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            United States
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                     CERI-87-49
Workshop on
Emerging
Technologies for
Drinking Water
Treatment:

Filtration
EPA
CERI
87-
"49

-------
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(V,
                                                                   CERI-87-49
                         WORKSHOP ON EMERGING TECHNOLOGIES  FOR

                          DRINKING WATER TREATMENT:  FILTRATION
                                    September,  1987
                                     Sponsored by:

                     United States Environmental Protection  Agency
            Office of Drinking Water and Office of  Research  and Development

                                          and

                   Association of State Drinking Water Administrators
                                Information Resources Center
                                US EPA (3404)
                              .  401 M Street SW
                                Washington, DC 20460

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Slide Presentation

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             REVISED
            DRAFT FINAL
      TECHNOLOGIES AND COSTS
               FOR
        THE TREATMENT OF
     MICROBIAL CONTAMINANTS
    IN POTABLE WATER SUPPLIES
             APRIL 1987
   SCIENCE AND TECHNOLOGY BRANCH
   CRITERIA AND STANDARDS DIVISION
      OFFICE OF DRINKING WATER
U.S. ENVIRONMENTAL PROTECTION AGENCY
          WASHINGTON, D.C.


                          SLIDE 3

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                   CONVENTIONAL TREATMENT
•  Complete treatment (coagulation, flocculation sedimentation, filtra-
   tion, and disinfection)
0  Most widely used
•  Process design criteria well established
t  Traditional concrete construction
                                                   SLIDE  5

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             DIRECT FILTRATION WITH FLOCCULATION
•  Pretreatment Including flocculatlon
•  No sedimentation step
•  Limited to good quality water supplies
   - Turbidity less than 5-10 NTU
   - Color less than 20-30
   - Coagulant dosage less than 20-30 mg/1
                                                  SLIDE 7

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            DIRECT FILTRATION WITH CONTACT BASINS
t  One hour basin for pretreatment
•  Used to level  out turbidity spikes
•  Provides silt and sand removal
•  Smooth out coagulant demands
                                                  SLIDE 9

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                 DIRECT "IN-LINE" FILTRATION
•  Commonly used with pressure fitters
•  Iron and manganese removal groundwater
•  Limited to low turbidity surface waters with less than 2-3 NTU  sea-
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•  Not permitted in many states
                                                   SLIDE 11

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                       CYST REMOVAL -
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              WATER TURBIDITY (AFTER ENCESET)
                                          SLIDE 14

-------
                 SPIKED GIARDIA PILOT STUDY
                 LAKE ARROWHEAD, CALIFORNIA
•  Adsorption clarification/filtration process
t  20 gpm pilot plant removal  groundwater
•  2,100 cysts per liter influent concentration
•  100 percent removal by filtration
t  Filtered water turbidity 0.05-0.06 NTU
t  Clarified effluent contained cysts at 0.3-0.4 NTU turbidity
                                                  SLIDE 15

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                         POTENTIAL REMOVAL EFFICIENCIES
PARAMETER
Coliforms
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Enterovirus
Giardia
CLARIFIED
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  50-70
  70-99
  40-75
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 90-99
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                                                            SLIDE 17

-------
WHAT IS IT GOING TO COST?
                                SLIDE 18

-------
                   WHAT DO COSTS INCLUDE?
•  Capital  (construction, engineering,  administration)
t  Operation and maintenance (energy, maintenance,  materials and  labor)
•  Total  costs (capital costs at 20 years,  10 percent  Interest  plus
•  Total costs presented as cents per 1,000 gallons
                                                  SLIDE 19


-------
                ESTIMATED COSTS - FILTRATION PROCESSES
                             LARGE SYSTEMS
Conventional Treatment
Direct Filtration
Diatomaceous Earth
Total Cost
0/1,000 Gal
 30-60
 20-50
 35-50
                                                       SLIDE 20

-------
                ESTIMATED COSTS - FILTRATION PROCESSES
                            MEDIUM SYSTEMS
Conventional Treatment
Direct Filtration
Diatomaceous Earth
Slow-Sand Filter
Total Cost
6/1,000 Gal
 70-100
 55-90
 40-50
 25-35
                                                       SLIDE 21

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-------
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               ADDING CHEMICAL DOSAGE CONTROL
•  Mandatory for low filtered water turbidity
•  Common dosage control techniques
   - Jar tests
   - Particle charge
   - Pilot filters
                                                  SLIDE 36

-------
                   PARTICLE CHARGE DEVICES
t  Streaming current detector
•  Measures relative particle charge with electrodes
•  Electrode output current related to Zeta potential
•  Use output to control chemical  feed pumps
•  Calibrated from jar test results
                                                  SLIDE 37

-------
                     SYNCHRONOUS
                     MOTOR
           LOOSE FITTING PISTON OF  "*•
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CUTAWAY OF CELL BODY AND PUMP
BORE OF INSULATING PLASTIC
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           SIMPLIFIED DIAGRAM OF SCO INSTRUMENT
                                       SLIDE 38

-------
           COAGULATION CONTROL WITH PILOT FILTERS
•  Direct measurement of fllterability of coagulated plant water
•  Determines adequacy of coagulant dosage
0  No correlation to other test procedures required
•  Use output signal to control coagulant feed pumps
t  Precise coagulant dosage control can save costs
                                                  SLIDE 39

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           IMPLEMENTING FLOCCULATION IMPROVEMENTS

•  Improves clarification efficiency

•  Generally required when increasing capacity

•  Detention time requirements: 10-40 minutes

t  Mixing intensity G values: 10-100 seconds

•  Numerous design types widely used  .
   -  Slow-speed paddles
   -  Vertical turbine
   -  Oscillating paddles
                                                  SLIDE 41

-------
               METHODS TO IMPROVE FLOCCULATION
•  Install new mixing equipment
t  Add baffling
•  Improve inlet and outlet conditions
                                                  SLIDE 42

-------
Stator beam
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        a) Paddle type with rotors and stators.
        b) Plate turbine type.
        c) Axial flow propeller type with straightening vanes.
                          TYPICAL FLOCCULATION  UNITS
                                                  SLIDE 43

-------
               Biffles
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d) Schematic of radial flow
   pattern In baffled tank.
e) Schematic of axial flow
   pattern in baffled tank.
           (CONT.X   TYPICAL  FLOCCULATION  UNITS
                                          SLIDE 43

-------
I
                                   Axial Flow
                                    Turbine
                                   Propallar
                                   Turbin*
         f) Basic impeller styles,
g) Walking beam flocculator.
                             (Cont.).  TYPICAL FLOCCULATION- UNITS
                                                            SLIDE  43

-------
INSTALLATION OF WALKING BEAM FLOCCULATOR
                                        SLIDE 44

-------
NEW- AND OLD-STYLE FLOCCULATORS
                    SLIDE 45

-------
    IMPROVING INLET CONDITIONS AND BASIN SHORT-CIRCUITING
•  Major overlooked problem
o  Contributes to unbalanced coagulant dosage
t  Breakup of floe
•  Reduces effective detention time
                                                  SLIDE 46

-------
         CORRECTING FLOCCULATION HYDRAULIC PROBLEMS
•  Install Inlet diffusers
•  Add baffling to compartmentalize basins
0  Enlarge connecting conduits
                                                   SLIDE 47

-------
              SEDIMENTATION BASIN DEFICIENCIES
o  Poor inlet conditions
•  Basin turbulence
•  Excessive clarification rate
•  Improper outlet facilities
•  Inadequate or no sludge removal
                                                  SLIDE  48

-------

               TECHNIQUES TO IMPROVE SETTLING
•  Inlet and outlet modifications
•  Install sludge collection equipment
•  Add tube or plate settling devices

                                                  SLIDE 49

-------
                        TUBE SETTLING
•  Established technology
e  Widely used
9  Reduce floe carryover In existing basins
e  Permit increasing capacity up to 100 percent
o  General  application rates: 1-3 gpm/sq ft
                                                 SLIDE 50

-------
A MODULE OF  STEEPLY INCLINED TUBES
(COURTESY OF  MICROFLOC PRODUCTS
GROUP, JOHNSON DIVISION, UOP)
                       SLIDE 51

-------
INFLUENT ZONE
 EFFLUENT
COLLECTION
   ZONE
                EXISTING LAUNDERS    NEW LAUNDERS
      NEW BAFFLE
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    IN RECTANGULAR BASIN
                           SLIDE  52

-------
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SECTIONAL VIEW THROUGH SEDIMENTATION BASIN

SHOWING VACUUM SLUDGE REMOVAL SYSTEM
                            SLIDE 53

-------
CLOSE-UP VIEW OF VACUUM SLUDGE REMOVAL ASSEMBLY
                            SLIDE 54

-------
                             TUBE SETTLING MODULES (TYPICAL
                                SEGMENTS)
                                        TUBE MODULE
                                        SUPPORT FRAME
                                          LAUNDERS NOT SHOWN
                                          TO PROVIDE CLARITY
                                           NEW VARIABLE SPEED
                                             CIRCULATION PUMP
           PLAN
SOLIDS CONTACT CLARIF1ER WITH TUBE SETTLERS
                              SLIDE 55

-------
VARIABLE SPEED
RECIRCULATION PUMP
•TUBE SETTLING MODULES
      •SLUDGE WASTING SUMP
                                         COLLECTOR DRIVE
                                                   SLUDGE COLLECTOR
                                 SLUDGE SLOWDOWN
                           SECTIONAL ELEVATION
               (ContJ.  SOLIDS CONTACT CLARIFIER WITH TUBE SETTLERS
                                             SLIDE 56

-------
PHOTOGRAPH OF TUBE SETTLERS IN SOLIDS CONTACT CLARIFIER
                                               SLIDE 57

-------
PHOTOGRAPH OF ALUM FLOC CARRIED UP THROUGH TUBE SETTLERS
                                                SLIDE 58

-------
PHOTOGRAPH SHOWING ACCUMULATION OF SOLIDS ON SURFACE OF TUBE SETTLING MODULES
                                                          SLIDE 59

-------
             TOTAL COSTS FOR ADDING TUBE SETTLING MODULES
     Tube Settling Modules
Small plants (less than 100,000 gpd)
Medium plants (less than 6 mgd)
Large plants (greater than 10 mgd)
Total Cost of Modification
$0.009 to $0.027 per 1,000
gallons
$0.004 to $0.009 per 1,000
gallons
$0.004 per 1,000 gallons
                                                       SLIDE 60

-------
                        REPLACE MEDIA            t ,
•  Improves filtered water quality
•  Most rapid sand filters suitable for.conversion
•  Hydraulic and structural modifications may be needed
t  Doubling plant capacity with no structural additions possible
                                                  SLIDE 63

-------
   IMPROVING EXISTING DUAL- OR TRI-MIXED MEDIA FILTRATION
•  Filter aid polymer prior to filtration
e  Polymer application to backwash water
•  Install individual filter turbidimeters
t  Provide filter to waste
                                                  SLIDE 64

-------
PHOTOGRAPH OF TYPICAL GRAVITY FILTERS
                                      SLIDE 65

-------
CUTAWAY VIEW OF TYPICAL MIXED-MEDIA FILTER
                                         SLIDE 66

-------
MIXED-MEDIA FILTER BED
                               SLIDE 67

-------
            ESTIMATED COSTS - PLANT MODIFICATION
Small Systems
Medium Systems
Large Systems
                                        Total Cost
                                          . OOP Gal
0.8-5
0.5-3
0.1-2
                                                  SLIDE 68

-------
                  NEW FILTRATION TECHNOLOGY
•  Deep bed mono media
•  Popular with ozone pretreatment
•  Coarse media: 1.0 to 2.0 mm
                                                   SLIDE 69

-------
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                                                                  Microprocessor
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                                                                  Integrity Chock
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                       SKID-MOUNTED MEMBRANE FILTRATION ASSEMBLY
                                                     SLIDE 72

-------
                                        FILTERED
RAW WATER
CLARIFIED
RECYCLE
DISCHARGE
                                             HOLLOW FIBER
                                             MEMBRANES
                                                MEMBRANE
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AIR INLET FOR
BACKWASHING


BACKFLUSH
WASTEWATER
                                        BACKFLUSH CLARIFIER
              FLOW SHEET OF MEMBRANE FILTRATION SYSTEM
                                     SLIDE 73

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           PROCESSES APPROPRIATE FOR SMALL SYSTEM
•  Slow Sand Filtration
•  Package Plants
•  Diatomaceous Earth Filtration
                                                  SLIDE 75

-------
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PERCENT EXCEEDING  SPECIFIED FILTERED  WATER TURBIDITY
                AVERAGE FILTERED WATER TURBIDITIES AT
                SLOW-SAND FILTER PLANTS SURVEYED
                                        SLIDE 79

-------
PHOTOGRAPH OF MECHANICAL SLOW SAND FILTER CLEANER
                                            SLIDE 80

-------
               PACKAGE WATER TREATMENT PLANTS
t  Capacity range:  10 gpm to 40 mgd
•  Factory built and compact
•  650-700 in service
•  Simple to operate, designed for unattended operation
•  Require basic operator skills
•  Cost effective                                .
                                                  SLIDE 81

-------
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PHOTOGRAPH OF 100 6PM PACKAGE PLANT INSTALLATION
                                             SLIDE  83

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-------
          FLASH
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FILTRATION
INFLUENT

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                           DESLUDGE   BACKWASH-  BACKWASH
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           FLOW DIAGRAM OF ALTERNATIVE PACKAGE PLANT
           (COURTESY OF WATER TECH, INC., VANCOUVER, WASHINGTON)
                                           SLIDE 86

-------
                    ADSORPTION CLARIFIER
•  Removal mechanism - Adsorption
•  Settling not required
•  Settleable floe not needed
                                                  SLIDE 87

-------
VIEW OF POLYETHYLENE ADSORPTION MEDIA
                                      SLIDE 88

-------
                    ADSORPTION CLARIFIER
                        FLOCCULATION
•  G = 110/second to 300/second
•  Gt = 1 x 104 to 3 x 104
                                                  SLIDE 89

-------
                    RATES
Clarlfier:       10 gpm/sq ft
Filter:           5 gpm/sq ft
                                          SLIDE 90

-------
                        APPLICATIONS
•  At 10/5 gpm/sq ft: Long-term operation
•  Turbidity: 100-150 NTU
•  Color:  75-125 units
•  Iron and Manganese: No limits established
•  No lime softening
                                                  SLIDE 91

-------
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         ESTIMATED COSTS FILTRATION PROCESSES
                     SMALL SYSTEMS

                                               Total Cost
                                               4/1.000 gal
Package Plant                                    100-950
Direct Filtration                                150-350
Diatomaceous Earth                                50-650
Slow-Sand Filter                                  50-400
                                               SLIDE 93

-------
Table of Contents

-------

-------
                                TABLE OF CONTENTS


Section                               Title                                Page

    I                FILTRATION TECHNOLOGIES                                1-1
                         Introduction                                       1-1
                             Requirements for Filtration                    1-1
                         Established Filtration Technologies                 1-2
                             Conventional Treatment                         1-2
                             Direct Filtration                              1-2
                             Diatomaceous Earth Filtration                  1-3
                             Slow-Sand Filtration                           1-3
                             Package Plants                                 1-4
                         Other Applicable Filtration Technologies           1-4
                         Effectiveness of Filtration Process                 1-4
                         Basis of Costs               .                      1-6
                             General                                        1-6
                             Capital Costs                                  1-7
                             Operation and Maintenance Costs                 1-7
                         References                                        1-15

    II               TECHNIQUES FOR UPGRADING EXISTING WATER                II-l
                       TREATMENT PLANTS
                         Introduction                                      II-l
                         Upgrading Techniques                              H-2
                             Modifying Chemical Treatment                  II-2
                                 Alum and Ferric Chloride                  H-2
                                 Coagulation with Polymers                 II-3
                                 Coagulant Aids                            II-4
                                 Providing pH Control                      II-5
                                 Chemical Feed Costs                       II-6
                                     Conceptual Design                     II-6
                                     Operation and Maintenance             I1-6
                                       Requirements
                                 Liquid Alum Feed                          I1-7
                                     Conceptual Design                     I1-7
                                     Operation and Maintenance             11-7
                                       Requirements
                                 Polymer Feed                              11-8
                                     Conceptual Design                     II-8
                                     Operation and Maintenance             11-8
                                       Requirements
                                 Sodium Hydroxide Feed                     I1-9
                                     Conceptual Design                     I1-9
                                     Operation and Maintenance             H-9
                                       Requirements
                                 Sulfuric Acid Feed                       11-10
                                     Conceptual Design                    11-10
                                     Operation and Maintenance            11-10
                                       Requi rements
                             Modifying or Adding Rapid Coagulant          11-10
                               Mixing
                                 General                                  11-10
                                 Changing Point of Coagulant  Addition     11-11

-------
TABLE OF CONTENTS (Continued)
Section
   II (Continued)
         Title                                Page

    Coagulant Diffusers                      11-12 '
    Mechanical Mixing                        11-12
    In-Line Blenders                         11-13
    Jet Injection Blending                   11-13
    Static Mixers                            11-14
    Cost of Rapid Mix                        11-15
        Conceptual Design                    11-15
        Operation and Maintenance            11-15
          Requi rements
Adding Chemical Dosage Control Provisions    11-15
    Techniques Available                     11-15
    Jar Tests                                11-17
    Techniques Based on Particle Charge      11-17
        Zeta  Potential                       11-17
        Streaming Current Detector           11-18
    Continuous Filtration Techniques         11-18
        Pilot Filters                        11-18
        Design for Automated Coagulant       11-20
          Control
    Turbidity Monitoring          •           11-21
        Particle Counting                    11-21
Implementing  Flocculation Improvements       11-22
    Type of Flocculators                     11-23
    Flocculation Design Guidelines           11-23
    Flocculation Alternatives                11-23
    Improving  Inlet and Outlet Conditions    11-25
    Correcting Short-Circuiting              11-25
    Installing High-Energy Flocculators      11-26
    Case History                             11-27
    Cost of Adding  Flocculation Basins       11-28
Improving Sedimentation Performance          11-23
    General                                  11-28
    Improving  Inlet Conditions               11-29
    Improving  Outlet Conditions              11-29
    Installing Sludge  Collectors             11-29
    Installing Tube Settlers                 11-30
    General Design  Considerations            11-31
    Application Requirements                 11-31
        Horizontal  Flow Sedimentation        11-31
          Basins
        Upflow Clarifiers with Solids        11-32
          Contact
    Recommended Design Criteria              11-33
        Upflow Clarifiers -  Loading  Rates    11-33
        Horizontal  Flow Basins -             11-33
          Loading Rates
        Location  of Tube Modules Within      11-33
          the Basin
    Example  Applications                     11-34
         Horizontal  Basins                    11-34
                                        ii

-------
        TABLE OF CONTENTS (Continued)
        Section
            II (Continued)
           HI
it.
                 Title                                Page

                Upflow Basins                         11-35
            Costs of Installing Tube Settlers         11-36
        Modifying Filtration Facilities               II-36
            General                                   11-36
            Filter Upgrading Evaluation               11-37
            Regulatory Agency  Design Standards       11-40
            Filter Design Checklist                  11-41
            Case Histories                           11-42
                Sacramento, California               11-42
                Erie County, New York                11-44
                Corvallis, Oregon                    11-46
                North Marin County Water District.   11-47
                  Novato, California
    References                                       11-93

NEW TREATMENT TECHNOLOGY                             III-l
    Introduction                                     III-l
    Package Plants                                   III-l
        General                                      III-l
        Types Available                              II1-2
            Conventional Package Plants               II1-2
            Tube Type Clarification Package Plants   III-2
            Adsorption Clarifier Package Plant       II1-3
        Application Criteria and Requirements        III-5
        Operational Considerations                   III-6
            Cost of Package Conventional             II1-7
              Complete Treatment
                Conceptual Design                    II1-7
                Operation and  Maintenance            III-7
                  Requirements
                Chemical Requirements                II1-7
        Conventional Package  Plant Performance -     II1-8
          Case Histories
            EPA Survey of Six  Plants                 III-8
        Adsorption Clarifier  Package Plants -        III-9
          Case Histories
            Greenfield,  Iowa                          II1-9
            Lewisburg, West Virginia                111-10
            Philomath, Oregon      •                  I11-10
            Harrisburg,  Pennsylvania                111-10
            Red Lodge, Montana                      I11-11
    Slow-Sand Filtration                            III-ll
        Process Description                         III-ll
        Design Standards                            I11-12
        Operating Characteristics                   111-13
        Effluent Quality Requirements               II1-13
        Laboratory and Pilot  Plant Studies          111-14
        Costs of Slow-Sand Filters                  111-15
            Conceptual Design                        111-15
            Operation and Maintenance Requirements  111-16
                                               iii

-------
TABLE OF CONTENTS (Continued)
Section

  III (Continued)
             Title                                Page

    Case Histories                              111-16
        Survey of 27 Plants                     II1-16
        New York State                          II1-17
        Mclndoe Falls, Vermont                  111-18
        Village of 100 Mile, British            111-19
          Columbia, Canada
            Operating Results                   II1-20
            Cost                                II1-21
Diatomaceous Earth Filtration                   111-21
    General                                     111-21
    Design Criteria                             II1-23
    Operating Requirements                      111-24
    Effluent Quality Requirements               II1-24
    Treatment Capability                        111-24
    Costs for Diatomaceous Earth Filtration     111-26
Membrane Filtration                             II1-26
    Introduction                                111-26
    Membrane Cleaning                           II1-27
    Typical Installation                        III-28
    Performance Capabilities                    111-29
        Giardia Removal                         III-29
        Coliform Removal                        II1-29
        Turbidity Removal                       II1-30
    Capital Costs                               111-30
    Application Concerns                        111-30
        Membrane Failure                        I11-30
        Organics Removal                        II1-31
        Pilot Testing                           111-31
Cartridge  Filters                               111-31
    Equipment Description                       111-31
    Cartridge Cleaning                          111-32
    Application Considerations                  111-32
    Removal Capabilities                        II1-33
Qualifying Filtration  Processes                 111-33
    Need for Pilot Studies                      II1-33
    Regulatory Agency  Requirements              111-34
    Conducting  Pilot  Studies                     II1-35
        Flocculation  and Sedimentation Studies  III-36
        Filtration Studies                       111-37
    Case Study  -  New  Treatment Facilities        II1-38
       Pilot Study  Selection  Process
        Background                               111-38
        Quality and Treatment                    111-39
        Pilot Study Program                      II1-40
        Pilot Study Results                      111-40
        Recommended Design Criteria              111-41
                                         iv

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TABLE OF CONTENTS (Continued)
Section

  III (Continued)
  APPENDIX
                 Title

        Case Study - Untreated Supply for Small
          Community  .
            Example
            Evaluation Procedures
            Cost Analysis
    References

Chemical Costs

Design Standards for Filtration Plants -
  Texas Department of Health
  Paje

111-41

111-41
111-42
II1-43
III-84
                     Pilot Study Report

-------
LIST OF TABLES
Number
SECTION 1
Table 1-1
Table 1-2
Table 1-3
SECTION II
Table II-l
Table II-2
Table II-3
Table II-4
Table II-5
Table 1 1-6
Table 1 1-7
Table 11-8
Table II-9
Table 11-10
Table 11-11
Table 11-12
Table 11-13
Table 11-14

Title
Generalized Capability of Filtration Systems to
Accommodate Raw Water Quality Conditions
Removal Efficiencies of Viruses by Water Treatment
Processes
Removal Efficiencies of Giardia Lamblia by Water
Treatment Processes
Summary of Potential Problems in Water Treatment Unit
Operations
Estimated Costs for Surface Water Treatment by Adding
Alum Feed Facilities (10 mg/1)
Estimated Costs for Surface Water Treatment by Adding
Polymer Feed Facilities (0.3 mg/1)
Estimated Costs for Surface Water Treatment by Adding
Polymer Feed Facilities (0.5 mg/1)
Estimated Costs for Supplementing Surface Water
Treatment by Adding Sodium Hydroxide Facilities
Estimated Costs for Supplementing Surface Water
Treatment by Adding Sulfuric Acid Feed Facilities
Estimated Costs for Supplementing Surface Water
Treatment by Adding Rapid Mix
General Design Criteria for Flocculation Basins
Flocculator Design Guidelines
Estimated Costs for Supplementing Surface Water
Treatment by Adding Flocculation
Upflow Clarifier Loading Rates for Cold Water
Upflow Clarifier Loading Rates for Warm Water
Horizontal Flow Basins Loading Rates for Cold Water !
Horizontal Flow Basins Loading Rates for Warm Water
vi
Page
1-9
1-10
1-10
11-51
11-52
11-53
11-54
11-55
11-56
11-57
11-58
11-59
11-60
11-61
11-61
11-62
11-62


-------
 List of Tables (Continued)
  Number
 SECTION II (Continued)
                      Title                                 Page
 Table 11-15

 Table 11-16
 SECTION III
 Table III-l

 Table II1-2

 Table 111-3
 Table 111-4
 Table 111-5
 Table 111-6
 Table III-7
 Table II1-8
 Table III-9
 Table 111-10
 Table 111-11

 Table  111-12

 Table  111-13
 Table  111-14

 Table  111-15"
 Table  111-16
Table  111-17
Table  111-18
 Estimated Costs for Upgrading Surface Water Treatment    11-63
 by Adding Tube Settling Modules
 Turbidity Ranges During Demonstration Test               11-64
 Summary of Results of Adsorption Clarification          II1-45
 Package Plants (Microfloc Products Group)
 Estimated  Costs for Surface Water Treatment by          111-46
 Complete Treatment Package Plants
 Water Treatment Facilities Surveyed in Field Study      II1-47
 Treatment  Process Characteristics                       111-48
 Plant Turbidity Values  (NTU)                             111-49
 Operating  Data - Greenfield,  IA                         II1-50
 Operating  Data - Lewisburg,  WV                           111-51
 Operating  Data - Philomath,  OR                           111-52
 Operating  Data - Harrisburg,  PA                         111-53
 Operating  Data - Red  Lodge,  MT                           II1-54
 Estimated  Costs  for Surface  Water Treatment by Slow-    II1-55
 Sand  Filtration
 Characteristics  of  Slow-Sand  Filter Installations  in    111-56
 New York .
 Filter  Ripening  Data  - Summary                           II1-57
 Estimated  Costs  for Surface Water Treatment by Direct   II1-58
 Filtration Using Diatomaceous Earth
 Hollow Membrane  Filtration Facility  Design  Information   II1-59
 Estimated  Costs  for Surface Water Treatment by Package   II1-60
Ultrafiltration Plants
 Clear Lake Water Quality Analysis                        111-61
 Clear Lake Water Quality at DWR  Sampling Station         II1-62
 No. 1 at Lakeport
                                       vii

-------
 Number
SECTION I
Figure 1-1

Figure 1-2
Figure 1-3
Figure 1-4

SECTION II
Figure II-l
Figure 11-2
Figure II-3
Figure I1-4
Figure 11-5
Figure II-6
Figure 11-7
Figure I1-8

Figure II-9
Figure 11-10
Figure II-lla
   and II-llb
Figure 11-12

Figure 11-13
Figure 11-14

Figure 11-15
Figure 11-16
                LIST OF FIGURES
                     Title                                 Page

Flow Sheet of a Typical Conventional Water Treatment       1-11
Plant
Flow Sheets for Typical Direct Filtration Plants           1-12
Typical Pressure Diatomaceous Earth Filtration  System     1-13
Relationship Between Cyst Removal  and  Filtered  Water       1-14
Turbidity (After Engeset)
Coagulant Diffuser
Diffuser for Coagulant Application
Jet Mixing Facility
Typical Flash Mixing Facility
Motionless (Static) Mixer  (Courtesy of  Komax)
Simplified Diagram of SCO  Instrument
Typical Flocculation Units
A Perforated Baffle with Square-Nozzled Ports
Distributes Flow from the Flocculators  at Rio De
Janeiro's Guandu Treatment Plant
New- and Old-Style Flocculators
Compartment Plan for One Flocculation Unit
Flocculator Outlet System  and  Settling  Basin  Inlet
System  (Side and End Views)
Sectional View Through Sedimentation Basin  Showing
Vacuum  Sludge Removal System
Close-Up View of Vacuum Sludge Removal  Assembly
A Module of Steeply  Inclined Tubes  (Courtesy of
Microfloc Products Group, Johnson Division, UOP)
Lamella® Separator (Courtesy of Parkson Corp.)
      11-65
      11-66
      11-67
      11-68
      11-69
      11-70
11-71,72,73

      11-74

      11-75
      11-76
      11-77

      11-78

      11-79
      11-80

      11-81
Typical Tube  Settler  Installation  in  Rectangular Basin   11-82
                                       viii

-------
 List of Figures (Continued)
  Number
 SECTION II (Continued)
                      Title
 Figure 11-17

 Figure 11-18
 Figure 11-19

 Figure 11-20
 Figure 11-21

 Figure 11-22

 Figure 11-23
 Figure 11-24
 SECTION III
 Figure III-l
 Figure III-2

 Figure III-3

 Figure 111-4

.Figure 111-5
 Figure 111-6
 Figure III-7

 Figure 111-8

 Figure 111-9

 Figure 111-10
Partial Tube Settler  Installation  in  Circular
Clarifier
Solids  Contact  Clarifier with  Tube Settlers
Package Solids  Contact  Tube  Clarifier (Courtesy
ERC/Lancy)
Variable Declining Rate Filtration (J. AWWA)
Typical Rate of Filtration Patterns During a Filter
Run  (Bauman and Oulman, 1970)
Hypothetical Optimum  Filter  Headioss/Turbidity
Breakthrough Curve
Flow Diagram of the Pilot Filtration  Equipment
Clarifiers Showing Tube Settling Modules
Flow Diagram of a Package Plant
Flow Diagram of Alternative Package Plant  (Courtesy
of Water Tech, Inc., Vancouver, Washington)
Operating Cycles of Package Plant (Courtesy of
Microfloc Products)
Pictorial View, Package Plant  (Courtesy Neptune
Microfloc, Inc.)
Typical Covered Slow-Sand Filter Installation
Typical Uncovered Slow-Sand Filter Installation
Average Raw Water Turbidities  at Slow-Sand Filter
Plants Surveyed
     Page

11-83,84

11-85,86
   H-87

   11-88
   11-89

   11-90

   11-91
   11-92

  111-63
  111-64

  111-65

  111-66

  111-67
  II1-68
  111-69
Average Filtered Water Turbidities at Slow-Sand Filter   111-70
Plants Surveyed
Average Coliforms in Raw Waters at Slow-Sand Filter      111-71
Plants Surveyed
Average Coliforms in Filtered Waters at Slow-Sand        II1-72
Filter Plants Surveyed
                                       ix

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List of Figures (Continued)
 Number
                 Title
Section III (Continued)
Figure III-ll

Figure 111-12

Figure 111-13

Figure 111-14
Figure 111-15
Figure 111-16
Figure 111-17
Figure 111-18
Figure 111-19
Figure IH-20
Figure 111-21
Giardia Cysts in the Raw Water (Village of
100 Mile House)
Average Raw and Filtered Water Turbidity
(Village of 100 Mile House)
Typical Pressure Diatomaceous Earth Filtration
System
Hollow Fiber Membrane Operational Description
Skid-Mounted Membrane Filtration Assembly
Flow Sheet of Membrane  Filtration System
Tube Settling Test Module
Pilot Filter Assembly
Pilot Filter Schematic
Typical Pilot Filtration Data Log
Flow Schematic 20 gpm Pilot Plant
   Page

111-73
111-74

111-75

111-76
111-77
111-78
111-79
II1-80
111-81
111-82
111-83

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                                    SECTION  I

                              FILTRATION TECHNOLOGIES
 INTRODUCTION

 The 1986 Amendments to the Safe Drinking Water Act (SWDA) require that within 18
 months  of  enactment,  the  EPA must  promulgate regulations  specifying criteria
 under  which filtration (including coagulation  and  sedimentation as appropriate)
 is  required for surface water sources,  and disinfection  is  required  for public
 water  systems  using surface water sources. The EPA must  consider the  quality of
 the  source water,  protection  affected  by watershed management,  treatment prac-
 tices  {such  as disinfection and length of water storage), and other factors rele-
 vant to health.  Specific procedures are  required  to be formulated by  the EPA by
 which  states will  determine which  water  systems shall  adopt  filtration. The fil-
 tration  and disinfection  requirements  are being proposed as  treatment techniques
 regulations  to  protect  against the potential  adverse  health  effects  of exposure
 to Giardia  Iambiia, viruses,  Legionella, and heterotrophic bacteria,  as  well as
 many other  pathogenic  organisms  that may be present.and  are  removed  under these
 conditions.

 Requirements for Filtration

 EPA  is in  the  process of  preparing  a  guidance manual for  compliance with the
 filtration  and  disinfection requirements for public.water systems using surface
 sources. This document will ensure the proper implementation of the Surface Water
 Treatment Rule (SWTR). The SWTR pertains to all  public water systems that utilize
 a surface  water  as their source. The SWTR defines  a surface  water as  all waters
which  are   open  to  the  atmosphere  (e.g.,  rivers, , lakes, streams,  reservoirs,
 impoundments) and any subsurface sources such  as springs, infiltration  galleries,
wells  or other collectors that  are  at risk of being  contaminated by  a  surface
water.
                                      1-1

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Surface water supplies  that  are often used as  sources  of drinking water include
two major classifications, namely  running  and  quiescent waters.  Streams, rivers,
and brooks  are  subdivisions  of running water;  while  lakes,  reservoirs, impound-
ments and ponds  are subdivisions  of quiescent  waters.  These sources are subject
to the requirements of the SWTR.

ESTABLISHED FILTRATION TECHNOLOGIES

The following methods  of  filtration are identified as  the Most Applicable Tech-
nologies or established filtration technologies and  are those most  widely used
for removal  of turbidity and microbial contaminants:

•    Conventional treatment
•    Direct filtration  {gravity and pressure filters)
t    Diatomaceous earth filtration
•    Slow-sand filtration
•    Package plants

Conventional Treatment

Conventional treatment  is the  most widely  used technology for removing turbidity
and microbial  contaminants from  surface water  supplies. Conventional treatment
includes the pretreatment steps of chemical  coagulation, rapid mixing, floccula-
tion and  sedimentation followed  by filtration. A typical  flow  schematic  for a
conventional treatment  plant  is  shown on  Figure  1-1.   Section  II describes the
application of existing as well as recently developed techniques for the upgrad-
ing of filtration facilities.

Direct Filtration

The direct filtration process  can  consist of any one  of  several different process
trains  depending  upon  the  application.   In  its  most  simple form,  the process
includes only filters  (oftentimes pressure units)  preceded  by chemical coagulant
application  and mixing.  Raw   water  must  be of seasonally  uniform  quality with
turbidities routinely  less  than 5  NTU in  order to be effectively filtered by an
in-line direct  filtration system.  A second common, configuration  of the process

                                       1-2

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 Includes flocculation as pretreatment for  the  filters,  in addition to  coagulant
 application and mixing.  Typical  flow schematics for direct filtration plants  are
 shown on Figure  1-2.  Direct filtration  is  an  established filtration technology
 and will be more  widely  used on water supplies that  up until  now received only
 chlorination because raw  water quality permitted elimination of traditional sedi-
 mentation processes  prior to filtration.

 Diatomaceous Earth Filtration

 Diatomaceous  earth  (DE)  filtration,  also known as  precoat  or  diatomite filtra-
 tion,  is applicable to direct  treatment  of surface waters  for  removal  of rela-
 tively  low  levels  of turbidity.  Diatomite filters  consist of a layer of DE about
 1/8-inch thick  supported  on  a septum or filter element.  A typical flow schematic
 of  a  diatomaceous earth filtration process  is  shown on  Figure  1-3. The problems
 inherent  in maintaining  a   perfect  film  of  DE between filtered  and unfiltered
 water have  restricted the use of diatomite filters for municipal  purposes, except
 under  favorable conditions.  Diatomaceous  earth filtration  is classified as "new
 technology" and discussed in Section III because it has received renewed interest
 in  light of the  need  to  filter surface waters of  low turbidity  previously only
 chlorinated.  Since  it  can  remove  Giardia  cysts  it  is  a  viable  filtration
 technology.

