Wastewater Collection System Odor Control

Mark M. Smith, P.E.

2010 PNCWA Conference, Bend OR

October 25 | 2010

• Causes of Collection System Odors• Liquid Phase• Gas Phase

• Case Studies• Los Angeles, CA• Henderson, NV

Outline

Brown and Caldwell 2

Causes of Odors in Collection Systems2010 PNCWA Conference

Bend, OR

3

Two Causes of Odor Complaints

• Production of Hydrogen Sulfide

• Air Escape from Sewer to Atmosphere

Liquid Phase Odor Causes

2010 PNCWA Conference,Bend, OR

Brown and Caldwell 5

Generation of H2

S in Sanitary Sewers

• Wastewater Characteristics:• pH• BOD• Temperature

• Flow Patterns

• Physical Pipe Characteristics

Sulfide Production

•

Bacteria in Slime Layer Reduce Sulfate (SO4

2-) to Sulfide (S2-)

•

Equilibrium Established in Wastewater based on pH

% Combination of S2-, HS-, H2S

65 7 8 9 10 11

0

20

40

60

80

100

%

pH

H2 S

HS-

S2-

Sulfide Speciation Breakdown

Gas Phase Odor Causes

2010 PNCWA Conference,Bend, OR

Brown and Caldwell 9

Hydrogen Sulfide Release

•

H2

S Mainly Stripped out of Solution due to Turbulent Flow Conditions

Drop StructuresLocations of Radical Slope ChangesLocations of Changes in Direction

Odor Emissions from Gravity Sewers to Atmosphere

• Positive Differential Air Pressure• Wastewater Drag Effect• Pipe Physical Characteristics

Wastewater Drag Effect in a Gravity Sewer

Headspace (Air)

Wastewater(Liquid)

Sufficient Headspace = No Positive Air Pressure

Insufficient Headspace = Positive Air Pressure

Physical Pipe Characteristics

Diameter Constriction

Positive Pressure Point

Slope Reduction

Positive Pressure Point

Physical Pipe Characteristics

Presence of a Siphon

Pressure Point

Air Jumper

Primary Method to Solve Odor Problem in a Gravity Sewer System

• Withdraw Odorous Air

• Treat in an Appropriately-sized Scrubber

Typical Air Treatment Systems in Collection Systems

• Biological•Biofilters•Biotrickling Filters

•Carbon Scrubbers

• Uses Thiobacillus bacteria

• Low operating cost

• Minimal maintenance

• Can be aesthetically pleasing

• No chemical usage

• Environmentally acceptable

Biological Treatment

Brown and Caldwell 19

Carbon Adsorption

Brown and Caldwell 20

• Can treat most odors

• Minimal maintenance

• Stack discharge increases dilution

• No chemical usage

• New high-capacity carbons available

Case Studies2010 PNCWA Conference

Bend, OR

21

Los Angeles, CA Interceptor System

2010 PNCWA ConferenceBend, OR

Brown and Caldwell 22

Downtown LA

Hollywood Hills

Hyperion

WWTP

CentralLos AngelesSewers

NOTF

WRS

WLAIS

Abandoned

N. NOS

S. NOS

MLK Jr. Bl.

NOSRodeo Rd.

Diversion

Structure 1

LA C

iene

ga B

l.

La B

rea

Ave

.

LCSF

VRS

Wes

tlake

Rel

ief

Sew

er

Jeffe

rson

Bl.

LCIS

N

Fu

ture

ECI

S Ti

e-in

Diversion

Structure 2

NOS

NCO

S

North Portal

To Hyperion

WWTP

Diversion

Structure 3

LARGE DIAMETER SEWERS IN LA CIENEGA/RODEO

VICINITY

Not to Scale

NO

RS

Stoplogged

Stoplogged

Direction of Flow Sewer Out of Service Siphon

Maze

Existing “Maze”

Sewer System

Pre-Design Analysis

• Three Odor Control Locations Identified

• Airflow Withdrawal Rates Estimated

• Needed Confirmation of Rates (“Fan Test”)

• Baseline Period• 12 data loggers installed in sewers• Pressures Recorded

• Three Air Withdrawal Sites• La Cienega (LCSFVRS)• Rodeo (NCOS)• Culver City Park (NORS)

• Fans Were Operated Over a 7-Day Period in 21 Possible “On-Off”

