Water Treatment design 6
sludge collectors can put limitations on the design of the sedimentation basin
Filtration types
Conventional filtraition
most common filtration system
used with surface water
responds well to rapid changes in water quality
Coag(mixing)>flocculation>sediment>filtration
Direct filtration
Good for waters with high or variable turbidity
lakes and reservoirs
<15NTU
coag(mixing)> flocc> filtration
In-line filtration
Requires high quality surface water
no clay or sediment particles
<10 NTU
coag(mixing)>filtration
Two stage filtration
used in small water treatment plants
<100Ntu
Coag(mixing)>roughing filter> filtration
Groundwater typically has <5NTU
Gravity media filtration
Pressure media filtration
slow sand filtration (0.1 gpm/ft^2)
Diatomaceous earth filtration(roughing filter)
Cartridge/ bag filtration
biofiltration
Adsorption filters
Filtration Goals
Regualotry MCL is less than 0.3 NTU in 95% of samples
Additional lOg removal credit under LT2ESWTR tool box
0.5 log added credit if combined filter less than 0.15 NTU 95 percent of time
cn add combined individual filter credits .25 NTU 95 percent of time
EPA surface water treatment rules require systems using surface water or ground water
under the direct influence of surface water
Crypto, Viruses(legionella), turbidity
Log(3) = 99.9% log(4) = 99.99%
Hotels change up how visitors check into rooms to deal with water moving throughout
the hotel because stagnant water can develop viruses and bacteria
Key Filtration Design Factors
Chemical and physical conditioning particles
INCREASE particle to particle atttraction
Key to effective filtration is adequate surface area of media
determined by diameter and depth of media
Effective sizes( ES) -10 percent of media is smaller in a a size distribution
Uniformity coeffecient (UC) - D(60)/ D(10) ratio
measure of uniformity of media
median size of media foe aguven effective size caries with UC
Change in UC changes media sizes as well as uniformity even if EC remains the
same
Typical filtration media design
Dual media
10 to 12 in of sand
20 to 24 in of anthracite
Deep bed
60 to 72 in
requires deeper filter box
number of filters
N,n+1,N-1 design
Number of filters affects impact of removing a filter from service for backwash
100 percent increase in flow during backwash if 2 filter go down (n-2)
Hydraulic loading
State reguleation will often st maxima
3- 5 gpm/ sqft
Dual media
6gpm/ sq ft
Stable flow control essential for lifting flow surges
key to avoid undesired particles
Control velocitutye sin piping to limi t floc damage
1 to 2 ft/ sec flocculated water sec
2.5-3.5 ft/sec clarified water
Constant rate filtration
has a variable water level
constant water rate
valve with flow meter between filter bed and clearwell
Constant level filtration
clear well has a weir to deal with pressure changes
Declining rate filtration
not often used
Filter performance
Production vilume
untu filter rate volume
UFRV= filtration rate* filter run time* 60 min/hr
UFRV= gal/ft^2
Water quality
overall quality
