The following must be considered when sizing a water softening system:
Flow rate (gallons per minute)
Influent water hardness (grains per gallons)
Usage (gallons per day)
Hours of operation
Economics
Physics
Flow rate
In general, it is best to base the size of your water softening system on continuous flow rather that peak flow rates. During peak flow rates the jeopardy of hardness break through is present. If flow rates are not known, helpful charts are included to approximate flow rates.
The following information has been prepared as a guide for estimating maximum flow rates for private and public buildings. The numbers assigned the various fixtures are based on a combination of flow rate and probability of use.
1. Count and total the number of each type of fixture to be serviced by the water softening system.
2. Mulitply the number of each type of fixture by the UNIT COUNT given in the Fixture Unit able.
Private – Motels
Apartment Buildings
Trailer Parks
Group Homes
Public - Office Buildings
Hospitals
Country Clubs
Schools
3. Find the total FIXTURE COUNT by adding up the values found in step 2.
4. Using the correct table below, find the FIXTURE COUNT closest to the calculated value. The figure given the right hand column is the approximate maximum GPM required.
EXAMPLE:
Type of Fixture Qty. Unit Count Total
Water Closet (FV) 8 X 10 = 80
Shower 10 X 4 = 40
Lavatory 15 X 2 = 30
TOTAL FIXTURE UNIT COUNT = 150
Estimated Flow Rate = 80GPm
Fixture Unit Table
Type of Fixture
Units
-Private-
Units
-Public-
Bar Sink
Bathtub
Bedpan Washer
Bidet
Combination Sink &Tray
Dental Unit or Cuspidor
Dental Laboratory
Drinking Fountain
House Bib or Sill Cock (Std)
House Trailer (each)
Laundry Tub or Washer
Lavatory
Lawn Sprinkler (each head)
Shower
Sink; Service (Janitor’s)
Sink or Dishwasher
Sink (flushing rim, clinic)
Sink (wash up, each set)
Sink (circular spray)
Urinal (wall or stall)
Urinal (flush tank)
Water Closet:
Flushometer Valve
Tank Type
1
2
-
2
3
-
1
1
3
6
2
1
1
2
2
2
-
-
-
-
-
6
3
2
4
10
4
-
1
2
2
5
6
4
2
1
4
4
4
10
2
4
5
3
10*
5*
*Double this amount for schools
Water supply outlets fro items not listed above shall be computed at their maximum demand, but in no case less than:
3/8 inch pipe
1/2 inch pipe
3/4 inch pipe
1 inch pipe
1
2
3
6
2
4
6
10
OR
You can determine your approximate flow rate by the size of your plumbing feeding the water softening system.
COPPER PIPE – SIZE VS. FLOW RATE
Size of Pipe
GPM through 100’ or type “L” copper tubing
at 5 pound pressure drop
At 10 pound pressure drop
at 15 pound pressure drop
½”
¾”
1”
1-1/4”
1-1/2”
2”
2-1/2”
3”
4”
5”
6”
2
6
12
21
33
70
122
195
410
720
1180
3
9
18
30
49
100
178
283
595
1050
1720
4
11
22
38
60
126
222
355
740
1310
2150
PLASTIC PIPE – SIZE VS. FLOW RATE
Size of Pipe
GPM through 100’ or type “L” copper tubing
at 5 pound pressure drop
At 10 pound pressure drop
at 15 pound pressure drop
½”
¾”
1”
1-1/4”
1-1/2”
2”
2-1/2”
2
6
12
21
33
70
122
3
9
18
30
49
100
178
4
11
22
38
60
126
222
Water Hardness, Water Quality and Daily Use
Hardness is present in the water supply as calcium and magnesium bicarbonate, CaCO 3. Other water quality factors will influence the way the water softening system works. Dissolved iron, If present, must be taken into account when sizing the water softening system. Maximum allowable iron is 2 ppm.
To calculate the required capacity of a water softening system take a water sample and have it analyzed for hardness and iron content, or call the local municipal water treatment facility. Hardness, as CaCO 3, if expressed in parts per million (ppm) or milligrams per liter (mg/l) is converted to grains per gallon (gpg) by dividing ppm or mg/l by 17.1. If iron is present, multiply the amount of dissolved iron (ppm) by 4 and add it to the total grains of hardness. At this point, your total grains per gallon has been determined.
