cee 421, lecture #1. municipal ww management systems sources of wastewater processing at the source...
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CEE 421, Lecture #1
Municipal WW Management Systems
Sources of Wastewater
Processing at the Source
WastewaterCollection
Transmissionand Pumping
Treatment Reuse/Disposal
Elements of a WW Mgmt. SystemElement Description
Sources Sources of WW in a community, such as residences, commercial est., and industries
Processing at the source
Facilities for pretreatment or flow equalization of WW before it is discharged to a collection system
Collection Facilities for collection of WW from individual sources in a community
Transmission Facilities to pump and transport collected WW to processing and treatment sites
Treatment Facilities for treatment of wastewater
Reuse/Disposal Facilities for reuse and disposal of treated effluent and residual solids resulting from treatment
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 BOD30 mg/L BOD55
– 30 mg/L TSS30 mg/L TSS
Conventional WW TreatmentBiological ProcessPreliminary
Treatment
SecondarySedimentation
SludgeSludge
Disinfection
PrimarySedimentation
SludgeSludge
TYPICAL AERIAL VIEW OF A WASTEWATER TREATMENT PLANT
Wastewater Treatment
Primary – Removes Solids Physical Operations – Screening , Sedimentation
Secondary – Removes Organics Biological and Chemical Operations
Tertiary – Removes Nutrients Biological and Chemical Operations
Wastewater Characteristics (Table 3-1)
Physical– Temperature, Odor, Taste, Solids
Chemical– Organics, Inorganics
Biological– Animals, Plants, Microorganisms
Typical WW Characteristics
Parameter Conc.BOD 250 mg/LTSS 250 mg/LCOD 500 mg/LAmmonia 30 mg/LTOC 100 mg/LChloride + 50 mg/L
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
Solids Analysis
Total Solids
Total Dissolved SolidsTDS
TS
Total Suspended SolidsTSS
FSS
VSS
Fixed S.S.
Volatile S.S.
Filtration
filtrate retained matter
ignition
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
Table 3-5 Odorous Compounds
Compound Odor Quality
Ammonia
Diamines Decayed Flesh
Hydrogen Sulfide Rotten Eggs
Mercaptans Decayed Cabbage, Skunk
Organic Sulfides Rotten Cabbage
Skatole Fecal Matter
Amines Fishy
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
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
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
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
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 ?
BOD: A Bioassay
Briefly, the BOD test employs a Briefly, the BOD test employs a bacterial seed to catalyze the bacterial seed to catalyze the oxidation of 300 mL of full-oxidation of 300 mL of full-strength or diluted wastewater. strength or diluted wastewater. The strength of the un-diluted The strength of the un-diluted wastewater is then determined wastewater is then determined from the dilution factor and the from the dilution factor and the difference between the initial difference between the initial D.O. and the final D.O.D.O. and the final D.O. BOD
BottleBOD DO DOt i f
BOD with dilution
ti f
s
b
BOD = DO - DO
V
V
WhereBODt = 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]
When BOD>8mg/LWhen BOD>8mg/L
BOD - Oxygen Consumption
CBOD
NBOD
yor
BOD(mg/L)
Time
L=oxidizable carbonaceous material remaining to be oxidized
BOD y L Lt t o t
BOD - loss of biodegradable organic matter (oxygen demand)
Lo
Lt
L o
r B
OD
rem
aini
ng
Time
Lo-Lt = BODt
BODBottle
BODBottle
BODBottle
BODBottle
BODBottle
BOD Modeling
"L" is modelled as a simple 1st order decay: dL
dtk L 1
L L eok t 1Which leads to:
We get: BOD y L et t ok t ( )1 1
BOD y L Lt t o t And combining with:
Temperature Effects
Temperature Dependence
Chemist's Approach: Arrhenius Equation
d k
dT
E
RTa
a
a
(ln ) 2
k k eT K
E T RT
ao
a a a 293
293 293( )/
Engineer's Approach:
k kT C
T Co
o
20
20
NBODNitrogeneous BOD (NBOD)
NH O NO H O HNitrosomonas3 2 2 215 .
