Evaluation and Design Advanced Oxidation Processes (AOPs)

1. UV/H2O2 Processes for Methyl tert-Butyl Ether (MtBE) and Tertiary Butyl Alcohol (tBA) Removal from Drinking Water Source: effect of pretreatment options and light source

2. Mitigation of Bromate during Ozonation -kinetic study-

Daisuke Minakata, John C. Crittenden, Ke Li

1

Department of Civil and Environmental Engineering, Arizona State University

Water Quality Technology Conference Workshops Sun 5 Advanced Oxidation Technologies in WaterNov. 4th 2007, Charlotte, NC.

David. Hokanson, and R.Rhodes. Trussell

Trussell Technologies, Inc.

2

Outline

1. UV/H2O2 processes for methyl tert-butyl ether (MtBE) and tertiary butyl alcohol (tBA) removal from drinking water source: effect of pretreatment options and light source

• Background of study• Pretreatment options• Light source

• Model simulations

2. Mitigation of bromate during ozonation: kinetic study

• Background of study• Kinetics of bromate formation and control

• Model simulations

3

Background

• MtBE was used as gasoline additive to enhance octane number. • Despite the ban in 1992, MtBE is still found nationwide as ground water contaminants.• Difficult to remove using adsorption or air stripping• Exposure to large dose causes significant non-cancer-related-health risk (WHO). • Ruin taste of water at 5-15 µg/L • Established treatment target at MtBE ≤ 2.5 µg/L and tBA ≤ 6 µg/L, respectively, by California Department of Health Services (CDHS)

4

Initial Conditions + Major Raw Water Quality • 7000 gpm (=10.1MGD)• MtBE: 300 µg/L• tBA: 30 ug/L • TDS: 940 mg/L • Alkalinity: 318 mg/L as CaCO3

• Chloride: 138 mg/L • Nitrate: 0.9 mg/L • Iron: 0.44 mg/L • pH: 7.6 • TOC: 1.4 mg/L

Objective

MtBE ≤ 2.5 µg/L and tBA ≤ 6 µg/L

5

Pretreatment options -4 alternatives + dealkalization-

• NAIX: ion exchange softening with seawater

• Pellet Softening: softening with Pellet reactor

• WAIX: weak acid Ion exchange

• RO: lime softening + reverse osmosis

Dealkalization

AlternativeTOC

(mg/L)

Alkalinity

(mg/L as CaCO3)pH

Ferrous Iron

(mg/L)

Raw water 1.4 318 7.6 0.44

NalX 1.4 318 7.6 0

NalX + Dealkalization 1.4 0 4.65 0

Pellet Softening 1.4 203 9.1 0

Pellet Softening +

Dealkalization1.4 0 4.75 0

WAIX 1.4 118 6 0

WAIX + Dealkalization 1.4 0 4.4 0

RO 0.07 54.1 7 0

RO + Dealkalization 0.07 0 4.5 0

Table 3.

Water constituents in feed to the UV/H2O2 process

Estimated major water quality after pretreatment

6

Impact to UV/H2O2 process by compound i

Parameters for evaluations

k HO•/Ri = second-order reaction rate constants of HO• with compound iCi = concentration of compound i

Fe2+15.1%

HCO3-42.6%

CO3--2.9%

MtBE4.5%

tBA0.2%

TOC27.9%

H2O26.6%

HO2-0.2%

Raw water

*H2O2 conc. is assumed 10 mg/L.** Fe2+ is included only for raw water.

