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CEE 371 Lecture #15 11/21/2009

Lecture #15 Dave Reckhow 1

CEE 371Water and Wastewater

Updated: 21 November 2009

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Water and Wastewater Systems

Lecture #15

David Reckhow CEE 371 L#15 1

Drinking Water Treatment: DBPs and Alternative DisinfectantsReading: Chapter 7, pp.238-242; Chapter 11, pp.416-418

Chlorination: Chap. 2

Johannes RookBrewery chemistStarted with Rotterdam WW in 1963

Found THMs in finished waterDeduced that they were formed as byproducts of chlorination

Others

2

OthersUden, Christman

HAAs: 1980

Rook, 1974, Water Treat. & Exam., 23:234

CEE 371 Lecture #15 11/21/2009


Reactions with ChlorineOxidized NOMand inorganic chloride

HOCl + natural organics

(NOM)

and inorganic chloride•Aldehydes

Chlorinated Organics•TOX•THMs•HAAs

3

Cl

ClCl C H

Br

ClCl C H

Br

ClBr C H

Br

BrBr C H

Chloroform Bromodichloromethane Chlorodibromomethane Bromoform

The Trihalomethanes (THMs)The Trihalomethanes (THMs)

The Haloacetic AcidsHAA5 & HAA6 include the two monohaloacetic acids (MCAA & MBAA) plus

One of the trihaloacetic acids:One of the trihaloacetic acids:

Cl

ClCl C COOH

Br

ClCl C COOH

Br

ClBr C COOH

Br

BrBr C COOH

Trichloroacetic Bromodichloroacetic Chlorodibromoacetic TribromoaceticAcid Acid Acid Acid

(TCAA) HAA6 onlyHAA6 only

4

And 2 or 3 of thedihaloacetic acids

(TCAA)Cl

ClH C COOH

Br

ClC COOH

Br

BrH C COOH

Dichloroacetic Bromochloroacetic DibromoaceticAcid Acid Acid

(DCAA)

H

HAA6 onlyHAA6 only

4

CEE 371 Lecture #15 11/21/2009


Case Study: Impact of time & chlorine dose

THM200

220

THMTr

ihal

omet

hane

s (μ

g/L)

80

100

120

140

160

180

5Time (hrs)

0 20 40 60 80 100 120

Tota

l T

0

20

40

60

10 mg/L 5 mg/L 2.5 mg/L

Loss of Residual

Chlorine Dose

SignificanceOnly instantaneous

THMs HAAs Stage 1&2 0.080 0.060

concentrations are regulatedFormation kinetics are important for managing systems (mg/L)

6

Formation potential are important for controlling organic precursors

assess process performancecompare waters

6

CEE 371 Lecture #15 11/21/2009


DBPs: Formation in Plant

140160

F.P.Inst

NitrosaminesTrihalomethanesHaloacetic Acids

(Inst.)

Precursor Organic Compounds (F.P.)

+ Cl2

020406080

100120

DBP

s (ug

/L)

Inst.

7

Dist.Sys.

Cl2 Coagulant Cl2 NH3

SettlingFiltration

0

Dave Reckhow, UMassDave Reckhow, UMass--AmherstAmherst

Nov 13, 1996TTHM

8

CEE 371 Lecture #15 11/21/2009


Epidemiology

Bladder CancerDBPs linked to 9,300 US cases every year

Other CancersRectal, colon

Reproductive & developmental effectsNeural tube defectsMiscarriages & Low birth weightCl ft l t

137,000 at risk in US?

9

Cleft palateOther

Kidney & spleen disordersImmune system problems, neurotoxic effects

National Distribution241,000,000 people in US are served by PWSs that apply a disinfectant

High THMsHigh THMsare levelsare levels

10

Gray et al., 2001 [Consider the Source, Environmental Working Group report]

are levels are levels of at least of at least 80 ppb over 80 ppb over a 3 month a 3 month averageaverage

CEE 371 Lecture #15 11/21/2009


TOX: Known & UnknownData from the Mills Data from the Mills Plant (CA) AugustPlant (CA) August

Trihalomethanes20%

Chloral Hydrate

Haloacetonitriles2%

HaloketonesChloropicrin

Plant (CA) August Plant (CA) August 1997 (courtesy of 1997 (courtesy of Stuart Krasner)Stuart Krasner)

