PROTECTING NEIGHBORS AND INFRASTRUCTURE

Transcription

1 16 August 2016 PROTECTING NEIGHBORS AND INFRASTRUCTURE COLLECTION SYSTEM ODOR AND CORROSION CONTROL LYNNE H. MOSS, PE, BCEE RESIDUALS AND ODOR CONTROL PRACTICE LEADER

2 OVERVIEW Odor Generation and Release Treatments Liquid Phase Vapor Phase Predictive Tools 2

3 ODOR GENERATION AND RELEASE 3

4 WASTEWATER AND SLUDGE ODORANTS Hydrogen Sulfide Odorant Examples Dominate Sewer systems Wastewater treatment systems Organic Sulfur Compounds Dimethyl Sulfide Methyl Mercaptan Carbon Disulfide Sludge holding, thickening, dewatering and stabilization processes Nitrogen Compounds Ammonia Amines Skatole Indole Wastewater anoxic basins Sludge digestion (anaerobic, ATAD) CAMBI cake Sludge lime stabilization Polymer (amines) Volatile Fatty Acids Acetic Acid Butyric Acid Valeric Acid Gravity thickeners ATAD Aldehydes and Ketones Acetaldehyde Methyl Ethyl Ketone Acetone Sludge holding, thickening, dewatering and stabilization processes Collection System Odorant 4

5 9/6/2016 SELECT ODORANT THRESHOLD CONCENTRATIONS (OTC) AND CHARACTERISTICS Compound Odor Threshold (ppm) Odor Characteristic Ammonia 5.2 Sharp, pungent Carbon disulfide Sweet, disagreeable Dimethyl disulfide Sulfide, unpleasant Dimethyl sulfide Rotten cabbage Hydrogen sulfide Rotten egg Methyl mercaptan Decaying cabbage Trimethylamine Pungent, fishy From WEF MOP 25 (Table 9.1) NOTE: Published values vary 5

6 H 2 S entering air Laminar Flow Layer SULFIDE GENERATION IN GRAVITY SEWERS H 2 S flux to pipe wall oxidaton to sulfuric acid Acid condensate Slime layer (typically 1 mm) Pipe Wall Sulfide producing zone Inert anaerobic zone Diffusion of SO4 and nutrients Diffusion of sulfide into liquid 6

7 Dissolved Sulfide (mg/l) SULFIDE VS LIFE EXPECTANCY OF RCP < 5 Years 5-10 Years Years Pipe Diameter (Feet) Years > 50 Years

8 100 SULFIDE SPECIES ARE A FUNCTION OF PH 80 % H 2 S Odorous HS - Non-odorous S = Non-odorous ph 8

9 FACTORS THAT AFFECT SULFIDE GENERATION AND RELEASE Generation Release Organic material (BOD) Dissolved oxygen (DO) ph Turbulence Temperature Many treatment approaches focus breaking the chain of sulfide generation and/or release 9

10 TREATMENTS 10

11 Black & Veatch 6 September 2016 COLLECTION SYSTEM ODOR AND CORROSION CONTROL Typical Odor Control Approaches Liquid Treatment Odorous Air Treatment Precipitants Oxidizers Nitrates Carbon Adsorbers Biological Treatment Chemical Scrubbers Chemicals Oxygen Bioscrubber Inorganic Biofilter Organic Biofilter Other tools: Vortex flow inserts, hydroxylion addition, dispersion fans 11 11

12 GENERAL CHEMICAL TREATMENT ADVANTAGES AND DISADVANTAGES FEED PUMP TO WASTEWATER SYSTEM CHEMICAL TANK CONTAINMENT AREA Advantages Ease of installation (often turnkey) Low capital cost Disadvantages High annual costs Some chemicals are hazardous to handle Chemical deliveries in neighborhoods If chemicals added near WWTP, must carefully consider process impacts 12

13 LIQUID PHASE TREATMENTS PRECIPITATION ph ELEVATION PREVENTION OXIDATION Iron Salts Sodium Nitrate Air injection hydroxide (shock dosing) formulations Oxygen injection Magnesium Hydrogen hydroxide peroxide Sodium hypochlorite Potassium permanganate 13

