9/27/02
Original Signed by
Gordon Bellen
9/27/02
Gordon Bellen
Vice President, Federal Programs
NSF International
E. Timothy Oppelt
Director
National Risk Management Research
Laboratory
Office of Research and Development
United States Environmental Protection
Agency
NOTICE: Verifications are based on an evaluation of technology performance under specific,
predetermined criteria and the appropriate quality assurance procedures. EPA and NSF make no
expressed or implied warranties as to the performance of the technology and do not certify that a
technology will always operate as verified. The end user is solely responsible for complying
with any and all applicable federal, state, and local requirements. Mention of corporate names,
trade names, or commercial products does not constitute endorsement or recommendation for use
of specific products. This report is not a NSF Certification of the specific product mentioned
herein.
Availability of Supporting Documents
Copies of the ETV Protocol for Equipment Verification Testing Induction Mixers
Used for High Rate Disnfection of Wet Weather Flows dated July, 2002, the
Verification Statement, and the Verification Report (NSF Report
#02/02/EPAWW399) are available from the following sources:
(NOTE: Appendices are not included in the Verification Report. Appendices are
available from NSF upon request.)
1. Water Quality Protection Center ETV Program Manager (order hard copy)
NSF International
P.O. Box 130140
Ann Arbor, Michigan 48113-0140
2. NSF web site: http://www.nsf.org/etv (electronic copy)
3. EPA web site: http://www.epa.gov/etv (electronic copy)
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Environmental Technology Verification Report
Performance of Induction Mixers for Disinfection of Wet Weather Flows
The Mastrrr Company
GAS MASTRRR Series 32 Submersible Chemical Induction Mixer
Prepared for:
NSF International
Ann Arbor, Michigan 48105
Prepared by:
Alden Research Laboratory, Inc
30 Shrewsbury Street
Holden, MA01520
With a supplemental text prepared by:
Moffa & Associates
A Unit of Brown & Caldwell
5710 Commons Park
Syracuse, NY 13214
Under a cooperative agreement with the U.S. Environmental Protection Agency
Mary K. Stinson, Project Officer
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Edison, NJ 08837
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Notice
The U.S. Environmental Protection Agency (USEPA) through its Office of Research and
Development has financially supported and collaborated with NSF International (NSF) under
Cooperative Agreement No. CR825712-01-0. The Wet Weather Flow Technologies Pilot
operating under the Environmental Technology Verification (ETV) Program supported this
verification effort. This document has been peer reviewed and reviewed by NSF and USEPA and
recommended for public release.
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Foreword
The following is the final report on an Environmental Technology Verification (ETV) test
performed for the NSF International (NSF) and the United States Environmental Protection
Agency (USEPA) by Alden Research Laboratory, Inc., in cooperation with The Mastrrr
Company. The test was conducted in November 2000 at the S.O. Conte Anadromous Fish
Research Center, a United States Geological Survey Facility in Turners Falls, Massachusetts.
Testing was conducted in accordance with the ETV Verification Protocol for Induction Mixers
Used for High Rate Disinfection of Wet Weather Flows, June 2000, developed for the Wet
Weather Flow Technologies ETV Pilot under the guidance of the ETV Technology Panel on
High Rate Disinfection.
Throughout its history, the USEPA has evaluated the effectiveness of innovative technologies to
protect human health and the environment. A new USEPA program, the Environmental
Technology Verification Program (ETV) has been instituted to verify the performance of
innovative technical solutions to environmental pollution or human health threats. ETV was
created to substantially accelerate the entrance of new environmental technologies into the
domestic and international marketplace. Verifiable, high quality data on the performance of
new technologies is made available to regulators, developers, consulting engineers, and those in
the public health and environmental protection industries. This encourages development of new
approaches to protect the environment.
The USEPA has partnered with NSF, an independent, not-for-profit testing and certification
organization dedicated to public health, safety and protection of the environment, to verify
performance of wet weather flow technologies under the Wet Weather Flow Technologies ETV
Pilot (WWF Pilot). A goal of verification testing is to enhance and facilitate the acceptance of
innovative and effective technologies by regulatory officials and consulting engineers while
reducing the need for testing of equipment at each location where the equipment's use is
contemplated. NSF will meet this goal by working with manufacturers and NSF-qualified Field
Testing Organizations (FTO) to conduct verification testing under the approved protocols.
NSF is conducting the WWF Pilot with participation of manufacturers, under the sponsorship of
the USEPA Office of Research and Development, National Risk Management Research
Laboratory, Urban Watershed Management Branch, Edison, New Jersey. It is important to note
that verification of the equipment does not mean that the equipment is "certified" by NSF or
"accepted" by USEPA. Rather, it recognizes that the performance of the equipment has been
evaluated by these organizations in accordance with an established Verification Protocol and that
objective performance data is available.
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Table of Contents
Verification Statement VS-i
Notice i
Foreword ii
Table of Contents iii
List of Tables iv
List of Appendices v
List of Figures v
Abbreviations and Acronyms vii
Acknowledgments viii
1 Introduction 1
1.1 Environmental Technology Verification Program 1
1.2 Scope of Induction Mixer Verification 1
1.3 Testing Participants and Responsibilities 2
1.3.1 NSF International 2
1.3.2 Field Testing Organization 2
1.3.3 Manufacturer 3
1.3.4 Test site 3
1.3.5 U.S. Environmental Protection Agency 3
1.4 Chemical Disinfection of Wet Weather Flows 4
1.5 The Use of Mechanical Induction Mixers in WWF Applications 5
1.6 Verification Objectives 6
2 Equipment Description and Operating Processes 8
2.1 General Description 8
2.2 Series 32 Specifications 8
2.3 Operating Requirements 8
2.4 Mixer Flow (Disinfection Feed Rate) 8
3 Description of Hydraulic TestFacility 10
3.1 Test Location 10
3.2 Test Flume 10
3.3 Flume Flow Control 11
3.4 Instrumentation For Tracer Dilution 13
3.4.1 Tracer Injection 13
3.4.2 Tracer Sampling Rig 13
3.4.3 Fluorometer 14
4 Methods 16
4.1 Test Objectives 16
4.2 Test Series 16
4.3 Tracer Dilution Procedures 18
4.3.1 Tracer Injection 18
4.3.2 Tracer Sampling 18
4.3.3 Fluorometer Calibration 19
4.3.4 Tracer Concentration 21
4.4 Test Flume Velocity Distribution 21
4.5 Test Flume Flow Calibration 22
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5 Results and Discussion 26
5.1 Tracer Concentration Distributions 26
5.2 Mix Factor 40
5.2.1 Affect of Downstream Distance on Mix Factor 40
5.3 Maximum (Peak) Normalized Concentration 41
5.3.1 Affect of Downstream Distance on Maximum (Peak) Normalized Concentration.. 43
5.4 Uniformity of Tracer Distribution of Tracer (Standard Deviation) 43
5.4.1 Affect of Downstream Distance on Uniformity of Concentration 43
5.5 Mixer Power 43
5.6 Summary of 5 FTP Mixer Performance 45
5.7 Summary of 10 FTP Mixer Performance 47
5.8 Summary of 20 FTP Mixer Performance 49
5.9 General observations 52
5.10 Determining Mean Velocity Gradient 53
5.10.1 An Approach to Calculating Mean Velocity Gradient (G) 53
5.10.2 Criteria for Defining a Mixing Zone 54
5.10.3 Calculated G Values 56
5.10.4 Discussion of G Calculations 58
5.11 Assessing the Uniformity of Mix 59
5.12 Sizing of Mixers for Disinfection Applications 60
5.12.1 Flow condition #1: 0.5 ft/sec 60
5.12.2 Flow Condition #2: 1.2 ft/sec 62
5.12.3 Flow condition #3: 3.0 ft/sec 63
5.12.4 Mixer Sizing Criteria 64
6 Quality Assurance 65
6.1 Uncertainty of Measurements (Bias and Precision) 65
6.2 Repeat Test Data 65
6.3 Repeat Concentration Sample Analysis 66
7 References 72
List of Tables
Table 2-1: Tracer Feed Rates 9
Table 3-1: Instrumentation/Equipment List 12
Table 4-1: Test Matrix - Gas Mastrrr 17
Table 4-2: Dilution Ratios for 2500 ppb Stock Solution 19
Table 4-3: Dilution Ratios for Calibration Samples 20
Table 5-1: Summary Of The 5 FTP Mixer Performance 45
Table 5-2: Summary Of The 10 FIP Mixer Performance 47
Table 5-3: Summary Of The 20 FIP Mixer Performance 50
Table 5-4: Calculated G Values 57
IV
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List of Appendices
APPENDIX A: GAS MASTRRR Product Description and Specifications
APPENDIX B: Testing and Calibration Procedures and Sample Data Sheets
APPENDIX C: Measurement Uncertainty of Tracer Concentration and Flume Velocity
APPENDIX D: Test Conditions and Concentrations Raw Data
APPENDIX E: Raw Data For Mixer Power Calculations
List of Figures
Figure 1-1: Typical Induction Mixer 6
Figure 3-1: Plan And Elevation of Test Setup 11
Figure 3-2: Location of Sampling Tubes 15
Figure 4-1: Schematic of Dye Injection System 23
Figure 4-2: Typical Calibration Data 24
Figure 4-3: Flume Velocity Distributions 25
Figure 5-1: Typical Mixer Plume AtMedium Flume Velocity 27
Figure 5-2: Typical Mixer Plume At High Flume Velocity 28
Figure 5-3: Typical Mixer Plume At Low Flume Velocity 29
Figure 5-4: Non-Dimensional Concentration Distribution For The 5 HP Mixer At 0.5 ft/sec
Flume Velocity 30
Figure 5-5: Non-Dimensional Concentration Distribution For The 5 HP Mixer At 1.25 ft/sec
Flume Velocity 31
Figure 5-6: Non-Dimensional Concentration Distribution For The 5 HP Mixer At 3.0 ft/sec
Flume Velocity 32
Figure 5-7: Non-Dimensional Concentration Distribution For The 10 HP Mixer At 0.5 ft/sec
Flume Velocity 33
Figure 5-8: Non-Dimensional Concentration Distribution For The 10 HP Mixer At 1.25 ft/sec
Flume Velocity 34
Figure 5-9: Non-Dimensional Concentration Distribution For The 10 HP Mixer At 3.Oft/sec
Flume Velocity 35
Figure 5-10a: Non-Dimensional Concentration Distribution For The 20 HP Mixer At 0.5 ft/sec
Flume Velocity—Rejected Due To Defective Diffuser 36
Figure 5-10: Non-Dimensional Concentration Distribution For The 20 HP Mixer At 0.5 ft/sec
Flume Velocity 37
Figure 5-11: Non-Dimensional Concentration Distribution For The 20 HP Mixer At 1.25 ft/sec
Flume Velocity 38
Figure 5-12: Non-Dimensional Concentration Distribution For The 20 HP Mixer At 3.0 ft/sec
Flume Velocity 39
Figure 5-13: Example Of Mix Factor Versus Distance From Mixer—5 HP Mixer 41
Figure 5-14: Example Of Similar Mix Factors With Differing Maximum (Peak) Concentrations
42
Figure 5-15: Example Of Maximum (Peak) Concentration Versus Distance From Mixer, 5 HP
Mixer 44
Figure 5-16: Example Of Standard Deviation Of Normalized Concentration Versus Distance
From Mixer 44
v
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Figure 5-17: Summary Of The 5 HP Mixer Performance Data 46
Figure 5-18: Summary Of 10 HP Mixer Performance Data 48
Figure 5-19: Summary Of 20 HP Mixer Performance Data 51
Figure 5-20: Example of Defined Mixing Chamber 53
Figure 5-21: Decision Flow Diagram for Selecting Smallest Mixing Zone Volume 56
Figure 5-22 : Mixing Zone Patterns 58
Figure 5-23: Comparison of Uniformity of Mix at Different Flume Velocities 60
Figure 5-24: Test 1: 5 HP at 5 ft & 0.5 ft/sec 61
Figure 5-25: Test 16: 10 HP at 5 ft & 0.5 ft/sec 61
Figure 5-26: Test 13: 10 HP at 5 ft & 1.2 ft/sec 62
Figure 5-27: Test 19R: 20-HP at 5 ft & 1.2ft/sec 63
Figure 5-28: Test 11: 10-HP at 10 ft & 3.0 ft/sec 63
Figure 5-29: Test26: 20-HP at 10 ft & 3.0 ft/sec 64
Figure 6-1: Comparison Of Original And Repeat Testing—Non-Dimensional Concentration
Distribution For The 10 HP Mixer At 1.25 ft/sec Flume Velocity 67
Figure 6-2: Comparison Of Original And Repeat Testing—Non-Dimensional Concentration
Distribution For The 10 HP Mixer At 0.5 ft/sec Flume Velocity 68
Figure 6-3: Comparison Of Original And Repeat Testing—Non-Dimensional Concentration
Distribution For The 20 HP Mixer At 1.25 ft/sec Flume Velocity 69
Figure 6-4: Comparison Of Original And Repeat Testing—Non-Dimensional Concentration
Distribution For The 5 HP Mixer At 1.25 ft/sec Flume Velocity 70
Figure 6-5: Comparison Of Original And Repeat Testing—Non-Dimensional Concentration
Distribution For The 10 HP Mixer At 1.25 ft/sec Flume Velocity 71
VI
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Abbreviations and Acronyms
ARL Alden Research Laboratory, Inc.
CAFRC S.O. Conte Anadromous Fish Research Center
CSO combined sewer overflow
USEPA United States Environmental Protection Agency
ETV Environmental Technology Verification Program
ft foot (or feet)
FTO Field Testing Organization
G mean velocity gradient
gpm gallons per minute
FTP horsepower
MGD million gallons per day
ml milliliter
NSF NSF International, formerly known as National Sanitation Foundation
ppb parts per billion
RMS root mean square
RPM rotations per minute
sec second
TMC The MASTRRR Company
USGS United States Geological Survey
VTP Verification Test Plan
WWF Wet Weather Flow
WWF Pilot Wet Weather Flow Technologies ETV Pilot
ppb parts per billion
vn
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Acknowledgments
The Field Testing Organization, Alden Research Laboratory, was responsible for all elements in
the testing sequence, including design of the test flume and sampling rig, calibration and
verification of instruments, data collection and analysis, data management, data interpretation
and the preparation of this report.
Alden Research Laboratory, Inc.
30 Shrewsbury Street
Holden, MA 01520
Contact Person: Dr. M. Padmanabhan and Mr. Philip Stacy
Moffa & Associates, A Unit of Brown & Caldwell, Syracuse, New York provided technical
guidance and documentation review during various stages of this verification. Moffa &
Associates also provided supplemental text for this Verification Report on the use of induction
mixing systems in treating wet weather flows and the potential applications of the data contained
in this Verification Report.