Sum of 5 Haloacetic Acids10%

Bromochloroacetic Acid3%

Unknown Organic Halogen

64%

Chloral Hydrate1%

1111

QuestionWater utilities are required by law to:q y1. Keep THMs below 80 ug/L in the raw water2. Control all carcinogenic DBPs3. Remove all HAAs4. Keep HAA levels in the distribution system

b l 60 /Lbelow 60 ug/L5. All of the above

12

CEE 371 Lecture #15 11/21/2009


US Disinfection Practices% of utilities using

Free Chlorine only73%

ChlorineDioxide 4 9%

Ozone0.4%

Other0.7%

gparticular disinfectantsStatus as of 1992

Little changed in recent years, except

f Ul i l li h


Chloramines20.8%

Dioxide 4.9%use of Ultraviolet lightOzone plants tend to be larger fraction based on population served

Data from: Jacangelo et al., 1992, JAWWA, pp.121-128

John J. Carroll Treatment PlantMWRA Service area

405 MGD; ~1 log Crypto inactivationThe plant was successfully activated at 11:45 p.m., July 27, 2005

14

CEE 371 Lecture #15 11/21/2009


Introduction: Uses of OzoneDisinfectionOxidation of Fe & MnOxidation of VOCs & pesticidesTaste and Odor controlColor removalCoagulant aidControl of disinfection byproductsPretreatment to biological filtration

15

Introduction: Elements of Ozonation

Very powerful oxidant & disinfectanty pMultiple points of additionReacts quicklyDecomposes in waterCan “engineer” the chemistryR i i iRequires on-site generationGenerators require air preparationOff gas from contactor must be treatedSignificant Power costs

16

CEE 371 Lecture #15 11/21/2009


Growth of Ozone Plants in US

200

Base data: courtesy of Rip G. RiceUpdate: courtesy of Craig Thompson, Kennedy Jenks

6080

100120140160180

Number of New Plants

June 1997 June 2000In Operation 170 332Under Construction 14 58

2000-2004: 30 new startups >1MGD

0204060

pre-1970

1970-1974

1975-1979

1980-1984

1985-1989

1990-1994

1995-1999

17

Plant Update

Some known ozone plants since 2005Median size is 100 MGDSouthern Californiaplants are very large

San Jose CA Longview CADeKalb County GA San Diego CACouncil Grove KS San Diego CAFort Scott KS New Haven CTWinfield KS Tampa FL

18

Franklin MA Gwinnett County GAManchester NH Passaic County NJDallas TX Medford ORSan Jose CA Denton TXWichita KS Upper Trinity TXLawton OK Fairfax County VAFt. Worth TX Tacoma WAFairfax County VA Las Vegas NVSan Jose CA Homer AK

CEE 371 Lecture #15 11/21/2009


Five Basic Components

#2Electric

Power Supply

#1 #3 #4 #5

19

GasPreparation

OzoneGenerator

OzoneContactor

ExhaustGas Destruct

From Rice et al., 1999 [AWWA conf.]

Water

Marius-PaulMarius Paul Otto

Inventor of the ozone generatorShown with hi fihis first prototypeCourtesy of Trailigaz

20

CEE 371 Lecture #15 11/21/2009


Typical ozone generatorShown with pipes and valves for gas and cooling water as well as electrical

MWDSC

as electrical conduits


Corona Discharge

22Source: USEPA, 1999 “Alternative Disinfectants and Oxidants Guidance Manual”

CEE 371 Lecture #15 11/21/2009


Ozone GenerationDielectric:usually a glass tubeDielectric:usually a glass tube

Brushes forming Brushes forming electrical electrical contacts insidecontacts inside

Portland, ME

23

Small TubesCambridge, MA

Better tolerances

24

3.5 to <1 mm gap

CEE 371 Lecture #15 11/21/2009


Corona Ozone GeneratorSilent or “corona” discharge between electrodesElectrodes separated by a dielectric

DesignHorizontal Tube, water cooled

low frequencylow frequencymedium frequency

Vertical Tube

p y

Frequencylow: 50-60 Hz (var. voltage)medium: 60-1000 Hz (const. Voltage, variable voltage or frequency control)high: >1000 Hz

water cooled, low fr.Dual cooled, high fr.