By multiplying the gallons of usage per day by grains per gallon will determine the capacity per day. If daily usage is not known, a helpful chart has been included to assist you in estimation the daily usage of many types of facilities.
Water softening systems are typically rated at 30,000 grains of removal per cubic foot of resin. However, the systems are typically operated at 20,000 grains of removal per cubic foot of resin for economy salt dosing.
EXAMPLE:
Hardness 250 ppm
Convert to grains per gallon divide by 17.1
Hardness in grains per gallon 14.6
Iron 1 ppm
Convert to grains per gallon 4
Iron in grains per gallon 4
Total grains per gallon 18.6 grains
– add iron + hardness
Daily Usage 1000 grains
Daily Capacity – Multiply usage by total 18,600
grains per gallon
Daily Water Usage Estimations
Facility Daily Water Usage Facility Daily Water Usage Assembly Halls 2 gals/seat Food Service Operations Apartment Baildings 150-200 gals/unit Average Restaurant 70 gals/seat Barber Shops 55 gals/chair 24 Hour Restaurant 100 gals/seat Beauty Salons 270 gals/station Curb Service 50 gals/car space Bowling Alleys 75 gal/lane Hotels .256 gal/sq. ft. Camps Institutions Day -(no meals) 15 gals/person Hospitals 250 gals/bed Resorts -(day & night 50 gals/person Rest Homes 100 gals/bed
with limited plumbing) Laundries Tourist- (with central 35 gals/person Coin Operated 2.17 gals/sq. ft.
Bath & toilet facilities) Commercial .253 gals/sq. ft. Country Club Motels 100 gals/unit
per resident member 100 gals Office Building 20 gals/employee
per non- resident member 25 gals Schools Dance Halls 2 gals/person Boarding 80 gals/student Department Store .216 gals/sp. ft. Day (with cafeterias, 25 gals/student
of sales area gym and showers) Factories Day (with cafeteria only) 20 gals/student
(excluding process water) Day (no cafeteria or gym) 15 gals/student
without showers 25 gals/person/shift Service Stations 1000 gal-first bay
with shower 500 gal/add’l bay Farms or 10 gal/vehicle
Cow, beef 12 gal/head Shopping Center .160 gal/sq.ft.
Cow, dairy 20gal/head Stores 400 gal/toilet room
Goat 2 gal/head Theatres
Hog 12 gal/head Drive-In 5 gals/car space
Horse 12 gal/head Movie 2 gals/seat/movie
Mule 12 gal/head Trailer Parks 100 gals/space
Sheep 2 gals/head
Chickens 10 gals/100 Turkeys 18 gals/100
Hours of Operation
One of the most important factors in determining the size and configuration of a water softening system is the hours of service the system will be called upon to produce soft water. If the system will be required to produce soft water 24 hours per day and no down time can be determined, a dual system will be required. If the system is only required to produce soft water part of the day and down time can be determined, a single tank water softening system may be used. However, in certain circumstances when capacity greatly exceeds flow rate requirements, a dual system can provide a cost savings.
Economics
Once the minimum size and type of water softener needed have been determined, you may have several water softener options. You may only want to spend a minimum amount of money for the water softener, or you may want a more expensive meter initiated system in order to spend less money on salt in the years to come. If the capacity required greatly exceeds the flow rote requirements, a multiple tank system could be more economical than a single tank water softener.
Physics
A water softener may be the right type and may be properly sized for the application it will serve, but there are other factors to be considered before quoting the system. The water softener must fit in the space allowed. The brine tank must fit through the door. A drain must be within the specified range and must be capable of handling the drain flow. The temperature of the water must meet specifications. The drain line should not be susceptible to freezing, etc.
Water Softening System Sizing Worksheet
Hardness (ppm) ____________
divide by ________ 17.1
Hardness (gpg) ____________
Iron (ppm) X 4 add ____________
Total grains per gallon ____________
Usage per day (gallons) multiply ____________
Capacity per day (grains) ____________
Required flow rate (gpm) ____________
Peak flow rate (gpm) ____________
Hours of service ____________
Down time ____________
Grains Per Day vs. Flow Rate
Water softener must meet or exceed both:
--Flow rate specified by the water softening system and
--Total capacity in grains per day specified by the water softening system
Single-Tank Water Softening System vs Dual Tank Water Softening System
Down-time of water softening Soft water requirement is for 24 hours or
system is known. exact down time is not known.