 Slow-Sand Filtration

 Slow-sand   filters  are  similar  to  single-media  rapid-rate  filters  in  some
 respects, yet they differ in a number of  important  characteristics.  In addition
to  (1)  slower flow rates  (by a factor of 50 to 100  versus direct filtration for
example),  slow-sand   filters  also:   (2)  function   using  biological  mechanisms
 instead  of  physical-chemical  mechanisms,  (3)  have-smaller pores between  sand
particles,   (4)  do not  require  backwashing,  (5) have  longer  run  times between
cleaning,  and   (6)  require  a ripening  period  at  the  beginning  of each  run.
Although applicable  to  medium to large size plants,  they  are most commonly used
for small   communities  because  of  the operational  simplicity.  Because of  the
revived interest in this  filtration method  it  is  referred  to in  this document as
"new technology."
                                      1-3

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Package Plants

Package  plants  are  not  a  separate  technology  in  principle from  the preceding
technologies. They are, however, different  enough  in design criteria, operation,
and maintenance  requirements  that  they  are discussed separately  in  Section III
and are regarded as new technology.

The package plant is designed as a factory-assembled, skid-mounted unit generally
incorporating a single, or  at the  most,  several  tanks.  A complete treatment pro-
cess typically consists of  chemical  coagulation,  flocculation,  settling and fil-
tration. Package plants, for purposes  of this  document,  generally can be applied
to flows ranging from about 25,000 gpd to approximately 6 mgd.

OTHER APPLICABLE FILTRATION TECHNOLOGIES

Technologies classified as  Other Applicable Technologies which  may have applica-
tion for removal of turbidity and microbial contaminants are listed as follows:

•    Membrane (ultrafiltration)
•    Cartridge

These  technologies  have not  been  widely  used  for  filtration  of drinking water
supplies and  could  therein be  classified as truly  emerging  technologies. Along
with package plants, slow  sand  filters,  and diatomaceous earth  filtration, these
filtration  technologies  are best  suited to small  systems and  are  collectively
classified  as new technology and are fully  discussed  in Section III.

EFFECTIVENESS OF FILTRATION PROCESSES

The  application  of  these  technologies  will depend on certain  raw water condi-
tions,  as shown in Table 1-1.

Filtration  processes provide  various  levels  of microbial  contaminant removal.
Tables  1-2  and 1-3 summarize microbial removal  efficiencies determined from field
and pilot plant studies completed on a range of filtration  processes.
                                       1-4

-------
 Table  1-2  includes virus removal  results by several filtration processes without
 disinfection.1  As  shown  in the table, all of the processes are capable of remov-
 ing  99 percent  of  viruses  without disinfection.

 Giardia  Iambi i a removal  data  by conventional  treatment,  direct filtration, dia-
 tomaceous  earth filtration,  and  slow-sand filtration  are shown  in  Table  1-3. 2
 Very high  levels (>99.9%)  of Giardia  reduction can  be achieved by  chemical coagu-
 lation followed by settling and filtration, or  by  direct filtration. The impor-
 tance of coagulation  to  achieve high  levels of Giardia removal is noted for both
 processes. Diatomaceous  earth  filtration is also extremely effective in removing
 Giardia cysts.  Slow-sand  filtration which relies on biological as well as physi-
 cal mechanisms to  remove microbial  contaminants is  especially effective in remov-
 ing GUjrdiA cysts.
 In  his  review  of  performance data,  Logsdon compared slow-sand filtration, diato-
maceous earth filtration, and conventional and direct filtration.1 Using informa-
tion from filtration  studies  at  pilot-scale,  full-scale,  or both, he showed that
all of  the  filtration  processes,  when  properly  designed and operated, can reduce
the concentration of  Gi a rd i a  cysts  by  99 percent or more, if they are treating a
source  water of  suitable  quality.  Many of  the studies also  contained Giardia
 removals of  99.9 percent, agreeing with  the values shown in Table 1-3.

Effective particulate removal has been found to be a critical factor in producing
a  safe  water where  the water is  at  risk for  or contaminated with Giardia. Pilot
studies by  Engeset  et.  al.  using low  turbidity  raw water found the relationship
between cyst removal and filtered water turbidity shown in Figure 1-4. 1 Achieving
a  99  percent reduction in cysts  required a  finished  water of 0.1  NTU  or less.
Studies at  Colorado  State  using  low  turbidity  raw  water found  effective  cyst
removal to be associated with a 70 percent removal of turbidity.

Filtration processes  provide various levels of  turbidity  and microbial  contami-
nant  removal.  However, when  properly designed  and  operated and when  treating
source waters of suitable quality,  the above  filtration processes are capable of
achieving  at least  a  2 log (99 percent)  removal  of Giardia cysts and a 1 log (90
percent)  removal  of  enteric  viruses  without  disinfection.  A  summary of  the
removal capabilities  of  the  various filtration  processes is presented  in Table
1-3.  As  indicated,   conventional  treatment  without  disinfection  is  capable  of
                                      1-5

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achieving up to a 3 log reduction in Giardia cysts and a 2 log removal of enteric
viruses. Direct  filtration  can  achieve up to a 2  log reduction of Giardia cysts
and a 3 log reduction of enteric viruses. Achieving the maximum removal efficien-
cies of those constituents  with  these  treatment  processes requires the raw water
be properly coagulated and filtered.

The technologies  available  to a community searching  for  the most economical and
effective means to comply with the surface water treatment rule include modifica-
tion of existing treatment plants and installation of new plants. Both filtration
and disinfection  processes  are capable  of achieving high removals  of microbial
contaminants.  Some  examples of  their  removal  efficiences  based on  data from a
number of; plants are shown below:

                                  	Percent  Removal
Parameter

Coliforms
Turbidity
Enterovirus
Giardia

*After disinfection.

It is important  to  note  that  virus  removal (based on mean virus density) in four
of the treatment plants  surveyed exceeded  99 percent through prechlorination and
clarification  processes only. Very high  levels  (>99.9 percent)  of Giardia reduc-
tion can be achieved by chemical coagulation followed by settling and filtration,
or by direct filtration. The  importance  of coagulation  to achieve high levels of
Giardia removal  is noted for both processes.

BASIS OF COSTS

General

Capital  and operating  costs provided  in the following  sections  for  technologies
in this  document are  based upon updated  costs  originally  presented  in several
                                      1-6
Clarified
90-99
50-70
70-99
40-75
Filtered
98-99.99
90-99
90-99.9
96-99.9
Finished*
>99.99
90-99
98-99.99
96-99.99

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cost  documents prepared  for  EPA.3!1* Specific  details regarding  how  costs were
calculated for  individual.processes  and process groups are presented in following
sections.             •

Capital Costs

The  construction cost  data presented  in  this document  are based  on  late 1986
costs.  Methods of  calculating  construction costs  are described  in  the two  EPA
reports  mentioned  above.3,1*  Construction   costs  are converted  to capital   costs
by use  of typical percentages of  construction  costs for such factors as contin-
gencies (15%),  contractor's overhead and profit (1256), sitework  (15%), subsurface
considerations  (5%),  engineering  and  technical  fees  (15%),  and interest during
construction  (10%).  Costs for acquiring  new land  for  treatment sites, however,
are  not  included  in project costs since these costs are extremely site specific.
To estimate  annual  costs  and  costs per 1,000 gallons,  capital  costs were  amor-
tized over 20 years at a  10 percent  interest rate.               •  .

Operation and Maintenance Costs

Operation  and  maintenance requirements  are developed  for  energy,  maintenance
material,  and  labor.  The  energy category  includes process  electrical  energy,
building  electrical  energy,   and diesel   fuel.  The  operation  and  maintenance
requirements were determined from operating data at  existing plants to the extent
possible, or  from assumptions  based  on  the experience of both the author and  the
equipment manufacturers.

Electrical  energy  requirements  were  developed   for  both   process  energy  and
building-related  energy,  and they are presented  in terms of kilowatt-hours  (kWh)
per year.

Maintenance material costs  include  the  cost of periodic replacement of component
parts necessary to  keep  the process  operable and  functioning. Chemical  costs  are
added separately, and  units costs  of  chemicals used  in this document  represent
late  1986 conditions.  Chemical  costs are  shown  in  Table  A-l  of  the  Appendix.
Labor requirements include both operation and maintenance labor.
                                      1-7

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Total operation  and  maintenance cost  is  a  composite of the  energy,  maintenance
material,  and labor  costs.  To determine  annual  energy  costs,  unit  costs  of
$0.068/kWh  of electricity and  $0.80/gallon  of diesel  fuel  are used.  Thei labor
requirements  are converted  to an annual cost  using  hourly  labor rates  of $5.90/
hour for small water  systems  (less  than 150,000 gpd design capacity) and $14.30/
hour for larger systems,  based on labor costs  found at existing  plants during
conduct of this project.
                                       1-8

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TABLE 1-1.  GENERALIZED CAPABILITY OF FILTRATION SYSTEMS TO
            ACCOMMODATE  RAW  WATER  QUALITY CONDITIONS
        Treatment Technology
 Conventional  Treatment
     General Constraints
   (Indicated values could
   occasionally be exceeded)

  Total
Conforms   Turbidity  Color
(I/1QO ml)    (NTU)     (CU)


 <20,000        no       75

          restrictions
     (with no predisInfection)
  <5,000
 Direct Filtration
    <500
<7-14
<40
 Slow Sand Filtration
    <800
           <5
 01atomaceous  Earth Filtration
    
-------
    TABLE 1-2.  REMOVAL  EFFICIENCIES  OF  VIRUSES BY
    	WATER  TREATMENT PROCESSES	

                Unit Process                   Percent Removal

           Slow sand filtration                    99.9999
                                                  99.8
                                                  99.8
                                                  91

           Olatomaceous  earth                     >99.9S
             filtration                             *

           Direct filtration                       90-99

           Conventional  treatment                  99
     *No viruses recovered.
     TABLE 1-3. REMOVAL EFFICIENCIES OF GIARDIA LAMBLIA BY
	WATER TREATMENT PROCESSES	

   Unit  Process                                Percent Removal
 Rapid filtration  with                           96.6-99.9
 coagulation, sedimentation
 Direct  filtration with                           95.9-99.9
 coagulation
 -  Mo coagulation                                     48
 -  With  flocculatlon                                95-99
 -  No coagulation                                   10-70

 Olatomaceous earth                              99-99.99
   filtration
                                                  >99.9
 Slow sand filtration                                100
                             1-10

-------
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-------
INFLUENT
            -COAGULANTS
 RAPID MIX
30 sec • 2 min
 DETENTION
DUAL OR MIXED
 MEDIA FILTER
 4-5 gpm/ft2
 INFLUENT
            -COAGULANTS
RAPID MIX
30 sac - 2 mln
DETENTION


1-HR
CONTACT BASIN
                                         DUAL OR MIXED
                                          MEDIA FILTER
                                           4*5 gpm/ft2
                                                        ' NONIONIC POLYMER
                                                        0.05-0.5 mg/l OR
                                                        ACTIVATED SILICA
            i-COAGULANTS
 INFLUENT
1
p

RAPID MIX
30 sac • 2 mln
DETENTION


FLOCCULATtON
15-30 mln


DUAL OR MIXED
MEDIA FILTER
4-5 gpm/ft2
          Figure 1-2.  FLOW SHEETS FOR TYPICAL DIRECT FILTRATION PLANTS
                                         1-12

-------
-V'
           Filtrate
Clear liquid line
q
Precoat
tank
Raw 	 -j 	 _Q_
(
\
>
q
Body
feed
tank
(
i
(
S '
)
i

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line
Filter
Body feed
pump
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••••
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cake

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Precoat
drain
line
source 	 '"t^/Klter" Backwash^/
feed drain line
                    pump
                     Figure 1-3. TYPICAL PRESSURE DIATOMACEOUS
                              EARTH FILTRATION  SYSTEM
                                                                     *-To drain
                                       1-13

-------
      1.0
z
I

H
Q
m
DC
3
III
     0.5
     0.1
u.   0.05
ui
    0.01
                            I  ....... I   t
            40    50     60     70     80     90
                         CYST  REMOVAL -  %
                                                        100
     Figure I-4.  RELATIONSHIP BETWEEN CYST REMOVAL AND FILTERED
               WATER  TURBIDITY (AFTER ENGESET)
                               1-14

-------
REFERENCES

1.  Logsdon,  G.S.,  "Comparison  of  Some  Filtration  Processes  Appropriate  for
    Giardia Cyst Removal,"  presented at  the Calgary Giardla Conference, Calgary,
    Alberta, Canada, February 23-25, 1987.

2.  Lippy,  E.C.,  and S.C.  Waltrip,  "Waterborne Disease  Outbreaks—1946-1980:  A
    Thirty-Five Year Perspective," J.AWWA, p. 60, February 1984.

3.  Culp/Wesner/Culp,  "Estimation  of  Small  System  Water Treatment  Costs,"  EPA
    Contract  No.  68-03-3093,  U.S.  Environmental Protection  Agency,  Cincinnati,
    OH. In publication.

4.  Culp/Wesner/Culp,  "Estimating  Water  Treatment  Costs, Volume  2:  Cost Curves
    Applicable  to  1  to  200 mgd   Treatment   Plants,"   EPA-600/2-79-162b,  U.S.
    Environmental Protection Agency, Cincinnati, OH, August 1979.
                                      1-15

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                       Section II
      Techniques for Upgrading
Existing Water Treatment Plants

-------

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                                    SECTION  II
             TECHNIQUES  FOR  UPGRADING  EXISTING WATER TREATMENT PLANTS
 INTRODUCTION

 Experience has shown that many existing water treatment plants can be upgraded to
 provide  significantly  increased output by  application  of  newly developed treat-
 ment techniques. In many cases these techniques can be applied to improve perfor-
 mance while also  increasing capacity.  If the existing  structures are sound, and
 if traditional design parameters were applied to the original installation, plant
 output  often  can be  increased  by  as  much as  100  to 200  percent  without major
 plant structural additions, and for substantially less than costs associated with
 construction of new facilities.

 When  an  existing water  treatment  plant does not  meet required  standards  it is
 necessary to  upgrade  the plant  performance or  provide additional  treatment. In
 general, upgrading water  treatment plants  is carried out  for one or more of the
 following reasons:

 0    Water quality improvement
 0    Plant capacity increase
 0    Reliability improvement
 0    Maintenance reduction
 0    Cost reduction

 The  extent  of remediation  could range from adjustment  of a chemical  dosage or
 loading  rate,  addition  of  new  chemical  feed  systems,  and baffling to improve
 flocculation or sedimentation basin hydraulics,  to  major  structural  changes. The
 principal objective  of  these  improvements  is  that  of  improved finished  water
quality.  Brief guidance and instructions for evaluating and upgrading the perfor-!
 mance of existing treatment plants is furnished  in this section.                 ;
                                     II-l

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Treatment  facility  evaluation  should  be  carefully  planned  in  advance.   As  it
proceeds,  the  plant  evaluation should  be carried  out  in an  organized,  logical
fashion that results  in  consideration  of all necessary  and  important aspects of
the plant and its operation.

Table  II-l provides a general  overview  of  some  of the problems in various treat-
ment processes that must be corrected in order for the facility to produce accep-
table water quality at manageable cost.  Some  are  of major importance and will be
discussed in the following paragraphs.  Others are of lesser importance and relate
primarily to plant operating reliability and maintenance concerns.

UPGRADING TECHNIQUES

The following techniques  for  upgrading  water treatment  plants  will  be described
and discussed in this section:

*    Modifying chemical  treatment
•    Modifying or adding rapid coagulant mixing
•    Adding chemical  dosage control  provisions
t    Implementing flocculation improvements
*    Improving sedimentation performance
t    Modifying filtration facilities
                                                                                      i
Modifying Chemical Treatment

Alum and Ferric Chloride--
Primary  coagulants such  as aluminum sulfate  (alum), ferric  chloride,  and other
metallic salts  are  widely used in  surface water treatment  plants.  The specific
choice  of  coagulant  is  often  determined  by cost  and  availability as well  as
effectiveness.  Alum,  because  it is  widely  available, effective  at  low dosages,
and easy  to store and  apply,  is  used   in  most treatment facilities.   However,          „
health concerns  related  to the aluminum ion  in filtered water has caused  utili-
ties to consider alternative metallic salt  primary  coagulants,  or in some cases,         ^
organic  coagulants.  Use  of  ferric  chloride,  for  example,  would  eliminate  the
potential  problem  of excessive  aluminum ions  in the filtered  water.  Likewise,
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 organic  coagulants of  either  the cationic  or  anionic type do  not  present this
 problem.
                                                                     /
 Occasionally,  changing  from  alum  to  ferric  chloride as the primary coagulant may
 be  appropriate to achieve either improved  plant performance  or better finished
 water  quality.  For waters containing high  concentrations  of  dissolved color and
 of  low alkalinity and pH, ferric  chloride  could prove to provide more effective
 removal of  color  at  lower dosage  and less cost.  Ferric hydroxide floe is heavier
 than  alum  floe,  and where  raw water  contains  little  turbidity  but  is  highly
 colored,  improved sedimentation basin performance could  be achieved  by changing
 from  alum to  ferric chloride  as a  primary  coagulant.  However,  where trihalo-
methane formation  potential  (THMFP)  of a particular water  supply  is  of concern,
 several investigators have  found  alum to be more effective than ferric chloride
 in  reducing  THMFP and total  organic  carbon  (TOC) on  various  waters  of both acid
 and alkaline characteristics.1

 To  establish which  metallic  coagulant  is  best suited  for  a  particular  water
 supply, use  of  standard  jar  testing  procedures  as  a means of  determining optimum
 dosages in  terms  of  turbidity  as  well as  organic removal is the preferred proce-
dure. Jar test results can then be used to establish appropriate costs for alter-
 native metallic  coagulants.  In general,  both metallic  coagulants perform  quite
similarly on a particular water  supply,  such factors  as cost; safety;  ease in
storing,   handling  and application; and  availability influence selection.  Alum is
generally preferred because  it  is  superior  to  ferric  chloride in the above major
categories of concern.

Coagulation with Polymers—                                                       <•
Synthetic organic  polymers have been shown  to be effective coagulants or coagu-
lant aids.  Polymers  are long-chain  molecules  comprised  of many  subunits  called
monomers.  A polymer is called a polyelectrolyte if its monomers consist of ioniz- 't
able  groups.  Polyelectrolytes having  a  positive  charge upon ionization  are1
referred to  as cationic  polymers.  Negatively  charged  polyelectrolytes  are termed
anionic polymers.  Finally,  polymers that  do  not  contain  ionizable  groups  are
called nonionic polymers.
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Catiom'c polymers can be effective  in  coagulating negatively charged clay parti-
cles.? Cationic polymers do not  require  a large molecular weight to be effective
in destabilization.

Anionic  particles  generally  are ineffective  coagulants  for  negatively  charged
clay particles. When anionic polymers are used in conjunction with another coagu-
lant such as alum, their coagulating effectiveness is increased.

Dosages  of  only  1.5 to 10 mg/1  of  cationic polymer frequently are sufficient to
achieve coagulation. In contrast, 5 to 150 mg/1 of alum is often needed to obtain
similar  results.  Other  important  differences  between  the  use of  polymers and
metallic salts are  sludge  quantities and  dosage  control.  The  use of  alum or
ferric chloride  can result  in copious  volumes  of  sludge that  must be handled,
whereas the additional sludge quantity is negligible when a  polymer is used.

Replacement of alum  by either cationic polymers or mixtures of cationic polymers
and  alum or  sodium aluminate  in  prepared concentrated  solutions  is  becoming
increasingly popular  because  these materials  can achieve effective coagulation,
but produce less  sludge.  They are particularly  attractive  to treatment of  rela-
tively  low  turbidity  (less  than  5  NTU)  surface  waters where  formation  of  a
settleable floe is not a prerequisite to effective removal by filtration. Rather,
the relatively small floe settles poorly, but  is  readily filterable.

Of great benefit is the reduced sludge volume produced through use of the organic
or  organic/metallic coagulants.  However,  because these  coagulants  are  highly
selective,  extensive jar testing as well as frequent changes in coagulant types
(anionic or cationic) may be  needed as raw water  conditions  change seasonally.

Also,  some  waters  of  high  organic content characterized  by  color  imparted by
humic and fulvic acids are  not  effectively  treated because the coagulants do not
impart a pH depression in addition to charge  neutralization which is a require-
ment to precipitate organic color.

Coagulant Aids—
The performance of many water treatment  plants can be improved by the addition of
a  coagulant aid  (generally nonionic)  to overcome some of the deficiencies of a

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 poorly  designed  flocculation  basin.  Flocculation  is  a time-dependent process that
                                T  ' -    •      ' ' ,•   *
 can be enhanced and  accelerated  by the  addition  of organic coagulant aids. The
 resulting  floe generally  settles  more rapidly than  unaided alum floe,  permitting
 the treatment plant to  perform more efficiently  at higher plant throughput*  It
 should  be  noted, however, that  application of  coagulant aids  is no substitute for
 adequate upstream  mixing  of  coagulant with incoming  raw water.

 A coagulant aid dosage is influenced by  numerous operational parameters and raw
 water characteristics.  In general,  organic  polymer coagulant aids are  applied  at
 an  alum-to-polymer ratio ranging from 100:1 to 50:1. Plant jar tests must be run,
 however, to establish the proper  dosage  ratio for  optimum  results.  For a rela-
 tively  modest  investment in capital  costs, the application of a coagulant aid can
 provide marked improvement  in  the  flocculation  and sedimentation  process  in  an
 existing plant.  The  improved  sedimentation will  reduce turbidity loadings to the
 filters, extending filter operation  cycles,  and  in  some instances, can provide a
 higher-clarity filtered effluent.

 Providing  pH Control-
 Adding  artificial  alkalinity  in the form of  soda ash,  lime, sodium hydroxide  or
 sodium  bicarbonate may  be  required  in  certain  instances  where  conditions  for
 optimum coagulation cannot be provided. Addition  of  alum to water forms sulfuric
 acid which  can depress  the pH excessively if the buffering capacity of the water
 supply  is  insufficient. At pH values below  optimum,  less than complete formation
 of  aluminum  hydroxide, occurs  resulting  in   incomplete  coagulation  and  turbid
 filtered water.  Additionally, postflocculation occurs  in  filtered water leading
 to  high residual filtered water aluminum  ion concentration.

 In  these situations, feeding  pH control  materials will ensure complete  precipita-
 tion of the coagulant, and enhance turbidity removal  by sedimentation and filtra-
 tion processes.  Floe  formed  in  proper  pH  ranges   is more dense,  settles  more
 rapidly, and has greater strength to resist shearing forces in the filters.

 Occasionally,  where  raw  water pH  is artifically  high  due  to the action of algae
 or  other aquatic plants, the  pH may  need  to  be depressed by adding acid to bring
the pH  into the  effective range for  optimum  coagulation.  In this situation, acid
 either  in the  form of sulfuric or hydrochloric can be added to depress  the pH.

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Chemical Feed Costs—                                '
Capital  and  operating  costs  are  discussed  for  addition  of  coagulants or  pH
control chemicals of the following types:

•    Basic chemical feed
•    Liquid alum feed
t    Polymer feed
•    Sodium hydroxide feed
•    Sulfuric acid feed

The  costs  reported are derived from  those presented in  "Technologies  and Costs
for the Removal of Microbial Contaminants  from Potable  Water Supplies," prepared
in  February  1987, Contract  No.  68-01-6989,  under contract  to the  Science  and
Technology  Branch,  Office  of Drinking   Water,   U.S.  Environmental  Protection
Agency. Costs are presented for 12 categories of treatment plant capacity ranging
from 0.026 mgd to 1,275 mgd.

Conceptual Design—The  costs  were derived for  the most  common type  of chemical
feed system consisting of a mixing tank, mixer,  and metering pump.  Chemical solu-
tions of known concentrations  are prepared on a  batch  basis by manually adding a
chemical and water to the dissolving tank.  This  system can be used  to feed either
liquid or dry chemicals. For dry chemicals,  the  mixing  tank is used for dissolv-
ing and mixing the chemicals with  water and for  storage of the chemical  solution.
For  liquid chemicals,  the  mixing  tank  {day tank)  is used for initial mixing  and
solution storage. The costs assume bulk storage  of the delivered liquid chemical.
A metering pump is used to accurately feed  a  solution of known concentration at a
set rate.

Operation  and Maintenance Requirements—Operation  labor  requirements for  the
basic chemical feed  system include  labor for emptying  bags  of dry chemicals,  or
containers of liquid chemicals, into the dissolving tank for turning the mixer on
and  off,  for  calibrating  the chemical metering   pump, and for occasional  preven-
tive maintenance of the mixer and  metering pump.
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 Electrical  requirements  are for the mixer and the metering pump. Mixer operation
 ranges from 30 minutes/day  for  the smallest  system up to 55 minutes/day for the
 largest system.  It is assumed  that the chemical  metering pumps operate continu-
 ously 24 hours/day. Maintenance  material  costs are  primarily  for  the mixer and
 metering pump, but maintenance  material costs  for a hydrated lime feed system are
 increased due to  the  continuous operation of  the  mixer.  Chemical  costs used  in
 determining  operation and  maintenance costs  are  included  in  Table A-l  in the
 Appendix.

 Liquid Alum  Feed-
 Liquid  alum  feed  systems   are  assumed to  be  custom-designed and  contractor-
 constructed  facilities for  treatment systems  in  Categories 5 through  12.  For
 smaller systems,  the basic  chemical feed  system described above is satisfactory.
 Costs  for these systems are  presented in Table 11-2.

 Conceptual Design—The design of these systems  is based  upon  the  use  of liquid
 alum,  which  has  a  weight of 10 pounds/gallon. Fifteen days of storage  are pro-
 vided,  using fiberglass  reinforced  polyester (FRP)  tanks.  The  FRP tanks  are
 assumed  to be  uncovered  and located  indoors for  smaller  installations,  and out-
 doors  for larger  installations.  Outdoor tanks  are  covered and  vented, with insu-
 lation  and heating provided  to  prevent  crystallization, which  occurs at  tempera-
 tures  below 30°F.

Operation and  Maintenance Requirements—Electrical  requirements are for  feeder
 pump  operation,  building lighting, ventilation,  heating,  and  heating  needs  of
 outdoor  storage  tanks.  Maintenance  materials  include repair  parts for  pumps,
motors, valves,  and electrical starters and controls.

Labor  requirements  consist  of time  for chemical unloading and  routine  operation
and  maintenance  of  feeding  equipment.  Liquid alum  unloading   requirements  are
calculated on  the basis  of 1.5  hours/bulk   truck  delivery.   Time  for  routine
inspection and adjustment of feeders is 15 minutes/metering pump/shift.  Mainte-
nance requirements are assumed to be 8 hours/year  for liquid  metering pumps.
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Polymer Feed-
Polymers  are used as  coagulants or  filter  aids. Polymer  addition  in treatment
plants  in  Categories  1 through 4  is  assumed  to  use a basic polymer feed system
that  is similar to the basic chemical feed system previously described. Plants in
Categories  5 through  12  use  a  polymer feed  system like  that  described below.
Costs for  these systems are presented in Tables 11-3 and 11-4.

Conceptual  Design—The conceptual design  of all  polymer  feed systems  is based
on preparation of a 0.25 percent stock  solution.

The basic  polymer feed system for Categories 1 through 4 consists of two tanks (a
mixing tank and a storage tank), a mixer, and a metering pump. The mixing tank is
elevated on  a stand  to  just  above  the top water  level  in the  storage  tank to
allow gravity flow of  mixed polymer solution  into  the storage tank.  The storage
tank  is  the same  size as  the mixing  tank,  since  the transfer  of  aged polymer
solution to the storage tank should only be required once daily.

The  larger polymer feed  system for Categories  5 through  12 consists of  a  dry
chemical storage hopper, a dry chemical feeder, two tanks, and a metering pump.

Operation  and Maintenance  Requirements—The  operation  labor requirements  for
the basic polymer feed system are primarily for daily measurement of dry polymer,
adding  it  to  the  mixing  tank, operating the  mixer,  and transferring  the polymer
solution to the  storage  tank.  Additional  labor is  required for  periodically
checking the metering pump,  preventive maintenance,  and occasional repairs on  the
mixer and pump.

Operation  and  maintenance costs  for larger  polymer  feed  systems  (Categories  5
through 12}  are  based on 3  percent  of  the  manufactured equipment and  pipe  and
valve costs. These costs  do not include the  cost of polymer.  Labor requirements
are for bag  unloading  (1  hour/ton of  bags),  the  dry chemical  feeder  (110 hours/
year for routine  operation  and 24 hours/year for maintenance),  and the solution
metering  pump  (55  hours/year  for   routine  operation  and  8  hours/year  for
maintenance).
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 Sodium Hydroxide Feed-
 Sodium  hydroxide  is added  for  pH  adjustment.  Sodium hydroxide is  in  a  dry form
 for  plants in Categories  1  through 4  (up  to  200 pounds/day). A  basic  chemical
 feed  system  can  be used for this  purpose.  Plants  in Categories 5  through  12 use
 liquid  sodium hydroxide. Costs  for  these systems are presented in Table II-5.

 Conceptual Design—Dry  sodium  hydroxide (98.9 percent pure)  is delivered  to the
 plant site in  drums and then mixed to a 10 percent solution on-site. A volumetric
 feeder is utilized to feed sod'ium hydroxide to the mixing tank. Two day-tanks are
 necessary: one for  mixing  a  10  percent  solution,  and one for feeding. The use of
 two  tanks is  necessary  because of  the slow  rate  of sodium  hydroxide  addition
 caused by the  high  heat  of the  solution.  Each  tank is equipped with a mixer, and
 a dual-head metering pump  is used  to convey the 10 percent solution to the point
 of application.

 For  feed  rates greater  than 200 pounds/day, a  50  percent  sodium  hydroxide solu-
 tion is purchased premixed and  delivered  by bulk  transport.  The 50 percent solu-
 tion contains  6.38  pounds  of sodium hydroxide/gal Ion.  For the 50 percent solu-
 tion, 15  days  of storage are provided in  FRP tanks.  Dual-head metering pumps are
 used to convey solution to the  point of application, and a standby metering pump
 is provided in each case.

 Pipe and  valving  is  required  for water conveyance  to  the dry sodium hydroxide
 mixing tanks  and  between  the metering  pumps  and  the point  of application.  The
 storage tanks  are  located  indoors,  since  50 percent sodium  hydroxide begins to
 crystallize at temperatures less than 54°F.

 Operation and  Maintenance  Requirements—Process energy  requirements  are  for the
 volumetric feeder and mixer (smaller installations only)  and the metering pump.  A
maintenance material  requirement  of 3  percent  of  equipment  cost,  excluding the
 storage tank  cost,  is utilized.

 Labor requirements  are based on  unloading  time for dry sodium hydroxide in drums,
 or  the  liquid  50   percent sodium  hydroxide purchased  in bulk  for  the  larger
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installations.  For  installations using  dry sodium  hydroxide, additional  labor
required  for  routine  operation  time  for  the  volumetric  feeder  is  about  10
minutes/day  feeder.  In  addition, for each  installation,  operation  time  for the
dual-head metering pump  is  15 minutes/day,  with an  annual  maintenance  time of 8
hours.
                                                                                        -»*
Sulfuric Add Feed-
Sodium hydroxide -and  lime  are used  to raise pH values. Sulfuric.acid is  used to
lower  pH.  The  feed  system  discussed  in  this  report  is  capable of  metering
concentrated (93 percent) sulfuric acid  from a  storage tank directly to  the point
of application.  Costs for these systems  are  presented in Table II-6.

Conceptual  Design—For sulfuric  acid  feed rates  up to  200 gpd,  the concentrated
acid  is  delivered to the  plant site in  drums,  and  at  larger flow rates  it is
delivered in  bulk.  Acid  purchased in bulk  is  stored outdoors in  FRP tanks, and
acid purchased in drums  is  stored indoors.  Fifteen  days of sulfuric acid  storage
is provided, and a standby metering pump is  included for all installations.

Operation and Maintenance  Requirements—Process  electrical  energy  requirements
are for the metering pump.  Building  energy requirements are for indoor  storage of
the sulfuri.c  acid  drums. Maintenance material  requirements were  estimated  at  3
percent  of   the equipment  cost,  excluding the  cost  of  storage  tanks.  Labor
requirements  are  for chemical  unloading  and  for  the metering  pumps.  Unloading
times of 0.25 hour/drum  of.acid  and  1.5  hours/bulk  truck  delivery were utilized.
Metering pump routine operation  is 15 minutes/pump/day,  and maintenance require-
ments are 8 hours/feeder/year.

Modifying or Adding Rapid Coagulant Mixing

General—
The rapid mixing  process usually requires  improvement if it  is  to perform ade-
quately at higher plant throughputs.  Effective  coagulation requires instantaneous
mixing of the  coagulant  with the incoming  water. If  the  coagulant does not come       ,
in  contact  with  all  colloidal  turbidity particles,  the  uncoagulated  turbidity
will pass through the filters. Proper design of the rapid mixer can result in Tow
coagulant doses and improved  aggregation during flocculation.

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 Many  devices  have  been  used  for  rapid  mixing,  including  baffled  chambers,
 hydraulic jumps, mechanically mixed tanks, and in-line jet blending. The mechani-.
 cally  mixed tanks,  which  are typically  termed  "completely  mixed  or back-mixed
 units,"  have been the  most  commonly  used devices.  The  tanks have been designed
 for  detention  times  of 10 to 30  seconds  and velocity gradients (G) 1n the  range
 of 200 to 1,000 sec-1.                                                        .

 The  principal mechanisms for  alum coagulation,  as  discussed earlier, are adsorp-
 tion and destabilization and  sweep-floe coagulation.

 The  reactions  are extremely  rapid, occurring in microseconds without the forma-
 tion  of  polymers, and  less  than 1 second  if  polymers  are  formed.3»**  However,
 sweep-floe  coagulation  is  slower,  occurring  in the  range  of 1 to 7  seconds.

 The  coagulants should be dispersed as rapidly as possible in the raw water stream
 for adsorption-destabilization.  The suggested dispersion time is 0.1 second. This
 will  allow  the hydrolysis products  that  develop  in  0.001  to  1  second  to  cause
 destabilization of the  colloid.  The rapid mixer most suited  to this requirement
 is in an in-line blender.5 »6»7
Changing Point of Coagulant Addition-
Improvements to  rapid mixing  facilities  usually  involve adjustments to the means
and  point  of application  of  the coagulated chemical.  These improvements can  be
accomplished at  little  capital  cost,  but can reduce chemical dosages and  related
operating costs  substantially and improve finished water quality. Tests performed
by the  Metropolitan  Water District of Southern  California (MWD) have shown that
filter  effluent  turbidities could be  reduced  by as much  as  50 percent with the
same  coagulant dosage  by properly diffusing the  coagulant into the flowstream.8
Figure  II-l  illustrates a coagulant diffuser used  successfully by  MWD  at one  of
its facilities.

At a water treatment plant  in Rio de Janeiro, the alum  solution  application point
was  moved  from 25 feet  upstream  of  a hydraulic jump in the influent channel  to
the  bottom  of the  hydraulic jump,  which  is  the  zone of  maximum turbulence.9
Approximately 5  to 7 tons  of  alum per day was saved by this improvement.  It also
resulted in better settled  and  filtered  water  quality.  A reported  $100,000 (1981
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dollars) in chemical  savings  and operating costs was  realized through reduction
in  alum use.   These  results  indicate  the  importance  of applying  the coagulant
solution at the point of maximum turbulence in the rapid mix process.

Coagulant Diffusers—
A  1978  report  on  upgrading of the 200-mgd  Potomac  filtration plant, prepared by
the  Washington Suburban  Sanitary  Commission,  recommended  that the  mechanical
mixers  be  replaced with  diffusers  to  provide  more effective  dispersion  of the
coagulant  with  the  incoming  raw water.10  In  the  evaluation  of  the  rapid mix
arrangement at the Potomac plant, it was  found  that  single pipe diffusers  placed
in large influent lines would not adequately  and  completely  disperse the coagul-
ant in the incoming  raw water. Also, there  was  excessive travel time between the
point of  coagulant addition  and rapid mixers  that  permitted  hydrolysis  of the
coagulant to occur  before the raw water  reached  the mixer. A third problem was
excessive detention time in the rapid mix chamber that prevented rapid dispersion
of the  coagulant.  Rapid dispersion is  required  in order to prevent completion of
the hydrolysis reaction before  contact is made with  all  colloidal  matter  in the
water.