Vertical Plate (only small system)

water cooled low fr.Air cooled, high fr. 25

26

CEE 371 Lecture #15 11/21/2009


Horizontal Tube Ozonator

27

From IDI literature (1977)

Feed Gas SelectionAir

1 5 2 5% b F l f1.5-2.5% ozone by wt. For low frequency generatorsUp to 4.5% with higher frequencyRequires extensive drying

Oxygen-enriched airOxygen concentrators; often used in small systems without drying

Oxygen3-5% by wt. For low frequency generators3 5% by wt. For low frequency generators8-12% for medium frequency generators with ceramic dielectricsCan lead to O2 supersaturationSometimes add N2

28

CEE 371 Lecture #15 11/21/2009


Air, Oxygen & EnergyCorona generators

Specific energy for dry air vs. oxygen

29

From: Warakomski, 1989; Langlais et al., 1991

Air Feed Gas TreatmentConventional air treatment

P (5 filt )Precompressor (5 μm paper filter)Main compressor (60% moisture removal)(60% moisture removal)Aftercooler (<35ºC)Oil coalescer (sometimes)Refrigerant dryer (20% removal)(20% removal)

Used by 70% of air systems in 1991Heat-reactivated desiccant dryer (remainder removed)(remainder removed)

Used by almost all air systemsWith activated alumina, molecular sieves or silica gel, 1 µm filter, hygrometer, gas flow meter and pressure-regulating valveShould it be redundant?

Filter to remove dust(recommended, but not always provided)

30

CEE 371 Lecture #15 11/21/2009


Pure Oxygen SystemsLiquid Oxygen (LOX)q yg ( )

External SupplierPresent economics are favorable

Less space, fewer controls, lower capital, operation & maintenance costs (LOX is currently $3.00/cu ft, or $0.04 / lb)Especially attractive for small to medium size systemsMost new systems (designed after 1990) use LOXUp to 60 days of storage generally providedUp to 60 days of storage generally provided

Exception: plants using LOX to boost ozone production as needed for air systems

LOX supplier also supplies tanks and evaporators (in UK)On-site Generation

Cryogenic Plant (LA)31

LOX Feed

32

CEE 371 Lecture #15 11/21/2009


Cyro PlantLA Aqueduct Filtration Plant

Cryogenic oxygen system

33

Pure Oxygen SystemsGaseous O2 (GOX):2 ( )

Characteristicsrequire complex mechanical and control systemsCan be noisy, unsightlyHowever, new molecular sieves may be making this more economical

Options“Over the fence” supplyOn-site generation

Pressure swing adsorption (PSA)Pressure Vacuum swing adsorption (PVSA)

34

CEE 371 Lecture #15 11/21/2009


GOX feedLas Vegas: Alfred Merritt Smith WTP

600 MGD l t600 MGD plant2003 upgrade included pre-O3Pressure Vacuum swing absorbers

With backup LOXSome use GOX as backup to LOX

Mills (‘03) MWDOthers

PSA: Dallas Elm Fork; Moorhead, MNPVSA: Bossier, LA; Fairfax Co., VA; Las Vegas River Mt.; Dallas Eastside 35

Oxygen System vs. sizeIn general, as plant size increases

From Langlais et

LOX→PSA→Cryo

36

al., 1991

Zone for onsite O2 may be dropping to include smaller plants

CEE 371 Lecture #15 11/21/2009


Ozone ContactingPurpose

Needed to transfer O3 (a low solubility gas) to waterAlso provides mixing

Typesbubble diffusers (Most widely used)turbinesInjectors (most common with >10% conc. in feed gas)

Positive pressure (U-tubes)Negative pressure (venturi tubes)

Otherspacked columns, spray chambers, sweeping porous plate diffuser

37

Bubble ContactorsNumber of chambers Advantages

2 may be sufficient for fast, mass transfer limited reactions3 or more are generally needed for slow, reaction rate limited

no moving parts, proven technology, high efficiency, easy scale-up, low head loss

Disadvantagesdeep tanks clogging

applicationsbetter plug flow behavior for larger number of chambers

deep tanks, clogging possible, vertical channeling may occur

38

CEE 371 Lecture #15 11/21/2009


Design Considerations with bubble contactors

Typical Hydraulic Contact times5 10 minutes for regular oxidation/disinfection5-10 minutes for regular oxidation/disinfection15-20 minutes for Crypto inactivation

Concrete or 316 SS, Completely enclosedDepth: 18-20 ft (5.5-6 m)

Helps assure 95% ozone transfer efficiency1991 data: 22% < 15ft; 56% at 16-20 ft; 22% >20 ft.