7

Pretreatment 1. -IX Softening with seawater (NAIX) w/o dealkalization-

Cl2

Cl2

WasteGAC

Replacement GAC

AOP

GAC*

GAC

downhole Cl2Seawater

Brine

Na IXH2SO4

Decarbonator NaOHcontactor

O2 Strip

H2O2

mix

*Treatment scheme courtesy of R.Trussell

8

Pretreatment 2. – Softening with Pellet Reactor w/o dealkalization -

GAC*

GAC

Replacement GAC Waste

GAC

NaOH

O2 Strip

Pellet softener

AOP

Filtration

NaOH

HClWastePellets

washwater

H2O2mix

contactor

HCl

DecarbonatorCl2

Cl2

downhole Cl2

HCO3-20.7%

CO3--44.6%MtBE

3.5%

tBA0.2%

TOC21.5%

H2O25.1%

HO2-4.5%

Pellet Soft

MtBE11.5%

tBA0.5%

TOC71.1%

H2O216.8%

Pellet+Dealk

*Treatment scheme courtesy of R.Trussell

9

Pretreatment 3. - Weak Acid IX w/o dealkalization -

GAC*

GAC

downhole Cl2H2SO4Weak Acid IX

Replacement GAC

WasteGAC

BrineH2O2 mix

AOP

Decarbonator NaOH

Cl2

contactor

O2 Strip

HCO3-12.4%

CO3--0.0%

MtBE10.1% tBA

0.5%

TOC62.3%

H2O214.7%

WAIX

MtBE11.5%

tBA0.5%

TOC71.1%

H2O216.8%

WAIX + Dealk

*Treatment scheme courtesy of R.Trussell

10

Pretreatment 4. - Lime softening + RO w/o dealkalization -

WasteGAC

LP RO

AOP

GAC*

GAC

downhole Cl2

Replacement GAC

H2O2mix

DecarbonatorNaOH

Cl2

contactor

O2 Strip

Cl2

H2SO4

Seawater

softeningBrine

GAC

Brine

GAC*

HCO3-33.1%

CO3--0.6%

MtBE23.5%

tBA1.0%

TOC7.3%

H2O234.3%

RO

MtBE35.6%

tBA1.6%

TOC11.0%

H2O251.8%

RO + Dealk

*Treatment scheme courtesy of R.Trussell

11

Advanced oxidation process - UV/H2O2 -Elementary Reactions

H2O2 + hν → 2HO•

H2O2 = quantum yield of H2O2 (=0.5)

I0 = incident light intensity, einstein cm-2

sec-1

A=2.303b(εH2O2CH2O2+εRCR + εSCS + εHO2-CHO2-)

b=pathlength, cm

fH2O2= 2.303 b (εH2O2CH2O2 + εHO2-CHO2-)/A

H2O2/HO2- + HO H2O/OH

- + HO2 2.7×10

7, 7.5×10

9

H2O2 + HO2/O2- HO + H2O/OH

- + O2 3.0, 0.13

HO + HO H2O2 5.5×109

HO + HO2/O2- H2O/OH

- + O2 6.6×10

9, 7.0×10

9

HO2 + HO2/O2- H2O2/HO2

- + O2 8.3×10

5, 9.7×10

7

R + hv Products

R + HO Products kMtBE=1.6×109, ktBA=6.0×10

8

HO + CO32-

/HCO3- CO3

- + OH

-/H2O 3.9×10

8, 8.5×10

6

HO + NOM Products 2.4×104 (mgC/L)

-1s

-1

NOM + hv Products

Molar absorption coefficient &Absorption spectra

0.00.10.20.30.40.50.60.70.80.91.0

200 220 240 260 280 300

Ab

sorb

ance

(cm

-1)

wavelength (nm)

Raw water

NO3-

H2O2 10mg/L

Fe(II)

(mgC/L)-1

cm-1

Wavelength (nm) NOM H2O2 Fe(II) Nitrate

200 0.764 179 642 9624

210 0.425 144 650 7943

220 0.180 100 551 3744

230 0.051 64 494 788

240 0.021 38 584 93

250 0.017 22 518 9

254 0.017 18 444 3

260 0.016 12 354 1

270 0.015 7 313 1

280 0.014 3 288 3

290 0.014 2 255 5

300 0.013 1 255 7

Molar absorption coefficient

M-1

cm-1

Table 4.

Absorbance of raw water of the Charnock wells, iron(II), nitrate, and calculated

NOM in the range from 200 to 300 nm of wavelength

12

Calculated f (H2O2) = 0.0044* 200-300 nm, 10 mg/L of H2O2

** H2O2 absorbs photons efficiently in the range of 200-300 nm

13

Property of Low Pressure UV system and Medium Pressure UV system

• LPUV lamps generate light more efficiently than MPUV lamp.• Above 254 nm, MPUV lamps generate less HO• due to the lower extinction coefficient of H2O2.

