Website download address

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Website download address

• Wastewater Treatment
• ttp//www.public.iastate.edu/sung/ce326/wastew
  ater.ppt

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• What is Wastewater?
• 99 water impurities
• Impurities include
• Insoluble Particulates Suspended Solids (SS)
• Inorganic SS or Fixed SS, e.g., silt
• Organic SS, or Volatile SS, e.g., cell mass
• Soluble Solutes
• Soluble Inorganics, e.g., salts
• Soluble Organics, e.g., sugars
• Nutrients N and P
• Could be organic/inorganic or particulate/soluble
• Could cause eutrophication in receiving water
  body (page 394)
• Organic nutrients plus ammonia (NH4) have oxygen
  demand

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• Major pollutant categories and principal sources
  of pollutants
• Evaluate the potential for water pollution from
  the following categories
• H high potential, M moderate potential, L
  low potential for pollution

M H H L M H H M H
L-M M L M H H H L
H L H L H L M L H
L M L H L L
Point source collected by a network of
pipes and conveyed to a single point of
discharge into receiving water Non-point source
polluted water flows over the surface of the land
or along natural drainage channels to
receiving water
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Biochemical Oxygen Demand (BOD)
. When microorganisms oxidizing the organic
matter as a food source, the quantity of the
oxygen consumed is known as BOD . BOD test
is done in a series of special 300 mL bottles
Dissolved Oxygen Meter
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Biochemical Oxygen Demand (BOD)
. Each BOD bottle filled with a appropriately
diluted wastewater sample plus blank bottles
and inoculates with microorganisms .
After a desired number of days (5 days typical),
dissolved oxygen (DO) concentration is
measured BODt ( DOb,t DOs,t ) x dilution
factor DOb,t DO in blank after t days of
incubation, mg/L DOs,t DO in sample after t
days of incubation, mg/L
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• Biochemical Oxygen Demand (BOD)
• BOD and oxygen-equivalent relationships

Page 362
Lo ultimate BOD Lt oxygen equivalent of
remaining organic BODt Lo Lt Lo Lo e-kdt
Lo ( 1 ekt )
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• Example 1.
• Wastewater treatment plant is discharging a waste
  with a BOD5 of 30 mg/L and k is 0.3 d-1. What is
  the ultimate BOD?
• 30 mg/L Lo ( 1 ekt ) Lo ( 1 e(0.3?5) )
• Lo 38.6 mg/L
• Example 2.
• BOD3 of a waste is 25 mg/L, and k is 0.0125 h-1.
  What is its BOD5?
• 25 mg/L Lo ( 1 ekt ) Lo ( 1
  e(0.0125?24?3) )
• Lo 42 mg/L
• BOD5 42 x ( 1 e(0.0125?24?5) ) 32.6 mg/L

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• Temperature correction of kinetic constant k
• kT k20 (?)T-20 page 365
• T oC
• where ? 1.135 4 T lt 20oC
• ? 1.056 20 T 30oC
• Example 3.
• A waste is being discharged into a river has a
  temperature of 10oC. What fraction of the
  maximum oxygen consumption could be occurred in 4
  days if standard k is 0.115 d-1?
• BOD test is conducted at standard temperature of
  20oC
• kT k20 (?)T-20 k10 0.115 (1.135)10-20 0.032
  d-1
• BOD4 / Lo (1 e-(0.032)(4)) 0.21

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Page 375
Oxygen Sag
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• DO Sag Curve Page 374 384

Eq. 5 41
Where Dt oxygen deficit in river water after
exertion of BOD for time, t, mg/L La initial
ultimate BOD after river and wastewater have
mixed, mg/L kd deoxygenation rate constant,
d-1 kr reaeration rate constant, d-1 t
time of travel of wastewater discharge
downstream, d Da initial deficit after river
and wastewater have mixed, mg/L
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Deoxygenation Rate Constant, kd
Eq. 5 43
Where v average speed of stream flow, m/s k
BOD rate constant determined in lab at 20oC,
d-1 H average depth of stream, m ?
bed-activity coefficient
Reaeration Rate Constant, kr
Eq. 5 44
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Critical Point lowest point on the DO sag curve
Eq. 5 45
Where tc the time to the critical point Da
initial deficit after river and wastewater have
mixed, mg/L La initial ultimate BOD after
river and wastewater have mixed, mg/L
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• DO Sag Curve - Example Problem

