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UNIVERSITY OF OKLAHOMA
WATER TREATMENT [Type the document subtitle]
Trang Phan Damian Ramirez Guillermo Lopez
Felix Lopez
Mach 15,2013
Table of Contents INTRODUCTION & BACKGROUND ................................................................................................................. 4
1. Projected Demand ................................................................................................................................ 4
2. Design ........................................................................................................................................................ 5
2.1. Softening ............................................................................................................................................ 5
2.1.1. Chemical Dose ............................................................................................................................. 5
2.1.2 Reaction Basin .............................................................................................................................. 6
2.1.3 Stabilization .................................................................................................................................. 8
2.2 Coagulation ......................................................................................................................................... 8
2.2.1 Optimal Coagulant Dose and pH .................................................................................................. 8
2.2.2 Rapid Mix Basin Design ................................................................................................................ 9
2.2.3 Flocculation Tank Basin Design .................................................................................................. 11
2.3 Sedimentation basins ........................................................................................................................ 14
2.3.1 Overflow Rate and Detention Time ........................................................................................... 14
2.3.2 Dimensions ................................................................................................................................. 17
2.3.3 Estimated sludge volume ........................................................................................................... 18
2.4 Rapid Sand Filter ............................................................................................................................... 19
2.4.1 Number of Beds ......................................................................................................................... 19
2.4.2 Area of Individual Beds .............................................................................................................. 19
2.4.3 Bed Depth of Sand and Amount Required ................................................................................. 20
2.4.4 Bed Depth of Gravel and Amount Required .............................................................................. 21
2.4.5 Headloss ..................................................................................................................................... 22
2.4.6 Rate of Backwash ....................................................................................................................... 23
2.5 Disinfection and Fluoridation Facilities ............................................................................................. 25
2.5.1 Disinfection ................................................................................................................................ 25
2.5.2 Fluoridation ................................................................................................................................ 25
3. Integration .............................................................................................................................................. 25
3.1 Pipe Sizes ....................................................................................................................................... 25
3.2 Treatment Train ............................................................................................................................ 25
3.3 Recommendations ........................................................................................................................ 26
4. References .............................................................................................................................................. 26
5. Appendix ................................................................................................................................................. 27
5.1 Rapid mixing cost estimation ............................................................................................................ 27
5.2 Flocculation cost for flocculation ...................................................................................................... 29
5.3 Sedimentation basin ......................................................................................................................... 31
5.4 Filter cost estimate ........................................................................................................................... 32
Executive Summary
This presentation is a technical memo looking at a possible treatment facility for Sooner City
water for local use. This project is estimated to last 27 years, at which point the expected
population would be around 75,000 and the average daily demand would be around 38,500 m3/d.
Both well water and river water are available, so a combination of both will be used to efficiently
balance contaminants that this treatment plant will focus on. The facility will intake the water
from both sources, mix them, send through a softening treatment which includes the addition of
Lime and Soda Ash in an upflow contact basin, and then treated with the coagulant aluminum
sulfate. Due to the high levels of hardness and contributing constituents, a split treatment is used,
sending a portion of the water around the softening basin and directly to the rapid mix basin with
the alum, which is followed by flocculation, sedimentation basins, filtration systems, treated with
disinfectants, and finally held in a reservoir until it is ready to public consumption
INTRODUCTION & BACKGROUND Sooner City needs to update its water supply system to handle its growing population and their
growing consumption of water. The current system does not meet the need requirements so this
presentation will analyze different methods of processing and recommend an ideal treatment
train for Sooner City. Local sources of water include ground water from Wells and Sooner
River, both of which can meet demand individually. Samples of both were collected and
included in the analysis as well to further maximize potential. The following analyses are done
to ensure local, state, and federal regulations are not violated.
1. Projected Demand The major factor in the design for this system is the growing demand in the area. With both the
population and consumption increasing, projections for future demand were calculated. Table 1
shows the projected population and consumption in gallons per capita to determine the final flow
required to meet demand. The initial values from the year 1980-2010 were used to predict future
values.
Table 1- Population and Water demand
[Table 1.1]
The design life for this water treatment facility is 27 years, at which point in time the average
daily demand is projected to be about 38,493 m3. The following calculations will be based on
this daily demand along with the peak daily demand of 76987 m3. A conservative peaking factor
(Pf = 2.0) was determined from Figure 2-1 of Water and Wasterwater Engineering (Davis p.2-8)
based on the projected population of roughly 7500 inhabitants.
