CE 342 - Block 2 for Exam 2 (Filtration, Water Chemistry, Softening)

Lecture 6 Filtration / Lesson 7 Water Chemistry

Write the equilibrium expression for any balanced chemical reaction at equilibrium and the expression for equilibrium constant

large K value means

reaction favors products

small K value means

reaction favors reactants

what is the definition for activity?

list the purposes of granular media filtration

remove small suspended particles that aren’t removed in sedimentation basins, decrease turbidity, and remove biodegradable compounds

describe what is headloss

the loss of mechanical energy of a fluid as it flows trough a system caused by friction

in a large pore space, does the fluid experience low or high headloss and why?

there’s more space between particles, so water experiences less friction and has lower headloss value

which independent variables in filtration can engineers control easily without major expenses?

filter media and superficial velocity

what does grain shape and roundness affect in the filter?

bed porosity, head loss, and filtration performance.

how does grain density and size affect a filter?

affects backwash flow needed for fluidization; allows stratification in bed after backwashing

grain hardness impacts on filter?

can determine the durability of grains

in a sand based filter, where is the most efficient particle removal and what does this indicate about grain size?

the most particle removal is at the top of the bed because the smallest grains are located at the top, while larger grains are at the bottom of the bed. the smaller pores act like a sieve

Based on the filter schematic in slides, what valves need to be open for filtration mode?

1 and 2

For backwash mode, what filter valves are open

3 and 4

what does backwashing do?

increases the force to encourage space between particles to create space between the filter media to remove the captured particles out of the valve for the backwash waste

true of false, in a multimedia filter the finest material has the lowest density and why?

false, the finest material has the highest material density and will settle faster, going to the bottom.

explain what these maximums in the graph mean when monitoring filter effluent turbidity and its implications for backwash.

describe in terms of (on the left) and (on the right)

(on the left), the filter undergoes ripening where the accumulated particles capture new particles

(on the right), the filter is too dirty to clean water, so this affects the effluent quality, which triggers backwashing

what the reason for triggering backwash in drinking water treatment?

Protect health from excess turbidity

rank the following filtration mechanisms for particle capture from important to least:

straining, sedimentation, impaction, interception, brownian motion

brownian motion, interception, sedimentation, impaction, straining

true or false, brownian motion is more important for small molecules and sedimentation/interception matters more for larger particles?

true

as alpha increases, what happens to the attachment efficiecy of the particle?

it increases. an alpha 1 means complete particle collision

what kids of losses in a clean filter bed does headloss consider?

loss of energy as fluid flows (frictional and viscous)

In the Carman-Kozeny equation, the head loss is proportional to L and filtration velocity, but for spherical media grains, how does the collector diameter influence head loss?

as diameter increases, the headloss decreases

what happens to filter effluent turbidity when the filter bed depth (L) increases?

improved particle removal efficiency since turbidity lowers with deeper filters

what happens to headloss when the filter bed depth (L) increases?

deeper filters capture more particles, so headloss increases faster ocmpared to baseline. deeper filter higher headloss

what impact does an increase in media size have in filter effluent turbidity?