Biological Reactions in Wastewater Treatment

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Biological Reactions in Wastewater Treatment
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Process Design/Optimization

• Goal Alignment
• Plant - wastewater treatment
• Organic C Removal (BOD/COD ? CO2)
• Nitrification (NH3 ? NO3-)
• Denitrification (NO3- ? N2)
• P Removal (? bio-P in sludge)
• Good Sludge Settling/Retention (minimize TSS,
  turbidity, bacteria, virus)
• Microbes
• Survival
• Growth

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Maintenance
Survival
Energy
Oxidation
Growth
Oxidant
Growth
Materials
C5H7NO2
Assimilation
Biomass Source
C 50 N 14 P 3 K Na Trace elements
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• Heterotrophs
• Organics for both energy and C sources
• Organic C removers (? CO2)
• Denitrifiers (NO3-/NO2- ? N2)
• Enhanced P removers (PAOs, Polyphosphate
  Accumulating Organisms)
• (Chemo)Autotrophs
• Inorganics for Energy Source (chemo) CO2 for C
  source (auto)
• Nitrifiers (NH3 ? NO2-/NO3-)

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Nitrifiers
CO2
O2
NH3
Biomass
Ammonia Oxidizers (Nitrosomonas)
NO2-
H2O
NO2-
NO3-
Nitrite Oxidizers (Nitrobacter)
Low energy available from NH3/NO2- oxidation
High energy requirement for CO2 fixation
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Heterotrophs
More reduced environment
Less energy derived
CO2
N2
CH4
H2O
H2S
Biomass
NO2-
CO32-
SO42-
O2
NO3-
Organic C
(Aerobic) Respiration
Methanogenesis
Denitrification
Organic C Removal
Sulfate Reduction
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P Removal by PAOs
H3PO4
PHB
Poly-P hydrolysis
Organic C
H3PO4
CO2
H2O
Biomass
O2
Poly P formation
Organic C
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Competition for Food in Anaerobic Selector
PAOs
Breakage of high-energy bonds
Fermentative Microbes
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Limiting Nutrient Effect of HRT, SRT, F/M EPS
Production
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Environmental Parameters

• Temperature
• pH/Alkalinity
• DO
• ORP
• Mixing

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Temperature
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Temperature-Induced Population Change
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Some points about T

• Cell activities release heat, rates depend on
  cell concentration and activities
• Heat transfer (aeration, water vaporization,
  insulation, mixing)
• High foaming at high temperatures
• High temperature sensitivity of nitrifiers

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Process Parameters in BNR

• Nitrification

Temperature Min. Sludge Age
5oC 22 days
10oC 10 days
15oC 6 days
20oC 4 days
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pH -logH
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Some points about pH

• Cell energy generation depends on
  proton-motive-force (essentially a pH gradient
  across cell membrane)
• Affects ionic charges of molecules consequently,
• Transport across cell membrane
• Water solubility
• Hydrophobic/hydrophilic properties
• Coagulation/flocculation/aggregation
• Etc.

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pH

• Basic Compounds/Ions
• NH3
• Acidic Compounds/Ions
• CO2/H2CO3
• HNO3/HNO2
• H3PO4

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pH vs. Alkalinity

• Alkalinity Concentration of bicarbonate HCO3-
• CO2 H2O ? H2CO3 ? H HCO3- ?2 H CO32-
• Primarily consumed or generated in pH-regulation
  (a buffer)
• Very small amounts consumed in building nitrifier
  biomass, or generated (as CO2) from
  metabolism/respiration

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pH
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pH in Anoxic/Anaerobic Stage of SBR
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pH in Aerobic Stage of SBR
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DO

• Concentration of dissolved O2 in the water
• Available for respiration (energy generation)
• Upper Limit (Solubility)
• Air (21 O2, 79 N2)
• 8 ppm (mg O2/L) at 200 C
• Pure O2 (100 O2)
• 36 ppm
• Decrease w/ increasing T