Year Population % Pop. Change Consumption (gpc) m3 Q (m3/day)
1980 14445 0.0% 100 0.379 5467.4325
1990 20686 43.2% 109 0.413 8534.31959
2000 26425 27.7% 113 0.428 11302.10463
2010 38500 45.7% 118 0.447 17195.255
2020 50575 31.4% 124.5 0.471 23832.58369
2030 62650 23.9% 130.3 0.493 30898.07158
2040 74725 19.3% 136.1 0.515 38493.72441
2050 86800 16.2% 141.9 0.537 46619.5422
2. Design
2.1. Softening
2.1.1. Chemical Dose
From the provided information in the data extracted form water report, the concentration for
the water source that we decided to use (25% of river water and 75% of well water) can be
calculated using the following equation
With all the calculated concentration of water quality, the total hardness TH, Carbonnate
hardness CH, Noncarbonate hardness NCH ~ Soda Ash, and lime are calculated using the
equations below
∑
( ) (
)
( ) ( ) ( )
Since the Mg2+
concentration of our water source is greater than 40mg/L as CaCO3, the extra
lime added is 40mg/Las CaCO3 and split treatment is also required. The concentration of CO2 is
estimated at 79.5 mg/L as CaCO3 for calculating the needed lime for softening the water. The
following table shows calculated values for concentrations of relevant constituents in the mixture
of River and Well water.
Table 2- Estimate chemical dose
Finding the flow that skips the primary treatment is given by the
equation (Davis 4-14):
(
)
(
) = 0.24Q
This equation assumes that the final Mg2+
concentration of the water leaving the primary
treatment is 10mg/L as CaCO3. When it is recombined with the bypassed water, the calculated
Mg2+
concentration is then
Constituent
Concentration
(mg/L) as
CaCO3Estimate CO2 79.5
Ca2+ 201.16Mg2+ 137.08HCO3- 289.15
TH 338.24
[Mg2+
] = (1-0.24)(10mg/L as CaCO3) + (0.24)(137.08mg/L as CaCO3) = 40.5mg/L as CaCO3,
which is at an acceptable concentration for Mg2+
and no longer needs to be treated. To find the
final Total Hardness, it is assumed that the final Hardness leaving the primary treatment is
40mg/L as CaCO3 (10mg/L Mg2+
+ 30mg/L Ca2+
) times the portion entering the treatment plus
the initial hardness gives the new Hardness:
TH = (40mg/L)(1-0.24) + (338.23mg/L)(0.24) = 111.6mg/L as CaCO3
This falls within the acceptable range of 80-120mg/L as CaCO3 and no longer needs to be
treated. To get to these levels, Lime and Soda are added according to the concentrations of the
constituents. The following table shows these values:
Table 3- Chemicals need for softening
Considering the demand, the amount of each is calculated by the following:
[Lime(mg/L)] = (505.7mg/L as CaCO3)(37.05/50) = 374.72mg/L Lime
Mass Lime (kg/d) = 374.72mg/L*(1-0.24)(38442.9(m3/d)*2)(1000L/m
3)(kg/1E06mg) =
21896.3kg/d Lime
[Soda(mg/L)] = (137.05mg/L as CaCO3)(53/50) = 145.3mg/L Soda Ash
Mass Soda Ash (kg/d) = (145.3mg/L) *(1-0.24)(38442.9(m3/d)*2)(1000L/m
3)(kg/1E06mg) =
8490.5kg/d Soda Ash.
2.1.2 Reaction Basin
To add these chemicals into the incoming water, a softening basin must be design to
effectively disperse the softening agents for an optimum cost. While conventional coagulation
and flocculation mixing basins have historically been used, Upflow Solids Contact Basins are
Addition
equal to:
Lime,
mg/L as
CaCO3
Lime,
meq/L
Soda,
mg/L as
CaCO3
Soda,
meq/L
CO2 79.5 1.59 0 0HCO3- 289.15 5.783 0 0
Ca+ 0 0 0 0Mg2+ 137.05 2.741 137.05 2.741Total 505.7 10.114 137.05 2.741
increasingly employed to reduce materials for facilities. These basins have criterion defined by
GLUMBR to aid in the choosing of design parameters. Using Table 4-4 (Davis p. 4-32), a series
of contact basins are given. 3 of these basins will be designed for redundancy, but only 2 will be
calculated to find the appropriate dimensions. First the overflow rate must be calculated, using
an initial trial separation zone area of 390m2:
(
( )(
)( ))
A detention time (t), volume of truncated cone (V), mixing time (tm), weird length (L), and weir
hydraulic loading rate (WL) are calculated using the corresponding values of the basin with a
separation zone of 390m2:
(
) [(
) ( )( ) ( )] (
( )
) [ ]
( ) (
)
( )
( )( )( )
(
)
All of these values are within the acceptable range (Davis p. 4-31), so the reaction basin will
have the following dimensions:
Table 4-Estimate dimensions of reaction basin
2.1.3 Stabilization
Water is considered stable when it exhibits neither scale forming nor corrosion properties
(Davis p.4-34). This is particularly important to maintain the quality of the rapid mix filter due
to precipitation of CaCO3 in the media. The final step in the softening process is recarbonation.
