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)