Medium Pressure UV

0

0.25

0.5

0.75

1

200 220 240 260 280 300

Wavelength, nm

Rela

tive lam

p o

utp

ut

0.00

0.25

0.50

0.75

1.00

200 220 240 260 280 300

Rela

tive lam

p o

utp

ut

LPUV

MPUV

LPUV MPUV

Diameter, D (inches) 30 48

Length, L (inches) 148 180

Number of lamps 144 18

Nominal power per lamps (kW) 0.25 15

UV efficeincy of lamps (%) 35-40 10-15

Wavelength of emit (nm) 254 200-300*

* wavelength for hydrogen peroxide to absorb photons efficiently

Table 6.

Comparison of the LPUV reactor and the MPUV reactor associated with

physical properties and lamp efficiency.

Low Pressure UV System (LPUV)

Lamp ConfigurationLPUV System 14

Medium Pressure UV System (MPUV)

Lamp ConfigurationMPUV System

15

16

Tool utilized for simulations

• Solved with AdoxTM (AOP Simulation Software)• no pseudo-steady-state assumption• no constant pH assumption• Gear algorithms utilized to solve stiff ODEs • completely mixed flow reactors with tank-in-series

Assumptions

• MtBE and tBA are the only target compounds.• Direct photolysis of MtBE and tBA is negligible. • 15 mole% of tBA is formed from MtBE oxidation. • NO3

-, Fe2+ and NOM are the only interference with UV.• Fe2+, NOM and HCO3

-/CO32- are the only HO• scavenger.

• Decrease of UV irradiation due to scaling and bulb aging is 70%. • All UV irradiation is absorbed by the water matrix.

Approach

17

Approach (cont’d)

Configuration of reactors and Modeling approach (LPUV/H2O2)

• Consist of four parallel train (each Q= 1750 gpm). Each train includes the required number of LPUV reactors in series. • Dye study data suggests 8 tanks-in-series (TIS) described reactor mixing conditions. • If both MtBE and tBA do not meet treatment objectives, the model run up to 9 maximum reactors (72 TIS).• If proved impossible to meet the criteria above, H2O2 dose is increased.

Q = 7000 gpmEach Q = 1750 gpm

Target effluent conc.MtBE ≤ 2.5 µg/L

tBA ≤ 6 µg/L

18

Approach (cont’d)

Configuration of reactors and Modeling approach (MPUV/H2O2)

• No more than two reactors in series is allowed in design.• 4 TIS was chosen to described the mixing condition.• The number of trains would be increased until 9 parallel trains (18 reactors) to achieve the treatment target.• If proves impossible to meet the objectives, H2O2 dose would be increased.

Q = 7000 gpm

Target effluent conc.MtBE ≤ 2.5 µg/L

tBA ≤ 6 µg/L

19

EE/O (electrical efficiency per order of contaminant destruction)

P = lamp power output, kWQ = water flow rate, gal/hCi = influent conc. of MtBE or tBA, µg/LCf = effuluent conc. of MtBE or tBA, µg/L

, kWh-kgal/order

Parameters for evaluations

20

in out MtBE tBA MtBE tBA

None (raw) 25 13 1.1 4.4 0.5 5.7 9 4

NalX 25 13 1.0 4.0 0.6 6.0 8 4

NalX + Dealk 10 6.9 0.77 3.0 0.6 5.8 6 4

Pellet 70 35 1.4 5.3 0.4 5.4 11 4

Pellet + Dealk 10 6.9 0.77 3.0 0.6 5.8 6 4

WAIX 10 6.3 0.83 3.1 0.3 4.7 7 4

WAIX + Dealk 10 6.9 0.77 3.0 0.6 5.8 6 4

RO 7.0 4.9 0.15 0.49 1.3 5.7 1 4

RO + Dealk 4.0 2.9 0.11 0.29 0.2 1.8 1 4

Number

of trainsPretreatment process

H2O2

(mg/L)

EE/O

(kwh-kgal/order)

Effluent concentration

(μg/L)

Number of

reactors

per train

Table 7.

Summary of results for using the LPUV reactor with all pretreatment alternatives.

