Odor Control Chemical ScrubberOdor Control Chemical ScrubberBleach Only Mode of Operation -

OCSD’s Experience

Shabbir Basrai. Thomas Hendy. Kishora Panda. May Kyi.y y

June 5, 2013

General Information• Two Treatment Plants

– Plant 1 - Fountain Valley – Plant 2 - Huntington Beach

• About 100 MGD treated at each Plant• Treat wastewater for 80% of Orange County

residents• Final effluent

– GWRSGWRS– Ocean outfall

OCSD Service Area Map

Plant 1 – Fountain Valley

Plant 2 – Huntington Beach

General Odor Control Strategy • Collections SystemsCollections Systems

– Chemical odor control Ferrous chloride magnesium hydroxide calcium Ferrous chloride, magnesium hydroxide, calcium

nitrate, caustic

Headspace 25 ppm H2S target

• Treatment Plants:– Chemical scrubbers– Biofilters and biotrickling filters– Activated carbon AQMD Permit levels – 1 to 3.5 ppm H2S

Plant 1 Chemical Scrubbers• Headworks

– Roughing Scrubbers – inlet H2S loading 10 – 35 ppm One biotrickling filter

One chemical

Fi i hi bb i l t H S l di 1 5 – Finishing scrubbers – inlet H2S loading: 1 – 5 ppm

• Primary Treatment– Inlet loading H2S: 0 – 5 ppm Chemically enhanced primary treatment

Chemical Scrubbers• H2S, pH and chlorine monitoring – Vapex

• PLC controlled

• Originally until about a year ago – Operation in manual caustic + bleach mode About 9.5 pH and bleach at 2 gph

Chemical Scrubbing Process Concept

Foul Air

OverflowOverflow Makeup

DrainDrain

Makeup Water

pH Curve - Hydrogen Sulfide Dissociation

Increasing Calcium Precipitation Potential

Caustic Use Impacts

Scrubbers Operation Mode Change

• Drivers– MaintenanceMaintenance Instrumentation and

controls

Media head loss

– Reaction time to H2S ikspikes

– Chemicals usage and dependencedependence

Scrubbers Operation Mode Change

• Initiated February y2012– Initially manual

control mode

– Currently in outlet H S b d l H2S based control mode

Outlet H2S ControlBleach Flow Strategy

H2S OULET BLEACH FLOW

<0 3 PPM 1 0 GPH<0.3 PPM 1.0 GPH

0.5 PPM 2.0 GPH

1.0 PPM 5.0 GPH

2.0 PPM 7.5 GPH

3.0 PPM 9.0 GPH

Findings• Maintenance Impacts

– Decline in instrumentation maintenance• Frequency of service required

– Increase the period between acid washing

• Performance improvement– System response

• Chemicals usageg

Impeller Condition DifferenceBleach only mode service Caustic - Bleach mode service

Scrubber MaintenanceBefore Acid Wash After Acid Wash

Caustic-Bleach mode service

Bleach only mode service

Chemical Cost Savings

80

90

100

$20 000

$25,000 

Monthly Chemical Cost

H

50

60

70

80

$15,000 

$20,000 H2S Loading

alCo

st

2S Loading lbs/D

10

20

30

40

$5,000 

$10,000 

Chem

ica D

ay

0

10

$‐

Month/YearMonth/Year

Next Steps• Application to Plant 2

scrubbers– Primary Scrubbers

• Chemical use optimization• Scrubber permit change

– Headworks Scrubbers AQMD Permit constraints

Recommendations

• Consider utilizing bleach-only modebleach-only mode– Lower H2S loading

• Ensure flexible • Ensure flexible AQMD permit conditions conditions

Questions?Q

Trunkline complex Headworks complex

Metering&

Di i

20,000 cfm20,000 cfm

B BChemicalScrubber 4

ChemicalScrubber 3

SunflowerDiversionStructure

Pump Station

20,000 cfm 20,000 cfm

B BChemicalScrubber 1

ChemicalScrubber 2

8000 cfm B 8000 cfm

5400 cfm

B

ChemicalScrubber 9

BiotricklingScrubber 10

Rag & GritBuilding

3500 cfm 4000 cfm

B

Bar screen

Grit chambers

20000 cfm

B B

B B

Grit chambers

21000 cfm

building