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NitrificationandDenitrification Prepared by Michigan Department of Environmental Quality Operator Training and Certification Unit.

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Presentation on theme: "NitrificationandDenitrification Prepared by Michigan Department of Environmental Quality Operator Training and Certification Unit."— Presentation transcript:

1 NitrificationandDenitrification Prepared by Michigan Department of Environmental Quality Operator Training and Certification Unit

2 Nitrogen Environmental And Public Health Concerns

3 Ammonia – NH 3 Nitrite – NO 2 - Nitrate – NO 3 - N Forms of Nitrogen in Wastewater Toxic Oxygen Demand Chlorine Demand Health Concern All Are Nutrients (fertilizer)

4 N Organic Nitrogen Forms of Nitrogen in Wastewater Complex Compounds Protein (plant & animal) Amino Acids etc. Oxygen Demand Nutrient Source

5 N Forms of Nitrogen in Wastewater Total Kjeldahl Nitrogen - “TKN” Total Inorganic Nitrogen - “TIN” Sum of Organic N + Ammonia Sum of Ammonia + Nitrite + Nitrate

6 N Ammonia – NH 3 Nitrite – NO 2 - Nitrate – NO 3 - Organic Forms of Nitrogen in Wastewater “Transform” In Environment And Treatment Plants TKN TIN ?

7 Total Kjeldahl Nitrogen (TKN) NITROGEN CYCLE

8 N Secondary Clarifier Pri.Eff.Sec. Eff. Aeration Tank MLSS WASTEWATER “TREATMENT” OfNitrogen

9 N “Raw” Sewage Organic Nitrogen & Ammonia No Nitrite or Nitrate WASTEWATER “TREATMENT” OfNitrogen

10 N Primary Clarification Some Organic Nitrogen Removed (settled solids) No Ammonia Removed May Increase (Solids Handling) WASTEWATER “TREATMENT” OfNitrogen

11 N Primary Effluent (Secondary Influent) Organic Nitrogen (Less) Ammonia WASTEWATER “TREATMENT” OfNitrogen

12 N Secondary “Treatment” (Biological) WASTEWATER “TREATMENT” OfNitrogen

13 Some Nitrogen Will be Removed By the Biomass (assimilation) Heterotrophic Bacteria Breakdown Organics (Proteins, etc.) To Ammonia 100 : 5 : 1 C : N : P N Bacteria Also Take Up Ammonia

14 N To Meet an Ammonia Limit or a Total Inorganic Nitrogen (TIN) Limit the Process Must be Capable of Nitrification Some Nitrogen Will be Removed By the Biomass (assimilation) NH 3 NO 2 NO 3 Biological Oxidation of Ammonia to Nitrite to Nitrate

15 Nitrification *Heterotrophic Bacteria Break Down Organics Generate NH 3, CO 2, and H 2 O *Autotrophic Bacteria Utilize Inorganic Compounds (and CO 2 as a Carbon Source)

16 Nitrification NH 3 -N Ammonia N NO 2 -N Nitrite N NO 2 -N Nitrite N NO 3 -N Nitrate N Nitrosomonas Nitrobacter Nitrification of Ammonia Occurs in Two Steps *Autotrophic Bacteria Utilize Inorganic Compounds (and CO 2 as a Carbon Source)

17 Operational Controls for Nitrification Air Requirements 1.5 lbs O 2 / lb BOD 4.6 lbs O 2 / lb TKN Increase D.O. in Aeration Tank to 3 - 5 mg/L

18 Nitrification VS D.O. NH 3 -N Removal, % Dissolved Oxygen, mg/L 0 1 2 3 4 5 6 7 8 9 100 90 80 70 60 50 40

19 Aerobic React Time Must Be Long Enough (> 5 hrs.) F:M Ratio Must Be Low Enough (< 0.25) (BOD Removal Must Occur First) Operational Controls for Nitrification

20 Effluent BOD Vs % NH 3 -N Removal Effluent BOD, mg/L 0 10 20 30 40 50 60 70 80 NH 4 -N Removal, % 100 90 80 70 60 50 40 30 20 10 0

21 Control Solids Handling In-plant Return Flows High in BOD and Ammonia Return Slowly Low Quantities At Low Loading Times Inhibit Nitrification Exceed Nitrification Capability Operational Controls for Nitrification

22 Nitrifiers Grow Slowly CRT Must Be Long Enough > 5 Days (minimum) Best > 8 Days Operational Controls for Nitrification

23 Nitrogen, mg/L CRT, Days 25 20 15 10 5 0 0 5 10 15 20 25 30 Effluent NH 3 -N Total Nitrogen Nitrified Nitrification VS CRT

24 Effect of Temperature on Nitrification Lower Temperatures Cause Slower Nitrifier Growth Rate

25 0 5 10 15 20 25 30 35 40 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Temperature, o C Effect of Temperature on Nitrification

26 Minimum of 59 Degrees F. (15 o C) for 90 % Nitrification Lower Temperatures Cause Slower Nitrifier Growth Rate Below 50 Degrees F. (10 o C) Expect Maximum of 50 % Nitrification Effect of Temperature on Nitrification

27 Lower Temperatures Cause Slower Nitrifier Growth Rate Higher MLSS Concentration May Compensate for Lower Temperature Limited By: Oxygen Transfer Maximum MLSS Controllable High CRT Problems Effect of Temperature on Nitrification