The modification  selected to solve these  problems  is shown  in Figure II-2. The
mechanical  mixers  were removed  and replaced with  concentric  diffusers  located
downstream of  the  existing  mix  chambers.  The diffusers  were  positioned with the
orifices facing upstream  into the flow  to affect complete and almost instanta-
neous dispersion across the entire cross section of the pipe.

Mechanical  Mixing—
Mechanical  mixing  is  the  most commonly used  system  for rapid mixers.  The  system
is effective,  has  little  headloss, and  is  unaffected by the  volume of flows or
flow variations.  Typical  design  practice  provides a  contact time in the range of
10 to 30 seconds  and a G-value in the range of 700 to 1,000 sec-1.

The mechanical mixer has  been used  in numerous water  treatment plants.  Because
the mixer  speed can  be changed by including  a  variable  speed  drive, it is amen-
able to operational  changes  due to  changing  conditions. Lower speeds  result in
lower G-values, which are used with the addition of polyelectrolytes.
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 In-Line Blenders—
 The  adsorption-destabilization reactions  are very  rapid,  and  in-line blenders
 were  developed  to  approach  instantaneous  mixing  of  chemicals.  The  G-value
 suggested  is  in the range of  3,000  t  5,000 sec-1. In-line blenders with a resi-
 dence  time of  0.5  seconds  and  a  water  hp  of  0.5  hp/mgd of  flow  have  been
 recommended.11

 In-line blenders are preferred for the following reasons:12,13

 •    In-line  blenders  provide virtually  instantaneous mixing with  a  minimum of
     short-circuiting.

 •    There is no need to consider headlosses.

 •    In-line systems are less expensive than more conventional rapid mix units*

 Jet Injection Blending-
 Other investigators have recognized shortcomings of turbine or impeller mixers in
 rapid mixing basins and suggested  that this inefficiency may be due to back mix-
 ing, which  generally  results  in  less  efficient  use of  coagulation  chemicals.
 Mixing  inefficiencies  have resulted  in  a  move  toward in-line blenders  using a
 principle known as  "in-line  jet  injection." A jet  injection  rapid mixing system
 is illustrated in Figure II-3. In  this system alum solution is introduced to the
 incoming raw water through a series  of jets positioned radially around a central
 injection  pipe.  The  jets  discharge  in  a  plane  perpendicular  to  the incoming
water.  The dilution water is provided by  a pump taking suction from the raw water
 line.

 In this system  the  impact  of diluting the  alum solution with the raw water must
be considered.  This  dilution  (coagulant  dilution)  effect  was  evaluated at a
treatment plant  in  Florida, where  it was  found  that dilution of  the delivered
liquid   alum  solution  in  ratios  of  1:80 had  no  adverse impact  on coagulation
efficiency.11*
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Based on  these experiences,  the  supply pump  for the  injection  jets should  be
sized so that a dilution ratio of  1:80 is  not  exceeded.

A unit used for full-scale applications is shown  in  Figure  II-4.  The utilization
of this type  of  unit  is limited .in practice,  although  it has been  shown  to have
potential  advantages.  Disadvantages include plugging  of  the  orifices and the fact
that mixing intensity cannot be varied. The unit  shown  in  Figure  II-4 has design
criteria of:13

•    G = 750 to 1,000 sec-*
•    Dilution ratio at maximum alum dose = 100:1
•    Flow velocity at injection nozzle = 20 to 25 ft/sec
•    Mixing time = 1 second

The  power  input, P  (ft-lb/sec or  watts),  for this  type  of flash  mixer can be
computed from:

                                   P - q (AH)p                              (1)
     Where:

     P = power input, ft-lb/sec
     q = flow  rate from orifice hole—jet discharge, cu ft/sec
       = v-a  = C
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edye  of one  element  is  perpendicular  to  the  trailing edge  of the  preceding
element. The  mixing  element  produces a  radial  (cross-sectional) mixing  action
promoting intimate mixing of the process streams thus eliminating possible short-
circuiting.  This system  is  relatively  maintenance  free  but  requires  headloss
(typically around 1.0 to 6.6 feet). The  only  disadvantage  of this  type of mixer
is the dependence of mixing intensity on flow rate, which may vary widely. Such a
device  could  be installed  in  influent  raw  water piping of  facilities  having no
rapid mix for modest cost and contribute to improved plant performance.

Cost of Rapid Nix-
Costs provided are for newly constructed mechanically mixed basins intended to be
added to facilities not equipped with this process.

Conceptual Design—Construction  costs  are  based  on  reinforced  concrete  basins
sized for a 1-minute  detention time at  plant design capacity. The largest single
basin capacity  is  2,500 cu  ft.  Common-wall  construction is  used when  more than
one basin is required. Mixer costs are for vertical shaft, variable-speed turbine
mixers.  Mixing energy  is based on  a G-value  of 900 sec-1. Costs for adding rapid
mix facilities are presented in Table 11-7.

Operation  amd  Maintenance  Requirements—Power  requirements  are  based on  the
number of mixers, the G-value of 900 sec-1, a water  temperature of  15°C,  and an
overall  mechanism efficiency of 70 percent.  Maintenance material costs consist of
oil for the gearbox drive unit.

Labor requirements  are  determined  using a  jar testing time of 1  hour/day  for
plants under 50  mgd  and  2  hours/day for plants over 50 mgd,  15 minutes/mixer/day
for  routine  operation  and maintenance,  and  4  hours/mlxer/6  months  for  oil
changes.  An  allowance of  8  hours/basin/year  is  also  Included for  draining,
inspection, and  cleaning.

Adding Chemical Dosage Control Provisions
Techniques Available—-
An  excellent  physical  treatment  plant  design  and  good equipment  selection are
worthless  unless  the  chemical  coagulation  of the  raw water  being treated  Is
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properly carried out. Inadequate doses of coagulant will result in an excessively
turbid finished water.  Excessive  coagulant  doses may also  cause  this result and
are wasteful  of the public's funds. Excessive turbidity makes the water aestheti-
cally unacceptable besides  increasing  the probability of microorganisms escaping
subsequent disinfection processes.

Since achieving proper ^coagulation has been a universal  problem  of water treat-
ment operators  for many  years,  a wide variety of  techniques have been developed
for controlling the  coagulation process. Most  of these involve laboratory tests,
the  results  of which then  must  be manually transferred to the full-scale plant
operation by the plant operator.

Whether or not the coagulant dose that provides the optimum result in the labora-
tory tests will also  provide  optimum  results on  a plant scale depends on whether
the  same  efficiency  of  mixing  is  achieved in  both  cases  (which  is unlikely).
Also, the  fact that  the  procedure is a batch procedure results  in  an inherent
time lag  in  responding  to changes in  raw water  conditions.  This  lag  may be only
an hour if the  operator  is  on duty and alert to  raw water conditions, but it may
be several hours if the operator is off duty or involved in another task, such as
equipment maintenance.  This method may give satisfactory—even  if not optimum—
results when applied  to a raw water of  relatively uniform quality that contains
only a moderate amount of organic  turbidity. For low-turbidity waters and waters
containing large amounts of organic material, no sharp distinction between coagu-
lant doses  near  optimum  may exist;  so it is  difficult  to determine  from the
appearance of  the  sample whether adequate  plant-scale  results  will  be obtained.
Although  adequate  control  can  be  achieved under  certain  conditions  by  visual
monitoring of  jar tests, at  other times it becomes  a guessing  game,  with each
observer seeing characteristics that may or may not affect  plant performance.

Available  coagulation  control  techniques  fall  into  three  general  categories:
conventional  and  modified  jar  tests  where visual observations  of supernatant,
floe formation  time,  floe density, and so  on  are  used;  techniques based on par-
ticle charge;  and  techniques  based upon filtering  the  coagulated water and mea-
suring the filtrate turbidity.
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Jar Tests—
A  standard  jar test  procedure  is  contained  within  AWWA  manual  M-12,  titled
Simplified   Procedures  for  Mater   Examination.   A  standard   testing   plan   is
required  to  provide  a means  for the comparison  of coagulants  or for coagulation
aids.  The procedure  basically  consists of  adding varying coagulant dosages  to
several  samples  of the water in beakers, mixing  them  simultaneously  with  a gang
mixer,  allowing  them to settle, and observing the  results.

Techniques Based on Particle Charge—
Zeta  Potential—The  first technique  of this  type to  receive  attention as  a
possible  means   of coagulation  control was  the  zeta  potential technique.  Zeta
potential is  a  measure,  in millivolts,  of  the electrical potential  between  the
bulk  liquid  and  the  layer of counterions surrounding the  colloids,  as  described
earlier.  Because like  charges  repel,  colloids in  water—which  are almost  always
negatively  charged—resist coagulation.  When  this negative  zeta  potential  is
reduced,  the  repulsive  forces  are likewise reduced, and  if  agitated  gently,  the
colloids  will flocculate.  In the treatment process,  the  reduction of  zeta  poten-
tial  is  accomplished by the addition of a  positively charged ion or  complex from
such   coagulants   as  aluminum  sulfate,   the   iron  .salts,  and  cationic
polyelectrolytes.

The use of  this technique is also  a  batch  procedure, as  is  the jar  test.  The
general procedure involves varying the coagulant dosage and measuring  the result-
ing zeta  potential.  However,  each  water requires  comparative tests to  determine
the correlation between zeta  potential  and  finished water turbidity  in the  plant.
Organic colloids such as those constituting  organic color  generally  require zeta
potentials near  zero,  while  clay-related turbidity  is  best removed  at somewhat
negative zeta potentials.  Typical  values for  optimum coagulation range from +5 to
-10 millivolts, depending upon the nature of  the material  to be removed.

Although  zeta potential measurements are useful  as a research  tool,  it  is  gener-
ally agreed  that this method  is not easily  adapted to the typical treatment plant
because  of  the  considerable degree  of skill and  patience required  to  make  the
measurements, and the amount  of interpretation  required to make the data useful.
It  is  subject  to the same shortcomings as any  other batch test, in  that  sudden
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changes in raw water conditions may not be detected until  a poor-quality finished
water is produced in the full-scale plant.

Streaming Current Detector—A  streaming  current detector may be  used  to provide
a  continuous  measure  of  the relative charges.  This  technique  involves placing a
sample in a special cylinder containing  electronic sensing electrodes  at the top
and the bottom. A loose-fitting  piston  is then  partly submerged into the sample,
and is reciprocated along  its  axis  to  produce an alternating current between the
electrodes when the cylinder contains moving  charges.  A synchronous motor drives
the piston and a synchronous rectifier switch,  by  means of which the alternating
current generated by  the  alternating  fluid  motion is  made  to  register on  a dc
meter (Figure  I1-6).  An  amplifier  with  adjustable negative feedback  is used to
provide  an  output  proportional  to the  current  collected by  the  electrodes.
Readout may be by a  microammeter, with calibration in arbitrary units.  The alter-
nating current  is  analyzed and  related  to  zeta potential, which can  be used to
control  coagulant dosage.

The use of this  approach  for continuous  control of coagulation is subject to the
other limitations of  the  zeta  potential  approach,  including definite limitations
when used to  evaluate synthetic polymer coagulants,  such  as when the  polymer is
anionic and is used to coagulate negatively  charged particles.  Because the tech-
nique involves  only  the  aspects  of electronic  charge, it may  lead to erroneous
conclusions when it is used to study  coagulants not following  the electrokinetic
theory.  As  with  zeta potential,  the data  must  be  correlated  with   the  usual
indices of  plant performance,   as there may  not be  any  consistent relationship
between charge  and  filtered  water clarity  even  at  a given  plant for various
seasons  of  the year.  However,  the continuous  nature  of the  streaming current
detector may make it  attractive in some  instances  where  cationic coagulants are
used in a water that shows little variation from season to season.

Continuous Filtration Techniques--
Pilot Filters—The  goal  of the water treatment plant  should  be to produce the
minimum possible filter effluent turbidity at the minimum chemical cost. The best
measure of the efficiency of the coagulation-filtration steps would  be  the direct
continuous measurement  of  the  turbidity  of coagulated  water  that  has  passed
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         directly through a pilot granular filter.  The application of continuous turbidity
         monitoring equipment to the effluent of the  plant-scale  filters  should be a must
         for monitoring plant performance, but it has  limited value as a control technique
         because of the substantial  lag time between the point of  chemical  coagulant addi-
         tion and  the  point  of  filtrate turbidity monitoring.  For  example,  improper coa-
K
         gulation  of  the incoming  raw water will   result  in a clarifier  (with typically
 '        1 1/2 to 3 hours of detention time) being  filled with improperly  coagulated water
         before the results become fully apparent at the discharge of the  plant filters.

         The pilot filter technique is  applied  by  sampling  plant-treated  coagulated water
         from the  discharge of  the plant  rapid mix  basin. This  sample  stream  is  then
         passed  through  a  small  {usually 4  1/2-inch-diameter)  pilot filter to determine
         whether the coagulant dose  is  proper,  by continuously monitoring  the pilot filter
         effluent turbidity. This technique provides  a continuous, direct measurement of
         the turbidity, which is achieved by filtration  of  water  that has  been coagulated
         in the actual plant. Thus,  no  extrapolation  from  small-scale laboratory coagula-
         tion experiments is required.  The  only purpose of  this  test  is to  determine the
         proper  coagulant  dose;  it  is  not  to  predict  the  length  of filter run,  nor to
         determine the optimum   filter aid  dose,   nor  to  predict  the  rate of  headless
         buildup.

         The pilot filter technique  has the  advantages of offering a continuous monitoring
         of the  plant-scale  coagulation  process with a minimum  lag time.  Filtering  the
         water through the pilot  filter yields  immediate information.about  the adequacy of
         the coagulant  dose.  In  a  typical  situation,  correctness  of  coagulant  dose  is
         determined within 10 to 15 minutes after  the raw  water enters  the plant.  Experi-
         ence at many  locations  shows  that  the pilot filter effluent turbidity is a very
         accurate prediction of  the turbidity  that will  be produced by the  plant-scale
         filter  when the corresponding water reaches the plant-scale filter.

>        The turbidity  of  the  pilot filter is  monitored continuously  and  recorded.  High
         turbidity in  the  filter  effluent could result from either an  improper coagulant
-        dose or a breakthrough  of  floe from a  properly coagulated water. To  ensure that
         breakthrough  does not occur,  supplemental  doses of polymers are injected into the
         pilot filter  influent   line.  These  large polymer  doses  may  shorten the  pilot
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filter run times,  but,  to prevent breakthrough, it  is  desirable  to backwash the
filter every 1 to 3 hours in any case.

The pilot-filter system can be used to accurately indicate coagulation conditions
with  a minimum  lag time so that  the  operator  can  make  the necessary adjustments
in the plant  chemical  feed. Alternatively, the  coagulant  feed can be controlled
automatically through the use of  turbidity data from the pilot filter.

Design for Automated Coagulant  Control—This  system is  used  in  conjunction with
a  pilot-filter  system  and  automatically  varies  the plant  coagulant dosage  to
maintain  the  effluent  turbidity  from the pilot  filter at the  desired  setpoint
value regardless of  variations  in raw  water  quality and  other  related  factors.
Other chemicals can be  varied automatically by  this  system in direct relation to
the coagulant dosage. The coagulant  control  system  normally  consists of a pilot
filter system, an automatic control unit, and switches and controls for the chem-
ical   feed  equipment.  The  output  signal from  the  automatic control  unit  to the
chemical  feeders can  be a  time  duration,  current,  pneumatic,  or other standard
instrumentation control  signal.

Basically, this  automated  control  is accomplished  by  comparing  a 0 to  10 NTU
signal from the  pilot  filter turbidimeter with the desired  turbidity  value.  If
the turbidity  signal is greater than  the desired turbidity,  the alum dosage will
be increased.  If the input turbidity is  less  than  the setpoint  turbidity, the
alum  dosage   is  automatically  decreased.  The  plant  -operator  establishes  the
desired quality through a setpoint potentiometer,  and the  unit adjusts the coag-
ulant dosage to maintain the setpoint value.  This unit continuously optimizes the
alum dosage for a  given water treatment  condition and  consequently is constantly
changing to establish the precise dosage.

The system may  incorporate  provisions for automatic plant  flow  pacing.  When the
flow  pacing  feature is incorporated,  the dosage output  will  be automatically
adjusted for changes in plant  flow.  At  the same time,  changes in coagulant feed
dosage requirements  will  be maintained  by the  control  unit.  The  system  may  be
provided with  an override  means  so  that the  plant coagulant  feed system  may  be
operated in several modes.
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 Turbidity  Monitoring—
 With the  currently  available,  low-cost  turbidimeters,  which  are  accurate  and
 require little maintenance,  every  municipal water  plant in  the United  States,
 regardless of  size,  should provide  a  continuous record  of the  quality  of  its
 filial  product.  Turbidity is an  .important  parameter in  that it:

 o    Reflects the efficiency  of the  coagulation  process and  the  overall  treatment
      provided.
 e    Is related to probability  of escape  of  potentially pathogenic organisms  from
     the treatment plant.
 •    Is a  sensitive  indicator  of  the aesthetic  acceptability  of the product to
     the consumer.

 An  appalling  number of  plants provide no continuous monitoring  of plant effluent
 turbidity.  For  the measurement  of  very  small amounts of turbidity, the  principle
 of  light scattering (nephelometry)  is used.  In  this process, light is  reflected
 at  right angles to the  light beam by  the  particles of turbidity  in the liquid, as
 the beam of  light passes through the liquid. The amount of  reflected (scattered)
 light depends directly  upon the amount of turbidity  present  in the liquid.

,If  the  liquid is  entirely  free  of particles  of turbidity, no scattered light  will
 reach  the  photocells,  and  the  indicating meter  will  read  zero; thus increasing
 turbidity  gives an increase in  the meter  reading.

 Turbidimeters  is  available  from numerous manufacturers  and their comparatively
 modest  cost  places them within  economic  reach  of the smallest  of water systems.
 Implementation  of the  Safe Drinking Water  Act  Amendments  of  1986  will  require
 continuous effluent  turbidity monitoring  of  all  surface water treatment  plants.

 Particle Counting—By  use  of  recently  developed sophisticated  electronic equip-
 ment for particle counting, it  is possible  to obtain a more precise description
 of  particles  in water than is afforded  by conventional turbidity  measurements.15
 With  instrumentation currently  available,  the number of  particles  within given
 size  ranges  can  be  measured.  Particle  counters   have  sensors available in
                                     11-21

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different size ranges such as 1.0-60  ym  or a 2.5-150 urn sensor. From these data,
particle size distribution and particle volume can be estimated. Such information
can then be analyzed to more thoroughly evaluate treatment process performance.

Particle counting is especially useful in research and pilot-plant work, but also
has potential  for improved plant  operational  control.  A total  particle counter
provides a direct measurement of  the  particulate matter present in water, and in
contrast to turbidity measurements, is not influenced by particle size, shape, or
refractive index. For these reasons, the total particle counter offers promise of
being a  very  useful  and sensitive process control tool  in  water treatment prac-
tice,  especially  when  asbestiform fibers  are  present in water supplies.16  How-
ever,  existing particle counters  are  designed to be  accurate for particles  with
at least one dimension greater than 1  ym, and in some waters, submicron particles
may predominate..  In  these cases,  both turbidimetric  and  particle size distribu-
tion measurements would be necessary.17

Implementing Flocculation Improvements

Upgrading water  treatment  plants  often  requires improvements to  the existing
flocculation  basins.  This is  especially  true  if. the  capacity of  the existing
facilities is  to be  expanded  greatly. For  example,  a  100  percent  expansion in
plant capacity is possible by changing the existing  rapid sand media operated at
2  gpm/sq  ft  to  mixed  or dual  media  operated  at  4  to  5 gpm/sq  ft.  This would
reduce the flocculation detention time from  30  minutes  to 15 minutes or less. At
these shortened  detention times,  it  is  vitally important that all  factors  that
might contribute  to poor flocculation performance  be. identified  and corrected
during the modifications.

The objective of flocculation is  to provide  multiple  contacts between coagulated
particles suspended in water by  gentle and prolonged agitation. During agitation,
particles collide and produce a larger and more rapidly settling floe.

In designing flocculation facilities,  several factors should be considered:

t    Characteristics of raw water turbidity and suspended particulates
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 •    Water temperature
 t    Downstream treatment  process
 t    Coagulant(s)  used

 Table II-8 presents  general  design  criteria  for  flocculation basins.18

 Type of  Flocculators—
 Several  types of mixers have been  designed  for  use in the flocculation process.
 The most  common  type  of  flocculator is  the mechanical  mixer.  Reel  or paddle
 flocculators  are  currently used for low-  or medium-energy  mixing,  and propeller
 or turbine flocculators are  used for medium- to  high-energy mixing.

 The size  of  the  flocculation  basin  is determined  by the required  reaction or
 detention  time.  Typically, reaction times  range  from 15 to 45 minutes, depending
 on the characteristics  of  the raw water, the type of coagulant used, and the type
 of downstream treatment provided.  For treatment of  low-turbidity  raw water in a
 cold region,   the  appropriate  design flocculation  time could  be  as much  as 30
 minutes. A short  flocculation  time (15 minutes) would be appropriate for direct
 filtration  in warm regions or where the raw  water can be easily flocculated year-
 round. Also,  in small  plants where volumetric mixing  efficiency  is  superior in
 small tanks,  flocculation  times in  the 10  to 15 minute  range may be acceptable.
Flocculation Design Guidelines-
Table  II-9  prepared  by  James  M.   Montgomery  Consulting  Engineers,  includes
generalized  flocculation  design  guidelines  for  various  type of  flocculation
methods  and devices.18  The  table  also  includes  a listing  of  advantages  and
disadvantages  of each  type  which must  be  factored  into  selection of  a proper
design.'

Flocculation Alternatives—
The  following  types  of mechanical  mixing  devices  are  typically  used  in water
treatment flocculation:
0
o
Paddle or reel-type devices
Reciprocating units (walking beam flocculator)
                                     11-23

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t    Flat blade turbines
•    Axial flow propellers or turbines

Typical  units  are  shown  in  Figure  II-7. The  paddle  or  reel-type  devices  are
mounted horizontally or vertically and rotate at low speeds (2 to 15 rpm). Design
is based on limiting the tip speed of the paddle farthest from the center axis to
1  to  2 ft/sec. When  paddle flocculators are chosen,  the  paddle  area  should be
kept below  20  to  25  percent of  the tank section  area to avoid  the rotational
movement of water.

Walking beam flocculators are driven  in  a vertical  direction,  in a reciprocating
fashion. The unit contains a series of cone-shaped devices  or a series of paddles
on a vertical  rod.  These  devices impart energy to the  water as  they  move up and
down, thereby creating velocity  gradients,

Turbines are flat-bladed units connected  to  a disc  or shaft.  The flat blades are
in the  same  plane as the  drive  shaft. The  blades  can be mounted vertically or
horizontally,  and  typically operate  at  10  to  15  rpm.  These  plate turbines  are
                                                                   /
effective up to a  G-value  of 40  sec-1,  but produced  high-velocity  currents at
G-values greater than 45 sec-1.19

Accepted  design  criterion  for  these  units  is  to  limit  the  maximum peripheral
velocity to  2  ft/sec for weak  floe  and  4 ft/sec  for  strong  floe.  Because they
impart  high  velocity  gradients,  turbines  often  will  not  provide  effective
flocculation where floe strength is weak.

The axial flow  unit  "pumps"  liquid because the  impeller has  pitched blades. This
unit may  be installed  vertically or  horizontally.  Typically,  these units  are
high-energy flocculation devices  operating at  150 to 1,500 rpm,  and  there is no
limitation on  the tip speed. Some engineers favor these units  because  they  are
simple  to   install   and   maintain,   and  produce  uniform  turbulence   in  the
flocculator.11 »19
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 Improving Inlet  and Outlet Conditions-
 Sufficient time  and intensity of flocculation  are  essential  to effective opera-
 tion.  However,  a  common cause  of  flocculation  basin deficiencies  is  improper
 physical  arrangement of  the basins, allowing unequal flow distribution and short-
 circuiting of  the  influent  flow.  Maximum use of the available flocculation basin
 detention time  must  be  made . by  distributing the  coagulated raw  water  evenly
 across the flocculation  basin  inlet to prevent short-circuiting. This may require
 modifying the  existing  influent  flumes,  either by  adding  openings  or perhaps by
 installing a  secondary  baffle across the  inlet to  the flocculation basin.  These
 inlet baffles  are  commonly  constructed of  wood with openings  sized and placed to
 impart enough  headless so that the flow is distributed uniformly across the inlet
 end  of  the flocculation basin. An elaborate perforated  flocculation basin  inlet
 baffle was installed  in Rio de Janeiro's  Guandu  treatment plant,  as illustrated
 in  Figure II-8.9 It should  be noted that the  velocities  through  these  openings
 should not provide  a  G-value  greater than the G-value provided by the floccula-
 tion equipment in the first chamber.

 Correcting Short-drculting--
 Short-circuiting  is a  major  problem with  many  existing flocculation  basins.
 Elimination  of  the  short-circuiting can  be  accomplished  by  installing  either
 around-the-end or over-under baffles within the basin.  A serious short-circuiting
 problem was  identified  in the Guandu plant  in Rio de Janeiro.9 The problem was
 solved by  installing baffles  and  changing  the  flocculator from a single-stage to
 a 6-stage  flocculator.  A secondary  improvement involved  installation of  a perfo-
 rated timber  baffle with square  nozzle  ports  between the  flocculation  and set-
 tling basin. The headloss imparted  by these  nozzles resulted  in a more even flow
 distribution to the settling basins.

 Similar techniques  were  applied  to the  Potomac filtration plant  in Washington,
D.C. At this facility, existing 2-compartment  flocculation basins  were converted
to  6-compartment basins  using a  perforated  baffle  to  distribute flow  evenly
across the width  and depth of the downstream settling basin. It was noted that to
accomplish  even  distribution,  the  headloss  through the  ports must be  signifi-
cantly greater than the kinetic  energy  of the water  moving   laterally  past  the
                                     11-25

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orifices. Care  must  be exercised  so that the  velocities  through the  ports  are
kept low enough to prevent shearing of the floe particles.

Installing High-Energy Flocculators--
Many existing conventional water treatment plants  were  designed with low-energy,
paddle-style, mechanical  flocculators.  Often,  these were  designed with  either
variable or  constant  speed  drives.  With these original  designs,  emphasis  was on
formation of a  large floe, which might  or might  not settle rapidly. At high-rate
treatment  plants,  at   reduced  flocculation  and  downstream  settling  detention
times, it is imperative that the floe formed  in the flocculation basins settle at
the fastest possible  velocity.  The  existing  flocculation equipment must be evalu-
ated with  respect  to  its capability  of  meeting  the  new  requirements.   If  the
existing  equipment  is  inadequate,  consideration  should be  given  to  replacing
existing  flocculators  with   new  high-energy  turbine-style  units.  Where  turbine
units have been installed and operated side  by  side with slow-speed, paddle-style
units, they have provided a  more dense floe  with more rapid settling characteris-
tics than were achieved with the old-style,  slow-speed units.

The City of San Diego upgraded two  of its  major water treatment plants by modifi-
cations  to  the existing  flocculation  facilities.20. In both  plants,  the rapid
mixer and the first  two rows of the  old-style  paddle flocculators were replaced
with new  high-energy mixers.  Figure 11-9  shows the basin with  the new- and old-
style  flocculation   equipment.   The  above-described  modifications,  along  with
conversion of the existing  rapid sand to  dual-media  filters,  effected  a  30 per-
cent increase in the treatment capacity of these two treatment plants.

Before  recommending  replacement  of  existing  low-intensity,  reel-style horizontal
flocculators with  new  high-energy  units,  a careful  plant  evaluation  should be
made to determine whether this modification  is  necessary.  The existing equipment
should be inspected  t-o determine whether  a  higher energy  gradient could be pro-
duced by simple modifications to the  existing  equipment.  These modifications may
include the addition  of paddles or  new mechanical drives to impart greater mixing
intensity. The  condition  as  well  as the  capability of  the  existing drive equip-
ment will determine whether a modification of this type is  physically possible or
economically practical.
                                     11-26

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 Case History—
 The Manatee County, Florida, water treatment  plant  was  designed with an initial
 capacity  of 27  mgd.11*  A laboratory and plant test was carried out to investigate
 the feasibility of  increasing  the capacity to  50 mgd by  process  changes. Both
 laboratory  and  plant tests were carried  out to  enable the designers to identify
 process  deficiencies  and  develop  modifications to  permit operation  at   higher
 plant  throughput.  During the evaluation it was established that flocculation was
 inadequate  at the  expanded flow.

 To  obtain  state approval for increasing the capacity of the flocculation facili-
 ties  without  major construction,  a plant  test was  necessary.  Modifications were
 made  to the  existing   flocculation  basins to minimize  short-circuiting  at the
 higher  flows.   An  existing  single-compartment flocculator was  modified  into an
 8-compartment flocculator with  alternate  connecting  top  and bottom ports.   These
 modifications are  illustrated in  Figure  11-10.  In  addition,  a perforated  baffle
 wall  was  installed at  the flocculation basin  outlet to improve inlet conditions
 to  the settling  basin. The perforated  baffle  wall  is  illustrated  in  Figures
 II-lla and  lib.

 During  plant  tests at   a flow of  63 mgd,  the  settled  water turbidities  from the
 portion of  the plant  containing  the  modified  flocculator were  slightly   better
 than those  from the unmodified  plant at a flow  of 37  mgd.  On  the basis  of these
 experiments,  a  state  agency  granted  approval  of  essentially  doubling the flow
 through the modified portion  of the plant.  Doubling  of the capacity was achieved
 by eliminating two mechanical rapid mixers, dividing the existing single compart-
 ment  into  an 8-compartment  flocculator,   and  installing  perforated  baffles for
 better distribution of  flocculated water into the settling basins.

 These  improvements  reduced  the average  alum  dosage  from  70  to  50 mg/1.  The
 settled water color was reduced  from the previous 18 to 23 pcu  to 10 pcu  or less.
The  estimated  savings  in  capital  costs  {1983  dollars)  were  approximately
 $2,000,000, and the estimated power savings were  $10,000 per year.'
                                     11-27

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Costs of Adding Flocculation Basins-
Table 11-10 provides  costs  for adding flocculation basins  to  existing treatment
plants originally constructed without this process.  Flocculation basin costs are
for  rectangular,  reinforced  concrete structures  12  feet deep, with  a detention
time of 30 minutes at plant design flow.  A length-to-width ratio of approximately
4:1  is used for  basin sizing, and the maximum  individual  basin size  utilized is
12,500 cu  ft.  Common-wall   construction  is used  where the  total basin  volume
exceeded 12,500 cu ft. Costs  are  calculated  for use  of horizontal paddle floccu-
lators, since horizontal  paddles  are  less  expensive  for use in large basins, and
they generally provide more  satisfactory  operation in the  larger basins,  parti-
cularly when tapered flocculation is practiced.

A  G-value  of 80  sec"1  is  used  to  calculate  manufactured equipment  costs. All
drive  units  are  variable-speed   to  allow  maximum flexibility.  Although  common
drive for  two  or more parallel basins is  commonly utilized,  the estimated  costs
were calculated using individual  drive for each basin.

The  capital  cost of  installing  new  mechanical  flocculators   in  existing  basins
varies  widely  depending   upon type  of  equipment,   needed basin  modification,
required  inlet  and outlet  revisions, etc.  In  general, the equipment cost will
range from 35  percent for small   plants to  less  than  15 percent for large plants
of the total costs presented  in Table 11-10.

Improving  Sedimentation Performance

General--
Increasing treatment plant capacity may require modifications  and improvements to
the  existing  settling basins. In  most  cases,  a significant  increase  in  plant
capacity reduces settling basin detention times and increases  clarification  rates
to the point where they will not  perform efficiently at expanded flows. Problems
caused by  poor entry  and  exit conditions  as well as inadequate sludge collection
and  removal may  also  have  to be  corrected when the capacity of existing sedimen-
tation basins is  increased.
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 Improving Inlet Conditions—
 The  manner  in which flocculated water is delivered  to the settling basin influ-
 ences  the  efficiency  of the clarification process.  Many  older plants have sepa-
 rate flocculators  that  require  transfer  of  the flocculated  water  in  open  or
 closed  conduits.  The  velocity and associated  turbulence  in  these channels break
 up floe and thus prevents good clarification. Wherever  possible,  these channels
 should  be eliminated and the flocculated water should be introduced directly into
 the  settling  basin  through a  perforated  baffle wall. Such improvements should be
 considered  if observations  during plant tests indicate  potential  major problems
 in obtaining  good inlet flow  distribution.  Care must be  exercised in  design  of
 perforated  inlet  baffles  so  that  velocities through these openings  are not high
 enough  |to  break  up floe.  Proper  distribution of the  flocculated water  at  the
 settling basin inlet is critical to realizing maximum efficiency from the basin.
        t
 Improving Outlet Conditions—
 A well  designed settling basin  should  have  an effluent collection system to uni-
 formly  withdraw water from the  clarification  zone.  In  rectangular basins, finger
 launders extending  inward from  the end wall and  located  at  uniform spacing pro-
 vide the best assurance against  short-circuiting.  Weir loading rates  should  be
 within  the  range  of 10,000 to  20,000 gpd per foot of weir length. These launders
 should  be designed  with  adjustable V-notch  weir  plates,  or  have orifices placed
 in the  sides  of the launders at  uniform centers over the length  of  the trough.
 Circular,  radial-flow  basins   should  have  a continuous  peripheral  collection
 launder  with  a  sufficient  length  of  weir  to  match  the loading criteria  for
 rectangular basins.
        ''f
 Installing Sludge Collectors—
 The  sludge collection equipment should be inspected, and  it  should be determined
whether it will  adequately  handle greater quantities of  sludge at the increased
plant  throughput,  sludge piping  and  pumps  should  also  be  inspected  to verify
adequate capacity.  If  a  sedimentation  basin has  no  mechanical  sludge collection
facilities   these  should  be  added to  provide  complete  and  continuous  sludge
 removal at higher plant flows. A vacuum sludge removal  system such as  illustrated
 in Figure 11-12 and shown used with tube  settlers can be adapted to many existing
sedimentation  basins.   Figure  11-13   illustrates the  air-driven,  track-guided
 sludge  removal assembly.

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Installing Tube Settlers—
Where clarification rates at expanded flows are too  high  for adequate clarifica-
tion, tube  or  plate  settlers  can be installed to  increase  the effective surface
settling area  and  thus  increase the capacity of the basin.  Tube settlers can be
installed in most conventionally designed settling basins to permit a significant
increase  in capacity without  loss  of clarification  efficiency. In  many cases,
settling capacity  can  be more  than  doubled by introduction of  tube  settlers.  A
number of case histories describing water treatment plants where the capacity was
increased significantly  by  installing tube settlers  and  other modifications are
presented later in this section.

Tube settlers  as well  as plate settlers apply the theory of shallow  depth sedi-
mentation.  The use of very shallow basins  with  small-diameter tubes (2 inches in
diameter or less)  or plates spaced  at  close intervals  (2  to 4 inches)  enables
effective removal  of settleable  materials in  detention times  of only  several
minutes, in contrast  to conventional settling  basins designed with  1  to 4 hour
detention times.  Various manufacturers  have  developed alternative tube settler
designs using lightweight plastics fashioned into structural modules which can be
installed in rectangular or  circular basins.  Application of shallow  depth sedi-
mentation theory through installation of tube or plate settlers offers tremendous
potential for  minimizing the  size 'of  newly constructed  sedimentation  basins or
upgrading performance and capacity of existing basins.

