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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