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Advanced WW Treatment Systems: Phosphorous and Nitrogen Removal

Learn about the basics of advanced wastewater treatment systems, including the removal of phosphorous and conversion of ammonia to nitrate. Explore methods to inactivate pathogens, remove heavy metals, and eliminate organic and inorganic salts.

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Advanced WW Treatment Systems: Phosphorous and Nitrogen Removal

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  1. CTC 450 Review • WW Systems Operations

  2. Objectives • Understand the basics with respect to advanced WW treatment

  3. Two systems • Advanced (tertiary and ww reclamation) • Remove phosphorous • Convert ammonia to nitrate (nitrification) • Convert nitrate to nitrogen (denitrification) • Inactivate pathogens • Remove heavy metals • Remove organic chemicals • Remove inorganic salts • Eliminate all pathogens

  4. Limitations-Biological Treatment • Doesn’t remove phosphorous or ammonia • Incomplete disinfection • Doesn’t remove all toxins • Doesn’t remove non-biodegradable soluble chemicals

  5. Excess Phosphorous • “Fertilizes” receiving waters • Causes algal blooms • Depletes DO • Reduces water transparency • Releases foul odors • Can lose “finer” fish species

  6. Excess Nitrogen • Ammonia can be toxic to fish/aquatic animals • Can increase eutrophication (but usually phosphorous is limiting)

  7. Pathogens • Conventional biological treatment • Up to 99.9% removal • With disinfection up to 99.99% • Protozoal cysts and helminth eggs are resistant

  8. SS Removal-Advanced • Granular-Media filters (similar to water treatment) • Cloth Media filters • Membrane filters

  9. Pathogen Removal-Advanced • Remove solids first via filtration (pathogens can be protected in the solids) • Chlorination (similar to water treatment)

  10. Toxic Substance Removal • Toxic-Hazardous to aquatic life or human health • Priority toxic water pollutants-over 100 • Evaluating toxicity • Test influent/effluent for specific substances • Biomonitor-fathead minnows, water fleas

  11. Phosphorous Removal • Soluble or organic (organically bound) • Conventional treatment removes 20-40% of phosphorus • Example 13-1 • Advanced treatments • Chemical-biological • Reverse osmosis

  12. Example 13-1 (Where is the PO43-) • Given the following, trace the inorganic, organic and total phosphorus through a conventional activated-sludge treatment plan. • Assume: • Primary clarifier removal of 35% BOD • Primary clarifier removal of 50% solids w/ 0.9% phosphorous • Activated sludge • F/M ratio of 0.40 & 2% phosphorus in the sludge • Filtrate recycles 5% of the influent phosphorus

  13. Example 13-1

  14. Example 13-1 (Refer to Figure 13-11)Plant Influent / Primary Influent • Total P is 7 mg/l into the plant (100%) • Primary influent is not the same as plant influent because of recycle of dewatered sludge filtrate • Recycled P=5% so influent P=105% • Total P is 7.35 mg/l into the primary

  15. Example 13-1 (Refer to Figure 13-11)Primary Effluent (2 routes) • Sludge (15%) • 0.9%*120 mg/l = 1.1 mg/l • 1.1/7 = 15% • Effluent (90%); 7.35-1.1=6.25 mg/l total • Pi=4.35 (see table; no change in inorganic P) • Po=1.90 (6.25-4.35) • 6.25/7 = 90%

  16. Example 13-1 (Refer to Figure 13-11)Secondary Effluent (2 routes) • Sludge (20%) • From Fig 11-45 (pg 415) k=0.5 • Biological sludge solids=0.5*130 mg/l=65mg/l • 2% of 65 mg/l = 1.3 mg/l • 1.3/7 = 20% • Effluent (70%); 7.35-1.1=6.25 mg/l total • Pi=3.05 (see table; inorganic P is removed) • (6.25-1.3-1.9) • Po=1.90 (see table; organic P is not removed) • 4.95/7 = 70%

  17. Example 13-1 (Refer to Figure 13-11) • 70% of P remains in the treated WW • 30% of P removed in sludge solids

  18. Chemical-Biological • Chemicals used • Alum • Iron Salts • Chemical-Biological • Chemicals added in primary clarifiers • Chemicals added before secondary • Chemicals added before final clarifier

  19. Example 13-2 (Refer to Figure 13-12)Add alum to remove P • Alum applied to primary tank • 18% of P remains in the treated WW • 82% of P removed in sludge solids

  20. Nitrogen-Atmospheric • Atmospheric Nitrogen to Organic Molecules • Nitrogen-fixing bacteria (rhizobia) • Live in root nodules of plants (symbiotic relationship) • Legumes (beans, clover, peas, peanuts,…) • Plants get nitrogen in a usable form • Animals get nitrogen from eating plants • Animals excrete nitrogen as a waste product, usually in the form of ammonia

  21. Nitrogen • Organic • Excreted or Decomposed to ammonia • Ammonia • Nitrosomonas oxidize ammonia to nitrite • Nitrite • Nitrobacter oxidize nitrite to nitrate • Nitrate • Under anaerobic conditions via facultative heterotrophs, nitrates are converted to nitrogen gas (which escapes into the atmosphere) • Nitrogen gas

  22. New Type of Microbe • Ammonia to nitrogen directly • NH4+ + NO2− → N2 + 2H2O • Anammox (anaerobic ammonium oxidation) • Advantage: No oxygen needed • Strangeness: anammox bugs also produce hydrazine (rocket fuel) • Bugs store the hydrazine in a dense membrane structure of fused carbon rings • Ref: The Invisible Kingdom, Idan Ben-Barak

  23. Identified in 1999 https://en.wikipedia.org/wiki/Anammox

  24. Nitrogen in WW • 40% ammonia; 60% is bound in organic matter • Usually not enough oxygen is available to convert to nitrites or nitrates

  25. Nitrogen Removal-Conventional • Primary sedimentation (15% removal) • Biological treatment (another 10%) • Remainder is mainly in the form of ammonia unless oxidation occurs (activated sludge at low BOD loading)

  26. Nitrogen Removal-Advanced • After biological treatment: • Aeration • Final settling • Alkalinity is reduced when nitrification takes place; lime or soda ash is added to maintain alkalinity

  27. Nitrate removal • Nitrate can pollute groundwater • Denitrification converts nitrates to nitrogen gas • Process is anaerobic or anoxic • Process requires an organic carbon source (methanol or raw ww) • Via recycle, denitrification can be placed ahead of nitrification

  28. EBPR-Enhanced Biological Phosphorous Removal • Anoxic zone (0.5 to 3 hours detention time) followed by aerobic zone (6-24 hrs) • Helps remove both N and P

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