This will drop the pH and effectively stop the precipitation process. Due to the split treatment of
the process, the amount of CO2 reentering the total flow from the bypassed flow should be
enough to consider the water as stable.
2.2 Coagulation
2.2.1 Optimal Coagulant Dose and pH
An optimum dosage of aluminum sulfate (Al2(SO4)3*18H2O), or alum, and pH of the water
must be determined to efficiently reduce the turbidity while minimizing costs. A jar test with
samples from Sooner River was employed to determine the optimum dosage of alum as seen in
Table 1.2. At a dosage of 60 mg/L of alum, the turbidity stops meaningfully decreasing. Though
raising the alum dosage to 120 mg/L would not meaningfully affect the turbidity, it would
decrease the pH to 6.5 in the samples. This would optimize disinfectants in the water and if daily
demand were to peak (Pf = 2.0), the concentration of alum would drop from 120 to 60 mg/L and
still would be an effective coagulant.
Considering the main water source is from ground water, significantly less water would have
to be treated for turbidity because the well data shows the turbidity to be below determinable
levels. To determine the amount of coagulant required, the amount of water treated is calculated
by multiplying the demand by 25%, the amount coming from Sooner River.
D = (38,500 m3/d) * .25 * (1000 L/m
3) * (120 mg/L) * (kg/10E06 mg) = 1,150 kg/d
Final Turbidity = T = Triver/4 = 1.3/4 = 0.33 NTU
In conclusion, the optimum dosage of aluminum sulfate is at 120 mg/L to provide the best sized
floc particles, equivalent to 1,150 kg/d which would lower the pH .
Number of
Units
Nominal
Diameter
(m)
Nominal
SWD (m)
Nominal
Volume
(m3)
Height (m) r1 (m) r2 (m)Separation
Zone (m2)
Column
diameter
(m)
Motor
power
(kW)
Number
of weirs
3 24 5.8 2850 4.6 10 5 390 2.6 10 10
Cone Dimension
Representative dimensions for upflow solids contact basin
2.2.2 Rapid Mix Basin Design
The design for the rapid mix basin is aimed to efficiently disperse the alum into the incoming
water, coming from both the river and well for the given max daily demand (Qmax = 2.0*Q) at the
lowest cost. From the demand (m3/s), number of tanks, and a range of suggested hydraulic
retention times, or HDR, and gradient velocities, G (s-1
) the volume of fluid in reactor (m3) can
be determined by multiplying the demand by the HDR and dividing by the number of tanks.
Based on Figure 3-9a from Water and Wastewater Engineering (Davis p. 3-16), the primary
mechanism for coagulation based on pH and the dosage of alum is sweep coagulation. The ideal
reactor for this mechanism is typically a completely mixed flow reactor or CMFR (Davis p. 3-
33). The criteria for CMFRs include HDR ranging from 20-60 seconds, G values from 600 -
1000 s-1
, max volume (V) = 8 m3, and radial flow impellers. The aspect ratio of water height, H
(m) to tank diameter T (m) ranges from 0.28 – 2, so H = 1.25T was chosen. B, the water depth
below the impeller, is (H/3). T and the power into vessel, P (W), can be calculated from the
following equations:
( )
( ) {
} ⁄
(Davis p. 3-34)
(
)
(Davis Eqn 3-12)
The following table shows the expected power for a range of HRT and G values.
Figure 1- Turbidity vs. pH Figure 2- Turbidity vs. Dose
Table 5- Estimate dimensions for Rapid mixing tank
HDR = 30 seconds and G = 600 s -1
are chosen as the major parameters because of the low
resulting power required. From the velocity gradient and the calculated volume of the tanks at
each hydraulic detention time, the cost can be estimated using the cost curves provided in the
Estimation Water Treatment Cost- EPA 1.
Table 8-2 in the Unit operations and Processes in Environmental book gives the values of NP
and n for different impellers. In order to use this table, we assume that our basin has four baffles
at tank wall, with width = 0.1D. In table … below, the impeller diameter, Di (m) is determined.
The highlighted cells are considered within the acceptable limits for the given ratios (Davis
Table 3-5).
