Environmental Engineering CIVE225

Laws of Thermodynamics

1. Energy cannot be created or destroyed, it simply changes form.

2. Systems move spontaneously from being highly organized to more random (entropy increases)

3. Entropy 0 at absolute temp 0 K

Acid

a substance that donates protons (H+) in a chemical reaction

Base

a compound that can accept H+ protons, produce OH-

Strong acids and bases

Acids

HCl hydrochloric

H2SO4 sulfuric

HNO3 nitric

Bases

KOH

NaOH

Ba(OH)2

Why are acid-base reactions so important in environmental engineering?

• Aquatic forms of life are sensitive to small pH changes (∴waste must be neutralized)

• pH can affect mobilization of pollutants in the environment

• pH can be manipulated to drive contaminants out of solution (precipitate them) before effluent is released

Importance of carbonate system

• most important acid-base system in environment

• controls pH in natural waters

• controls pH in drinking water

• provides buffering system for water treatment (alkalinity)

components of carbonate system

• dissolved CO2

• carbonic acid (H2CO3 aq)

• Bicarbonate ion (HCO3- aq)

• Carbonate ion (CO3 2- aq)

chemical equations of the carbonate system

see ipad

alkalinity

measure of a waters’ capacity to neutralize acids (mol/L)

buffering capacity

ability of water to resist changes in pH when acids or alkaline material are added.

(acids: H+, H2CO3*, HCO3-)

(bases: OH, CO32-, HCO3-)

open vs closed carbonate systems

• based on speed of gas/water exchange relative to speed of reactions affecting acid-base equilibrium

• Open: gas/water exchanges faster than other reactions (henry’s law true)

• Closed: gas/water exchanges slower than other reactions, no new C from air

sorption

any process by which one substance becomes attached, fixed or captured by another

absorption vs adsorption

absorption: captured substance buried randomly within the sorbate (density differences, capillary action) like a sponge

adsorption: captured substance adheres to the surface on specific adsorption sites (e.g. hydrophobicity)

Adsorption equilibrium: isotherms

• experiments conducted at constant temperatures showing relationship between qe (concentration of adsorbate on adsorbent) and Ce (concentration of adsorbate in solution)

• Two common isotherms:

  • langmuir - derived from theory

  • freundlich - derived empirically

what does the octanol-water partition coefficient Kow indicate?

• correlate biological effects of organic substances

• small for highly polar compounds, high for long non-polar

• measure of how lipophilic (fat loving) vs hydrophilic (water loving) a compound is

  • helps assessing potential toxicity

  • more likely to stick to fat - bioaccumulates in fatty tissue and cause chronic toxicity

differences between CMFR and PFR

• CMFR: completely mixed flow reactor, can be steady state or transient, conservative or non-conservative compound

• PFR: plug flow reactor, only interested in steady state, rivers where upstream and downstream don’t mix

what do alpha 0, 1, and 2 represent in the carbonate cycle?

see ipad notes

three pillars of sustainability

• Economy: create and maintain a prosperous society

• Environment: maintain a sufficient stock of natural resources for current and future generation

• Society: ensure high quality of life for population with equity between classes

through what process does active carbon remove contaminants? what contaminants does it remove?

adsorption

• VOCs

• Pesticides (atrazine)

• Petroleum products

• General: hydrophobic compounds adsorb better (stick to hydrophobic carbon surface better, prefer to be there than in water)

• Non-polar compounds

1 ppm

= 1 mg / L in water

Evolution phases of micro-organisms in aerated batch culture

1. Lag phase

   1. Acclimation period

2. Log phase

   1. exponential increase in cell growth

3. Stationary phase

   1. rate of cell division and death equal

4. Death phase

   1. substrate no longer available to support bacteria growth

how to simplify charge balance?

if comparing with H+ concentration, consider pH and concentration of given chemical, is it significantly lower? can cross out

why is temperature increase bad for marine life

solubility of O2 decreases as temperature increases (faster molecules evaporate more, less O2 stays in water)

difference between collecting sample from effluent tube and inside a reactor

tubing length

small delay caused by volume moving through tube = volume / flow rate

sedimentation

• Use gravity settling to remove particles from water

• Need long enough retention time to let particles settle out before they leave the tank

• Sedimentation tank = clarifier or settling tank

what do sedimentation tanks do to water to settle out particles?

