Environmental Engineering Exam 1

Water density

only common liquid that expands when it freezes, most dense at 4 degrees C

Water specific heat

very high, 4148 J/kgC

Water heat of vaporization

high!

Water stores on earth

world oceans, saline groundwater, fresh groundwater, antartic glaciers, greenland glaciers

Clean Water Act (1972)

Goal - to make surface water "fishable and swimmable". Pertains to water quality in rivers, lakes, estuaries and wetlands.
CWA made it unlawful to discharge any pollutant from a point source into navigable waters, unless a permit was obtained.

Point Source Pollution

Discharged from a discrete point, such as a pipe or smokestack. Easier to regulate, treat, and control.

Nonpoint source pollution

contamination as a result of contaminated rain, runoff, or snowmelt. not subject to CWA

Siltation

aesthetics of surface water, ecological harm, lake fill-in

Turbidity

a measure of light scattering by particles in water (cloudiness)

Told suspended solids (TSS)

sample is filtered, and recovered solids are dried and weighed

Waterborne pathogens

most important objective in drinking water is removal of pathogenic microorganisms

Vibrio cholerae

Bacteria
- Cholera
- Gram negative, rod-shaped proteobacterium
- Contaminated water, shellfish
Infects small intestine, causing fluid loss of up to 20 L per day

Cholera

restricted largely to the developing world

Legionella pneumophila

Bacteria
- Legionnaires disease, a form of respiratory pneumonia
- Prefers warm water, such as in HVAC cooling towers, distributions systems in warmer climates, hot tubs, water heaters
- Spreads through inhalation of aerosols, via showering or HVAC etc
- An opportunistic pathogen

Opportunistic pathogens

Organism that normally does not cause disease, often ubiquitous in the environment, but can infect individuals with compromised immune systems.

Giardia

Protozoan pathogen
- can be transmitted by wildlife and the water getting in your nose --> into your brain
- Flagellated protozoan
- Exists as active trophozoites or infective cysts
- Infects intestines and causes severe diarrhea and cramps
- Only 5-10% of infected people show symptoms, but still spread the cysts (dormant)
- Resistant to chlorine- not indicated by coliforms
- Effectively removed by filtration

Cryptosporidium parvum

Protozoan pathogen
- forms highly resistant oocysts
- a major consideration for drinking water treatment, as it shows the greatest chlorine tolerance
- removed by filtration or UV

Norovirus

Waterborne viral pathogen
- rare with water, common with food
- fecal/oral route
- easily transmitted through surfaces

Schistosoma

Animal pathogen
- type of nematode ("Blood fluke")
- complex life cycle that involves both snail and mammalian hosts
- Infection in humans causes schistosomiasis
- causes liver disease

Biofouling

Water at high pressure leading to bacteria
Ex: bacteria clogging reverse osmosis membrane element

Atom

indivisible unit containing at least a proton, and usually neutrons and electrons

element

a type of atom with a unique number of protons

isotopes

variations among a single element having different numbers of neutrons

ions

atoms having fewer or more electrons than protons, positive or negative charge

molecule

two or more atoms bonded together with either a covalent or ionic bond

anion

negatively charged ion

cation

positively charged ion

Ionic bond

Atoms bound by electrostatic attraction between ions of opposite charge
- very strong until polar solvent like water
- Can dissociate in water

covalent bond

When two or more atoms share electrons
- Retain their bonds/structure in water

metallic bond

bonding characterized by a delocalized electron cloud

hydrogen bond

an electrostatic attraction between partially charged hydrogen atoms and an electronegative atom

Polyatomic ions

ions consisting of two or more covalently bound atoms. they typically remain as a single unit when dissolved in water

liquid phase

(l)

solid phase

(s)

gas phase

(g)

aqueous/dissolved phase

(aq)

solvent

a liquid into which substances dissolve

solute

a compound that dissovles into the solvent

solution

the mixture of a solvent and one or more dissolved solutes

molecular solutions

contain dissolved neutral molecules that disperse from one another but remain intact as a molecule

ionic solutions

are formed by dissolutions of salts, acids, or bases. results in dissociation

dissociation

the breakage of ionic bonds and formation of separate dissolved cations and anions that are stabilized by interaction with polar water molecules

pH of pure water

7

low pH means

acidic, pH<7, H+>OH-

high pH means

basic or alkaline water pH>7, H+<OH-

pH = -log[H+]

[H+] = 10^-pH

Oxygen-demanding waste

Chemical contaminant
Healthy surface waters need dissolved oxygen

Eutrophication

"well fed", enriched in nutrients, results in algal blooms
- Algae essentially convert CO2 into organic carbon via photosynthesis, thus creating potentially oxygen demanding compounds.
- bacteria feed on algal byproducts and dead algae, thus consuming O2
- leads to hypoxic zones aka dead zones

Limiting nutrients

nutrient which limits further growth of plant and microbial populations in an ecosystem, and addition of which may cause eutrophication (N for seawater and P for freshwater)

Fresh water

TDS < 1500 mg/L

Brackish water

1500<TDS<5000 mg/L

Saline water

TDS>5000 mg/L

TDS

total dissolved salts

Drinking water standard TDS

<500mg/L

Lead (Pb) sources of water contamination and risks

- legacy lead soldered plumbing and lead service lines
- coal ash
- runoff from shooting ranges
- atmospheric deposition from polluted air
risks:
- lead poisoning
- exposure of children even at low levels can result in developmental problems later in life