All testing and sample analysis was conducted under the direction of Alden Research Laboratory
at:
S.O. Conte Anadromous Fish Research Center (CAFRC)
One Migratory Way
PO Box 796
Turners Falls, MA 01376
Contact Person: Mr. John Noreika
CAFRC is a USGS Facility, without which the testing would not have been possible. The staff at
CAFRC was instrumental in establishing and maintaining the required test conditions, including
the flume dimensions, flows, flow velocities, and electrical power needs.
The manufacturer of the equipment is:
The Mastrrr Company
205 Laurel
Friendswood, TX 77546
Contact Person: Mr. David Macauley
Vlll
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1 Introduction
1.1 Environmental Technology Verification Program
The U.S. Environmental Protection Agency (USEPA) created the Environmental Technology
Verification (ETV) Program to facilitate the deployment of innovative or improved
environmental technologies through performance verification and dissemination of information.
The goal of the ETV program is to further environmental protection by substantially accelerating
the acceptance and use of improved, cost-effective technologies. ETV seeks to achieve this goal
by providing high quality, peer reviewed data on technology performance to those involved in
the design, distribution, permitting, purchase, and use of environmental technologies.
ETV works in partnership with recognized standards and testing organizations; stakeholders
groups which consist of buyers, vendor organizations, and permitters; and with the full
participation of individual technology developers. The program evaluates the performance of
innovative technologies by developing test plans that are responsive to the needs of stakeholders,
conducting field and/or laboratory testing, collecting and analyzing data, and preparing peer
reviewed reports. All evaluations are conducted in accordance with rigorous quality assurance
protocols to ensure that data of known and adequate quality are generated and that the results are
defensible.
NSF International (NSF) in cooperation with the USEPA operates the Wet Weather Flow
Technologies Pilot (WWF Pilot). The WWF Pilot evaluated the performance of
USFilter/Stranco Products Water Champ® F Series Chemical Induction System, a mixing
technology whose many uses include the rapid mixing of chemical disinfectants for the treatment
of wastewater and combined sewer flows. The objective of verification was to characterize the
ability of the system to rapidly transfer a chemical into a flowing body of water by measuring the
uniformity of chemical concentrations over measured portions of the flow cross-section at
various distances downstream from the mixer. Testing was conducted in accordance with the
June 2000 version of the Generic Verification Protocol for Induction Mixers Used for High Rate
Disinfection of Wet Weather Flow.
1.2 Scope of Induction Mixer Verification
The WWF Pilot developed a program for the verification of induction mixers intended for use in
the chemical disinfection of wet weather flows, such as combined sewer overflows and sanitary
sewer overflows. The objective of the verification is to evaluate the performance of induction
mixers with respect to their ability to transfer chemicals into the process water. The volume of
water affected by a mixer, herein referred to as the mixing zone, was used to portray the
performance of each mixer. The velocity of the process water and the size of the mixer (i.e.
horsepower) have the greatest influence on the induction mixer's ability to transfer chemicals
into the water. Therefore a series of different size mixers were tested over a range of flow
velocities. These mixers sizes and velocities were representative of typical installations at wet-
weather treatment facilities.
-------
The scope of each verification test was to define the mixing zone volume by introducing a
conservative dye at the point of the impeller and measuring the dye downstream the impeller.
The measured dye was then used to define the volume of water affected by the mixer. These
tests were performed at a hydraulic laboratory for a combination of different mixer sizes, flow
velocities and mixing times.
The transfer of chemicals into the process water is a function of mechanical dispersion and
molecular diffusion. In the case of induction mixers, the mechanical dispersion is several orders
of magnitude greater than molecular diffusion, and therefore molecular diffusion was not
accounted for in these verification tests. The mechanical dispersion is a function of the energy
imparted by the mixer and the energy imparted by the velocity of the process water. The
difference between the active mixing of the induction mixer and the passive mixing of the
process water velocity is addressed.
1.3 Testing Participants and Responsibilities
The ETV testing of the GAS MASTRRR Induction Mixer (GMIM) was a cooperative effort
between the following participants:
• NSF International (NSF)
• Alden Research Laboratory, Inc. (ARL)
• The Mastrrr Company (TMC)
• USGS S.O. Conte Anadromous Fish Research Center (CAFRC)
• U.S. Environmental Protection Agency (USEPA)
The following is a brief description of each ETV participant and their roles and responsibilities.
1.3.1 NSF International
As the Verification Partner for the USEPA's Wet Weather Flow Technologies Pilot, NSF
provided administrative and quality assurance oversight of the verification process. NSF was
responsible for the selection of the Field Testing Organization (FTO). NSF coordinated the
review and approval of the Verification Test Plan (VTP) and this Verification Report. NSF
personnel conducted an audit of the testing facilities and operations at CAFRC prior to the start
of testing.
1.3.2 Field Testing Organization
ARL, an independent testing and research organization, conducted the verification testing of the
GMEVI. The primary responsibilities of ARL included:
• Preparation of a VTP, including revisions in response to review comments;
• Coordination with the manufacturer (vendor) of the mixers tested;
• Implementation of the approved VTP;
• Providing logistical support for establishing a communication network and
scheduling and coordinating the activities for the verification testing;
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• Overseeing and conducting the testing in accordance with this VTP;
• Managing, evaluating, interpreting and reporting of data generated during the testing;
• Providing all data generated during testing in electronic and hard copy format; and
• Preparation of Verification Report.
ARL employees conducted the onsite analyses and data recording during the testing. Mr. Phil
Stacy, ARL Project Engineer managed the on-site operations and oversight of the daily testing
activities.
1.3.3 Manufacturer
TMC manufactured the tested mixers. TMC supplied three submersible chemical mixers (5 HP,
10 HP, and 20 HP) and the necessary mounting hardware, chemical feed lines and other ancillary
equipment needed for their operation. A list of any special requirements, limitations and
instructions was also provided, as well as descriptive details about the capabilities and intended
function of the mixers. The manufacturer maintained communication with ARL to insure on-
time delivery of all equipment, consistent with the schedule in the VTP. A representative of
TMC was on site for the duration of the mixer testing. He provided guidance to FTO personnel
on the proper installation and operation of the mixers.
1.3.4 Test site
Verification tests were conducted using a large test flume at the CAFRC facility in Turners Falls,
Massachusetts. CAFRC is a United States Geological Survey (USGS) Facility where research
and equipment testing is conducted on a regular basis. CAFRC has previously participated in the
testing of high rate induction mixers and has large indoor flumes and flow capacity of about 150
ft3/sec, which are uniquely suited for this purpose.
The CAFRC personnel had the following responsibilities:
• Modifying the existing test flume to provide the required dimensions and features;
• Providing steady flow to achieve the required velocities;
• Measuring, evaluating and reporting velocities and flows established during testing;
• Providing the needed electrical power for the mixers and sampling equipment;
• Assisting with installation and repositioning of the sampling rig; and
• Providing any needed QA/QC documentation for the flow and velocities.
1.3.5 U.S. Environmental Protection Agency
The USEPA's National Risk Management Research Laboratory (NRMRL) provides
administrative, technical and quality assurance guidance and oversight on all WWF pilot
activities. USEPA personnel were responsible for:
• Review and approval of the VTP;
• Review and approval of the Verification Report;
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• Review and approval of the Verification Statement; and
• Posting of the Verification Report and Statement on the USEPA website.
1.4 Chemical Disinfection of Wet Weather Flows
Disinfection of WWF discharges is generally practiced to control the discharge of pathogens and
other microorganisms into receiving waters. The disinfection of WWF can present challenges
because of their intermittent nature, variable and high flow rate, wide temperature variation, and
variable water quality.
A number of studies published in the 1970s investigated how effective bacterial kills may be
achieved at lower contact times by using increased mixing intensity, increased disinfectant dose,
and alternate chemicals having a higher oxidation rate than chlorine, or a combination thereof
(Crane Co. 1970, Moffa, Tifft and Richardson 1975, Geisser and Garver 1977, lift et al. 1977,
USEPA 1973a,b, 1975, 1979a,b). These methods are generally refereed to as "high-rate
disinfection." There has been no clear definition as to what constitutes high-rate disinfection
other than achieving the required bacterial reductions at detention times less than 15 to 30
minutes (USEPA 1993).
Disinfection is generally governed by the following relationship:
Kill = cxt (1-1)
Where:
c = concentration of disinfectant
t = time of contact (within a contained volume)
However, to identify the benefits of intense mixing, this relationship was expanded to include a
factor for mixing intensity, which is herein referred to as "G." Disinfection processes that use
mechanical mixing are generally governed by the following relationship:
= cxGxt (1-2)
Where:
G = mixing intensity
c = concentration of disinfectant
t = time of contact (within a contained volume)
The mixing intensity is a function of the power imparted into a volume of water. Mean velocity
gradient (G) is a measure of mixing intensity and has become an industry standard for
representing the fluid mechanics of mixing. It is directly related to the total shear per unit
volume per unit of time. The G number gives an indication of turbulence as it relates to head
loss, which in turn relates to mixing (White, 1992). The mean velocity gradient is therefore a
parameter of disinfection efficiency. G can be expressed by the following equation:
G = ((PxC/)/(uxV))1/2 (1-3)
-------
Where:
P = power requirement (HP)
V = volume of affected process water (ft3)
u = absolute fluid viscosity (lb»sec/ft2)
C/= conversion factor (550 ft»lb/sec/HP)
The mean velocity gradient for a typical well designed diffuser grid system is on the order of
200-500/sec. Research by White (1992) indicates that a G number between 700 and 1,000/sec
may be appropriate for disinfection mixing regardless of disinfection requirements.
Collins and Kruse (USEPA 1973a) demonstrated the influence of mixing intensity on bacterial
kills and formation of chloramines with C^. When chlorine or hypochlorite is added to
wastewater containing ammonia, the free chlorine will react to form chloramines. The rate of
bactericidal efficacy of chloramines is significantly less than that of free chlorine. It is theorized
that by instantaneously dispersing hypochlorite in the wastewater stream using high-rate mixing,
more of the organisms in the wastewater are subjected to chlorine in its free form prior to the
formation of chloramines and, therefore, resulting in greater kills.
1.5 The Use of Mechanical Induction Mixers in WWF Applications
Use of induction mixers as compared to other mixing techniques, such as diffusers and paddle
mixers, reduces power and chemical consumption and therefore annual operation and
maintenance costs (White 1992, Diaz 2001). Additionally, experience has shown that the long
contact time required for conventional wastewater treatment is extremely costly for the treatment
of WWF due to the magnitude of peak flow rates that occur on an infrequent basis. However,
disinfection of WWF can be achieved at shorter contact times by providing intense mixing and
an increased disinfection dosage to ensure disinfectant contact with the maximum number of
microorganisms (Benjes 1976). Reduced contact tank volume can significantly reduce the
capital cost associated with constructing a WWF disinfection facility.
The mechanical induction mixer is fairly simple in construction. The major elements are
illustrated in Figurel-1. In general, a submersible motor rotates a shaft on which an impeller is
mounted. The impeller rotates at a speed greater than 3,000 RPM within a housing that
encompasses the impeller. The impeller and housing is similar in concept to a submersible pump
in that the rotating impeller within a confined volume creates a negative pressure. This negative
pressure is used to draw or induct flow through the chemical induction port.
The induction capability of the induction mixers is not typically utilized in WWF applications
because of the extreme variation in flow rates characteristic of a WWF treatment facility. As
described above, the chemical is inducted into the impeller housing by the negative pressure
produced by the rotating impeller, which remains relatively constant during the operation of the
mixer. This means the induction rate (i.e. disinfection feed rate) is relatively constant during
operations. This is not appropriate for WWF disinfection facilities because this disinfection feed
rate needs to be paced to correspond with the highly variable WWF rate to provide a constant
disinfection dose (i.e. Qi x Ci = Ch x €2). For example, throughout the duration of a WWF
event, flows processed by a single 20-HP mixer can range from 1 ft3/sec to 220 ftrVsec.
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Therefore, the disinfectant feed rate must also vary in order to maintain a constant disinfectant
dose. Disinfection feed rates with such a wide range are typically provided by a series of
variable speed feed pumps controlled by flow sensors in the influent to the treatment facility.
These feed pumps negate the need for the induction capabilities of the mixers. However, the
high rpm and the resulting energy it imparts into the WWF to disperse chemical is very
important for the efficient use of the disinfectant in a "high-rate disinfection" application.
High RPM
Impeller
Chemical
Induction Port
Negative
Pressure
Zone
\
Impeller
Housing
Motor Shaft
Submersible Motor
Figure 1-1: Typical Induction Mixer
1.6 Verification Objectives
In the past, researchers have related bacterial reductions to the parameters G and t (USEPA
1973a,b, 1975, 1979a,b). This relationship holds true when the mixing devices are operated in a
mixing chamber of fixed size. This relationship does not necessarily hold true when the mixing
devices are operated in an open channel, allowing the mixing zone volume to change as a result
of mixer horsepower, channel geometry, and or flow velocity. As such White (1992) stated that
the subject of mixing intensity as it relates to disinfection efficiency needs more research and
laboratory study of the fluid mechanics of mixing the chemical with wastewater. The objective
would be to quantify intensity versus homogeneity of the mixture in a given time frame.
Manufacturers of induction mixers have made claims about the mixing capabilities of their
product and their ability to provide rapid, uniform chemical transfer resulting in reduction or
elimination of chemical breakout and stratification. Since these claims are subjective,
manufacturers will often provide a G factor for each specific induction mixer installation.
However, in some installations, e.g., an open channel, there is no standard method or approach
used for calculating this G factor. As presented in Section 1.4, G is a function of the mixer
power, fluid viscosity, and the volume of the affected process water. The power and viscosity
variables are standard and therefore the manufacturers use consistent values, but each
manufacturer defines the process water volume differently. As a result each manufacturer may
claim a different G for the same application, based on their definition of volume. Additionally, a
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high G value (G> 700/sec) has generally implied a homogenous dispersion of chemical, but this
is not well documented especially in an open channel application where flow velocities can vary
throughout a WWF event.
Data collected in accordance with the ETV Protocol can be used to determine the volume of
process water affected by the induction mixer, or mixing volume, and to characterize the
uniformity of chemical concentrations within the mixing volume.
The verification testing was performed in a hydraulic laboratory, during which the induction
mixers were operated as though installed in an open-channel of a WWF disinfection facility.
However, instead of mixing a chemical disinfectant into the process water, a conservative tracer
was used, which allowed the researchers to observe the extent of mixing provided by the mixers.
The conservative tracer (Rhodamine WT) was used as a surrogate to a disinfection chemical such
as chlorine because it was easier and more accurate to measure.
In practice, a disinfection chemical such as chlorine is not conservative in that it reacts with other
chemicals to form a variety of different compounds. For example, when sodium hypochlorite is
injected into a wastewater for the purpose of disinfection, it instantaneously dissociates into
hypochlorous acid and hypochlorite ion. These compounds in turn react and form other
compounds such as chloramines and other chlorinated compounds. Therefore, many species of
chlorine including reactive and inert forms exist throughout the mixing zone affected by the
mixer. However, disinfection facilities are designed to provide for residual chlorine to ensure
that the chemical demand is exceeded. Therefore, it can be assumed that in a properly designed
and operated disinfection facility there is sufficient chlorine in its various forms being applied to
reach the boundaries of the mixing volume.