Figure  11-14 is  a cut-away drawing of a tube  settling module  which provides
2-inch-square passageways either  2  or 3 feet in  length.  The alternating rows of
tube passageways are  sloped  60 degrees from the  horizontal  to permit continuous
gravity draining  of  settled  solids.  Other  manufacturers  construct tube settlers
by  bonding  continuous  sheets  of corrugated plastic  into  a  circular module where
all channels slope in the same direction at 60 degrees from the horizontal.

All of  the  previously  mentioned systems are used  in configurations in which the
influent  is introduced  beneath  the  tubes  with the  flow passing  up  through the
tubes but  in the  Lamella separator,  introduced by  the  Parkson  Corporation, the
influent  enters  at  the  top  of  the clarification  basin  and  is  then directed
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 downward  through a series of parallel plates as shown in Figure 11-15. The sludge
 is  collected at the bottom of  the  basin  with  the sludge-water flow being in the
 same  direction  rather  than  countercurrent as  in the other systems. The clarified
 water is  conveyed to  the  top  of the clarifier by returning  tubes,  as  shown in
 Figure  11-15.  The plates are  typically  5 feet wide  by 8 feet  long,  are spaced
 1  1/2 inches apart,  are inclined at 25 to 45  degrees to the horizontal, and are
 usually constructed of PVC.

 General Design Considerations-
 Tube  settlers  can be  used  in  either upflow  solids contact  clarifiers  or hori-
 zontal  flow  basins to improve  performance  and/or  increase  capacity.  Of course,
 they  can  also  be incorporated  into the design  of new facilities  to reduce their
 size  aricl cost. The overflow rate at which tubes can be operated is dependent upon
 the  design  and  type  of clarification  equipment,  character  of the  water being
 treated; and the desired effluent quality. The following paragraphs describe the
 most  important design and operational  variables that affect tube installations in
       J!
 existing clarifiers.
Application Requirements-
Horizontal  Flow Sedimentation Basins—The  nature of the  existing clarification
equipment • determines  to  some  extent  the  allowable tube  overflow rate  and  the
physical  arrangement of modules  in  a  basin.  Ideal flow  patterns are rarely expe-
riencedMn practice in clarification basins. Velocities  in rectangular horizontal
flow  basins vary  throughout the  basin.  Flow  lines diverge  at  the  inlet  and
converge  at  the outlet.  The  velocity  gradient  across  the basin does  not remain
uniform due  to  basin  drag,  density currents, inlet  turbulence,  temperature  cur-
rents, and  so on.  In  radial flow circular  basins,  the  flow  cannot be introduced
to  impart velocity components  in  the horizontal  direction   only.  The use of  a
center  feedwell  imparts  downward  currents  that  cause  turbulence  and  produce  a
general rolling motion of the contents in an outward and upward direction.

When  tube modules are  installed in horizontal  flow basins,  it is best not  to
locate them  too near entrance  areas  where possible turbulence could  reduce  the
effectiveness of the tubes as clarification devices. For example, in a horizontal
basin, often as much  as one-third  of  the  basin  length  at the  inlet  end may  be
                                     11-31

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left uncovered  by  the tubes so  that it may  be used as  a  zone for  stilling  of
hydraulic currents.  This  is permissible  in  most basins because the required quan-
tity of  tubes  to achieve  a  significant increase in  capacity will cover  only  a
portion of  the  basin.  Figure 11-16  is  a typical  tube settler  installation  in  a
rectangular basin illustrating arrangement of  tube  settling  modules and utiliza-
tion of collection troughs in the covered area to ensure uniform flow collection.
In  radial  flow  basins, the required quantity of modules  can  be placed  in a ring
around the  basin  periphery,  leaving an  inner-ring open area  between the modules
and the  centerwell  to dissipate  inlet  turbulence.  Figure 11-17  illustrates one
method of installing tube settling modules  in a circular, horizontal flow basin.

Upflow Clarifiers with Solids  Contact—The flow  paths  in solids  contact  basins
of  the  upflow  type  are  in a  vertical  direction through  a  layer  or blanket  of
flocculated material,  which  is   held  at   a  certain  level  and  maintained  at  a
certain concentration by  the controlled  removal of sludge. The clarification rate
is governed by the settling velocity of this  blanket.  The purpose of maintaining
this blanket is to entrap  slowly  settling, small  particles  which would  otherwise
escape the basin.  When the flow is increased,  the.level  of the blanket will rise.
The efficiency  of the tubes  is   dependent upon both the overflow  rate  and the
concentration of incoming solids. The allowable loading rate on the tubes in this
situation  is  dependent  upon the average  settling  velocity  of the blanket,  the
ability of  the  clarifier to concentrate solids,  and the capacity  of the sludge
removal system to maintain an equilibrium  solids  concentration.  If sludge is not
withdrawn quickly enough  or  if  the upward  velocity  exceeds  the average settling
velocity of the blanket,  the unit can become  solids  critical  with the result that
the blanket will  pass  through  the tubes with  excessive  carryover of solids into
the effluent.

In expanding the capacity  of an  upflow, solids contact clarifier, the ability to
handle increased  solids  may be  the limiting  factor.  The solids  loading  of the
basin establishes its maximum capacity.  The amount of increased capacity is often
limited to 50 to 100 percent of the original  capacity.

A typical tube settler installation  in  a solids contact  clarifier is illustrated
in  Figure  11-18.  Typically  the  tube modules  are placed 2  to 3  feet  below the
                                     11-32

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 surface In the clarification zone and well above the top of the sludge blanket as
 is  noted  in the sectional view.

 Figure  11-19  illustrates a  factory-built  package tube settling  clarifier.  This
 particular unit, provided in rectangular steel tankage, is designed to operate as
 a  sludge  blanket  clarifier  and includes special  baffling  to  force incoming flow
 containing settleable  material  through the blanket. Continuous  chain  and flight
 sludge collectors move settled sludge to a central withdrawal  point.

 Recommended Design Criteria--
 Loading rate design criteria for tube settlers for both upflow solids contact and
 horizontal flow basins for winter and  summer  water  temperatures  have been devel-
 oped  by  one  tube settler manufacturer.  These are intended to be general  guide-
 lines only and many other factors previously  mentioned can influence performance
 of  tube settlers. Based upon performance data from many operating facilities they
 appear to be conservative.

 Upflow Clarlfiers - Loading  Rates—In  areas where cold water temperatures (less
 than  40°F) occur  frequently,  the guidelines in Table  11-11 apply.  In  warm water
 areas in which temperatures  are nearly  always above 50°F,  the  guidelines in Table
 11-12 apply.

Of  course, these  guidelines are based  on the assumption  that both  the chemical
coagulation and  flocculation steps  have  been  carried out  properly.   Also,  the
 sludge removal equipment has been assumed adequate.

Horizontal Flow  Basins  - Loading  Rates—As  indicated  in the  tables,  the raw
water turbidity has a direct influence  on  allowable  tube  overflow rates, as does
the raw water temperature. In cold water  areas  where temperatures are frequently
40°F or less,  the guidelines in Table  11-13  apply.  In  warm water areas (tempera-
ture nearly always above 50° F),  the guidelines in Table 11-14 apply.

Location  of  Tube Modules Within the  Basin—The tubes  should  be  located  such
that they are  not placed in a zone of  unstable hydraulic  conditions.  Thus,  they
are  frequently  placed  over  one-half   to  three-quarters   of   the basin  located
                                     11-33

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nearest  the effluent  launders  to permit  the  Inlet portion  of  the clarifier to
dampen out hydraulic currents. The top of  the tubes should be located 2 to 4 feet
below  the  water  surface.  In general,  the 2  foot minimum  is  used  in shallow
basins.  The submergence of 4 feet would  be considered only  in clarifiers with .a
sidewater  depth  of  16 to 20  feet.  In most basins, where sidewater depths rarely
exceed  13  feet,  a  submergence  of 2  to  3 feet  is  used.  The collection  launders
should be  placed  on 10- to 15-foot centers over the entire area  covered  by tubes
to ensure  uniform flow distribution.
Example Applications-
Horizontal Basins—An  existing  water treatment plant with  a rated capacity of 4
mgd  has  a horizontal,  rectangular  settling  basin  and  rapid sand  filters.  The
basin dimensions are 30 feet  wide  by 133 feet long. The surface overflow rate at
design capacity  is  1,000 gpd/sq ft. The average depth of  the basin is 15 feet.
The basin has a  single overflow weir across the outlet end of the basin. The raw
water is obtained from  a  river which has a normal  maximum  turbidity of 25 to 30
NTU.  The water  temperature  rarely  falls  below   50°F.  The  settling  basin  is
preceded by mechanical flocculation  with 40 minutes of  detention  time at 4 mgd.
Coagulant  aids  are  fed  during  periods  of   high  turbidity   and  low  water
temperatures to improve coagulation.

A  capacity  increase from  4  to  8  mgd  is desired.  At  8  mgd, the  overflow rate
increases to  2,000  gpd/sq ft or 1.4 gpm/sq  ft.  The total   basin  loading of 1.4
gpm/sq ft is below the values shown in the above guidelines for a horizontal flow
basin under warm water  conditions.  However, at  a higher  basin loading of 2 gpm/
sq  ft and a tube rate of  3 gpm/sq ft,  the  expected effluent  turbidity is 1 to 5
NTU. This value is compatible with dual- or mixed-media  filters.  In light of the
moderate raw  water,  temperature  and turbidity, a tube  rate  of 3 gpm/sq  ft  and a
basin loading  rate of 1.4 gpm/sq ft should give excellent results.
     Quantity of tubes required -
                                          Capacity, gpm
(2)
                                  Allowable tube rate, gpm/sq ft
                                _.  8 mgd^x 700 gpm/mgd
                                       3 gpm/sq ft
                                = 1,870 sq ft
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 The  dimensions  of the area to  be  covered by the tube modules  are  determined as
 follows:
                         Area = length x width
                   1,870 sq ft = length x 30 feet
                       Length = 1.870 sq ft  = 62.3 feet
                                  30 reet

 The  length of 62 feet would be rounded off to be a length readily compatible with
 the  standard module dimensions associated with the specific modules purchased.

 The  modules would  be installed, over an area extending back from the discharge end
 of the basin for a distance of 62 feet.  A baffle wall would be installed at inner
 edge  to  force  all  flow through the modules. To  improve  uniform  flow through the
 modules, three new effluent launders extending 62 feet back from the existing end
 wall  launder would be  required.  The launders would  be  installed on 10-foot cen-
 ters  and the tubes would be  submerged for  a depth of 4 feet because the basin is
 deep. The appearance of the basin would  be similar to that shown  in Figure 11-19.
Upflow
Basins—Assuming  a  plant has two  42-foot-square upflow clarifiers,  each
designed for a flow  of  3,000  gpm,  with peripheral  collection launders. The total
surface area is 1,760 square  feet.  The influent  centerwell  reduces the available
settling area  by  200 square  feet.  The peak overflow rate  now  reaches 1.92 gpm/
sq ft,
which is high enough that the  clarifier  does  not  perform well,  especially
when water temperatures drop.

It is desired to  increase  the  plant  capacity  to 4,000 gpm per settling basin. At
this flow, the loading on the total basin settling area is 2.6 gpm/sq ft. The raw
water turbidity is moderate, 30 to 70 NTU, and the water temperature seldom falls
below 50°F.

The guidelines for  upflow  basins indicate that  a  maximum total  basin loading of
2.5 gpm/sq ft  with  a corresponding tube rate of 2.5 to  3 gpm/sq ft can be used.
Complete coverage of the settling area would provide a tube rate of 2.6 gpm/sq ft
and would also provide a simplified support problem when compared to only partial
                                     11-35

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coverage. Thus,  coverage of  the  settling area with  1,560 square feet  of tubes
would be provided. Radial  launders  would be added to  improve  the flow distribu-
tion in the basin.

Costs of Installing Tube Settlers—
The conceptual design for which costs in Table 11-15 were developed is based upon
a rise  rate of  2.0 gpm/sq  ft  through.the area covered by the modules. By leaving
a portion of  the  basin  open,  a zone is created for inlet turbulence dissipation.
This transition  zone is separated  by  a baffle extending from the bottom of the
modules to 6  inches  above the  operating water  level.  Uniform effluent collection
is a requirement  for optimum  utilization  of  tube  settlers.  To  meet this require-
ment, effluent  launders are spaced  at  12-foot centers in all basins.  Since the
hydraulic and structural requirements  for tube clarification systems  are unique,
the costs include tube modules, tube module supports and anchor brackets, a tran-
sition  baffle,  effluent  launders  with V-notch  weir  plates,  and  installation.
These costs may  be  added to the  conventional  basin  construction costs to arrive
at a total  facility cost.

Modifying Filtration Facilities

General~
Upgrading existing  filters  to  provide  improved  filtered  water  quality  and  for
increased plant capacity can be done by:

*   Changing  existing rapid-sand media to dual- or tri-mixed media

t   Removing  6 to 10 inches of sand and replacing with anthracite coal, known as
    "capping"

Improving quality without increasing plant capacity could be achieved on existing
dual-media filters by:

•   Adding facilities to feed a polymer  filtration aid  to  clarified  water prior
    to filtration
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•   Adding  polymer  to backwash  water to precoat  filter media  particles  during
    backwashing  to  improve filtered  water  quality during the  "ripening"  period
    immediately  following  restoration of filtration

•   Installing  turbidimeters  on  each filter to provide  continuous  indication of
    filtered water turbidity

•   Providing  filter-to-waste provisions on  each filter  to  permit wasting  higher
    turbidity water immediately following completion of backwashing

Filter Upgrading Evaluation—
To determine the feasibility of expanding plant capacity  by  filter modifications,
a thorough  filter hydraulic  study  should be completed.  Because  the plant  origi-
nally  was   probably  designed  for  2  gpm/sq  ft filtration  rates if  traditional
rapid-sand media was used, settled  water collection  and  distribution systems may
reflect  these  rates  and  in  some instances, may not have adequate  capacity for
expanded throughput.  A hydraulic analysis  of  transfer channels,  pipes,  opening,
weirs, etc.  can  determine the maximum amount  of water which  can be delivered to
the existing filters.  In  some cases, minor  changes  in piping,  gates,  weir open-
ings,  etc.  will  permit these  greater flows. In other plants,  entire segments of
the settled water distribution  piping  may  have to be  modified or  replaced in
order to deliver the  water to  the filters. If possible,  field  tests should be
carried  out  to  establish  the maximum carrying capacity of  influent  piping and
channels.                                            :

Existing filter boxes should be examined to identify,whether there are any  poten-
tial problems in converting the filters  to  high-rate filtration.  In general, most
well  designed  rapid  sand filters  are  easily  converted to  high-rate dual-  or
mixed-media  filters.  Backwash rates  for  dual- and  mixed-media  are the same as
those for rapid sand filter beds. In some instances,  filter  wash troughs  may have
to be modified in order to provide  the required clearance from the surface  of the
filter media to the lip of the wash trough.  If  the  clearance is inadequate  in the
existing filter, there is a  potential for excessive loss of  the lighter anthra-
cite  coal  media.  As  a general rule  where  rotary surface wash is used,  a  filter
should have  24  to  27  inches  of clearance between  the filter  surface and the lip
                                     11-37

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of the wash trough and 8 inches between  the  underside  of the wash trough and the
filter surface.

Excessive anthracite coal loss during backwash can also  occur if rise velocities
in the  area  between wash troughs  is too high.  This  problem occurs  where  wide,
shallow troughs at close spacing were used resulting in  as much as 50 percent of
the area being covered  by  troughs. At velocities of 30  gpm/sq  ft {rise velocity
48 inches per minute), coal  will  be washed out during backwash.  New, narrower and
deeper troughs should be considered if this potential  problem exists.

The condition  of  the existing underdrain  can often  be  established by  observing
the condition of  the filter media.  The presence of boils  during  backwashing  or an
uneven mounded appearance  of the  filter could  indicate an  underdrain  failure.
Only  removal  of the filter  media  and gravel and inspection of the underdrain will
establish its physical condition.  If the  underdrain is found to be damaged  or in
poor condition, its replacement must be a part of the filter renovation project.

If the existing  filters are  not  equipped  with surface wash  facilities,  they
should be installed during the rebuilding  project. Dual- and mixed-media filters
operating at  filter rates  of  4  to  6  gpm/sq ft  with, poly electrolyte filtration
aids   being  used  to  control  floe  breakthrough are more  difficult  to clean than
rapid  sand  filters.  A well designed  surface wash system is  needed  to  scour the
upper  layers  of  the filter during or just prior to backwashing.  This  procedure
breaks up surface  accumulations  and prevents formation  of  "mud balls."  Either a
rotary surface sweep with nozzles  which  penetrate the  surface as the arm rotates
or a  fixed  jet surface  wash  system should  be  installed. Some  advocate  a  2-arm
rotary  surface wash  system  with  one  arm placed at the surface  and  the  other
located  at  the  coal-sand  interface  in  a   dual-media   filter.  The theory  of
operation of  this  configuration  is  that  "mud balls"  have a  tendency to form at
the coal-sand interface  and additional agitation is  required at this location to
assist in cleaning adequately the filter bed.

Air  scour  has also  been used in  a limited  number  of  plants  to supplement the
backwashing procedure and to achieve  the same purpose  as surface wash equipment.
In general,  air  scour  must be  used  only  with  underdrain  systems  that do not
                                      11-38

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 require supporting  gravel  layers.   Specially  designed  nozzles  with  retaining
 screens on  which  the filter media can be placed directly are typically used where
 air scour is  used.  Introducing air beneath the sand and coal in a  dual-media fil-
 ter thoroughly  mixes  and scrubs  the filter media. Backwashing at  a flow of about
 15 gpm/sq  ft reclassifies  the  media. Advocates  of  air-scour  systems claim less
 backwash water  is used  with this  system.

 Although most well  designed rapid sand filter plants have adequately sized back-
 wash supply and  waste  piping,  rate-of-flow  controllers and other flow limiting
 devices in  filter  effluent  piping may  not  pass  the higher flows possible with
 dual-  or mixed-media  filters.  Replacing undersized rate-of-flow controllers with
 new  pneumatically  or   electrically  controlled controllers  may  be  required  to
 handle  the  higher flows.  Frequently,  filter effluent piping  is  also undersized
 and  will not  handle flows associated with filter rates  of  5 to 10 gpm/sq ft and
 must  be replaced. To  offset filter gallery  space limitations, more compact but-
 terfly  valves and fabricated steel piping can be  used in place of  bulky cast iron
 gate  valves and piping.

 A  modification  of  the  method  of  filter rate control  can also  be a beneficial
 technique for increasing  the capacity of an  existing rapid sand filter. Variable
 declining rate filtration can be adapted to an existing plant at minimal expense.
 Figure  11-20  shows a  desirable  design  for  variable declining  rate operations.
 This  modification, eliminates  rate-of-flow  controllers  which   contributes  to
 troublesome operation  and in old  plants are often  totally  inoperative.  Another
 advantage is that the filter media is submerged at all times eliminating negative
 heads  which  cause air  binding.  As illustrated  in Figure  11-21,  the  rate  on a
 clean  filter  is  initially constant  and declines  as  the filter  becomes dirty.
 Proponents  of the variable declining  rate  method of filter  flow control regard
 the  simplicity  of operation and  the  lack of  expensive  and troublesome rate-of-
 flow  controllers  as  the overriding  reason  this  technique  should  be seriously
 considered in any plant that must be upgraded.
Conversion to dual- or mixed-media filters which operate at a filter rate of 4 to
10 gpm/sq ft  should be  accompanied  by installation of filtration aid application
equipment. Filtration aids, which are typically  nonionic polyelectrolytes,  are a
useful tool  in  optimizing  the performance of  high-rate  filters.  These materials
                                     11-39

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prevent premature  filter  turbidity breakthrough by controlling  floe  penetration
into the  filter.  A dosage sufficient  only  to retain floe  in the bed  until  the
maximum operating headloss is  reached  represents  optimum  conditions.  This condi-
tion is illustrated by the hypothetical  headloss/turbidity  breakthrough curve in
Figure  11-22.  Typically,  polyelectrolyte dosages  ranging  from 0.02 to  0.1  mg/1
are  appropriate  depending upon  applied  water  characteristics.  Polyelectrolytes
are  especially  valuable  in  preventing  premature  floe breakthrough where waters
are cold.

By  adding a  polymer  to the water to be  used  for  filter backwashing,  a  reduction
of the initial  turbidity  breakthrough period and peak  can  be obtained  in addition
to a much  improved settling-thickening rate  for the backwash solids.21  Polymer is
added only during  the first  half of  the 10 to 15 minute backwashing  period.  In
pilot studies  it  was  found that adding  0.1  to 0.15 mg/1  of  nonionic  polymer to
the  backwash water reduced the relative initial turbidity  breakthrough  (ITB)  by
about 50  percent  to  a 15 to  30  minute period on  dual-media  filters.  Savings  in
backwash water would be realized by  preconditioning filters with polymer through
this technique.

Regulatory Agency Design Standards-
Design of new  facilities as  well as  upgrading of  existing water treatment plants
must conform to regulatory agency requirements. Some state agencies have specific
design  criteria  for  unit  processes  used in  treatment  facilities  and  encourage
design consultants to conform  to these  regulations. Design  standards  for filtra-
tion  plants  established by  the Texas Department  of  Health  is  included  in  the
Appendix and is one example of a good standard. Many standards are based upon the
"Ten State Standards for Design  of Water Treatment Facilities."  Others  have been
developed through years of experience  in a  specific state with treating particu-
lar  water supplies.  Most have provisions to consider and  accept  waivers  to  the
specific requirements and have procedures by  which new  or alternative technology
can be considered. In Section III policies and procedures  involving pilot testing
to demonstrate alternative treatment technology are discussed.
                                     11-40

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Filter Design Checklist—
 1.  Filter media sizing and selection should be based on pilot tests.  If this is
     not possible, data should be obtained from similar applications to determine
     the suitability of the media design.

 2.  In dual- and mixed-media filter systems,  provisions should be  made for the
     addition of polyelectrolytes directly to the filter influent.

 3.  The  turbidity  of  each  filter  unit  should  be  monitored continuously  and
     recorded.

 4.  The' flow and headloss  through  each filter should  be monitored continuously
     and recorded.

 5.  Provisions  should be made  for  the addition of disinfectant directly to the
     filter influent.

 6.  Pressure filters  must  be  equipped  with   pressure  and  vacuum air  release
     valves.

 7.  Provisions  should be made  to divert  any  filter effluent  of  unsatisfactory
     quality  (i.e.,  provide a filter to waste cycle).

 8.  Provisions  should  be  made for  automatic   initiation and completion  of  the
     filter backwash  cycle.  The  filter controls  and pipe  galleries should  be
     housed.
        \
        /
 9.  Filter piping should be color coded.

10.  The filter system  layout must enable  easy removal  of  pumps and  valves  for
     maintenance.

11.  The backwash  rate selected  must be based upon the specific filter media used
     and the  wastewater temperature variations  expected.
                                     11-41

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12.  Filter  backwash  supply  storage  should have  a  volume at  least  adequate to
     complete 2 filter backwashes.

13.  Adequate surface wash  or air scour facilities must be provided.

14.  There should  be  adequate backwash  and  surface wash pump capacity available,
     with the largest single  pumps out of service.

15.  Backwash supply  lines  must be equipped with air relese valves.

Case Histories-
Sacramento,  California—The City of  Sacramento has  two water  treatment  plants
with  a combined treatment  capacity  of  140 mgd.  The  newer  of these  two water
treatment plants is  located on the  American River. It was  constructed in 1963,
and  has  a design  capacity  of  60 mgd.  Increased  demand, especially  during  the
summer irrigation season placed  a  strain on both facilities,  and additional water
capacity was needed to meet  present  as well  as future water requirements.

Although  both  water  treatment  plants  were  amenable  to expansion,  the  city
selected the newer American  River  Plant  for the  first phase of the  project.  A
comprehensive study  was carried  out  by the  city's consultant  to  determine  how
much  additional  capacity could  be gained  from the  American  River  Plant by  a
staged expansion program.22 The preliminary review indicated  that  replacing  the
existing rapid sand filter  media with either more  efficient  dual-  or mixed-media
would accomplish a significant  expansion  in capacity and  could  be  achieved with
no major plant  structural modifications  or additions.  The existing filters were
designed at  3 gpm/sq  ft and consisted of 24 inches of  silica  sand  over a  graded
gravel  underdrain.  At the expanded flow  of 105 mgd, the filter rate was increased
to 5.3 gpm/sq ft,  which is  well within  the  capabilities of a well  designed dual-
or mixed-media filter.

The  existing 60 mgd  conventional  plant at design  flow,  provided  25  minutes of
flocculation and  115 minutes of  settling prior to  filtration.  At  105  mgd,  the
flocculation and settling times would be  reduced  to 14 and 65  minutes,  respec-
tively. Although the amount  of pretreatment would be substantially  reduced  at the
                                     11-42

-------
 expanded  flow,  either  dual-  or  mixed-media  filters  could  handle anticipated
 higher  turbidity  loadings.
 Following  preliminary assessment of the feasibility of increasing the capacity of
 the American  River Plant extensive pilot filtration tests were carried out by the
 city.  The  specific  purpose of  the  tests  were to  evaluate the  performance of
 various  types  of filter  media  and  determine the  economics of  their  use in
 expanding  the capacity of  the  plant.  These tests were  done in February through
 May of  1982.
 Four  types of  filter  media were  evaluated  simultaneously in  four side-by-side
 pilot  filters.  Each  filter  was  equipped  with  instrumentation  for  measuring
 turbidity  and headloss. Figure 11-23 is a flow diagram showing the general layout
 of the pilot  filtration equipment.  Feedwater to  the pilot filters could be drawn
 from  either of two  sources:  (1)  from the raw river  water pipeline (before alum
 addition);  or  (2)  from the plant filter  influent  flume  following alum addition,
 mixing,!flocculation,  and settling.

 During the  three months of testing, influent turbidities varied from 3 to 33 NTU.
 For  the  controlled variables: (1)  alum  dosages  ranged  from  12 to  21  mg/1;  (2)
 polymer:dosages  varied from 0 to 0.3 mg/1;  and  (3) filter rates were  set  at 5,
 6.5,  or'j 10 gpm/sq ft.  Test runs  were terminated for one  of  two  reasons, either
 high  headloss  or high  turbidity.  The City of Sacramento,  established  a maximum
 turbidity goal for drinking water of 0.1 NTU. During a particular pilot test run,
 an upper  tubidity limit of 1 NTU was selected  as the point at  which  a run was
 terminated.
All of the pilot filtration tests performed on plant settled water clearly demon-
strated that the turbidity  goal  of  0.1  NTU could be obtained at all filter rates
examined  (5  to  10  gpm/sq  ft)  by  either  dual-   or  mixed-media.  Mixed-media
possessed a greater reliability in achieving the turbidity goal.

Based upon the results of the pilot filtration study, it was recommended that the
treatment  plant  be expanded  by  replacing the  existing  sand filter  media  with
either dual- or mixed-media. It  was  also recommended that equipment be installed
for preparing and feeding a polyelectrolyte filtration aid.
                                     11-43

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The treatment plant has been operated  successfully  at  101 mgd which is the maxi-
mum capacity  of  the existing  raw water pumps. Before  the treatment plant can be
operated at sustained  flows  beyond  100 mgd, additional  raw  water pumps and high
service finished water pumps  will  be  required. During qualifying tests effluent
turbidities averaged  less  than 0.1  NTU  (generally 0.06 to  0.08  NTU)  and filter
cycles between backwashes exceeded 48 hours.

Erie  County,  Hew  York--The application  of mixed-media to  this plant  in Erie
County, New York, is of special interest because it provided side-by-side compar-
isons of the  efficiency of mi-xed-media filters and  rapid sand filters in a large
plant. The results have been reported by Westerhoff and are summarized below.23

The Erie  County  Water Authority serves  filtered  water  to  approximately 390,000
persons in all or part of 12 towns  and the City of Lackawanna in Erie County, New
York.  The average water production in 1969 was 44.3 mgd. Water is taken from Lake
Erie,  treated in the Water Authority's two  filtration  plants (Sturgeon Point and
Woodlawn  filter  plants),  and  pumped  into  the   transmission and  distribution
systems. Most of the  water  is treated at  the Water  Authority's  Sturgeon Point
filter plant, located  in  the town of  Evans, approximately  30 miles south of the
City of Buffalo.  This plant was originally constructed in 1961.

The water treatment processes at the Sturgeon Point filter plant consist of aera-
tion,  chemical addition,  rapid mixing,  flocculation  and  sedimentation,  filtra-
tion,  and chlorination.

In 1965, the  water demanded by  a  burgeoning population  in  the suburban Buffalo
area brought  about  expansion  requirements.  The first  stage  (to a capacity of 60
mgd)  was needed  immediately.  The  Water Authority decided  during  the first-stage
expansion to  install  mixed-media  in six  new filters.  The  four original  filters
contain fine-to-coarse graded-sand media.

Special  data  were  collected  from  a total  of 48  parallel-filter runs  during  a
12-month study period. The sand filters were operated at the standard 2 gpm/sq ft
filtration rate as a control. The filtration  rate  on the mixed-media filters was
varied between 2 to 10 gpm/sq ft.
                                     11-44

-------
 During the  parallel  tests,  the filter  runs  were  terminated at  a headless  of
 8 feet. Typical turbidities  applied  to the filters were  2  to 4 NTU with  little
 variation  as the  clarifier overflow  rate was varied  from 625 to 940 gpd/sq  ft.
 Alum feed  rates  were typically  14 to  16  mg/1. The  following conclusions were
 reached:
i
 •    More  than  80  percent  of  the time,  the  filtered  water  turbidity  from the sand
      filters  was 0.10  NTU  or  less.
 •    Nearly  88 percent of the time, the filtered water turbidity  from the mixed-
      media  filters  was 0.10  NTU  or  less.

 •    The mixed-media  filters operating at filtration  rates  of 2 to 10 gpm/sq  ft
      consistently  produced  a lower filtered water  turbidity than the sand media
      filters  operating at a  filtration  rate  of  2  gpm/sq ft.

 •    At  filtration  rates  up  to 6 gpm/sq ft,  the mixed-media-filter effluent had a
      lower  total  microscopic count  than  the  sand  media filters  operating  at, a
      2 gpm/sq  ft rate.        '                                   .

 *    The mixed-media  filters operating at  5 gpm/sq ft had  an average length  of
      filter  run of  29  hours. At  6  gpm/sq  ft they had an average filter run of 20
      hours.

 •    The mixed-media  filters operating at  5 to  6  gpm/sq  ft used a considerably
      lower  proportion  of wash  water than the  sand filters  operating  at 2 gpm/
      sq  ft  (1.8 percent as compared to  2.5 percent  on the average).

 As  a result  of  these tests,  it was  concluded  that the  mixed-media  filters  at
 6 gpm/sq  ft  produced an  end  product superior to that from the rapid sand beds at
 2 gpm/sq  ft with concurrent  economic advantage. The finished water goals adopted
 for  filtered water  at  this plant were established for the mixed-media filters at
 6  gpm/sq ft as follows:
                                     11-45

-------
     Turbidity                  Less than 0.10 NTU average
                                Less than 0.50 NTU maximum
     Total microscopic count    Less than 200 su/ml average
                                Less than 300 su/ml maximum
     Color                      Less than 1 unit
     Odo.r                       Not detectable
     Aluminum                   Less than 0.05 mg/1
     Iron                       Less than 0.05 mg/1

Corvallis,  Oregon—Corvallis  increased   the capacity  of  its  municipal  water
treatment plant in the early  1970's  by two  and  one-half times without increasing
the  size  of  the  plant.  Using the  Willamette River  as  a source of  supply,  the
original treatment plant  was  designed and built  in  1949  as  a conventional rapid
sand filtration  plant.  It  was designed  in  increments of  4 mgd capacity,  each
increment  consisting  of  floccu.lation-sedimentation  basins  and two  rapid-sand
filters.

The  initial  plant  capacity  of 4 mgd rose to 8 mgd with  the  addition of a second
increment in 1961. Under the original plan, the plant was scheduled for expansion
to  its  ultimate capacity of  16 mgd  with construction  of  the  third  and fourth
increments in 1968 to  1969. Capacity  of  the Willamette River treatment plant was
increased  without  structural   addition  from 8 mgd  to 21  mgd.   The  expansion  of
capacity was achieved by application of:  (1) mixed-media filtration, (2) shallow-
depth sedimentation with tube settlers, and  (3) coagulation control  techniques.

The  turbidity  of  the  raw water  drawn from the Willamette  River normally ranges
from 15 to 30  NTU,  with  surges up to 1,000 NTU. The water is soft (15 to 30 mg/1
hardness) and exhibits periodic taste and odor problems. Typically, the following
chemical  dosages  are used:  alum, 20  to  40 mg/1;  lime, 10 to 20 mg/1; chlorine,
2  mg/1;  polymer (as coagulant aid),  0.1  to 0.2  mg/1; activated carbon,  5 to 10
mg/1 (for taste and odor control).

Virtually  all  of  the treatment piping had to be enlarged to handle the increased
plant  flow.  Settling  tube  modules  were  installed over  about 60 percent  of  the
3,500  sq  ft  of rectangular  settling basin  area.  The  tubes were  installed  on
simple  "I"  beams   spanning  the  width  of  the  basins  and   are located  at  the

                                      11-46

-------
discharge end  of  the basin. New effluent weirs  and launders were also installed
to  provide good flow distribution through the area  covered by the tubes.

Overflow  rate in   the   sedimentation   basin   area  covered  by  the  tubes  is
4.2 gpm/sq ft. This  compares  with  the 1.05  gpm/sq ft design loading on the basin
before they were installed.

Utilization of the  existing basins with the tube settlers  reduces the turbidity
loading  on filters, especially  during  periods  of high river turbidity, and pro-
vides  more  economical  operation by  increasing  filter  runs  during  normal  river
conditions.  With an  extreme turbidity range of  2 to  1,000  NTU,  filter runs have
been increased from 40 hours experienced with the old conventional basins at much
lower  plant throughput  rates  to 60 to 65 hours.  Operating  on  raw water turbidi-
ties of 15 to  30 NTU, the tube effluent has had turbidities of 1 to 2 NTU.

The capacity  of  the filtration  portion  of  the  plant was  increased  by modifying
the filter piping and by  replacing the  rapid  sand filter media with mixed-media.
At the 21 mgd  rate, the filtration rate is 7.5 gpm/sq ft.

The pilot filter  coagulation  control  system is  used  in  conjunction  with contin-
uous reading turbidimeters  on  each  plant filter  to assure  satisfactory filtered
water quality. The  full-scale  plant  continuously produces a finished  water tur-
bidity of 0.2  NTU or less.  •

The cost  to expand the  plant  from 8 to  21 mgd  capacity  (including a  new  5 MG
reservoir,  a new  high-service  pump  station .and  a crosstown  16-inch  transmission
line to the new reservoir)  was  $430,000  (1969  prices).  It was estimated that the
same expansion through  the addition of new settling basins and filters would have
been at  least  $650,000 (1969  prices).  Thus,  improved performance and increased
capacity were  achieved while realizing a substantial savings in cost.

North  Harin  County  Mater  District,  Novato, California—In  1973,  the Stafford
Water Treatment Plant owned by  North  Marin  County Water District, which provides
water service to Novato,  California,  and nearby areas, was expanded by installing
tube settlers and  mixed-media filtration materials.  The turbidity of  the Stafford
                                     11-47

-------
Lake supply varies from about 2  NTU  to about 35 NTU, with a usual range of about
10 to  20 NTU. Coliform MPN  values range  from  5 to 72,400  per  100  ml. The  lake
water color ranges from 25 to 50 units.

Experience at  the Stafford plant  had  not indicated  any  operating problems  with
high  raw water turbidities  or  coliform  densities.  However, high  color and  low
turbidity in the range of 5 to 10 NTU in raw waters produced problems of clarifi-
cation.  Further,  high plankton  populations  caused  taste and odor  problems  and
other biological forms had seriously shortened filter runs on occasion.

The  basic steps  in  the existing  treatment  process  prior  to upgrading  were as
follows:

•    Raw water was disinfected with chlorine and coagulated with alum  in a down-
     flow hydraulic mixing chamber.