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DO
Microbe
Bubble
O2
DO100
Bulk
DO measured
0
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DO
Oxygen Transfer Rate Oxygen Uptake Rate
Supply - Demand
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DO

• OTR kLa (DO100 - DO)
• kLa Oxygen Transfer Coefficient
• Aerator design
• Mixing speed
• Aeration rate
• Mixed-liquor properties (esp. viscosity)
• DO100 Solubility
• gas (air or O2-enriched air)
• Temp
• ML properties (weakly)

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DO

• OUR (TS) ? (SOUR)

• SOUR depends on
• DO
• Energy Source Concn

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Monod Behavior
SOUR
max
½ max
Km
DOcrit.
DO

• DOcrit. differ w/ microbial species
• 0.15 ? mg/L Heterotrophs
• 0.75 1.5 mg/L Nitrosomonas (NH3 oxidizers)
  
• 2.0 5.0 mg/L Nitrobacter (Nitrite
  oxidizers)

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kLa (DO100-DO) - (TS)(SOUR)
Aerobic
Anoxic/Anaerobic
Ammonia Valley
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ORP (Oxidation-Reduction Potential)

• Extension of DO to anoxic/anaerobic stages
• Other oxidants, NO3-/NO2-, Fe2, SO42-, CO32-
  present for anaerobic respiration
• A measure of oxidizing ability, lumping effects
  of all components present
• ORP f(DO, pH, everything)
• Decrease linearly w/ increasing pH
• Increase w/ log(DO), more sensitive at low DO

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ORP in SBR Experiments
Nitrate Knee
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Process Parameters in BNR
ORP Metabolic Conditions/Reactions
50 to 225 mV Aerobic / Oxidation of Organic Carbon
100 to 325 mV Aerobic / Nitrification
50 to -50 mV Anoxic / Denitrification
-100 to -400 mV Anaerobic / Fermentation
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Mixing

• Bulk mixing minimize variation of local
  environmental conditions sensed by microorganisms
• Interfacial mixing create shear or relative
  motion
• between air(bubble) and water, affects
  oxygenation efficiency
• bewteen membrane surface and water, affects
  biofilm thickness in MBR
• between water and flocs, affects floc size

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Monitoring/Control Parameters

• Water-Phase Properties
• DO (Dissolved Oxygen Concentration)
• pH
• ORP (Oxidation-Reduction Potential)
• Sludge-Phase (Microbial) Properties
• Culture Fluorescence
• NADH
• Protein

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Fluorescence

• absorption of light at a specific wavelength,
  followed by emission of light at a longer
  wavelength
• high selectivity
• high sensitivity
• high speed
• high stability, low maintenance

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NO2-
Present in ALL living organisms
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• (NAD NADH) relatively constant for each
  species
• NADH/NAD ratio varying w/ metabolism, responding
  to environment

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• NADH is fluorescent
• excitation 340 nm, emission460 nm
• NAD is not fluorescent

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NADH Fluorescence

• Intracellular ORP (opposite)
• Not affected by pH per se (Intracellular PH
  constant)
• selectively reflecting the oxidation-reduction
  pair involved, insensitive to interferences

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• Step change w/ oxidation mechanisms
• Anaerobic gt Anoxic gt Aerobic

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Online NADH Fluorescence at Oaks WWTP
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Increase w/ (F/M)
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(No Transcript)
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SND in a sludge floc - Microscopic
DO concentration gradients can create anoxic
zones within sludge flocs
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Protein Fluorescence

• Primarily from tryptophan residues
• Excitation 290 nm
• Emission 350 nm
• Regardless live or dead organisms
• Proven useful in sludge digestion

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Los Lunas, NM5.1 TS, Low DO
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Protein Fluorescence

• Not studied for applicability in liquid side of
  WWT
• For plants w/ protein-rich influent water,
  protein fluorescence of influent water as a
  measure of BOD
• For plants w/ water of minimal protein contents,
  ML protein fluorescence may correlate w/ MLVSS