Capacity requirement greatly exceeds flow rate requirement (i.e., softener needed tosatisfy capacity requirement is much larger than the softener required to satisfy the flow rate)
Daily usage requirements fluctuate or actual daily usage cannot be determined.
PRINCIPLES OF REVERSE OSMOSIS
Reverse osmosis is a process for removing dissolved mineral salts, organic molecules, and certain other impurities from water by permitting water under increased pressure to pass through a semi-permeable membrane. It is called reverse osmosis as it is the reverse of the natural osmotic process in which fluids with a low concentration of suspended and dissolved solids pass through a membrane into an area of higher concentration. With reverse osmosis water treatment, water is make to pass from a state of high dissolved solids concentration to a state of low concentration.
Since reverse osmosis does not occur naturally, it must be created by applying higher pressure to the high dissolved solids water in order to force it through the membranes. Membranes must be strong and resistant enough to withstand the high pressures of the RO operation… from 200 to 400 psi in most applications: 1000, or even 1200psi for sea water desalination. The pressure applied to the feed side of the RP membrane must be higher than the natural osmotic pressure of the water in order for the osmotic process to be reversed. High pressure pumps are used to created the needed pressure.
Reverse Osmosis Membranes – Several types of membranes have been developed for RO applications. Three types are widely used.
Thin Film Composite The first type of commonly available membrane capable of high salt rejection is the composite membrane, usually called a thin film composite (TFC) membrane. TFC membranes are three layers of material; a thin (0.25um) barrier coating on the surface of a micro-porous layer of polymers, such as polyamines, polyimines, or polyethers.
TFC membranes have high salt rejection rates, usually operate at lower pressures that CA or HF, and have exhibited good performance under wide ranging pH and temperature conditions. They are not degradable by microorganisms and hold their flux rates over long periods of time. Like hollow fiber membranes, they do not withstand chlorine well, so chlorine removal is needed as a pretreatment step. Most TFC membranes are produced in a spiral wound module configuration.
Cellulose Acetate Another commonly used membrane is made of cellulose acetate (CA). These membranes are asymmetric. This means they consist of a thin dense salt barrier attached to a thicker micro-porous layer manufactured in one step so it is essentially one layer.
Polyaramid Hollow Fiber A third membrane used in the past and used occasionally is the hollow fiber (HF) membrane. These membranes have been developed in the form of bundles of thousands of tiny hollow filaments. These hollow fibers are approximately the diameter of a human hair in the form of a tiny tube that can take the high pressure of RO operations. Like CA membranes, they are asymmetric. A dense skin on the outside serves as the salt barrier to reject mineral salts, and a porous inner layer allows the water to pass through to service.
Polyaramid membranes normally operate at higher flow volumes, have good temperature and pH stability, good corrosion resistance and are not degradable by microorganisms. Due to the tiny sixe, they are more prone to turbidity fouling than spiral wound types. Hollow fiber membranes have low resistance to chlorine. Pretreatment of the water to remove chlorine is required for successful application.
All three membranes perform essentially the same task…they allow purified product water to pass through the membrane while stopping the passage of dissolved and suspended matter. RO membranes also have excellent rejection of organic matter, colloids and turbidity (although, turbidity can foul them). The percent rejection of each impurity varies somewhat according to the type of impurity and the membrane. Rejection tables are available for each membrane.
Design Considerations – Ro units do not deliver to service all of the water that is fed to them. During operation, some of the incoming water is used to wash down the membrane and only part becomes finished product water. Product water is referred to as permeate, and waste water is referred to as concentrate. The percent of water delivered as permeate is called the recovery and depends on the membrane and total RO unit design considerations.
Ro membranes are volume rated at 77 º F (25 º C) incoming water temperature. Conversions must be made if the incoming water temperature varies. For optimum RO unit performance, mixing valves or heaters are often used to maintain deed water at the rated temperature.