S l llSeveral cellsEach with drain

Capable of handling 50% of max daily flowCheck valve needed in gas feed line

To avoid back flow of water39

Design considerations (cont.)Gas flow

to ensure good mixing and stable ozone residualsRecent research suggests that they may not be adequate

See: Schulz & Bellamy, 2000Criteria

Min. gas loading rate: 0.12 scf/ft2 (0.005m3/m2) of contactorMin. gas-to-liquid volume ratio: 5%

If criteria cannot always be metProduce ozone at lower concentrations (4-6%) during the critical periods (periods of low flow or low ozone demand)Provide dense coverage (<18 in OC) of low capacity diffusers to minimize channelingIntroduce supplemental mixingImprove plug flow behavior of contactor

40

CEE 371 Lecture #15 11/21/2009


Ozone ContactingOzone Gas

Three Stage Contactor with Bubble DiffusersOff G T t tOzone Gas Off Gas Treatment

41

Stage 1 Stage 2 Stage 3

Fine BubbleDiffusers

Bubble Diffusers

42

Photos Courtesy of Chris Schulz, CDM

CEE 371 Lecture #15 11/21/2009


Sidestream Ozone InjectionOzone Gas

A. In-line Injector System

Source: USEPA, 1999 “Alternative Disinfectants and

Injector

InfluentContactor

Off Gas

B. Sidestream Injector System

43

Disinfectants and Oxidants Guidance Manual”

Ozone GasInjector

InfluentContactor

Off Gas

StaticMixer

Side Stream injection using backwash supernatantYorkshire Water’s Eccup

44

Water s Eccupplant

CEE 371 Lecture #15 11/21/2009


Sidestream VenturiGwinnett County (GA)’s SVI-DT ozone contactor

45From Schulz & Bellamy, 2000 [OSE 22:4:329]

Ozone Destruction

Thermal-Catalytic Destruct Unit

Altoona, PA

46

CEE 371 Lecture #15 11/21/2009


Bromate

Bromate formation favored at high pH

Br-

Bro

OBr-

O3

HOBr/OBr-

OH O3Dispropor-tionation

H2O2

g pcomplex behavior with peroxide (von Gunten & Oliveras, 1998)BrO3- formation: initial Br- ratio

17% at pH 7.5

BrOo

OH

BrO2-

Disproportionation

O3

O3

OH 1 mg-O3/mg-CSong et al., 1997

10% at pH 6.540% at pH 8.0

Ct=10 mg/L minLegube et al., 2004

47

BrO3-

O3BrO2o

OH

Disproportionation

Chlorine DioxidePowerful oxidant and disinfectantSecond only to ozone in speed of reactionMost often used as a primary disinfectant

Sometimes used as a secondary disinfectant to maintain residual in distribution systems

Must be generated on-sitegMay result in some odor problemsProduces less of the organic disinfection byproducts, but produces much more chlorite and chlorate


CEE 371 Lecture #15 11/21/2009


UV disinfectionQuite effective against protozoansQ g pCauses damage to DNA preventing replication

dimerization in cytosine and thymine


140

Costs for Controlling ProtozoansMicrofiltration (MF), Ozone, UV

4060

80100

120

Tec

hnol

ogy

cost

(c

ents

/kga

l) MF/UFOzoneUV

020

0.6 MGD 6 MGD 60 MGDSystem design flow

From USEPA

CEE 371 Lecture #15 11/21/2009


UV Disinfection: MechanismPhysical Process

UV

Light Energy Absorbed by DNAPyrimidine Dimer Formation (C’s and T’s)

Inhibits ReplicationO i h C

51

AC

GTAACTT A

G

G C

T

DNA

Organism that Cannot Replicate, Cannot Infect

Courtesy of Erik Rosenfeldt

Medium pressure lampLow pressure (high intensity) lamp

Low pressure vs medium pressureCourtesy of WEDECO

Medium pressure lamp= polychromatic spectrum

200 250 300 350 400 450 500 550 600Wavelength [nm]

0102030405060708090

100

norm

ed si

gnal

Low pressure (high intensity) lamp= monochromatic spectrum

200 250 300 350 400 450 500 550 600Wavelength [nm]