Conducting the verification testing in a hydraulic laboratory also provided the researchers with
the ability to operate and evaluate the mixers under different flow velocities. The flow velocity
influences the ability of the mixer to disperse chemical in two ways; both of which relate to the
kinetic energy of the process water. The first is that a higher flow velocity represents a higher
kinetic energy, which reduces the mixer's ability to disperse the chemical. The second is that a
higher flow velocity creates greater turbulence, and in some cases the turbulence may be so great
that a mixer is not required at all (i.e. passive mixing, which is not covered in this Verification
Report). These are conflicting statements; but depending upon site-specific conditions, flow
velocity may or may not improve mixing. For example, in a hydraulic laboratory setting,
turbulence can be minimized by the use of hydraulic apparatus, and therefore passive mixing is
minimized, which was the case in this verification testing. However, in a wet-weather
disinfection facility where there may be hydraulic bends and drops, turbulence could play a
significant role in mixing.
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2 Equipment Description and Operating Processes
2.1 General Description
TMC provided three induction mixers from its Series 32 product line nominally rated at 5 HP,
10 HP, and 20 HP. The mixers were typical of the product line, and no special provisions or
changes were made to the mixers. All mixers were powered electrically at 460 VAC, 3 phase
using the standard power cable. The manufacturer provided a line for the induction flow, and an
orifice plate flow meter assembly was added by ARL as part of the test equipment. Drawings,
photographs, and specifications provided by TMC, including the geometry of the propeller tested
for each mixer, are included as Appendix A.
The principle of operation is that rotation of the non-fouling designed mixing distributor induces
a flow rate into its face and discharges the induced flow and chemical mix radially outward
toward the outer channel walls. The high shear and discharge velocity from the mixing
distributor drives the chemical mix into the surrounding water (flow). The chemical is pumped
from the chemical source via a chemical metering pump to the mixing point and is not induced
by vacuum. The non-vacuum design eliminates the potential of chemical siphoning and the need
for anti-siphon valves or air gaps. All available HP energy is directed into high-rate mixing
intensity and dispersion.
2.2 Series 32 Specifications
GAS MASTRRR Series 32 units are available in 1/2 - 20 HP ranges. 1 to 20 HP units operate on
208, 230, or 460 VAC (specify voltage), 60 Hz, 3 phase motors. The motors are constructed of
316 stainless steel outer shell with Tivar (UHMW Polyethylene) cone and distributor. The
power cord is 30 ft long, 4 conductor, 10 G.
For the purpose of ETV testing, the 5 HP, 10 HP, and 20 HP units tested were each 460 VAC, 60
Hz, 3 phase units.
2.3 Operating Requirements
Each mixer was submerged at least 18 inches at all times during testing. All power supplies
were locked out when performing any maintenance to the system. Units were operated between
the rated input and full load amps, and were provided with a SAVVY 3 control panel. This panel
is a Nema 4X stainless steel-housed Allan Bradley disconnect panel with disconnect switch,
control power transformer, HOA switch, function lamps, combination starter, and motor monitor.
Units were supplied with a stainless steel guide rail and horizontal motor mounting bracket that
is universal for all three HP ranges (normally supplied for commercial users).
2.4 Mixer Flow (Disinfection Feed Rate)
The specification for mixer flow, or disinfection feed rate, for each mixer size (HP) can vary
depending on the mixer application. The appropriate disinfection feed rates for each size mixer
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were established in the VTP in consultation with Moffa & Associates. The details are given
below.
The disinfectant feed rate (Qc) to an induction mixer is a function of the:
• Wastewater flow (Qf),
• Disinfectant feed concentration (Cc), and
Required disinfectant dose (Cf).
Additionally, the mixer horsepower is related to the wastewater flow; a typical mixer sizing
criteria for CSO applications (per the manufacturer or vendor) is 0.14 HP/MGD (Moffa &
Associates, 1999). Therefore, the proposed mixer sizes for the verification testing and their
associated wastewater design flows are:
5 HP for 35 MOD
10 HP for 70 MOD
20 HP for 140 MOD
A mass balance equation was used to estimate the disinfectant feed rates or mixer flow based on
the mixer horsepower and design wastewater flows listed above.
Qf x Cf = Qc x Cc
(2-1)
Assuming a 7.5% sodium hypochlorite feed (injected) concentration (Cc) and a final mixed dose
of 20 mg/1 (Cf) in the wastewater flow, solving for Qc (the required mixer flow or disinfectant
feed rate) yields the mixer flows shown in Table 2-1.
Table 2-1: Tracer Feed Rates
Qf, MGD
35
70
140
Mixer Size
HP
5
10
20
Mixer Flow
(Disinfectant /Tracer
Feed Rate), gpm
7
13
26
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3 Description of Hydraulic Test Facility
3.1 Test Location
The CAFRC is situated in the town of Turners Falls, Massachusetts, on bank of a canal to the
Cabot Hydroelectric Power Station. Water enters the building containing the test flume from an
inlet structure on the bank of the canal. The inlet to a below ground conduit was used for intake
flow. Flow from the buried conduit was controlled by a sluice gate in the building. This flow
was distributed to a forebay upstream of the test flume by an inlet chamber and floor diffuser.
Testing required the use of only one of the three concrete flumes in the building. Temporary
walls, constructed of plywood, narrowed the width of the flume and achieved the dimensions
specified in the VTP.
3.2 Test Flume
A rectangular channel section 7 ft wide with a water depth of 7 ft was established for testing. To
achieve a relatively uniform velocity distribution at the mixer, the length of the flume upstream
of the mixer was 20 ft, and the test channel entrance was rounded to avoid flow separation, as
shown in Figure 3-1. Upstream of the test channel entrance, the flow was guided by a straight
flume 10 ft wide and 32 ft long, with an upstream flow distributor (see Figure 3-1). The test
channel had a once-through flow system drawing water from the power plant canal and
discharging the outflow to the canal with no possibility of discharged water re-entering the
channel.
The 7-ft wide test flume was extended 28 ft downstream of the mixer before expanding to the
wider 10-ft flume width. Using mounting hardware supplied by the manufacturer, the mixer was
installed in accordance with the manufacturer's instruction at the designated location in the test
flume.
A 25-point water (tracer) sampling rig was positioned at locations 5 ft, 10 ft, and 15 ft
downstream from the mixer (impeller). Only one location was sampled at a given time, with
provisions made for locating and moving the sampling rig between sampling intervals.
10
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INFLOW
[
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(
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^FLOW
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in
- MIXER
1!
FLOW CONTROL^
GATE \
\
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j FLOW
J
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f/ FLOW 70
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- MIXER
. is .
FLOW CONTROL^,
GATE \
FLOW /
DIMENSIONS IN FT
ELEVATION
Figure 3-1: Plan And Elevation of Test Setup
3.3 Flume Flow Control
A hinged steel weir controlled flow and water level in the flume. The weir was calibrated prior
to initiation of tests to obtain the head-flow relationship of the weir at three positions and the
desired water level of 7 ft. The weir was located 24 ft downstream of the end of the test flume so
that there were no effects on the flow distribution in the test flume caused by the weir.
The maximum velocity in the flume required by the Verification Protocol was 3 ft/sec. To
achieve this velocity, water flows of up to 150 ft3/sec were supplied to the flume. Lower
velocities were set by reducing the inflow with the upstream sluice gate and raising the weir to
maintain the desired water level. The flow required for a given test was established by presetting
the weir and adjusting the flume inflow until the required depth (7 ft) was achieved. As a part of
the weir calibration, the velocity distribution at a 7 ft x 7 ft cross-section just upstream of the
mixer location was measured for each flow using a Sontek Acoustic Doppler Velocimeter
available at CAFRC. Table 3-1 contains a list of all instruments and equipment used to measure
11
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and maintain the required flow conditions. A description of the weir calibration is provided in
Appendix B.
Table 3-1: Instrumentation/Equipment List
Variable/Parameter
Flume Width
Water Depth
Weir Position
Water Velocity
Water (Flume)
Temperature
Mixer Location
Mixer Power
Mixer Flow
Orifice Meter Manometer
Tracer Injection
Concentration
Tracer Injection Rate
Tracer Injection Timer
Tracer Injection
Temperature
Sample Port Location
Sample Concentration
Sample Water
Temperature
Fluorometer Filter (light)
Temperature
Fluorometer Calibration
Instrument Number and Description
1
2
3
4
5
1
6
7
8
9
10
11
12
1
13
14
15
16
Stanley® 25 ft retracting tape measure (or equivalent)
UNIDATA™ model 654 1/c water level instrument with internal
data logger
RITTmeyer Angle Transmitter resistive/optical model MGAx
Sontek® ADV three axis velocity probe.
Platinum RTD and Omega® digital readout
ARL S/N: 0500
Stanley® 25 ft retracting tape measure (or equivalent) reference to
flume floor and walls
Fluke® 4 IB Power Meter
Orifice Meter Section S/N: 1064
Lufkin® 066D 6ft Red End Engineer's Folding Wood Rule
Serial Dilution of 20% Stock using Class A pipettes and flasks
Timed 100 ml Class A pipette (Integral with tracer injection
system)
Newport® Model 6130A Digital Timer (Integral with tracer
injection system)
Omega® Model 199B platinum RTD (Integral with tracer
injection system)
Stanley® 25 ft retracting tape measure or equivalent
Reference to mixer impeller
Fluorometer; Turner Designs Model 10
Newport® RTD (Integral with fluorometer system)
Omega® Model 199 Platinum RTD (Integral with fluorometer
system)
Serial Dilution of 2500ppb Stock using Class A pipettes and flasks
12
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3.4 Instrumentation For Tracer Dilution
3.4.1 Tracer Inj ecti on
Rhodamine WT was used as the tracer. Rhodamine WT has low adsorption characteristics and is
supplied at nominal 20% concentration by weight. Stock injection solutions were prepared at
ARL to a concentration of 2 x 107 ppb by serial dilution of the supplied solution with distilled
water. The injection rate was established for each plume velocity to produce a theoretical
(perfect mixing) concentration at the sampling locations of approximately 12 ppb, using the
following mass balance equation:
CixQi = CtxQt (3-1)
Where
C; = injected tracer concentration
Qi = injected tracer flow
Ct = mixed concentration
Qt = mixed flow
Based on experience with mixers of this type, it was expected that the actual flume
concentrations could be up to five times greater than the theoretical average. Therefore, it was
necessary to establish an injection rate so that the potential highest sample concentration was
within the linear response range of the fluorometer, or below approximately 80 ppb. Tracer
injection rates of 0.4 ml/s, 1.0 ml/s, and 2.5 ml/s were selected for the three flume velocities of
0.5 ft/sec, 1.25 ft/sec, and 3.0 ft/sec, respectively.
Fluorescence of the tracer is a function of water temperature. Variations from the water
temperature during calibration were accounted for by using the following equation:
C = Crxekx(Tr-Tc) (3-2)
Where
C = actual concentration (ppb)
Cr = apparent concentration at Temperature Tr (ppb)
Tc = calibration temperature (°F)
k = temperature connection coefficient (1/°F)
Tr = water temperature (°F)
The standard temperature coefficient, k, for Rhodamine WT is 0.01444/°F.
3.4.2 Tracer Sampling Rig
A sampling rig with five vertical arrays of sampling ports was fabricated. The sample ports were
located at 10%, 30%, 50%, 70%, and 90% of the total depth (center of five equal distances) at a
13
-------
longitudinal spacing selected to generate equal areas of sampling for each port, as shown in
Figure 3-2. Thus, the sampling rig had 25 suction tubes across the 7 ft x 7 ft cross-section.
The number of sampling ports deviated from the minimum specified in the Verification Protocol.
The 7 ft x 7 ft flume cross-section, which exceeds the minimum cross section of 6 ft x 6 ft
recommended in the Verification Protocol, was chosen to improve the experimental design by
moving the walls and their potential effects on mixing away from the mixer (NSF, 2000). To
adhere to the Verification Protocol requirement of one port per square foot in a 7 ft x 7 ft flume
would have required 49 sample bottles. This was considered impractical in terms of the
sampling and analysis effort. In previous similar testing of induction mixers, ARL had found
that 25 ports with similar spacing (in terms of percent depth and width) were adequate to map the
tracer plume within a flume with an even larger cross-section (8 ft x 8 ft and 8 ft x 10 ft). NSF
approved this variance from the Verification Protocol prior to the start of testing.
Using individual pumps and valves, a portion of the flow was directed to each of the 25 sample
collection bottles while the remainder was returned to the flume. The necessary flow to each
sample bottle was obtained by manually adjusting a separate rotameter at each sampling port.
3.4.3 Fluorometer
A Turner Designs Model 10 fluorometer was used to measure tracer concentration. The
fluorometer has a minimum detection level of 0.01 ppb. Rhodamine tracer in concentrations
below 20 ppb, although undetectable visually, provided sufficient measurement accuracy.
Concentration of tracer in the samples was determined by fluorescence intensity, which is
proportional to the voltage output of the fluorometer.
The Turner Designs Model 10 fluorometer has multiple settings to increase the range of
measurable concentrations. Two settings are available, XI and X100, having a 100 to 1 effect on
output. Within each range, the sensitivity may be changed from XI to X31.6 in four equal steps,
having about a 30-fold effect on output. The instrument span and zero offset are also adjustable
to match the output to the measured concentration. The fluorometer was set up to read in the
upper one-third output of the XI sensitivity scale to ensure good resolution for a wide
concentration range.
A portable computer recorded fluorometer voltage output and water and instrument temperature
readings from two Resistance Temperature Detector (RTD) thermometers with a 12-bit analog to
digital converter. Full scale on the computer is two volts with a resolution of 0.0005 volt.
Transmission characteristics of the primary light filter in the fluorometer change slightly with
temperature, affecting instrument sensitivity. Therefore, a platinum resistance temperature
sensor was mounted on the filter to monitor the temperature and assure instrument drift was
within acceptable limits. A similar temperature sensor, mounted in a 1/8" diameter rod,
measured the water sample temperature, which was used to correct measured fluorometer
voltage output to calibration water temperature with Equation 3-2. The temperature sensors used
to determine the water temperatures at the fluorometer and the tracer injection temperature were
calibrated against a NIST traceable thermometer standard. Resolution of the digital temperature
sensors was 0.1 °F.
14
-------
1
1
I
, 1
1
I
\
I
' 1
r
L
r
L
r
k
r
k
r
A1
0
A2
A3
A4
A5
4
B1
O
B2
B3
B4
B5
1 ^ ^ 1
C1
0
C2
C3
C4
C5
1 ^ ^ 1
^7
D1 ~
0
D2
D3
D4
D5
E1
0
E2
o
E3
E4
E5
„ h.
-fe
DIMENSIONS IN FEET
Figure 3-2: Location of Sampling Tubes
15
-------
4 Methods
4.1 Test Objectives
The objective of this testing was to characterize the performance of high rate induction mixers
manufactured by The Mastrrr Company with respect to their ability to rapidly transfer a non-
reactive tracer (as a surrogate for a chemical disinfectant) into a flowing body of clean water.
