Odor and Corrosion Control in Sewerage Systems - UNO-EF

Report
ODOR AND CORROSION
CONTROL IN SEWERAGE
SYSTEMS
Enrique 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
MAIN CAUSE OF ODOR
Bacteria need oxygen to consume org. matter
Oxygen sources
(order of preference):
1. Oxygen (limited)
2. Nitrate (limited)
3. Sulfate (unlimited)
Sulfide Generation in Sewers
SO42-
Anaerobic bacteria
H2S
Anaerobic slime layer
Condensate: Location of H2S oxidizing bacteria
H2S is released from solution as gas (rotten egg odor)
Anaerobic slime layer
Corrosion of moist pipe surface
H2S + O2
(EPA Manual)
Thiobacillus
sulfuricans
H2SO4
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 main
Source: 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 Bank
 At Marrero WWTP got black precipitate (Fe2S) all over the
plant
 Got 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 System
 Assumptions 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.
E6-7
Transcont. &
Vineland
8153.3 gpm
32.66 ft
F6-2 W. Napoleon
8065.0 gpm
66.64 ft
F6-11 Houma & W. Napoleon
2012.6 gpm
66.4 ft
G6-4 Galleria
3795.5 gpm
60.1 ft
G6-9 Helios
3340.4 gpm
55.1 ft
3.7 fps
22,636.8 gpm
2.12 fps
30,790.0 gpm
2.89 fps
14,571.8 gpm
2.04 fps
12,115.1 gpm
2.15 fps
10,102.5 gpm
1.79 fps
F6-5 Clearview & W. Napoleon
2456.7 gpm
46.0 ft
F6-5 Cleary & W. Napoleon
2966.6 gpm
53.8 ft
E5-4 Transcontinental & W. Metairie
3384.6 gpm
42.6 ft
Pumping Station
34,174.6 gpm
2.69 fps
0.77 fps
7136 gpm
1.27 fps
G6-9 Helios
G6-4 Galleria
F6-2 West Napoleon
E6-7 Transcontinental & Vineland
TOTAL OXYGEN NEEDED
Amount of oxygen required, lb/d,
to satisfy
OUR
697
1172
792
162
8191
DS
702
399
726
1102
3926
Total
1399
3263
6192
1264
12118
Amount
to be
added,
lb/d
1748
4079
7741
1579
15147
Amount to be added
considering 90%
efficiency and 93% O2
purity
2089
4873
9248
1887
18097
EBWWTP
SCHEMATIC DIAGRAM OF THE EAST BANK SEWAGE PUMPING SYSTEM
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?

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