Combinations

• Data Loggers Recorded Air Pressure Responses in the Sewer

Fan Test Procedure

NOTF

WRS

WLAIS

N. NOS

S. NOS

NOS

Diversion

Structure 1

LCSF

VRS

Wes

tlake

Rel

ief

Sew

er

LCIS

N

Fu

ture

ECI

S Ti

e-in

Diversion

Structure 2

NOS

NCO

S

North Portal

To Hyperion

WWTP

Diversion

Structure 3

AIR PRESSURIZATION

SOURCES AND AFFECTED SEWERS

Not to Scale

NO

RS

Stoplogged

Stoplogged

Abandoned

Direction of Flow Sewer Out of Service Siphon Path of Air Backpressure Effect

Maze

Siphon Backpressure

Cochran (NOS) & Drakewood (NCOS)Baseline Pressures

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

4/26 4/27 4/28 4/29 4/30

Date

Air

Pre

ssur

e (in

. H2O

)

Cochran

Drakewood

Typical Baseline Air PressuresUpstream of a Siphon

Air P

ress

ure

(in w

g)

Date4/26 4/27 4/28 4/29 4/30

0.75

0.50

0.00

-0.25

-0.50

-0.75

0.25

Cochran (NOS) & Drakewood (NCOS)Baseline Pressures

0.00

0.05

0.10

0.15

0.20

0.25

12:00 15:00 18:00 21:00 0:00

Time

Air

Pre

ssur

e (in

. H2O

)

Cochran

Drakewood

4/26/03

Typical Baseline Air PressuresUpstream of a Siphon (12 hr. Period)

Time

0.25

0.20

0.15

0.10

0.05

0.00

12:00 15:00 18:00 21:00 00:00

Air P

ress

ure

(in w

g)

Daily Airflow Extraction Rates

Ti me Inte r va l Ex tr acti on Rate (cfm)

8 am - 4 pm 10,000

4 pm - 12 am 7,500

12 am - 8 am 5,000

Vinton, Ivy & Jackson ManholesMay 2, 2003

All Fans Running @ 10,000 cfm

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

8:00 12:00 16:00

Time

Sew

er A

ir P

ress

ure

(in. w

c)

Jackson (WRS)

Vinton (WLAIS)Ivy (NORS)

Vent Hole at Ivy Covered at This Time

10:00 14:00

Typical Air Pressure Responses3 Fans Withdrawing 10,000 cfm Each

8:00 10:00 12:00 14:00 16:00

Time

0.0

Air P

ress

ure

(in w

g )

0.2

0.1

-0.2

-0.1

0.3

0.4

-0.4

-0.3

Kalsman, Corbett & Fairfax ManholesMay 2, 2003

All Fans Running @ 10,000 cfm

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

8:00 12:00 16:00Time

Sew

er A

ir P

ress

ure

(in. w

c)

Kalsman (LCSFVRS)

Corbett (LCIS)

Fairfax (LCSFVRS)

La Cienega Fan

is Started

Rodeo and

Culver City Fans are Started

La Cienega Connection

is Short-Circuiting

Short-Circuiting

is Corrected

14:0010:00

Typical Air Pressure Responses3 Fans Withdrawing 10,000 cfm Each

8:00 10:00 12:00 14:00 16:00

Time

0.0

0.2

0.1

-0.2

-0.1

0.3

0.4

-0.4

-0.3

Air P

ress

ure

(in w

g )

Summary of Test ResultsAll Fans Running at 10,000 cfm

Manhole Location

% Change in

Avg Pressure

Cochran (NOS) -259 Vinton (WLAIS) -183

Fairfax (LCSFVRS) -167 Jackson (WRS) -165

Kalsman (LCSFVRS) -161

Corbett (LCIS) -156 Ivy (NORS) -152

Hannum (NORS) -120 Grayburn (NOS, N.

Branch) -101

Imperial Hwy. (NORS) -12 Somerset (NOS, S.

Branch) -4

Drakewood (NCOS) 28

Conclusions

• Siphons Were The Primary Cause of Positive Pressure

• Significant Reductions in Pressure

were Achieved

• Greatest Success Occurred When All Fans

Were Withdrawing 10,000 cfm Simultaneously

Recommendations

• Withdraw 12,500 cfm at Each of the Three ATF Locations (1.25 SF)

• Further Evaluate Pressure and Ventilation Dynamics in Areas Unaffected by Fan Testing

Force Main Odor Production

• Problems are made worse due to• Full Pipe Flow

• 360°

Slime Layer

• Long Detention Times• In Wet Well

• In Force Main

H2

S Release from Force Main

• Typically occurs at the point of discharge into a gravity pipe

• Turbulence Induced

How to Solve an Odor Problem in a Force Main?