0102030405060708090

100

norm

ed si

gnal

Efficiency ~ 12%Lamplife 3,000 – 5,000 hrsLamp temperature 600 – 800°CCool-down before re-startLiquid mercurySolarization of quartz sleeve

g [ ]

Efficiency ~ 40%Lamplife 12,000 hrsLamp temperature 120°CNo cool-down before re-startSolid state mercuryNo solarization of quartz sleeve

CEE 371 Lecture #15 11/21/2009


Major Manufacturers of Commercial UV Equipment for Drinking Water

Trojan Technologies, Inc. (Canada) j g , ( )- MPCalgon Carbon Corporation (U.S.) -MPWedeco (Germany) - LPHO and MPHanovia/Severn-Trent (U.K.) - MPOndeo Degremont (France) - MP

MTBE (90%)

UV Doses

Virus (2-log)

NDMA (90%)

Geosmin (90%)

HPC (4-log)

1 10 100 1,000 10,000

Applied UV Dose (mJ/cm2)

Crypto. (>2-log)

( g)

MWD-Southern CaliforniaFrom: Bruce Chalmers, CDM

CEE 371 Lecture #15 11/21/2009


Multiple lohi lamps, parallel to flowCylindrical reactorFlow rates:max. ~ 10 MGDBaffles required

LoHi Design #2:WEDECO B Series

Multiple lohi lamps, perpendicular to flowIn-line reactorFlow rates:750 – ~ 9,000 m3/hInlet baffle recommended(dependent upon inlet

LoHi Design #3:WEDECO K Series

conditions)

CEE 371 Lecture #15 11/21/2009


Spektrotherm lamps in staggered rows, perpendicular to flowIn-line reactorFlow rates: 5 – ~ 60 MGDDose accumulation by multiple “intensity walls“Complete coverage of reactor cross-section

Fl

Reactor Irradiation Geometry“No Chance to Miss“ Concept

Flow

Plant ILocation: Wahnbachtalsperren-Wahnbachtalsperrenverband, GermanySystem:3 x K3000(2 duty - 1 stand-by)Flow rate:5,675 m³/h= 36 MGD 36 MGD

CEE 371 Lecture #15 11/21/2009


Plant IILocation: Pitkaekoski Water Works Helsinki, FINSystem:3 x K90(2 duty - 1 stand-by)Flow rate:7,000 m³/h= 44.4 MGD

Some Actual UV SystemsPoughkeepsie, NY - Hanovia/ST, validated and operatingCCWA GA - Wedeco validated and operatingCCWA, GA - Wedeco, validated and operating

CEE 371 Lecture #15 11/21/2009


Some Actual UV SystemsCedar Rapids, Iowa - Ondeo, demonstration facilityHenderson, NV - Hanovia/Aquionics, validated and operatingp gNorth Bay, Ontario, validated and operating

Some Actual UV SystemsSeattle, WA - Trojan, validated and nearing startupFort Collins - Trojan, in use for backwash recycle

CEE 371 Lecture #15 11/21/2009


Some Actual UV SystemsWinnipeg - Calgon, validated and completing designBig Bend Water District, NV - constructed and operatingoperating

Typical Design Approach and Issues

CEE 371 Lecture #15 11/21/2009


Typical UV Design ApproachCollect Data (UVT,

sleeve fouling factors, power quality)

Regulator InvolvementENTIRE PROJECT

Establish Design Criteria:(UVT, flowrate, aging/

fouling factor, target pathogen and inactivation level,

redundancy)

Evaluate UV Equipment Options,

including Control Strategy

Evaluate Alternatives for Location, including

Hydraulic Analysis

Identify Validation Approach

Define Goals for UV Disinfection

Identify Potential Locationsfor UV Facility

Construct UV Disinfection FacilityDevelop Detailed Design

(Drawings and Specifications)

UV System Start-up and Testing

UV System Operation

Validation Testing (On-site or Off-Site)

OPTION OPTION

OPTION

Procure UV Equipment

Typical UV Disinfection Design Criteria

Design FlowrateDesign FlowrateUV Transmittance Target Pathogen and Inactivation (Dose) Fouling/Aging Factor (and tie lamp aging to lamp life guarantee)L f li / l i th d d fLamp fouling/cleaning method and frequencyLevel of redundancyFuture considerationsValidation approach

CEE 371 Lecture #15 11/21/2009


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