WASTEWATER 101 Fo r MOWA

Transcription

1 WASTEWATER 101 For MOWA

2 iochemical xygen emand

3 BOD Reactions BOD 5 = 0.68 BOD u Lu Carbonaceous BOD BOD 5 Time, Days

4 BOD w/ Nitrification Oxygen Used for Nitrificationifi ti BOD Point Nitrification Begins Time, Days

5 Typical BOD Values 300 mg/l for domestic waste or 0.2 lbs/capita/day

6 How to calculate lbs. BOD/day FLOW (mgd) x Waste x 8.34 Strength (mg/l)

7 otal uspended olids

8 Removed by settling &/or filtration Consists of grit, organic matter, inert material, & bacteria

9 Nitrogen Phosphorus Trace Nutrients: Ca, Na, S, K, Fe, Mg, Mn, Co, Zn, Cu, other metals

10 Forms of Nitrogen: Organic TKN Ammonia Nitrite TN Nitrate KNOW YOUR PROJECT REQUIREMENTS!

11 EXPRESS NITROGEN AS N MULTIPLY BY EQUIVALENT WEIGHTS FOR NO 3 : 30 mg/l as NO 3 x14/(14+3x16) or 6.8 mg/l as N FOR NH 3 : 40 mg/ as NH 3 x 14/(14+3x1) or 32.9 mg/l as N

12 PHOSPHORUS Removed biologically or chemically Typical values are 8-10 mg/l Phosphorus h Precipitation it ti and flocculation with Ferric Chloride or alum Larger Sludge Storage Volume Required

13 Pathogens are Disease Causing Bugs Pathogens are Very Difficult to Detect --- Test for possible presence using Indicator Organisms: Coliforms -- Example: Escherichia coli Fecal Coliforms, and Fecal Streptococcus

14 OTHER WATER CONTAMINATANTS Pesticides Salts Thermal Solvents Quaternary Ammonium Compounds Acid and Caustic Materials

15 Quaternary Ammonium Compounds - Disinfectant Ammonium Ion with 4 Radicals Attached Not oxidizers - Surface-active agents Breakdown bacterial cell walls Internal contents of bacteria leak out Commonly used at 200 ppm Effective at High Temperatures Do not kill all gram negative bacteria

16 Uses for QUATs Disinfectants & Sanitizers Cosmetic Products Hair-cosmetic Products Pharmaceutical Products Preservatives Fabric Softeners Diagnostic Reagents

17 Problems with QUATs in Wastewater Treatment Toxic/Inhibitory to Nitrifying Bacteria Concentration Limit <2 mg/l Nonbiodegradable NH3 Nonbiodegradable Organic Nitrogen Exponential Increase in Use Slow -- Difficult to Biodegrade

18 Clean Water Act of 1972 Required 85% removal of BOD and TSS for all POTWs National Pollutant Discharge Elimination System (NPDES) Control point source discharge Control nonpoint source discharge

19 Humans and animals: Pathogen removal Methemoglobinemia Aquatic life: DO Nutrients

20 Primary Treatment Screening and Sedimentation Septic Tanks Grease Trap Disinfection of Raw Waste- optional 30-35% BOD removal 60% TSS removal DOES NOT eliminate nutrients or oxygen depletion problems

21 Secondary Treatment Aeration - Bacteria growing usually under aerobic conditions Clarification - Removal of TSS and/or Bacteria

22 Secondary Treatment Biological treatment: Dispersed Growth Systems (CMAS) Attached Growth TF and FAST BOD Removed Inorganic Nutrients not normally removed

23 Review of Units BOD as 5 day, unless specified Alkalinity as CaCO 3 TKN as N NH 3 as N NO 2- as N NO 3- as N Phosphorus p as P

24 What Kind of BUGS? Classify by Energy Source: Heterotrophs Autotrophs Classify by Oxygen Source: Aerobic Facultative Anaerobic

25 BUGS CONTINUED BOD Removal - ordinary soil type bacteria Nitrification - very specialized bacteria Denitrification ifi ti - facultative ti type from the group of the bugs removing BOD Anaerobic - very specific - methane formers and acid formers Higher forms of life - protozoa, worms, & rotifers

26 Bacterial Cell Growth Heterotrophs C 5 H 7 O 2 N Cell Mass Trace nutrients t required Carbon from organics in wastewater Energy from oxidation of organics in wastewater

27 Bacterial Cell Growth Autotrophs t C 5 H 7 O 2 N Cell Mass Energy from oxidation of inorganic material Carbon from CO 2, NaHCO 3 (alkalinity ) Trace nutrients required Strict aerobes

28 Tertiary treatment Nutrient removal High effluent quality Filtration Nitrification Denitrification Phosphorus removal

29 NITRIFICATION Step One: Nitrosomonas NH O 2 2H + + H 2 O + NO 2-2H+ + HCO 3 H 2 O + CO 2 - Alkalinity (HCO33 ) is destroyed!!

