wk2:water pollutionweb.iitd.ac.in/~arunku/files/cvl100_y17/wk2aug1to4.pdf · volatile and fixed...
TRANSCRIPT
August 10, 2017 Arun Kumar ([email protected])
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Wk2
by Dr. Arun Kumar ([email protected])
Wk2:Water Pollution
Objective: To introduce water pollutants (chemical, biological) and nutrients which might cause problems
August 10, 2017 Arun Kumar ([email protected])
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Water Treatment Plant Schematic
Objective: To introduce water treatment plant schematic and need for different unit processes
Step 1. List water quality characteristics which need to be removed
• Parameters:
– Ions (arsenate; chromate ions;nitrate)
– Organic compounds (pesticides, etc.)
– Pathogens (viruses, if we have human fecal pollution)
– Solids (depends if there is a fracturing in subsurface)
– Gases(methane, etc.)
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Step 2. Identify unit(s) which can remove at least one type of contamination
• Ions (removal by: adsorption; coagulation-
flocculation; chemical precipitation; bio-adsorption;
membrane process)
• Organic compounds (degradation/removal by:
oxidation; adsorption; biodegradation; reduction-
oxidation; irradiation; membrane process)
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Step 2 contd.
• Pathogens (killed by : adsorption; coagulation-
flocculation; chemical precipitation; disinfection;
boiling; irradiation; membrane process)
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Step 2 contd.
• Solids (removal by : settling; filtration; membrane
process)
• Gases (removal by) : aeration; adsorption;
solubilization)
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Example 1: Groundwater �produce drinking water)
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Treatment schematic (GW� Potable drinking
water)
• Raw Ground water � aeration chamber �
Softening unit � Filtration with chlorination
�Disinfection � Storage
• See sequence of units used
• Chemical is required to be added
• Water is treated
• Chemical sludge is produced
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Units used for (GW� Potable drinking water)
• Aeration chamber (to remove gases; using air)
• Softening unit (to remove cations; using softener and/or cation exchangers)
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Treatment schematic (GW� Potable drinking
water)
• Filtration with chlorination (to remove solids; to kill microbial growth on filter unit surface)
• Disinfection (to kill microorganisms before water is supplied for public consumption)
• Storage
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Example 2: Yamuna River Water �produce drinking water)
• Think for 5 minutes for two steps.
• Step 1: water quality characteristics determination
• Step 2: selection of units, their order
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Example 2: Yamuna River Water �produce drinking water)
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Example 2 schematic contd.
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Pathogenic Microorganisms
1. Microorganisms
Pathogenic Microorganisms
1. Microorganisms
Q: Can you list sources which might give you exposure of pathogenic microorganisms?
Sizes of Microorganisms and Other
Particles (size influences removal through
filtration method)
1. Microorganisms
Inorganic Pollutants
• Heavy Metals
• Arsenic
• Nitrates
• chromium
• Asbestos
• Other?
2. Inorganics
Effect =f(valency type,
concentration)
For example: toxic effects of
arsenate(AsIV)) and
arsenite (As(III)) might be
different.
Q: Can you list sources which might give you exposure of these inorganic pollutants?
• Petroleum constituents:
– benzene and substituted benzenes
– prevalent in gasoline, diesel fuel, heating oil
– most easily transported, slow degradation, toxic
CH2CH3CH3 CH3
CH3
Benzene Toluene Ethylbenzene m-Xylene
Volatile Organic Compounds (VOCs)
3. Organics
• Oxygentated gasoline additives
– added to gasoline to improve air quality
– very soluble, resistant to degradation, toxic
– attempt to solve one problem caused another
(spills)
CH3 C
CH3
CH3
O CH3
Methyl tertiary butyl ether (MTBE)
Volatile Organic Compounds (VOCs)
3. Organics
• Chlorinated solvents
– C1 and C2 aliphatics
– widely used in degreasing, dry cleaning, extraction
– somewhat soluble, volatile, difficult to degrade
C
Cl
Cl
Cl
Cl C
Cl
Cl
Cl
H C C
Cl
Cl
Cl
H
H
H
C C
H
H
Cl
H
carbon tetrachloride chloroform 1,1,1-trichloroethane vinyl chloride
Volatile Organic Compounds (VOCs)
3. Organics
Pesticides (hydrophobic organic
compounds)• Organochlorine Insecticides: were commonly used
in the past (e.g. DDT and chlordane).