14 IRON SALTS Chemicals used Ferrous/ferric chloride Ferrous/ferric sulfate Removal mechanisms Bind with dissolved sulfide and precipitate Reduce Sulfate Reducing Bacteria activity by 50% (Zhiguo, 2016) Provided as solution with low ph (1 to 2+) Typical dose rates ~ 3.5 lb Fe/lb sulfide Quick reaction times 14

15 IRON SALT ADVANTAGES/DISADVANTAGES Advantages Sulfide specific, can be overdosed Sulfide fully reacted not re-released Disadvantages Corrosive Hazardous materials a concern in neighborhoods Adds solids to wastewater Darkens wastewater: issue for UV systems Residual sulfide mg/l 15

16 NITRATES Calcium nitrate most common Non-hazardous Prevention mode Provides substitute food source for microbes when oxygen depleted Typical dose ~ 2.1 gal/lb sulfide Removal mode Nitrate biochemically oxidizes sulfide Typical dose ~ 0.7 lb gal/lb sulfide Long reaction time needed (1-2 hrs) 16

17 NITRATE ADVANTAGES/DISADVANTAGES Advantages Non-hazardous chemical Provides prevention and treatment Reduces sulfide to very low level No solids added to system Disadvantages High costs Detention time (for removal) Some issues with nitrates at WWTP 17

18 MAGNESIUM HYDROXIDE Dosing independent of sulfide concentration Economical for high (>5 mg/l) sulfide levels Maintains ph at 8 8.5, inhibits SRB activity Adds alkalinity Generally requires mixer to maintain slurry in suspension Source: Premier Chemicals 18

19 MAGNESIUM HYDROXIDE ADVANTAGES/DISADVANTAGES Advantages Non-hazardous chemical Can provide downstream benefits (alkalinity, etc.) Reduces sulfide to very low level No solids added to system Disadvantages Holds sulfide in suspension - inflows may reduce ph and release H 2 S Not generally costeffective for low sulfide streams Mixing required 19

20 LIQUID TREATMENT TRENDS: OXYGEN INJECTION (ECO 2 ) Process Sidestream flow pumped through oxygenation cone Super saturation mg/l 95% transfer efficiency Oxygenated sidestream blended back into main stream System Equipment Sidestream pump Stainless steel oxygenation cone (Speece cone) Oxygen source Oxygen generator Delivered liquid oxygen (LOX) Can be used in prevention or removal mode 20

21 ECO 2 OXYGEN INJECTION Sidestream Pump ECO 2 Cone 90-95% O2 Absorption Efficiency Pure Oxygen Gas Force Main Oxygenated Raw Water D.O. Levels of mg/L

22 CHEMICAL INJECTION TRENDS: TWO ARE BETTER THAN ONE PRI-SC Ferric chloride injection with downstream regeneration of iron with hydrogen peroxide Saves cost, reduces alkalinity impacts Generally best for long segments Bioxide 71 Calcium nitrate plus oxidant 22

23 VORTEX INSERTS Flow through/down vortex aerates wastewater Sizing Based on peak flow, but can handle variations Can accommodate large flows Drop depth Effective from 10 ft. to 100 ft. Low cost, but not applicable for some locations Source: Ipex 23

24 Page - 24 WHERE IS VAPOR-PHASE TREATMENT NEEDED? Areas of possible positive pressure located near sensitive receptors Can include: Lift station wet wells Force main discharge manholes Siphons Areas of high turbulence Junction structures Drop structures 24

25 VAPOR PHASE ODOR CONTROL TECHNOLOGIES Biological treatment: bioscrubbers and manufactured biofilters Chemical treatment: chemical scrubbers, hydroxyl ion/ozone systems Physical treatment: carbon/alumina adsorbers Dispersion: induced flow fans 25

26 BIOLOGICAL TREATMENT Use microorganisms to metabolize compounds Common elements Humidification/irrigation Air Distribution Media to support microbes Key to success: Keep bugs happy Autotrophs (thiobacillus) Heterotrophs Bioscrubber Biofilter 26

27 BIOSCRUBBERS Also known as biotrickling filters Small footprint (comparable to carbon/chemical scrubbing systems) Design basis: Empty bed residence time (EBRT) 5-20 seconds Effective H 2 S removal Best for concentrations > 50 ppm Limited effectiveness for other compounds (at low ph) Synthetic media Loose packing or structured open-cell foam 27