Simulation results (LPUV/H2O2) -overall-

• Pretreatment (i.e. Dealkalization) significantly improves the treatment efficiency and decrease the EE/O and the # of reactors. • NaIX + Dealk would be preferred because less residues of H2O2

and less complexity.

21

Simulation Results (LPUV/H2O2) – NAIX + Dealkalization -

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

5 10 15 20

EE

O (k

Wh

/kg

al-

ord

er)

H2O

2re

sid

ua

l co

nc.

(m

g/L

)

H2O2 Dosage (mg/L)

Residual of H2O2 MtBE tBA

• 10 mg/L of H2O2 dosage would be the better choice although the optimum dosage of H2O2 is over 20 mg/L. This is because the cost required for over 20 mg/L of H2O2 dose overweigh the energy cost.

22

in out MtBE tBA MtBE tBA

None (raw) 30 15 7.3 23 1.3 5.2 2 8

NalX 30 12 6.2 18.0 0.5 3.4 2 8

NalX + Dealk 10 6.6 4.6 15.0 1.4 5.8 2 5

pellet 50 19 8.3 27 1.4 5.9 2 9

Pellet + Dealk 10 6.6 4.6 15.0 1.4 5.8 2 5

WAIX 10 5.9 5.2 16 1.0 4.8 2 6

WAIX + Dealk 10 6.6 4.6 15.0 1.4 5.9 2 5

RO 4.0 1.9 0.99 2.8 2.1 5.0 1 2

RO + Dealk 4.3 2.2 0.48 1.3 1.8 4.5 1 1

Number of

reactors

per train

Number

of trainsPretreatment process

H2O2

(mg/L)

EE/O

(kwh-kgal/order)

Effluent

concentration

(μg/L)

Simulation results (MPUV/H2O2) -overall-

• Pretreatment (i.e. Dealkalization) significantly improves the treatment efficiency and decrease the EE/O and the # of trains. • NaIX + Dealk would be desired as well as in the case of LPUV/H2O2 system.

23

Simulation Results (MPUV/H2O2) – NAIX + Dealkalization -

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

5 10 15 20

EE

O (k

Wh

/kg

al-

ord

er)

H2O

2re

sid

ua

l co

nc.

(m

g/L

)

H2O2 Dosage (mg/L)

Residual of H2O2 MtBE tBA

• 10 mg/L of H2O2 dosage would be the best choice although the optimum dosage of H2O2 is over 20 mg/L. This is because the cost required for over 20 mg/L of H2O2 dose overweigh the energy cost.

24

Cost comparison

# of

reactors

Total power

per day

(kWh)

Cost of

energy

($/day)

H2O2

dose

(mg/L)

Total amount

per day

(lb)

Cost of

chemical

($/day)

LPUV/H2O2 24 21,300 $2,130 10 600 $899

MPUV/H2O2 10 108,000 $10,800 10 600 $899

Table 11.

Cost comparison for the desing comparing of the LPUV reactor and the

MPUV reactor

NaIX + Dealkalization pretreatment

* Unit prices for H2O2 and electrical energy are $ 1.5/lb and $0.10 kWh, respectively.

• Cost of energy for MPUV system is 5 times higher than for LPUV system.• In the design process, a comparison of EE/O versus the H2O2 dosage provides valuable insight into the tradeoffs and support determination an appropriate H2O2 dosage.

Mitigation of Bromateduring Ozonation Process

Daisuke Minakata

John C. Crittenden, Ph.D., P.E., N.A.E.

Arizona State University

25

Application of ozone to water treatment

• Direct reactions with O3

26

O3 + NOM → HO• + byproducts

• HO• is quenched by the reaction with NOM

HO• + NOM → byproducts

Factors to reduce stability of aqueous ozone residuals• High pH• Low alkalinity• High TOC• High temperature

• Indirect reactions with HO• produced by O3 with NOM

Concern about bromate

• Formation of bromate (BrO3-) during ozonation

in the presence of bromide ion (Br-)

• A nationwide survey of Br- in drinking water sources: approximately 80 μg/L (Amy et al., 1994)

• Br- in costal area is expected higher

• 10 μg/L of BrO3- standard of MCL associated with

cancer risk, Stage 1 of the Disinfectant/Disinfection

By-Product (D/DBP) Rule (EPA, 1998)