Mixer performance was characterized by the degree of tracer uniformity achieved over measured
portions of the flow cross-section (the mixing zone) at various distances downstream from the
mixer impeller. This characterization was for a range of flow velocities representative of those
in wet weather flow collection and treatment facilities.
4.2 Test Series
Three GAS MASTRRR Series 32 induction mixers (5 HP, 10 HP, and 20HP) were tested. Table
4-1 shows the test matrix employed. Test series A, B, and C correspond to the test series for the
5, 10, and 20 HP mixers, respectively.
Each test series evaluated a single induction mixer under three flow velocities: 0.5 ft/see, 1.25
ft/sec, and 3.0 ft/sec. The Verification Protocol had called for testing at flow velocities of 0.5
ft/sec, 2.0 ft/sec, and 3.0 ft/sec in order to represent flows typical of a wet weather flow treatment
facility. It was agreed during development of the Verification Test Plan that a 1.25 ft/sec
velocity would be used in place of the 2.0 ft/sec prescribed in the Verification Protocol to
provide a better distribution of data in the 0.5 ft/sec to 3 ft/sec range. As shown in the Text
Matrix of Table 4-1, each test series consisted of nine tests and one or two repeat tests for quality
assurance purposes. When the tests of the 20 HP mixer at the 0.5 ft/sec flow velocity at each of
the three downstream locations were conducted (Tests 19, 20, and 21) an abnormal tracer
distribution was observed in the flume. The manufacturer's representative suspected a problem
with the mixer and, upon further inspection, determined that the impeller was defective. Test
Series C was restarted from the beginning with a new impeller in place. This repeat testing is
described in more detail in Section 5.8 and Section 6.
For each test, the flow velocity was held steady and the water depth was maintained at 7 ft. The
cross-sectional mixing was evaluated for each test at one selected flume cross-section by
concentration measurements of the 25 samples collected across the cross-section using the
described sampling rig. One sampling rig was installed in the channel and was moved to the
designated distances of 5 ft, 10 ft, and 15 ft downstream of the mixer, as needed to perform the
required sampling.
In addition to the unplanned repeat tests, two types of scheduled repeat tests were included in the
test matrix for quality assurance purposes. Repeat tests designated as RT-tests in Table 4-1
involved duplicating all sample collection and analysis steps for a given set of test conditions.
Repeat tests designated as RA-tests in Table 4-1, only involved repeating the fluorometer
analyses of each of the 25 samples collected during a previous test. The test matrix included one
RT- test for each of three test series (A, B, and C) and one RA- test for each of the test series A
andB.
16
-------
Table 4-1: Test Matrix - Gas Mastrrr
Test
Series
A (5 HP)
B(10HP)
C (20 HP)
Test
Number
1
2
3
4
4RA
5
6
7
8
9
10
11
12
13
13RT
14
14RA
15
16
16RT
17
18
19
20
21
19R
20R
21R
22
22RT
23
24
25
26
27
Mixer
(HP)
5
5
5
5
5
5
5
5
5
5
10
10
10
10
10
10
10
10
10
10
10
10
20
20
20
20
20
20
20
20
20
20
20
20
20
Flume
Velocity
(ft/sec)
0.50
0.50
0.50
1.25
1.25
1.25
1.25
3.00
3.00
3.00
0.50
0.50
0.50
1.25
1.25
1.25
1.25
1.25
3.00
3.00
3.00
3.00
0.50
0.50
0.50
0.50
0.50
0.50
1.25
1.25
1.25
1.25
3.00
3.00
3.00
Distance
From Mixer
(ft)
5
10
15
15
15
10
5
5
10
15
15
10
5
5
5
10
10
15
5
5
10
15
5
10
15
5
10
15
5
5
10
15
5
10
15
17
-------
4.3 Tracer Dilution Procedures
4.3.1 Tracer Inj ecti on
Diluted Rhodamine WT tracer solution (stock injection solution prepared by serial dilution of
20% commercial solution with distilled water) was injected into the mixer flow by a constant
displacement pump, whose variable stroke controls the tracer injection rate. Figure 4-1 is a
schematic of the injection system. The injection pump and a 100 ml pipette with reduced area
measuring stations were supplied from a 20-liter Mariotte vessel (a vessel which maintains a
constant inlet pressure on the injection pump regardless of liquid level in the vessel).
Tracer injection flow was constant for each test and was measured by the volumetric method.
The supply line from the Mariotte vessel was shut off via a valve. Tracer was supplied to the
pump solely from a Class A pipette having a volume uncertainty of 0.1%. A digital timer with
0.001-second resolution was started and stopped, as the meniscus of the tracer passed the
measuring locations on the pipette. The tracer injection rate was recorded one to two times per
test (sample data sheets are included in Appendix B). The tracer injection flow was low (from
0.4 ml/sec to 2.5 ml/sec) and thus a secondary transport flow was needed. The secondary
transport flow was flume water drawn from a location upstream of the mixer using a sump pump.
Secondary transport flows of between 2 gpm to 10 gpm were introduced via a tee in the inlet
pipe of the pump providing flow to the mixer.
The mixer flow (disinfectant feed rate) was provided by a 2 HP pump, that withdrew flow from
the flume approximately 4 ft to 6 ft upstream of the mixer. The tracer was injected into the
intake pipe of the pump, ensuring that it was fully mixed with the flow delivered to the mixers.
The mixer flow was adjusted using a valve downstream of the orifice meter.
The flow pumped to the mixers was measured using an ASME design orifice plate meter section
calibrated at ARL's gravimetric calibration facility. This produced a flow measurement accuracy
of ±2%. Without pumping, the use of the orifice meter for flow determination could artificially
reduce the induced flow.
The orifice meter produced a pressure differential proportional to the square of the flow passing
through it. This differential was measured manually on a manometer board, and recorded before
and after each test (see Appendix B for a sample test data sheet).
4.3.2 Tracer Sampling
A continuous flow was withdrawn from each sample port using individual pumps with control
valves. The majority of the flow was discharged back to the test channel (downstream of the
sampling ports). The balance of the sample flow was piped through a rotameter and control
valve to exit as a free jet. Twenty-five one-liter bottles were installed on a tray, and slid under
the discharge jets of the sample lines to obtain simultaneous samples from all 25 points. The
sample collection flows were adjusted using the rotameters so that approximately one liter of
sample was collected over a period of 10 to 12 minutes at each location simultaneously. The
Verification Protocol had recommended that a larger sample (two-liters) be collected over a
18
-------
longer sampling period (30 minutes). However, it was agreed during the development of the
Verification Test Plan that a shorter sampling period and smaller sample volume was adequate to
obtain a representative sample given that the flow was well stabilized by the upstream flow
straightener and long approach section. Further, one-liter samples provided ample volume for
the required fluorometric analysis. The sample bottles were amber glass to protect light sensitive
contents, with threaded green melamine caps with a chemical resistant Teflon seal. Information
identifying each sample, with respect to mixer make and size, sample location, and test, was
written on the bottle caps at the time of sampling (see Appendix B for a test procedure check list
and test data sheet).
4.3.3 Fluorometer Calibration
A 2,500 ppb preliminary calibration solution was prepared from the stock injection solution at
ARL with distilled water to expedite fluorometer calibration during testing. This was
accomplished by serial dilution of the commercial 20% concentrated Rhodamine WT tracer
using the dilution ratios shown in Table 4-2.
Table 4-2: Dilution Ratios for 2500 ppb Stock Solution
From Initial Stock 20%
Concentration, Serial Dilution Ratio
Tracer: Distilled Water
1:19
1:19
1:19
1:9
Resulting
Concentration (ppb)
1E7
5E5
2.5E4
2.5E3
At CAFRC, the 2,500 ppb concentration was further diluted using flume water to prepare the
calibration samples. By this method, flume water became the primary constituent of the
calibration samples, and therefore, any effects related to the water quality were common to the
calibration and test samples. Calibration samples were prepared by sequential dilution using the
dilution ratios shown in Table 4-3.
19
-------
Table 4-3: Dilution Ratios for Calibration Samples
From Initial 2,500 ppb Solution
Serial Dilution Ratio
Tracer: Flume Water
1:9
1:49 using 2,500 ppb
1:99 using 2,500 ppb
1:19 using 250 ppb
0:1 Flume Water
Resulting Calibration
Concentrations (ppb)
250
(used only to produce the
12. 5 ppb sample)
50
25
12.5
0
The 1:9 dilution with flume water was used to produce the 12.5 ppb concentration. The 50 ppb
and 25 ppb solutions were prepared directly from the 2,500 stock solution. All calibration
solutions were mixed in the field so that the flume water was the major constituent (always >
98%) in each calibration sample. This ensured that both the calibration samples and the test
samples were subjected equally to any effects due to flume water quality.
The 2,500 ppb solutions were used to prepare four calibration solutions of 0, 12.5, 25, and 50
ppb for fluorometer calibration (all concentrations are relative to the injected stock solution of
2 x 107 ppb). The fluorometer was calibrated with the above samples and recorded on individual
calibration data sheets (provided in Appendix B).
From each calibration, a linear equation was generated that was used to convert the recorded
fluorometer output (volts (V0)) to a tracer concentration for each sample collected at:
where
m
b
V0
Concentration = (m x V0) + b
slope of the linear equation
intercept of the linear equation
voltage (fluorometer output)
(4-1)
Equation 4-1 was used to determine the tracer concentration of all samples based on the recorded
fluorometer voltage output.
Based on experience, the calibrations of this type, using field water, can be expected to produce a
linear response in fluorometer output that was within ±2% full scale, or about 2 to 3 ppb.
Deviation above this limit would be suspect, and a second set of calibration samples would be
prepared using the prepared stock (2,500 ppb) and flume water (enough flume water was
withdrawn to prepare multiple calibration samples). All calibration data proved to be within the
±0.5% full-scale limit.
20
-------
The fluorometer was calibrated in this way for each mixer at each flume velocity. Each
calibration was evaluated in the field in terms of the correlation between the serial dilution
samples and the best-fit calibration equation (Equation 4-1). All calibration samples proved to
be within ±0.5% of the best-fit line, based on the usual full-scale value (100 ppb) of the
fluorometer scale being used. For repeat analysis tests, the corresponding calibration samples
were used to re-calibrate the fluorometer. Typical calibration results (linear curve fit and error
plots) are included in Figure 4-2.
4.3.4 Tracer Concentration
A portable computer with a 12-bit analog-to-digital converter recorded fluorometer voltage
output and the output from the two RTD thermometers, which measured the sample water and
instrument (light source filter) temperatures. A platinum resistance temperature sensor, mounted
in an 1/8-inch diameter rod, was used to measure each water sample temperature, so as to correct
measured fluorometer voltage output to calibration water temperature (Equation 3-2).
Fluorometer output, water temperature, and filter temperature were read at eight hertz and, after
80 readings (about 10 seconds), the averages and standard deviations were calculated, stored, and
printed. During data acquisition, individual temperature and fluorometer readings were
displayed on the PC monitor for manual recording on data sheets. Variation of the corrected
output from the previous test point was displayed as a percent to show trends on a magnified
scale. After the fluorometer output reached a steady value for each sample (approximately 20
seconds), three 10-second readings were averaged and recorded on a test data sheet (see
Appendix B). The linear fluorometer calibration equation established for each mixer test and
flume velocity was used to convert the voltage output to tracer concentrations (in ppb) for each
of the corresponding samples.
The concentration of each sample collected during tests was determined once at CAFRC and two
sets of the mixer samples were chosen at random and re-analyzed while at CAFRC. The results
of the repeat analyses (RA Tests) are discussed in Section 6.3.
4.4 Test Flume Velocity Distribution
The velocity profile upstream of the mixer location in the test flume was mapped by measuring
the velocities at 49 discrete points using an acoustic Doppler velocity meter. A flow conditioner
located at the upstream end of the flume was adjusted by changing porosity until the distribution
profile was within ±10% of the overall average. The measured velocity distribution was uniform
with measured velocities within ±4% of the average at the low flume velocity and within ±8% of
the average at the higher velocities. Figure 4-3 illustrates the velocity distribution within the test
flume for the three test velocities of 0.5 ft/sec, 1.25 ft/sec, and 3.0 ft/sec.
Each point velocity measurement was recorded over a period of two minutes at a sampling
frequency of 10 hertz and included all the three components of the velocity at each location. The
RMS values of fluctuations of each component of the velocity from its mean were used to
characterize the flume turbulence intensity. Using this method, the turbulence intensity was, on
the average, 12% of the average flume velocity. The root mean squared (RMS) turbulence
intensities for each velocity are identified to the right of each plot in Figure 4-3.
21
-------
4.5 Test Flume Flow Calibration
The average of the 49 velocity measurements recorded for each desired flume test velocity (or
flow) was used as the actual flume velocity. Using the flow calculated from the actual flume
velocity and the flume test section area, a weir discharge coefficient at each of the three weir
positions required to achieve the test flows was calculated using the following equation:
where
Q = (C x L x H)3/2 (4-2)
Q = the flow in ft3/sec,
C = the weir discharge coefficient (specific to each weir position),
L = the weir length (10 ft), and
H = the depth of water over the weir in feet.
The discharge coefficient C varied, as listed below for the three flows (velocities):
Average Flume Velocity (ft/s) C
0.547 4.78
1.24 4.10
3.06 4.16
These position-sensitive weir coefficients were used to calculate the flows (and therefore, flume
velocities) using the recorded values of water level and weir position during each test.
22
-------
n VENT
CLASS A
MEASURING
VOLUME
MARRIOT
VESSEL
w
DIGITAL TIMER
DIGITAL RTD
THERMOMETER
SHUT OFF
VALVE
TO TEST
MIXER
VARIABLE SPEED CONSTANT
DISPLACEMENT PUMP
FLOW CONTROL
VALVE
ROTAMETER
TRANSPORT
FLOW PUMP
FLUME WATER FROM
UPSTREAM OF MIXER
Figure 4-1: Schematic of Dye Injection System
23
-------
m
PH
PH
100
90 -
80 -
70 -
60 -
50 -
40 -
30 -
20 -
10 -
0 -
o
Calibration Samples
Linear curve fit
0.00 0.25 0.50 0.75 1.00 1.25 1.50
Fluorometer Output, DC Volts
1.75 2.00
s •
C3
O
5 i n
H3 n ^ -
O
8 °'°
^ n s -
o
Sin
a
0 0
o.
i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i
0 10 20 30 40 50 6
Predicted Concentration, PPB
Figure 4-2: Typical Calibration Data
24
-------
P-.