Table 6- Design criteria for impeller
1Estimating Water Treatment Costs. Volume 2 Cost Curves Applicable to 1to 200 mgd Treatment Plants. United
States Environmental Protection Agency
Type of impeller Np n (rpm) n(rps) Di D/T H/D H/T B/D
Propeller, pitch of 1,3 blade 0.32 400.00 6.67 0.67 0.41 3.03 1.25 1.01
Propeller, pitch of 2,3 blade 1.00 400.00 6.67 0.53 0.33 3.81 1.25 1.27
Turbine, 4 flat blades, vaned disc 5.31 10.00 0.17 3.48 2.15 0.58 1.25 0.19
Turbine, 6 flat blades, vaned disc 5.75 10.00 0.17 3.43 2.11 0.59 1.25 0.20
Turbine, 6 curved blades 4.80 10.00 0.17 3.55 2.19 0.57 1.25 0.19
Fan turbine, 6 blades at 45ᴼ 1.65 10.00 0.17 4.40 2.71 0.46 1.25 0.15
Shrouded turbine, 6 curved blades 1.08 10.00 0.17 4.79 2.95 0.42 1.25 0.14
Shrouded turbine, with stator, no blades 1.12 10.00 0.17 4.75 2.93 0.43 1.25 0.14
Flat paddles, 2 blades (single paddle), 2.25 20.00 0.33 2.73 1.68 0.74 1.25 0.25
Flat paddles, 2 blades, Di/Wi = 6 1.70 20.00 0.33 2.88 1.78 0.70 1.25 0.23
Flat paddles, 2 blades, Di/Wi=8 1.15 20.00 0.33 3.12 1.93 0.65 1.25 0.22
Flat paddles, 4 blades, Di/Wi=6 2.75 20.00 0.33 2.62 1.62 0.77 1.25 0.26
Flat paddles, 6 blades, Di/Wi=6 3.82 20.00 0.33 2.45 1.51 0.83 1.25 0.28
Standard Impeller Values
Flow rate Q
( m3/s )
hydraulic
detention time,
t (s)
velocity gradient
G (s-1)Gt Volume, V (m3)
Volume, V
(4 tanks)
Diameter of
Basin, T (m)
water depth, H
(m)B (m) Power, P (W)
0.891 10 1000 10000 8.91 2.23 1.12 1.40 0.47 11648
15 900 13500 13.37 3.34 1.29 1.61 0.54 14152
20 800 16000 17.82 4.46 1.42 1.77 0.59 14909
25 700 17500 22.28 5.57 1.52 1.91 0.64 14269
30 600 18000 26.74 6.68 1.62 2.03 0.68 12580
Rapid Mix Basin Dimensions based on HRD and G
Based on this data, a propeller with 3 blades at a pitch of 1 would be most efficient. With P =
12580 W, Np is the impeller constant for turbulent flow, n is the rotational speed (rps), Di is the
impeller diameter (m), and density of water at 10 C = 999.7kg/m3 (Davis p.A-1), we can now
use Equation 3-17 (Davis p. 3-34) that defines power as
√
√( )
( )( ) ( )
Which means the selection of propeller is valid. The power input assumes that the efficiency of
the turbine is 0.8 and freeboard of 0.60 m is added to the water height to get the tank depth. An
additional tank is added for redundancy. The following table lists the specifications for the rapid
mix tanks.
Table 7- Final design for rapid mixing tank
According to EPA the cost estimation for each rapid tank mixing is about $ 11,700 for the
construction and about $4,600/year for maintaining plus laboring.
2.2.3 Flocculation Tank Basin Design
The flocculation basin is designed to optimize the coagulant additives for the given demand at an
optimum price. These basins will have a cubical design, and are divided into 3 separate tanks.