• When ozone is applied to disinfection, tradeoff

between inactivation of cryptosporidium and

bromate formation should be concerned. 27

Mechanisms of bromate formation

28

Simplified reaction scheme for bromate formation during ozonation

Ozone involving pathway HO• involving pathway

O3 + Br - → OBr

- + O2 160

OBr- + O3 → 2O2 + Br - 330

OBr- + O3 → O2 + BrO2 - 100

HOBr + O3 → O2 + BrO2 - + H+ <0.013

BrO2 - + O3 → BrO3 - + O2 5.7×10

4

O3 + Br• → BrO• + O2 1.5×108

HO• + HOBr → BrO• + H2O 2.0×109

HO• + OBr- → BrO• + OH- 4.2×10

9

HO• + Br- → Br• + OH- 1.1×109

BrO• + BrO• + H2O → BrO2- + OBr- +2H+

5.0×109

BrO• + BrO2- → OBr- + BrO2• 4.0×108

At lower pH (pH<pKa=8.8), less BrO3- is produced via ozone

pathway since HOBr is dominant. As a result, O3 decay is slower.

pKa = 8.8

Disproportionation

k (M-1 s-1)

0.0

0.2

0.4

0.6

0.8

1.00.0

0.2

0.4

0.6

0.8

1.0

1.00E-09 1.00E-08 1.00E-07

f O3

f HO

•

*HO•+/*O3+

29

Contribution of O3 and HO• to the reactions with Br-

• More than 90% of oxidation of Br- occurs with O3.• Only at high [HO•+/*O3+, HO• oxidizes Br-.

Typical range for water treatment

30

Contribution of O3 and HO• to the reactions with HOBr/OBr-

• At [HO•+/*O3]=10-8, pH=7.0, the fraction of [HOBrtot] oxidized by HO• is 70%.• HOBr is mostly oxidized by HO•.

0.0

0.2

0.4

0.6

0.8

1.00.0

0.2

0.4

0.6

0.8

1.0

1.00E-09 1.00E-08 1.00E-07

f O3

f HO

•

*HO•+/*O3+

HOBr/OBr-pH=6.0

pH=6.5pH=7.0

pH=8.5

pH=7.5

pH=8.0

Control of bromate formation 1 – pH depression-

• pH depression resulting in more HOBr due to pKa=8.8 of

HOBr reduces BrO3- formation. However, in drinking water

treatment at around neutral pH, HOBr is mainly oxidized by

HO•. Therefore, pH depression does not reduce BrO3-

formation drastically.

• At reduced pH, O3 decay is slower and the [HO•+/*O3] is

decreased during ozonation. As a result, reduction of BrO3-

at the steady state is distinctive. It is noted that it cannot

be expected the proportional relationship between

[HO•+/*O3] and BrO3- formation.

31

32

Model simulation - pH effect -HO• + NOM → products k = 19000 (mgC/L)-1s-1 Westerhoff et al 2007

Br• + NOM → Br- + products k = 83000 (mgC/L)-1s-1 Pinkernell and von Gunten 2001

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60

O3

(mg

/L)

Time (min)

pH=6.0

pH=6.5

pH=7.0

pH=7.5

pH=8.0

pH=8.5

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60

BrO

3-

(ug/

L)

Time (min)

pH=6.0

pH=6.5

pH=7.0

pH=7.5

pH=8.0

pH=8.5

Reactor type CMBR

Init O3 (mg/L) 1.0

pH 6, 6.5, 7, 7.5, 8, 8.5

Br- (µg/L) 300

NOM (mgC/L) 1.0

33

0.0E+00

5.0E-07

1.0E-06

1.5E-06

2.0E-06

2.5E-06

3.0E-06

3.5E-06

4.0E-06

0 10 20 30 40 50 60

HO

Br

(mo

le/L

)

Time (min)

pH=6.0

pH=6.5

pH=7.0

pH=7.5

pH=8.0

pH=8.5

0.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

5.00E-07

6.00E-07

0 10 20 30 40 50 60O

Br-

(mo

le/L

)

Time (min)

pH=6.0

pH=6.5

pH=7.0

pH=7.5

pH=8.0

pH=8.5

HOBr and OBr- concentration profiles at different pH

It is observed that pH depression lowers OBr- concentration, which reacts with O3 at k=330 and 100 M-1 s-1 to produce Br-and BrO2-, respectively, whereas HOBr does not.