Q
£
W
P
Q
7 FT WIDTH
NORMALIZED VELOCITY
DISTRIBUTION
FLUME VELOCITY
NOMINAL: (0.5 FT/SEC)
MEASURED: 0.547 FT/SEC
AVERAGE TURBULENCE:
(RMS) 11.5%
NORMALIZED VELOCITY
DISTRIBUTION
FLUME VELOCITY
NOMINAL: 1.25 FT/SEC
MEASURED: 1.24 FT/SEC
AVERAGE TURBULENCE:
(RMS) 11.0%
NORMALIZED VELOCITY
DISTRIBUTION
FLUME VELOCITY
NOMINAL: 3.0 FT/SEC
MEASURED: 3.06 FT/SEC
AVERAGE TURBULENCE:
(RMS) 13.0%
Figure 4-3: Flume Velocity Distributions
25
-------
5 Results and Discussion
5.1 Tracer Concentration Distributions
The tracer concentration (in ppb) was determined for each of the 25 samples collected per test as
described in section 4.3. This data is tabulated in Appendix D. To facilitate interpretation, tracer
concentration values were normalized by dividing the value of each sample by the theoretical
uniform mixed concentration (Cu) for test condition under which the samples were collected.
The theoretical uniform mixed concentration is calculated using Equation 5-1 (derived from
Equation 3-1), as follows:
Cu=(C1xQ1)/Qt (5-1)
where:
C;= injected tracer concentration
Qi = injected tracer flow
Qt = total flow in flume
The total flume flow (Qt) and average tracer injection flow (Q;) were calculated as the averages
of the flows measured just prior to and immediately following each test. The injected tracer
concentration, Q, was constant for all tests (2 x 107 ppb).
The average tracer concentration for each sampling port, as described in Section 4.3.3, was
normalized by dividing the sample concentration by the theoretical uniform concentration Cu,
which is defined as:
Cu = tracer stock concentration x tracer feed flow rate / flume water flow rate
A normalized concentration of one represents perfect mixing. The normalized concentrations at
the 25 sampling ports for each of the three cross-sections were used to generate an isopleth
diagram for each flow condition and sampling location.
For some test conditions, the peak tracer concentrations were above the range used to calibrate
the fluorometer. In order to calculate the higher concentration samples, the fluorometer
sensitivity setting was adjusted from X31.6 to X10.0. The sensitivity setting, as described in
Section 3.4.3, changes the output of the fluorometer to allow reading of the higher
concentrations.
The normalized values for each test were plotted at their respective locations and lines of equal
concentration (isopleths) were drawn by interpolation to define the mixer plume.
In general, the mixers produced a roughly circular plume with higher concentrations in the
center. Figure 5-1 illustrates such a distribution produced five feet downstream of the 5 HP
mixer operating with the nominal flume velocity of 1.25 ft/sec (actual velocity 1.28 ft/sec).
26
-------
o
o
H
PH
W
Q
6 -
5 -
2 -
1 -
• • • 0.2-
TEST: 6
HP: 5
Flume Velocity (ft/s): 1.28
Sampling Location (ft): 5
Max. Normalized
Concentration: 6.55
Normalized Sample
Standard Deviation: 1.84
Mix Factor: 0.32
-3-2-10 1 23
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-1: Typical Mixer Plume At Medium Flume Velocity
In general, smaller plume areas and higher peak concentrations were observed under the higher
flow velocity conditions. In other words, as the energy imparted by the mixer became smaller in
relation to the kinetic energy of the flow in the flume (related to flow velocity), the level of
mixing observed also lessened. The plume in Figure 5-2 is from the same 5 HP mixer operating
at the higher nominal flume velocity of 3.0 ft/sec (actual velocity 3.08 ft/sec). The maximum
(peak) normalized concentration was approximately 6.5 ppb at the 1.25 ft/sec velocity (Figure
5-1) while it was approximately 13 ppb at the 3 ft/sec velocity (Figure 5-2). The cross-sectional
area of the tracer plume is notably smaller at the higher velocity as evidenced by the absence of
measurable tracer concentrations at greater distances from the flume walls.
27
-------
H
PH
W
Q
6 -
5 -
4 -
3 -
2 -
1 -
"0.2-
»0.2'v
TEST: 7
HP: 5
Flume Velocity (ft/s): 3.08
Sampling Location (ft): 5
Max. Normalized
Concentration: 13.34
Normalized Sample
Standard Deviation: 2.61
Mix Factor: 0.17
-3-2-10123
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-2: Typical Mixer Plume At High Flume Velocity
At the lowest flume velocity (0.5 ft/sec), the tracer concentrations are more evenly distributed
across the flume cross-section and may approach uniform mixing, as the plume was able to
spread rapidly. An example of this is shown in Figure 5-3, where it can be seen that the mixer
was able to disperse the tracer more uniformly throughout the flume cross-section. In this case,
the normalized concentrations measured near the center of the flume were approximately twice
the theoretical uniform concentration. Measurable tracer concentrations were observed near the
outer boundaries of the flume.
28
-------
6 -
5 -
J 4-
i
3 -
Ss 2^
1 -
TEST: 1
HP: 5
Flume Velocity (ft/s): 0.55
Sampling Location (ft): 5
Max. Normalized
Concentration: 2.14
Normalized Sample
Standard Deviation: 0.69
Mix Factor: 0.47
-3-2-10 1 23
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-3: Typical Mixer Plume At Low Flume Velocity
The complete set of concentration distribution plots is shown in Figures 5-4 through 5-12. Each
figure shows the data plots from a single mixer at a single velocity and includes a plot for each of
the three downstream distances (5, 10, and 20 ft) from the mixer. The plots for Test Series A
(5 HP) are found in Figures 5-4 through 5-6. The plots for Test Series B (10 HP) and Test
Series C (20 HP) are found in are found in Figures 5-7 through 5-9 and Figures 5-10 through
5-12, respectively. Figure 5-10a contains the initial distribution plots from Tests 19, 20 and 21
(20 HP, 0.5 ft/sec) that were subsequently repeated due to a suspected defect in the impeller.
The plots in Figure lOa are provided for informational purposes but are not included in the data
analyses and summary that follows in this report.
Although these plots of the mixer plumes provide a visual means to evaluate the performance of
the mixer, the following sections attempt to quantify mixer performance in terms of the area of
the mixer plume (mix factor), the maximum (peak) concentration, and the variation in
concentration within the mixer plume.
29
-------
1
IJH
ffi
dn
w
Q
1
IJH
ffi
w
Q
IJH
1
IJH
ffi
w
Q
'-?-.
' 'O.BSI.
TEST: 1
HP: 5
Flume Velocity (ft/s): 0.55
Sampling Location (ft): 5
Max. Normalized
Concentration: 2.13
Normalized Sample
Standard Deviation: 0.69
Mix Factor: 0.47
TEST: 2
HP: 5
Flume Velocity (ft/s): 0.55
Sampling Location (ft): 10
Max. Normalized
Concentration: 1.68
Normalized Sample
Standard Deviation: 0.47
Mix Factor: 0.48
TEST: 3
HP: 5
Flume Velocity (ft/s): 0.55
Sampling Location (ft): 15
Max. Normalized
Concentration: 1.47
Normalized Sample
Standard Deviation: 0.33
Mix Factor: 0.54
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-4: Non-Dimensional Concentration Distribution For The 5 HP Mixer At 0.5 ft/sec
Flume Velocity
30
-------
1-1
IJH
O
IJH
fc
w
Q
IJH
_1
IJH
O
IJH
fc
w
Q
IJH
_1
IJH
O
IJH
fc
w
Q
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
6
5
1.28
5
6.55
1.84
0.32
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
5
5
1.28
10
4.47
1.51
0.35
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
4
5
1.27
15
3.66
1.22
0.39
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-5: Non-Dimensional Concentration Distribution For The 5 HP Mixer At
1.25 ft/sec Flume Velocity
31
-------
1
O
ffi
fc
TEST: 7
HP: 5
Flume Velocity (fl/s): 3.08
Sampling Location (ft): 5
Max. Normalized
Concentration: 13.34
Normalized Sample
Standard Deviation: 2.61
Mix Factor: 0.17
TEST: 8
HP: 5
Flume Velocity (ft/s): 3.09
Sampling Location (ft): 10
Max. Normalized
Concentration: 8.52
Normalized Sample
Standard Deviation: 2.08
Mix Factor: 0.28
TEST: 9
HP: 5
Flume Velocity (ft/s): 3.10
Sampling Location (ft): 15
Max. Normalized
Concentration: 6.66
Normalized Sample
Standard Deviation: 2.00
Mix Factor: 0.32
DISTAMCE FROM FLUME CENTERLINE, FT
Figure 5-6: Non-Dimensional Concentration Distribution For The 5 HP Mixer At 3.0 ft/sec
Flume Velocity
32
-------
3
fe
1
§
Q
O
ffi
O
ffi
..0.*-...
TEST: 16
HP: 10
Flume Velocity (ft/s): 0.53
Sampling Location (ft): 5
Max. Normalized
Concentration: 1.49
Normalized Sample
Standard Deviation: 0.30
Mix Factor: 0.57
TEST: 17
HP: 10
Flume Velocity (ft/s): 0.54
Sampling Location (ft): 10
Max. Normalized
Concentration: 1.28
Normalized Sample
Standard Deviation: 0.17
Mix Factor: 0.56
TEST: 18
HP: 10
Flume Velocity (ft/s): 0.54
Sampling Location (ft): 15
Max. Normalized
Concentration: 1.16
Normalized Sample
Standard Deviation: 0.11
Mix Factor: 0.43
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-7: Non-Dimensional Concentration Distribution For The 10 HP Mixer At
0.5 ft/sec Flume Velocity
33
-------
8
8
fe
I
fe
ffi
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
13
10
1.24
5.00
3.02
1.04
0.44
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
14
10
1.24
10
2.39
0.74
0.43
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
15
10
1.25
15
2.13
0.61
0.46
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-8: Non-Dimensional Concentration Distribution For The 10 HP Mixer At
1.25 ft/sec Flume Velocity
34
-------
s
lie
ffi
s
lie
ffi
ffi
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
12
10
3.08
5
12.00
2.41
0.23
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
11
10
3.07
10
7.11
2.02
0.33
10
10
3.07
15
4.88
1.56
0.33
DISTANCE FROM FLUME CENTERLINE, FT
n Distribution For The 10 HP Mixer At
3.0 ft/sec Flume Velocity
35
-------
6 -
H
fe 5 -
o
hj 4 -
^
|
ffi
1
Q
1 -
6 -
£
O
hj 4 -
H-i
o
g
ffi
H
Q
1 -
6 -
£
-J'
Q
3
n-c
o
£ 3"
ITI
g
n 2"
i -
n -
•......-v;,.»,,.
. \ \ '•. • ?
1^ 'V> '•' ^ V '• ' ' ^
v •... ..•• ^ .•••' ^~ // •' : P :
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^&
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/^•'' ••' ••' '•
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ft • H?
w . • • . •
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-------
o
ffi
H
f£
o
£
1
ffi
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
19R
20
0.55
5
1.79
0.28
0.46
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
20R
20
0.56
10
1.41
0.20
0.49
TEST: 21R
HP: 20
Flume Velocity (ft/s): 0.56
Sampling Location (ft): 15
Max. Normalized
Concentration: 1.25
Normalized Sample
Standard Deviation: 0.20
Mix Factor: 0.52
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-10: Non-Dimensional Concentration Distribution For The 20 HP Mixer At
0.5 ft/sec Flume Velocity
37
-------
I
fe
ffi
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
22
20
1.26
5
2.82
0.76
0.52
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
23
20
1.27
10
2.16
0.53
0.51
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
24
20
1.27
15
1.96
0.42
0.52
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-11: Non-Dimensional Concentration Distribution For The 20 HP Mixer At
1.25 ft/sec Flume Velocity
38
-------
I
fe
ffi
TEST: 25
HP: 20
Flume Velocity (ft/s): 3.05
Sampling Location (ft): 5
Max. Normalized
Concentration: 7.73
Normalized Sample
Standard Deviation: 2.11
Mix Factor: 0.32
TEST: 26
HP: 20
Flume Velocity (ft/s): 3.07
Sampling Location (ft): 10
Max. Normalized
Concentration: 5.01
Normalized Sample
Standard Deviation: 1.51
Mix Factor: 0.36
TEST: 27
HP: 20
Flume Velocity (ft/s): 3.07
Sampling Location (ft): 15
Max. Normalized
Concentration: 3.73
Normalized Sample
Standard Deviation: 1.20
Mix Factor: 0.38
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-12: Non-Dimensional Concentration Distribution For The 20 HP Mixer At
3.0 ft/sec Flume Velocity
39
-------
5.2 Mix Factor
For each test, a Mix Factor was calculated using the corresponding tracer concentration
distribution plot (isopleth diagram). A Mix Factor of 1 represents the concentration if the tracer
was equally dispersed throughout the cross-section of the flume. The Mix Factor is defined as,
Mix Factor = A.95/AT (5-2)
where
A.95 = channel cross-sectional area where tracer concentration >(.95 x Cu)
AT = total channel cross sectional area
The Mix Factor indicates the area of the channel that experienced complete mixing. In the above
definition, the 95% value instead of the 100% value was used to allow for likely inaccuracies of
flow and concentration measurements.
The concentration distribution plots were used to calculate the Mix Factor for each set of plume
data. The Mix Factor for each test is reported in the margin of the corresponding concentration
distribution plot (Figures 5-4 through 5-12). The Mix Factor provides insight into the area
(relative to the test flume cross-section) affected by a concentration of chemical greater than the
theoretical uniform concentration.
Due to the complex and varying shape of the 0.95 isopleths, no reliable automated method
was available to measure its area. Instead, the areas bounded by the 0.95 isopleths or higher
were measured manually using a planimeter on a hard copy of each plot. The planimeter was
also used to measure the area of the flume cross-section on each plot (roughly 3" x 3" in the
plots) so as to verify and correct the planimeter predicted areas. The former was divided by the
latter to produce the Mix Factor. For cases where the 0.95 isopleth extended to the limits of the
sampling rig and did not form a closed boundary, the lines were extended, following their ending
slope, until they intersected the flume wall or each other.
5.2.1 Affect of Downstream Distance on Mix Factor
The Mix Factor for perfectly uniform mixing would be a value of 1.0. It is evident from a plot of
Mix Factor versus distance downstream from the mixer that the extent of mixing is enhanced
with distance. An example of such a plot is shown in Figure 5-13 for the tested 5 HP mixer.
Figure 5-13 shows the Mix Factor increasing with distance from the mixer; meaning that the area
within the 0.95 isopleth was increasing as the plume moved away from the mixer. Presumably,
the Mix Factor may asymptotically approach the value of 1.0 at some large distance downstream
of the mixer.
40
-------
o
PH
X
l.UU
OTC
. /J
Ocn
.3U
O^c
000 -
4
^
1
» 0
7 ;
1
1 1 • 0.5 ft/s
: : V 1 25 ft/s
1 1 • 3.0 ft/s
• i :
V : ': :
7 S i i
0
25
30
5 10 15 20
Distance From Mixer, ft
Figure 5-13: Example Of Mix Factor Versus Distance From Mixer—5 HP Mixer
5.3 Maximum (Peak) Normalized Concentration
The Maximum (Peak) Normalized Concentrations are reported for each test as an indicator of the
uniformity of the plume concentrations produced by the mixer. The maximum normalized
concentration for each test is reported in the margin of the corresponding concentration
distribution plot (Figures 5-4 through 5-12).
