ODOR AND CORROSION CONTROL IN SEWERAGE

SYSTEMSEnrique J. La Motta, Ph.D., P.E.

Professor of Civil and Environmental Engineering

THE SOUTHEAST SYMPOSIUM ON CONTEMPORARY ENGINEERING TOPICS (SSCET)

University of New Orleans

September 2014

PRESENTATION OUTLINE

1. Cause of H2S odor and corrosion

2. Odor and corrosion control technology overview

3. Problems and solution in NO metropolitan area

4. Pure oxygen injection

5. Applications and case studies

Bacteria need oxygen to consume org. matter

MAIN CAUSE OF ODOR

Oxygen sources

(order of preference):

1. Oxygen (limited)

2. Nitrate (limited)

3. Sulfate (unlimited)

Anaerobic slime layer

SO42-

Anaerobic bacteriaH2S

Sulfide Generation in Sewers

Condensate: Location of H2S oxidizing bacteria

Anaerobic slime layer

H2S is released from solution as gas (rotten egg odor)

Corrosion of moist pipe surface

H2S + O2

Thiobacillus

sulfuricansH2SO4

(EPA Manual)

EFFECTS OF SEWER CORROSION

(Vitrified Clay Pipe Manual)

RATE OF CORROSION

At H2S concentrations of

20ppm in the headspace,

concrete will corrode at a rate of

1 inch in 5 years(Clidence and Shissler, 2008)

MAJOR H2S CORROSION TARGET AREAS

Gravity concrete or cast iron sewers

Pump stations and force mains

Treatment facilities

TREATMENT OBJECTIVES

Maintain DO > 0.5 mg/L.

Keep dissolved sulfides (DS) less than 0.1 (difficult and costly to achieve) to 0.3 mg/L.

Maintain H2S in the air at less than 3 to 5 ppm.

Increase pipe crown pH to 4.0 or higher

TECHNIQUES AVAILABLE TO CONTROL H2S CORROSION

Oxidations systems: Pure oxygen injection Air injection Hydrogen peroxide Chlorine Potassium permanganate.

Precipitation systems Iron salts Zinc salts

pH elevation

Other methods

HYDROGEN SULFIDE CONTROL AT ORLEANS

PARISH

Significant amount of sulfide generation occurs in the sanitary sewer systems of the New Orleans metropolitan area.

Orleans Parish produces approximately 120 MGD of municipal wastewater

S&WB has tried hydrogen peroxide and Bio-Kat addition

Roughly 24 MGD is being treated with Bio-Kat

The annual cost of Bio-Kat ≈ 0.6 million dollars

The unit cost is roughly $25,000 per MGD treated.

BEST METHOD: PURE OXYGEN INJECTION

A more cost-effective H2S control system is wastewater super-oxygenation.

Oxygen can be generated in situ using modern technology.

Pure oxygen is injected at selected sewage pumping stations.

High oxygen transfer efficiency (>90%)

Typical in situ oxygen generation system using the pressure swing adsorption (PSA) technology (Source: OGSI.)

Schematic diagram of the ECO2 oxygen injection system. (Clidence and Shissler, 2008).

Typical installation of the ECO2 pure oxygen injection system at a raw sewage pumping station (Source: ECO2 web site)

ADVANTAGES OF PURE OXYGEN INJECTION

Wastewater remains aerobic through the treatment plant: No H2S generation

No odors No corrosion

Wastewater arrives partially treated to the treatment plant

Modern technology makes this system cost effective

Examples of positive results:

Untreated H2S levels in the Laguna Beach force mainSource: Clidence and Schissler, WEF/A&WMA, 2008

H2S levels in the Laguna Beach force main after pure oxygen injection. Source: Clidence and Schissler, WEF/A&WMA, 2008

H2S in the sewer headspace near Gulf Pond force main discharge, Milford, Conn.Source: Bradstreet and Smith, WEFTEC 2012

Cost of pure oxygen injection systems

Milford, Conn.: Unit annual cost = $5,400/MGD

Madison, ME: Unit annual cost = $5,200/MGD

Elk Vale, SD: Unit annual cost = $5,400/MGD

Trinity River Authority, Dallas, TX (primary clarifiers, 150 MGD): Unit annual cost = 1,700/MGD

The cost of super-oxygenation for H2S and corrosion control is close to one-fifth of the cost of Bio-Kat.

HYDROGEN SULFIDE CONTROL AT JEFFERSON PARISH

Jefferson Parish tried iron salts addition on West BankAt Marrero WWTP got black precipitate (Fe2S) all over

the plantGot Fe(HO)3 precipitate at the chlorination chamber

Suspended iron salt addition in 1997.

Severe odor and corrosion problems at the East Bank Wastewater Treatment Plant

UNO has been cooperating with JP by developing a pure oxygen injection program

Pure Oxygen Injection At JP East Bank Pumping Station SystemAssumptions made to calculate oxygen demand:

Oxygen concentration to meet the oxygen uptake rate = 10 x HRT.

HRT was based on continuous flow at average dry weather flow rate

Oxygen concentration needed to oxidize hydrogen sulfide = 5 x DS at each pumping station.

DS data base was limited.

Calculations were performed, and several changes and adjustments were made.

Final amounts of oxygen to be added are on the next diagram.

G6-9 Helios3340.4 gpm55.1 ft

0.77 fps

G6-4 Galleria3795.5 gpm60.1 ft

7136 gpm1.27 fps

F6-5 Cleary & W. Napoleon2966.6 gpm53.8 ft

10,102.5 gpm1.79 fps

F6-11 Houma & W. Napoleon2012.6 gpm66.4 ft

F6-5 Clearview & W. Napoleon2456.7 gpm46.0 ft

12,115.1 gpm2.15 fps

F6-2 W. Napoleon8065.0 gpm66.64 ft

14,571.8 gpm2.04 fps

E6-7 Transcont. &Vineland8153.3 gpm32.66 ft

3.7 fps

30,790.0 gpm2.89 fps

E5-4 Transcontinental & W. Metairie3384.6 gpm42.6 ft

34,174.6 gpm2.69 fps

EBWWTP

SCHEMATIC DIAGRAM OF THE EAST BANK SEWAGE PUMPING SYSTEM

22,636.8 gpm2.12 fps

SECOND PHASE, JEFFERSON PARISH

Implement the oxygen injection program.

Monitor the successful removal of hydrogen sulfide in the pumping system.

Monitor the remaining odor levels at the EB WWTP.

If odors continue, focus on improving the sludge management system. Inject pure oxygen into sludge holding tank.

Questions?