Control of bromate formation 2 - NH3 addition -

34

Simplified reaction scheme for controlling bromate formation

• The maximum effect is at high NH3 as HOBr becomes very small. However, it is observed that excess NH3 decreases the efficiency of bromate control. • Not efficient in water containing medium to high NH3

k (M-1

s-1

)

HOBr + NH3 → NH2Br + H2O 7.5×107

OBr- + NH3 → NH2Br + OH- 7.6×104

NH2Br + OH- → OBr- + NH3 7.5×106

35

Model simulation - NH4+ addition -

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60

O3

(mg/

L)

Time (min)

NH4+ = 0 ug/L

NH4+ = 50 ug/L

NH4+ = 100 ug/L

NH4+ = 200 ug/L

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60

BrO

3-

(ug/

L)

Time (min)

NH4+ = 0 ug/L

NH4+ = 50 ug/L

NH4+ = 100 ug/L

NH4+ = 200 ug/L

NH4+ = 400 ug/L

NH4+ = 800 ug/L

Reactor type CMBR

Init O3 (mg/L) 1.0 (= 21 µM)

pH 8.0

Br- (µg/L) 300 (= 3.8 µM)NOM (mgC/L) 1.0

NH4+ (µg/L)0, 50, 100, 200, 400, 800

(0, 2.9, 5.8, 11, 23, 47 µM of NH3 tot)

Control of bromate formation 3 – Cl2-NH3 process -

36

• HOCl hinders Br- oxidation to Br• by HO•

NH3 additionCl2 addition OzonationSource water

HOCl + Br- → HOBr + Cl- 1550

OCl- + Br- → OBr- + Cl- 0.001

HOCl ↔ OCl- + H+ pKa = 7.5

• NH3 reacts with both HOBr and HOCl

• Effective to hinder HO• during ozonation to reduce BrO3-• HOCl and NH2Cl oxidize specific moieties of NOM and reduces their reactivities toward O3, and also scavenge HO•.

* HOCl, NH2Br, and HOBr react with NOM to produce THMs and TOX

HOBr + NH3 → NH2Br + H2O 7.5×107

OBr- + NH3 → NH2Br + OH- 7.6×104

HOCl + NH3 → NH2Cl + H2O 4.2×106

37

Model simulation – Cl2-NH3 process 1 -

• HOCl (5 min.): Bromide ion is converted into HOBr by HOCl. HOBr produced reacts with NOM.

0

50

100

150

200

250

300

0 1 2 3 4 5

Br-

(ug/

L)

Time (min.)

HOCl = 5 uM

HOCl = 10 uM

HOCl = 15 uM

0.0E+00

5.0E-07

1.0E-06

1.5E-06

2.0E-06

2.5E-06

0 1 2 3 4 5

HO

Br

tot

(M)

Time (min.)

HOCl = 5 uM

HOCl = 10 uM

HOCl = 15 uM

HOCl (µM) 0, 5, 10, 15

Br- (µg/L) 300 (=3.8 µM)

TOC (mgC/L) 1.0

pH 8.0

phosphate (M) 0.001

NH4+ (ug/L) 400 (23 µM of NH3 tot)

reactor type CMBR

O3 (mg/L) 1 (=21 µM)

Chlorination 5 min.

Ammonia addition 1 min.

Ozonation 60 min.

38

Model simulation – Cl2-NH3 process 2 -

0.0E+00

2.5E-07

5.0E-07

7.5E-07

0 0.5 1

HO

Br

(M)

Time (min.)

HOCl = 5 uM

HOCl = 10 uM

HOCl = 15 uM

• NH3 addition (1 min.):HOBr is significantly masked by NH3.

• O3 (60 min.): Pre-addition of HOCl followed by NH3 decreased BrO3- by factor of 2~7 as compared with the case of only NH3

addition.

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60

O3

(mg

/L)

Time (min.)

HOCl = 0 uMHOCl = 5 uMHOCl = 10 uMHOCl = 15 uM

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 20 40 60

BrO

3-(

ug/

L)

Time (min.)