Pretreatment – Pretreatment of water prior to the RO process is almost always required. Chlorine has been mentioned, but high hardness minerals should also be controlled by a softener or other suitable methods. For example, hard water scale build-up causes membrane hydrolysis and impairs RO unit performances. Turbidity, iron and other impurities must be controlled for optimum RO performance.
System Engineering – RO units are often used to provide low dissolved solids feed water to deionizers. This extends the deionizer service cycle and lowers regeneration frequency. Considerable costs can be saved through reduction of regenerant chemicals. Systems engineering of water treatment problems takes on added significance as RO and DI processes are put into use together.
CA membranes are usually fabricated in spiral wound module configurations with a fabric support to provide a great deal of membrane surface area in a small space. As water is forced against the barrier layer, the dissolved salts are rejected and low dissolved solids product water passes through to an inner cylinder or tube and then to service.
Cellulose triacetate (CTA) is also used in RO applications. It has a higher rejection of salt than regular cellulose acetate, is more resistant to chlorine and can operate at higher pH values (up to 8.5). Blends of cellulose diacetate and cellulose triacetate are also used. This blend has good resistance and salt rejection, but with higher flux than cellulose acetate. Flux is the rate at which water is transported through the membrane.
Temperature Correction Factors
TEMPERATURE
CORRECTION FACTOR
º C
º F
FILMTEC
FLUID SYSTEMS TFCL
DESAL
C.A.
DESAL
N.F.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
33.8
35.6
37.4
39.2
41.0
42.8
44.6
46.4
48.2
50.0
51.8
53.6
55.4
57.2
59.0
60.8
62.6
64.4
66.2
68.0
69.8
71.6
73.4
75.2
77.0
78.8
80.6
82.4
84.2
86.0
87.8
89.6
91.4
93.2
95.0
96.8
98.6
100.4
102.2
104.0
105.8
107.6
109.4
111.2
113.0
114.8
116.6
118.4
120.2
122.0
2.43
2.34
2.25
2.16
2.08
2.00
1.92
1.85
1.77
1.71
1.63
1.58
1.53
1.48
1.42
1.37
1.33
1.28
1.24
1.19
1.14
1.11
1.07
1.03
1.00
0.97
0.94
0.91
0.89
0.86
2.15
2.07
2.04
1.94
1.87
1.81
1.75
1.70
1.64
1.59
1.54
1.49
1.44
1.40
1.35
1.31
1.27
1.23
1.20
1.16
1.13
1.09
1.06
1.03
1.00
0.97
0.94
0.92
0.89
0.87
0.84
0.82
0.80
0.77
0.75
0.73
0.71
0.69
0.68
0.66
0.64
0.62
0.61
0.59
0.58
0.56
0.55
0.54
0.52
0.51
1.98
1.93
1.87
1.82
1.77
1.72
1.67
1.62
1.57
1.52
1.48
1.44
1.41
1.37
1.34
1.30
1.26
1.22
1.19
1.15
1.11
1.08
1.06
1.03
1.00
098
0.96
0.94
0.91
0.88
0.86
0.83
2.27
2.21
2.14
2.08
2.01
1.94
1.87
1.80
1.74
1.67
1.62
1.55
1.48
1.41
1.34
1.37
1.32
1.28
1.23
1.18
1.14
1.10
1.07
1.03
1.00
0.93
0.94
0.91
0.88
0.85
0.82
0.79
Conductivity Conversions
CONDUCTIVITY
(micro-mhos-cm)
RESISTIVITY
(ohms)
TOTAL DISSOLVED SOLIDS
(ppm or mg/l)
0.056
0.059
0.063
0.067
0.072
0.077
0.084
0.091
0.100
0.111
0.125
0.143
0.167
0.200
0.250
0.333
0.500
1.000
1.110
1.250
1.430
1.670
2.000
2.500
3.330
5.000
10.00
11.10
12.50
14.30
16.70
20.00
25.00
33.30
50.0
100.0
111.0
125.0
143.0
18,000,000
17,000,000
16,000,000
15,000,000
14,000,000
13,000,000
12,000,000
11,000,000
10,000,000
9,000,000
8,000,000
7,000,000
6,000,000
5,000,000
4,000,000
3,000,000
2,000,000
1,000,000
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
9,000
8,000
7,000
0.0277
0.0294
0.0313
0.0333
0.0357
0.0384
0.0417
0.0455
0.0500
0.0556
0.0625
0.0714
0.0833
0.1000
0.1250
0.1670
0.2500
0.5000
0.5560
0.6250
0.7140
0.8330
1.0000
1.2500
1.6700
2.5000
5.0000
5.5600
6.2500
7.1400
8.3300
10.000
12.500
16.700
25.000
50.000
55.600
62.500
71.400
Ultraviolet Technology & Applications
What is Ultraviolet Light?