It is possible to have two sets of plume data with similar Mix Factors but with substantially
different maximum (peak) concentrations. Figure 5-14 shows the results of concentration
measurements for the 5 HP mixer at the 0.5 ft/sec flume velocity at the 5 ft and 10 ft downstream
sampling location. At both the 5 ft and 10 ft downstream sampling locations, the calculated Mix
Factor is approximately equal, at 0.35. With no further information, this could lead to an
erroneous conclusion that the plume does not spread as it moves downstream away from the
mixer. The maximum (peak) normalized concentrations from the two sets of data however
reveal that the plume is in fact continuing to disperse as it moves downstream, with the
maximum (peak) value decreasing from 2.13 to 1.68 times the theoretical average as it moves
from five feet downstream to 10 feet downstream.
41
-------
fc
PH"
PH
W
Q
H
PH
W
Q
6 -
5 -
4 -
3 -
2 -
6 -
5 -
4 -
3 -
2 -
.•CP
TEST: 1
HP: 5
Flume Velocity (ft/s): 0.55
Sampling Location (ft): 5
Max. Normalized
Concentration: 2.13
Normalized Sample
Standard Deviation: 0.69
Mix Factor: 0.47
TEST: 2
HP: 5
Flume Velocity (ft/s): 0.55
Sampling Location (ft): 10
Max. Normalized
Concentration: 1.68
Normalized Sample
Standard Deviation: 0.47
Mix Factor: 0.48
-3-2-10123
DISTANCE FROM FLUME CENTERLINE, FT
Figure 5-14: Example Of Similar Mix Factors With Differing Maximum (Peak)
Concentrations
42
-------
5.3.1 Affect of Downstream Distance on Maximum (Peak) Normalized Concentration
The Maximum (Peak) Normalized Concentration versus distance downstream of the mixer can
be plotted as shown in Figure 5-15. As with the Mix Factor, perfect mixing would be indicated
by a maximum normalized concentration value of 1.0. The maximum (peak) normalized values
quickly decreased with distance, by approximately 50% between the 5 ft and 15 ft sample
location. This indicates that the mixer is imparting significant turbulence that continues to mix
and distribute the chemical within the plume as it travels downstream. However, as the Mix
Factors were much less than 1.0, the effective mixing (disinfectant dispersion) was maintained
within a limited area of the flume cross-section and the area occupied by the plume itself did not
increase rapidly with increasing distance downstream.
5.4 Uniformity of Tracer Distribution of Tracer (Standard Deviation)
As described above, the area bounded by concentrations above the theoretical uniform
concentration can represent the mixing zone, and the overall range of concentration can be
expressed by the highest and lowest measured concentrations. The uniformity of the distribution
of tracer concentrations across the flume flow cross-section, i.e., the variation around the average
concentration, can be expressed mathematically as the standard deviation of the (25 point)
sample data sets. The concentration standard deviation for each test is reported in the margin of
the corresponding concentration distribution plot (Figures 5-4 through 5-12). More uniform
mixing is represented by smaller standard deviations. A Standard Deviation of 0.0 would
represent complete uniformity of mixing.
5.4.1 Affect of Downstream Distance on Uniformity of Concentration
The standard deviation of concentrations within the flume cross-section is directly related to the
variations of the concentration values. Therefore, when the standard deviations of the
normalized concentrations versus distance from the mixer are plotted, as shown in the example
Figure 5-16, the extent and uniformity of mixing is realized, as good mixing would be indicated
by a low standard deviation.
5.5 Mixer Power
The power used by each mixer was recorded for each test. The average values of voltage and
amperage were calculated from readings taken just before and after the samples were collected
(see Appendix E for raw data). Mixer power was calculated using equation 5-3:
Power (Watts) = Amps x Volts (5-3)
The power calculations for each mixer are summarized in Tables 5-1, 5-2, and 5-3.
43
-------
15.00
o
1
O
O
O
10.00 -
N
T3
a
J3 5.00
-
ctf
(L)
fin
0.5 ft/sec
25 ft/sec
0 ft/sec
10 15 20
Distance from Mixer, ft
25
30
Figure 5-15: Example Of Maximum (Peak) Concentration Versus Distance From Mixer, 5
HP Mixer
3.00
c
.2 2.00 H
1.00 -
si
-M
GO
•
V
•
0
1
3
5ft/s
25ft/s
Oft/s
10 15 20
Distance from Mixer, ft
25
30
Figure 5-16: Example Of Standard Deviation Of Normalized Concentration Versus
Distance From Mixer
44
-------
5.6 Summary of 5 HP Mixer Performance
Figure 5-17 summarizes the performance of the 5 HP mixer for all three velocities and brings
together the three defining characteristics described in the sections above. These data are also
contained in Table 5-1.
The average Mix Factor (the average of the Mix Factors for the 5, 10 and 15 ft downstream
locations) increased from 0.26 at a flume velocity of 3.0 ft/sec to 0.50 at 0.5 ft/sec. The plume
size, as represented by the Mix Factor, increased by approximately 15% from the 5 ft to the 15 ft
downstream location at the 0.5 ft/sec flume velocity. At the 1.25 ft/sec velocity, the Mix Factor
increased by approximately 22% when going from the 5 ft to 15 ft downstream location. The
corresponding increase in Mix Factor at the 3.0 ft/sec velocity was 88%.
The Maximum (Peak) Normalized Concentration was highest at the 3.0 ft/sec flume velocity at
the 5-ft downstream location, with a concentration 13.3 times the theoretical average. At each
velocity, the maximum (peak) concentrations decreased significantly with distance from the
mixer. At 0.5 ft/sec, the peak concentration decreased by 31% between the 5 ft and 15 ft
location, while decreases observed at 1.25 ft/sec and 3.0 ft/sec were 44% and 50%, respectively.
Table 5-1: Summary Of The 5 HP Mixer Performance
Mixer
HP
5
Flume
Velocity
(ft/sec)
0.5
1.25
3.0
Sample
Location
(ft)
5
10
15
5
10
15
5
10
15
Mix
Factor
0.47
0.48
0.54
0.32
0.35
0.39
0.17
0.28
0.32
Peak
Normalized
Concentration
2.13
1.68
1.47
6.55
4.47
3.66
13.34
8.52
6.66
Standard
Deviation
0.69
0.47
0.33
1.84
1.51
1.22
2.61
2.08
2.00
Power
(W)
4141
4094
4149
4138
4111
4132
4144
4134
4142
The standard deviation in the plume concentrations followed the trends of the maximum (peak)
normalized values; decreasing quickly with increasing distances from the mixer. At the 0.5
ft/sec flow velocity, the standard deviation decreased by 52% between the 5 ft and 15 ft sample
locations. The standard deviations for the 1.25 ft/sec and 3.0 ft/sec tests decreased by 33% and
23%, respectively, between the 5-ft and 15-ft downstream locations.
Based on the consistency of the power calculations over the range of test conditions (listed in
Table 5-1), it can be concluded that the mixer power requirements were not significantly affected
by changes in flume velocity.
45
-------
15.00
oj
-M
GO
0.00
3.00
c
.2 2.00 ^
(L)
Q
1.00 -
10 15 20
Distance from Mixer, ft
10 15 20
• 0.5 ft/s
V 1.25 ft/s
• 3.0 ft/s
25
25
30
30
0.00
Figure 5-17: Summary Of The 5 HP Mixer Performance Data
46
-------
5.7 Summary of 10 HP Mixer Performance
The 10 HP mixer performance is summarized graphically in Figure 5-18 and tabulated in Table
5-2. Compared to the 5 HP mixer, the average Mix Factor for the 10 HP mixer increased by 4%,
26%, and 15%, respectively, for the 0.5 ft/sec, 1.25 ft/sec, and 3.0 ft/sec flume velocities. This
means that the plume generated by the 10 HP mixer, as defined by the 0.95 isopleth, occupied
approximately 4% more area than that of the 5 HP mixer at the lowest flume velocity, 26% more
area at the middle flume velocity, and approximately 15% more area at the highest flume
velocity.
The plume distribution plots for the 10 HP mixer at the 0.5 ft/sec flume velocity differed from
those generated by the smaller 5 HP mixer. As shown in Figure 5-7, the highest concentrations
were not in the middle of the flume, as they were for the smaller mixer. The likely cause of this
behavior may be the size of the plume relative to the size of the flume (cross-section). This is
discussed in more detail in Section 5.8.
Table 5-2: Summary Of The 10 HP Mixer Performance
Mixer
HP
10
Flume
Velocity
(ft/sec)
0.5
1.25
3.0
Sample
Location
(ft)
5
10
15
5
10
15
5
10
15
Mix
Factor
0.57
0.56
0.43
0.44
0.43
0.46
0.23
0.33
0.33
Peak
Normalized
Concentration
1.49
1.28
1.16
3.02
2.39
2.13
12.00
7.11
4.88
Standard
Deviation
0.30
0.17
0.11
1.04
0.74
0.61
2.41
2.02
1.56
Power
(W)
7683
7679
7664
7698
7754
7692
7677
7773
7816
To quantify the performance improvement between the 5 HP and 10 HP mixer, one can compare
the downstream location maximum (peak) normalized concentrations. The maximum (peak)
normalized concentrations are lower for the 10 HP mixer compared to the 5 HP mixer. At the
0.5 ft/sec velocity and 15 ft downstream, the 10 HP mixer maximum (peak) is 21% lower than
that for the 5 HP mixer, indicating that some improvement is achieved by doubling the mixer
power. At the 1.25 ft/sec and 3.0 ft/sec flume velocities, the maximum (peak) concentrations
recorded 15 ft downstream with the 10 HP mixer were 42% and 27% lower, respectively, than
those recorded for the 5 HP mixer.
As the mixing improves, the standard deviation in the plume concentration data decreases. At
the downstream sampling location, the concentration profile of the 10 HP mixer produced 67%
to 50% lower standard deviations within the plume for the low and medium flume velocities. At
the 3.0 ft/sec velocity, the deviation within the plume was 22% lower that the 5 HP mixer.
47
-------
The power for the 10 HP mixer varied by less than 2% throughout the test data, indicating again
that there was no significant effect of the flume velocity on power consumption.
15.00
o
I
g 10.00
N
I
o 5.00 -
(D
PH
1.00
0.75 -
fa 0.50 -\
X
0.25 -
3.00
.2 2.00 -
1.00 -
0.00
10 15 20
Distance from Mixer, ft
10
15
20
25
25
30
30
Figure 5-18: Summary Of 10 HP Mixer Performance Data
48
-------
5.8 Summary of 20 HP Mixer Performance
As discussed above, the 5 HP and 10 HP mixer showed a trend of decreasing mixing
performance as the flume velocity increased. For these mixers, the Mix Factor decreased with
increasing velocity and peak values and Standard Deviation increased. The 20 HP mixer
produced similar results, except for the Mix Factor at the two low velocities, which were within
4% of each other at the 10 and 15 ft sample locations. These results are shown in Figure 5-19
and Table 5-3.
The 20 HP mixer showed a strong tendency to drive the plume toward the flume floor for the
0.5 ft/sec and 1.25 ft/sec flume velocity. The 1.0 isopleth divides the plots roughly in half, as
shown in Figure 5-17.
It is possible that the plume produced by the 20 HP mixer tends to spread further towards the
boundaries of the test flume to the point of "saturating" the cross-section at the two lower
velocities. The larger HP mixers impart enough energy to affect the general flow pattern within
the flume and the resulting plumes no longer show the characteristic circular shapes. The
upstream region (5 ft and 10 ft sample locations) of the plume for this mixer at 0.5 ft/sec, had
slightly lower concentrations in the center of the flume (see Figure 5-10). Similar lower center
concentrations were also noted for the 10 HP mixer at the lowest flume velocity. It is possible
that the mixer changes the flow distribution of the flume significantly. The basic design of the
mixer is to propel flow radially, so the flow pattern downstream of the mixer may have a strong
cross-channel (outward from center) component. With generally higher velocities in the center
region of the flume, there is also additional flow in the center of the flume, compared to the
regions close to the boundary. Assuming that the mixer drives the tracer throughout the section,
the higher center flows would dilute the center concentrations and the tracer, in effect, would
"pool" in the lower velocity regions around the perimeter of the flume.
Testing of the 20 HP mixer began at the 0.5 ft/sec condition. After witnessing a strong
asymmetric boiling of the mixer plume, the representative from Gas Mastrrr suspected the mixer
was not functioning properly. The 0.5 ft/sec tests (three locations) were completed with the
malfunctioning impeller and then the mixer was removed for inspection. The Gas Mastrrr
representative determined that the impeller clearance to the housing was not correct due to a
machining error. The mixer was fitted with a spare impeller and the visual performance of the
mixer was acceptable to the Gas Mastrrr representative. The 0.5 ft/sec tests were repeated. The
original plume plots may be seen in Figure lOa. The higher concentrations in the upper left of
the 5 ft location data are indicative of the strong jet, which was seen disturbing the water surface
in this region.
The 0.5 ft/sec plume plots with the replaced impeller are shown in Figure 10. Comparing
Figures 10 and lOa, the replacement impeller produced an average of 69% increase in Mix
Factor over the three sample locations at the 0.5 ft/sec flume velocity. The peak values
decreased by an average of 6%. The Standard Deviation at the 5 ft and 10 ft sample locations
decreased by 48% and 41%, respectively, with the replacement impeller. The Standard
Deviation at the downstream location was unaffected by the replacement impeller.
49
-------
Table 5-3: Summary Of The 20 HP Mixer Performance
Mixer
(HP)
20
Flume
Velocity
(ft/sec)
0.5
1.25
3.0
Sample
Location
(ft)
5
10
15
5
10
15
5
10
15
Mix
Factor
.46
.49
.52
.52
.51
.52
.32
.36
.38
Peak
Normalized
Concentration
1.79
1.41
1.25
2.82
2.16
1.96
7.73
5.01
3.73
Standard
Deviation
.28
.20
.20
.76
.53
.42
2.11
1.51
1.20
Power
(W)
14096
14120
14389
14108
14226
14163
14122
14224
14188
50
-------
15.00
si
-M
GO
0.00
3.00
c
.2 2.00 -\
(L)
Q
1.00 -
0.00
10 15 20
Distance from Mixer, ft
10 15 20
• 0.5 ft/s
V 1.25 ft/s
• 3.0 ft/s
O 0.5 ft/s (2)
25
25
0.5 ft/s
1.25 ft/s
3.0 ft/s
0.5 ft/s (2)
30
30
(2) Results with defective diffuser
Figure 5-19: Summary Of 20 HP Mixer Performance Data
51
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5.9 General observations
Application of the Mix Factor predicts the plume area, as the Mix Factor multiplied by the test
flume area (7 ft x 7 ft = 49 ft2) gives the plume area for the 0.95 isopleth. For cases where the
plume (area) is much smaller than the flume (e.g., about 0.5 or less), the results were
independent of the test flume used, and vice versa. For the former case, the 0.95 isopleth may be
considered to be circular.
