M2U1 Coagulation and Flocculation Flashcards
first process in the wwt plant to remove a significant fraction of organic particulate matter
primary treatment
principal form of primary treatment
sedimentation
consists of grease, oil, plastic, leaves, rags, hair, and other floatable materials
scum
constitute the backbone processes in most water and advance wwt plants
coagulation and flocculation
DBP
disinfection by products
coagulating agent used by egyptians to clarify water
almonds
coagulating agent used by Romans and used in municipal water treatment in England
alum
NOM
natural organic matter
particulate and dissolved organic matter when collected is called
NOM (natural organic matter)
treated to remove natural organic water
surface water
treated to remove hardness, or iron or manganese
groundwater
T/F
The object of coagulation (and subsequently flocculation) is to turn the small particles into larger particles called flocs
true
addition of one or more chemicals to condition the small particles for subsequent processing by flocculation
coagulation
the
process of aggregation of the destabilized particles and precipitation products.
flocculation
5 properties of colloids why they are suspended in water
- Electrokinetic Properties
- Hydration
- Brownian Movement
- Tyndal Effect
- Filterability
most important electrical property of the colloidal and suspended particles
surface charge
Four principal ways or Electrokinetic Properties
- Ionization
- Adsorption
- Isomorphous replacement
- Structural imperfections
accept or donate protons
ionization
a solute becomes bound to the solid surface
adsorption
Under geologic conditions, the metal in a metal oxide is replaced
by a metal atom with a lower valence.
isomorphous replacement
In the formation of the mineral crystal, bonds are broken on the edge of the crystal. These lead to development of surface charge.
Structural imperfections
Colloidal particles that have water-soluble groups on their surface such as hydroxyl, carboxyl, amino, and sulfonic exhibit high affinity for hydration and cause a water film to surround the particles.
hydration
Colloids exhibit a continuous random movement caused by bombardment by the water molecules in the dispersion medium
brownian movement
Colloidal particles have an index of refraction different from water, light passing through the dispersion medium and hitting the particles will be reflected.
tyndall effect
colloidal particles can be readily removed by ultrafiltration but require coagulation prior to their efficient removal by ordinary filtration
filterability
Mechanisms of coagulation
- adsorption and charge neutralization
- entrapment of particles in precipitate
- adsorption and bridging between particles
Hydrolyzed metal salts, prehydrolyzed metal salts, and cationic polymers have a positive charge. They destabilize particles through charge neutralization.
adsorption and charge neutralization
With doses exceeding saturation for the metal hydroxide, aluminum
and iron salts form insoluble precipitates and particulate matter is entrapped in the precipitate.
This type of destabilization has been described as sweep coagulation
entrapment of particles in precipitate
Other sites
on the polymer chain extend into solution and adsorb on surfaces of other particles, thus creating
a “bridge” between the particles. This bridge results in a larger particle that settles more quickly
and forms a more dense sludge.
adsorption and bridging between particles
A solution that resists large changes in pH when an acid or base is added or
when the solution is diluted is called
buffer solution
law of mass action
Le Chatelier’s principle
defined as the sum of all titratable bases down to about pH 4.5
alkalinity
serves
as a measure of buffering capacity
alkalinity
T/F
The greater the alkalinity, the greater the buffering capacity.
True
series of steps involved as dosage increases
1st: aquocomplexes
2nd: hyrodroxocomplexes
3rd. hyroxometal polymer
4th: aluminum hydroxide precipitates
Two important factors in coagulant addition
pH and dose
means of reducing disinfection byproducts
NOM removal
recommended technique for removing NOM.
enhanced coagulation
PACl
Polyaluminum Chloride
primary coagulant when turbidity and alkalinity are high
cationic polymers
They are used in waters that have low concentrations of particles and, thus, have few nucleating sites to form larger floc
coagulant aids
They are added after the coagulants are added and the particles are already
destabilized.
flocculant aids
most commonly used chemical because of its lower cost
lime
it does not increase water hardness
soda ash
a measure that directly depends on the pH scale
basicity
how much acid is needed to lower the pH into a significant acid value; also known as the buffering capacity of a water body.
alkalinity
Process Steps of Coagulation and Flocculation
- Flash Mixing
- Coagulation
- Flocculation
T/F
Flash mixing typically lasts a minute or less. If the water is mixed for more than 60 seconds, the mixer blades will shear the newly forming floc back into small particles
True
T/F
Gentle mixing brings the fine particles formed by coagulation into contact with each other; typically lasts for about 30-45 minutes
true
often has a number of compartments with decreasing mixing speeds as the water advances through the basin
flocculation basin
Types of Colloidal Systems
Type I: High colloidal concentration, low alkalinity (pH 4-6).
Type II: High colloidal concentration, high alkalinity.
Type III: Low colloidal concentration, high alkalinity.
Type IV: Low colloidal concentration, low alkalinity
intended to simulate the coagulation/flocculation process in a water treatment plant
jar test
function of the power input into the water
velocity gradient, G
The difference in velocity between adjacent layers of the fluid
velocity gradient
Dispersion of the coagulant into water
flash or rapid mixing
most important factor affecting particle-removal efficiency
flocculation
most important physical factor affecting coagulant efficiency
rapid mix
used to separate the flocculation basin compartments
baffle wall
