ESM 214 Winter 2005

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ESM 214Winter 2005

• Lecture 7 Biological Treatment

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Biological Treatment

• Transform organics into end products
• New biomass (sequestration)
• CO2, H2O, nutrients, gas and other
• Capture solids in biological floc
• Removes nutrients (P N)
• Removes trace organics

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Biological Trmt Processes

• Activated sludge (in secondary treatment)
• Fixed film treatment (attached growth)
• Trickling filters
• Rotating biological contactors
• Aerobic digestion
• Anaerobic Digestion
• Lagoons
• Aerated
• Non-aerated

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Biological Reactions in Aerobic Treatment
Oxidation
Synthesis food(COHNS) O2 energy
C5H7NO2
Endogenous respiration C5H7NO2 5 O2 ? 5CO2
2H2O NH3
overall
food (COHNS) O2 CO2 H2O NH3
products C5H7NO2
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Stoichiometry in Biological Trmt

• Useful in estimating proportions
• 1. Yield Y
• 2. Oxygen demand
• 3. Nutrient requirements

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Microbes Need (a review)

• Source of C
• CO2 autotroph
• Organic compounds heterotroph
• Source of energy
• Sunlight phototroph
• Chemicals chemotroph
• Electron acceptor
• Electron transport phosphorylation (ETP)
• Molecular oxygen aerobe
• Not oxygen (e.g. NO3-) anaerobe
• Substrate level phosphorlyation
  (fermentation)substrate

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Microbes need (a review, cont.)

• Nutrients
• Macronutrients N, P, K, etc.
• Trace elements Mn, Mg, etc.
• Environmental Conditions
• Temperature
• Psychrophiles -10 to 20 C
• Mesophiles 10 to 50C
• Thermophiles up to 140 C
• pH
• Acidophiles generally below pH 7
• Alkalophiles above pH 7

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Bacterial growth

• In well-mixed system with no nutrient
  limitations, its first order
• Where X biomass concentration, m specific
  growth rate (1/t)

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Bacterial Kinetics

• Varies with
• Microbes
• Substrate (s)
• Concentration
• Temperature
• Described by
• Monod eqn (growth)
• Michaelis Menten (no growth)

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Kinetics

• Monod growth
• Yield Y
• substrate utilization rate

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Kinetics
Observed Growth (7-21)
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Mass Balance Suspended Growth Biological
Treatment

• CFSTR or plug
• flow aeration basin
• RAS
• WAS
• No influent biomass
• Well-mixed, aerated

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Mass Balance Biomass
Solids retention time (a.k.a. MCRT)
SRT is the average time solids are in the system.
SRT is a design criteria.
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Suspended Growth Biological Treatment

• Mass balance-based relationships used in
  operation /design
• SRT
• X
• F/M also use in operation and design
• SRT 20 to 30 days, F/M 0.1 to 0.05
• SRT 5 to 7 days, F/M 0.3 to 0.5

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Process Selection Considerations What type of
reactor when where? (ME table 4-11)

• Has to be applicable (worked before)
• Will work for characteristic flows, waste
• Will enable meeting treatment goals
• Fit with upstream/downstream processes
• Resource needs (capital , chemicals, energy,
  personnel, OM, life cycle, site)
• Reliability
• Ease of use (operability)
• Expected life

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Process Sizing Depends on

• Process goals
• Flow and mass loading (Q, C, etc.)
• Reaction kinetics
• right math expression for r
• rate constant (k or other)
• temperature
• concentration of reactants
• Planning (future growth, current redundancy)

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Pilot Testing

• Processes are frequently pilot tested to
• Determine if the process is right
• Demonstrate performance on small scale
• Gather better cost data
• Gather criteria for large scale design and
  operation