The application of the standard deviation allows a fuller description of the distribution of
concentrations above the theoretical uniform concentration isopleth. For a normal distribution,
plus and minus one standard deviation from the 1.0 isopleth would include 68% of the data, plus
and minus two standard deviations includes 95% of the data, and plus and minus three standard
deviations include 99.1% of the concentration data (i.e., almost the peak high and low values).
For most measured plumes, the distribution is not normal but is highly skewed; so equal
percentages of the data do not denote equal changes in concentration above and below 1.0. The
value below 1.0 is limited by zero (0.0), but the value above 1.0 is given by the maximum value.
Therefore, the standard deviation is used only to give an indication of concentration values
above 1.0.
For example, a test condition giving a Mix Factor of 0.50, a maximum (peak) normalized
concentration of 3.5 and a standard deviation of 1.2 indicates the area of the uniform 1.0
concentration isopleth is 0.5 x 49 = 24.5 ft2, has a central peak value of 3.5 and has 95% of all
concentration data between approximately zero and [1.0 + 2 (1.2)] = 3.4.
Based on the test results, the following conclusions are drawn regarding the relative performance
of each mixer:
• As flume velocity increased, the performance of the mixer decreased. For example, at
0.5 ft/sec flume velocity, the Mix Factor and the maximum (peak) normalized
concentrations were 0.54 and 1.47, respectively, for a 5 FTP mixer 15 ft away from the
mixer. For the same mixer at the same location, a flume velocity of 3 ft/sec resulted in
Mix Factor and maximum (peak) normalized concentrations of 0.32 and 6.66,
respectively, indicating a decrease of the Mix Factor by about 40% and a nearly five fold
increase of the maximum (peak) concentration.
• For higher flume velocities, a larger HP mixer performed better. For example, at 3 ft/sec
flume velocity, the Mix Factor and maximum (peak) normalized concentration at 15 ft
downstream for a 20 FTP mixer were 0.38 and 3.73, respectively, compared to 0.32 and
6.66, respectively, for a 5 FTP mixer. The standard derivation of concentration variations
for a 20 FTP mixer was on average almost 50% of that for a 5 FTP mixer.
• Mixing is observed to increase with distance from the mixer, more so for a lower FTP
mixer compared to the higher HP mixer. For example, at 3 ft/sec velocity, the Mix
Factors changed from 0.17 to 0.32 as the distance increased from 5 ft to 10 ft downstream
for a 5 HP mixer, while the corresponding change was from 0.32 to 0.38 for a 20 HP
52
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mixer. In general, the maximum (peak) normalized concentrations and standard
deviations decreased with distance downstream of each mixer.
• The 20 HP mixer produced roughly identical results at the 0.5 and 1.25 ft/sec flume
velocities, with Mix Factors of 0.52 and maximum (peak) concentrations of 1.25 and
1.96, respectively, at 15 ft downstream from the mixer (impeller). The similarity of these
data, despite the different flume velocity, may have been due to the rapid spreading of the
mixer plume toward the boundaries of the flume, thus "saturating" the flow. At a flume
velocity of 3 ft/sec, the corresponding Mix Factor was 0.38 and the maximum (peak)
concentration was 3.73 times the average.
5.10 Determining Mean Velocity Gradient
5.10.1 An Approach to Calculating Mean Velocity Gradient (G)
The data collected through this verification testing identifies parameters related to mechanical
induction mixing, namely horsepower and flow velocity and their effects on the volume of
process water influenced by the mixers.
Many engineers use the mean velocity gradient, or G as a measure of the mixing intensity needed
for a particular mixing application. White (1992), proposed a G of 700/sec, as a rule of thumb.
An example of this calculation is illustrated in Figure 5-20 and explained below.
Mechanical Mixer
4.25 ft
I
4.25 ft
Figure 5-20: Example of Defined Mixing Chamber
53
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Using Equation 1-3, the mean velocity gradient, G, can be calculated for the mixing chamber
pictured in Figure 5-20 while assuming a uniform mix is achieved with 3 horsepower mixer.
G_ 3hpx550ft*lb/sec/hp/ -950/sec
V /0.000027ft • sec/ft2 x lift3 ~
This example shows how G is calculated when there is defined volume (in this case 77 ft3) in
which the mixer is operating and providing a uniform mix. The theoretical G for this example is
950/sec. Considering White's recommendation that a G value of 700/sec is desired, the 3-HP
mixer may be slightly oversized for this application.
When designing a mixing system in an open channel as often done in WWF treatment facilities,
the volume of the mixing zone is a function of the boundary conditions (i.e. channel walls), in
addition to mixer horsepower and flow velocity.
In order to calculate G for the purposes of this verification, criteria must be established for
defining the volume of the mixing zone in the open channel. A description of this criterion is
included below. It is important to note that these criteria and the related assumptions are based
on the site-specific conditions and results of this verification testing, and may not translate
exactly to other induction mixer applications.
5.10.2 Criteria for Defining a Mixing Zone
For the purposes of this verification, the volume of the mixing zone used to calculate G is
defined as the smallest volume in which the mixer meets an established mixing criterion. The
mixing criteria are established as described here.
Mixing Criteria I: cross-sectional mixing zone extent
The cross-sectional boundary of the mixing zone is based on the extent of the 0.5
normalized tracer concentration. The normalized tracer concentration, as defined in
Section 5.4.4, is the theoretical tracer concentration if the tracer were instantaneously
dispersed over the entire cross section of the channel. There were two reasons for selecting
a normalized tracer concentration of 0.5. The first being that if two mixers were required,
their mixing zones could be overlapped at the 0.5 concentration for a cumulative affect
equivalent to a concentration of 1.0. The second reason being that half the theoretically
applied dose at the extents of the mixing zone is assumed to provide sufficient bacteria
reductions. Under such a mixing condition bacteria reductions in the center of the mixing
zone where the concentrations are highest would likely exceed the needed bacteria
reductions, while the bacteria reductions at the extents would likely be less than needed. It
is important to note that this assumption was made for the purpose of calculating G for this
verification test, and may not relate to site-specific bacteria requirements.
Mixing Criteria II: downstream mixing zone extent
The downstream boundary of the mixing zone is based on the channel length, beyond
which the Mix Factor ceases to improve by more than 5%. The Mix Factor is the percent
54
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of the total cross-sectional channel area that has experienced a normalized tracer
concentration of 1.0. This criteria was made based on the assumption that volume of the
mixing zone could not be larger than the volume of water directly affected by the mixer. In
this verification report, the energy imparted by the mixer to disperse tracer appeared to
diminish after 10 feet downstream of the mixer. This is not to say that tracer stopped
dispersing at 10 feet, but rather the energy imparted by the mixer no longer played a
significant role for the dispersion of tracer. After 10 feet the tracer continued to disperse,
but at a much slower rate, and probably as a result of the passive mixing provided by the
kinetic energy of the process water, than the active mixing provided by the induction
mixer.
To calculate G in an open channel using the data generated by this ETV verification, the smallest
mixing zone volume can be defined as:
• The shortest channel length required to meet the cross-sectional mixing zone extent
criteria at the channel wall (Criteria I); or
• The shortest channel length in which the direct effects of the mixer are no longer
considered significant (Criteria II).
The flow diagram presented in Figure 5-21 is used to select the cross-sectional area and length of
channel that defined the smallest volume for each mixer at each flow velocity. Using this
approach, a mixing zone volume is estimated for each size mixer at each velocity. The mixing
zone volume is then used in Equation 1-3 to calculate G.
55
-------
Does the required
concentration (0.5)
reach the channel wall
at 5-foot downstream
of the mixer?
Yes
Use the 5 ft channel
length to calculate
the mixing zone
volume.
No
Is the Mix Factor at 10 ft
downstream of the mixer
5% greater than at 5-foot
downstream of the
mixer.''
Yes
No
Use the 5 ft channel
length to calculate
the mixing zone
volume.
Does the required
concentration (0.5)
reach the channel wall
at 10 ft downstream of
the mixer?
No
Is the Mix Factor at 15 ft
downstream of the mixer
5% greater than at 10 ft
downstream of the
mixer?
No
Use the 10 ft
channel length to
calculate the mixing
zone volume.
Yes
Use the 10 ft
channel length to
calculate the mixing
zone volume?
Yes
Use the 15 ft
channel length to
calculate the mixing
zone volume?
Figure 5-21: Decision Flow Diagram for Selecting Smallest Mixing Zone Volume
5.10.3 Calculated G Values
Using the assumptions and criteria defined above, G values were calculated for each of the three
mixer sizes at each of the three flow velocities under which testing was conducted. The
calculated G values for each are shown in Table 5-4, along with the distance downstream mixing
criteria and the mixing zone volume determinations used to calculate G.
At a flow velocity of 0.5 ft/sec, the 10-HP and the 20-HP mixers met the cross-sectional mixing
criteria at the channel wall within 5 ft. At a flow velocity of 3.0 ft/sec, none of the mixers met
the cross-sectional mixing criteria at the channel wall within 15 ft. It is important to note that the
minimum sampling location downstream of the mixer was 5 ft. In many cases the mixers met
the required dispersion in less than 5 ft, but due to sampling limitations establishing the actual
56
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mixing criteria at a distance of less than 5 ft is not possible. It is also important to note that
mixing continued to improve after the 5 ft location, but the mixing requirement was met at or
before the 5 ft location and improvements thereafter were attributed to the passive mixing of
process water.
Table 5-4: Calculated G Values
Flow Velocity Condition: 0.5 ft/sec
Mixer
(HP)
5
10
20
Distance Downstream
Mixing Criteria (ft)
5
5
5
Cross-Sectional Area
(ft2)
28 (6 ft diameter)(1)
49 (T x 7')(2)
49 (T x 7')(2)
Resulting Mixing
Zone Volume (ft3)
140
245
245
Calculated G
(I/sec)
853
912
1290
(1): For the 5 HP mixer, the 0.5 dye concentration did not reach the channel wall, and the Mix
Factor ceased to improve after 5 ft. Therefore, the cross-sectional mixing extent (i.e. the smallest
volume) was delineated by the 0.5 dye concentration plume at a distance of 5 ft.
(2): For the 10 FTP and 20 Hp mixers, the 0.5 dye concentration reaches the channel wall within
5 ft. Therefore, the cross-sectional mixing extent (i.e. the smallest volume) was delineated by
the channel wall at a distance of 5 ft.
Flow Velocity Condition: 1.2 ft/sec
Mixer
(HP)
5
10
20
Distance Downstream
Mixing Criteria (ft)
10
5
5
Cross-Sectional Area
(ft2)
28 (6 ft diameter)(1)
28 (6 ft diameter)(2)
36(2)
Resulting Mixing
Zone Volume (ft3)
280
140
180
Calculated G
(I/sec)
603
1206
1504
(1): For the 5 FTP mixer, the 0.5 dye concentration did not reach the channel wall, and the Mix
Factor ceased to improve after 10 ft. Therefore, the cross-sectional mixing extent (i.e. the
smallest volume) was delineated by the 0.5 dye concentration plume at a distance of 10 ft.
(2): For the 10 FTP and 20 Hp mixers, the 0.5 dye concentration reaches the channel wall within
5 ft. Therefore, the cross-sectional mixing extent (i.e. the smallest volume) was delineated by
the channel wall at a distance of 5 ft.
Flow Velocity Condition: 3.0 ft/sec
Mixer
(HP)
5
10
20
Distance Downstream
Mixing Criteria (ft)
10
5
5
Cross-Sectional Area
(ft2)
16(4.5ftdiameter)(1)
20 (5 ft diameter)(1)
24(5.5ftdiameter)(1)
Resulting Mixing
Zone Volume (ft3)
160
200
240
Calculated G
(I/sec)
798
1009
1303
(1): For each mixer, the 0.5 dye concentration did not reach the channel wall, and the Mix
Factor ceased to improve after 10 ft. Therefore, the cross-sectional mixing extent (i.e. the
smallest volume) was delineated by the 0.5 dye concentration plume at a distance of 10 ft.
57
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5.10.4 Discussion of G Calculations
The calculated G values shown in Table 5-4 are consistent with the definition of mixing intensity
as defined by Equation 1-3; as horsepower increases or volume decreases, G increases. The
following observations regarding G can be drawn from these calculations:
There are two types of mixing zones that are evident from the review of the data. One is the
mixing zone that is delineated by the channel walls as depicted in Figure 5-22A. The other is the
mixing zone that is delineated by the tracer plume as depicted in Figure 5-22B. In Table 5-4, a
cross-sectional area of 49 ft2 (7 ft x 7 ft) signifies that the channel walls delineate the mixing
zone.
Channel Wall
Channel Wall
Flow
Mixer
0.05
Plume
Tracer
5ft
Downstream
A. Channel Wall Delineated Mixing Zone,
Plan View.
5ft
Downstream
B. Plume Delineated Mixing Zone,
Plan View.
Figure 5-22 : Mixing Zone Patterns
5.10.4.1 Channel Wall Delineated Mixing Zone
When the channel wall delineates the mixing zone, as mixer horsepower increases and volume
remains the same, G increases. For example, during this verification testing the 10-HP and
20-HP GAS MASTRRR mixers met the required mixing criteria before the 5 ft sampling
location at 0.5 ft/sec. Therefore, the mixing zone volume was defined by the cross-section area
of the channel and the distance 5 ft downstream of the mixer. As presented in Table 5-4, G
increases as horsepower increases. This is analogous to the example illustrated in Figure 5-20
and Equation 1-1, where G increases as horsepower increases in a defined mixing zone volume.
58
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5.10.4.2 Transition from Channel Wall Delineated Mixing Zone to Plume Delineated Mixing
Zone
The mixing zone pattern changes at higher velocities due to the higher kinetic energy of the
process water working against the mixer energy to disperse the tracer. At higher velocities the
tracer plume of 0.5-tracer concentration delineates the mixing zone, and not the channel walls.
This is because the higher velocities tend to "concentrate" the mixer's energy within a smaller
volume. This in effect produces a higher G value, but it is applied over a smaller volume of the
process water, which may not be an efficient use of horsepower (i.e. energy).
This transition between mixing patterns occurs at 1.2 ft/sec for the 5-HP mixer and at 3.0 ft/sec
for the 10-HP and 20-HP mixers. Comparisons of G between the two mixing zone patterns
should not be made because the volumes are determined differently.
5.10.4.3 Plume Delineated Mixing Zone
When the tracer plume delineates the mixing zone, as velocity increases and the size of the mixer
remains the same, the volume of mixing zone decreases and therefore the G increases. Although
the G value increases, it does not imply a better mix. It simply means that the same horsepower
input is being applied over a smaller volume. For example, at 1.2 ft/sec, the 5-HP mixer
influences a cross-sectional area of 28 ft2 at a channel length of 10 feet downstream from the
mixer. This cross-sectional area decreases to 16 ft2 at 3.0 ft/sec, and therefore the calculated G
increases. Again, this does not imply a better mix, but rather the horsepower being applied over
a smaller volume.