The number of basins needed for a given design is also considered, but this number should be
kept as low as possible. Two types of flocculators are considered for the design: vertical mixing
turbines and paddle flocculators. While both are used in modern designs, paddle flocculators are
best for larger volumes and when flocculation is followed by sedimentation (Davis p. 3-37), so it
is chosen as the optimal flocculator. Using design criteria defined by GLUMRB and modern
Volume
per Tank
(m3)
Tank
height (m)
Tank
diameter
(m)
Impeller
diameter
(m)
Number of
TanksHDR (s) G (s-1) Gt
Power
input (W)
Power
needed
(W)
6.68 2.63 1.62 0.63 5 30 600 18000 9765 12206.25
Rapin Mix Basin Parameters
Design Flow (m3/d) 76885.74
Flow per basin (m3/s) 38442.87
Design Flow (m3/min) 26.70
HDR (min) 22
Volume (m3) 587.32
Volume per comparment (m3) 195.77
Trial water depth (m) 4
Surface area (m2) 48.94
Paddle wheel diameter (m) 3
Min stage length (m) 4
Nominal width (m) 12.24
Number of wheels 3
Required Clearance (m) 2.6
Paddle wheel length (m) 3.21
Distance between paddles (m) 0.50
Paddle widths (m) 0.15
Paddle Area (m2) 0.482
3-comparment Paddle Flocculator Dimensions
practices (Davis p. 3-37), the retention time will be set at 22 minutes with a gradient velocity
range of 20-50 s-1
. For redundancy, 2 basins will be used. Following the criteria listed on page
3-45 of Davis and assuming a water depth of 4.0 m, clearance = 0.3m, and paddle width of
15cm, the table below shows the calculated values for the dimensions of the basins, wheels, and
paddles:
V = Q*HDR = (26.70m3/min)*(22min)
Vcompartment = V/3
Surface Area = Vcompartment/(water depth)
Dwheel = water depth – 1m
Min stage length = Dwheel + 1m
Nominal width = Surface Area/stage length
Required clearance = 2(0.3m) + 2m
(two 1m gaps for 3 wheels)
Lpaddle = (width – clearance) / (# wheels)
Spacing of paddles = Dwheel/3
Paddle area = paddle width * Lpaddle
L/W = 3.21m / .15m = 21.4
Table 8- Design data for flocculation basin
Each compartment has a designate gradient velocity in a tapered fashion; in the first
compartment, G1 = 40 s-1
, the second G2 = 30 s-1
, and the third G3 = 20 s-1
. Starting with the first
compartment, the power required is calculated:
( ) ( )( )
(Davis Eqn 3-12)
Using this power, Equations 3-19 and 3-20 from Davis (p. 3-44) are rewritten to find the
rotational speed, n (rps), of the first chamber
(
[ ( )] [( ) ( ) ( ) ]) ⁄
where , the drag coefficient, is 1.50 when L/W is close to 20 (Davis Table 3-7), the density of
water at 10 C is
, and the relative velocity of the paddles is defined as
, where the constant k = 0.75, r = radius to centerline of paddle (m), and n is the rotational
speed (rps). The radii first must be calculated:
(
)
(
)
(
)
(
)
(
(
)( )( )( )[( ) ( ) ( ) ])
)
⁄
For the second and third chamber, the same calculations are carried through but using G2 = 30 s-1
and G3 = 20 s-1
to calculate the new rotational velocities. A limiting criterion is the tip speed,
which can range from 0.15 – 1 m/s. Tip speed are calculated from Equation 3-20 from Davis.
(Davis p. 3-44)
The following table lists values associated with the chambers to check this criterion:
Table 9- Power of flocculation
None of the tip speeds exceed 1m/s, so the design is valid. Motor power is calculated assuming
an efficiency of 65% and scaling up the power by at least 1.5.
Based on the graph and information provided by the EPA, the cost a flocculation-horizintal
paddle system is estimated around $130,00 for construction and $37,000 for tocal and labor
cost/year.
2.3 Sedimentation basins
With the provided settling test data, the following information was obtained: the overflow rate,
Dimension, Detention time, estimated sludge volume, and the sludge disposal method.
Table 10-Settling test data
2.3.1 Overflow Rate and Detention Time
The overflow velocity was obtained by using the equation =
Eq 7-21. Before calculating
the overflow velocity, the sampling time must be defined. In order to define the sampling time,
isoconcentration lines for Type II using the settling test data were potted on the graph below
Comparment
#G (s-1) Power (W)
Rotational
speed (rps)
Rotational
speed (rpm)
Tip speed
(m/s)
Motor Power
(W)
1 40 409.40 0.14 8.53 0.96 944.77
2 30 230.30 0.12 7.04 0.79 531.46
3 20 102.40 0.09 5.38 0.60 236.31
Total 742.10 1712.54
3-comparment Paddle Flocculator Speed and Power
Settling Test Data
Percent Suspended Solids Removed at Given Depths
Time (min) 0.5m 1.5m 2.5m 3.5m 4.5m
10.00 50.00 32.00 20.00 18.00 15.00
20.00 75.00 45.00 35.00 30.00 25.00
40.00 85.00 65.00 48.00 43.00 40.00
55.00 90.00 75.00 60.00 50.00 46.00
85.00 95.00 87.00 75.00 65.00 60.00
95.00 95.00 88.00 80.00 70.00 63.00
.
Figure 3- Isoconcentration lines Type 2 settling
Sampling time was first determined in minutes, which then were converted into hours
followed by days. The maximum depth for the suspended solids is 4.5m. The variable H will stay
constant throughout the chart. Once the overflow was determined in m/day it was then converted
in to gal/day-m2. Figure 2 demonstrates the overflow rates:
Table 11- Design criteria for sedimentation
With the use of the plotted isoconcentration lines, the total fraction removed for settling time
was calculated. The following procedure was taken: A vertical line is drawn from to intersect
all the isoconcentration lines crossing the time. The midpoints between isoconcentration lines
define height , and so on used to calculate the fraction of solid remove. (Davis p. 7-13)
The following equation was used to determine the fraction solids removal:
=
( )
( ) … Eq 7-22
The following chart demonstrates the midpoints between the isoconcentration lines:
Table 12- Data from the traction solids removal
The Hydraulic Retention Time and the Overflow Rate were then calculated with the use of the
following graphs. The following factors were used in order to determine HRT and OFR:
Safety of factor for HRT = 1.75
Safety of factor for OFR = 0.65
Hand calculation were also done, this made us sure that we were on the right track.