• Chemical Feed• Calcium Nitrate• Sodium Hypochlorite• Sodium Hydroxide• Magnesium Hydroxide• Iron Salts

• Ferrous Chloride

• Ferric Chloride

Calcium Nitrate Ca(NO3

)2

• Trade name BIOXIDE®

• Provides bacteria with alternative oxygen source• They prefer nitrate over sulfate

• Sulfate remains in non-odorous form• Safe to handle• Fairly expensive

Sodium Hypochlorite (NaOCl)

• “Bleach”• Oxidizes H2

S to elemental sulfur at basic pH• Oxidized H2

S to sulfate at acidic pH• Relatively safe to handle• Inexpensive unit cost• Strong oxidant

Sodium Hydroxide (NaOH)

• “Caustic”• High pH• Intended to Kill the Slime Layer• Typically Introduced in “slug doses”, Not Continuously

• PRI-SC System• Combination of NaOH & FeCl3

Magnesium Hydroxide (MgOH)2

• “Mag”, “Milk of Magnesia”• Intended as a pH Adjustment• Original Use (in sewers) Was to Slow Concrete Corrosion

Rates• Operators Noted Reduction in Downstream Odor Complaints

• Relatively Inexpensive• Safe to Handle• Can Require a Large Dosage, Depending on the

Alkalinity of the Wastewater

Lake Las Vegas Resort

North Shore•Hyatt Hotel•High $$ Homes•Golf Courses

South Shore•High $$ Homes•Golf Courses

Lake Las Vegas

South Shore Collection System

• 60,000 GPD

• 42,000 LF of pipe• 2 inches to 15 inches in diameter

• 5 Lift Stations

South Shore Odor Problem

• Very high hydrogen sulfide concentrations

• Housing construction was booming (2004)

• Several odor complaints arose

Odor Investigative Team

• City of Henderson• Collection System Field Personnel• Engineers

• Lake Las Vegas • Management• Lift Station Operators

• Consulting Team

Project Approach

• Compile and map odor complaint locations

• Develop and execute a sampling plan

• Compile and analyze the resulting data

• Develop and implement an odor control plan

Sampling Plan• Install 8 hydrogen sulfide monitors throughout

collection system

• Data collected for 1 week

• Inspect and analyze existing lift stations, pipes and O&M procedures

• CCTV’d suspected problem pipes

Henderson, NV “911”

Odor Study

2010 PNCWA ConferenceBend, OR

Brown and Caldwell 53

A

B

C

D

EF

GH

LS 17

LS 18

LS 19

LS 25

LS 27 Grand

Cor

niche

Dr.

Rue

Med

iterra

Grand Mediterra Blvd.

Rue de

Rivo

li

Via di Como

Grand Barcelona

Direction of FlowH2S Sampling Location

Lift StationR

ue P

rom

enad

e W

ay

Surcharged MH 289-076

N

Findings

• Hydrogen sulfide between 50 and 300 ppm• Regularly over 100 ppm

• Elevation problems and sags in pipes and manholes

• Out-of-service chemical feed facilities

• Detention times between 7 and 90 hours in lift stations(!)

H2S Concentrations at MH 283-013 (A)

0

50

100

150

200

250

300

9/29/20040:00

9/30/20040:00

10/1/20040:00

10/2/20040:00

10/3/20040:00

10/4/20040:00

10/5/20040:00

10/6/20040:00

10/7/20040:00

Time

H2S

(ppm

)

Incoming 8-in Sewer

To Lift Station

Stub Out

Short Term Recommendations

• Restore BIOXIDE®

feed facilities

• Periodically clean and flush problem manholes and pipes

• Install rubber flapper

Incoming 15-in Sewer6% Slope

RubberFlapper

Incoming 8-in Sewer

100 ft. DSSags

Air

Air

Air

Hydrogen Sulfide in MH 283-013 w/ Bioxide Addition & Flushing

0

50

100

150

200

250

300

10/8/2004 0:00 10/9/2004 0:00 10/10/20040:00

10/11/20040:00

10/12/20040:00

10/13/20040:00

10/14/20040:00

Time

H2S

(ppm

)

Long Term Recommendations

• Continue feeding BIOXIDE®

, monitoring hydrogen

sulfide and force mains

• Perform chemical feed optimization study

• Find permanent solution to sags and manhole elevation problems