28 MANUFACTURED BIOFILTERS Much larger footprint than bioscrubbers Effective treatment for a variety of compounds Media life warranty Synthetic media 10 years Organic media 5 years Effective treatment for a variety of compounds But limited to moderate H 2 S For high H 2 S, use hybrid system (bioscrubber+biofilter unit) Biofilter Hybrid Schematics Courtesy BioRem 28

29 PHYSICAL ADSORPTION Odorants adsorbed onto granular or pelletized carbon or alumina Adsorptive capacity varies by compound and carbon type Suitable for low H 2 S (<10 ppm airstreams) Media replacement required periodically Design accordingly, consider ease of access Simple, low capital 29

30 ADSORPTION TRENDS: BLENDING MEDIA High H 2 S Capacity Carbon Different Media Layers/Blends To Optimize Performance Activated Alumina Media Blend Iron-based Adsorbent Apply high H2S capacity carbons with care.they do not have a great affinity for other odorants 30

31 HYDROXYL RADICAL FOG SYSTEM (VAPEX) Wet well/tank/sewer applications Combines ozone with water to create a hydroxyl radical fog Delivered by nozzle Oxidizes H 2 S Image source: -26/issue-80/editorial-features/hydroxyl-ionfogging.html 31

32 ENHANCED DISPERSION: MIXED FLOW IMPELLER FANS Applications Polishing Dilute low strength exhausts Up to 170% of free outside air is pulled into the fan Dilutes exhaust Accelerates exhaust Enhances dispersion Very low maintenance direct drive motor Low-profile Can be equipped with silencers Courtesy: Strobic Air 32

33 PREDICTIVE TOOLS 33

34 SULFIDE GENERATION MODELS: THE FOUNDATION Sulfide Generation Model Dissolved Sulfide Interceptor Age Remaining Pipe Wall Thickness Remaining Depth to Rebar Pipe Life Model Corrosion Rate Alkalinity of pipe Coefficient of Efficiency ph % Sulfide as H 2 S Jkljlj Remaining Interceptor Life Without Chemical Treatment % Reduction Remaining Interceptor Life With Chemical Treatment 34

35 PREDICTING SULFIDE GENERATION IN SEWERS: VINTAGE 1977 Pomeroy and Parkhurst Eq. (filled pipes) S 2 =S 1 +(M)(t)[EBOD(4/d+1.57)] Where: S 2 = predicted sulfide concentration at time t 2 (mg/l) S 1 = predicted sulfide concentration at time t 1 (mg/l) M= sulfide flux coefficient (m/h) t = detention time in sewer with constant diameter and flow EBOD = effective biochemical oxygen demand (mg/l) d = pipe diameter, m T = wastewater temperature ( o C) 35

36 INTO THE FUTURE: Proprietary model Developed through Sewer Corrosion and Odour Research (SCORe) program $21M collaborative effort between Australian govt, water industry and research organizations Driver: Infrastructure protection Lack of tools to support decision-making and cost-effective sewer operations Operated by University of Queensland Advanced Water Management Centre MATLAB/SIMULINK platform 36

37 SEWEX CAPABILITIES Predictions Biological carbon transformations under aerobic, anoxic and anaerobic conditions Biological sulfur transformations: sulfur reduction, microbial oxidation (O2 and NO3), sulfur release from hydrolysis of organo-sulfurs Chemical oxidation of sulfide with oxygen Chemical precipitation of sulfide and several other competing anions by metal ions ph variation in wastewater caused by biological and chemical reactions Gas phase hydrogen sulfide and methane concentrations: temporal and spatial Considerations Biological and chemical processes in the sewer biofilm and the bulk liquid: these include aerobic, anaerobic and anoxic transformations, chemical oxidation and precipitation Convective transport (liquid and gas phase as applicable) Gaseous transfer between the liquid and the gas phases (in gravity sewers) Transport of gases in headspace (in gravity sewers) Uptake of hydrogen sulfide in the headspace Weak acid-base equilibrium calculations for ph prediction 37

38 CONCLUSIONS Exciting times! Revolutionary tools Expanding treatment options Support to advance new tools/techs: WERF LIFT Added Odor Control as a new Focus Area in 2015 Initial focus: development of a better methodology for technical evaluation of odor reduction products for efficacy and performance optimization Stay tuned 38

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