Close to a century ago, scientists first identified that part of the electromagnetic spectrum responsible for the bacterial effect of sunlight. The most biologically disruptive frequencies causing this well-known effect are the shorter wavelengths within ultraviolet (UV) light known as the UV – C spectrum. This form of light ranges from 200nm to 300nm, where a nanometer (nm) is one billionth of a meter. Such energy can now be produced commercially by electrical discharge devices. UV technology is harnessed for a range of applications from disinfection to oxidizing organics.
How is UV Light Generated?
The UV lamp, a quartz tube similar to a standard fluorescent bulb with electrodes at each end, is filled with an inert gas and a minute amount of mercury. Electrical energy, applied across the electrodes, provides the initial discharge and means of exciting the gases present. With relatively small amounts of energy input, a “Low Pressure” glow is created which produces UV emissions at 185nm and 254nm. As the electrical input energy is increased the lamp heats up rapidly; causing the internal pressure to increase, producing the characteristic “Medium Pressure” spectrum shown. The high output of the medium pressure lamp is as a result of a complex combination of atomic spectral, continuum and absorption lines characteristic of mercury vapor.
How Does UV Destroy Microorganisms?
High-energy ultraviolet light will pass easily through cell walls, cytoplasm, and nuclear membranes. Here, the photons are readily absorbed by the cellular DNA (the reproductive material). This UV energy causes permanent, irreparable, inactivation of the microorganism by fusing together and forming dimmers within portions of the DNA strands prohibiting replication. The microorganism becomes unable to maintain metabolism or reproduce itself and subsequently perishes. All cells, when subjected to germicidal UV, undergo similar processes:
Ultraviolet light penetrates the cell wall.
UV photons are absorbed by cellular DNA.
DNA is permanently altered ceasing any capability for reproduction.
Organisms, unable to metabolize or reproduce, perish and become unable to cause disease or spoilage.
OZONE REMOVAL
Ultraviolet systems are highly effective for destroying ozone in process water. Ozone is commonly used as a disinfection chemical and also as an oxidant for organic compounds. Residual ozone can cause harm to process equipment, affect the final product, or cause health hazards. As chemicals or heat are unwanted processes in most high purity water treatment processes, UV is the method of choice to break down the ozone in a simple flow-through physical process. Aquionics medium pressure UV technology offers many advantages in imparting the high UV doses needed to disassociate the ozone molecules in water in a simple and compact UV chamber design.
There if often a synergistic affect in using UV in ozonated water which accelerates the destruction of more difficult to remove organic compounds as an advanced oxidation process.
CHLORINE AND CHLORAMINE REMOVAL
Chlorine and chloramines are commonly used to provide residual disinfection in water. Chorine will damage RO membranes and other process equipment and can otherwise affect a product or process. UV provides a reliable, cost-effective alternative to activated carbon or bi-sulphite injection. These chlorine removal process can cause microbiological problems and high maintenance costs. UV installed before RO to remove free chlorine will also allow the membranes operate more efficiently by reduced biofouling and have longer runs between cleaning cycles.
Chloramination, a more common practice used by municipalities instead of liquid or gaseous chlorine when organic levels in the water source are high, can cause problems with carbon filters. Chloramines will break-through the activated carbon at a much faster rate and must be steamed and replaced more frequently. UV dechloramination prior to carbon filters has been shown to extend carbon life.
These applications normally require very high doses of UV and require UV wavelengths that are not generated by conventional low-pressure UV lamps. Aquionics' technology using high- intensity, broad spectrum UV has been shown to be most effective in the removal of chlorine and combined in these applications.