5.11 Assessing the Uniformity of Mix
While the data from the verification tests produce G values that exceed the accepted value for
superior mixing, they alone do not characterize the volume and uniformity of the mixing zone.
For example, as illustrated in Figure 5-23, the 20-HP mixer at 1.2 ft/sec provides a much more
uniform mix than at 3.0 ft/sec, even though the G values are similar (G = 1,504/sec at 1.2 ft/sec,
G = 1,303/sec at 3.0 ft/sec). This example illustrates the importance of considering the volume
of the mixing zone and the uniformity of the mix within this zone rather than relying only on G
values to characterize the mixing.
59
-------
o:
o
o
o
DC
o.
LLt
Q
..-OSS'"'.--
Test 22: 20 HP at 5 ft & 1.2 ft/sec
Test 26: 20 HP at 10 ft & 3.0 ft/sec
Figure 5-23: Comparison of Uniformity of Mix at Different Flume Velocities
The uniformity of the mixing zone can be depicted by the variance within the tracer
concentrations throughout the cross-section are of the plume. For the purpose of this verification
test the standard deviation of the tracer concentration as calculated for each mixer is directly
related to the uniformity of the mix. A more uniform mix is indicated by a lower standard
deviation. For this verification test a standard deviation of less than 0.5 appears to provide a
sufficient uniform mix. When using a standard deviation of 0.5, the maximum tracer
concentration is approximately twice that of the 1.0 normalized tracer concentration.
Establishing a uniform mix is important so that disinfection chemicals are used efficiently; it is
not efficient to have a mixing zone where a portion of the volume has a concentration of
disinfectant several times greater than required for the application.
5.12 Sizing of Mixers for Disinfection Applications
The mixing zone and the uniform mix criterion presented in Sections 5.10 and 5.11 can assist in
determining an appropriate mixer sizing criteria for a given flow condition. By determining the
smallest size of mixer that satisfies the mixing criteria and the desired minimum G value of
700 sec"1, an appropriate minimum ratio of horsepower to flow (MGD) can be established.
5.12.1 Flow condition #1: 0.5 ft/sec
The 5-HP mixer almost meets the mixing criteria at a flow velocity of 0.5 ft/sec within a 7 ft x
7 ft open channel assuming a required G = 700/sec (see Figure 5-24). The actual cross-section
area that meets the criteria is 28 ft2 (approximate diameter: 6 ft). Based on this cross-sectional
area, the horsepower to MGD ratio is 0.50.
60
-------
a:
8
O
tr
u.
D.
LLJ
Q
6 -
5 -
2 -
Figure 5-24: Test 1: 5 HP at 5 ft & 0.5 ft/sec
The 10-HP mixer meets the mixing criteria at a flow velocity of 0.5 ft/sec within a 7 ft x 7 ft
open channel assuming a required G = 700/sec (see Figure 5-25). Both the mixing zone and the
uniform mix criteria are met within 5 ft downstream of the mixer. This equates to a horsepower
to MOD ratio of 0.57.
v-
u.
of
O
O
8
Q.
LLJ
O
6-
3-
2-
1-
Figure 5-25: Test 16: 10 HP at 5 ft & 0.5 ft/sec
61
-------
5.12.2 Flow Condition #2: 1.2 ft/sec
The 10-HP mixer almost meets the mixing criteria at 1.2 ft/sec within a 7 ft x 7 ft open channel
(see Figure 5-26). The actual cross-section area that meets the criteria is 28 ft2 (roughly a circle
6 feet in diameter). Based on this cross-sectional area, the horsepower to MOD ratio is 0.46.
a.
tr
O
o
u_
O
a:
a_
in
a
2-
Figure 5-26: Test 13: 10 HP at 5 ft & 1.2 ft/sec
The 20-HP mixer meets the mixing criteria at a flow velocity of 1.2 ft/sec within a 7 ft x 7 ft
open channel assuming a required G = 700/sec (see Figure 5-27). Both the mixing zone and the
uniform mix criteria are met within 5 ft downstream of the mixer. This equates to a horsepower
to MOD ratio of 0.53.
62
-------
on
o
o
o
o:
Q.
LU
Q
4 -
3 -
2 -
0.65'"-'
'••.. &
Figure 5-27: Test 19R: 20-HP at 5 ft & 1.2ft/sec
5.12.3 Flow condition #3: 3.0 ft/sec
The 10-HP mixer does not meet the criteria at 3.0 ft/sec within a 7 ft x 7 ft open channel. The
actual cross-section area that meets the mixing zone extent criteria is 20 ft2 (roughly a circle 5 ft
in diameter) (see Figure 5-28). Based on this cross-sectional area, the horsepower to MGD ratio
is 0.26.
a:
o
o
o
a:
u_
i
a.
LJJ
Q
5 .
2 -
Figure 5-28: Test 11: 10-HP at 10 ft & 3.0 ft/sec
63
-------
The 20-HP mixer does not meet the criteria at 3.0 ft/sec within a 7 ft x 7 ft open channel. The
actual cross-section area that meets the mixing zone extent criteria is 24 ft2 (roughly a circle 5.5
ft in diameter) (see Figure 5-29). Based on this cross-sectional area, the horsepower to MGD
ratio is 0.43.
u_
of
O
O
u.
u.
X
Q.
LJJ
Q
6 -
5 -
3 .
2 •
Figure 5-29: Test 26: 20-HP at 10 ft & 3.0 ft/sec
5.12.4 Mixer Sizing Criteria
In summary, the data indicated a mixer sizing criteria of between 0.46 and 0.53 HP/MGD
resulted in mixing sufficient for disinfection for mixing applications in the 7 ft x 7 ft open
channel with flow velocities between 0.5 and 3.0 ft/sec. The data also indicated a break point at
1.2 ft/sec, where at higher velocities the influence of higher horsepower on the size of the mixing
zone volume diminishes. It is clear that flow velocity significantly influences the ability of the
mixers to effectively disperse tracer. Therefore, expected range of flow velocities must be
considered when selecting an appropriate sized mixer during the design of open channel mixing
facilities.
64
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6 Quality Assurance
Testing was conducted in accordance with the Quality Assurance Project Plan (QAPP) contained
in the VTP. The QAPP was based on the quality assurance program of Alden Research
Laboratory, which addressed test plan development, data retrieval, data reduction, reporting, and
test review procedures. In general testing proceeded as planned and on schedule with what was
presented in the VTP. One test of the 10 HP mixer (Test 16) was aborted when the QA check of
pre-sample and post-sample tracer injection rates revealed that the post-sampling timing of the
injection rate deviated from the pre-sample recording by 6%. The injection pump was
disassembled and cleaned and the test was repeated. The data of the repeated tests are included
in the report. No further problems were experienced with the injection system during the testing.
No further errors or deviations from the VTP were observed during the duration of the test.
6.1 Uncertainty of Measurements (Bias and Precision)
Two areas of measurement that were fundamental to data quality were flume velocity and tracer
concentration. Measurement of each of these parameters requires a variety of instruments and
analytical procedures. The calculation of estimate of uncertainty associated with these
measurements was derived from "ANSI/ASME PTC 19.1-1985 Measurement Uncertainty, A
Supplement to the ASME Performance Test Codes." Appendix C of this report contains a
detailed uncertainty analysis for the determination of tracer concentration and flume velocity. In
summary, the estimate of uncertainty in the determination of tracer concentration sampled
downstream of the induction mixers was 2.9 percent at the 95% confidence interval. The overall
uncertainty in the measurement of flume velocity was 3.3%.
6.2 Repeat Test Data
In accordance with the quality assurance project plan in the VTP, one test for each size mixer
was repeated in full. The repeat tests are identified in Table 4-1 by an "RT" added to the test
number. The concentration data from the repeat tests were plotted for comparison to the original
test data, as shown in Figures 6-1, 6-2, and 6-3 for Tests 13, 16, and 22. Visually, the size,
location, and general shapes of the repeat test isopleths are a close match to the original results.
This observation was confirmed by comparing the calculated values of: Mix Factor, Maximum
(Peak) Normalized Concentration, and Standard Deviation. In general, there was considerable
agreement between the values recorded in the original and repeat tests. The Maximum
Normalized Concentrations measured during each of the repeat tests deviated from the respective
original tests by 5% or less. The Standard Deviations calculated for the repeat Tests 13, 16, and
22 differed from the calculated values of the original tests by 6%, 3% and 3% respectively. For
the Mix Factor, the calculated values from the three repeat tests differed from those of the
original tests 2%, 7 %, and 0%. The 7% deviation in the Mix Factor for Test 16 may be
explained by the fact the distribution of the normalized concentrations was fairly flat, and
therefore, a slight change in the measured concentrations near the mean can shift the 0.95
isopleth and, in turn, affect the area which is measured to calculate the Mix Factor. The repeat
tests were incorporated into the test program to provide a check on the repeatability of the mixer
performance and the methods used to evaluate performance. They were not intended to provide
65
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for a statistically valid analysis of the study data. The results of the repeat tests suggest that there
were not significant changes in mixer performance or test procedures from one day of testing to
another.
6.3 Repeat Concentration Sample Analysis
Sample from two selected tests (Test 4 and Test 14) were re-analyzed for tracer concentration
within 24 hours of the original analysis in order to assess the performance of the fluorometer and
to provide a check of the analyses process, from handling of the sample bottles to calibrating the
fluorometer. In order to re-analyze the samples on a different day, with (possibly) different
operating temperatures of the fluorometer and samples, the fluorometer was recalibrated using
the appropriate calibration sample set. The tests of the repeat analysis are identified with the
letter "RA" added to the test number.
The concentration distribution plots and the calculated values for Tests 4 and 14 and their
respective repeat tests are shown in Figures 6-4 and 6-5, respectively. For Test 4, the Maximum
(Peak) Normalized Concentration measured during the repeat test was 5% less than that for the
original test. The Standard Deviations were within 6% of one another and the Mix Factors
differed by less than 3%. For Test 14 the Maximum (Peak) Normalized Concentration measured
during the repeat test was approximately 3% greater than that for the original test. The Standard
Deviations were within 4% of one another and the Mix Factors were identical. These results
suggest that the repeatability of analytical procedures was suitable for the data quality objectives
of the testing program.
66
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CH*
H
PH
W
Q
PH*
tn
H
PH
W
Q
-3-2-10 1 23
DISTANCE FROM FLUME CENTERLINE, FT
TEST: 13
HP: 10
Flume Velocity (ft/s): 1.24
Sampling Location (ft): 5.00
Max. Normalized
Concentration: 3.02
Normalized Sample
Standard Deviation: 1.04
Mix Factor: 0.44
TEST: 13RT
HP: 10
Flume Velocity (ft/s): 1.24
Sampling Location (ft): 5
Max. Normalized
Concentration: 3.17
Normalized Sample
Standard Deviation: 1.10
Mix Factor: 0.45
Figure 6-1: Comparison Of Original And Repeat Testing—Non-Dimensional
Concentration Distribution For The 10 HP Mixer At 1.25 ft/sec Flume Velocity
67
-------
fc
§
H
PH
W
Q
£
§
tn
H
PH
W
Q
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
16
10
0.53
5
1.49
0.30
0.58
16RT
10
0.53
5
1.47
0.29
0.62
DISTANCE FROM FLUME CENTERLINE, FT
Figure 6-2: Comparison Of Original And Repeat Testing—Non-Dimensional
Concentration Distribution For The 10 HP Mixer At 0.5 ft/sec Flume Velocity
68
-------
fc
§
H
PH
W
Q
£
§
tn
H
PH
W
Q
.-0.35- •••';...
0.&6 '....
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
22
20
1.26
5
2.82
0.76
0.47
22RT
20
1.26
5
2.88
0.78
0.47
DISTANCE FROM FLUME CENTERLINE, FT
Figure 6-3: Comparison Of Original And Repeat Testing—Non-Dimensional
Concentration Distribution For The 20 HP Mixer At 1.25 ft/sec Flume Velocity
69
-------
H
PH
CH"
o
o
PH
I
PH
K
H
PH
W
Q
PH"
O
o
PH
K
H
PH
W
Q
•0.2-..
.. -0.20
0.20 •..
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
TEST:
HP:
Flume Velocity (ft/s):
Sampling Location (ft):
Max. Normalized
Concentration:
Normalized Sample
Standard Deviation:
Mix Factor:
4
5
1.27
15
3.66
1.22
0.39
4RA
5
1.27
15
3.46
1.15
0.38
DISTANCE FROM FLUME CENTERLINE, FT
Figure 6-4: Comparison Of Original And Repeat Testing—Non-Dimensional
Concentration Distribution For The 5 HP Mixer At 1.25 ft/sec Flume Velocity
70
-------
CH*
H
PH
W
Q
PH*
tn
H
PH
W
Q
'«> =
....•0.20--"
TEST: 14
HP: 10
Flume Velocity (ft/s): 1.24
Sampling Location (ft): 10
Max. Normalized
Concentration: 2.39
Normalized Sample
Standard Deviation: 0.74
Mix Factor: 0.44
TEST: 14RA
HP: 10
Flume Velocity (ft/s): 1.24
Sampling Location (ft): 10
Max. Normalized
Concentration: 2.47
Normalized Sample
Standard Deviation: 0.77
Mix Factor: 0.44
DISTANCE FROM FLUME CENTERLINE, FT
Figure 6-5: Comparison Of Original And Repeat Testing—Non-Dimensional
Concentration Distribution For The 10 HP Mixer At 1.25 ft/sec Flume Velocity
71
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7 References
Benjes, H.H. 1976. Cost Estimating Manual- Combined Sewer Overflow Storage and
Treatment. USEPA-600/2-76-286 December 1976. National Environmental Research Center,
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Collins and Kruse (USEPA-670/2-73-077).
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Diaz J. A. 2001. Whipped into Shape. Environmental Protection. February 2001.
Geisser, D.F. and S.R. Garver. 1977. High-rate disinfection: chlorine versus chlorine dioxide.
ASCE Journal of Environmental Engineering V\\. EE6. December.
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Smart, P.L. and Laidlaw, I.M.S An Evaluation of Some Fluorescent Tracers for Water Tracing ,
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Tchobanaglous, G. and F.L. Burton. 1991. Wastewater Engineering Treatment, Disposal, and
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USEPA. 1993. Manual: Combined Sewer Overflow Control. EPA/625/R-93/007, Office of
Research and Development, Washington DC.
USEPA. 1973a. U.S. Environmental Protection Agency. High-rate disinfection of combined
sewer overflow. In Combined sewer overflow papers. EPA/670/2-73/077.
USEPA. 1973b. U.S. Environmental Protection Agency. Microstraining and disinfection of
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72
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USEPA. 1975. U.S. Environmental Protection Agency. Bench-scale high-rate disinfection of
combined sewer overflow with chlorine and chlorine dioxide. EPA/670/2-75/021. Syracuse,
NY. April.
USEPA. 1979a. U.S. Environmental Protection Agency. Disinfection/treatment of combined
sewer overflow - Syracuse, NY. EPA/600/2-79/013b.
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Nostrand Reinhold, New York, New York.
73
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