2004 Biological Wastewater Treatment Operators School

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2004 Biological Wastewater Treatment Operators
School

• Advanced Treatment Systems
• May 13, 2004
• Dean Pond, Black Veatch

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Advanced Treatment Systems

• What are the forms of nitrogen found in
  wastewater?

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What are the forms of nitrogen found in
wastewater?

• TKN 40 Organic 60 Free Ammonia
• Typical concentrations
• Ammonia-N 10-50 mg/L
• Organic N 10 35 mg/L
• No nitrites or nitrates
• Forms of nitrogen
• Organic N
• Ammonia
• Nitrite
• Nitrate

TKN
Total N
4
Advanced Treatment Systems

• Why is it necessary to treat the forms of
  nitrogen?

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Why is it necessary to treat
the forms of nitrogen?

• Improve receiving stream quality
• Increase chlorination efficiency
• Minimize pH changes in plant
• Increase suitability for reuse
• Prevent NH4 toxicity
• Protect groundwater from nitrate contamination

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Advanced Treatment Systems

• What are the effects of N and P in receiving
  waters?

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What are the effects of N and P in
receiving waters?

• Increases aquatic growth (algae)
• Increases DO depletion
• Causes NH4 toxicity
• Causes pH changes

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Advanced Treatment Systems

• Why is it sometimes necessary to remove P from
  municipal wastewater treatment plants?

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Why is it sometimes necessary to remove P from
municipal WWTPs?

• Reduce phosphorus, which is a key limiting
  nutrient in the environment
• Improve receiving water quality by
• Reducing aquatic plant growth and DO
  depletion
• Preventing aquatic organism kill
• Reduce taste and odor problems in downstream
  drinking water supplies

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Advanced Treatment Systems

• How is P removed by conventional secondary
  (biological) wastewater treatment plants?

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How is P removed by conventional secondary
(biological) WWTPs?

• Biological assimilation
• BUG C60H86O23N12P
• 0.03 lb P/lb of bug mass
• GROW BUGS, WASTE BUGS REMOVE P

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Advanced Treatment Systems

• Where in the treatment plant process flow could
  chemical precipitants be added?

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Where in the treatment plant flow could chemical
precipitants be added?

• At pretreatment
• Before primary clarifiers
• After aeration basins
• At final clarifiers
• Ahead of effluent filters
• Considerations
• Effective mixing
• Flexibility
• Sludge production

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Advanced Treatment Systems

• How is N removed or altered by conventional
  secondary (biological) treatment?

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How is N removed or altered by secondary
(biological) treatment?

• Biological assimilation
• BUG C60H86O23N12P
• 0.13 lb N/lb of bug mass
• Biological conversion by nitrification and
  denitrification

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Nitrification

• NH4 ? Nitrosomonas ? NO2-
• NO2- ? Nitrobacter ? NO3-
• Notes
• Aerobic process
• Control by SRT (4 days)
• Uses oxygen ? 1 mg of NH4 uses 4.6 mg O2
• Depletes alkalinity ?
  1 mg NH4 consumes 7.14 mg
  alkalinity
• Low oxygen and temperature
  difficult to operate

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Denitrification

• NO3- ? denitrifiers (facultative bacteria) ?
  N2 gas CO2 gas
• Notes
• Anoxic process
• Control by volume and oxic MLSS recycle to anoxic
  zone
• N used as O2 source 1 mg NO3- yields 2.85 mg O2
  equivalent
• Adds alkalinity ? 1 mg NO3- restores 3.57 mg
  alkalinity
• High BOD and NO3- load and low temperature
  difficult to operate

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Advanced Treatment Systems

• What are typical flow application rates in
  tertiary filters?

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What are typical flow application rates in
tertiary filters?

• Automatic backwash filters
  (1-2 ft media depth) 2 to 4 gpm/sf
• Deep bed filters
  (4-6 ft media depth) 4 to 8 gpm/sf

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Advanced Treatment Systems

• What are typical backwash rates for a tertiary
  filter (in gpm/sf)?

21
What are typical backwash rates for a tertiary
filter (in gpm/sf)?

• Automatic backwash filters
• 20 to 25 gpm/sf
• 5 to 10 of throughput
• Deep bed filters
• 15 to 20 gpm/sf
• 3 to 5 of throughput

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Advanced Treatment Systems

• Define advanced treatment

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Define advanced treatment

• Treatment that improves or enhances secondary
  treatment processes
• Further removal of organics, nutrients and
  dissolved solids

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Advanced Treatment Systems

• Explain circumstances under which advanced
  treatment may be necessary

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Explain circumstances under which advanced
treatment may be necessary

• Limited assimilative capacity of stream
• Toxicity reduction / elimination
• Nutrient control
• Closed systems
• Water reuse

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Advanced Treatment Systems

• Identify and explain the objectives of the
  following advanced treatment systems
• Further removal of organics
• Further removal of suspended solids
• Nutrient removal (N and P)
• Removal of dissolved solids

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Identify and explain the objectives of the
following advanced treatment systems