• Organophosphate Pesticides: most are
insecticides, some are very poisonous (they were
used in World War II as nerve agents)
• Carbamate Pesticides: affect the nervous system
• Pyrethroid Pesticides: were developed as a
synthetic version of the naturally occurring pesticide
pyrethrin, which is found in chrysanthemums
3. Organics
naphthalene anthracene phenanathrene
pyrene benzo[a]pyrene
Polycyclic Aromatic Hydrocarbons (PAHs)
Polycyclic aromatic hydrocarbons (PAHs) are a group of over 100 different chemicals that are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances.
They are potent carcinogens, hydrophobic organiccompounds and they tend to associate with particles.
3. Organics
• Polychlorinated biphenyls are mixtures of individual chlorinated compounds (known as congeners).
• PCBs are either oily liquids or solids that are colorless to light yellow.
• PCBs have been used as coolants and lubricants in transformers, capacitors, and other electrical equipment.
• The manufacture of PCBs was stopped in the U.S. in 1977.
• They are hydrophobic and they bio-accumulate in the food chain.
Polychlorinated biphenyls (PCBs)
Biphenyl
Cl
Cl
Cl
2,3',4-trichlorobiphenyl
3. Organics
Other Organic Pollutants
• Fertilizers
• Surfactants
• Explosives, propellants
• Chlorination By-Products (e.g. trihalomethanes)
• Antibiotics
• Pharmaceuticals
• Personal care products
• Cyanobacterial toxins
• nanomaterials
3. Organics
Microcystin-LR(hepatotoxin)
Excess Nutrients
• Nitrogen and phosphorus are nutrients required by all living organisms. They are considered pollutants when they are in excess.
• Excessive nutrients often lead to large growths of algae which in turn become oxygen-demanding material whey they die and settle.
4. Excess Nutrients
Excess Nutrients
106 CO2 + 16 NO3- + HPO4
2- + 122 H2O →
C106H263O110N16P + 138 O2
Algae + O2 => CO2 + H2O + NH3
algae
Nitrogen and phosphorus are typically the limiting factors
Phosphorus
• Phosphorus is typically the limiting nutrient in lakes, and algae growth is linked to phosphorus inputs.
• P Sources
– fertilizers
– detergents
– wastewater
• P can exist in a variety of chemical forms
Excess Nutrients
Nitrogen
• Nitrogen is often the limiting nutrient in ocean waters and some streams
• Nitrogen can exist in numerous forms, but nitrate (NO3
-), nitrite (NO2-), ammonia
(NH3) are most commonly measured
• Sources are primarily from fertilizers and acid deposition
Excess Nutrients
Factors Controlling Eutrophication
• Stoichiometry of photosysnthesis (C,N,P, O & H)
106 CO2 + 16 NO3- + HPO4
2- + 122 H2O → C106H263O110N16P + 138 O2
• Liebig’s law of the minimum – growth will be limited by the availability of the nutrient that is least available relative to the need
• Most fresh water systems are phosphorus limited
2.7311
1416=
×
×=
P
N It takes ~ 7 times more N than P to produce a given mass of algae
• Dissolved solids, or salts, may be present as any number of ions
– cations: Na+, K+, Mg2+, Ca2+
– anions: Cl-, SO42-, HCO3
-
• Typically measures as total dissolved solids (TDS)
• Water classification
– freshwater <1500 mg/L TDS
– brackish water 1500 – 5000 mg/L
– saline water >5000 mg/L
– sea water 30-34 g/L
Salts
Salts
• Sources
– industrial discharges
– deicing
– evaporative losses
– minerals
– sea water intrusion
• Effects
– natural fresh water population threatened
– limits use for drinking
– crop damage/soil poisoning (cannot use for
irrigation)
Salts
Salts
Suspended Solids• Organic and inorganic particles in water are
termed suspended solids
• May be distinguished from colloids, particles that do not settle readily
Suspended Solids
• Problems
– sedimentation
– may exert oxygen demand
– primary transport mechanism for many metals, organics and pathogens
– aesthetic
– complicates drinking water treatment
• Sources
– storm water
– wastes
– erosion
• When organic substances are broken down in water, oxygen is consumed
organic C + O2 → CO2
• For example:
CH3COOH + 2O2 => 2CO2 + 2H2O
C6H15O6N + 6O2 => 6 CO2 + 6 H2O + NH3
Oxygen-Demanding Wastes
Oxygen Demanding Wastes
Oxygen-Demanding Wastes
• High oxygen levels necessary for healthy stream ecology.