Figure 4- Calculation of fraction solids removal
% 10.00 20.00 30.00 40.00 50.00 60.00 70.00
meter meter meter meter meter meter meter
10-20 3.25
20-30 1.63 3.50
30-40 1.00 2.00 3.50
40-50 0.50 1.20 2.00 3.50
50-60 0.30 0.75 1.20 2.00 3.40
60-70 0.20 0.40 0.75 1.25 2.50 3.75
70-80 0.10 0.20 0.25 0.75 0.75 2.40 3.00
Midpoints between Isoconcentration Lines
Table 13- Time of the fraction of solids removal
Table 14- Over flowrate of the fraction of solids removal
2.3.2 Dimensions
The following are the dimension for a circular clarifier. When calculating the Area, the peak
flow was used, and the overflow velocity and detention time for 70% are used based of Figure #.
Using this area, the diameter and side water depth (SWD) can be calculated:
Area = ⁄
Diameter = [
]
SWD =
=
( )
detention time
% mins hrs
10.00 0.00 0.00
20.00 0.00 0.00
30.00 12.00 0.20
40.00 19.20 0.32
50.00 33.00 0.55
60.00 48.00 0.80
70.00 72.00 1.20
% R OFR
10.00 0.00
20.00 0.00
30.00 675.00
40.00 360.00
50.00 200.00
60.00 140.00
70.00 80.00
Figure 5- Graph of time vs. fraction solids removal
Figure 6- Graph of over flow rate vs. the fraction of solids removal
Table 15- Data of detention time and dimensions of sedimentation tank based on the fraction of solids removal
2.3.3 Estimated sludge volume
Rs= (116ml/ 2 L) *(1L/1000 ml) = 0.058
Vs = (76886.00 m3/day /2) * 0.058 = 2,230 m
3/day
Sludge disposal method
The sludge disposal method will consist of transporting the majority of the sludge to a land field,
while the rest will be sold to the public.
http://water.me.vccs.edu/courses/ENV149/disposal2.htm
Equations
=
Eq 7-21 Overflow Rate
Where: H = height of the column
= time defined by intersection of isoconcentration line and bottom of column (x-axis)
where the subscript, , refers to the first, second, third, and so on intersection points
=
( )
( ) … Eq 7-22 Fraction of Solids Removal
Where: = total fraction removed for settling time,
= isoconcentration fractions a,b,c, etc.
Area = ⁄
Where: Q = flow rate
= Overflow rate
detention time
% mins hrs
10.00 0.00 0.00
20.00 0.00 0.00
30.00 12.00 0.20
40.00 19.20 0.32
50.00 33.00 0.55
60.00 48.00 0.80
70.00 72.00 1.20
Area Diameter SWD
% m^2 meter meter
10.00 88.99 10.65 0.00
20.00 177.98 15.06 0.00
30.00 355.95 21.29 3.15
40.00 474.60 24.59 3.78
50.00 759.37 31.10 4.06
60.00 1008.54 35.84 4.45
70.00 1127.19 37.89 5.97
Diameter = [
]
Where: A= Area
Side Width Depth
SWD =
=
( )
Where: A = Area
Q= Flowrate
(HRT) = Hydraulic detention time
Vs = (Q/n) *Rs
Where: Vs = Sludge Volume
Q = Flowrate
N = number of tanks
Rs = Sludge Ratio
Safety of factor for HRT = 1.75
Safety of factor for OFR = 0.65
Safety of factor for Peak Demand = 2.0
By using the chart provided by the EPA, the estimation cost for each sedimentation is about
600,000 for construction and $69,000/year for the total cost.
2.4 Rapid Sand Filter For this water treatment plant rapid sand filter is used since it takes less amount of land use and
is cheaper to maintain compared to a slow sand filter and dual-media filter.
2.4.1 Number of Beds
The number of beds needed was determined by using the equation in the textbook Water and
Wastewater Engineering by Mackenzie L. Davis professional edition. If the maximum design
flow is less than 8,000 m3/d, the minimum number of filters is two, but if the flow is greater so
minimum number of filters is four. For our water treatment plant the maximum design flow, Q,
is 76,996 m3/d, is used to calculate the number of filters needed:
( ) (
)
The number of filters needs to be whole numbers and an even number of filters so the filters,
needed are six.
