2004 Biological Wastewater Treatment Operators School Advanced
Treatment Systems May 13, 2004 Dean Pond, Black & Veatch Slide
2 Advanced Treatment Systems What are the forms of nitrogen found
in wastewater? Slide 3 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 Slide 4 Advanced Treatment Systems Why is it
necessary to treat the forms of nitrogen? Slide 5 Improve receiving
stream quality Increase chlorination efficiency Minimize pH changes
in plant Increase suitability for reuse Prevent NH 4 toxicity
Protect groundwater from nitrate contamination Slide 6 Advanced
Treatment Systems What are the effects of N and P in receiving
waters? Slide 7 Increases aquatic growth (algae) Increases DO
depletion Causes NH 4 toxicity Causes pH changes Slide 8 Advanced
Treatment Systems Why is it sometimes necessary to remove P from
municipal wastewater treatment plants? Slide 9 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 Slide 10 Advanced
Treatment Systems How is P removed by conventional secondary
(biological) wastewater treatment plants? Slide 11 How is P removed
by conventional secondary (biological) WWTPs? Biological
assimilation BUG = C 60 H 86 O 23 N 12 P 0.03 lb P/lb of bug mass
GROW BUGS, WASTE BUGS = REMOVE P Slide 12 Advanced Treatment
Systems Where in the treatment plant process flow could chemical
precipitants be added? Slide 13 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 Slide 14 Advanced Treatment Systems How is N
removed or altered by conventional secondary (biological)
treatment? Slide 15 How is N removed or altered by secondary
(biological) treatment? Biological assimilation BUG = C 60 H 86 O
23 N 12 P 0.13 lb N/lb of bug mass Biological conversion by
nitrification and denitrification Slide 16 Nitrification NH 4 +
Nitrosomonas NO 2 - NO 2 - Nitrobacter NO 3 - Notes: Aerobic
process Control by SRT (4 + days) Uses oxygen 1 mg of NH 4 + uses
4.6 mg O 2 Depletes alkalinity 1 mg NH 4 + consumes 7.14 mg
alkalinity Low oxygen and temperature = difficult to operate Slide
17 Denitrification NO 3 - denitrifiers (facultative bacteria) N 2
gas + CO 2 gas Notes: Anoxic process Control by volume and oxic
MLSS recycle to anoxic zone N used as O 2 source = 1 mg NO 3 -
yields 2.85 mg O 2 equivalent Adds alkalinity 1 mg NO 3 - restores
3.57 mg alkalinity High BOD and NO 3 - load and low temperature =
difficult to operate Slide 18 Advanced Treatment Systems What are
typical flow application rates in tertiary filters? Slide 19
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 Slide 20
Advanced Treatment Systems What are typical backwash rates for a
tertiary filter (in gpm/sf)? Slide 21 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 Slide 22 Advanced Treatment Systems
Define advanced treatment Slide 23 Treatment that improves or
enhances secondary treatment processes Further removal of organics,
nutrients and dissolved solids Slide 24 Advanced Treatment Systems
Explain circumstances under which advanced treatment may be
necessary Slide 25 Limited assimilative capacity of stream Toxicity
reduction / elimination Nutrient control Closed systems Water reuse
Slide 26 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 Slide 27 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 = C 60 H 86 O 23
N 12 P) Protects stream sediment oxygen demand Improves efficiency
of disinfection Slide 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
N&P control of runoff, groundwater recharge) Slide 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 Slide 30 Advanced
wastewater treatment Describe 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 Slide 31 Activated Carbon Adsorption Purpose
Tertiary treatment Removal of low concentration organic compounds
Application: Influent Primary Trt Biological Trt Filtration Carbon
Disinfection Many variations Slide 32 Activated Carbon Adsorption
Carbon Regeneration 5 to 10% loss Less capacity than new carbon Hot
air @ 350 o F Chemicals (sodium hydroxide) Fire / Explosion Carbon
usually replaced after 5 regenerations Mechanism: Active sites
Activated Carbon Molecular bonding Particles adhere to surface
Continued Slide 33 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 Slide 34 Chemical
Coagulation Lime + Heavy metals Alum + SS removal SS removal P
removal P removal Polymer + - SS controlIron + SS removal P removal
Mechanism: Destabilization by ionic charge neutralization Reduce
charge that keeps small particles apart Continued Aluminum sulfate
Ferric chloride Ferric sulfate Ferrous sulfate + ++ + + + + + ++ +
+ + + + + ++ + + + + + + ++ + _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _
_ _ _ _ _ _ _ ___ + + + + + + + + + Slide 35 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 Rapid Mix / Coagulation
Infl Q Q Sludge Gentle Mix / Flocculation Slide 36 Mechanism
Coagulated particles strung together into larger floc particles
(snow flake floc) Continued + ++ + + + + + ++ + + + + + ++ + + + +
+ + + + ++ + + + + + ++ + + + + + ++ + + + + + + + Slide 37
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 Slide
38 Phosphorus Removal Biological Continued Final Clarifier RAS WAS
Effl Q P Release Anaerobic Zone Aerobic Zone P Luxury Uptake P
Removal Slide 39 Phosphorus Removal Chemical Continued Final
Clarifier RAS WAS Effl Q Aerobic Zone Chemical Coagulant P Removal
Primary Clarifier Chemical Coagulant Slide 40 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 1. Advanced Activated
Sludge Processes Nitrification (remove ammonia) NH 4 NO 2 NO 3
Slide 41 Nitrogen Removal Denitrification (remove nitrate) NO 3 NO
2 NO, N 2 O or N 2 gas 2. Deep Bed Filtration Anaerobic fixed film
bacteria (denitrify) 3. Air Stripping Removes ammonia Elevated pH
10.8 to 11.5 NH 4 as gas Continued Q Methanol (carbon) Media Q 6-8
Slide 42 Effluent Filtration Purpose Remove SS (usually after FC)
Reduce BOD and insoluble P Application 1. 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 Slide 43 Effluent Filtration
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 Continued Slide 44 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 Slide 45 Polishing
Lagoons 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. Continued Aerobic
Anaerobic Settling Algae Sunlight M Surface Aerator methane gas
Slide 46 Nitrification Purpose Reduce ammonia on plant effluent
High ammonia concentrations are toxic to streams Quickest impact on
DO versus nitrates Application SRT > 3 days in activated sludge
process Grow Nitrosomonas and Nitrobacter NH 4 NO 2 NO 3 Mechanism
Biological conversion of ammonia to nitrate Slide 47
Denitrification Purpose Reduce nitrate on plant effluent Usually in
combination with nitrification to reduce Total N to the stream
Application 1. Activated Sludge Process 2. Deep Bed Filters
Mechanism Biological conversion of nitrate to N 2 gas AnxOxic FC
Oxic Recycle RAS WAS Q Slide 48 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 @ 25 0
C and pH 11 NH 4 gas = 98% Slide 49 Ammonia Stripping 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 Floc Lime Sludge Air Precip. Q Continued Lime
NH 4 Stripper Q NH 4 Air Slide 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 + + PO 4 Aluminum or Iron Phosphate Rapid Mix RAS Q Al + or Fe +
Q Filtration Optional WAS + Precipitate Precipitate Slide 51 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 Slide 52 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 Slide 53 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 Slide 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 OH - Cl - _ + H20H20 H+H+ Na + + _ Bipolar
Membranes Slide 55 Advanced wastewater treatment What 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 Slide 56 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