• For example:
– trout require 5-8 mg/L dissolved oxygen (DO)
– carp require 3 mg/L DO
Oxygen Demanding Wastes
Oxygen Demanding Wastes-
measurement/estimation• Estimated stoichiometrically by theoretical oxygen
demand (ThOD)
• Measured by oxygen demand potential
– biochemical oxygen demand (BOD)
– Nitrogenous oxygen demand (NBOD)
– chemical oxygen demand (COD)
August 10, 2017 Arun Kumar ([email protected])
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by Dr. Arun Kumar ([email protected])
Parameter Measurements
Objective: To introduce parameters to indicate pollution and methods to measure them
Parameters• Suspended solids
• Pathogens
• Inorganic ions
• Organic compounds
• Excess nutrients
• Oxygen demanding wasters– Estimated stoichiometrically by theoretical oxygen demand
(ThOD)
– biochemical oxygen demand (BOD)
– Nitrogenous oxygen demand (NBOD)
– chemical oxygen demand (COD)
Solids• Used in controlling biological process; drinking water
quality, etc.
• Gravimetric analysis is based on the determination of
constituents or categories of materials by measurement
of their weight.
• Three analytic operations:filtration, evaporation, and
combustion.– Filtration is used to separate suspended or particulate (non-filterable)
fraction from dissolved or soluble (filterable) fractions.
– Evaporation separates water from material dissolved or suspended in it.
– Combustion differentiates between organic and inorganic matter.
Organic matter will be destroyed completely by burning at 550oC for 30
min.
•
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Ref: AWWA, WEF, APHA, 1998, Standard Methods for the Examination of Water
and Wastewater (2540 D. Total Suspended Solids Dried at 103-105oC; 2540 E.
Fixed and Volatile Solids Ignited at 550oC)
Total Suspended SolidsProcedure:
• Filter samples (50 ml); Oven dry at 103oC for 30 min ; At this stage all water will be evaporated and only suspended solids will be retained on filter.
• Total suspended solids
mg total suspended solids =1000*(A-B)/(sample volume in mL) (1)
Weight crucibles (mass=C) and then weight crucible and filter (total
mass=E); Initial filter weight=B; Weigh filters now (mass =A g).
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Volatile and Fixed Suspended Solids
• Put crucibles with filter paper in muffle furnace and Ignite at 550oC for 15 min. At this stage all volatile components of solids will be volatilized and only fixed inert solid materials will be left in crucible. Weigh crucible after proper cooling (mass=D g).
• Volatile suspended solids (F) :
mg volatile suspended solids/L =1000*(E-D)/(sample volume in mL) (2)
• Fixed suspended solids (G) :
mg volatile suspended solids/L =1000*(D-C)/(sample volume in mL)
•
•
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