2.4.2 Area of Individual Beds
The area of the filters is obtain by using equation 11-18 (Davis):
The filtration rate for a conservative filtrations design is of 7.5 m/h (180 m3/d m
2) and 5 m/h
(120 m3/d m
2). The best filtration rate is 5 m/h because the 7.5 m/h filtration rate would give a
headloss greater than 0.6 m which is the boundary for a clean bed filtration. Also the area was
calculated for 5 filters since you need to be able to still provide the demand of water if one filter
is out of service. So the area is:
The width of the filter is 5.5 m which is less than 6 m and each filter has two cells of 2.75 m to
get the length:
( )
( )
2.4.3 Bed Depth of Sand and Amount Required
For a single-media filter the recommended depth of the sand, D, is between 0.6-0.75 m from
table 11-11(Davis). Our design chose to use .6 m of sand it would cost less and provide a lower
headloss. The sand used was from Hawkeye Quarries, IA and has a specific gravity of 2.65,
shape factor of 0.75, and porosity of 0.41. The sand was given a sieve analysis to see if it had a
good effective size, E, and uniform coefficient, U. in order for the sand to have a good effective
size it has to fall in between 0.3-0.6 mm and the uniform coefficient 1.3-1.8. From the Figure 7
the effective size and uniform coefficient are:
Figure 7- Graph of comultive mass passing vs. Sieve Size
Figure 8- Typical properties of filter media data
Which fail in the effective size and uniformity coefficient criteria. So the sand is good to use. So
the volume of sand needed for all for a filter and the total amount of sand need for the filters is:
2.4.4 Bed Depth of Gravel and Amount Required
The depth of gravel needed was determined to be 0.25 m from Table 11-5 (Davis). So the
amount required is:
0
0.2
0.4
0.6
0.8
1
1.2
0 10 20 30 40 50 60 70 80 90 100
Sie
ve S
ize
(m
m)
Comulitive Mass passing %
2.4.5 Headloss
To get the headloss, hL, you have to use the sieve analysis and determine the Reynolds number,
drag coefficient, and the product of the fractional mass retain and the drag coefficient by the
diameter of each sieve boundary. Table 16 below shows the results.
Table 16- Estimate ...
Equations:
( ) ( )( )( )
( )
So the headloss is:
Sieve Size#
Weight
Retained (%) d, mm d, m R
14-20 0.44 1.125 0.001125 0.896614 29.9696 117.2144
20-28 14.33 0.747 0.000747 0.595352 44.23436 8485.6547
28-32 42.78 0.602 0.000602 0.479788 50.02206 35547.2378
32-35 27.07 0.53 0.00053 0.422405 56.81751 29019.8110
35-42 9.76 0.4485 0.000449 0.35745 67.14221 14611.1024
42-48 4.22 0.3595 0.00036 0.286518 83.76434 9832.6985
48-60 0.54 0.286 0.000286 0.227939 105.2912 1988.0155
60-100 0.42 0.2 0.0002 0.159398 150.5664 3161.8944
Σ= 102763.6287
Σ( )
( )
( )
( )( )( ) ∑
( )( )
(
)
( )
( ) (
) ( ) ( )
2.4.6 Rate of Backwash
The maximum backwash rate has to be less than the smallest sand practical settling velocity so it
won’t get washed away. The smallest sand practical is 0.0002 m and from Figure 9 the estimated
settling velocity which is 0.023 m/s and the appropriate backwash velocity would be .02 m/s.
Once the backwash rate is obtained it had to achieve a 50% bed expansion. To get there the
estimated settling velocity, estimated Reynolds number, drag coefficient, the settling velocity
using equation 10-8 (Davis), a new Reynolds number using equation 10-12 (Davis), porosity of
expanded bed, and the mas fraction of sand retain divide by 1 minus porosity of expanded bed
for each diameter of sand. The calculated data are shown in Table 17
Figure 9- Graph of estimated settling velocity vs. particle diameter
Table 17- Calculation data of backwash
Equations:
( ) [ ( )( )
]
( )( )
( ) (
)
The depth of the expanded bed is:
( )( )∑
( ) ( )( )( )
The bed expansion ration is D_e/D = 1.67 a 67% expansion.
Cost of gravel (Washed) from Yong’s Sand & Gravel cost $4.00 ton and filter sand cost $30 a
ton.
