Lecture 8d Flashcards
why is filtration used?
The water leaving the sedimentation tank still contains floc materials and the turbidity level is still significant
* filtration process is used to reduce this turbidity
what is filtration?
In filtration, a porous medium is used to separate non-settleable solids (suspended or colloidal) from water.
types of filtration?
granular-media filtration
membrane filtration
list out processes in traditional conventional filtration
list out processes in direct filtration
DOESNT HAVE SEDIMENTATION
what is removed thru granular media filtration?
flocs
organics/inorganics
pathogen (crypto / giardia)
how are filters classified?
based on medium
what are some types of granular-media filters
sand or anthracite (coal)
dual media (sand + anthracite)
mixed media (> 3 layers coarse to fine gradation)
ALL BASED ON ALLOWABLE LOADING RATE
what can filtration systems be typically classified as?
slow filtration systems
rapid filtration systems
what are some removal mechanisms in filter media?
straining (particles are removed bc they are too large to pass through pores)
impingement aka interruption (adsorption, impaction, sedimentation)
flocculation (particles collide with each other, grow in size and are removed by straining
How do u want your filter media to function?
coarse enough to retain floc for depth filtration
fine enough to prevent passage of particles
deep enough to allow relatively long filter runs
what 2 characteristics can filter media be defined as?
effective size d10 (10th percentile diameter)
uniformity coefficient (d60/d10)
what are the functions of an underdrain system?
perform important functions: support filter media, collect filtered water, and distribute water for backwashing and air for scouring
when are filters required to be backwashed?
what is the most critical problem in filter operation?
proper cleaning of filter bed
what happens if filter bed not cleaned properly?
fine materials accumulate into mud balls
what are some cleaning methods for filter beds?
backwashing, surface washing, air scouring, chemical cleaning, combo of these procedures
how is backwashing completed?
Flow is reversed through the filter bed the suspended matter in the filter bed is removed by the shear forces created by the backwash water as it moves up through the bed.
Additional clean is done by the particles of the filtering medium abrading against each other.
backwashing diagram
how do we model head loss thru media?
flow through capillary tubes
granular media idealized as a bundle of tubes
what is fluidization?
upward flow through granular bed at sufficient velocity to suspend grains in water
what is the case where fluidization occurs?
what does the graph for fluidization look like?