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• Example continued
• DOsaturation _at_ 16oC 9.95 mg/L (Table A-3,
  page 979)
• kd _at_16oC kd 20oC x ?16-20 ? 1.135 4 T
  20
• 0.14 x 1.135-4 0.084 d-1
• kr _at_16oC kr 20oC x ?16-20
• 0.16 x 1.135-4 0.096 d-1
• Da 9.95 6.91 3.04 mg/L

Distance 7.97 day x 86,400 s/day x 0.1 m/s
68,900 m 68.9 km
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• Example continued

Critical DO DOsaturation Dt 9.95 5.87
4.08 mg/L
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Typical composition of untreated domestic
wastewater Table 6 - 1,Page 422
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Typical Organic Pollutants in Sewerage 40-60
proteins 25-50 carbohydrates 10 fats and
oils Trace miscellaneous organic
compounds (urea, pesticides, surfactants,
phenols, ethylene glycol, and priority pollutants)
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Minimum national standards for secondary treatment
Page 423
a Average removal shall not be less than 85
percent. b Only enforced if caused by industrial
wastewater or in-plant inorganic addition. c May
be substituted for BOD5 at the option of the
NPEDS permitting authority.
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Solid Matrix
TS TSS TDS

VS VSS
VDS
TFS FSS FDS
particulate organic
soluble organic
soluble inorganic
particulate inorganic
salts
sand, silt
T Total S Solids or Suspended D Dissolved V
Volatile F Fixed
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Example A water sample contains Sugar
100 mg/L Fine sand 60 mg/L Bacteria 25
mg/L Salts e.g., NaCl, KHCO3 125 mg/L What is
the TDS and VS/TS of this sample?
T Total S Solids or Suspended D Dissolved V
Volatile F Fixed
TS TSS TDS

VS VSS
VDS
TFS FSS FDS
310
85
225
125
100
25
60
125
185
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• Four levels of wastewater treatment
• Preliminary treatment - screening, grit removal
• Primary treatment - settling of solids in primary
  clarifiers
• Secondary treatment - biological treatment
• 4. Tertiary treatment - nutrient (N, P) removal,
  filtration

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• 1. Preliminary Treatment
• Screening (Bar Racks) Remove debris such as
  rocks, branches, pieces of lumber, leaves, paper,
  tree roots, plastics and rags.
• Grit Chamber Remove grits such as sands,
  gravel, heavy solids materials, anything with
  specific gravity (s.g.) greater than organic
  solids (s.g. 1.03-1.05)

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Bar Screen
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Vortex Grit Chamber
Flow in
Flow out
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Aerated Grit Chamber
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• 2. Primary Treatment
• Primary Clarifier (Primary Sedimentation)
  Remove settleable suspended solids (mainly VSS)
• Typical removal efficiency (p 448)
• TSS 50 60
• BOD5 30 35
• Design Criteria
• Overflow rate Weir Loading
• gal/ft2/day gal/ft/day
• at Average Flow 800 1,200 10,000 - 40,000
• at Peak Flow 2,000 - 3,000
• Detention time 1.5 2.5 hours
• Side Water Depth 15 ft

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Primary Treatment Circular Clarifier
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Primary Treatment - Rectangular Clarifier
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Theory of Sedimentation Tank Sizing
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Theory of sedimentation tank sizing
A Inlet Zone B Settling Zone C Outlet
Zone D Sludge Zone
Vc critical settling velocity, all particles w/
settling velocity greater than Vc will
be removed
td hydraulic detention time V / Q td (A x
H) / Q ----- (1) A surface area Width x
L vc H / td ----- (2) (1) (2) ? vc Q
/ A H / td
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• Three types of sedimentation
• Type I Sedimentation Discrete Particle Settling
• Goal remove all particle w/ a settling velocity
  greater than a specified velocity
• In regards to design
• Tank design is independent of depth
• Tank design depends only on surface overflow
  (Q/A)
• Sedimentation efficiency is independent of
  detention time
• Type II Sedimentation Flocculent Sedimentation
• Goal remove small particles which flocculate
  during sedimentation
• In regard to design
• Tank design depends on time and depth
• Particle size and average settling velocity are
  constantly increasing
• No theoretical way to predict the amount of
  flocculation