28 Importance of Alkalinity in Nitrification NH 4 HCO 3 + O 2 HNO 3 + H 2 O + CO 2 7 mg Alkalinity Destroyed Per mg NH 3 -N Oxidized Chemicals Added For Phosphorus Removal Also Destroy Alkalinity 5.3 - 13.5 lbs Alkalinity per lb Fe Added 6.0 - 9.0 lbs Alkalinity per lb Al Added pH May Become Depressed If Not Enough Alkalinity is Present Nitrifiers are pH Sensitive Most Efficient at pH 8.0 - 8.5

29 pH VS Nitrification Rate at 68 o F pH 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 100 90 80 70 60 50 40 30 20 10 0 % of Max Nitrification Rate

30 Importance of Alkalinity in Nitrification NH 4 HCO 3 + O 2 HNO 3 + H 2 O + CO 2 7 mg Alkalinity Destroyed Per mg NH 3 -N Oxidized Assure Adequate Alkalinity Effluent Above 50 mg/L Influent Above 150 mg/L

31 Importance of Alkalinity in Nitrification NH 4 HCO 3 + O 2 HNO 3 + H 2 O + CO 2 7 mg Alkalinity Destroyed Per mg NH 3 -N Oxidized Assure Adequate Alkalinity Effluent Above 50 mg/L Influent Above 150 mg/L

32 Importance of Alkalinity in Nitrification NH 4 HCO 3 + O 2 HNO 3 + H 2 O + CO 2 7 mg Alkalinity Destroyed Per mg NH 3 -N Oxidized Assure Adequate Alkalinity Effluent Above 50 mg/L Influent Above 150 mg/L Sodium Bicarbonate

33 Dissolved Oxygen CRT, F/M Temperature Alkalinity Return Flows From Solids Handling pH Swings *Toxics in Influent Nitrification Problems NH 3 NO 2 NO 3

34 DENITRIFICATION NO 3 NO 2 N 2 Why Denitrify ??? Groundwater Discharge Permits Limit Total Inorganic Nitrogen (5 mg/L NO 3 -N + NO 2 -N + NH 3 -N) Biological Phosphorus Removal Depends on Removal of Nitrate

35 Definitions Aerobic – Dissolved (Free) Oxygen Present – O 2 Oxic – Dissolved (Free) Oxygen Present – O 2 Anoxic – No Free Oxygen (Combined Oxygen –Nitrates NO 2 and Nitrites NO 3 ) Anaerobic – Oxygen Absent

36 DENITRIFICATION NO 3 heterotrophic bacteria + BOD Anoxic environment N2N2 In an anoxic environment, heterotrophic bacteria will use the oxygen from nitrates as they assimilate BOD, producing nitrogen gas. OxicAnoxicOxic RAS

37 Added Benefits Minimizes Rising Sludge Helps Recover Oxygen May Help Control Filamentous Bacteria Recovers Alkalinity anoxic NO 3 + ORG het. bact. N 2 CO 2 H 2 O OH - 3.57 mg Alkalinity per mg NO 3 Reduced DENITRIFICATION

38 Nitrite and Disinfection Nitrite is a Chlorine “Sponge” Chlorine reacts with Nitrite Instead of Disinfecting Can’t Meet Fecal Coliform Limits Even With Increased Chlorine Dosage

39 Nitrite and Disinfection Amount of Cl 2 Consumed: 5 mg Cl / mg NO 2 Cl 2 + H 2 0 HCl + HOCl HOCl H + + OCl - OCl - + NO 2 - NO 3 - + Cl - NO 2

40 Nitrite and Disinfection Above 63 o F (17 o C) First step is slowest NH 3 NO 2 NO 3 Nitrification (results in < 1 – 2 mg/L NO 2 )

41 At 54 to 57 o F (12 to 14 o C) Second step becomes slowest NH 3 NO 2 NO 3 Nitrite and Disinfection Disinfection with Chlorine Becomes Very Difficult Cold Water NO 2 Problem Nitrification NO 2 can reach 15 mg/L

42 Nitrite and Disinfection Warm Water NO 2 Problem Denitrification NO 3 NO 2 N 2 Second step is slower Worst when carbon (BOD) is limited

43 Nitrite and Disinfection Warm Water NO 2 Problem Denitrification NO 3 NO 2 N 2 Second step is slower Keep System Aerobic Denitrification Not Needed

44 Nitrite and Disinfection Warm Water NO 2 Problem Denitrification NO 3 NO 2 N 2 Second step is slower To Intentionally Denitrify Make Sure BOD is Available During Denitrification

45 Nitrite and Disinfection Toxicity Nitrifiers are more affected than other bacteria Some toxins affect the Nitrobacter more than the Nitrosomonas Results in a build-up of NO 2

46 Nitrite and Disinfection Effect of Ammonia NH 3 NO 2 NO 3 If ammonia is not present, Free Cl reacts quickly with NO 2 Cl = + Disinfection Problems If enough NH 3 is present, Cl reacts to form Chloramines. Chloramines disinfect, but don’t react quickly with NO 2 NH 3 + Cl Chloramines

47 ORP O xidation- R eduction P otential The electrical potential (mv) required to transfer electrons from one compound to another. Used as a qualitative measure of the state of oxidation.

48 ORP O xidation- R eduction P otential

49 ORP

50 ORP

51 NitrificationandDenitrification Prepared by Michigan Department of Environmental Quality Operator Training and Certification Unit


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