Management
ESM 202
‰ Value of Monitoring Water Quality
Parameters
Understanding
Water Quality
Parameters
‰ Human Health
‰ Sustainable management
‰ Restoration
‰ Remediation
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Water Quality Parameters
‰ Dissolved Oxygen
‰ Temperature
‰ Biochemical Oxygen
Demand
‰ Nutrients: N & P
‰ Minerals: Anions &
Cations
‰ Trace Elements
‰ Toxic Organic
Compounds
Dissolved
Oxygen
(DO)
‰ Coliform Bacteria,
other Microbes,
Viruses
‰ Solids (TDS, SS)
‰ Alkalinity, pH
‰ Hardness
‰ Turbidity
‰ Color
‰ Taste and Odor
O2 (gas)
Æ
O2 (aq)
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3
Increasing
Salinity
High
DO
Increasing
Temp
Low
DO
Basic
Concepts
in Water
Chemistry
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Basic Concepts
Basic Concepts
‰ Equilibrium
‰Concentration in aqueous or solid
systems
A + B = C + D
Products
[C] [D]
=
[A] [B]
Reactants
K=
‰[HCO3-] = mol / L = M
‰Convert from mol/L to g/L using
the Molecular Weight (MW), g/mol
‰Concentration in gas phase:
‰PCO2 = atm
‰ Thermodynamic equilibrium
‰ Reversible vs. irreversible
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Dissolution
Dissolution
‰ O2 dissolution in water
‰ CO2 dissolution in water:
O2(aq)
KH,O2 =
10.07 mg/L
32.00 g/mol
PO2
[O2(aq)]
=
=
0.209 atm
3.15 x 10-4 mol/L
10.07 x 10-3 g/L
32.00 g/mol
O2(g)
=
CO2(aq) = CO2(g)
KH =
663 atm.L/mol
PCO2
[CO2(aq)]
= 26.9 atm L/ mol
= 0.000315 mol/L
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Oxygen Demand
Oxygen
Demand
How much Oxygen is needed to
degrade a load of pollutant?
‰ Chemical Oxygen Demand (COD)
‰ Biochemical Oxygen Demand (BOD)
‰ Nitrogenous Biochemical Oxygen Demand
(NBOD)
‰ Total Oxygen Demand (TOD)
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CaHbOcNdSe + x O2
a CO2 + 1/2 b H2O + d NO3- + e SO4212
Chemical Oxygen Demand
Biochemical Oxygen Demand
‰ Quick test to determine Oxygen Demand
‰ Measures “rapidly” biologically oxidizable
organic matter
‰ Usually expressed as 5-day BOD = BOD5
‰ Depending on BOD concentration and
water characteristics:
‰ Strong oxidizing agent in acidic medium
with catalyst (silver sulfate)
‰ No info on biologically oxidizable matter
‰ Issues
‰ Dilution
‰ Some organic matter is quite inert
‰ Essential nutrients (N, P, K, Fe, etc.)
‰ Interference from minerals in water
CaHbOcNdSe + Cr2O7 2-
‰ Bacterial seed
Cr3+ + a CO2 + 1/2 b H2O + d NO3- + e SO4213
EZ BOD
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Nitrogenous BOD
¾Simply
¾ Place a sample of the
microbial biomass into
the test bottle with the
wastewater
¾ Insert integrated DO
probe
¾ Follow instructions
that appear on the liquid
crystal display (LCD)
¾Test provides a quantitative
prediction of BOD5 (based on
correlation to BOD5)
¾ For specific plant
conditions
¾ Data collected in 15 to
60 minutes
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Effect of BOD in a River
Nitrogenous Oxygen Demand
Pollutant
discharge
‰ Two-step oxidation of ammonia:
NH4+ + 3/2 O2
Nitrosomonas
NO2- + 1/2 O2
Nitrosobacter
NH4+ + 2 O2
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NO2- + H2O + 2 H+
NO3NO3- + H2O + 2 H+
‰ Can inhibit nitrification to measure CBOD and
NBOD separately
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Microorganisms
‰ E.