•    Flocculation was provided using additions of  recirculated sludge and lime.

t    Flocculated water was  clarified  and sludge was  removed and sprayed on  land
     for disposal.

•    Activated  carbon was added  immediately prior  to  filtration in  rapid  sand
     filters.

•    Dechlorination to the desired residual was  accomplished by the use of sulfur
     dioxide in the filtered water clearwell.

•    Elevated storage of water for backwash!ng filters was provided.

•    Water used in washing filters  was stored in a recovery pond and pumped  at  a
     controlled rate  back to the head of the plant for reprocessing.

In  March,  1973, the  district  retained a  consultant  to  prepare  a  report  on  the
design  of. plant  improvements  to  increase the  capacity  from  3.75  to  6.2  mgd.
                                     11-48

-------
 Previous  preliminary studies by the district engineering staff had indicated that
 this  might  be possible to accomplish  in a short time period without the need for
 major plant  additions.

 The major changes  required  were  modification of the clarifier by adding settling
 tube  modules,  replacement of the  existing filter sand with  new mixed media and
 the installation of a  coagulant control and  turbidity monitoring center.

 To  handle the  higher  flow  rates  it  was  necessary  to increase the  capacity of
 certain   pumps,  pipelines,   meters,   chemical   feeders  and  valves,   and  modify
 controls.

 Cost  of  the improvements amounted to $337,445  (1974  prices).  This made possible
 an increase of 2.45 mgd in plant capacity at a unit cost of $137,770 per mgd. The
 expanded  plant  was ready for operation  in just eight months  after  award  of the
 construction contract  in time for the high demand Memorial  Day weekend on May 24,
 1974.

 Other modifications were needed to permit operating at higher  plant  flows.  The
 mixing chamber, previously  operating  hydraulically, was equipped with  a vertical
 mechanical rapid mixer. Provisions were made to add  polymer as an aid to floccu-
 lation. Facilities were furnished for storing  and  feeding  sodium hydroxide solu-
 tion  replacing  lime for pH adjustment.

 A major requirement was to increase the capacity of the settling basin.  This was
 done  by  installing tube  settling  modules.  As  a general  rule,   installing tube
 settling  modules  in  an existing basin  will  permit clarifying two to  four times
more  water  than can be  clarified  within  the  same  basin  volume with  no  loss in
efficiency.   In  this particular  case,  because of the  light  alum  floe present, it
was recommended that the flow rate be increased from 4.0 mgd to not more than 6.5
mgd, or 1.6 times the existing capacity. This would increase the surface overflow
 rate  from 1.52 to 2.5 gpm/sq ft,  decrease the detention time from 1.3 to 0.8 hour
 and would increase the weir loading from  7  to  11  gpm/ft.  Despite  the  high over-
 flow  rates  and shortened  clarification times,  good operation  was  obtained  at
 these  loadings.
                                     11-49

-------
The tube  settling  modules  were installed in the  annular outer settling compart-
ment of the circular clarifier. Figure 11-24 illustrates the arrangements of tube
modules in the existing basin. The existing sludge collection mechanism still has
enough room to operate in the modified basin.

The  sand  filters were  completely  rebuilt.   The  filter  bottoms  were removed and
replaced. The single-media sand bed  was  replaced  with mixed-media supported on  a
gravel bed with an intermediate layer of coarse garnet gravel. New rotary surface
washers were  installed.  Filter piping  and  valves were  modified as  necessary to
accommodate  the  increased flows  and gate  valves were  replaced with  butterfly
valves.

A new coagulant control center with  turbidity  monitoring was added to the exist-
ing facilities.  The coagulant control center was  installed to provide the opera-
tors with a precise method for optimizing the coagulant dosage. Continuous filter
effluent  turbidity  monitoring assures that  the California  Department  of Health
Services mandated standard of 0.5 NTU is never exceeded.

Since 1974, the plant operating experience has been good. The expanded facilities
have been operated routinely  at their maximum design  capacity. The settling tubes
have functioned well  at surface overflow rates of 2.5 gpm/sq ft and  the mixed-
media filters have  performed very satisfactorily  at  rates up to 6.5  gpm/sq ft.
Finished water turbidities are consistently  less  than 0.15 NTU and  the bacterio-
logical quality has been excellent.

A demonstration test  was  conducted for two weeks  in  June  1975,  to  show that the
design  flow  criteria  and  water  quality requirements  of  the  California  State
Department of Health  Services would be  achieved  and maintained. The  results  of
the June 1975 test are shown  in Table 11-16.
                                     11-50

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          TABLE IM.  SUMMARY OF POTENTIAL PROBLEMS IN WATER
                      TREATMENT UNIT OPERATIONS
Operation
Potential  Problems
1.   Chemical  Feed
2.   Rapid Mix
3.   Flocculation
4.   Sedimentation
5.   Filtration
-  Choice  of  chemical (s).
-  Choice  of  chemical dose and pH.
-  Control  of chemical addition. Performance of
   chemical pumping  equipment.
-  Maintenance of  chemical feed lines.
-  Flexibility in  feed system to allow for
   changing the point of addition, adding
   chemicals  at more than one point, etc.
-  Sequence of adding different chemicals.
-  Degree  of  dilution of chemicals before
   Injection.
-  Type of rapid mix. In-line versus mechanical
   mix.
-  Number  of  rapid mixers.
-  Method  of  chemical addition.
-  Mixing  speed/detention time.
-  Optimum detention time.
-  Optimum mixing  intensity.
-  Number  of  stages.
-  Adequate baffling to  approximate plug flow
   conditions.
-  Surface loading rates.
-  Short circuiting  due  to wind, temperature,
   density differences,  inlet and outlet design.
-  Amount  and rate of accumulation of sludge.
-  Sludge  removal.
-  Filter  rate and rate  control.
-  Hydraulics.
-  Chemical pretreatment of water reaching the
   filter.
-  Inadequate backwashing.
-  High filtered water turbidity.
-  Excessive  headloss.
                                  11-51

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TABLE 11-11. UPFLOW CLARIFIER LOADING RATES FOR COLD WATER*
Overflow Rate, Based
on Total Clarifier
Area
gpm/sq ft
1.5
1.5
1.5
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2.0
* Water temperatures
Overflow Rate,
Portion of Basin
Covered by Tubes
gpm/sq ft
2.0
3.0
4.0
2.0
3.0
less than 40°F
TABLE 11-12. UPFLOW CLARIFIER LOADING RATES
Overflow Rate, Based
on Total Clarifier
Area
gptn/sq ft
2.0
2.0
2.0
2.5
2.5
* Water temperatures

Overflow Rate,
Portion of Basin
Covered by Tubes
gpm/sq ft
2.0
3,0
4.0
2.5
3.0
i
above 50°F


Probable Effluent
Turbidity, NTU
1-3
1-5
3-7
1-5
3-7
FOR WARM WATER*
Probable Effluent
Turbidity, NTU
1-3
1-5
3-7
3-7
5-10
i
                        11-61

-------
 TABLE 11-13.  HORIZONTAL FLOW BASINS LOADING RATES FOR COLD WATER
Overflow Rate, Based
 on Total  Clarifier
•	Area	
    gpm/sq ft	
 Overflow Rate,
Portion  of Basin
Covered  by Tubes
    gpm/sg ft
Probable  Effluent
 Turbidity. MTU
Raw Water Turbidity = 0-100

       2.0

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       2.5

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       1-5

       3-7
Raw Water Turbidity = 100-1,000

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       5-10
* Water temperatures are frequently 40°F or less,
TABLE  11-14.  HORIZONTAL FLOW BASINS LOADING  RATES FOR WARM WATER
Overflow Rate, Based
 on Total  Clarifier
       Area
 Overflow Rate,
Portion  of Basin
Covered  by Tubes
Probable  Effluent

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Water Turbidity - 0-100
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2.0
2.0
3.0
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2.0
* Water temperatures are frequently
gpm/sq ft

2.5
3.0
4.0
3.5

2.5
3.0
50° F or above.
Turbidity, NTU

1-3
1-5
3^7
1-5

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3-7

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                                     11-62

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              11-65

-------
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                               11-66

-------
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                                          11-68

-------
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Figure 11-6. SIMPLIFIED DIAGRAM OF SCO INSTRUMENT
                         11-70

-------
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            Figure 11-7. TYPICAL FLOCCULATION  UNITS

                                11-71

-------
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Figure il-7  (CONTJ.  -TYPICAL  FLOCCULATION  UNITS
                        ,   11-72

-------
                          Axial Flow
                           Turbine
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g) Walking  beam flocculator.
         Figure 11-7 (Cont.).  TYPICAL  FLOCCULATION  UNITS
                                   11-73

-------
Figure 11-8. A PERFORATED BAFFLE WITH SQUARE-NOZZLED PORTS
         DISTRIBUTES FLOW FROM THE FLOCCULATORS AT
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                          11-74

-------
Figure 11-9.  NEW- AND OLD-STYLE RQCCULATORS
                  11-75

-------
PERFORATED
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                                      11-76

-------
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                         11-77

-------
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                                            11-78

-------
Figure IM3.  CLOSE-UP VIEW OF VACUUM SLUDGE REMOVAL ASSEMBLY
                           11-79

-------
Figure 11-14. A MODULE OF STEEPLY INCLINED TUBES
          (COURTESY OF MICROFLOC PRODUCTS
          GROUP,  JOHNSON  DIVISION, UOP)
                      11-80

-------
FLOW DISTRIBUTION ORIFICES
OVERFLOW BOX
     OVERFLOW
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                                       DISCHARGE FLUMES
                                                   FEED BOX
                                                     FEED (INFLUENT)'
                 SLUDGE HOPPER
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           Figure 11-15. LAMELLA*'SEPARATOR
                      (COURTESY OF PARKSON  CORP.)
                                11-81

-------
      INFLUENT ZONE
                      EXISTING LAUNDERS    NEW LAUNDERS
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                    11-82

-------
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                           11-85

-------
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    Figure 11-18 (ContJ.  SOLIDS CONTACT CLARIFIER WITH TUBE SETTLERS
                               11-86

-------
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                         11-88 :


-------
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Figure 11-21.  TYPICAL RATE OF FILTRATION PATTERNS DURING
            A FILTER RUN (BAUMAN AND OULMAN, 1970)
                         11-89

-------
EFFLUENT
TURBIDITY
                                                            MAXIMUM
                                                            HEADLOSS
                                                            HEADLOSS
             FILTER RUN TIME
                                             TURBIDITY
                                             BREAKTHROUGH
     Figure 11-22: HYPOTHETICAL OPTIMUM FILTER HEADLOSS/TURBOTY
            ;    BREAKTHROUGH CURVE      .
                               11-90

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RAW RIVER WATER
  PLUS ALUM
         PLANT FILTER INFLUENT WATER
        (FOLLOWING ALUM ADDITION,  MIX-
        ING, FLOCCULATION, AND  SETTLING)
             -ALTERNATE INFLUENT
             v   SOURCES—-^
¥
                                     NOTE:   FINE FILTER MEDIA
                                            DEPTH IS 24 INCHES
                                            THROUGHOUT
!
PILOT FILTER/""^ INFLUENT
^ ^
TRI -MIXED
MEDIA NO. 1
TRI-MIXED
MEDIA NO. 2

SAND
WATER
DUAL- MIXED
MEDIA


ANTHRACITE-
CAPPED
SAND

*




,

-
_^" _J

i




•


'

i




'


\

I

i

MULTIPOINT TURBIDITY RECORDER
                                                           J


                                                           }
                                                               PILOT FILTERS
                                             EFFLUENT RATE' OF
                                             FLOW CONTROLLERS
                                             AND METERS


                                             TURBIDIMETERS
 Figure 11-23.  FLOW DIAGRAM OF THE PILOT FILTRATION EQUIPMENT
                               11-91

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Figure lt-24.  CLARIFIERS SHOWING TUBE SETTLING MODULES
                       11-92

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REFERENCES

 1.   Chadik, Paul  A., and Gary I. Amy, "Removing Trihalomethane Precursors From
      Various Natural  Waters  By Metal  Coagulants," J.AWA, 75:532-536, 1983.

 2.   Ruehrwein,   R.A.,   and   D.W.  Ward,   "Mechanisms  of  Clay  Aggregation  By
      Polyelectrolytes,"  Sell  Science, 673:485,  1952.

 3.   O'Melia,   C.R.,  "Coagulation   and  Flocculation,"  in  Physlochemical
      Processes  for  Mater Quality  Control,  by  Walter  J.  Weber,  Jr.,  Wiley-
      Interscience,  New  York,.1972.

 4.   Hahn,  H.H.,  and   W.   Stumm,  "Kinetics   of   Coagulation  With  Hydrolyzed
      Al(IIIj," J. Colloid Interface Scl.,  28:134-144,  1968.

 5.   Vrale,  Lassi,  and  Roger M. Jorden,  "Rapid  Mixing  in  Water Treatment,"
      J.AWA, 63:52-58,  1971.

 6.   Chao,  Junn-Ling,  and Brian  G.  Stone,  "Initial  Mixing  by  Jet  Injection
      Blending,"  J.AWA,  71:570-573, 1979.

 7.   Hudson, H.E.,  and J.P. Wolfner,  "Design of Mixing and Flocculation Basins,"
      J.AWA, 59:1257-1267, 1967.

 8.   Bowers, A;  Eugene,  and James D.  Beard II,  "New Concepts in Filtration Plant
      Design and  Rehabilitation," J.ANUA, 73:9:457,  1981.

 9.   Forbes, Robert E.,  Gary  L. Nickerson, E. Herbert Hudson, Jr., and Edmund G.
      Wagner,  "Upgrading  Water  Treatment   Plants:   An  Alternative   to  New
      Construction," J.AWWA, 72:5:254, 1980.

10.   "Upgrading  Study,  Potomac  Water  Filtration  Plant,"  Washington  Suburban
      Sanitary Comm.,  Hyattsville, MD, September 1978.
                                    11-93

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11.   Hudson,  H.E., Jr., "Dynamics of  Mixing  and Flocculation,"  in: Proceedings
      of the 18th Annual  Public Mater Supply Conference,  University of Illinois,
      Oept of  Civil  Engineering.                *•

12.   Kawamura,   Susumu,   "Coagulation  Considerations,"   J.AWHA,  65:6:417-423,
      1973.

13.   Kawamura,  S.,  "Considerations  on  Improving Flocculation,"  J.ANWA,
      68:328-336, 1976.            :

14.   Brodeur,   Timothy  P.,   "Upgrading   to  Increase   Treatment  Capacity,"
      J.AHHA,  73:9:464, 1981.

15.   Tate, C.H., and  R.R. Trussell,  "Optimization of Turbidity Removal by Use of
      Particle Counting  for Developing Plant  Design  Criteria,"  in: Proceedings
      of AWWA  Technology  Conference,  San Diego, CA, p.  I, December 1976.

16.   Schleppenbach,  F.X.,  "Water  Filtration at Duluth." EPA-600/2-84-083, report
      prepared, by the  Duluth  Water and Gas  Department under Grant No.  S-804221
      from  U.S.  Environmental  Protection  Agency, MERL,  Cincinnati, OH,  April
      1984. NTIS:  PB-84-177807.

17.   Kavanaugh,  M.C.,   C.H.  Tate,  A.R.  Trussell,  R.R.  Trussell,  and  Gordon
      Treweek, "Use of Particle Size  Distribution Measurements for Selection and
      Control  of Solid/Liquid  Separation  Processes,"  in:  Particles In  Hater,
      M.C. Kavanaugh  and 0.0.  Leckie,  Eds.,  Advances  in Chemistry  Series  189,
      American Chemical Society, Washington, D.C., 1980.

18.   James  M.  Montgomery,   Consulting   Engineers,  Inc.,  Hater  Treatment
      Principles  and Design, John  Wiley & Sons, Inc., 1985.

19.   Walker,  J.D.,  "High Energy Flocculation," J.AWHA, 60:1271-1279, 1968.

20.   King, Richard W., and Eugene  I.  Crossley, "Upgrading Water Treatment  Plants
      in San Diego," J.AHWA, 73:9:476,  1981.
                                     11-94

-------
21.   Yapijakis, Constantine,  "Direct  Filtration:  Polymer 1n Backwash Serves Dual
      Purpose," J.AWIA,  74:8:426,  1982.

22.   Sequelra, James  A.,  Lee  Harry,  Sigurd P.  Hansen,  and  Russell  L.  Culp,
      "Pilot  Filtration  Tests  at  the  American  River  Mater Treatment  Plant,"
      Public Works,  114:1:36,  1983.

23.   Westerhoff,   Garrett  P.,   "Experiences  with   Higher  Filtration  Rates,"
      J.AWWA, 63:6:376,  1971.
                                     11-95

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                  Section III
New Treatment Technology

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                                   SECTION III
                            NEW TREATMENT TECHNOLOGY
 INTRODUCTION

 This  section  describes  new treatment  technology that could be regarded as estab-
 lished  or emerging.  Package plants,  slow-sand filtration, and diatomaceous earth
 filtration  are regarded  to be  new  technologies,  especially  as they  relate to
 small systems. Membrane and cartridge filtration, because they have not been used
 in  treatment  of  raw water  supplies  for  potable use,  are defined  as  emerging
 technologies.

 Each  technology  is  described  and cost  estimates  provided.  Case  histories  and
 performance   data   from   full-scale   installations,   where  available,   is  also
 presented.

 Following  presentation of  the  specific treatment technologies,  the use  of pilot
 studies to determine if a  process  is appropriate for  a  certain application  and
 development of design criteria is discussed.  Also,  case studies  involving use of
 pilot studies to determine  suitability of  particular processes  for  new treatment
 facilities are also  described. These  studies trace  the development of a project
 from  initial  feasibility  evaluations  through pilot  studies to qualify  a partic-
 ular process for design.

 PACKAGE PLANTS
General
The package plant is defined as  a  factory-assembled,  skid-mounted unit generally
incorporating a single tank or,  at the most,  several  tanks.  A complete treatment
process typically consisting of  chemical  coagulation,  flocculation,  settling and
filtration is used in many designs.
                                     III-l

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Package  plants  are most  widely used  to treat  surface  supplies for  removal  of
turbidity, color and  coliform  organisms  prior to  disinfection.  Presently, it is
estimated that over 650 package  plants,  ranging  in capacity from 5 gpm to 4 mgd,
are  in  service  in the United  States.  Package plants can be  used  to treat water
supplies for communities as well as recreational  areas, state parks, construction
camps, ski resorts, remote military installations and other locations where pota-
ble  water  is  not  available from a municipal  supply.  Several  state agencies have
mounted  package plants  on  trailers for  emergency  water  treatment.  Their compact
size, low cost, minimal installation  requirements,  and.ability to operate virtu-
ally unattended makes  them an  attractive option in  locations where revenues are
not  sufficient to pay for a full-time operator.

Types Available

Conventional  Package Plants—
Package water treatment plants  are available from several manufacturers in a wide
range of capacity, incorporating a complete treatment process (coagulation, floc-
culation,  settling,   and  filtration). Design criteria  used  for these  package
plants varies widely.  Some manufacturers adhere  closely  to accepted conventional
design practices such  as  20- to 30-minute  flocculation  detention  time, a 2-hour
sedimentation detention time and rapid sand  filters  rated  at 2  gpm/sq ft. Other
manufacturers have utilized new  technology  including  tube  settlers  and high-rate
dual- and mixed-media  filters  to reduce  the size of a plant and hence extend the
capacity range  of  single  factory-assembled units. Often,  state  regulatory agen-
cies dictate the design criteria which must be met by package plant manufacturers
and  exclude  units  using  new  technology   that does not meet  arbitrary standards
adopted by these agencies.

Tube Type Clarification Package Plants—
A flow diagram for a package plant incorporating  tube settlers is shown in Figure
III-l.  Plants of this type are manufactured  in two versions:   Microfloc Products
"Water Boy"  with  a  treatment   capacity  range of  10 to  100  gpm;  and Microfloc
Products "Aquarius,"  which generally  consists of  dual  units with  a capacity  of
200  to  1,400 gpm.  The coagulant  and disinfectant  chemicals are  added  at  the
influent control valve. A  polyelectrolyte coagulant aid is applied  as the water
enters the flash mix  chamber.  After the  treatment  chemicals are added and mixed,
                                     III-2

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 the  water  is  introduced  into a  mechanical  flocculator.  Flocculation  detention
 time can vary  from  10 minutes in small units to 20 minutes  in  larger units.  The
 flocculated  water  is  then  distributed through  a bank  of tube  settlers,  which
 consist of many 1-inch-deep, 39-inch-long  split-hexagonal-shaped passageways that
 provide an overflow rate,  related to available settling surface  area of less than
 150 gpd/sq ft.  This overflow rate, together with a settling depth of only 1  inch,
 results in effective  removal  of  flocculated  turbidity with a  detention  time  of
 less than 15  minutes.

 After passing through  the tube  settlers,  the clarified water flows  to  a gravity
 mixed-media filter.  The filters  are designed to operate  at  a constant flow  rate.
 Rate control  is accomplished  with  a low-head filter effluent transfer  pump dis-
 charging through a float-operated valve. The package plant  filter is designed  to
 backwash automatically once  a  preset filter headloss is reached. The operator may
 override the automatic  controls  and backwash the  filter manually.  During  back-
 wash, the  material  accumulated in  the tube  settlers is  automatically  drained from
 the  unit.  Combining  backwashing  with  draining  of the tube settlers for sludge
 removal  eliminates  the need  for an operator to judge how  often or how much sludge
 should  be wasted from  the clarifier. This particular feature  simplifies  operation
 and reduces the required skill level  of the operator.

 Figure  IH-2  is  a  flow diagram of  a  package treatment plant  of slightly  different
 design.  Again,   low-detention  time,  high-efficiency- tube  settlers  are used  to
 reduce  the  detention  time and hence the volume  of  the clarification portion  of
 the plant.  A  dual-media filter rated at 4   gpm/sq ft also contributes to the com-
 pactness of this plant.

 Adsorption  Clarifier Package Plant—
 A  package  plant  manufacturer introduced a  new concept   in package  water  treatment
 plant (Trident  by  Microfloc  Products) design in the early 1980s  that utilized  an
 upflow filter of low-density plastic bead media  (termed an adsorption clarifier),
 followed  by a mixed-media filter  for final  polishing.  The adsorption  clarifier
 replaces  the  flocculation and settling processes  and  results   in  an  extremely
compact unit.  The manufacturer claims that  it further  reduces chemical  coagulant
dosage  requirements  over other  systems. Figure  III-3  is a  flow  diagram of the
Trident Water System manufactured  by Microfloc Products illustrating the various
                                     III-3

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operating  cycles.  During  operation,  chemically  coagulated  water  is introduced
into the  bottom  of the adsorption clarifier compartment  where it passes upwards
through a bed of buoyant  adsorption media.  The adsorption clarifier combines the
processes of coagulation, flocculation, and settling into one unit process.

In  passing  through the  adsorption  media,  the  chemically coagulated water is sub-
jected to:  {1} mixing, (2) contact flocculation, and (3) clarification. At opera-
ting flow rates, the mixing  intensity  defined  by the mean temporal velocity gra-
dient  value,  6,  ranges  from 150 to 300  sec-1. Flocculation  is  accomplished by
turbulence  as water passes  through the adsorption media  and  is enhanced by con-
tact with flocculated solids attached  to the media.

Turbidity removal  in.the adsorption  clarifiers  is accomplished by adsorption of
the coagulated,  flocculated solids on  the surfaces of the adsorption media and on
previously attached solids. The adsorption clarifier provides excellent pretreat-
ment,  which  frequently  is better  than  the performance achievable with  complete
flocculation and settling processes.  Turbidity removal  in this stage ranges up to
95 percent.

Cleaning  of the adsorption  clarifier   is  accomplished by  flushing.   This  flush
cycle  is initiated by a timer, but the  equipment also  includes a pressure switch
that monitors headloss  across the adsorption media and  can automatically  initiate
a flushing cycle if required. Figure III-3  illustrates  the operation  of  the unit
during  a  flushing  cycle.  When  a  cycle is initiated,  the plant  effluent  valve
closes, causing  the water level  to rise in the plant  as the influent flow contin-
ues. When  the water  level  reaches a  predetermined  level,  a  switch  causes  the
influent valve to  close.  Air is  distributed through perforated laterals  beneath
the adsorption media.  This causes  an immediate  expansion  in  the adsorption media
and a  vigorous scrubbing action takes place. Dislodged  solids  are then hydrauli-
cally  flushed out  of the  top of  the  adsorption  clarifier  to waste.   Influent
water  is  used  to  flush  the adsorption  clarifier.  Flushing frequency may  vary,
depending upon  influent water  quality. Typically,  the controls  are set  up  to
initiate a  flushing cycle  every  4 to  8 hours.  Unlike  conventional filters,  com-
plete  cleaning of  the  adsorption clarifier is  not required, as  the  majority  of
solids  are removed by the violent  agitation provided during  the first minutes of
                                     III-4

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 the  flush  cycle. Also,  more efficient  performance  of the  adsorption clarifier
 occurs if some residual solids are left on the media.

 The  mixed-media  filter is backwashed in a manner  similar to a conventional fil-
 ter. Although the filter  may  not  necessarily  be backwashed each time the adsorp-
 tion clarifier  is  flushed, the equipment  is  designed to  ensure  that a backwash
 cycle is always  preceded  by  a flushing  cycle.   The backwash cycle is illustrated
 in Figure 1II-3.

 Extensive pilot evaluations of the adsorption  clarifier package plant design have
 been conducted. Table  III-l provides a  summary  of  test results obtained at three
 sites.  More than 40 installations of these type  plants are presently in service.
 The package plant is available in  four  models  with  capacities ranging from 350 to
 4,200 gpm.  Figure III-4 is a pictorial  cut-away view of this type package plant.

 Application Criteria and Requirements

 Before  selecting a  package plant for a  particular  application,  it  must be deter-
 mined that  it  can  produce the  required quality and quantity  of water from  the
 proposed  raw  water  supply.  Package  plants characteristically have  limitations
 (especially  those  employing  high-rate  unit  processes)  related  to  the  quality
 limitations  of the  raw water supply, which must  be  recognized.  For example,  such
 factors as  low raw  water temperature, high or flashy turbidity,  excessive color,
 or  atypical  coagulant dosages  (higher than  expected  based upon normal, turbidity
 levels) may influence  the selection and  rating of  a. particular package  plant.
 The manufacturer's nameplate capacity of a package  plant may  have to  be  downrated
 or  a  larger unit selected to handle difficult  treatment  conditions. Water  sup-
 plies of  consistently  high turbidity  (greater  than  200 NTU) may require presedi-
 mentation prior to treatment  in a package plant.

 It  is recommended that all records of raw water  quality be reviewed  to  determine
 the full  range of treatment conditions  to  be  expected before  a particular  capa-
 city  package plant   is  selected.  Especially  valuable are  laboratory  analyses  of
 representative  raw  water  supplies  to provide  information  critical  to  a proper
application. Under certain conditions,  on-site pilot tests  may be justified and
                                     III-5

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warranted to verify the suitability of a package plant. This  is  especially  impor-
tant  because many  of  the new  package  plant  designs employ  high-rate,  short-
detention  time  unit  processes  which  require  close control  in  order to perform
effectively. Advance  information  on the  quality of the proposed raw  water  supply
and  its treatment characteristics  helps to ensure  a  successful installation.

Operational Considerations

Equally  important to  the  success  of  package plant applications  is  the quality  of
plant  operation.  Regardless  of the size of  the facility, if operating personnel
do not  possess  an adequate  understanding  of the  process  and equipment  they are
responsible for operating, production of a  safe and palatable finished water may
be a hit-or-miss proposition. Some manufacturers have  incorporated  automatic con-
trols such  as effluent  turbidity  monitors  that shut down the plant when the tur-
bidity  of  the  filtered  water exceeds  a  preset  limit.  This  fail-safe  device
(assuming  that  it is  not bypassed by  the  operator)  ensures that  if the plant
produces any water at  all, that  it meets a given  turbidity standard. An effluent
turbidity control device should be mandatory on all package plants, especially  if
the raw water source is contaminated.

Package plants from several manufacturers have an  accessory to automate the chem-
ical   feed  system  to  maintain a  specified  finished  water  turbidity.   This   is
advantageous where  plants do not  have  full-time  operators  and  raw water condi-
tions change frequently.

No matter what control systems are used, the burden of producing a safe palatable
water supply rests with the  operator.  In this regard,  there  is no substitute for
a well-trained  operator who  has  the  necessary skills and  dedication to operate
the equipment properly.

Most package plant manufacturers'  equipment manuals include  at  least brief sec-
tions on operating principles, methods for  establishing  proper chemical  dosages,
instructions for operating the equipment and troubleshooting guides.  An  individ-
ual  who  studies  these basic  instructions  and receives a  comprehensive  start-up
and operator training session from the manufacturer's start-up technicians should
be able to operate the equipment satisfactorily.
                                     III-6

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          The  engineer  designing  a  package plant facility should specify that  start-up  and
          training  services  be  provided  by  the  manufacturer,  and  also  should consider
          requiring  the manufacturer to  visit the  plant at 6-month  and 1-year intervals
          after  start-up  to adjust  the  equipment,  review operations,  and retrain operating
          personnel.  Further,  this  program should be ongoing and funds should be budgeted
          every  year  for  at  least one revisit by the package plant manufacturer.

e"        Cost of Package Conventional Complete Treatment-
          Costs  for  use of  package  water  treatment  plants  are  developed for surface water
          treatment plants  in Categories  1 through 6. These are presented  in Table III-2.
          These  units include coagulation, flocculation,  sedimentation, and filtration,  but
          exclude raw water  pumping, clearwell storage, and finished water pumping.

          Conceptual  Design—Cost estimates  are for  standard manufactured  units incorpor-
          ating  20  minutes  of flocculation,  tube  settlers  rated, at 150  gpd/sq ft, mixed-
          media  filters  rated'at 5  gpm/sq ft, and  a  media depth of  30  inches.  The costs
          include premanufactured  treatment   plant  components,  mixed  media,  chemical  feed
          facilities  {storage tanks and feed  pumps),  flow measurement  and control devices,
          pneumatic air supply {for plants of 200  gpm and larger) for valve and instrument
          operation, effluent and backwash pumps, and all necessary controls for a complete
          and- operable  unit  and  building.   Smaller  plants  (below 50  gpm) utilize low-head
          filter effluent transfer pumps and  are used with an above-grade clearwell. Larger
          plants gravity discharge to a below-grade clearwell.

          Operation  and  Maintenance Requirements—Process energy  requirements  are   for
          chemical  mixers,  chemical  feed  pumps,  mechanical  flocculators,  backwash pumping,
          and where applicable, surface wash pumping.

         Building energy  is  required  for  heating, ventilating and- lighting,  with  the
         latter assumed  to be 3 hours/day.  Maintenance materials are for  replacement  of
         mechanical  and  electrical  components that wear out  or break down  during normal
*
         operation.
<*•
         Chemical  Requirements—Chemicals most   commonly  used  in  package  conventional
         plants  include alum, polymer,  chlorine,  and soda ash.
                                              III-7

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 Conventional  Package  Plant  Performance - Case Histories

 EPA Survey of Six Plants—
 The widespread  acceptance of  package  plants as an  economical  solution to water]
 treatment  needs  of small systems  has  resulted in  construction of a significant
 number  of plants during  the 1970s.  The quality of water produced by these plants
 is  of  concern,  and led to  an  on-site  investigation at six selected facilities.1
 The six selected plants were in year-round operation, used surface water sources,
 and served small populations. Plants were monitored to assess the performance and
 ability to supply water meeting the interim  primary drinking water regulations.

 At  each facility, grab samples of the raw water, treated water and water from the
 distribution  system were  collected  intermittently  over a  2-year  period and ana-
 lyzed. Data on  effluent  turbidity,  total  coliforms,  and  chlorine residuals were
 recorded on  all  visits.  Table III-3  is  a  description  of the  results from six
water treatment plants surveyed during  the study.  Only three of the plants (C, T,
 and  W)  consistently  met the  1  NTU  effluent  standard.   Three of  these  plants
obtained their  raw  water from a relatively  high quality  source.  The other three
 plants  (P,  V,  and R)  met  the  turbidity  standard  on  fewer  than  one-half  the
 visits. Table III-4 is a listing of the treatment  process characteristics for the
six  plants  surveyed.  Table  III-5 compares  raw to filtered  effluent turbidities
measured during the visitations.

According to the authors of the survey, the performance difficulties  of plants P,
V,  and  R were related to the short detention time inherent  in  the design  of the
treatment units, the  lack of skilled operators  with  sufficient  time  to devote to
operating the treatment  facilities, and  {in the  cases  of  plants  V and  R)  the
wide-ranging variability and quality of the raw water source. It is reported that
the  raw water turbidity  at  the  site  of plant  V  often exceeded  100 NTU.  Later,
improvement  in  operational  techniques   and  methods  resulted  in   substantial
improvement in effluent quality.  After the adjustments were made, plant  filters
were capable of producing a  filtered water with turbidities  less  than 1 NTU even
when influent turbidities increased from 17 to 100 NTU within a 2-hour period.
                                     III-8

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 To Illustrate the importance of raw water quality knowledge prior to the applica-
 tion of  a  package  plant,  plant M was subjected  to  raw water turbidities ranging
 from 3.5 to greater than 500  NTU  for  short durations.  It was specifically stated
 by the manufacturer's  representative and supported by the product literature that
 a water with turbidity this high could not be treated satisfactorily by the plant
 selected at plant site M.

 Even though the raw water  supply for plant site P was a reservoir where raw water
 turbidities seldom  exceeded 17 NTU,  filtered effluent exceeded the 1 NTU standard
 on six of  the  nine samples taken during  the visitation. However,  at  this  site,
 equipment was  not the  source of the problem  in  obtaining a  satisfactory filtered
 water quality.  The  poor record was traced  to lack of adequate operator  attention.

 One  of  the major  conclusions  of this  survey was  that  package water treatment
 plants with competent  operators can  consistently  remove turbidity  and bacteria
 from surface waters of  a fairly  uniform  quality.  Package  plants applied where raw
 water turbidities;  are  variable require a high  degree of operational   skill  and
 nearly  constant  attention  by  the operators.  Further, it was  pointed out  that
 regardless  of  the quality  of  the  raw  water source,  all package  plants require  a
 minimum  level of  maintenance and operational skill  if  they are  to  produce satis-
 factory  water quality.

 Adsorption  Clarifier Package Plants -  Case Histories

 The performance record of  package plants   has  improved in recent years,  perhaps
 due to better equipment, more  skilled  operators, greater surveillance  by  regula-
 tory  personnel, or  a combination of these  factors. The  adsorption clarifier  pack-
 age  plant (Trident),  equipped with automatic  chemical  dosage control  appears to
 provide  consistently  higher quality finished  water  meeting  current standards in
 almost  all  instances.   Following  are  operating data  from  several   of  these
 installations:

Greenfield, Iowa—
 This  1.0  mgd plant  has been in operation  since May 1984.2  It  treats  a surface
water from  Lake Greenfield. The water contains  turbidity,  taste, odor, and  iron
                                     III-9

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 compounds.  The plant Is equipped with  powdered  activated carbon feed  facilities
 that are used when  taste  and odor are  a problem.  It  is fed to the  water as  a
 slurry in  the influent  line to the treatment plant.

 Operating  data are  summarized  in Table  111-6  for the  period  from July through
 December,  1984.  Plant  operation  reflects well the results that were obtained in
 pilot  studies conducted previously at the  site.  Alum dosages are somewhat  lower
 than used  in  the pilot  study, at 7 to 20 mg/1. Filtered  effluent quality  is  typi-
 cally  in the  range of 0.3 to  0.5 NTU, similar to  the  pilot  results.

 Lewisburg, West Virginia—
 This 2.0  mgd facility  started up  in  December 1983  as  the second Trident system
 on-line. Records  of  turbidity removals  through  the  system  for  three  months are
 summarized in  Table  III-7.  Turbidity  removal  through the clarifier is generally
 over 90 percent.

 Philomath, Oregon—
 This 1.0 mgd  facility  treats  a surface  water supply, and started up in February
 1986. A summary of operating data is shown in Table III-8.

