CEE 421, Lecture

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CEE 421, Lecture 1
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Municipal WW Management Systems
Sources of Wastewater
Processing at the Source
Wastewater Collection
Reuse/Disposal
Treatment
Transmission and Pumping
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Elements of a WW Mgmt. System
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1972 Federal Water Pollution Control Act

• PL 92-500 subsequently amended and now called the
  Clean Water Act
• established water quality goals fishable
  swimmable and timetable
• established National Pollution Discharge
  Elimination System (NPDES)
• construction grants for WW treatment
• required secondary treatment (30/30)
• 30 mg/L BOD5
• 30 mg/L TSS

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Conventional WW Treatment
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TYPICAL AERIAL VIEW OF A WASTEWATER TREATMENT
PLANT
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Wastewater Treatment

• Primary Removes Solids
• Physical Operations Screening , Sedimentation
• Secondary Removes Organics
• Biological and Chemical Operations
• Tertiary Removes Nutrients
• Biological and Chemical Operations

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Wastewater Characteristics (Table 3-1)

• Physical
• Temperature, Odor, Taste, Solids
• Chemical
• Organics, Inorganics
• Biological
• Animals, Plants, Microorganisms

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Typical WW Characteristics
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Solids significance

• TDS used as a measure of inorganic salt content
  in drinking waters and natural waters
• TSS used to assess clarifier performance
• VSS used to estimate bacterial populations in
  wastewater treatment systems

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Solids Analysis
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ODORS

• Gases produced by decomposition of organic matter
  (Hydrogen Sulfide)
• Effect of odors psychological stress, nausea,
  vomiting, headaches, poor appetite, deterioration
  of community, lower socio-economic status etc.
• Classification of odors See Table 3-5

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Table 3-5 Odorous Compounds
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Odor Characterization and Measurement

• Factors Intensity, Character, Hedonics,
  Detectability
• Methods Sensory Method Olfactometer (Human
  Errors), Electronic Nose
• TON- Threshold Odor Number
• MDTOC Minimum Detectable Threshold Odor
  Concentration

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Temperature

• Higher in wastewater than waster supply
• Mean annual temperature 10-21.1oC
• Effects reaction rates, chemical reactions,
  suitability of the water for beneficial reuse,
  solubility

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Chemical Characteristics

• Organics and Inorganics
• Organic Matter 75 of Suspended Solids and 40
  of the filterable solids are organic in nature
• Principal groups proteins, carbohydrates, fats
  and oils, surfactants, VOCs, Pesticides
• Priority Pollutants 129 Compounds controlled by
  USEPA

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Oxygen Demand

• It is a measure of the amount of reduced
  organic matter in a water
• Relates to oxygen consumption in a river or lake
  as a result of a pollution discharge
• Measured in several ways
• BOD - Biochemical Oxygen Demand
• COD - Chemical Oxygen Demand
• ThOD - Theoretical Oxygen Demand

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ThOD
This is the total amount of oxygen required to
completely oxidize a known compound to CO2 and
H2O. It is a theoretical calculation that
depends on simple stoichiometric principles. It
can only be calculated on compounds of known
composition. C6H12O6 6O2 6CO2
6H2O If you have 100 mg/L of Glucose what is
the ThOD in mg/L ?
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BOD A Bioassay
Briefly, the BOD test employs a bacterial seed to
catalyze the oxidation of 300 mL of full-strength
or diluted wastewater. The strength of the
un-diluted wastewater is then determined from the
dilution factor and the difference between the
initial D.O. and the final D.O.
BOD Bottle
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BOD with dilution
When BODgt8mg/L
Where BODt biochemical oxygen demand at t days,
mg/L DOi initial dissolved oxygen in the
sample bottle, mg/L DOf final dissolved
oxygen in the sample bottle, mg/L Vb sample
bottle volume, usually 300 or 250 mL,
mL Vs sample volume, mL
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BOD - Oxygen Consumption
Loxidizable carbonaceous material remaining to
be oxidized
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BOD - loss of biodegradable organic matter
(oxygen demand)
Lo
Lo-Lt BODt
Lt
L or BOD remaining
Time
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BOD Modeling
"L" is modelled as a simple 1st order decay
Which leads to
And combining with
We get
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Temperature Effects
Temperature Dependence ? Chemist's Approach
Arrhenius Equation
? Engineer's Approach
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NBOD
Nitrogeneous BOD (NBOD)
2 moles oxygen/1 mole of ammonia 4.57 grams
oxygen/gram ammonia-nitrogen Like CBOD, the NBOD
can be modeled as a simple 1st order decay
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COD A chemical test
The chemical oxygen demand (COD) of a waste is
measured in terms of the amount of potassium
dichromate (K2Cr2O7) reduced by the sample during
2 hr of reflux in a medium of boiling, 50 H2SO4
and in the presence of a Ag2SO4 catalyst.
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COD (cont.)
The stoichiometry of the reaction between
dichromate and organic matter is
Where

• COD test is faster than BOD analysis used for
  quick assessment of wastewater strength and
  treatment performance
• Like the BOD, it does not measure oxidant demand
  due to nitrogeneous species
• It does not distinguish between biodegradable and
  non-biodegradable organic matter. As a result
  COD's are always higher than BOD's.

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Organic Content

• TOC total organic carbon
• measured with a TOC analyzer
• related to oxygen demand, but does not reflect
  the oxidation state of the organic matter
• other group parameters
• oil grease
• specific organic compounds

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Organic Carbon Fractions
Total Carbon (TC)

.
Inorganic
Carbon (IC) Total Organic Carbon
(TOC)

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Purgeable Non-Purgeable Purgeable
Organic Non-purgeable Organic (Dissolved)
(Particulate) Carbon (POC)
Carbon (NPOC)

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Particulate Dissolved

(PtOC) (DOC)
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TOC
Total organic carbon analysis is a determination
of organic carbon in a sample regardless of its
oxidation state or biodegradability. Other
measures of total organic matter (e.g., COD, BOD)
may respond differently to solutions of equal
carbon concentration depending on the oxygen
content or the bidegradation kinetics. For the
measurement of total organic carbon, the sample
is exposed to an oxidizing environment often at
very high temperatures. With complete oxidation
all carbon is converted to carbon dioxide and
swept into a detector by the carrier gas. The
oxidation process is based on the following
stoichiometry
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TOC - Pyrolysis Instrument
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TOC - UV/persulfate Instrument
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TOC - The CO2 Detector
A non-dispersive infra-red analyzer (NDIR)