• Further removal of organics
• Reduce effluent BOD to reduce receiving stream DO
  depletion
• Improve disinfection
• Reduce effluent N to improve water quality
• Further removal of suspended solids
• Removing TSS removes BOD
• Removing TSS removes N and P
  (BUG C60H86O23N12P)
• Protects stream ? sediment oxygen demand
• Improves efficiency of disinfection

28
Identify and explain the objectives of the
following advanced treatment systems

• Removal of nutrients (N and P)
• Reduce oxygen demand of receiving stream
• Control nutrients and algae
• Control taste and odor in downstream drinking
  water
• Suitability for reuse (examples boiler water
  recycle, irrigation NP control of runoff,
  groundwater recharge)

29
Identify and explain the objectives of the
following advanced treatment systems

• Removal of dissolved solids
• Removal of specific pollutant
  zinc, chromium, lead
• Pretreatment of industrial waste
• Control effluent toxicity
• Make suitable for reuse

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Advanced wastewater treatmentDescribe the
purpose or procedure and mechanism by which it is
done for each of the following

• Activated carbon adsorption
• Chemical coagulation
• Flocculation
• Phosphorus removal
• Nitrogen removal
• Effluent Filtration
• Polishing lagoons

• Nitrification
• Denitrification
• Ammonia striping
• Alum or ion precipitation
• Lime precipitation
• Reverse osmosis (RO)
• Electrodialysis

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Activated Carbon Adsorption

• Purpose
• Tertiary treatment
• Removal of low concentration organic compounds
• Application
• Influent ?Primary Trt ?Biological Trt ?
  Filtration ?Carbon ?Disinfection
• Many variations

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Activated Carbon Adsorption
Continued

• Carbon Regeneration
• 5 to 10 loss
• Less capacity than new carbon
• Hot air _at_ 350oF
• Chemicals (sodium hydroxide)
• Fire / Explosion
• Carbon usually replaced after 5 regenerations
• Mechanism
• Active sites Activated Carbon
• Molecular bonding
• Particles adhere to surface

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Chemical Coagulation

• Purpose
• Enhanced removal of organics and fine particles
• Addition of lime, alum, iron, polymer to change
  ionic charge
• Application
• Chemical feed with rapid mix
• Ahead of final clarifiers
• Ahead of filtration

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Chemical Coagulation
Continued

• Lime Heavy metals Alum SS removal
• SS removal P removal
• P removal
• Polymer - SS control Iron SS removal
• P removal
• Mechanism
• Destabilization by ionic charge neutralization
• Reduce charge that keeps small particles apart

Aluminum sulfate
Ferric chloride Ferric sulfate Ferrous sulfate
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Flocculation

• Purpose
• Produce larger, more dense floc particles that
  will settle or filter easily
• Application
• Gentle mixing after rapid mix (coagulation)
• Mixing Mechanical or Aeration

Q
Infl Q
Gentle Mix / Flocculation
Rapid Mix / Coagulation
Sludge
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Flocculation
Continued

• Mechanism
• Coagulated particles strung together into larger
  floc particles (snow flake floc)

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Phosphorus Removal

• Purpose
• Reduce effluent P
• Biological or chemical method
• Reduce nutrient load on stream
• Reduce algae growth
• Reduce oxygen depletion
• Application / Mechanism
• Biological
• Chemical

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Phosphorus Removal
Continued

• Biological

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Phosphorus Removal
Continued

• Chemical

Effl
Aerobic Zone
Primary Clarifier
Final Clarifier
Q
Chemical Coagulant
Chemical Coagulant
RAS
WAS

P Removal
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Nitrogen Removal

• Purpose
• Reduce effluent N (ammonia and nitrates)
• Biological or chemical
• Reduce nutrient load on stream
• Reduce algae growth
• Reduce oxygen depletion
• Application / Mechanism
• Advanced Activated Sludge Processes
• Nitrification (remove ammonia)
• NH4 ? NO2 ? NO3

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Nitrogen Removal
Continued

• Denitrification (remove nitrate)
• NO3 ? NO2 ? NO, N2O or N2 gas
• Deep Bed Filtration
• Anaerobic fixed film bacteria (denitrify)
• Air Stripping
• Removes ammonia
• Elevated pH 10.8 to 11.5 NH4 as gas

Q
Media
6-8
Methanol (carbon)
Q
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Effluent Filtration

• Purpose
• Remove SS (usually after FC)
• Reduce BOD and insoluble P
• Application
• Deep Bed
• 4-6 sand and gravel
• Large cells 10 x 30
• Similar to WTP
• (batch backwash)
• hL 4 - 6 ft

• 2. Traveling Bridge
• 1-2 sand and anthracite
• Small cells 1 x 14
• Contiuous backwash
• hL 2 - 3 ft

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Effluent Filtration
Continued

• Loading Rate
• Backwash
• 2 4 gpm/sf
• Frequency depends on loading
• 20 25 gpm/sf
• 5 15 of throughput
• Must clean beds
• Air scour
• Mechanism
• Filtration by granular media