 Harrisburg, Pennsylvania—
 The  Dauphin  Consolidated  Water Supply Company,  owned .by  the General  Waterworks
 Corporation, operates the 6th  Street Plant in Harrisburg.3 The original plant was
 constructed in 1964,  and included a circular upflow  sludge blanket  clarifier and
 stored backwash gravity filters.  The filters were subsequently  converted  to dual
media.  Due to the limited capacity  of  the clarifier,  the filters were operated in
 the  direct filtration mode at a  rate of  about 4  gpm/sq  ft. In a recent expansion
 to 9.0 mgd  capacity,  the company elected, after  pilot  studies,  to  install  three
 adsorption clarifier  units for clarification ahead of the existing filters.  These
units  operate  at  variable  rates  between 10 and   15  gpm/sq  ft,  as  shown in the
 summary of three months data shown  in  Table 111-9.

The  operating results  have  been  quite satisfactory  at  this  plant,   Turbidity
 removal through the adsorption clarifiers has been in the range  of  70  to  90 per-
cent. The  filter  run lengths  have improved to  about 26 hours, from the  13-hour
                                     111-10

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 length experienced prior  to the  installation  of the  adsorption clarifiers,  in
 spite of  flow increases  of 20 to  30  percent.

 Red Lodge, Montana—
 The plant at Red Lodge  was  started  up in January 1984.  It  is rated at 1.4  mgd.
 This  was  a  new  treatment  facility  on  a  previously  unfiltered  surface water
 supply. The  raw water quality  is quite high, as  can be seen  in Table  111-10.  Raw
 water turbidity levels  are commonly  below 1 NTU. To aid  in treatment of this  low
 turbidity cold  water,  the  plant is equipped with bentonite feed  facilities.  This
 material  is  fed  into the influent  line,  just  ahead  of alum and  polymer  feed
 points.   The  plant  is  also  equipped  with  automatic  coagulant   feed   and  pH
 controls.

 The system is routinely  producing water with turbidity less than  0.1 NTU,  consid-
 ered to be  a goal  to minimize  the potential for  Giardia  contamination. Note  that
 the clarifier effluent turbidity is sometimes  higher  than the raw water  turbid-
 ity.  This  is  explained by  the  fact  that  the  raw  water measurement  does   not
 include the  impact of the  bentonite  and alum feed.

 SLOW-SAND FILTRATION

 Recently  there  has been  an increased interest in  slow-sand filters. This interest
 has  been  expressed principally in small communities that  have a protected  surface
 watershed and provide only chlorination.  The need for multiple barriers has  been
 demonstrated  for protection  against  giardiasis. Slow-sand filters are attractive
 to small water  systems since they require little  operator attention and no chemi-
 cal  pretreatment. For proper application of slow-sand filters, the raw water must
 be of  high quality (less than 10 NTU with no color problem).

 Process Description

 Slow-sand  filters  are  similar  to   single-media  rapid-rate  filters  in   some
 respects,  yet they differ  in a number of  important  characteristics. In addition
to  the obvious  difference of  flow  rate,  slow-sand  filters: (1) function using
biological mechanisms  instead  of  physical-chemical  mechanisms,  (2)  use  smaller
                                     III-ll

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 sand  particles,  (3)  are  not  backwashed,  (4)  have longer run times  between  clean-
 Ing,  and  (5) require a ripening period at the beginning of each  run.

 Design Standards

 Design filtration rates vary from 1 to 10 million.gallons :per acre  per  day  (mgad)
 with  3  to  6  mgad the  usual  range.  Filter  sand depth  ranges  up  to 42 inches.
 Cleaning  is accomplished by scraping  off  l,or 2 .inches  from  the  surface.  Typi-
 cally, once the depth is reduced to 24 inches, new sand is added. The sand  has  an
 effective  size  of  0.25  to 0.35 mm,  and  a  uniformity coefficient of  2  to  3. The
 underdrainage system usually  is  constructed from split  tile,  with  laterals  laid
 in  coarse stone and discharging  into a tile  or concrete main  drain.  Slow-sand
 filters constructed  recently include  perforated  PVC  pipe for laterals. Slow-sand
 filters are operated continuously  under  submerged  media  conditions,  generally
 about 4 to  5 feet. Jo avoid  air  binding,:the maximum head loss across  the  filter
 should not exceed the submergence. Buildup of head loss to maximum  is slow,  vary-
 ing.from 2 or 3 days to 6 months.  Manually adjusted, weirs, outlets,  and/or  valves
 are satisfactory for flow control..

 Inlet structures may be located at one end or side of the filter. Careful consid-
 eration should be given to preventing scouring or erosion of media  during filling
 of  the  filter.  Gradual  filling of  the filter may  be. necessary  until  the   depth
 above the media  is sufficient to .allow maximum  inlet rates and no  disturbance  of
 the surface.               .

 The filtered water  outlet  is a hydraulic  control  structure  designed to maintain
 submergence, of  the media  under  all  conditions. The  difference  in level of water
 in the collection  gallery  and  the level  above the media represents the headloss
 through the media.  Figure  III-5  is a  typical covered  slow-sand  filter installa-
 tion and Figure III-6 illustrates  an uncovered slow-sand filter.

 The initial loss of  head is  only -about 0.2 feet.  When the headloss  reaches  about
 4 feet, the surface, is usually scraped. The length.of  run .-between cleanings  is
normally   20 to  60 days.4  With  varying combinations  of-raw water  quality, sand
                                     111-12

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 size,  and filtration rate, however,  runs  may be shorter or longer than  are  nor-
 mally  experienced.  Slow-sand  filters  are cleaned  by  scraping  a surface  layer
 (generally  2 to 3  inches)  of  sand and washing  the removed sand, or washing the
 surface  sand  in  place by  a  traveling washer.  Since  slow-sand  filters must  be
 removed  from service for extended  time  periods for  cleaning,  redundant  or standby
 filters  are  needed.  When .repeated  scrapings of the  sand have  reduced  the depth of
 the sand bed to  approximately  one-half of its  design  depth,  the sand  should  be
 replaced.  Filter  bed  depths  of  less than 12  to  20  inches have  been  shown  to
 result   in  poor  filter  performance.  The   replacement  procedure  should  include
 removal  of the  remaining sand down to the  gravel support, the addition  of the new
 sand  to  one-half  of  the  design  depth,   and placement  of the  sand  previously
 removed  on top  of  the new sand.

 Operating Characteristics

 As  noted above, slow-sand  filters produce  poorer  quality filtrate at  the begin-
 ning of  a run (right after scraping), and  require a filter-to-waste (or ripening)
 period of 1  to  2  daysvbefore  being used to supply the  system.5 A  ripening period
 is  an interval  of time immediately after a scraped or resanded filter is  put  back
 on-line,  in   which  the turbidity  or  particle   count  results  are significantly
 higher  than   the  corresponding .values  for a control  filter.  More  recent   work
 indicates that  scraping does not significantly affect Giardia removal,  as long as
 the sand bed has developed a mature microbiological population.6'7

 Effluent Quality Requirements
          •-          i =
 The SUTR will require utilities using  slow-sand  filtration  treatment to  maintain
 an  effluent  turbidity of less than 1  NTU.  If  more than 5 percent of the  effluent
 samples  contain greater than  1  NTU turbidity,  the system  is  not in  compliance
with  this  requirement  of  the SWTR,  unless  the utility reports  the  dates  and
 results  of total  coliform  sampling of the  filter  effluent  prior to disinfection
conducted in  the  same manner  and   frequency as the  Proposed Total  Coliform Rule,
and dates and  results  of  sampling to demonstrate that  turbidity  does not inter-
fere with total coliform measurements.  If  a turbidity  greater than or equal  to 5
 NTU is detected at any time, the system is  not in compliance.
                                     111-13

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Laboratory and Pilot Plant Studies

A  14-month pilot  study  evaluated  the  effectiveness of  a slow-sand  filter  to
remove turbidity  and  coliform bacteria  from a surface  water  supply.5 The  pilot
filter contained a 37-inch-deep, 0.32 mm effective size  sand bed and was  operated
at a  filtration rate of 0.05  gpm/sq  ft (3 mgad). After.an  initial 2-day  ripening
period,  effluent  turbidity was  consistently  near  or  below  0.1  NTU  at  applied
water  turbidities  which  averaged  4  to  5  NTU.   Coliform bacteria  removal was
always 99.4 percent or  better' reaching  100 percent  in one  filter  run. Removal  of
Giardia  cyst-sized  particles  (7 to  12 ym  size  range)   averaged 96.8  percent  or
better for all test runs. Even though  Giardia removal was  not measured directly,
the results of this study clearly established the suitability of  slow-sand  filt-
ration as  a viable  technology for producing  high quality  filtered water.5  Other
studies,  like  those described below,  have confirmed that the biological action  in
a  sand bed adds significantly to  Giardia removal,  so  that higher removal  rates
than  those found for inorganic particles can  be expected.

Treatment efficiency of slow-sand filtration was studied under various design and
operating conditions to  ascertain  removal of  Giardia  Iambila  cysts, total  coli-
form  bacteria,  standard  plate  count   bacteria,   particles,  and turbidity.6.7
Filter removals were assessed at hydraulic  loading rates  of  1 mgad, 3 mgad, and
10 mgad; temperatures  of  0°,  5°, and 17°C;  effective sand sizes of 0.128,  0.278
and 0.615 ym;   sand bed  depths of 0.48 and 0.97 mm;  influent Giardia cyst  concen-
trations of 50 to 5,000 cysts/liter;  and various conditions of filter biological
maturity and influent bacteria concentrations.

Results  showed that slow-sand filtration is effective in removing microbiological
contaminants.  Giardia cyst removal was consistently  greater than 99.8 percent for
a  biologically mature fully  ripened  filter.  Total  and fecal coliform removal was
approximately   99  percent. Particle  removal  averaged  98  percent.  Standard  plate
count bacteria removal   ranged from negative  removals  to 99 percent, depending  on
the influent concentration. Turbidity displayed  a unique ability to pass  through
the filters, a characteristic not previously reported,  and removal ranged from 0
to 40  percent.  It  is  entirely possible that  the  particles measured as turbidity
                                     111-14

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 in this water supply were too small to  be  captured by the filter or perhaps were
 charged such that  they  were repelled by the  filter media and passed  through  in
 the effluent.  Some  of  the turbidity  could also be due to debris sloughing off the
 filter. Operating results from Waverly,  New York, tend to substantiate the former
 possibilities.8

 Changes in  process  variables resulted  in  decreased coliform  removal  efficiency
 for increased  hydraulic  loading rate, increased  sand size, decreased  bed  depth,
 and decreased biological  activity. Giardia  removal  was influenced by  the biologi-
 cal  maturity of  the filter, but  not by the variables  mentioned above.  During
 filter  start-up,  Giardia  removal  was 98  percent; and  once  the  filter was mature,
 removal  was  virtually complete.6*7

 Costs of Slow-Sand  Filters

 Conceptual Design—
 The slow-sand  filter  systems  are  based on  use of  a  cast-in-place,  concrete-
 covered  structures  for use in Categories 1 through 3 and  uncovered  earthen  berm
 structures for  Categories 4  through  7. Slow-sand filter systems  are  sized  on the
 basis of a filtration rate of 70 gpd/sq  ft  (3 mgad). The depth  of  the sand  bed  is
 3.5  feet over 1  foot  of  support  gravel. A supernatant box height  of 4 feet  is
 provided above the filter surface.
                           • v  .

 Covered  filters  incorporate  below-grade concrete structures with beam  and  slab
 covers.  All.*  piping  is  either cast  iron or steel  and is also below grade. Because
 slow-sand filters operate most  efficiently  at a  constant  filtration rate, flow-
 meters  for   each  filter  and a  below-grade,   concrete clearwater  reservoir are
 included. The  rate of  flow  through the filter is  established  by an  individual
 control valve for each filter in an  effluent flow control structure.

 Uncovered,  slow-sand  filters include  on-grade,   clay-lined structures  formed  by
 earthen  berms.  All  piping is PVC  and  is below grade.  A steel  tank reservoir,  an
effluent flow control structure, and a flowmeter  to measure total plant  flow are
also included.
                                     111-15

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Capital  costs  for  slow-sand filters conforming  to the above  design  concept are
provided in Table III-ll.

Operation and Maintenance Requirements-
Process energy requirements are negligible.  Building  energy requirements are for
heating, lighting,  and ventilation of the control and storage building.

Maintenance material requirements  are based upon anticipated costs of replacement
parts and  replenishment  of the minor  amount of consumable supplies  involved in
daily operation. The  cost of  replacement  sand  is not  included.  Experience with
operating filters suggests that careful  cleaning allows resanding to be necessary
as infrequently as every 10 years.

Labor requirements  are developed assuming  the  filters operate  unattended. They
include a  short  daily inspection and  control  valve  adjustment,  daily turbidity
measuranents,  quarterly  cleanings  of   each  filter  by  hand,  normal   repair and
replacement  of  equipment.  Table  III-ll  provides a  summary  of operation and
maintenance costs for the seven design flow categories.

Case Histories

Survey of 27 Plants—
A  survey  of 27  slow-sand  filtration  plants in the United  States indicated that
most of  the plants  serve  fewer than 10,000 persons,  are  more than 50 years old,
and are effective and economical to operate.9 Most facilities surveyed used  lakes
or reservoirs  as raw  water sources.  Filtration rates  ranged from less than 0.3
mgad to about  13 mgad.  Fifty  percent of the plants have filtration rates in  the
2.6 to  6.4 mgad range. Filter media depths fall  between 15  and  72  inches. Most
installations  use sieved sand  with  effective  sizes averaging 0.2 to 0.4 mm. Sand
uniformity  coefficients varied from 1,4 to 3.5.

Figure  III-7   presents  average raw water  turbidities  for  the  slow-sand  filter
plants surveyed. About 50 percent  of the plants process raw water with an average
turbidity exceeding 2  NTU.  All plants  surveyed treat  raw water with  turbidities
of less than 10 to 12 NTU.
                                     II.I-16

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'-*•
 Figure III-8 shows that 85  percent  of the plants1 produce  average  filtered water
 with  less  than  1  NTU, and 50  percent average   less  than 0.4  NTU.  One  plant
 reported  average  filtered  effluent  turbidities  of  less than  0.1 NTU.  Average
 annual coliform concentrations  in the raw water are shown in Figure 111-9.  Figure
 111-10 shows for  the three plants  reporting that  90  percent  of  the  facilities
 maintained effluent  coliform levels  of 1/100  ml or less.

 Filter cycle durations vary seasonally. The  mean  length of  filter cycles  ranged
 from 60 days in winter to 42 days in  spring.

 New  York  State—
 A  study  was performed at  seven  slow-sand filter  installations in  New York  to
 assess the  impact  on  filtered water quality of  the, cleaning  procedure  which
 involves  scraping a  thin  layer  of   sand  from the surface  of  the filter.8  The
 performance  of  each filter was  monitored before and after the scraping  procedure.
 Effluent  samples  were analyzed  for  turbidity,  total  particle  count,  standard
 plate  count,  and total  coliforms.  Table 111-12 lists the characteristic  features
 of the seven facilities.

 Table  111-13 is a summary  of  the data collected  during  plant  tests designed  to
 determine  the  impact  of  filter  scraping  on  filtered  water quality  during  the
 ripening  period.

 It  is  noted  in Table  111-13,  that  even  during  the  ripening  period,  filtered
effluent turbidities at all but the Waverly installation did  not exceed 0.43 NTU.
At the Waverly  facility,  it appears  that  the raw  water  contains submicron  par-
ticles  which  scatter  light  and  increase the turbidity,  but are not efficiently
removed by  slow-sand  filtration.  According to  the  particle  count  data, Waverly
removes particles larger than 2 pm as  efficiently as the  other plants visited.

Turbidity data  from  the control filters which have been  in service for  at  least
one month, typifies the performance, of these facilities.

The  study  included a  comprehensive  evaluation of  total .particle count,  standard
plate  count,  and coliform  removal  from both the  ripening  filter  and  a control
                                            LI 1-17

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filter. In general,  removal  of total particles  in  the size range 2  ym to 60 ym
measured by a total particle counter,  ranged  from 90 to 99.8 percent. Filtration
generally reduced the  total  plate count, however,  results  were widely variable.
Removals ranged  from  greater than 50  percent to no  removals.  Coliform removals
through the ripening and control filter were only measured at two facilities. One
facility achieved 98.5 percent  removal of coliform  organisms  after completion of
the ripening period..

Mclndoe Falls, Vermont—
A  2-year  study  at Mclndoe  Falls,  Vermont,  was  conducted to  evaluate the effec-
tiveness of a slow-sand filter for removal of turbidity, bacteria, coliforms, and
Giardia  cysts.10  The  community obtains  its  water  from two  impoundments which
capture water from two  springs.  The  ponds  are shallow and contain several beaver
dams and lodges. Because of  the presence of beavers, giardiasis was  a major con-
cern. Raw water quality is generally quite good with turbidities ranging from 0.4
to 4.6 NTU with a seasonal average of 2.1 NTU.

The  two  filters  have  an  individual  area  of 400  square  feet. They contain 42
inches of 0.33 mm effective size silica sand and have a  design  filtration  rate of
2.05 mgad. During the  evaluation, the following  results  were achieved:

t   Removed  turbidity  to less  than  1  NTU,  99.19 percent of  the time (after the
    first  100 days  of operation, .the  effluent values  were  below  1 NTU, 99.68
    percent  of  the  time)  and 72  percent  of the time the values were 0.2  NTU or
    less  (raw water  1.45 NTU or  less, 72 percent of the  time).

•   Reduced  total  coliform  to  10/100 ml or  less,  86  percent of  the time (raw
    water 1300/100 ml  or less, 86 percent  of the time)  and standard plate count
    to  10/ml  or  less, 94  percent  of  the  time  (raw water  500/ml   or  less,  94
    percent of the time) under  ambient load conditions.

•   The  average  coliform  content in  the filter effluent under  ambient conditions
    was  4 organisms/100  ml  (raw water  440/100 ml)  for total  coliform,  and 15
    heterotrophic organisms per ml (raw water 520/ml) for standard plate count.
                                      111-18

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 •   Removed  massive spikes of  total  coliform and  standard  plate count  bacteria
     from  raw water  at temperature conditions above  the range of 5 to 10°C.

 t   Did not  remove  bacteria  as  efficiently at temperatures below 5°C and partic-
     ularly around  0 to 1°C. Spiking  studies  demonstrated the temperature effect
     with  removal of total coliform deteriorating from 98 to 43 percent, and stan-
     dard  plate count  from 98  to 80  percent  in 9 days at  1°C. At 6  to 11DC,
     removal  remained  at  an average of 99  percent for total  coliform and 97 per-
     cent  for standard plate count during a  15-day spike.

 •   Removed  Giardia cysts very  dependably,  99.98  percent or  better,  under warm
     temperature conditions.

 •   Did not  remove Giardia cysts  as  completely at  low  temperatures.  Under 7°C,
     99.36 to 99.91  percent removal was achieved.

 •   During  cold water conditions  (below  5°C and particularly  around  0° to 1°C)
     the biologic treatment process  in the  slow-sand filter was less effective in
     ranoving  bacteria  and  Giardia   cysts.  Cyst  removal  was  reduced   to  93.7
     percent, and total  coliform and standard plate count removals  dropped to 43
     percent  and 79  to 82  percent, respectively.

 Village of 100 Nile House, British Columbia, Canada-
 Outbreaks  of waterborne  giardiasis  occurred at the Village of  100  Mile House,
 British Columbia,  Canada,  in 1981,  1982,  and 1983  with  60,  50,  and 30 confirmed
 cases, respectively, for  a service  area  population  of about 2,000 persons.11  The
 source was suspected  to  be beavers and muskrats subsequently  confirmed positive
 for  Giardia cysts and located upstream of the Village's surface water intake.  The
 addition  of  chlorine  solution,  with minimal  contact time provided in the distri-
 bution system, was the only treatment practiced.

 The  slow-sand  filtration  and chlorination  processes were chosen  after completion
of  successful  pilot studies  by the Village  for  incorporation in the  new water
treatment   facilities.  Construction on  the  water treatment plant was  completed
                                     111-19

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December 1984. A detailed evaluation of the plant was undertaken between  November
 15,  1985,  and  November 15,  1986.  Of  prime  concern  was whether  the slow-sand
filters were  effective  in  removal  of  Giardia  cysts. The  plant  includes a surface
water  intake, raw  and  treated  water pumping  stations,  chlorine  equipment  and
contact tank, a  clear well,  and three slow-sand filters. Each  of the three  cast-
in-place  concrete  slow-sand  filters  are  141-feet-long,  20-feet-wide, and  12 feet
6  inches  to 13  feet  3  inches deep (top  of wall  to top  of  floor)  for a  surface
area  of  2,820 square feet each  cell.  The total surface  of  the three filters  is
8,460  square  feet. The  filters are covered  with  precast panels  and the filter
walls  are insulated with rigid insulation and  backfilled with soil for full depth
to moderate against cold temperatures.

The  filter  media  was produced by  the washing, drying,  and sieving  of  natural
material  from one  site  located in the vicinity of  100  Mile House. The effective
size  of  filter  media, based  on samples  taken after placement  of the materials,
ranges between 0.20 mm and 0.30 mm with an average value of 0.25 mm. The  uniform-
ity coefficient  ranges  between 3.30 and 3.80 with  an  average value of 3.50.  The
depth  of media at startup was 45 inches.

The three  slow-sand filters  are typically  operated at rates up  to the  accepted
maximum unit  flow  of  640,000 gpd per  filter  or 1,917,000 gpd for three  filters.
The design  filtration rate is approximately 0.16 gpm/sq ft or 9.9 mgad.

Operating Results—Removals  of a wide range  of particles were measured  for .the
treatment plant.  As illustrated in Figure  III-ll, Giardia cysts were detected in
11 of the 21 raw  water samples, with counts as high  as  300 cysts.  Zero cysts were
detected in every sample of the filter effluent.

As illustrated in  Figure 111-12, the  turbidity  in  the raw  water  varied  between
0.15 NTU  and  3.5 NTU. The filtered water turbidity varied between  0.26  NTU and
1.15 NTU.  Generally better reduction was  observed in the  period June to November
1986 when the raw and filtered water turbidities ranged  between 0.4 NTU and  1.17
NTU and 0.15  NTU  and  0.62 NTU, respectively.  Increased removal seemed  to  occur
with  a maturing  filter.  Also, an  increase  in  filtered   turbidity  was  noted
immediately after filter cleaning.
                                     111-20

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 Operating cycles between filter cleanings  ranged  from a minimum of 52 days to  a
 maximum  of 215 days.  The longer cycles were experienced during winter and spring
 months.   Increased  solids  loadings during  late spring  and summer  (algae)  into
 early fall contributed  to  shorter  operating  cycles.

 Cost—The total  construction  cost  in 1984  for  the  slow-sand  water  treatment
 plant was $780,000  Canadian. Annual operating costs were determined to be $20,700
 including chlorination,  power, daily inspection, cleaning, and media replacement.
 The plant was  inspected  every day  for 0.5 to 1.0 hour. About 16 person-hours were
 required  for  cleaning  of  one filter,  with a  cost  of about  $225/cleaning.  The
 total  unit cost  of  water treatment was determined  to be $0.96 Canadian per 1,000
 gal Ions.

 DIATOMACEOUS EARTH FILTRATION
 General
Diatomaceous  earth  filters consist  of a  layer  of diatomaceous  earth  about 1/8
inch  thick  supported on  a  septum or  filter  element.  The thin  precoat  layer of
diatomaceous  earth  is subject  to  cracking  and must be supplemented by a continu-
ous body  feed of  diatomite.  If no body feed is added, the particles filtered out
will  build  up on  the surface  of  the filter  cake  and cause  rapid  increased in
headless. Figure 111-13 illustrates a typical  pressure diatomaceous earth filtra-
tion system.  The problems  inherent  in  maintaining  a perfect  film of diatomaceous
earth  between filtered  and  unfiltered water  have  restricted the use  of  diato-
maceous  earth filters  for municipal  purposes,  except  under certain  favorable
conditions.

An advantage  of  a diatomaceous earth  filtration plant for potable  water  is the
lower  first cost of  such  a  plant.  On waters containing low suspended solids, the
diatomaceous  earth  filter installation cost  should be  somewhat lower  than the
cost of  a conventional  rapid-sand  filtration plant.  Diatomaceous  earth filters
will   thus  find  application   in  potable  water  treatment  under  the  following
conditions:
                                     111-21

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•    In cases where  the  diatomaceous earth filtration  plant  will  be found to be
     capable of  processing  the raw water supply  and  to produce water at a lower
     total cost than any practical alternative.

•    In cases where  financial  capacity is tightly  circumscribed,  when the lower
     first  cost  of  a  diatomaceous  earth  filter  installation  may  be  the major
     factor in the final choice of plant.

•    For  emergency  or standby  service at  locations  experiencing  large seasonal
     variations  in water demand,  when the  lower first  cost  of the diatomaceous
     earth filter may prove to be economical.

Some of  the  important  operating characteristics  of diatomaceous  earth filters
have been summarized:12

•    A precoat of 0.1 to 0.2 Ib/sq ft is applied to prepare the filter.

•    A continuous  feed  of filter aid  as  body  feed  is  necessary to prevent  the
     cake from clogging with the particles  being filtered out.

•    Acceptable cleaning of the filter will maintain  at least 95 percent of the
     septum area available for flow after 100 filter run cycles.

•    Because of the precoat, diatomaceous earth filters  do not require filter-to-
     waste upon startup.

•    If the flow to  the filter is disrupted, the  filter cake drops off the sep-
     tum.  When  the filter  is  restarted,  clean  diatomaceous  earth  and filtered
     water should be used to recoat the filter  to reduce the potential  for pass-
     age  of pathogens.

•    It may be  necessary to adjust the body  feed  rate  in proportion to the  raw
     water turbidity  to prevent short runs.
                                     111-22

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 0    Although  filter  runs  can  be  2 to  4 days  long,  decomposition  of  organic
      matter trapped  in  the filter  cake  may  necessitate shorter  runs  to  avoid
      taste and odor problems.

 •    Vacuum diatomaceous  earth  filters  offer the  advantages of  not  requiring
      pressure  vessels  and being visible during backwash;  however,  they  have the
      disadvantage  that the increased potential  for release of  gases,  which can
      cause shorter  runs.

 •    Diatomaceous  earth  filters  can provide  very  effective  removal of cysts,
      algae,  and  asbestos.  In  some cases,  alum-coating  of the  diatomaceous  earth
      improves performance.

 •    The  rate  of  body feed and  size of diatomite  used  are  critical  variables
      affecting the  length of run.

 Desiign Criteria

 The minimum design criteria presented in the Ten State Standards for diatomaceous
 earth filtration are considered  sufficient  for the  purposes  of the SWTR with the
 following  exceptions:

 •  .   It is recommended that the quantity of precoat be increased to 0.2 Ibs/sq ft
     of filter area, and that the minimum  thickness of the precoat filter cake be
     1/8 to  1/5  inch.  Studies  have shown that  a  precoat thickness  of 0.2 Ibs/sq
     ft was most  effective in  Giardia cyst removal and that the precoat thickness
     was more important than the grade size in cyst removal.

•    It is recommended that treatment plants be encouraged to provide a coagulant
     coating (alum or suitable polymer)  of the body  feed. Although enhancement of
     the diatomaceous  earth is  not  required for Giardia  cyst  removal,  coagulant
     coating of the body feed has been  found to result in a significant  improve-
     ment  in percent removals  for viruses, bacteria and turbidity.
                                     111-23

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Operating Requirements

Operating  requirements specific to diatomaceous earth filters  include:

•     Preparation of body feed and precoat
•     Verification that dosages are proper
•     Periodic  backwashing and disposal of  spent filter  cake
•     Periodic  inspection of the septum(s)  for cleanliness  or damage
•     Verification that  the filter is  producing  a filtered  water that meets  the
      performance criteria

Effluent  Quality Requirements

The  SWTR  requires  that systems using  diatomaceous earth  filtration maintain an
effluent  trubidity  of  1  NTU.  If  more  than  5 percent of the  monthly effluent
samples contain turbidities  greater  than 1 NTU, the  system is not  in compliance
with  this requirement. In addition,  if any instantaneous filter effluent turbid-
ity exceeds 5  NTU, the system is not in compliance.

Treatment Capability

A study was conducted at Colorado State University to determine the effectiveness
of diatomaceous  earth filtration for  removal  of  G i a r d ia cysts.13  In  addition,
removals of  turbidity,  total coliform bacteria,  standard plate  count  bacteria,
and particles were determined. Parameters evaluated included type of diatomaceous
earth, hydraulic  loading  rates,  influent concentrations  of  bacteria and Giardia
cysts, headloss, run  time,  temperature,  and the use  of alum-coated diatomaceous
earth.

Hydraulic loading rates imposed were 1,  2,  and 4  gpm/sq ft.  Seven grades of dia-
tomaceous earth were used.  Temperatures varied  from 5° to 19°C; concentrations of
Giardia cysts ranged from 50 to  5,000 cysts/1;  and bacteria densities varied from
100 to 10,000/100 ml.
                                     111-24

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 The  results  of  this  study  showed that diatomaceous earth filtration 1s an effec-
 tive  process for water treatment.  Glardla  cyst removals were greater than 99.9
 percent  for  all  grades  of  diatomaceous  earth tested,  for hydraulic loading rates
 of  1.0 to 4.0  gpm/sq  ft,  and for all temperatures tested.  Percent reduction in
 total  coliform  bacteria, standard  plate  count bacteria,  and turbidity are influ-
 enced  strongly  by  the  grade  of diatomaceous earth. The coarsest grades of diato-
 maceous  earth recommended  for water  treatment will remove greater than 99.9 per-
 cent  of  Glardia cysts, 95 percent of cyst-sized  particles,  20  to 35 percent of
 coliform  bacteria, 40 to 70  percent  of  heterotrophic  bacteria, and 12 to 16 per-
 cent  of   the  turbidity  from   Horsetooth  Reservoir  water. The use of  the finest
 grade  of  diatomaceous  earth   or  alum coating on the  coarse  grades will  increase
 the effectiveness of the process,  resulting  in 99.9 percent removals of bacteria
 and 98 percent removals of turbidity.

 Diatomaceous  earth filtration  was evaluated  at  Mclndoe Falls,  Vermont,  during
 parallel   studies with slow sand  filtration.10 Filtration rates averaged 1 to 1.8
 gpm/sq ft on the 10  to  20  gpm pilot pressure unit. The key conclusions from this
 study  are as follows:

 •    Pressure diatomaceous earth   filtration removed Glardla cysts dependably,
     providing 99.97 percent   reduction.

 •    Total coliforms were  reduced 86 percent or  more in 70  percent  of  the sam-
     ples, and  standard plate count  bacteria were reduced  80 percent  or more in
     70 percent of the samples.

 •    The  average bacterial content in the effluent under ambient  conditions was
     38/100 ml for total coliforms and 6/ml  for standard plate count bacteria.

 Malina et al,  reported that  a  high  percentage of removal could be  attained for
pollovirus when  coated  diatomaceous  earth  filter  aid was used  or when  cationic
polymer was  added  to the  raw water.114   In  one 12-hour  filter run,  diatomaceous
earth  coated with  1  mg of cationic  polymer per gram of  diatomaceous  earth  pro-
duced filtered water in which  no viruses  were recovered  from 11 samples (removal
>99,.95%). In another run,  one of  12 samples  was positive,  and in  this instance,
                                     111-25

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virus  removal  was 99  percent.  In a  12-hour  run in which  uncoated diatomaceous
earth was used, but 0.14 mg/1  of  cationic  polymer was added to the raw water, no
viruses were recovered from any of the 12 samples analyzed.

Costs for Diatomaceous Earth Filtration

Costs  for  diatomaceous earth filtration of  surface water  in  plant Categories 1
through  10  are shown  in  Table 111-14.  Pressure diatomaceous  earth  filters are
assumed in these samples.

MEMBRANE FILTRATION

Introduction

Membrane or  ultrafiltration  is  a  process which  utilizes  a hollow fiber membrane
to remove undissolved, suspended or emulsified solids from water supplies without
requiring coagulation. There are a variety  of hollow fiber membranes of different
size and  porosity,  and systems wherein  the  feed water is  applied  either  to the
inside or the outside of the membrane.

The  traditional  ultrafiltration  process  applies feed  water  to  the  inside  and
collects permeate on the outside of the membrane. Systems  of this design are most
generally used in specialized applications  requiring extremely high purity  water,
as pretrestment prior to reverse  osmosis or  for  removal  of colloidal  silica from
boiler feed water. Application to  potable water treatment  would be limited  to the
production of  extremely  high quality  water  supplies of low turbidity  (1  NTU or
less) and with Fouling Indexes of  less than 10.

In this type of system, the hollow fiber membrane, which operates over a pressure
range  of  (10 to  100  psi),  excludes  particles  larger  than 0.01 v.m;  but  unlike
reverse osmosis membranes,  permits passage of inorganic  salts and electrolytes.
Bacteria, Giardja  cysts,  and  some  virus particles  are removed by the smallest
size hollow fiber membranes. The  hollow  fiber  membranes are contained in a pres-
sure vessel  or cartridge. During  operation, the  flow is  introduced to the  inside
of the fiber. Filtrate or  permeate collects  on the  outside of the membrane, con-
centrates at the end of the hollow fiber and is discharged to waste. In a typical
                                     111-26

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 single-pass application,  90 percent  of  the feed water is  recovered  as  permeate.
 The membranes are  cleaned  by  backflushing which  restores  the original  porosity
 and allows continuous  use for  indefinite periods.  In  some applications  a chlorine
 solution is added to the  backflushing flow.

 Hollow fiber membranes are  sensitive to the concentration of  suspended and col-
 loidal  solids in the feed water. The  flux  level {volume  of permeate  produced per
 unit area of membrane per day) and the  flux stability  are  influenced by the feed
 water quality,  the  filtering  cycle duration,  and the  quality of water  used for
 backflushing the membranes. Where  a  water supply has  a Fouling  Index  of  10  or
 less (typical  of most  groundwaters and high clarity  surface waters),  filtering
 cycles  will range up  to  8 hours with about  a  10 percent  reduction  in  flux.  In
 general,  capacity  can  be restored to nearly  clean  membrane values  by a  fast-
 forward flush of influent  to  waste.   However,  after  two  or three flushings,  the
 membranes must be backwashed to  restore  the initial flux  level.

 To overcome the  rapid fouling  and loss of  flux  rate  over a relatively short time
 period,  one  manufacturer (Memcor)  has  introduced a self-cleaning  hollow  fiber
 membrane  filtration system that  introduces the feed stream  tangentially to  the
 outside of  the  fiber.  The filtrate  is  collected  in  the hollow  interior of  the
 fiber and the rejected stream of concentrate is  either recycled or discharged.
 Continuous  recycling permits extremely high filtered .water  recovery with  the only
 water loss  from  the system being that associated with wasted  sludge  and  cleaning
 solution.  Recovery  rates  of  99 percent are  claimed by one manufacturer.

 The  outside-to-inside  hollow  fiber  filtration  system  uses  a  more  porous  (70
 percent)  membrane with a  0.2 um  (nominal)  pore  size  which  allows application  of
 water containing higher  suspended  solids  concentrations.  However, it  can  still
 produce a  product water meeting  present  drinking water  turbidity standards,  will
 exclude all  Giardia cysts,  and can remove  coliform and other bacteria.   The  pore
 size  of these membranes is. too large to  provide  effective virus removal.

 Membrane Cleaning

 In traditional inside-to-outside hollow fiber membranes,  cleaning is accomplished
by backflushing,  which  restores  the original porosity  and  allows continuous use
                                     111-27

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for indefinite periods. In some  applications  a  chlorine solution is added to the
backflushing flow.

Fouling has  been  a  major  problem, limiting the application of hollow fiber mem-
brane technology. To  prevent fouling,  one  manufacturer has  developed  a unique,
self-cleaning  "radial  pulse" system.  Gas  is  periodically injected,  under high
pressure,  into the  center of the  hollow fiber. The  specially designed membrane
expands as the gas accelerates through the fiber, explosively removing the resid-
ual layer of rejected material. This  radial  pulse system minimizes flux decay,
eliminates product loss, and does not require auxiliary pumps.