30 NITRIFICATION Step Two: Nitrobacter NO O 2 NO 3 -

31 NITRIFICATION Overall Nitrification NH NO 4 2 NO 2 NO 3 NH O 2 NO H + + H 2 O 2H + + HCO 3 H 2 O + CO 2

32 Nitrification and Temperature Te empera ature C SRT for Nitrification, Days

33 Nitrification and Temperature Wastewater Design Temperature ( C) 20 1 Multiplier

34 Nitrification is a Very Sensitive Process: Extended da Aeration Mode (Nitrifiers are Slow growers) Long SRT Required Extra Oxygen (How much?) Temp > 15ºC, 20ºC is better ph > Optimum ph = 8.50 Alkalinity

35 Nitrification Parameters Oxygen required = 4.6 lb/lb TKN Alkalinity required = 7.1 x influent TKN + 50 mg/l 0.66 lb alkalinity/lb NaHCO 3 Hydroxide H d alkalinity li it not used

36 DENITRIFICATION Reduction of nitrite and nitrate In absence of oxygen Requires an oxygen demandd Nitrite and nitrate provide O 2 Requires a carbon source to provide a BOD demand

37 DENITRIFICATION NO 3 +BOD+CO + 2 N 2 +H 2 O + HCO 3 Nitrogen is released as N 2 gas Resulting in nitrogen reduction Bicarbonate alkalinity is produced BOD is reduced

38 WHAT SYTEMS ARE USED FOR DENITRIFICATION? Pre Aeration Anoxic Systems Post Aeration Anoxic Systems

39 For > 70% TN Reduction BOD/TKN > 5

40 For > 70% TN Reduction BOD/TKN < 5

41 PRE AERATION ANOXIC SYSTEMS Require aeration effluent recycle No need to add a carbon source - use raw wastewater for BOD demand Limited by size of anoxic tank and rate of recycle Recover alkalinity and reduce BOD

42 POST AERATION ANOXIC SYSTEMS Require Feeding Carbon Source - BOD Capable of Reducing Nitrate to Very Low Levels Requires Reaeration System Does Not Recover Alkalinity Does Not Reduce BOD

43 POSSIBLE CARBON SOURCES Wastewater Bacterial endogenous respiration - very slow and requires large reactor Other easily biodegraded organic materials

44 POSSIBLE CARBON SOURCES S Methanol - most commonly used Micro C best for onsite systems Ethanol Acetic acid Coke syrup Sugar solution

45 Denitrification Parameters Oxygen Recov. = 2.8 lb/lb NO 3 Alkalinity Recov. = 3.57 lb/lb NO 3 MeOH = 2.5/NO /NO /O 2 Practical MeOH = 3 x Inf TKN MeOH = 0.9 lb BOD/lb; 6.59 lb/gal

46 Alkalinity Buffer system Maintains ph Measure of a waters ability to absorb H+ ions without change in ph 7.1 mg/l of alkalinity used up for each mg/l NH 3 oxidized Referred to in terms of as CaCO 3

47 Treatment Plant Example: Alkalinity: li it 50 mg/l TKN x 7.1 mg of alkalinity/mg TKN = 355 mg of alkalinity needed + 50 mg/l to maintain ph = 405 mg/l required in influent mg/l available in influent = -225 mg/l deficit

48 Treatment Plant Example: 225 mg/l x EW NaHCO 3 (84) = CaCO EW CaCO (50) mg/l NaHCO mg/l x mgd x 8.34 = 31.5 lb/day NaHCO 3

49 Do you have a Total Nitrogen Limit?

50 REVIEW - IS DENITRIFICATION REQUIRED NO 3- - O 2 N 2 NO 2- - O 2 N 2 Nitrate used as oxygen source for BOD removal by bacteria Nitrification must occur first to produce the p nitrates!

51 Denitrification Reduces NO3 to Nitrogen Gas: Optimum ph 7-8 Requires DO less than 0.5 mg/l Requires mixing i Requires es carbon (energy) e source for bugs Carried out by facultative bacteria

52 To or

53 Treatment Plant Example: Recycle Rate: 20 mg/l 3 mg/l NO3 = 6.7 RECYCLE FLOW = 6.7 x WASTE FLOW

54 IS RECYCLE RATIO TOO HIGH? INFLUENT TKN = 75 mg/l INFLUENT Q = 21,600 gpd REQUIRED EFFLUENT NO3 = 3 mg/l RECYCLE RATIO: 75/3 = 25 RECYCLE FLOW = 21,600 x 25 OR 540,000 gpd Excessive Min HRT of Anoxic Tank = 1 to 3 hrs ie. LARGE PUMP & LARGE TANK

55 BOD TO TKN RATIO IN ANOXIC TANK BOD TKN 5.0 DRIVING FORCE TO SPEED DENITRIFICATION