Urban Water Security Research Alliance

Disinfection By-product (DBP) Formation and Minimisation in South East QLD Drinking Water

Nicole Knight & Glen ShawSmart Water Research Centre, GU

Science and Stakeholder Engagement Forum29 September 2010

Disinfection By-products

• Chlorination & chloramination are widely used in South East Queensland for potable water disinfection.

• Toxic disinfection by-products (DBPs) can form.– Trihalomethanes (THMs)– Haloacetic acids (HAAs)– Nitrosamines (such as N-nitrosodimethylamine)

Trihalomethanes

• Concentration & species distribution of THMs depends on multiple factors – Disinfection method– Processes and physicochemical parameters at

individual treatment plants, e.g. DOC levels at chlorination/chloramination point

– Bromide concentration in source waters.

Chloroform Bromodichloromethane Dibromochloromethane Bromoform

C Cl

Cl

Cl

H C Cl

Br

Cl

H C Br

Br

Cl

H C Br

Br

Br

H

tTHM Guideline Value Compliance in QLD in 2007 - 2008

• Total THMs (tTHMs) and HAAs were within regulatory limits most of the time – ~ 12 % of regions failed to comply to tTHM guideline at least

once over twelve months sampling– ~ 18 % of regions failed to comply to HAA guideline at least once

over twelve months sampling • Three regions had multiple failures for both THMs and HAAs

• All failing regions use chlorination– Chlorinated waters had higher mean tTHM concentrations than

chloraminated waters

• Australian guidelines for tTHMs are high compared to many other countries, and do not have guidelines for individual THMs

• The proportion of brominated to non-brominated THMs was similar for chlorination and chloramination

• THM speciation was dependant on water source– Surface waters higher chlorinated THMs

• Typically lower bromide, higher DOC

– Bore waters higher brominated THMs• Typically higher bromide, lower DOC

• tTHMs were slightly higher in summer months than in winter

THM Speciation across QLD

• Sites: – Wyaralong dam (Teviot Brook), Cedar Grove weir

(Logan River), Traveston Crossing, Landers Shute, Molendinar

• Determined by dosing with typical WTP concentrations of hypochlorite/monochloramine at pH 7.65– All experimental THM formation potentials were within

the ADWG value.

THM Formation Potentials

Sampling date

5/10/2009

19/10/2009

2/11/2009

16/11/2009

30/11/2009

14/12/2009

tTH

M fo

rmat

ion

pote

ntia

l ( g

/L)

0

20

40

60

80

100

120

140

160Concentration of tTHMs formed from chlorination Concentration of tTHMs formed from chloramination

THM formation potentials• THM formation potentials were lower in chloraminated waters

than in chlorinated waters– Molendinar data shown

THM Formation Potentials

Sampling site

Lander's Shute

Traveston crossing

Molendinar

Site 1 - Teviot brook

Site 2 - Teviot brook

Site 3 - Cedar grove weir

Site 4 - Logan riv

er

THM

con

cent

ratio

n (

g/L)

0

20

40

60

80

100

120

140Chloroform Bromodichlormethane Dichlorobromomethane Bromoform

• Speciation arising from chlorination– Teviot brook had high bromide concentration– Molendinar had low bromide concentration

Sampling site

Lander's Shute

Traveston crossing

Molendinar

Site 1 - Teviot brook

Site 2 - Teviot brook

Site 3 - Cedar grove weir

Site 4 - Logan river

THM

con

cent

ratio

n (

g/L)

0

10

20

30

40

50

60

70

ChloroformBromodichloromethaneDibromochloromethaneBromoform

THM Formation Potentials – Speciation• Teviot Brook had much higher THMs than other sites when chloraminated

• Predominantly brominated THMs – high bromide source water

• Landers Shute & Molendinar form low THMs when chloraminated• Predominantly chloroform – low bromide source waters

[H2O2] mg/L

-5 0 5

tTH

M fo

rmat

ion

pote

ntia

l ( g

/L)

0

10

20

30

40

50

60

70

80

ChlorinationChloramination

No UV or H2O2

UV only

THM formation potential is decreased by pre-treatment with UV or UV/H2 O2

N-nitrosodimethylamine (NDMA)

• Formed during chlorine or chloramine disinfection of water containing secondary amines such as dimethylamine.

• Potent carcinogen– Draft Australian Drinking Water Guidelines suggest NDMA

guideline value of 100 ng/L

N Cl

H

H

+ HN

CH3

CH3

N N

CH3

CH3

ONH2Cl/H2O

NDMA formation potentials

• Sites – Mt Crosby, North Pine, Wyaralong dam, Cedar Grove weir, Landers Shute, Traveston Crossing, Molendinar.