Construction Cost estmation about $10,200
Sieve
Size# d, m
Estemated
Vs (m/s) Esimated R Cd Vs (m/s)
fraction
retain R exponent
Expanded
porosity
14-20 0.001125 0.178 114.9100995 0.82872 0.171166 0.0044 147.3314 0.370 0.448 0.008
20-28 0.000747 0.12 51.43840857 1.224867 0.114726 0.1433 65.57022 0.341 0.547 0.316
28-32 0.000602 0.1 34.54475899 1.545174 0.091697 0.4278 42.23537 0.327 0.604 1.079
32-35 0.00053 0.084 25.54705432 1.872984 0.078148 0.2707 31.68962 0.317 0.644 0.761
35-42 0.000449 0.073 18.78758607 2.309566 0.064738 0.0976 22.21512 0.306 0.693 0.318
42-48 0.00036 0.053 10.93353099 3.442362 0.047475 0.0422 13.05841 0.291 0.773 0.186
48-60 0.000286 0.04 6.564651875 5.166832 0.034563 0.0054 7.563227 0.275 0.855 0.037
60-100 0.0002 0.023 2.639632747 11.27867 0.019563 0.0042 2.993548 0.251 0.966 0.124
Sum = 0.9956 Sum = 2.829
2.5 Disinfection and Fluoridation Facilities
2.5.1 Disinfection
In order to achieve an acceptable level of microbial contaminants in the water, Chlorine will
be added to the end of the treatment train as Cl2. This will ensure no disease carrying bodies will
contaminate local users. The maximum residual disinfectant level goals, or MRDLGs, state that
the max residuals from the addition of free chlorine should not exceed 4mg/L.
2.5.2 Fluoridation
Fluoride levels should not exceed 2.0mg/L as set by the EPA (www.water.epa.gov) but its
presence is helpful to avoid tooth decay. The incoming water from both the river and well have
fluoride levels of 0.7mg/L, which is acceptable so no treatment for fluoridation is necessary.
3. Integration
3.1 Pipe Sizes
To integrated this system, appropriate pipe sizes must be chosen to withstand peak flow. A
minimum diameter must be determined, which can calculated by finding the cross sectional area
of the pipe considering the peak demand and the water velocity. Choosing a velocity of 20 fps,
this converts to 6.1m/s, and 2 pipes, the cross sectional area can then be calculated:
(
(
)
) * (d/86400s) = 0.073m
2
√
√
(
)
Using this value we can determine that the pipes required a diameter of at least 12 in. Adding a
level of freeboard, two pipes with diameters of 24 in will be used to keep pipe pressure down and
avoid overloading the pipes.
3.2 Treatment Train
The following figure shows a basic layout for this facility. Note that there are no rapid mix
basins as a limit of the program, but it is close to the layout as presented in this report. The
criteria inputs in WatPro also does not consider the split in the softening process so the resulting
values when running the process is not dependably accurate and not include in this report, citing
the calculations made earlier in this report.
Figure 10- Recommendation Treatment train
3.3 Recommendations
Our group believes that it is important that at least 75% of the water is taken from the ground.
This reduces the amount of chemicals needed to make the water potable and thus reducing costs
that would regularly have to be made. The calculations are based on a peaking factor of 2, but
texts often cite peaking factors ranging from 2.2-3, so the redundancies implemented may be
necessities. The life span of 27 years also extends past the typical lifespan of most ground water
facilities, so maintenance must be regularly done to ensure such a long life. This will increase
cost in the short term, but ultimately will prevent needing to build another facility in the near
future. To also ensure the quality of the water, recarbonation stations may be employed to keep
the pH at a reasonable level, which may fluctuate based on the temperature. Alkalinity may also
change with temperature, so additional Lime and Soda Ash may need called for to keep the water
hardness down to prevent scaling and calcium deposits.
4. References Estimating Water Treatment Costs. Volume 2 Cost Curves Applicable to 1to 200 mgd Treatment Plants.
United States Environmental Protection Agency.
http://water.epa.gov/drink/contaminants/basicinformation/fluoride.cfm
Mackenzie, Davis L. Water and Wastewater. New York: McGraw Hill, 2011.
5. Appendix
5.1 Rapid mixing cost estimation
Figure 11- Graph of estimating construction cost for rapid mixing tank
Table 18- Estimating cost for rapid mixing tank
Figure 12- Graph of estimating total and labor cost for rapid mixing tank
Table 19-Estimating total and labor cost for rapid mixing tank
5.2 Flocculation cost for flocculation
Figure 13- Graph of estimating construction cost for flocculation tank
Table 20- estimating construction cost for flocculation tank
Figure 14- Graph of estimating total and labor cost for flocculation tank
5.3 Sedimentation basin
Figure 15- Graph of estimating construction cost for sedimentation tank
Figure 16-Graph of estimating total cost for sedimentation tank
5.4 Filter cost estimate
Figure 17-Graph of estimating construction cost for filter
Table 21-E estimating maintenance and operation cost for flirtation
