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!!