• slow water down

• reduce turbulence (chaotic flow of water)

  • laminar flow

zones in a sedimentation basin and purposes

1. influent zone

   • decreases the velocity of incoming water, distributes flow evenly across settling zone

2. settling zone:

   • slow, calm area for suspended particles to settle out

3. effluent zone

   • transition from settling zone to effluent flow area

4. sludge zone

   • settled solids separated from other particles in the zone

overflow rate (OR) or critical velocity (Vc)

measure of how quickly water flows over the

surface of a sedimentation tank

OR = Q/A

• want particle (Vs) to move downward faster than water moves upward (Vs>OR)

assumptions for calculations of sedimentation tanks

• velocity vectors of particles evenly distributed

• plug flow (eliminates complexities of turbulence and differing residence times)

• any particle hitting bottom is removed

how would you make a settling tank more efficient?

• remove greater % of particles

• Adjust length of the tank (not depth) to increase area and decrease OR

• Lamella tank (inclined plates for increased settling area but still greater OR)

two types of granular media filtration

• slow sand filtration:

  • slow flow rate and big SA required

• fast filtration:

  • can process lots of water fast

  • includes routine backwashing

purpose of granular media filtration

• step after sedimentation tank

• remove finer particles that did not get settled out

• filtration: separating suspended particles by passing them through a porous medium

granular media filtration mechanisms

1. straining

2. interception: particle has affinity to surface

3. settling

4. impaction/brownian motion

rapid sand filtration and dual media filters

• backwashing: forcing water upward through filter at high velocity to remove/dislodge particles

• dual media filters: anthracite (big and light) and sand (small and dense)

  • after backwash, gradation remains

  • want big particles on top and smaller on the bottom - efficient use of length

slow sand filters

• good at removing biological particles

• large surface area

• does not require pre-treatment: coagulation/flocculation

• not as effective as fast filters

impacts of air pollution

• health (asthma, death)

• property damage

• visibility reduction

• forest decline

• fish death

• skin cancer

• severe weather

primary vs secondary air pollutants

primary

• emitted directly in the atmosphere

• volatile organic carbon

• particles

• NOx SOx CO

secondary

• created by physical processes and chemical reactions in the atmosphere

• e.g. Ozone

major sources of air pollutants

• stationary fuel consumption (industrial boilers, electric utilities)

• stationary petroleum processes (petroleum refineries)

• mobile sources (vehicles, construction equipment, planes)

smog

• smoke + fog = smog

• general term to describe poor air quality with reduced visibility

photochemical vs industrial smog

• photochemical: motor vehicles

  • CO, VOCs, NOx

  • O3 - most abundant

• industrial: stationary sources

  • SOx, particulate matter (PM)

criteria air pollutants

1. Nitrogen Oxides (NOx)

2. Ozone (O3)

3. Carbon Monoxide (CO)

4. Particulate Matter (PM)

5. Sulfur Oxides (SOx)

6. Lead (not discussed)

criteria air pollutants: NOx

• transportation sector + stationary fuel

• reaction: Thermal NOx (N2 becomes reactive at high temps) + Fuel NOx

• NO - no health effects

• NO2

  • eutrophication

  • acid rain

  • respiratory diseases

criteria air pollutants: O3

• no direct source - series of reactions

• health: airway constriction, reduced lung function, irritation

• vegetation: byproducts inhibit photosynthesis, loss of crop yield

• production mechanism (write in ipad)

criteria air pollutants: CO

• Most prevalent air pollutant

• Vast majority emissions from transportation sector

• Main source of CO: incomplete combustion (low temp, low O2)

