WASTEWATER 101 For MOWA
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BOD Reactions BOD 5 = 0.68 BOD u Lu Carbonaceous BOD BOD 5 Time, Days
BOD w/ Nitrification Oxygen Used for Nitrificationifi ti BOD Point Nitrification Begins Time, Days
Typical BOD Values 300 mg/l for domestic waste or 0.2 lbs/capita/day
How to calculate lbs. BOD/day FLOW (mgd) x Waste x 8.34 Strength (mg/l)
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Removed by settling &/or filtration Consists of grit, organic matter, inert material, & bacteria
Nitrogen Phosphorus Trace Nutrients: Ca, Na, S, K, Fe, Mg, Mn, Co, Zn, Cu, other metals
Forms of Nitrogen: Organic TKN Ammonia Nitrite TN Nitrate KNOW YOUR PROJECT REQUIREMENTS!
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
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
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
OTHER WATER CONTAMINATANTS Pesticides Salts Thermal Solvents Quaternary Ammonium Compounds Acid and Caustic Materials
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
Uses for QUATs Disinfectants & Sanitizers Cosmetic Products Hair-cosmetic Products Pharmaceutical Products Preservatives Fabric Softeners Diagnostic Reagents
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
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
Humans and animals: Pathogen removal Methemoglobinemia Aquatic life: DO Nutrients
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
Secondary Treatment Aeration - Bacteria growing usually under aerobic conditions Clarification - Removal of TSS and/or Bacteria
Secondary Treatment Biological treatment: Dispersed Growth Systems (CMAS) Attached Growth TF and FAST BOD Removed Inorganic Nutrients not normally removed
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
What Kind of BUGS? Classify by Energy Source: Heterotrophs Autotrophs Classify by Oxygen Source: Aerobic Facultative Anaerobic
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
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
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
Tertiary treatment Nutrient removal High effluent quality Filtration Nitrification Denitrification Phosphorus removal
NITRIFICATION Step One: Nitrosomonas NH 4+ + 1.5 O 2 2H + + H 2 O + NO 2-2H+ + HCO 3 H 2 O + CO 2 - Alkalinity (HCO33 ) is destroyed!!
NITRIFICATION Step Two: Nitrobacter NO 2- + 0.5 O 2 NO 3 -
NITRIFICATION Overall Nitrification NH NO 4 2 NO 2 NO 3 NH 4+ + 2O 2 NO 3- + 2H + + H 2 O 2H + + HCO 3 H 2 O + CO 2
Nitrification and Temperature Te empera ature C 25 10 4 15 SRT for Nitrification, Days
Nitrification and Temperature Wastewater Design Temperature ( C) 20 1 Multiplier 15 1.25 10 1.6
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 > 7.0 - Optimum ph = 8.50 Alkalinity
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
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
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
WHAT SYTEMS ARE USED FOR DENITRIFICATION? Pre Aeration Anoxic Systems Post Aeration Anoxic Systems
For > 70% TN Reduction BOD/TKN > 5
For > 70% TN Reduction BOD/TKN < 5
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
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
POSSIBLE CARBON SOURCES Wastewater Bacterial endogenous respiration - very slow and requires large reactor Other easily biodegraded organic materials
POSSIBLE CARBON SOURCES S Methanol - most commonly used Micro C best for onsite systems Ethanol Acetic acid Coke syrup Sugar solution
Denitrification Parameters Oxygen Recov. = 2.8 lb/lb NO 3 Alkalinity Recov. = 3.57 lb/lb NO 3 MeOH = 2.5/NO 3 + 1.5/NO 2 + 0.9/O 2 Practical MeOH = 3 x Inf TKN MeOH = 0.9 lb BOD/lb; 6.59 lb/gal
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
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 - 180 mg/l available in influent = -225 mg/l deficit
Treatment Plant Example: 225 mg/l x EW NaHCO 3 (84) = CaCO EW CaCO (50) 3 3 378 mg/l NaHCO 3 378 mg/l x 0.01 01 mgd x 8.34 = 31.5 lb/day NaHCO 3
Do you have a Total Nitrogen Limit?
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!
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
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Treatment Plant Example: Recycle Rate: 20 mg/l 3 mg/l NO3 = 6.7 RECYCLE FLOW = 6.7 x WASTE FLOW
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
BOD TO TKN RATIO IN ANOXIC TANK BOD TKN 5.0 DRIVING FORCE TO SPEED DENITRIFICATION