Activated Sludge Nitrification/Denitrification Fundamentals by R. Dale Richwine, P.E. Richwine Environmental, Inc. Session Overview » Forms of Nitrogen » Nitification/Denitrification Principles » Nitrification in a WWTP » Ammonia/Nitrogen Removal Processes 1 Nitrogen » Total Nitrogen (TN) » Total Kjeldahl Nitrogen (TKN) » Organic Nitrogen (Organic-N) » Ammonia Nitrogen (N-NH3 or N-NH4+) » Nitrite (NO2) » Nitrate (NO3) » Elemental Nitrogen (N2) Nitrogen » TN = TKN + NO2 + NO3 » TKN = Organic-N + N-NH3 » Nitrogen Cycle – – – – Nitrogen Fixation (N2 Organic-N) Ammonification (Organic-N N-NH3) Nitrification (N-NH3 NO2 NO3) Denitrification (NO3 N2) 2 Nitrogen Cycle Aerobic Respiration Oxidizes Organics to CO2 and H2O for Energy 3 Organic Nitrogen is converted to Ammonia OXIDATION AND SYNTHESIS bacteria COHNS + nutrients ⎯⎯ ⎯⎯→ CO2 + NH3 + C5H7NO2 + other end products ENDOGENOUS RESPIRATION bacteria C5H7NO2 + O2 ⎯⎯ ⎯⎯→ 5CO2 + 2H 2O + NH3 + energy Ammonification 4 Biological Nitrification » 2-step process » Step 1 – Ammonia converted to Nitrite » Step 2 – Nitrite converted to Nitrate Nitrification 5 Biological Nitrification Step 1: Ammonia oxidized to Nitrite. Hydrogens are released resulting in the reduction of alkalinity. Nitroso - bacteria 2NH + 3O ⎯⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯→ 2NO − + 2H O + 4H+ 4 2 2 2 Step 2: Nitrite is oxidized to Nitrate Nitro − bacteria 2NO − + O ⎯⎯ ⎯ ⎯ ⎯ ⎯ ⎯⎯→ 2NO − 2 2 3 Total Oxidation Reaction NH+ + 2O ⎯⎯⎯⎯→ NO- + 2H+ + H O 4 2 3 2 Ammonium Oxidation Bacteria Nitroso - bacteria 2NH + 3O ⎯⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯ ⎯→ 2NO − + 2H O + 4H+ 4 2 2 2 Ammonia Oxidizing Bacteria • Nitrosomonas • Nitrosospira • Nitrosococcus • Nitrosolobus • Nitosorobrio 6 Nitrite Oxidation Bacteria Nitro − bacteria 2NO2− + O2 ⎯⎯ ⎯ ⎯ ⎯ ⎯ ⎯⎯→ 2NO3− Nitrite Oxidizing Bacteria • Nitrobacter • Nitrococcus • Nitrospina • Nitrospira • Nitroeystis Rates of Nitrification by Various Bacteria Organism Substrate Product Rate of Formation Max. Product Accumulation Arthrobacter NH4+ Nitrite 375 – 9,000 0.2 – 1 Arthrobacter NH4+ Nitrate 250 – 650 2 – 4.5 Aspergillis NH4+ Nitrate 1,350 75 Nitrosomonas NH4+ Nitrite 1 – 30 million 2,000 – 4,000 Nitrobacter NH2- Nitrate 5 – 70 Million 2,000 – 4,000 7 Alkalinity Requirements NH+ + 2HCO− + 2O ⎯⎯→ NO− + 2CO + 3H O 4 3 2 3 2 2 For each gram of ammonia nitrogen (as N) converted 7.14 grams of alkalinity as CaCO3 is required. Biological Denitrification Carbon Source Required as Electron Donor − ⎯⎯→ NO ⎯⎯→ N O ⎯⎯→ N NO3 2 2 Wastewater C H O N + 10NO− ⎯⎯→ 5N + 10CO + 3H O + NH + 10OH− 10 19 3 2 2 2 2 3 Methanol 5CH OH + 6NO− ⎯⎯→ 3N + 5CO + 7H O + 6OH− 3 3 2 2 2 8 Denitrification Nitrification in the WWTP Org-N Ammonification Org - N → NH4 - N Influent TKN Nitrogen Gas NH4 - N Nitrification NH4 - N → NO3 - N Aerobic Denitrification NO3 - N → N2 (g) Anaerobic 9 Processes Used for Nitrogen Removal Nitrification Processes » Preanoxic – – – – – – Ludzack-Ettinger Modified Ludzack-Ettinger (MLE) Step Feed Sequencing Batch Reactor (SBR) Bio-denitro Nitrox 10 Nitrification Processes » Post-anoxic – – – – Single-sludge Bardenpho (4-stage) Oxidation Ditch Two-stage (two-sludge) » Simultaneous Nitification/Denitrification – Low DO Oxidation Ditch – Orbal Oxidation Ditch Ludzack-Ettinger Secondary Clarifier Influent Anoxic Aerobic Effluent Return activated sludge Sludge 11 Modified Ludzack-Ettinger (MLE) Internal recycle Secondary Clarifier Influent Anoxic Effluent Aerobic Return activated sludge Sludge Step Feed Influent Secondary Clarifier Anoxic Aerobic Anoxic Aerobic Anoxic Aerobic Anoxic Aerobic Effluent Return activated sludge Sludge 12 Sequencing Batch Reactor (SBR) Influent Air Effluent Fill Fill anoxic/anaerobic mix React/aeration Settle Decant Idle Bio-denitro Secondary Clarifier Aerobic Anoxic Effluent Influent Aerobic Aerobic Return activated sludge Return activated sludge Sludge Sludge Phase B Phase A Aerobic Aerobic Effluent Influent Effluent Influent Aerobic Anoxic Return activated sludge Return activated sludge Sludge Sludge Phase C Effluent Influent Phase D 13 Nitrox Aerator and mixer control PLC Aerator DO ORP Secondary Clarifier Effluent Mixer Return activated sludge Sludge Influent Single-Sludge Secondary Clarifier Influent Aerobic Anoxic Effluent Return activated sludge Sludge 14 Bardenpho (4-stage) Mixed-liquor return Secondary Clarifier Influent Anoxic Aerobic Anoxic Aerobic Effluent Return activated sludge Sludge Oxidation Ditch Aerators Anoxic Aerobic Secondary Clarifier Effluent Return activated sludge Influent Sludge 15 Two-Stage (two-sludge) Air Air Methanol Primary Clarifier Nitrification Clarifier Secondary Clarifier Effluent Influent Nitrification tank Denitrification tank Return activated sludge Return activated sludge Sludge Sludge Sludge Low DO Oxidation Ditch Aerators Influent Secondary Clarifier Effluent DO probe NADH probe (Sym-BioTM process) Return activated sludge Sludge 16 Orbal Aerobic First channel Second channel Third channel Anoxic Secondary Clarifier Anaerobic Effluent Influent Internal recycle (optional) Return activated sludge First channel Sludge Second channel Third channel Influent Effluent Session Summary » Forms of Nitrogen » Nitification/Denitrification Principles » Nitrification in a WWTP » Ammonia/Nitrogen Removal Processes 17
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