• health:

  • Greater affinity for hemoglobin—> low O2 in blood

  • Reduced mental clearness, headache, coma, death

criteria air pollutants: Particulate Matter (PM)

• Very diverse chemical composition

• Sources: fuel combustion, wildfires, dust, grinding, abrasion

• Cause of winter smog in Montreal

• PM10 short atmospheric life

• PM2.5 very long atmospheric life

• health:

  • anxiety

  • premature birth

  • cardiovascular disease

• Particulates = Aerosols or

  • Solid: Dust, Soot

  • Liquid: Fumes, Mist, Fog

criteria air pollutants: SOx

• Main source: combustion (electric power plants burning sulfur-containing coal)

• forms sulfuric acids - Acid rain

• health: similar to PM damages

how is air quality monitored?

• air quality index (AQI) - the lower the better

• 5 criteria pollutants, 7 standards

• worst standard becomes the index

how does air mix vertically?

difference in temperature

change of temperature with altitude

• pressure decreases as you go up, so does temperature (PV=nRT)

• dry and saturated adiabatic lapse rates

  • rate at which an air parcel (dry or saturated) cools and rises in the atmosphere WITHOUT heat transfer

why does saturated air cool more slowly than dry air?

• water condensates as temp decreases, releasing latent heat

• latent heat moderates cooling of parcel

how to predict vertical air mixing?

• graph compares ambient and adiabatic (ideal) lapse rates to determine stability of atmosphere

what is the solution to air pollution and why does it work

• solution to pollution is dilution

• dilute by creating taller stacks

• the taller the stack, the lower the concentration of the pollutant at ground-level

assumptions and overall accuracy of Point Source Gaussian Plume Model

• Rate of emissions from source =constant

• Wind speed = constant

• Pollutant is conservative

• Accuracy: uncertain model

  • within ± 50%

  • Widely accepted

  • good for comparison

conservative pollutant

• once it’s emitted it undergoes NO chemical reactions/degradation

• only changes by dilution and physical transportation

what are Gaussian Dispersion Coefficients (σy, σz)

• standard deviations

• depend on downwind dist (x) and atmospheric conditions

reducing air pollution from stationary sources

• pre-combustion: fuel switching, coal cleaning

• improving combustion

• post-combustion: emission capture, air treatment for each specific emission

average velocity vs Darcy velocity

• Darcy velocity = Q/A

• average velocity accounts for actual Surface Area that flow goes through

How do we describe contaminant transport with groundwater flow? (Transport mechanisms)

1. advection

   • plug flow of contaminants flowing with water at Darcy velocity

2. Diffusion

   • particles move in direction of their concentration gradient

   • no water movement required

3. Mechanical dispersion

   • solute spreads out from expected path and contaminant is diluted

   • differing velocities of particles

4. Retardation

   • slowing down of chemical relative to water movement

potable vs palatable drinking water

• potable: healthy for human consumption

• palatable: healthy and aesthetically acceptable to drink

physical characteristics of water: turbidity

• measures ability of particles suspended in water to scatter light

• water optical clarity

physical characteristics of water: particles

• solids greater than molecules but generally not visible to naked eye

• Total Suspended Solids (TSS) vs Total Dissolved Solids (TDS)

  • pass water through filter and the ones that are small enough to pass are “dissolved”

water hardness and how it is classified

• caused by presence of multivalence cations

• Most common inorganic constituents of water that cause hardness: Mg2+, Ca2+

• may be classified by cations themselves (Total Hardness) or by the associated anions

  • carbonate and non-carbonate (permanent) hardness

    • carbonate: hardness associated with carbonate anions

    • non-carbonate: hardness associated with other anions

why is water hardness an issue?

• bad lathering of soaps

• formation of hard to remove precipitates on infrastructure

good vs bad microorganisms

• bad = Waterborne organisms that cause disease in humans or damage the ecosystem

• good = Can be harnessed in biological treatment systems to degrade organic matter

pathogens

microorganisms capable of causing disease in humans

what are the stages/basins of a drinking water treatment plant?

