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Tertiary Treatment: Nutrient Removal, Solids Removal, and Disinfection

Tertiary Treatment: Nutrient Removal, Solids Removal, and Disinfection. Treated Wastewater Effluent Contains…. BOD (biochemical oxygen demand) Carbon matter, depletes O2, causes biomat growth TSS (total suspended solids) Depletes O2 NH3 (ammonia)

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Tertiary Treatment: Nutrient Removal, Solids Removal, and Disinfection

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  1. Tertiary Treatment:Nutrient Removal, Solids Removal, and Disinfection

  2. Treated Wastewater Effluent Contains… • BOD(biochemical oxygen demand) • Carbon matter, depletes O2, causes biomat growth • TSS(total suspended solids) • Depletes O2 • NH3(ammonia) • Toxic to fish, depletes O2, a nutrient that promotes biol. growth • NO3(nitrate) • Toxic to babies, drinking water regulated, a nutrient • TP(total phosphorus) • A nutrient • Pathogens (bacteria/viruses) • Disease causing

  3. First, We Must UnderstandWastewater Assimilation • A site’s ability to handle the amount of liquid or the amount of pollutants without causing a public health or environmental health concern • In-ground or In-stream discharge • Sometimes, high-quality effluent is necessary • Low BOD • Low fecal coliform • Low nutrients (Nitrogen and Phosphorus) • Protection of sensitive waterbodies, nearby… • Or drinking water supplies (groundwater & wells)

  4. “Discharge” Permits • In-ground dispersal • ADEM for flows of 10,000 gpd + • UIC Permit (underground injection control) • Specifies a certain effluent quantity and quality • BOD, TSS and groundwater monitoring for NO3 • ADPH for smaller systems • Surface dispersal • Stream Discharge • NPDES Permit(specifies BOD, TSS, NH3, NO3, TP, etc.) • Disinfection Required • Spray Irrigation • NPDES Permit • 7-10 day holding pond required • Disinfection Required

  5. Why is tertiary treatment needed? • To better protect public health and environment • To provide additional treatment when soils or receiving waters cannot

  6. Biological Nitrogen Removal • Uptake into biological cell mass • Nitrification (conversion to Nitrate) • Denitrification (conversion to N2 gas)

  7. Biological Nitrification Conversion of Ammonia to Nitrite (Nitrosomonas) NH4+ + 2 O2  NO2- + 2 H+ + H2O Conversion of Nitrite to Nitrate(Nitrobacter) NO2- + 0.5 O2    NO3-

  8. Nitrification (cont.) • For each mg of NH4+ converted… 3.96 mg of O2 are utilized(Need Oxygen) 0.31 mg of new cells are formed 7.01 mg of alkalinity are removed

  9. Nitrification (cont.) • Nitrifying bacteria are sensitive and susceptible to a variety of conditions. • The following factors affect nitrification: • Conc of NH4+ and NO2- • BOD/TKN ratio (BOD should be gone/removed) • Dissolved oxygen conc (need oxygen) • Temperature • pH (7.5 to 8.6)

  10. Nitrification Processes Suspended Growth Separate Stage Nitrification Single State Nitrification

  11. Nitrification Processes Attached Growth Attached Growth Nitrification following Act. Sludge

  12. A modification of aerobic pathways (no oxygen) Same bacteria that consume carbon material aerobically Denitrifying bacteria obtain energy from the conversion of NO3- to N2 gas, but require a carbon source NO3- + CH3OH + H2CO3  C5H7O2N + N2 + H2O + HCO3- Biological Denitrification Cell mass Organic matter

  13. Denitrification • Need low (no) oxygen (< 1 mg/L) • Need carbon source (BOD in Wastewater) • Neutral pH (pH 7) • Conc of nitrate

  14. Denitrification (cont.) • Separate denitrification reactor or • Combined Carbon Oxidation-nitrification-denitrification reactor • A series of alternating aerobic and anoxic stages • Reduces the amount of air needed • No need for supplemental carbon source

  15. Combined Nitrification/Denitrification(note alternating regions of aerobic and anoxic)

  16. Phosphorus Removal • Chemical Precipitation • Calcium (lime) addition at high pH (>10) • Reacts with alkalinity • Alum (Aluminum Sulfate) precipitation • Iron precipitation

  17. Disinfection • Selective destruction of disease-causing organisms • Chlorine • UV Light • Ozone (gas)

  18. Chlorine Disinfection • Liquid chlorine • Sodium hypochlorite (tablets) Note: not allowed to discharge chlorine (it must be removed after disinfection) * chlorine removed with either… a. sulfur dioxide b. sodium bisulfite

  19. Tablet Chlorinator(Calcium Hypochlorite)

  20. Chlorine Disinfection • To be effective… • Chlorine concentration • Contact time • Proper mixing • Temperature • Number and type of organisms

  21. Chlorine Dose

  22. UV Disinfection • UV Light • Specific wavelengths have biocidal properties (~254 nm) • Quartz, mercury-vapor lamps • Cleaning required • No residual

  23. UV Disinfectiona specific wavelength of light

  24. UV Disinfection

  25. Ozone Disinfection • O3 a gas, must be generated on-site • Bubbled into a basin (or pipeline) with treated effluent • Great disinfectant! • No residual…ozone degrades to oxygen, O2 • Costs More, Need equipment and electricity

  26. Ozone Disinfection Flow Diagram Ozone Generation

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