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Pre-Oxidation
Improved Particle RemovalBy Brad Zachman, Pam Benskin and Kevin Linder
Applications of Conventional Oxidants in Drinking Water Treatment
• Disinfection (CT)
• Biological control
• Improve coag./flocc/sed/filtration
• Inorganic metal removal
• Taste and odor control
Chemical Oxidation Processes–“A Balancing Act!”
Advantages Disadvantages
Biological Control
Nuisance Inorganic Control
Taste and 0dor Control
Coagulation/Filtration Optimization
Multiple Disinfection Barriers
Benefits of Combined Disinfectants
DBP Formation
Haz. Chemical Handling Risks
Monitoring/Control Challenges
Can be corrosive to equipment
Possible negative effects on downstream biofiltration
Possible discharge issues (DMR)
Lysing of algal cells causing Taste and Odor
VS.
Disinfection/Biological Control
• Oxidant affects a Microorganism’s Cell Wall
Chlorine gas water Hypochlorous acid chloride
Step 1 – Hydrolysis of Chlorine Gas
Cl2 H2O HOCl Cl-
Hypochlorous acid Active microbe Inactive microbe chloride
HOCl
HOCl
HOCl
Cl-Cl-
Cl-
Step 2 – Oxidation/Reduction Reaction Reaction
Pre-Treatment Optimization
• Coagulation Concept -- “Ideal Water”
Al2(SO4) 3
Pre-Treatment Optimization
Al2(SO4) 3
Coagulation Concept -- “Natural Water” w/o oxidant
NOM affects coagulation effectiveness
Particle settling less effective
Pre-Treatment Optimization
Al2(SO4) 3
Coagulation Concept -- “Natural Water” w/ Oxidant
Oxidant destabilizes NOM
Reduces negative surface charge
Promotes aggregation
Improves coagulation and particle settling
HOCl
HOCl
HOCl
HOCl
…Oxidation can also be Helpful!• Floc/Sed & Filter Optimization
– The addition of an oxidant can improve particle and turbidity removal
Disinfection/Biological Control
• Oxidant can affect a microorganism’s motility
Disinfection/Biological Control
• Oxidant can affect a microorganism’s motility
Historical Perspective on Biofilters
• Higher Turbidities
• Short filter runs
• Can’t prechlorinate
• Higher headloss accumulation rate
Case Study
• Binney Water Purification Facility• Aurora Water, Aurora, CO
• Two Treatment Trains– Conventional Train
– Advanced Train
–Biofilters
Binney
Cl2
What We Did
• Started Prechlorination on AR Train 2-2014
• Added upstream of Rapid mix
• Feeding KMnO4
• Dosed to raw water demand to ensure no Chlorine residual leaves the sed basins
• Watched and collected data
What we saw
• Improved Treatment
– Reduced turbidities
– Reduced particle counts
– Lower coagulant dosage
– TTHM’s not impacted
– HAA’s slightly increased
– Reduced chlorine dose at the chlorine contact basin
Pre-Treatment Optimization• Pre-Oxidant Can Improve Filtered Water Quality
Pre-chlorination started
Pre-Cl2 Addition to AR Train
Pre-Cl2 Addition to AR Train
Jun-14 Jul-14 Aug-14
0.03 0.04 0.03
0.03 0.04 0.03
0.04 0.04 0.04
0.04 0.05 0.04
0.04 0.05 0.04
0.04 0.05 0.04
0.04 0.05 0.04
0.04 0.05 0.05
0.03 0.04 0.03
0.02 0.03 0.02
0.05 0.06 0.05
16.6% 14.0% 18.0%
Before
After:(Pre-Cl2 started 2/2014)
Next Step
• We initiated prechlorination on the SP train
• Advanced treatment train
– H2O2 being fed as part of AOP
– Fed upstream of clarifier
– No residual leaving the clarifier
Hydrogen Peroxide
• Fed as part of Advanced Oxidation Process
– UV + H2O2
– 3-5 mg/l dose
• Try to carry 2 mg/l onto filter
– UFRV regularly > 50,000
– Minimize zooplankton regrowth on top of filter
– Control extracellular polymeric substances (EPS)
– Improve IFE turbidities and particle counts.
Binney
Cl2
What We Saw
• Improved Treatment
– Reduced turbidities
– Reduced particle counts
– Lower coagulant dosage
– TTHM’s not impacted
– HAA’s slightly increased
– Reduced chlorine dose at the chlorine contact basin
– Lowered regrowth of algae in uncovered clarifiers
Pre-Cl2 Addition on SP Train
DBP Impacts?
0
5
10
15
20
25
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
TTHM
(ug
/L)
Month
Binney Entry Point TTHM 2010 - 2015
2010
2011
2012
2013
2014
2015
DBP Impacts?
0
5
10
15
20
25
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
HAA5 (ug
/L)
Month
Binney Entry Point HAA5 2010 - 2015
2010
2011
2012
2013
2014
2015
Summary
• Oxidation Works– Improve coag./flocc/sed/filtration– Used Effectively on Biofilters
• Closely monitor residuals– Different oxidants for different goals– Weigh advantages vs. disadvantages– Be Tenacious!!
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