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Polishing Lagoons

• Purpose
• To further treat or polish the effluent
• After final clarifier
• Facultative pond (aerobic and anaerobic)
• Application
• Typical volume 1 day average flow
• i.e., 1 mgd plant 1 mgd lagoon
• 24 hour detention time
• Surface aerators

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Polishing Lagoons
Continued
Sunlight
Surface Aerator
Algae
M
Settling
Aerobic
Anaerobic

• Sunlight ? Photosynthesis ? Algae Organics
  Nutrients
• Organic Matter ? Anaerobic Decomposition
• Mechanism
• Algae and bacteria grow in pond consuming
  organics and nutrients in FC effluent. Algae
  settles and degrades by anaerobic process.

methane gas
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Nitrification

• Purpose
• Reduce ammonia on plant effluent
• High ammonia concentrations are toxic to streams
• Quickest impact on DO versus nitrates
• Application
• SRT gt 3 days in activated sludge process
• Grow Nitrosomonas and Nitrobacter
• NH4 ? NO2 ?NO3
• Mechanism
• Biological conversion of ammonia to nitrate

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Denitrification

• Purpose
• Reduce nitrate on plant effluent
• Usually in combination with nitrification to
  reduce Total N to the stream
• Application
• Activated Sludge Process
• Deep Bed
• Filters
• Mechanism
• Biological conversion of nitrate to N2 gas

Q
Anx
Oxic
FC
Oxic Recycle
RAS
WAS
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Ammonia Stripping

• Purpose
• Reduce ammonia either before or after biological
  treatment
• Not commonly used in the US
• Application / Mechanism
• Raise pH ? 10.8 to 11.5, usually by adding lime
• Move equilibrium point to ammonia gas _at_ 250C and
  pH 11
• NH4 gas 98

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Ammonia Stripping
Continued

• Break wastewater into droplets and strip off
  ammonia gas with air
• Freefall through tower that circulates a lot of
  air to remove ammonia to atmosphere

NH4 Air
Lime
Q
NH4 Stripper
Floc
Precip.
Lime Sludge
Air
Q
50
Alum or Iron Precipitation

• Purpose
• To remove orthophosphate
• Application
• As a backup to Bio-P process
• As chemical P removal
• As chemical process
• Mechanism
• Al or Fe PO4 ? Aluminum or Iron Phosphate

Al or Fe
Filtration Optional
Q
Q
Precipitate
Rapid Mix
RAS
WAS Precipitate
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Lime Precipitation

• Purpose
• P removal before primary clarifier or following
  biological treatment
• Application
• As a backup to Bio-P process
• As chemical P removal
• As chemical process
• High pH can be a problem in effluent or in
  biological treatment
• Mechanism
• Chemical conversion of phosphorus to calcium
  phosphate is in pH range of 9.5 to 11.0

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Reverse Osmosis (RO)

• Purpose
• High quality removal of various salts calcium,
  sodium, magnesium
• Application
• Water reuse
• AWT
• Mechanism
• Chemical separation / filtration across a
  semi-permeable membrane
• High pressure
• Tertiary process
• Used in Gulf War to treat sea water sodium removal

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Electrodialysis

• Purpose
• Removal of ionic inorganic compounds
• Application
• AWT
• Medical
• WTP
• Clinical
• Mechanism
• Apply electrical current between two electrodes
• Water passes through semi-permeable membranes
  (ion-selective)
• Alternate spacing of cation and anion permeable
  membranes
• Cells of concentrated and diluted salts are formed

54
Electrodialysis

• Purpose
• Removal of ionic inorganic compounds
• Application
• AWT
• Medical
• WTP
• Clinical

• Mechanism
• Apply electrical current between two electrodes
• Water passes through semi-permeable membranes
  (ion-selective)
• Alternate spacing of cation and anion permeable
  membranes
• Cells of concentrated and diluted salts are
  formed
• Sludge concentrated salt waste stream as
  process reject water
• Problems plugging, fowling of membranes, MUST
  pretreat activated carbon, multi-media filtration

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H20
Cl-
H
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OH-
Na
Bipolar Membranes
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Advanced wastewater treatmentWhat would be the
effect on sludge production for each of the
following advanced treatment processes?

• Activated carbon adsorption
• Chemical coagulation
• Flocculation
• Phosphorus removal
• Nitrogen removal
• Effluent Filtration
• Polishing lagoons

• Nitrification
• Denitrification
• Ammonia striping
• Alum or ion precipitation
• Lime precipitation
• Reverse osmosis (RO)
• Electrodialysis

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What would be the effect on sludge production for
each of the advanced treatment processes?

• TANSTAAFL (tanstaffull)
• There aint no such thing as a free lunch.
• REMOVE MORE STUFF GET MORE SLUDGE
• More BOD TSS Removal ? MORE SLUDGE
• Add chemicals ? MORE SLUDGE
• N P Removal ? MORE SLUDGE
• Some processes produce more sludge than others
• Electro/mechanical some sludge
• Biological more sludge
• Chemical MOST sludge