coli used as an indicator of water
quality: normal inhabitant of intestines of
many animals
‰ Indicator of presence of fecal matter
‰ Total coliforms are typically reported
‰ Cost of testing for all possible
microorganism is $$$$
Microorganisms
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Coliform test
‰ Results reported as Most Probable
Number (MPN) per 100 mL
‰ Incubation at moderate temperature (35
oC) for 48 hr
‰ Test does not account for normally
occurring microbes which also respond to
lactose
‰ New developments to deal with these
issues
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Sediments
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Turbidity
Turbidity
‰ Water clarity is an indicator of drinking
water quality
‰ In the field, use a Secchi disk
‰ In lab, measure transmission of light
through a standard cuvette
‰ Colloidal particles scatter light
‰ Colloidal particles may harbor pathogens,
toxics (metals, pesticides), radionuclides
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Hardness
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Hardness
‰ Soft
‰ Correlated with TDS
‰ Moderate
‰ Represents total concentration of Ca and
‰ Hard
Mg, and is reported in equivalent CaCO3
‰ Other ions (Fe2+) may also contribute
‰ Hard water leaves solid deposits (boilers,
hot water pipes, heaters, fixtures) and
requires more soap
‰ Hard water is less corrosive
‰ Very Hard
<
=
=
>
50 mg/L
50 - 150 mg/L
150 - 300 mg/L
300 mg/L
‰ Treatment usually left to consumer
(domestic, industrial, etc.) depending on
needs
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pH
‰ What is pH?
pH
‰ Concentration of H+
‰ Measured on a log scale
‰ Actually, an inverse log…
‰ pH = -log10([H+])
‰ pH = 7 means [H+] = 10-7 mol H+/L
‰ What does it mean?
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pH
pH
‰ Natural conditions
‰ Human (anthropogenic) changes to pH
‰ Acidic
‰Temperate forest soils (pH 4-6)
‰Raindrop through clean atmosphere (pH 5-5.5)
‰Sulfur vents (pH 2-4)
‰ Acid rain (deposition)
‰ Acid mine drainage
‰ Discharge of acidic or alkaline wastewater
‰ Open mining of limestone
‰ Alkaline
‰Arid soils (pH 8-11)
‰Limestone dominated soils (pH 7-9)
‰Ocean (pH 8-8.5)
‰ Cattle feedstock yards (NH3)
‰ Fossil fuel combustion
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pH
Dissociation of Water
H2O + H2O = H3O+ + OH-
‰ Why does it matter?
‰ pH controls the chemical form (species) of many
compounds
‰ Low pH leads to faster dissolution (weathering) of
surrounding minerals
Kw =
‰ Releases potentially toxic elements
‰ Changes in biodiversity
‰ High pH
‰ Can increase concentration of ammonia, toxic to fish
‰ Increased precipitation of metals
[H3O+] [OH-]
+
-14
= [H ] [OH ] = 10
[H2O ] [H2O ]
-log10(Kw ) = pKw = 14
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pH-pC Diagram
pH-pC Diagram
pH
pH
pH = 8
pH = 6
pC
pC
pCH+= 6
[H+]= 10-6 M
pCH+= 8
[H+]= 10-8 M
[H+]
[H+]
[OH-]
[OH-]
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Macro Nutrients
‰ Common Forms of Nitrogen:
‰ Ammonia/Ammonium
NH3 / NH4+
‰ Nitric Acid/Nitrate
HNO3 / NO3‰ Nitrous Acid/Nitrite
HNO2 / NO2‰ Organic Nitrogen
Macro
Nutrients
‰ Phosphate
PO43-, HPO42-
‰ Ratio of Uptake of Nutrients (typical):
C :N :P
100 : 16 : 1
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Dissociation
Acids:
KHNO3=
pH
HNO3 + H2O = H3O+ + NO3-
[H+] [NO3-]
= 101 mol/L
[HNO3]
Bases:
KNH3 =
pH-pC Diagram for NH3
pKHNO3 = -1.0
pC
[NH4+]
[NH3]
NH3 + H2O = NH4+ + OH-
[OH-] [NH4+]
[NH3 ]
= 10-9.3 mol/L
pKNH3 = 9.3
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[OH-]
[H+]
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