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• Three types of sedimentation
• Type III Sedimentation Zone Settling
  Sedimentation
• Goal accomplish sedimentation as a mass and some
  degree of
• thickening occurs
• In regards to design
• Distinct interface occurs between clear
  supernatant and sludge
• zone.
• Settling generally occurs together in a large
  mass.
• Zone settling velocity dictates the surface
  area of the tank.
• Need to look at the forces between particles
  zone settling velocity
• decrease with higher concentration of
  sludge

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• 2. Primary Treatment
• Design Criteria
• Overflow rate Weir Loading
• gal/ft2/day gal/ft/day
• at Average Flow 800 1,200 10,000 - 40,000
• at Peak Flow 2,000 - 3,000
• Detention time 1.5 2.5 hours
• Side Water Depth 15 ft

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Sedimentation Tank Circular Clarifier
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Sedimentation Tank Circular Clarifier
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Weir Arrangement Circular Sedimentation Tank
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Weir Arrangement - Rectangular Sedimentation Tank
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• 3. Secondary (Biological) Treatment

Activated Sludge System
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Aeration Basin
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Aeration Equipment Air Piping and Diffusers
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Typical Activated Sludge Treatment Plant
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Typical Trickling Filter Treatment Plant
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• Secondary Treatment
• Activated Sludge System Page 459 482 Lab
  Design Problem
• Tricking Filter System Page 482 - 488
• 2ndary Clarifier Design Criteria
• Overflow rate Solids Loading
• gal/ft2/day lb/ft2?hr
• For Activated Sludge System
• at Average Flow 400 800 0.8
  1.2
• at Peak Flow 1,000-1,200 2.0
• For Tricking Filter System
• at Average Flow 400 600 0.6
  1.0
• at Peak Flow 1,000-1,200 1.6
• Side Water Depth 12 20 ft

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• 3. Secondary (Biological) Treatment
• Classification of microorganisms by their carbon
  and
• energy source
• Heterotrophs - utilize organic matter to supply
  their carbon and energy needs. These are the
  predominant organisms in biological wastewater
  treatment plants, responsible for converting
  organic pollutants to carbon dioxide, water, and
  additional heterotrophic biomass.
• B. Autotrophs - get their energy from an
  inorganic source and their carbon from carbon
  dioxide. An example of autotrophs in wastewater
  treatment is nitrifying bacteria. They use
  ammonia for energy and carbon dioxide for a
  carbon source.

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• Classification of microorganisms by their
  Terminal
• Electron Acceptor (TEA)
• Aerobic microorganisms transfer electrons from
  the energy source to oxygen, O2. In the process
  oxygen and organic matter is converted to carbon
  dioxide, CO2, and water, H2O. Oxygen is termed
  the terminal electron acceptor or TEA.
• Anoxic microorganisms utilize some other oxidized
  compound to accept electrons. In the case of
  denitrifying microorganisms, nitrate, NO3-,
  serves as the TEA, as nitrate is converted to
  nitrogen gas, N2.
• C. Anaerobic microorganisms utilize CO2 and
  organic compounds as terminal electron acceptors.
  In this process, organic compounds are converted
  to fermentation products and carbon dioxide. In
  anaerobic digestion of wastewater solids, the
  fermentation products are converted to methane,
  CH4, and carbon dioxide.