HOCl = 0 uM

HOCl = 5 uM

HOCl = 10 uM

HOCl = 15 uM

39

Model simulation – Cl2-NH3 process 3 –

Effect of reactions of NOM with NH2Br, HOCl, HOBr

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 20 40 60

BrO

3-(

ug/

L)

Time (min.)

HOCl = 0 uM

HOCl = 5 uM

HOCl = 10 uM

HOCl = 15 uM

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 20 40 60

BrO

3-(

ug/

L)

Time (min.)

HOCl = 0 uM

Series1

HOCl = 10 uM

HOCl = 15 uM

With reactions

Without reactions

The reactions of NOM with HOBr and NH2Br significantly reduces HOBr/OBr concentrations which are the key intermediates for the subsequent BrO3- formation.

[TTHM] = [Cl2]{ATTHM(1-exp(-kt)}

ln(k) = 5.41 – 0.38 ln + 0.27 ln([NH3-N]) – 1.12 ln(Temp) + 0.05 ln([Br-]) – 0.854 ln(pH)

ln(ATTHM)=-2.11-0.87 ln -0.41 ln([NH3-N]) + 0.21 ln([Cl2]) + 1.98 ln(pH)

[TTHM]=predicted trihalomethane conc. in initial phase (~5h), µg/L

[Cl2]=applied chlorine dose, mg/L

[DOC] = dissolved organic carbon, mgC/L

[NH3-N] = ammonia-nitrogen conc., mg/L as N

[Br-]= bromide concentration, µg/L

Temp = temperature, °C

t = reaction time, h

Model simulation – Cl2-NH3 process 4 –

TTHM formation

Improved EPA 1998 empirical model (Sohn et al., 2004)

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60

TTH

M (

ug/

L)

Time (min)

HOCl = 5 uM

HOCl = 10 uM

HOCl = 15 uM

HOCl (uM) 0, 5, 10, 15

Br- (ug/L) 300

TOC (mgC/L) 1.0

pH 8.0

phosphate (M) 0.001

NH4+ (ug/L) 400

Chlorination 5 min.

Ammonia addition 1 min.

40

Control of bromate formation -optional (O3/H2O2 process)-

• Advanced oxidation process: O3/H2O2 process:

– HO2- + O3 → HO• + O2•- + O2 k = 2.2×106 M-1s-1

– H2O2 + O3 → O2 + H2O k = 0.0065 M-1s-1

– produce more HO• at higher pH due to pKa = 11.6 (H2O2)

– H2O2 also scavenges HO•

• H2O2 + HO• → HO2• + H2O k = 2.7×107 M-1s-1

=> optimum O3/H2O2 ratio (typically 2 ~ 3)

• H2O2 addition keeps the O3 concentration low.

• In the presence of Br-, H2O2/HO2- reacts with HOBr/OBr- to produce Br- resulting in BrO3- formation. In addition, there is significant contribution of the reaction of O3 with Br• in regard with BrO3- formation.

41

42

Model simulation – O3 with H2O2 process–CMBR

Init O3 (mg/L) 3

pH 7.5

Init H2O2 (mg/L) 1.5, 1.0, 0.5

ALK (mgCaCO3) 0

phosphate (mM) 0

Br- (ug/L) 300

NOM (mgC/L) 1

MtBE (ug/L) 300

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 20 40 60

O3

(mg/

L)

Time (sec)

H2O2 1.5 mg/L

H2O2 1mg/L

H2O2 0.5 mg/L

0

50

100

150

200

250

300

0 20 40 60

MtB

E (u

g/L)

Time (sec)

H2O2 1.5 mg/L

H2O2 1 mg/L

H2O2 0.5 mg/L

43

0

5

10

15

20

0 20 40 60

BrO

3-(

ug

/L)

Time (sec)

H2O2 1.5 mg/L

H2O2 1 mg/L

H2O2 0.5 mg/L

0.0E+00

7.0E-09

1.4E-08

0 20 40 60

HO

Br

tot

(M)

Time (sec)

H2O2 1.5 mg/L

H2O2 1 mg/L

H2O2 0.5 mg/L

Questions?

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