The impact  of  the radial  pulse  cleaning  procedure  on filtration rate is to pro-
long the operation until chemical cleaning of the membrane is required to restore
the original  flux rate.  Figure 111-14 shows the  operating mode  and  the radial
pulse cleaning sequence.

After several repeated intermittent radial pulse cleaning  cycles, chemical clean-
ing of  the  hollow  fiber  membrane is  needed to  restore  the  original  capacity.
This cleaning is done with the  aid of  a chemical  cleaning solution. The cleaning
solution is prepared with a  caustic-based detergent and hydrogen peroxide disin-
fectant. Typically,  cleaning is practiced once per week or more frequently if the
raw water suspended solids  content causes more rapid  membrane fouling. In cases
where the supply contains  iron,  an occasional  cleaning with hydrochloric acid may
be  necessary.  Spent  cleaning  solution  must  be disposed  of  in  accordance with
local   regulations. -Small  quantities  could be  discharged  to a  sanitary  sewer.
Larger  quantities  would  require accumulation  and disposal  in  accordance  with
local  regulations for nonhazardous detergents.

Typical Installation

A typical  membrane filtration installation  for  a small  water supply system would
include a  skid-mounted filtration unit,  as illustrated in Figure 111-15, contain-
ing the hollow fiber membranes  in cartridges,  automatic and manual  valves  for
backflushing and  unit  isolation,  flowmeters,  pressure  gauges,   integral  supply
pump,  and control panel.  A  separate  supply pump would  be  required, as  would all
                                     111-28

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 interconnecting  piping  serving  plants  with multiple  units.  Storage  tanks and
 chemical  feed pumps  for membrane  cleaning solutions  would be  needed.  Product
 water storage with  chlorination provisions  would also be  required.

 Table  111-15  provides  physical  information from  one manufacturer  on membrane
 filtration  systems  capable  of processing up to 300.gpm.  The extreme compactness
 along  with  the  simplicity  of  the  process  makes.  it  attractive   for  small
 installations.        .                               .   *

 Figure 111-16 illustrates a complete system  including provisions to clarify  back-
 flush water containing concentrated solids.  A  small  clarifier with facilities to
 add  a coagulant  are needed. Clarified water is either recycled or discharged to
 an  acceptable disposal location.  The  concentrated  sludge  with properties  similar
 to  those experienced  in conventional  water treatment  practice may  be  dried and
 disposed  of  as  landfill  or hauled  as a semi-solid to  an  appropriate disposal
 site..

 Performance Capabilities

 Giardia Removal —
 An evaluation of the  efficiency of  the Memcor  hollow fiber filtration system for
 removal of Giardia  lamblia  cysts  and  bacteria was  conducted  by the Department of
 Pathology at Colorado State University.15 The results showed the 0.2 urn membranes
 to be 100  percent  effective in removing Giardia cysts  at applied concentrations
 approaching 1,100 cysts/liter. The test  also showed  that  the radial  pulse clean-
 ing  procedure  effectively  prevented  fouling of the membranes and  purged cysts
 from the system.

 Coliform Removal--
A  second  series  of tests  were also  conducted at  Colorado  State University to
 establish the membrane removal  efficiency of E.  coli  bacteria.15 A tap water sam-
ple was  seeded with 2-3  x  10; organisms per 100 ml  and exposed  to  the membrane
 filtration unit.  The  test  run,  which  extended   over  130 minutes,  produced  a fil-
trate with <1 coliform organism per 100  ml.  No  membrane breakthrough was experi-
enced during  this 3-test  run evaluation.
                                     111-29

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Turbidity Removal —
Prior  to introducing  the  intermittent,  air-assisted  cleaning procedure, hollow
fiber  membranes were  subject  to rapid  loss  of  operating  flux or  rates as  the
membranes were  fouled  by suspended  solids  in  other than low turbidity water sup-
plies.  Recent  testing  of the radial pulse  system has revealed satisfactory per-
formance on water samples to which bentonite clay was added to impart turbidities
as  high as  30 NTU. Under these  conditions  a  filtrate with 0.2 NTU turbidity  was
obtained. Actual  field tests  on raw water with turbidities  of  190 NTU yielded
finished  water turbidities  of  0.6  NTU.  Tests  in  Colorado  on  natural  surface
waters  with turbidities in the 2.4 to 3.0 NTU range provided filtrate turbidities
of 0.57 to 0.25 NTU.

Capital Costs

The  application  of membrane filtration  to potable water  treatment  has not been
extensive. Therefore,  capital cost  information  is based upon estimates with very
little  supporting construction cost experience. Table 111-15 lists general design
parameters and  information  used to  develop cost estimates.  Table 111-16,  using
estimated costs developed by CWC-HDR  under contract to US EPA provides estimated
construction  costs  for  systems  of  the  capacities  listed  and  includes:  skid-
mounted membrane  filtration  units  containing the hollow-fiber membranes  in car-
tridges; automatic  and manual  valves for  backwashing and unit  isolation;  flow-
meters; pressure  gauges;  integral  backwash pump;  and control  panel.  A separate
supply  pump  is included, as  is all  interconnecting piping serving  plants  with
multiple units.19  The  costs also  include  storage  tanks and  solution  pumps   for
membrane cleaning  and  an air compressor.  Housing is provided  for equipment   and
supporting appurtenances.  Product  water storage  facilities  are  not  included  in
the  cost estimates. The  cost estimate excludes  filtrate chlorination facilities.
The  costs  do  include  limited  site  preparations,  a  backflush clarifier, and a
design  cost allowance.

Application Concerns

Membrane Failure--
Membrane filtration  systems  provide only  one  barrier  to  the passage  of poten-
tially  pathogenic  microbial  contaminants   into  the  finished  water. A  membrane
                                     111-30

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 failure would permit a direct bypass of unfiltered water into the filtered water.
 The Memcor system provides a membrane  integrity check  system that can be used to
 manually, or automatically verify  that  even a single membrane within  a cartridge
 has broken. The equipment can  either be shut down by  such a failure  or,  prefer-
 ably, initiate an  alarm signaling  the need for operator attention.

 Organics Removal —
 The larger membranes (0.2 iini) will not  effectively remove materials  contributing
 to color in raw water supplies.  The  smaller (0.01  urn)  inside-to-outside membranes
 will  remove some  smaller  molecules,  but may  not  totally remove  dissolved  mate-
 rial;;  of subcolloidal  size. However,  where  a  raw water  contains  organics  contrib-
 uting  to color, such as humic and fulvic acids, alternative  treatment techniques
 may be required for  removal of  these  contaminants.

 Pilot;  Testing-
 Experience  with hollow  fiber filtration of  potable  water supplies   is  limited.
 Although it is  used  extensively  in the  medical and electronics fields  for  polish-
 ing of process  water usually  obtained from  domestic service taps,  only one drink-
 ing v/ater facility (Keystone  ski area)  is known to use  the newer membrane  filtra-
 tion  process.   To  establish  appropriate design criteria  and  establish operating
 parameters,  pilot  testing  of  any surface water supply is  recommended.

 CARTRIDGE FILTERS

 Equipment Description

 Cartridge filters  using microporous  ceramic  filter  elements  with  pore sizes as
 small  as 0.2 ^m   may  be  suitable  for  producing  potable water from  raw water
 supplies containing moderate levels of turbidity,  algae, and microbiological con-
taminants,  according  to Kutadyne  Products  Incorporated's   literature.  Single-
filter elements may be manifolded in a pressurized housing to produce  flow capac-
ities  approaching  24 gpm  (34,000  gpd)  from a single assembly.  The clean filter
element  pressure drop  is about  45 psi  at maximum  capacity. The  ceramic elements
are cleaned when the  pressure drop reaches 88 psi.
                                     111-31

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Cartridge Cleaning

Cleaning  is  accomplished  by opening the  filter  housing and scrubbing each  indi-
vidual  vertical  filter element  with  a hand-operated  hydraulically  driven  brush
that  fits over  each element.  An  additional  feature offered with  one manufac-
turer's  equipment is  the  incorporation  of finely  divided particles  of silver
within the ceramic matrix,  which prevents the  growth of bacteria in the element.
Other  manufacturers  utilize, disposable  polypropylene filter  elements  in multi-
cartridge stainless steel  housings. These units are available  in capacities  rang-
ing  from  2  gpm to  720  gpm. Membrane pore  sizes  range from 0.2 urn to  1.0 ym in
equipment suitable  for  producing potable water.  A disadvantage of  the polypro-
pylene membrane  is  that it may  be  cleaned  only  once and  then must  be replaced.
However,  according  to manufacturers'  guidelines,  filtration  of a  low turbidity
surface  water (2  NTU  or   less) could be  expected  to provide service  periods
between filter element  replacement  ranging  form  5 to 20 days, depending upon the
pore size of the cartridge  selected.

Application Considerations

The application of cartridge filters using either cleanable ceramic or disposable
polypropylene cartridges to small  water systems  appears to be a feasible method
for  removing  turbidity  and most microbiological  contaminants,  although  data are
needed regarding  the ability  of cartridge  filters to  remove  viruses.  The effi-
ciency and economics  of the process must be closely  evaluated for each applica-
tion. Pretreatment in the  form of roughing filters (rapid-sand or multi-media) or
fine-mesh screens  may  be  needed to  remove larger  suspended solids that  could
quickly foul  the cartridges, reducing capacity. Prechlorination is  recommended to
prevent microbial growth  on the cartridges  and  to inactivate any organism  that
might pass through the filter elements, including viruses.

The  advantage  to small systems  is  that  with  the exception of  chlorination,  no
other chemicals are required.  The process is strictly  one  of physical  removal  of
small particles by straining the water as it passesxthrough the porous  membranes.
Other than occasional cleaning or membrane.replacement,  operational  requirements
                                     111-32

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 are  not  complex and  do not  require  skilled personnel.  Such  a  system  would be
 suited ideally to many small systems where, generally, only maintenance personnel
 are available for operating water supply facilities.

 Removal Capabilities

 Long  analyzed  a variety  of  cartridge  filters  for  removal  efficiency  by  using
 turbidity measurements, particle size analysis, and  scanning electron microscope
 analysis.16  The filters were challenged  with a solution of microspheres averaging
 5.7 urn in diameter  (smaller than  a  Giardia  cyst),  at  a concentration of 40,000 to
 65,000 spheres/ml.  Ten of 17 cartridge filters removed  over 99.99 percent of the
 microspheres.

 In tests  conducted  at Colorado State University using  live infectious cysts  from
 a  human source, cartridge  filters  were  found to be highly efficient  in  removing
 Giardia cysts.17  Each test involved challenging  a filter with 300,000 cysts.  The
 average removal  for  five  tests  was  99.86  percent,  with  removal  efficiencies
 ranging from 99.5 percent  to 99.99  percent.

 QUALIFYING FILTRATION PROCESSES

 Need for Pilot Studies

 The need for piloting  a water treatment process prior to design has  been  stressed
 by  practitioners of the "art" of water treatment for many years. It  has been  said
 that every water has its own special rate of filtration, which must  be determined
 by  local  experiments.  The  extent of pilot  testing  and the desired results may
 vary,  but the  basic need to determine if a  given  technology  is acceptable for a
 particular raw water source is prudent and. can assist in limiting the possibility
 of a design  or process application error.

 Some of the basic reasons for pilot testing a particular process might be to:

 •    Determine if the process is appropriate for  a given water source.
t    Establish  operating characteristics
                                     111-33

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•    Develop design criteria
t    Evaluate the effectiveness of alternative design and operating options
•    Optimize design and operating criteria
•    Uncover unforeseen design or operating problems
t    Provide information to assist in determining capital and operating costs
•    Demonstrate the process applicability to regulatory authorities

Techniques  for  upgrading  existing water  treatment  plants such  as  tube settlers
and dual- or mixed-media high-rate filtration may require either bench- or pilot-
scale evaluation before a satisfactory application to the full-scale plant can be
assured.  Section  II described  these and  other  technologies  and  presented  the
general limitations and design guidelines for successful application. For the new
treatment technologies discussed  in this  section,  there may  be a greater need to
prequalify a specific treatment process  because  of  limited  history of successful
performance or  the requirement  to establish appropriate  design criteria  for a
full-scale  application.   Additionally,   if  the   process  or  equipment  has  not
received  approval  of  the  regulatory  agency, a  successful  demonstration  of  the
process may be a requirement to gain probationary acceptance for its use.

Regulatory Agency Requirements

The State of California Department of Health Services Sanitary Engineering Branch
has developed guidelines for treatment of  surface waters,  stating that "all sur-
face waters used  for  domestic supply should be  provided  with complete treatment
consisting   of   coagulation,   flocculation,   sedimentation,    filtration,   and
disinfection."

A provision is provided for a  waiver  from the defined complete treatment process
but  requires  that  the  treatment  process  be equivalent  to  complete  treatment.
Further,  the  supplier must establish a  guaranteed  source of  funds,  such as  a
performance  bond,   that  may  be  used  to  install  additional  facilities if  the
treated   water   does   not  consistently   and  dependably  meet   water  quality
requirements.

For one such  installation  of  a package plant using  new technology,  the State of
California Department of Health Services required the following:18
                                     111-34

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      Engineering Evaluation  of  Plant  Performance

      Within 60 days  after the first year  of  operation,  the  owner must  submit
      an engineering  report prepared by  an independent consulting civil engi-
      neer,  who is experienced in  the  field of water treatment,  registered in
      State   of  California,  and  acceptable  to  the  Department   of   Health
      Services. It is  recommended that the  engineer be  involved  in  opera-
      tional  review of  the plant during the'entire twelve month period prior
      to submission of  the engineering report.  The report shall describe the
      operating experience of the plant  including any  problems  or failures
      encountered  with  the equipment.  The  report  shall  also  describe  the
      results  of all  water quality tests performed and evaluate the signifi-
      cance  of these results. Specifically,  the plant's performance will be
      compared  to the water quality goals  established  for turbidity as well
      as compliance with the California Safe Water  Drinking Act and regula-
      tions.  In addition,  the engineer's report  will  include any recommenda-
      tions  for the need for  flocculation  and sedimentation facilities prior
      to filtration.

      Treatment Process Guarantee                   '"•-..

      The Owner will  establish a quaranteed source of funds, such as perfor-
      mance bond agreement with the manufacturer, that may be used to install
      conventional  flocculation  and  sedimentation  facilities at the plant if
      the treated  water does not consistently and reliably meet or exceed the
      water quality requirements established.        '
Because of these particular verification of satisfactory performance requirements
it  is  incumbent upon  any  potential  user of new technology to establish the suit-
ability and applicability of a process before a commitment is made to construct a
full-scale facility. For this reason, demonstration pilot studies would indeed be
recommended.
                                                .*         ' .                   - " r
Conducting Pilot Studies                                  :
                                                   *?      ' '
                                                   -,      t
Regardless  of  specific regulatory  agency  requirements, pilot  studies  involving
operation  of  small-scale prototype  treatment  processes  may   be  necessary  in
                                     111-35

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Pilot  studies  are  also  recommended  more  frequently  where  a  high-rate
clarification/filtration 'process  1s  being  considered.  Processes using  contact
flocculation/clarification  such  as  the  Trident  package  plant manufactured  by
Microfloc Products  may require pilot-scale  qualification on  other  than  low  to
moderate turbidity  surface  water  supplies.  Although  the process has  been pilot
studied  extensively  on a  wide variety  of  water  supplies,  and many  successful
plants are in operation, the process is sensitive  to,proper chemical  conditioning
and because detention time  is  extremely  short  (less  than 15 minutes),  if removal
of some  contaminant requires greater  prefiltration contact  tinie ^"misapplication
could occur.

A  Trident  pilot plant  has  been developed  and used  extensively to qualify  the
process on a wide variety of water supplies.  Figure 111-21 is a flow  schematic of
a  trailer-mounted  20  gpm pilot unit  which  can be used  to qualify the  process.
Such a unit was used to qualify the process  in the following case study.

Case Study - New Treatment Facilities Pilot  Study  Selection Process

Background—
The following information was  obtained from a  water  supply  feasibility study  for
a  new  treatment and distribution system  to serve  approximately  2,500 connections
presently on private individual supplies. The  only source of water for  this large
area is  Clear  Lake in  Lake  County,  California.  Although the  lake is used as  a
source by several  communities,  they  all  experience major  difficulties in  handling
severe seasonal taste  and odor problems.  In  general,  it is classified as  a diffi-
cult supply to treat.

The  feasibility study  recommended   complete  treatment  including preozonation,
chemical  coagulation,   pH  control,   flocculation,  sedimentation, filtration,  and
postfUtration  activated carbon contactors followed by disinfection.  Because the
capacity  was projected  to  be  less than  2 mgd, a  package pl'ant of a  particular
design was  found  to  be  the  most  cost-effective treatment  plant alternative.
However,  since  package plants had  not  been  used previously on  this  supply,  a
pilot  study  was suggested  to  establish the  feasibility of the  process  and to
determine design criteria.
                                     111-38

-------
 Quality and Treatment-
 Treatment  of  Clear  Lake  water  to a satisfactory quality drinking water presented
 some  interesting challenges. The lake  is  eutrophic and Is plagued by a series of
 blue-green  algal  blooms  (Microcystls  and Anabaena), which  impart  serious taste
 and  odor  to the lake water. Taste  and odor  problems  develop as early as May and
 last  into early November. Taste and  odor threshold numbers  (TON) as  high as 10
 have  been measured  by other users  of  the supply. Other than the taste and odor
 problem,  Clear  Lake water is of  excellent mineral quality as is indicated in the
 water  analysis  presented in  Table 111-17. Additional water  quality  data is pro-
 vided  in  Table  111-18.  Turbidity can range from  less than 3 NTU to  greater than
 90 flTU during winter  storms. Other than turbidity removal,  disinfection and sea-
 sonal  taste and  odor control,  no additional  treatment  of the  lake water  is
 needed.

 Treatment  experience  on  Clear  Lake water .is  relatively  extensive.  Several water
 districts  use Clear Lake as  their sole supply  and have  been treating this water
 for many  years. The  City  of  Lakeport recently installed the most  sophisticated
 plant which uses both ozone and activated  carbon to eliminate taste  and odor from
 the finished  water.  During the  first year of operation, no taste and  odor com-
 plaints  were  registered by the  city,  attesting  to  the  effectiveness   of  the
 process.

 To gain information  on available procedures and their success in processing Clear
Lake water, four utilities using  lake water were  contacted.  Detailed information
 acquired during this survey is  not included in this document, but a  general over-
view of their experiences is  as follows.  In general, lake water  users are experi-
 encing increasing difficulties controlling taste and odor.  Previously,  several
 utilities were  able to  use potassium  permanganate  and powdered  activated carbon
with  reasonable success.  Recently, more expensive  postfliter granular  activated
carbon contactors have  been  installed.  At  least  two utilities  are  using ozona-
tion.   Those  using   ozone  have   received  the  lowest  percentage   of   customer
complaints.
                                     111-39

-------
Pilot Study Program-
Other utilities treating Clear Lake water have experienced difficulty with rising
floe due to air bubbles  released  by  algae and generally poor clarification expe-
rience  during  the algal  bloom season.  For  these reasons  it was  felt  that the
adsorption clarification  process  using an upflow bed of  bouyant  media as a pre-
filtration clarification process may perform more effectively. However, there was
still  the  concern that  the adsorption  clarifier could not handle  the  high and
widely  fluctuating raw water turbidity conditions.

Consequently,  the  supplier of the adsorption clarifier package  plant, Microfloc
Products was asked to perform  a pilot-plant-scale evaluation of  their process to
confirm its suitability for this  project.  In  addition to  establishing basic tur-
bidity  removal  capabilities,   another  objective of  the  study  was  to determine
whether  potassium  permanganate  or powdered  activated carbon  applied  prior  to
clarification would effectively remove trihalomethane  (THM)  precursors and taste
and odor substances should they be present.  If  so,  the  dependence upon expensive
ozone for taste and odor control could be lessened.

Pilot Study Results-
Data  collected by the  manufacturer is  presented  in a pilot study  report (see
Appendix).  Conduct of the  study was witnessed by the design consultant to verify
that results are representative of actual field experience.

The  results  were  favorable.   The adsorption   clarification/filtration  process
removed turbidity to extremely low residuals. Potassium permanganate was success-
ful in  removing the low conentrations of taste and odor substances present during
the test period.  Unlike  previous  years, no major algal bloom was experienced in
1986, which made taste and odor removal less difficult during the early September
pilot  test.  Powdered  activated  carbon  helped  remove  THM  precursors  and  the
adsorption clarification  process  performed  satisfactorily  at dosages up  to  25
mg/1 without filter breakthrough or seriously shortened operating cycles.
                                     111-40

-------
 Recommended Design Criteria--
 As  a  result  of  the  favorable pilot  study experience,  the  following general
 process design criteria is proposed for the  new treatment plant:
             Item
 Nominal Design Capacity

 Adsorption Clarifier Package Plant
      Clarifier Design Loading
      Filtration Rate
      Filter Type
    Parameter
2 mgd
10 gpm/sq ft
5 gpm/ sq ft
Tri-mixed media
 Chemical  Feed Systems
      Ozone
      Al urn
      Permanganate
      Cationic Polymer (Nalco 8109)
      Powdered Activated  Carbon
      Nonionic Polymer
      Sodium Hydroxide

 Case  Study -  Untreated Supply for Small  Community
Normal Dosage Range
   1 to 2 mg/1
   10 to 20 mg/1
   0.2 to 1.0 mg/1
   1 to 10 mg/1
   10 to 20 mg/1
   0.1 to 0.5 mg/1
   20 to 40 mg/1
 Example—
 A  small  community presently uses a  surface  source (small stream) fed from  snow-
 melt water  from  a relatively  isolated high mountain watershed. Beavers  and  musk-
 rats are  present in the upstream watershed.  Presently, the supply is only  chlo-
 rinated  since  seasonal   average raw water  turbidities  rarely  exceed  1   NTU.
 Giardla cyst presence is of concern.  The community has  about 70 connections  and  a
 peak water usage of about 68,000 gpd. The system is operated by a maintenance man
with entry-level  water  treatment certification  for  his  state.  The  community is
currently paying $20 per  month  for metered  water  service  and has  no capital
 reserves to build treatment facilities.
                                     111-41

-------
The objective of this case  study  is  to determine what treatment; technology would
be available for this application, considering raw water quality, operator skill
level, and construction and operating costs.  ;  ,-   ,

Evaluation Procedures—
The steps that would be followed to identify an appropriate treatment technology,
establish  preliminary  process  design  criteria,  prepare a  preliminary  facility
layout, and establish costs are as follows:

•    Review all raw water quality data available for specific  supply.

t    Establish possible alternatives to be considered.

t    Determine  if  bench  scale or field  pilot  studies  are  required  to qualify
     processses under consideration.

t    Select alternatives suitable for specific situation.
                                                         .*••
9    For this example, consider the following:     .        .
     -  Slow-sand filtration
     -  Package plants
     -  Membrane filtration

•    From literature  and  bench or pilot  studies,  establish treatability charac-
     teristics and other design considerations of each potential process.

•    Basic Process Alternative Concerns

     Slow-Sand Filtration
     -  Is turbidity filterable?
     -  Is color present at concentrations above standards?
     -  Will sand sizes available remove Giardia cysts?
     -  How will filters be cleaned and s'and renewed?

     Package Plant                         .•,.--•
     -  What treatment chemicals and dosages are needed?
     -  Will process reliably  remove cysts?
                                     111-42

-------
    .  -   What  operational  skilMevel  is  needed?
      -   What  regulatory  agency  design standards  must  be  met?
      -   Where will  sludge be  disposed?

      Membrane Filtration
      -   Will  it meet  effluent turbidity  standards?
      -   How will  color,  if present,  be  removed?
      -   What  steps  are required to gain  regulatory  agency  acceptance?
      -   What  operational  skill  level  1s  needed?

 t     Prepare  conceptual   design  criteria  and   preliminary  layouts  of  selected
      treatment alternatives.

 •     Develop  construction  costs;

 •     Compare  alternatives in terms  of  reliability, simplicity, flexibility,  and
      implementability.

 •     Select most  appropriate  process  for the application.

 •     Proceed with final  design.

 Cost  Analysis—
For this example,  using cost  tables presented  in this  section,  the  following
costs  are determined:
     Process
Package Plant
(Table 111-2)
Estimated Capital Cost, $

         295,000
  Total Cost,
t/1.000 Gallons

      277
Slow-Sand Filtration
(Table III-ll)
         273,000
      205
                                     II1-43

-------
     Process
Membrane Filtration
(Table 111-16)
Estimated CapitalCost, $

         269,000
Total Cost,
 ,000 Gallons
    179
All three  alternatives  are quite close  in capital cost.  Membrane  filtration is
the least-cost  alternative  both in-capital  and total costs.  Factors  other than
cost  will  probably-, influence the, decision on what  process to  adopt for  the
particular application.
                                     111-44

-------




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  TABLE  HI-7.  OPERATING DATA - LEWISBURG, WV
Month
                              Turbidity, MTU
Clarifier
 Influent
                                   Clarifier
                                    Effluent
                                      Filter
                                     Effluent
Dae.,  1984   Mean
Range
              5.0
                                      1.2
                            0.16
                         1.8-18      0.6-2.5     0.10-0.20
May,  1985    Mean          9.6
Range        2.0*50
                                      1.0
                                      0.18
                                    0.4-6.0     0.10-0.50
June,  1985   Mean
              1.7
                                     0.60
                            0.16
            Range      0.70-5.0      0.1-1.1      0.10-0.50
                        111-51

-------
TABLE tll-8.  OPERATING DATA - PHILOMATH,  OR









                            (Monthly Average Values)




               Turbidity. HTU           Chemical F«d, mg/L
Month
February, 1986
March, 1986
April, 1986
Nay, 1986
June, 1986
July, 1986
August, 1986
fttu Clarlfler
26.7 3.40
6.50 1.67
6.27 1.49
• 5.82 1.4S
4.25 1.21
3.43
3.02
Miter
• *
0.17
0.20
0.23 ,
0.14
0.22
0.26
Alua
15.5
11.4
• *
11.7
11.3
10.0
16.6
Soda Ash
21.2
4.5
••
1.2
4.8
5.7
• *
Polymer
0.29
0.08
•-
0.08
0.07
0.07
0.07
net
Production
• -
91X
90X
88X
93X
93%
93X
                         111-52

-------
         TABLE 111-9.  OPERATING DATA - HARRISBURG,  PA
(tenth
Turbidity,  MTU

  CUriftw   Filter
  feat  feed, mg/l    CUrifier
•	    Ratt;
Aim    Polyntr     gpn/tq ft
July, 198S  Mtan        8.1  .     1.36      0.17       MA        NA        NA

           Rang*     3.7*15.1   0.60-3.4  0.13*0.32



Aug.. 1985  Nmn        8.6       0.94      0.18        11       0.12         14

           •HW*     4.8*14.3   0.7*1.3   0.13-0.23    8.1-13.4  0.10-0.13    11.9*16.3



Sept., 1983  ttean        9.3        1.2      0.18         9       0.07         13

           Rang*      5.9*37   0.5*4.9   0.09*0.34    4.9*18.7   0-0.31      11.7-14.9
                                  111-53

-------
       TABLE  111-10.  OPERATING DATA - RED  LODGE, MT
Month
Jan.,  1985   Hean

            Ring*
        Turbidity, MTU

   Rau    CleHffer    Filter
                                                         Chemical Feed, mg/L '
                               Water
                            Temperature;
Aim    Polymer  Bentonite     Oeg. F
  0.20       0.29       0.04          2.J      0.48      0.93         36

0.15-0.33  0.21-0.35  0.03-0.05     1.4*3.5  0.48-0.48  0.93-0.93      34-38
ftb.,  1985   Hean       0.19       0.28       0.05          2.3      0.48      0.93         34   '

            Rang*     0.16-0.21  0.22-0.39  0.30-0.07     1.4-3.6  0.48-0.48  0.93-0.93      33-38




Har.,  1985   Mean       0.20       0.29        0.05         3.0       0.48     0.93          36

            Range     0.18-0.22  0.25-0.32  0.03-0.06     1.9-3.9  0.48-0.48  0.93-0.93      35-37
Apr., 1985

Hay, 1985

June, 1965

Naan
ft*nga
Hean
Range
Hean
Hang*
1.1
0.22-1.6
2.1
0.16-4.5
3.5
1.5-6.2
0.49
0.27-1.1
0.41
0.16-0.80
0.41
0.21-0.75
0.08
0.04-0.14
0.07
0.03-0.14
0.07
0.04-0.18
5.0
2.3-7.1
7.3
3.6-13.4
10.«
7.4-12.8
0.60 0
0.48-0.75
0.48 0
0.48*0.48
0.60 0
.0.48-0.75
40
38-43
44
43-47
45
43-49
                                      111-54

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                                     111-57

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                                 111-58

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                                  .111-59

-------
TABLE 111-18. CLEAR  LAKE WATER  QUALITY AT DWR SAMPLING
            STATION NO. 1 AT  LAKEPORT
DATE
SAMPLED
1/7/77
2/3/77
3/10/77
4/7/77
5/5/77
6/16/77
7/14/77
8/11/77
9/22/77
10/14/
11/4/77
12/9/77
1/6/78
2/10/78
3/9/78
4/6/78
5/11/78
6/8/78
7/13/78
8/10/78
9/14/78
10/5/78
11/9/78
12/7/78
1/5/79
2/16/79
3/15/79
4/5/79
5/10/79
6/8/79
7/12/79
8/10/79
9/7/79
10/4/79
11/8/79
12/7/79
1/11/80
2/6/80
3/6/80
4/10/80
5/8/80
6/6/80
7/11/80
8/22/80
9/18/80
10/15/80
U/13/80
TURBIDITY
(OTU)
21
9
25
18
14
35
14
7
60
50
33
36
67
49
20
13
6
3
3
7
18
12
22
20
21
18
12
20
8
5
6
4
13
17
28
19
28
17
3
19
3
6
5
5
12
9
13
Sp. Cond.
(UMHOS/cm
307
308
308
316
321
337
346
302
364
385
373
366
193
197
216
223
227
225
238
258
271
275
290
294
299
255
281
260
259
284
291
304
311
320
299
299
260
245
228
235
236
246
263
268
28r.
2!.S
256
V,
8.3
8.1
7.7
8.1
8.0
7,8
8.0
8.0
8.2
8.1
8.3
8.2
7.3
7.6
7.6
7.6
8.2
8.2
8.1
7.8
7.8
8.4
7.5
7.7
7.8
7.7
7.2
8.1
8.2
7.8
8.1
8.0
8.1
8.6
7.7
7.5
8.3
7.9
7.7
7.7
8.1
8.1
8.1
7.9
8.3
8.3
8.4
3
8l
9.9
11.8
9.2
7.7
9.1
4.5
5.0
4.3
2.6
3.6
5.7
6.8
9.7
10.0
9.1
9.1
10.4
6.9
8.1
5.9
7.0
10.6
4.3
9.5
10.4
10.4
6.7
10.2
9.9
7.0
7.0
5.8
5.3
7.0
8.5
7.1
10.2
10.3
9.8
9.6
8.8 ••
8.5
7.7
6.7
4.8
7.1
9rl
|
15
11
13-.
13
12
12
14
14
14
16
17
17
16 .
,16












13





12

13



.
: ;

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10




Alkalinity
(«CaC03)
142
144
144
147
156
154
160
138
165
170
174
169










'

138





130

143



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..
,








Chloride
(ng/D
6.8
7.0
6.6
6.4
6.5
7.9
8.8
9.6
8.8
10
7.7
8.5




.

•
, .