1. Raw water

2. Coagulation / Flocculation Basin

3. Sedimentation Basin

4. Filtration Basin

5. Disinfection/oxidation Basin

6. Softening/reducing inorganic constituents

7. Adjust pH and alkalinity

8. Fluoridation

9. Finished Water Storage

what does each unit of drinking water treatment address?

1. Coagulation / flocculation and Filtration: turbidity, colour, particles

2. Disinfection: pathogens, organic material

3. Fluoridation and water softening: inorganics and final chemical adjustment (adjust pH and alkalinity)

coagulation / flocculation / sedimentation / filtration

• coagulation: add a coagulant like alum (contains Al 3+) that neutralizes electric charges on suspended particles so they stop repelling

  • forms microflocs

• flocculation: gently stir the water to bring the particles together to create flocs

• sedimentation: now particles are ready to be settled out

• filtration: any remaining particles get caught on the filter

how much alkalinity does alum consume and why does it need to be restored?

• 1 mol alum = 6 eq of alkalinity

• 1mg/L of alum will consume about 0.5mg as CaCO3/L of alkalinity

• why restore:

  • treatment processes work best in certain pH ranges (coagulation included)

  • corrosion of pipes

  • aquatic organisms have narrow pH ranges to survive

  • alkalinity acts as a buffer against pH changes

what is the optimum alum dose in the jar test?

• reduces turbidity the most

• produces the most visible and fast settling flocs

• leads to the smallest change in pH (aka lowers alkalinity the least)

what is the purpose of water softening and how is it done?

• to remove Ca2+ and Mg2+ from solution

• processes

  1. ion exchange softening

  2. lime-soda softening

     • in water treatment plants

     • Precipitate Mg and Ca by increasing pH (adding lime)

Chick-Watson Kinetics

Rate of number of microorganisms killed is proportional to number of microorganisms and concentration of disinfectant

primary vs secondary disinfection

primary: disinfection in the treatment plant

secondary: disinfection before entering distribution system to protect against intrusion and biofilm formation in pipes

major approaches to disinfection

1. Adding oxidative agents

   1. free chlorine, O3

   2. stops cell metabolism

2. UV radiation

   1. stops cell capacity to reproduce

what is the log-removal concept?

• Microbes present in very high cell numbers

• Disinfection requires the cell removals by several orders of magnitude

• useful to discuss in terms of log removal: −log(Nt/N0)

• Log-removals with successive processes are additive

  • if process 1 has a 2-log removal and process 2 has a 3-log removal = total removal of 5-log

log-removal credit vs log-removal

• credit: # of credits assigned to a specific treatment process (e.g., chlorine disinfection), expressed in log units, for the inactivation of a given pathogen

• Log-Removal: a base-10 logarithmic scale used to describe the level of pathogen reduction achieved by a treatment process

  • log-removal = # of 9’s in a number 99.9% = 3-log removal

adsorption vs partitioning

• adsorption

  • adhere to surface of adsorbent

    • hydrophobicity, to reach a lower energy state

  • most common adsorbent = Activated Carbon (AC)

• partitioning

  • how much of a compound exists in each phase when multiple phases are present (air and water)

why treat wastewater?

• protect source of drinking water

• there’s always someone downstream!

• protect aquatic ecology

what are the stages of a wastewater treatment plan?

Primary treatment / Pretreatment

• Screening

• Grit chamber: Removal of settleable solids (grit)

• Possibly: Coagulation and settling tanks (like drinking water clarifiers)

Secondary (Biological) treatment

• Aeration basin: Removal of soluble BOD

  • injected O2 + Return Activated Sludge (RAS) aka good bacteria: remove BOD

• Removal of non-settlable solids

Advanced treatment

• Removal of nutrients

• No removal of dissolved BOD, nutrients, and pathogens

• Disinfection: Removal of micro-pollutants (biologically resistant)

• Removal of colour