• NDMA formation potentials determined by dosing with large excess of pre-formed monochloramine at pH 7.0 and reacting protected from light for 7 days– Dosing with typical WTP concentrations of disinfectant did not

form detectable NDMA concentrations (<5 ng/l)

• All concentrations ranged from 5 – 21 ng/L NDMA• Chlorination did not form detectable NDMA (<5 ng/L)

NDMA formation potential

Sampling date9/02/2009

16/02/2009

23/02/2009

2/03/2009

9/03/2009

16/03/2009

ND

MA

form

atio

n po

tent

ial (

ng/L

)

4

6

8

10

12

14Water pre-chlorinated prior to chloraminationWater NOT prechlorinated prior to chloramination

• Formation potential is lowered by allowing a free chlorine contact time prior to ammonia addition

• West Bank, Mt Crosby WTP– Pre-chlorinate at some filters but not others

Decay of NDMA concentration with exposure to UV radiation

UV dose (mJ/cm2)

0 10 20 30 40 50 60

[ND

MA

] (ng

/L)

70

80

90

100

110

120

130Sampled 8th September 2009Sampled 21st September 2009

y = 71 + 52e-0.04x

R2 = 0.96

[H2O2] (mg/L)

-10 0 10 20 30

[ND

MA

] (ng

/L)

80

100

120

140Sampled 10th August 2009Sampled 25th August 2009

UV dose 30 mJ/cm2

No UV or H2O2 dosing

NDMA Degradation with Advanced Oxidation is not Dependant on

H2 O2 Concentration

Seasonal Variation in Organic Matter Levels - Teviot Brook

Sampling date

03-Aug-09

17-Aug-09

31-Aug-09

14-Sep-09

28-Sep-09

12-Oct-09

26-Oct-09

Con

cent

ratio

n (m

g/L)

0

2

4

6

8

10

12TOC DOC DON

NDMA formation potential

DOC/DON (mg-C/mg-N)

2 4 6 8 10 12 14 16 18

ND

MA

con

cent

ratio

n (n

g / m

g D

OC

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5Site 2Site 1Site 3

• A loose relationship exists between DOC:DON and NDMA formation potential

Coagulant

No coagulation polyDADMAC Ferric chloride Alum

Dis

solv

ed o

rgan

ic m

atte

r (m

g/L)

0

2

4

6

8

10DOC 16/10/2009DON 16/10/2009DOC 28/10/2009DON 28/10/2009

Coagulation at high pH • Teviot Brook

– High Ca2+ and Mg2+ requires softening• None of the coagulants investigated lowered NDMA formation potential

despite significant removal of DOC and DON

Coagulant

No coagulation

polyDADMAC

Ferric chloride

Alum

ND

MA

form

atio

n po

tent

ial (

ng/L

)

0

20

40

60

80

100

120

140 Sampled 16/10/2009Sampled 28/10/2009

Coagulation at high pH• polyDADMAC

– Organic polymer, coagulant, quaternary amine anion exchanger – 6-fold increase in NDMA formation potential upon chloramination

Molendinar WTP use of polyDADMAC

Sampling date19/10/2009

02/11/2009

16/11/2009

30/11/2009

14/12/2009

28/12/2009

ND

MA

form

atio

n po

tent

ial (

ng/L

)

0

5

10

15

20

25

30

35Without polyDADMAC exposure After polyDADMAC exposure

• Increase in NDMA formation potential in polyDADMAC exposed source water when chloraminated

• No NDMA formation upon chlorination• No detectable NDMA in finished water

DOC (mg/L)

3456

THM

con

cent

ratio

n (

g/L)

20

40

60

140

160

180

tTHM Chloroform Bromodichloromethane Dibromochloromethane Bromoform

Coagulation at high pH• Teviot Brook

– High Bromide source waters can cause increasing tTHM concentrations with decreasing DOC

• NDMA is unlikely to be a contaminant of concern in SEQ finished waters

– UV radiation is effective in removing low concentrations of NDMA– pre-chlorination lowers NDMA formation potential

• THM concentrations were consistently compliant in most regions

– Pre-treatment with UV or UV/H2 O2 removes THM precursors, leading to low finished water THM concentrations

– Chloramination leads to lower THM concentrations than chlorination– Regions using chlorination were the only regions that exceeded the ADWG for THMs

• Three regions failed to comply to guidelines on multiple occasions

• Coagulation does not remove NDMA or THM precursors under the conditions studied

– Leads to an increase in bromo-THMs in high bromide source waters

• polyDADMAC and possibly other 4º amine anion exchangers contain NDMA precursors and should be avoided with chloramination but do not form detectable NDMA upon chlorination

Conclusions

• Improving coagulation to remove DBP precursors – Characterisation of DOC/DON not removed by enhanced

coagulation – Halide removal strategies such as SIACs and MIEX

• Modelling DBP formation in the distribution system using neural networks to predict ‘hot-spots’

• Emerging DBPs in SEQ water grid including their relationship to: – alternative water sources – exposure to multiple disinfection methods

Future Directions

ACKNOWLEGEMENTS

• Ms Kalinda Watson• Dr Maria José Farré• Ms Cherie Yin Lam Ng• Urban Water Security Research Alliance• Griffith University• Smart Water Research Centre

• Australian Rivers Institute

Urban Water Security Research Alliance

THANK YOU

www.urbanwateralliance.org.au