EPA action level for drinking water: 15 ppb

Mercury (Hg) sources of water contamination and risks

- atmospheric deposition from polluted air
- coal ash
risks:
- typically doesn't occur in hazardous conditions, however it bioaccumulates
- consuming too much fish can result in mercury poisoning

bioaccumulates

when a substance accumulates in biological tissues and increases in concentration up the food chain

Arsenic (As) sources of contamination and risks

- naturally occurring in some groundwater
- coal ash
Risks
- chronic exposure associated with skin, bladder, and lung cancer
- EPA MCL for drinking water Is 10 ppb

Organic compoud/molecule

a molecule containing one or more carbon atoms covalently bonded to other atoms

saturated vs unsaturated organic compounds

unsat = double bonds, less hydrogen, more reduced state

Aromatic compound

organic compounds that contain a ring of 6 carbon atoms with alternating double and single bonds

Endocrine disruptors

compounds that are either known hormones, mimic animal hormones, or otherwise interfere with the endocrine system

sources of water contamination of endocrine disruptors

pharmaceuticals passed through urine, pharmaceutical metabolites in urine, personal care products, leaching from plastics

PFAS

poly/perfluoroalkyl substances
endocrine disruptors
water repellent, grease repellent, foam forming, strong acids, flame retardants
chemical plants, military installations, landfill leachate and municipal wastewater

Equilibrium

a state in which the concentrations of the reactants and products of a chemical reaction stabilize and have no tendency to change further over time

Reaction Quotient

Qt = [B]/[A] products over reactants

Chemical equilibrium

Under fixed conditions, such reactions will eventually reach a condition wherein the rate at which the “forward” reaction is proceeding is equal to the rate at which the “reverse” reaction is proceeding

Acid

is a molecule that reversibly donates a proton (H+) to a solution upon dissociation

Acid dissociation constant, Ka

the equilibrium constant for acid-base dissociation reactions

Ideal gas law

PV=nRT
R = ideal gas constant = 0.082086 L atm mol -k

Henrys law constant

KH = [G](aq)/PG

Ion product constant (Kw)

Kw = [H+][OH-] = 10^-14

Municipal drinking water systems have three components

a source, a water treatment plant, a water distribution network

Drinking water sources

lake and reservoirs, rivers, groundwater, seawater, other ( snowmelt, rainwater, moisture from air, wastewater)

Main goals of water treatment systems

removal/inactivation of pathogens and provision of disinfectant residual, removal of harmful chemical contaminants, improve aesthetics of the water, reduce corrosiveness of the water

Safe Drinking Water Act(1974)

extended the responsibility of the federal government to regulate all community water systems with 25 or more customers. Establishes maximum levels for both chemical and microbial contaminants. Exceeding the limits can result in fines and legal penalties for municipalities.

Primary standards

these are mandated thresholds for the purpose of protecting public health coming in two forms MCL and TT

Maximum Containment Level (MCL)

most standards for drinking water are in the form of an MCL, states the maximum allowable concentration in treated water, typically upon exit from the treatment plant

Treatment technique standard (TT)

rather than state a maximum contaminant level, some standards simply require specific treatment practice to be employed

Secondary standards

these are not required by the EPA, but are suggested limits on contaminants which pose more aesthetic or distribution problems

the most critical quality parameters for source water quality are

turbidity, hardness, organic carbon and chemical contaminants, pH and alkalinity

Hardness

compromises the combined concentration of metal cations that can precipitate to form mineral scale

Water softening

removing hardness

Natural organic matter(NOM)

Most common chemical contaminant of concern in drinking water
- consists mostly of large molecules derived from the degradation of plant material
- not toxicity concern, can react with disinfectants to produce toxic disinfection byproducts
- need to remove can significantly affect design and operation of water treatment plants

Humic substances

Large molecules derived from the degradation of plant material

pH

influences the solubility of metals and NOM, can affect volatility of some compounds, affects the efficacy and efficiency of many treatment operations, affects the corrosivity of the water and the health of the distribution system

Alkalinity

is a quantity that reflects a water’s ability to resist changes in pH , due to the presence of buffering compounds

why remove solids?

Solids removal reduces pathogen concentrations to a greater extent than disinfection in most cases

Solids removal in conventional water treatment

coagulation, flocculation, sedimentation, granular media filtration

Coagulation

addition of dissolved cations to neutralize negative surface charge on solid particles

Flocculation

the formation of loose aggregates of destabilized solids via mixing induced collisions

Acid

Ionic compound that donates H+ to the solution upon dissociation.
Addition of acids increases [H+] and lowers pH

Base

An ionic compound that first dissociates, and then accepts H+ from the solution
Addition of bases decreases [H+] and raises pH

Indifferent

Na+ cations
Almost always exist in dissociated state in solution

Strong Acids

consists of an anion bound to one or more (H+), strong acids almost completely dissociate donating all of their protons to the solution

Why is HCI a “strong acid”?

because the chloride anion (CI-) has low charge density and doe not strongly attract H+, the water molecules easily grab the H+ away from the CI-

Is NaCL a base?

when dissolved in water, is dissociates. Since CI- does not attract protons, it does not accept any from solution

weak acids

consists of an anion bound to one or more H+

Why is HOCI a “weak acid”?

because the hypochlorite anion (CIO-) has high charge density and strongly attracts H+. When HOCI is added to water, the water molecules only grab a portion of the H+ awat from the CIO-

In NaOCI a base?

when dissolved in water, it dissociates. Sine OCI- attracts protons, it then accepts available H+ form solution, resulting in an increase in pH