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Process TEA Predominant Reactions Example
Aerobic O2 organics O2 ? CO2 H2O AS,
1st stage TF Aerobic O2 NH4
O2 ? NO3- Nitrification, 2nd stage
TF Anoxic NO3- organics NO3- ? N2
CO2 H2O Denitrification Anaerobic
CO2 organics ? CH4 CO2 H2O Anaerobic
organics Digestion
AS Activated Sludge System TF Trickling Filter
System
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• Classification of microorganisms by their growth
  temperature
• A. Psychrophiles - grow at temperatures below
  25C
• B. Mesophiles - grow at temperatures 25 - 45C
• C. Thermophiles - grow at temperatures 45 - 60C

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• Ten Growth Requirements for Microorganisms
• Carbon source
• Energy source
• Terminal Electron acceptor
• Macro-Nutrients C, N, H, O, P, K, S
• Micro-Nutrients Fe, Ni, Co, Mb, Zn, etc.
• Moisture
• Appropriate temperature
• Appropriate pH
• Absence of inhibition

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Monod Kinetic Equation
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Substrate (waste) Characteristics
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dx / dt µ X x biomass
concentration, mg/L Biomass growth rate µ
growth rate constant, 1/t
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Activated Sludge System Operating Parameters
. Effluent quality . HRT of aeration tank .
Mixed liquor solids (biomass) concentration .
Sludge production (solid wasting rate) . Sludge
recycling rate . Oxygen requirement quantity
of compressed air . 2ndary clarifier overflow
rate, HRT, depth, solid loading rate, etc.
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Activated Sludge Model
P 462 - 467
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HRT with Flow Recirculation
What is the HRT with V 10 m3, x 2, and Q 1
m3/min HRT V / Q 10 m3 / 1 m3/min 10
minutes No effect on recirculation flow!!!
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Activated Sludge Model
Mass balance approach mass IN mass OUT Q
X0 Qr Xr ( Q Qr ) X Qr Xr Q X
Qr X
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Activated Sludge Model
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Sludge Treatment and Disposal page 500-521
Sludge dewatering
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Importance of Sludge Treatment in Overall
Wastewater Treatment
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• Sludge Treatment and Disposal page 508
• The basic processes for sludge treatment are as
  follows
• 1. Thickening concentrating sludge using
  gravity or flotation methods. Primary sludge can
  be thickened to a maximum of about 10 solids and
  secondary sludge to a maximum of about 6-8
  solids.

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Dissolved Air Floatation (DAF)
Gravity Thickener
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Screw type thickener
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• 2. Stabilization converting the organic in the
  sludge to more stable (inert) forms so they can
  be handled more easily (more dewaterable, less
  potential for odors) and used as soil
  conditioners. Typically stabilization involves
  anaerobic or aerobic digestion. During digestion
  considerable volatile solids destruction occurs

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Organics Conversion in Anaerobic System
COMPLEX ORGANIC MATTERS
Carbohydrates
Lipids
Proteins
1
1
1
Hydrolysis
Amino Acids, Sugars
Fatty Acids, Alcohols
Intermediary Products (Organic acids Propionic,
Butyric acids, etc.)
2
2
Anaerobic Oxidation
Fermentation
2
3
Acetate
Hydrogen, Carbon dioxide
Homoacetogenesis
5
4
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Methane Carbon dioxide
Acetotrophic Methanogenesis
Hydrogenetrophic Methanogenesis
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Anaerobic Digester
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Anaerobic Digester
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Anaerobic Digester
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Aerobic Digester
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• 3. Conditioning Addition of chemical to allow
  better separation of the water and the solids.
  Ferric chloride and organic and inorganic
  polymers are frequently used for sludge
  conditioning.
• 4. Dewatering Belt press, vacuum, centrifuge,
  pressure, or drying methods for removing water
  from the solids. Typically about 25 to 35
  solids can be achieved.

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Belt Press
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Belt Press
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Belt Press
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Vacuum Filter Pressure Filter
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• 5. Destruction Incineration of sludge with ash
  residual for ultimate disposal.

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Circulating Fluidized Bed Incinerator
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Lab Supplemental Slides
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Nitrogen Cycle
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Nitrification
Step 1 Oxidation of Ammonia to Nitrite NH3 O2
Nitrosomonas sp. bacteria ? NO2- Step 2
Oxidation of Nitrite to Nitrate NO2- O2
Nitrobacter sp. bacteria ? NO3-
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CBOD vs. NBOD
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Denitrification
Denitrification converts nitrates to nitrogen gas
under anoxic (no free oxygen) condition