8.1





6;0

6.0














Nitrates

-------
                     s
                      fa
NlitAI
          1V9IH1N9
        111-63

-------
           FLASH
           MIX  FLOCCULATION
                 FILTRATION
 INFLUENT.
0   TUBE SETTLING
                                          u
i
                                                   lio
                            DESLUDGE    BACKWASH-  BACKWASH
                                       TO-WASTE   SUPPLY
                                                          SURFACE
                                                          WASH
                                                          SUPPLY
                                                          EFFLUENT
Figure III-2.  FLOW DIAGRAM OF ALTERNATIVE PACKAGE PLANT
            (COURTESY OF WATER TECH, INC., VANCOUVER, WASHINGTON)
                              111-64

-------
        MEDIA
     RETAINER
     INFLUENT

     AIR
    INLET
                               OPERATING
                              WATER LEVEL
                 "ADSORPTION-
                >•..-.. MEDIAE.
                   FILTRATION  MODE
                                                      FILTER
                                                      EFFLUENT
                           FLUSH CYCLE
                           WATER LEVEL
       MEDIA
     RETAINER
                ' COLLECTION
                   TROUQH
              : t-•*•••••• ••« '-V
              •> ADSORPTION '•
              «.„'  MEDIA -.•«.".
               EXPANDED FOR
               Tj CLEANING '•;

              'AIR AND WATER
                              oaoeeeooDeeoeoooo
     WASTE
   INFLUENT
 AIR
INLET
                                             BACKWASH
                                             INLET
                                                      FILTER
                                                      EFFLUENT
   ADSORPTION CLARIFIER FLUSH CYCLE
                                             SURFACE WASH
  \Muavnriiwn. f
    MEDIA'*.'/
.EXPANDED FOR
•4 CLEANING
' \ •' O'
.AIR AND WATER
      MEDIA
    RETAINER
 WASTE AND
 OVERFLOW
CONNECTION
                                                    SURFACE WASH
                                                    AGITATORS
                                                           '/I BACKWASH
                                                           •Vj
                                                          'INLET
                  BACKWASH CYCLE
                                                      FILTER
                                                      EFFLUENT
       Figure 111-3.  OPERATING CYCLES OF  PACKAGE PLANT
                  (COURTESY OF MICROFLOC PRODUCTS)

                             iII-65

-------
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      111-68

-------
 5
 m
    100.0
     80.0
     60.0
     50.0
     40.0
     300

     20.0
10.0
 80
 6.0
 5.0
 40
 3.0

 2.0
      10
      0.6
      0.6
      0.5
      04
      0.3

      0.2
      0.1
                         »   i   	'—I	1	1
        9999  99.8   9998 9590 80706050403020  10 5

PERCENT EXCEEDING SPECIFIED RAW WATER TURBIDITY
    Figure HI- 7
            AVERAGE RAW WATER TURBIDITIES AT
            SLOW-SAND FILTER PLANTS SURVEYED
                       111-69

-------



       o
       S
       a
           100
           8.0
           60
           50
           4.0
           3.0

           2.0
1.0
08
06
05
04

0.3

0.2
          0.10
          0.08
          0.06
          005
          004
          003

          002
          0.01
                           i   i
            99.9999.8  9998959080706050403020 10 5 21

PERCENT EXCEEDING SPECIFIED FILTERED WATER TURBIDITY
    Figure III-8.,  AVERAGE FILTERED WATER TURBIDITIES AT
                SLOW-SAND FILTER PLANTS SURVEYED
                          111-70

-------
                    10000
                     800.0
                     6000
                     500.0
                     400.0

                     300.0

                     200.0
                  o
                  o
                  (C
                  o
                  o
                  o
100.0
 80.0

 60.0
 50.0
 400

 30.0

 20.0
 10.0
 80

 6.0
 5.0
 4.0

 3.0

 2.0
                       1.0

                                            i  I  I  I
                       9999  998  9998 9590 80706050403020 10 5 2

      PERCENT EXCEEDING SPECIFIED RAW WATER COLIFORM CONCENTRATION
it--
                   Figure III-9. AVERAGE COLiFORMS IN RAW WATERS AT
                              SLOW-SAND FILTER PLANTS SURVEYED
                                      111-71

-------
                 10.0
                  9.0
                  6.0
                  7.0
                  6.0

                  5.0

                  4.0

                  3.0
              E
              §
                  2.0
             flC
             o
             u.
             Zj
             o
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i.o
0.9
0.8
0.7
0.6
05

0.4

03
                  0.2
                  0.1
                              I  I   I  I   i
                                I	1
I	I
                   9999  998   9998 95 90 80706050403020  10  5

PERCENT EXCEEDING SPECIFIED FINISHED WATER  COLIFORM CONCENTRATION
             Figure 111-10. AVERAGE COLIFORMS IN FILTERED WATERS AT
                    ' '"' SLOW-SAND FILTER PLANTS SURVEYED
                                 111-72

-------
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       111-73

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-------
Filtrate
Clear liquid line
q
Precoat
tank
watpr •- * -*• ii -ii
Wdve =*T* Jh ter
source W feed
pump
(
kj
>
i

(
i
)

Q
Body
feed
tank
(
i
)
r

(
(
J

" U/
Backwash
line
Body feed
pump
/~?— i
,' ^.«


Filter
)
-^
Septum
T /S^
f
\.
^
(
^
X_
\
•H
••
-Filter^
cake
> (
)
€
(
>
Precoat
drain
line
Backwash^/
drain line
       Figure III-1.3.-TYPICAL PRESSURE DIATOMACEOUS
                   EARTH FILTRATION SYSTEM
                         111-75

-------
             OPERATING MODE
             The feed stream is pumped into
             the cartridge shell and passes
             over the fiber walls. Some liquid
             filters through the walls and exits
             the cartridge as clean filtrate. The
             remaining feed and  rejected
             waste flows across  the fiber wall
             as concentrate and  exits  through
             the shell outlet.
                                Concentrated
                                watte
                                material It
                                rejected from
                                shell
                                Feed stream
                                is pumped
                                into shell and
                                separated
                                into two
                                component*

                                Clean Illtraia
                                exits from
                                end ol shell
RADIAL PULSE Sequence
The filtrate is temporarily shut off
and gas is introduced into the
lumens of the hollow fibers. The
gas explodes through the
microporous fiber walls into the
feed stream causing violent
agitation and purging the
cartridge of any waste buildup.
                                                                       2. Air pumped in
                                                                       •I higher than
                                                                       fMd pressure
                 5. Concentrated
                 waste buildup i>
                 forced out
                                                                       3. Air explodes
                                                                       through fiber
                                                                       walls Into con-
                                                                       centrate stream
                 4. Feed stream
                 Is pumped into
                 shell
                  1. Cleen filtrate
                  I* blocked off
Figure  111-14.   HOLLOW  FIBER  MEMBRANE  OPERATIONAL  DESCRIPTION
                                         111-76

-------
    . Non-Corrosive Piping
     System
                                     Chemical Resistant Membranes
Clean In Place
System
Stainless
S.teel Skid
Mounted
Frame
Pref iltration and Pretreatment System
When Required
                                                                      Microprocessor
                                                                      Controls lor Radial
                                                                      Pulse, CIP System,
                                                                      and Membrane
                                                                      Integrity Check
                                                                      Stainless Steel
                                                                      Centrifugal Pumps
        Figure 111-15.   SKID-MOUNTED MEMBRANE FILTRATION ASSEMBLY
                                  111-77

-------
                                         FILTERED
RAW WATER
CLARIFIED
RECYCLE
DISCHARGE
                       UNFILTERED
                       RECYCLE
                                              HOLLOW FIBER
                                              MEMBRANES
                                                 MEMBRANE
                                                 CARTRIDGE
                                         MEMBRANE CLEANING
                                         SOLUTION TO SEWER
AIR INLET FOR
BACKWASHING

BACKFLUSH
WASTEWATER
                                        BACKFLUSH CLARIFIER
   Figure 111-16.  FLOW SHOT OF MF.MBRANH FILTRATION SYSTF.M
                        111-78

-------
. -Si
                         FLOW
                         CONTROL
                         VALVE —
                   DISCHARGE
SAMPLE PUMP

DISCHARGE PIPE
          SUPPORT BRACKET
         2'-6
              4'-0
                                   FLOW
                                   INDICATOR

                                   PERFORATED
                                   COLLECTION PIPE
                                                            CORRUGATED
                                                            FIBERGLASS
                                                            SIDE PANELS
                                                             TUBE
                                                             SETTLING
                                                             MODULE
                   Figure 111-17. TUBE SETTLING TEST MODULE
                                   111-79

-------
                                             HJD1CATOB MlfcM
                                             PIES3SUBC COMUECTIOU
                                                       MIMTCK
                                             COKiVJCCTIOM
                                                   lOOiOM at
                                             FEMM.C. MOSC
Figure 111-18.  PILOT  FILTER ASSEMBLY
           111-80

-------
                            MIX! U
             r LAGH MIX.
             CONSTANT
             LEVLL TANK
J"
                              n
             G O A U U L A N T
             I
             -4—
OVERFLOW
TO DRAIN
                                       DIFFERENTIAL
                                       PRESSURE GAGE
                                                 SURFACE
                                                 . WASH-
Figure 111-19.  PILOT FILTER SCHEMATIC
             111-81

-------
CO
cr
D
o

O
<
OJ
I
               1?  1C  20  24  28  32  3G  40  44   48  52  56  60
                         RUN TIME, hours
               SAND MEDIA
            8  12  16  20   24  28  32   36  40  44   4B   52  56  60
                         RUN TIME, hours
Moffat Water Treatment Plant - Pilot Filtration Tests
Date: &•-'-' 1985
Mode:
direct filtration Q
convent iona 1 (3
Loading: 5 gpm/sf E3
4 gpm/sf O
gpm/ sf D
Filter T ype:
sand ™
mixed media •
dua 1 media no. 1 ID
dua 1 media no. 2 H
Filter Medi*
Type
Sand
Mixed Media
Dual Media No.l
Dual Media No. 2
Turbidity,
NTU
INF.
1 . (;
1 .1
-
1 .6
Alum Dosage:
m g / 1 20
Coagulant Aid
Dosage:
m5/l U-]J
Coagulant Aid Type:
Nalco 8 1 8 1 C3
Calgon .L-6 52 -E D
n
EFF.
(j.;>3
0.23
-
0.22
Filter
sand: n
Mixed:
Dual n
Dual n
Run
Length.
Hour*
•1 <1
1. u
49
-
T3
Run Ended
. Out To:
HL
x •
X
-

Aid Dosage:
10/1 . 0
m g / L 0
a. l:m j /L
D. 2 :mg/L
-ft—

TUR8


-
X
FPt
ClOOO's)

4S3
793
-
295
FPI
Rank
2
1
-
3
Filter Aid Type:
NP I 0 O
Nalco 8181 O
0

FIGURE NO. D-45
       Figure 111-20. TYPICAL PILOT FILTRATION DATA LOG

                            1II-S2

-------
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                                                                                                           00
                                                   11--83

-------
REFERENCES

 1.  Morand,  James  M.,  and  Matthew  J.  Young,  "Performance Characteristics  of
     Package  Water -Treatment Plants,  Project  Summary." Municipal  Environmental
     Research Laboratory, Cincinnati, OH, EPA Project 600/52-82-101, March 1983.

 2.  "High-tech  Water on  the  Green  Fields  of   Iowa,"  Mater  Engineering  and
     Management, January  1985.

 3.  Microfloc  Products,   "Dauphin   Consolidated   Water  Supply   Company,"   Case
     History No. 50.

 4.  Culp/Wesner/Culp,  "Technical   Guidelines   for   Public   Water   Systems,"
     U.S.    Environmental    Protection  Agency,  Cincinnati,   OH,   EPA   Contract
     No.  68-01-2971,  June 1975

 5.  Cleasby, J.L., D.J.  Hilmoe, and C.J. Dimitracopoulos,  "Slow-Sand  and Direct
     In-Line Filtration of  a  Surface  Water,"  J.AWWA,  p.  44,  December 1984.

 6.  Hendricks,  D.W., W.D., Bellamy,  and M. Al-Ani,  "Removal of  Giardia Cysts by
     Filtration,"  in:  Proceedings  of  the  1984 Specialty  Conference,  Environmental
     Engineering,  ASCE, June  1984.

 7.  Bellamy, W.D.,  G.P.  Silverman,  and D.W.  Hendricks,  "Filtration  of  Giardia
     Cysts  and Other  Substances, Vol.  2:  Slow Sand  Filtration," EPA-600/2-85-026,
     U.S.  Environmental  Protection   Agency,  MERL, Cincinnati,  OH,  April  1985.
     NTIS:  PB-85-101633/AS.

 8.  Letter-man,  R.D., and T.R.  Cullen, Jr.,  "Slow  Sand  Filter Maintenance  Costs
     and   Effects   on  Water  Quality,"   EPA-600/2-85-056,   U.S.   Environmental
     Protection  Agency, Cincinnati, OH, May,  1985.  NTIS: PB-85-199669/AS.

 9.  Slezak,  Lloyd  A., and  R.C.  Sims, "The Application and Effectiveness  of  Slow
     Sand Filtration  in the United States," J.AWHA, 76:12:38, 1984.
                                     MI-84

-------
10.  Pyper, Gordon R.,  "Slow  Sand  Filter and Package Treatment  Plant  Evaluation
     Operating Costs and Removal  of Bacteria, Giardia,  and Trihalomethanes,11  EPA-
     600/2-85-052, U.S.  Environmental  Protection  Agency, Cincinnati, OH,  April
     1985.

11.  Bryck, 0., B. Walker, and G. Mills,  "Giardia Removal  by Slow Sand Filtration
     -  Pilot  to  Full  Scale," presented  at the  AWWA  National  Conference,  June
     1987; .

12.  Logsdon,   G.S.,  and K. Fox,  "Getting Your  Money's  Worth from  Filtration,"
     J.AWHA,  p. 249,  May 1982.
13.  Lange, K.P., W.D. Bellamy, and D.W. Hindricks,  "Filtration  of  Giardia Cysts
     and Other Substances, Vol. 1: Diatomaceous  Earth  Filtration,"  EPA-600/2-84-
     114, U.S. Environmental Protection Agency,  MERL,  Cincinnati,  OH,  June 1984.
     NTIS: PB-84-212703.

14.  Malina,  J.F.,  Jr.,  B.p.  Moore,  and  J.L.  Marshall,  "Poliovirus  Removal  by
     Diatomaceous  Earth  Filtration,"  Center  for  Research  in  Water  Resources,
     University of Texas, Austin,  TX, 1972.
                                                                           )
15.  Hibler,   Charles  P.,   and Don   L.   Monzingo,   "Evaluation  of  the  Memcor
     Microfiltration  System   for  Removal   of   Giardia   Cysts,"  Department  of
     Pathology, Colorado State University, Fort Collins,  CO.

16.  Long, W.R.,  "Evaluation  of  Cartridge  Filters  for  the  Removal  of  Giardia
     Lamblia  Cyst  Models  from Drinking Water Systems," Journal  of Environmental
     Health,  45:5:220-225,  March/April 1983.

17.  Hibler,  C.P.,  "Evaluation of the 3M  Filter 124A  in the  FS-SR  122  Type 316
     s/s  #150  Housing for Removal  of Giardia  Cysts,"  Department of  Pathology,
     Colorado State University, unpublished, 1986.

18.  State of  California Department  of Health  Services, "Requirements  for the
     Design and Operation of the Trident Water Treatment  Plant," February 1987.

19.  CWC-HDR, "Technologies and Costs for  the Treatment of Microbial  Contaminants
     in  Potable  Water Supplies,"   U.S.  Environmental Protection  Agency,  Science
     and  Technology  Branch,  Office   of  Drinking Water,  Washington D.C.,  April
     1987.                                               .
                                     111-85

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CHEMICAL    COSTS

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TABLE A-l.  CHEMICAL COSTS USED TO DETERMINE O&M COSTS
Chemical
Alum (Dry)
Alum (Liquid)
Lime (Quick)
Lime (Hyd rated)
Ferric Chloride
Ferrous Sulfate
Ferric Sulfate
Soda Ash
Sodium Hydroxide
Chlorine
Sodium Hypochlorite
Liquid Carbon Dioxide
Sodium Hexametaphosphate
Zinc Orthophosphate
Ammonia, Aqua
Ammonia, Anhydrous
Sulfuric Acid
Hydrochloric Acid
Activated Carbon Powdered
Activated Carbon Granular
Activated Alumina
Potassium Permanganate
Sodium Bisulfate (Anhydrous)
Sodium Silicate
Sodium Chloride
Polyelectrolyte
Diatomaceous Earth
Hagnesium
Sodium Chlorite
Sodium Hydroxide 76%
Sodium Bicarbonate
Calcium Hypochlorite
Small (<1 mgd)
Systems, $/Ton
$ 500
300
100
150
500
277
200
250
595
500
190
350
1,160
1,520
230
410
140
171
950
1,900
1,694
2,800
909
400
105
1,500
680
650
3,200
590
490
2,700
Large (>1 mgd)
Systems, $/Ton
$ 250
125
75
100
275
250
155
200
316
300
150
100
• 1,100
1,000
200
350
100
166
800
1,600
1,156
2,500
673
200
85
1,000
310
582
2,800
316
380
1,540
                         A-l

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DESIGN   STANDARDS   FOR
   FILTRATION   PLANTS
      Texas Department of Health

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              Design  Standards for Filtration Plants
                   Texas Department of Health

(10) Flash nixing and flocculation equipment* capable of adequate
     flexibility of adjustment to provide  optimum flocculation
     under  varying raw water characteristics and rates  of  raw
     water treatment,  shall  be provided.

     (A)  Where  special types of equipment for rapid  mechanical
         mixing, softening, or sedimentation are proposed,  the
         manufacturer shall  be  required  to  meet the  design
         criteria in  .004(b)(11).

     (B)  Sufficient facilities for coagulation and sedimentation
         must  be provided  to  clarify  the  water so that  the
         settled water turbidity  is at a  level so as to produce
         a  finished  water  which  meets  the  turbidity  limits
         established  by  the Department's  "Drinking Water
         Standards."

         (i)  Settled water  turbidities of  less  than  10
              turbidity units are generally required  to produce
              a  filtered  water  turbidity which  meets  the
              requirements  of the "Drinking Water Standards."

         (ii) All  turbidity measurements must be  made  in
              accordance  with the method specified  in the
              "Drinking Water Standards."

(11)  In  order to ensure  continuous operation,  basins   for
     flocculation and straight-flow sedimentation of coagulated
     waters shall be  at least two in number,, shall be designed
     for  parallel operation,  and shall provide a total detention
     period  of at least six hours for clarification plants  and
     !|.5 hours for softening plants.  Where detention  periods of
     less time  are  desired,  engineering  data shall  be submitted
     to  the  Department to Justify the lesser approach;  however,
     in no case  shall the detention  time in the  clarification
     zone of any unit  be less than 2 hours.   The requirement  for
     two  parallel treatment plants  (or trains) will be suspended
     only with  specific approval of the  Department after  the
     review and evaluation of supporting material submitted  to
     substantiate the  suspension.

     (A)  Facilities  for  sludge removal  shall be provided  by
         mechanical  means  or by  the  provision of  hopper
         bottomed  basins  with  valves  capable of  complete
         draining of  the  units.

     (B)  Basins shall be so designed as to prevent the  short
         circuiting  of  flow  or  the  destruction  of floe.
         Coagulated water or water  from flocculators shall  be
         transported  to  sedimentation basins in such  a manner
         as to prevent destruction of floe.  Piping, flumes,
         troughs,  gates, ports, and  valves  shall be designed  at
         4 ft/sec  velocity in  the  transfer of water between
         units.

     (C)  Sedimentation basins may be square, rectangular,  round,
         or other shapes approved by the Department.  The length
         of rectangular  settling basins shall preferably be at

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          least  twice their width, with a side water depth of 10
          feet  to 12  feet  in non-softening water  treatment.
          Square and round sedimentation may also be used for
          clarification and  softening  plants;   however,  the
          detention times In  OOMbXll) Bust be observed.

     CD)   Surface loading for  clarification units  shall be 600 to
          800 gallons per square  foot  per  day, and for softening
          units, 700 to 900  gallons per square foot per day.

     (E)   Settled water weir overflow rates shall be 15,000 to
          22,000 gallons per foot per day.

     (F)   Sedimentation basins shall be provided with facilities
          for draining the  basin in a period not in excess of six
          hours.   In the event that  the plant site topography is
          such  that  gravity  draining  cannot be  realized,  a
          permanently installed electric powered pump station
          shall be provided  to dewater the basin.

(12)  Filters shall be gravity  or pressure  type.

     (A)   The design of gravity rapid send filters shall be based
          on a maximum design filtration rate of 2  gallons per
          square foot per  minute.   At the beginning of filter
          runs for declining rate filters,  a maximum filtration
          rate of three gallons  per square foot per minute is
          allowed. The  filter discharge piping shall be designed
          with an orifice or  other  permanently installed flow
          limiting device to ensure  that the maximum filter rate
          cannot be exceeded.

     (B)   Where  high  rate, dual or  multiply media,  gravity
          filters are used,  a maximum design filtration rate of 5
          gallons per square  foot per minute must be used.   At
          the  beginning  of  filter runs  for declining  rate
          filters, a maximum  filtration  rate of 6.5 gallons per
          square foot per minute is allowed.   The filter
          discharge  piping shall  be  designed with an orifice or
          other permanently installed  limiting  device  to ensure
          that the maximum filter rate  cannot be exceeded.

     (C)   Pressure sand filters shall be subject to the loading
          provisions in   .004.(b)( 12){A)  for  gravity  sand
          filters.  When used,  the  pressure filters  shall  be
          installed  such that duplicate  capacity is available
          to furnish the design capacity with one filter out of
         service.  In any case,  a minimum of two filter units
         shall be furnished.  The use  of  pressure filters shall
         be limited  to installations with less than 0.50 mgd
         capacity.

     (D)  The  depth  of filter  sand,   anthracite,  or  other
         filtering  materials  shall be between 21  inches and  30
         inches,  and  this filtering  material shall be free from
         clay,  dirt,  organic-matter, and  other impurities.   Its
         effective size shall range  from 0,35 to 0.45 mm  for
         fine sand, 0.45 to 0.55 mm for medium sand,  and 0.55
         to 0.65  mm  for   coarse  sand,   and its  uniformity

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     coefficient  shall not exceed  1.7.  The  grain size
     distribution  shall also be  as  prescribed by  AWVA
     Standards.   Material  for Dual or Mixed  media  filters
     shall  conform  to  AWWA Standards.  (Refer to rule  .001
     Glossary  of  Terms.)

(E)  Under the filtering  material,  at least 12 inches of
     gravel  shall be placed, varying  in  size  from 1/16 inch
     to 2 1/2  inches.   The gravel is usually arranged in 3
     to 5 layers such  that  each layer contains material
     about  twice the size of the material above it.  Other
     support material  may be  approved on a  case  by case
     basis.

(F)  The rate-of-flow  of  wash  water  shall not be less than
     20 inches vertical rise per minute and usually not more
     than 30 inches vertical rise  per minute,  which shall
     expand the filtering bed 30 to 50 percent. The free
     board in  inches shall  exceed the wash rate  in inches of
     vertical rise per minute.

     (i)  The  water for backwashing filters shall be of the
         same quality as that produced by the plant  and may
         be supplied  by elevated  wash water  tanks or by
         pumps provided for backwashing of filters only,
         and   take  suction  from   clear   wells.    For
         installations having  a  treatment capacity  no
         greater  than 150,000 gallons  per day, water for
         backwashing may be  secured directly from  the
         distribution  system if proper controls and rate
         of flow limiters are  provided.

     (ii) Rate of backwashing of  filters shall be regulated
         by rate-of-flow controllers.

(G)  If  surface  filter  wash  systems  are  provided,
     atmospheric vacuum  breakers  shall be  installed  in the
     system supply lines above the overflow level of the
     filters such  that  all-'water passes through them.

(H)  Each filter  unit  shall be  equipped with a manually
     adjustable rate-of-flow  controller,  with rate-of-flow
     indication or rate-of-flow indicators with  control
     valves.   These devices are in  addition to the  flow
     limiting  device required above  in .OOH(b)(12)(A) and
     (B).

(I)  Each filter  unit shall be equipped with  a device to
     indicate loss-of-head  through the  filter  box.

(J)  Filter-to-waste  connections,  if included, shall  be
     provided with an  air gap connection  to waste.

(K)  Filters shall be so located that common  walls will not
     exist   between  them  and  aerators,   mixing,   and
     sedimentation basins or  clear  wells.  This rule is not
     strictly  applicable, however, to partitions  open to
    view  and readily accessible for  inspection and repair.

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PILOT    STUDY    REPORT

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R   SYSTEMS
      PILOT STUDY REPORT
             TRIDENT* PILOT STUDY REPORT

                LAKEPORT, CALIFORNIA
                       by

                   W. R. Conley
                    Consultant
                   March 12, 1987
      Study Dates:  October 22 through October 29, 1986

               Operator:  Bob Thompson
                 Mlcrofloc Products
                                            =  mitraflo!
  PSR-26

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PILOT STUDY REPORT
                                                                    PAGE 1
                             TABLE OF CONTENTS
                                                                     Page
                                                                       2
                                                                       2
                                                                       3
I.    INTRODUCTION	
II.    SUMMARY AND CONCLUSIONS	
III.  METHODS AND EQUIPMENT	
IV.    RESULTS AND DISCUSSIONS
      A.  Study Scope	  4
      8.  Detailed Run Data....	  5
      C.  Net Mater Production	  7

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PILOT STUDY REPORT
                                                             PAGE 2
I.
INTRODUCTION
Johnson Division conducted pilot tests to treat raw water from Clear Lake
at Lakeport, California for CWC-HDR in October of 1986, using the TRIDENT*
trailer mounted pilot plant.  The pilot plant is described in Part III of
this report.  The purpose of the test was to determine if the TRIDENT*
process is suitable for producing a low color, iron, manganese and
turbidity effluent and has acceptable levels of THM's while at the same
time giving a net production of over 94% with filter runs of over 24
hours.  The results of the pilot tests along with conclusions and
recommendations are the subject of this report.

II.   SUMMARY AND CONCLUSIONS

The raw water containing low color, moderate alkalinity and moderate to
high turbidity was treated with alum, permanganate and polymer.  The raw
water because of the moderate alkalinity and low color was easily
coagulated.  The TRIDENT® AQUARITROL* which automatically adjusts the
chemical feed to a given turbidity setpoint worked well during the test.
The results were uniformly good in that the clarifier effluent turbidity
was usually below 2 NTU even though the raw water turbidity was as high as
130 NTU with an average for the four runs of 33 NTU.  The clarifier
effluent filtered well to give an excellent filtered water with long filter
runs.  The final filter effluent contained less than 5 color and the
turbidity ranged from 0.07 to 0.10 with an average for the four runs of
0.09 NTU.  Filter runs averaged 50 hours for the two runs that were
completed.  One incomplete run was for 11+ hours and was terminated when a
storm swamped the inlet pump.  The last run was terminated at 20 hours when
the inlet pump quit.  As the filter was operated at 5 gpm/ft?, this is
excellent performance.  The Adsorption Clarifier" had a flush cycle of 4 to
4.5 hours while operating at 10 gpm/ft^.  More detailed data are presented
under details of the runs and in the logs and figures.  Alum feed usually
ranged from 12 to 13 mg/L.  A cationic polymer {Nalco 8103) was fed at the
rate of 6 to 7 mg/L and a non-ionic polymer (Magnefloc 985N) was fed at the
rate of about 0.3 mg/L.  Permanganate was fed at the rate of 0.5 mg/L.
Finally, powdered activated carbon was fed at the rate of 25 mg/L for 6
hours on Run #3.  Results in terms of filter run lengths, headless and
water quality were about the same as without carbon.  This indicates that
carbon can be fed without operating problems to control tastes and odors
and to remove other organics to some degree.

Five samples (two of the raw water and 3 of the filtered water) were
collected for analysis of trihalomethane potential.  This test gives a good
indication of potential problems with THM's in the distribution system,
Fortunately, all of the results were excellent showing that organic
precursors are very low in the raw water and that treatment reduces the
precursors even further.  The analytical report from an outside lab is
appended to this report.

Because of the low alum feed used during the study, the alkalinity and pH
were reduced to only a small extent.  To bring the water back to the
                                                                             t

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PILOT STUDY REPORT
PAGE 3
alkalinity and pH of the original raw water will require about 5 to  10 mg/L
of soda ash or sodium hydroxide.  The pH control chemical should be  added
downstream of the filter.  Restoring the filtered water to the original pH
before treatment will minimize corrosion problems.  A further refinement
will be to maintain the pH and alkalinity in such a way as to hold a
slightly positive langlier index.  In order to do this the plant should
have the capability to feed 25 to 50 mg/L of sodium hydroxide or soda ash.

Polymers were fed to reduce alum feed and produce a better floe.  Details
of the chemical feeds will be found under details of the runs and attached
log sheets.

Th« data show that the TRIDENT* plant is an excellent treatment device for
the water encountered during the test period.

III.  METHODS AND EQUIPMENT

The pilot tests were conducted using the Mi.crofloc trailer mounted TRIDENT*
demonstration'pi ant.  Technical data for the plant are listed in Table 1.
The demonstration unit is a small scale replica of a complete treatment
system.  The plant includes complete raw water chemical feed capabilities,
is fully instrumented and has an integral clearwell to provide water for
backwash of the filter.

As the influent from the pipeline enters the pilot plant, chemicals  are
injected in-line.  The first stage Adsorption Clarifier™ combines the
functions of mixing, contact flocculation and solids removal.  This  system
provides a well conditioned, clarified water to the second stage which is a
mixed-media filter.  The clarifier consists of a packed bed of buoyant
media.  The flow is upward through the clarifier, and downward through the
mixed-media filter.

The TRIDENT* demonstration plant runs at a constant, but adjustable  flow
rate.  Automatic flow control devices ensure constant flow throughout a
run.  For this study the flow rates were 10 gpm/ft2 through the clarifier
and 5 through the filter;

Because of scale considerations, the clarifier is larger than needed for
flow to the ,filter.  Part of the clarifier effluent is split off to  waste
and the other part is passed through the mixed-media filter.  The bypass
and filter effluent flows are monitored with rotometers.  The clarifier and
filter are each equipped with a pressure gauge and recording device  to
monitor headloss development.  Cleaning of the Adsorption Clarifier1" is
accomplished in a multiple step process:

      1.  The influent to the clarifier is shut off.
                                  --•--.
      2.  The clarifier media is fluidized by injecting air into the bottom
          of the clarifier chamber.

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PILOT STUDY REPORT
                                  TABLE 1

                        TRIDENT* DEMONSTRATION PLANT
                               TECHNICAL DATA
I.    Chemical  Feed System

      A.  Number of Pumps/Tanks
      B.  Type   Liquid Metronics;
          Positive displacement,
          variable stroke and speed

II.   Adsorption Clarlfier

      A.  Plan  Dimensions:
      B.  Area, sq. ft.
      C.  Media Depth, in:
      D.  Media Type:

III.  Filter Design

      A.  Plan  Dimensions:
      B.  Area, sq. ft.:
      C.  Media Depth, in:
      D.  Media Configuration
          1. Anthracite  Coal (1.2mm)
          2. Silica Sand (0.6mm)
          3. High Density Sand (0.25
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WIfC
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 .V
**.
                                                                                                                                ^—-

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PILOT STUDY REPORT                                                 PAGE 4

      3.  After the media is totally fluidized, about 1 minute, the
          influent flow is restarted.  The influent water flushes solids
          upward and out through a waste trough.  This flush cycle was 4
          minutes.

      4.  The flow of air to the clarifier is stopped.  The flow of water
          through the clarifier to waste was continued for an additional 4
          minutes.  Upon completion of the flush cycle, the flow from the
          clarifier is diverted from waste back to the mixed-media filter.

Air for the flushing process is provided by a small compressor.

The flush cycle can be initiated by any of four means:

      1.  Manual initiation by pushbutton.

      2.  Initiation by loss of head across the Adsorption Clarifier"
          media.  The differential pressure across the plastic media is
          sensed by a differential pressure switch.  This pressure switch
          is normally set to be initiated at a pressure difference of 4
          feet of water.

      3.  Initiation by time clock which will provide flushing at preset
          intervals.  The time clock resets after the completion of each
          flush.

      4.  Initiation by the mixed-media filter backwash cycle.

The mixed-media filter was backwashed with treated water at a rate of 16
gpm/ft2 for a total of 7 minutes.   Supplemental  surface agitation if
provided with a fixed surface wash device.  A backwash cycle is initiated
either manually or automatically by a high headloss condition as sensed by
a vacuum switch set at 8 feet headloss.

IV.   RESULTS AND DISCUSSION

A.    Study Scope

      There were 4 runs.  Turbidity, color, and pH were measured at
      frequent intervals and a few samples were run for iron, and manganese
      by a field test kit.  Other  samples were sent to an outside lab for
      potential trihalomethane analyses.  Treatment chemical  feed rates,
      clarifier headloss and filter headloss were also recorded at frequent
      intervals.  All runs were at 10 gpm/ft2 on the clarifier and 5
      gpm/ft2 on the filter.

      At the 10 gpm/ft2 clarifier  rate the flush cycle consisted of 1
      minute of air fluidization,  4 minutes of air and water flush and 4
      minutes of rinse to waste.  The filter wash was for a period of 7
      minutes at 16 gpm/ft2.

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PILOT STUDY REPORT
                                                             PAGE 5
B.
Data were written on log sheets by hand, but headloss data were
recorded continuously for 2 of the runs.  The log sheets and recorded
headloss data are presented in this report as appendices.

Details of the Runs

Run #1
      For this run the water was treated with approximately 13 mg/L of
      alum, 7 mg/L of cationic polymer (Nalco 81093)  and 0.3 mg/L of a
      non-ionic polymer (American Cyanamid 985-N), and 0.5 mg/L of
      permanganate.  The alkalinity of the raw water  was moderate (137
      mg/L).  The pH of the raw water was about 8.5 while the treated was
      7.7.  The raw water turbidity varied from 26 to 130 NTU with an
      average of 46.  The apparent color was  15 units, the iron 0.2 mg/L,
      the manganese was <0.l mg/L and the temperature was about 60°F.
      Treatment results were excellent.  The  filtered water had a turbidity
      between 0.08 and 0.10 with an average of 0.09 NTU.  The effluent Iron
      was <0.1 and the manganese <0.1.  The effluent  color was <5.  The
      filter run was 11+ hours and was terminated when a storm caused the
      influent flow to stop.  The clarifier flush interval  was 4 hours.  It
      is interesting to note that the Adsorption Clarffler1" was doing most
      of the work in that the clarifier effluent ranged from 0.6 to 2 NTU.
      This of course explains the very long filter run of 47 hours at the
      high filter rate of 5 gpm/ft2.   See Log Sheet #1 for more details.

      Run #2

      The raw water turbidity ranged  from 17  to 63 with an average of 35
      NTU.  The alum was about 13 mg/L.  Chemical  treatment was almost the
      same as for Run #1, with essentially the same treatment results.  The
      final  turbidity ranged from 0.07 to 0.11 with an average of 0.09
      NTU.  The filter run was 47 hours to a  final headloss of 6.7 feet.

      Two samples were taken for potential  trihalomethane formation.  The
      raw water gave a potential  of 31 mg/L.   The filtered water gave a
      potential  of 9.1 mg/L.  Both results  are excellent and show that
      organic precursors in the raw water are very low.  The color of the
      water gives a rough idea of the organic precursors, but note that all
      results for color were apparent color.   The true color was no doubt
      considerably lower than the 15  units  shown on the log sheet.  The
      filtered THM potential is very  low.  Probably the organic precursor
      was removed by coagulation with alum and polymer.  The observed 71%
      removal  of precursor by coagulation and filtration is higher than
      usually observed.   This may mean that part of the precursor was
      associated with the raw water turbidity which was very efficiently
      removed.  It may also be we11-to note that analytical  results in this
      range may have a relatively large experimental  error.  If the samples
      are representative of the raw water throughout  the year,
      trihalomethanes should not  be a problem for future design unless the
      EPA changes the current standard.  See  Log Sheet #2 for more details'.

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PILOT STUDY REPORT                                                 PAGE 6
      Run 13

      The raw water turbidity ranged form 23 to 27 NTU with an average of
      25 NTU.  The chemical  feeds were about the same as for Runs #1 and #2
      except that powdered activated carbon was fed at the rate of 25 mg/L
      and permanganate feed  was discontinued for the last 6 hours of the
      filter run.  Continuous recording of the clarifier and filter
      headloss show no effect of the carbon as compared with the earlier
      part of the run.  Log  Sheet #3 shows no difference in clarifier or
      filter turbidity as compared with no carbon feed.  Treatment results
      were about the same as for Runs #1 and #2.  The final effluent
      turbidity ranged from  0.07 to 0.09 with an average of 0.08 NTU.  The
      filter run was 53 hours to a headloss of 6.3 feet.  The flush cycle
      was 4.5 hours, but the clarifier effluent remained good at 0.5 to 0.9
      NTU.

      Two samples of filtered water and one sample of raw water were taken
      for potential trihalomethane formation analysis.  The results were
      excellent as for Run #2.  The raw sample ran 16 mg/L.  The filtered
      sample that was collected during the period of powdered activated
      carbon feed was a very low 4.6.  This result is lower than would be
      expected and should be viewed with caution.  The result could be
      correct but more data  should be obtained before forming conclusions
      about the effectiveness of this rather low active carbon dose.  The
      filtered sampled collected during the period of the run when carbon
      was not fed ran 20 mg/L.  Note that for this run the filtered water
      sample ran higher than the raw water.  This could be caused by swings
      in the organic content of the raw water or experimental error.

      More detailed data will be found on Log Sheet #3, the headloss
      recordings and the analytical  report for trihalomethane formation
      potential.

      Run #4

      The raw turbidity ranged from 23 to 26 NTU with an average of 25.
      Chemical  feeds were similar to the other runs except no carbon was
      fed.  Permanganate was fed at 0.5 mg/L as in Runs #1 and #2.
      Treatment results were excellent as before.  The filtered water
      turbidity ranged from  0.08 to 0.1 with an average of 0.09 NTU.  The
      filter run was 20 hours to 3 feet headloss.  The run was terminated
      by failure of the inlet water pump.  The clarifier flush cycle was
      4.5 hours and the clarifier effluent ranged from 0.6 to 1 NTU.  More
      detailed data will be  found in the attached Log Sheet #4, and
      recorded headloss graphs.

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PILOT STUDY REPORT
PAGE 7
C.    Net Water Production

      Net production is defined as the fraction of the rated filtered water
      flow that is available for use.  Net production for a flush cycle of
      4.25 hours and 50 hour filter runs was 95.5%.

      The filter backwash was 0.75% of the rated flow.  The out-of-service
      time for filter backwash and clarifier flush was 3.8%.  The waste
      unfiltered water for clarifier flush was 3.1% of the rated, flow.

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     AnJbb
     ANALYTICAL LABORATORY
     A DIVISION Or OEWANTE » StOWtU.
I9t4 S STREET. SACRAMENTO. CALIFORNIA 95814 • 916-447-2948


   January  30, 1987
   Sample Date:   10/24 &  10/28/86
   Sample Rec'd.  Date:  10/30/86
   Report #111089
Culp-Wesner-Culp
3461  Robin Lane
Cameron Park, CA  95682

Attn:   Jerry Costah
SAMPLE DESCRIPTION      ANLAB ID*
Raw  Water Clearlake     111089-1
Filtered Effluent       111089-2
Clearlake Water  10/28   111089-3
 Filtered Effluent
 Run #3
Clearlake Water  10/28   111089-4
 Filter Effluent
 Run #3
Clearlake Water  10/28   111089-5
 Run S3
             TOTAL
    rRIHALOMETHANE  POTENTIAL
    	uq/1	
              31
               9.1
              20
               4.6
              16
                                                     Data Certified by
                                                     Report Approved by
     This report is applicant* only to ttw sampla rwMiMd By m« laboratory. Tha liability of th* liooratory u limitMl to ttw Mnount paid lorthto rwort TMa rtport Is tor m«
     «xctu»i«* us* of tn« cli«nt to whom it is «tdrtMW« «nd upon th» condition mat ttw client aaaurrMi all liability tor ttw> (Mittwr tflsinbutlon of trw nport or its comanls.

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