NO O NONitrobacter2 2 3
1
2
2 moles oxygen/1 mole of ammonia4.57 grams oxygen/gram ammonia-nitrogen
Like CBOD, the NBOD can be modeled as a simple 1st order decay:
dL
dtk L
N
NN
COD: A chemical test
The chemical oxygen The chemical oxygen demand (COD) of a waste is demand (COD) of a waste is measured in terms of the measured in terms of the amount of potassium amount of potassium dichromate (Kdichromate (K22CrCr22OO77) reduced by ) reduced by the sample during 2 hr of reflux the sample during 2 hr of reflux in a medium of boiling, 50% in a medium of boiling, 50% HH22SOSO4 4 and in the presence of a and in the presence of a AgAg22SOSO44 catalyst. catalyst.
COD (cont.)
C H O Cr O H nCO CraH On a b
2 72
23
28 2 42
2
3 6 3
n a b
The stoichiometry of the reaction between The stoichiometry of the reaction between dichromate and organic matter is:dichromate and organic matter is:
• COD test is faster than BOD analysis: used for quick COD test is faster than BOD analysis: used for quick assessment of wastewater strength and treatment assessment of wastewater strength and treatment performanceperformance
• Like the BOD, it does not measure oxidant demand Like the BOD, it does not measure oxidant demand due to nitrogeneous speciesdue to nitrogeneous species
• It does not distinguish between biodegradable and It does not distinguish between biodegradable and non-biodegradable organic matter. As a result non-biodegradable organic matter. As a result COD's are always higher than BOD's.COD's are always higher than BOD's.
Where:
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
Organic Carbon Fractions
Total Carbon (TC)Total Carbon (TC) | .| . | || | Inorganic Carbon (IC) Total Organic Carbon (TOC)Inorganic Carbon (IC) Total Organic Carbon (TOC) | | | . | . | | | || | | | Purgeable Non-Purgeable Purgeable Organic Non-purgeable OrganicPurgeable Non-Purgeable Purgeable Organic Non-purgeable Organic (Dissolved) (Particulate) Carbon (POC) Carbon (NPOC)(Dissolved) (Particulate) Carbon (POC) Carbon (NPOC)
| . | . | || | Particulate DissolvedParticulate Dissolved (PtOC) (DOC)(PtOC) (DOC)
TOC
Total organic carbon analysis is a determination of Total organic carbon analysis is a determination of organic carbon in a sample regardless of its oxidation organic carbon in a sample regardless of its oxidation state or biodegradability. Other measures of total state or biodegradability. Other measures of total organic matter (e.g., COD, BOD) may respond organic matter (e.g., COD, BOD) may respond differently to solutions of equal carbon concentration differently to solutions of equal carbon concentration depending on the oxygen content or the bidegradation depending on the oxygen content or the bidegradation kinetics. For the measurement of total organic carbon, kinetics. For the measurement of total organic carbon, the sample is exposed to an oxidizing environment the sample is exposed to an oxidizing environment often at very high temperatures. With complete often at very high temperatures. With complete oxidation all carbon is converted to carbon dioxide and oxidation all carbon is converted to carbon dioxide and swept into a detector by the carrier gas. The oxidation swept into a detector by the carrier gas. The oxidation process is based on the following stoichiometry:process is based on the following stoichiometry:C H N O a
b dO aCO
bH O
cNa b c d ( )
4 2 2 22 2 2 2
TOC - Pyrolysis Instrument
CO2 Detector Recorder
Syringe
O2
Condensor
Furnace
Sample Inlet
TOC - UV/persulfate Instrument
CO2 Detector Recorder
Syringe
O2
Condensor
SampleInlet
PersulfateSolution
UV Reactor
TOC - The CO2 Detector
DemodulatorAmplifier
SensingCell
Sample
Reference
In Out
Chopper
IR
Source
A non-dispersive infra-red analyzer (NDIR)