preventing disinfection by product formation
TRANSCRIPT
Preventing Disinfection By‐product Formation
What are some Affordable Alternatives?
Madjid MohseniUniversity of British Columbia
RES’EAU‐WaterNETAnnual Drinking Water Workshop
Gander, NewfoundlandMarch 27‐29, 2012
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MissionRES’EAU‐WaterNET
is dedicated to
maximizing benefits to small and rural communities by becoming the nation’s premier solution provider for the
drinking water treatment industry
DBPs What is the problem?
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Concern over possible human health risk (epidemiologic studies):
Risk of bladder cancer; some cause cancer in laboratory animalsRecent concerns about possible reproductive & developmental effects
Vancouver Sun (Oct. 15, 2011)
DBPs What are they?
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Halogenated DBPs•Halomethanes•Haloacids•Haloaldehydes•Haloketones•Halonitriles•Haloamides•Halonitromethanes•Halopyrroles•Haloquinones•Halofuranones (e.g., MX)•Oxyhalides (e.g., bromate)•Many others
Non-halogenated DBPs•Nitrosamines•Aldehydes•Ketones•Carboxylic acids•Others
More than 600 DBPs identified
DBPs Only 11 DBPs are regulated in U.S.
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DBPs MCL (g/L)•Total THMs 80•5 Haloacetic acids 60•Bromate 10•Chlorite 100
Note: No evidence of regulated DBPs causing bladder cancer in animals
Little known about occurrence, toxicity of unregulated DBPs
A few unregulated DBPs are animal carcinogens
DBPs
How are they formed?
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DBP Formation
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Natural Organic Matter (NOM)9
A possible structure of NOM
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NOM11
What is NOM?‐
Detritus generated by biological processes
‐
Complex, highly variable composition
Implications for drinking water treatment‐
Precursors to chlorination DBPs
‐
Bacterial regrowth potential
Implications for advanced processes‐
Screening of UV
‐
Membrane fouling
DBPs and DOC content12
Engelage et al. (2009)
DBP Formation Factors13
Temperature: Increasing temperature results in increased DBP formation ratepH: THMs increase somewhat with pH, HAAs increase with decreasing pHTime: Reaction is rapid for the first few hours and then decreases. Reaction will continue as long as there is disinfectant and precursorsDisinfectant Dose: Increasing dose results in increasing DBP formationType and concentration of NOM
What are the alternatives?
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Minimize the use of Cl2
Remove NOM
+ Cl2
Requirements NOM Removal Technologies
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1.
Applicable to a range of raw water qualities• Small systems are widely distributed and each has its unique
source water that varies seasonally and with climate
2.
Operator‐friendly
3.
Robust
4.
Affordable and cost‐effective to operate
5.
Low in maintenance
6.
Easily serviced with the assistance of remote expertise
Potential Alternatives16
Slow Sand Filter17
Used for more than 150 years for water treatment
Many advantages• Simple technology• Low cost • Low maintenance• Passive treatment• No chemicals used• Green technology
Multistage Slow Sand Filter
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Effluent
Drain
Overflow to Drain
Roughing Filter Slow Sand Filter
Silica Sand (0.30mm - 0.40mm)
Silica Sand (0.85mm – 1.20mm)
Support Gravel (2.36mm – 3.35mm)
Support Gravel (8.00mm – 12.50mm)Support Gravel
(8.00mm – 12.50mm)
Support Gravel(2.36mm – 3.35mm)
GAC(0.85mm – 1.20mm)
Influent
Ion Exchange Resins (IEX) 19
Show great promise as pre-treatment to reduce the formation of DBPs and increase the efficiency of many advanced treatments (e.g., H2 O2 /UV, ozone, and membrane)
Emerging as effective alternatives for the removal of NOM from raw surface water
Ion Exchange Resins (IEX) 20
• Removal mechanisms:– Ionic exchange of negatively charged NOM– Adsorption of neutral NOM
Cl-
Cl-
Cl-Cl-
Cl-
Cl-Cl-
Resin
NOM-
NOM-
Cl-
Cl-
Cl-
Cl-
Cl-Cl-
Resin
NOM-
NOM-
NOM-
NOM-
NOM-
NOM-
Cl-
Operational Aspect
Column Operation• Co-flow regeneration• Counter flow regeneration
Well-mixed• MIEX, other IEX resins
Fluidized or Suspended • MIEX or any other IEX resin
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DOC removal with IEX -
Batch22
0
1
2
3
4
5
6
7
8
9
0 500 1000 1500
DO
C c
once
ntra
tion
(mg/
L)
Contact Time (min)
SIR22MP500VPOC
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Practical limitations
Affinity difference
Effective for low concentrations (brackish or sea water )
Only ionized targets can be eliminated
Regeneration (cost, environmental burden)
Electro-coagulation (EC)25
Anode Cathode
Me+
2 H2 O
2 OH- + H2
e-
Anode Cathode
Me(OH)
Pollutants
1) Generates coagulant 2) Destabilizes and adsorbs pollutants
Electro-coagulation (EC)26
Advantages:1)No chemical supply chain2)No chemical handling3)No addition of sulfates or chlorine anions4)Minimal service: one electrode change per year5)No pH control necessary6)Possible flotation removal7)Tunable to quality, dose changing is electronic8)Very compact and small footprint
VS
EC
AlumDisadvantages:1)Electricity + water?2)Passivation
EC for NOM Removal River Water
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0
1
2
3
4
5
6
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 1 2 3 4 5
TOC
(mg/
L)
Abs
orba
nce
(UV 2
54)
Treatment time (min)
Absrobance
TOC
EC for NOM Removal River Water – energy consumption
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0
1
2
3
4
5
6
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 0.5 1 1.5 2
TOC
(mg/
L)
Abs
orba
nce
(UV 2
54)
Power (kWh/m3)
Absrobance
TOC
EC for FC and Turbidity Removal River Water
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0.1
1
10
100
1
10
100
1000
10000
0 1 2 3 4 5
Turb
idity
(NTU
)
Feca
l Col
iform
/100
mL
Treatment time (min)
Fecal Coliform
turbidity (NTU)
EC for NOM Removal Comparison of Metals
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0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6
DO
C/D
OC 0
Time (min)
FeAlZn
EC for NOM Removal Comparison of Metals for different waters
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0
0.2
0.4
0.6
0.8
1
1.2
Suwannee Nordic Natural
DO
C /
DO
C0
NOM Source
InitialFeAlZn
EC for NOM Removal Effect of NOM Concentration
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Fraction of NOM that cannot be removed
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 1 2 3 4
DO
C/D
OC
0
Time (min)
DOC(initial) = 21.59 mg/L
DOC(initial) = 13.79 mg/L
Take Home Message33
Removal of NOMReduces the formation of undesirable by-products
Increases the efficacy of many water treatment processes (filtration, chlorination, UV-disinfection)
Saves significant energy associated with downstream processes
EC and IEX are easily retrofitted to existing facilities
