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