Watts PWRO440 - Manual (Page 2)

C. Pretreatment
The RO feed water must be pretreated in order to prevent mem-
brane damage and/or fouling. Proper pretreatment is essential for
reliable operation of any RO system.
Pretreatment requirements vary depending on the nature of the feed
water. Pretreatment equipment is sold separately. The most common
forms of pretreatment are described below.
Media Filter - Used to remove large suspended solids (sediment)
from the feed water. Backwashing the media removes the trapped
particles. Backwash can be initiated by time or differential pressure.
Water Softener - Used to remove calcium and magnesium from
the feed water in order to prevent hardness scaling. The potential
for hardness scaling is predicted by the Langelier Saturation Index
(LSI). The LSI should be zero or negative throughout the unit unless
approved antiscalents are used. Softening is the preferred method of
controlling hardness scale.
Carbon Filter - Used to remove chlorine and organics from the
feed water. Free chlorine will cause rapid irreversible damage to the
membranes.
The residual free chlorine present in most municipal water sup-
plies will damage the thin film composite structure of the mem-
branes used in this unit. Carbon filtration or sodium bisulfite
injection should be used to completely remove the free chlorine
residual.
Chemical Injection - Typically used to feed antiscalant, coagulant,
or bisulfite into the feed water or to adjust the feed water pH.
Prefilter Cartridge - Used to remove smaller suspended solids and
trap any particles that may be generated by the other pretreatment.
The cartridge(s) should be replaced when the pressure drop across
the housing increases 5 - 10 psig over the clean cartridge pressure
drop. The effect of suspended solids is measured by the silt density
index (SDI) test. An SDI of five (5) or less is specified by most mem-
brane manufacturers and three (3) or less is recommended.
Iron & Manganese - These foulants should be removed to less than
0.1 ppm. Special media filters and/or chemical treatment is com-
monly used.
pH - The pH is often lowered to reduce the scaling potential. If the
feed water has zero hardness, the pH can be raised to eliminate
CO2.
Silica: Reported on the analysis as SiO2. Silica forms a coating on
membrane surfaces when the concentration exceeds its solubility.
Additionally, the solubility is highly pH and temperature dependent.
Silica fouling can be prevented with chemical injection and/or reduc-
tion in recovery.
2
I. Introduction
The separation of dissolved solids and water using RO membranes
is a pressure driven temperature dependent process. The membrane
material is designed to be as permeable to water as possible, while
maintaining the ability to reject dissolved solids.
The main system design parameters require the following:
• Internal flows across the membrane surface must be high enough
to prevent settling of fine suspended solids on the membrane
surface.
• The concentration of each dissolved ionic species must not exceed
the limits of solubility anywhere in the system.
• Pre-treatment must be sufficient to eliminate chemicals that would
attack the membrane materials.
PWRO4401 PWRO4402 PWRO4403
Maximum Productivity
(gallons per day)
2200 4400 6600
Quality (average membrane
rejection)
98 %
Recovery (user adjustable) 15 - 75 % 25 – 75% 32 - 75 %
Membrane Size 4” x 40”
Number Of Membranes 1 2 3
Prefilter (system ships with
one 5 micron cartridge)
20”
Feed Water Connection 3/4" NPTF
Product Water Connection
(tubing OD)
5/8"
Reject Water Connection
(tubing OD)
5/8"
Feed Water Required
(maximum)
10 gpm 12 gpm 14 gpm
Feed Water Pressure
(minimum)
10psi
Drain Required (maximum) 10 gpm 12 gpm 14 gpm
Electrical Requirement 230V 10 amps 230V 12 amps 230V 15 amps
Motor Horse Power 3/4 1 1 1/2
Dimensions W x D x H
(approximate inches)
20 x 20 x 50 20 x 26 x 50
Shipping Weight (estimated
pounds)
120 150 180
A. Specifications
RO Membrane
Feed Water Product Water
Reject Water
B. RO Overview
Reverse osmosis systems utilize semipermeable membrane ele-
ments to separate the feed water into two streams. The pressurized
feed water is separated into purified (product) water and concentrate
(reject) water. The impurities contained in the feed water are carried
to the drain by the reject water. It is critical to maintain adequate
reject flow in order to prevent membrane scaling and/or fouling.
Notes:
• Maximum production based on a feed water of 77°F, SDI < 1, 1000 ppm TDS, and pH 7.
Individual membrane productivity may vary (± 15%). May be operated on other feed waters
with reduced capacity.
• Percent rejection is based on membrane manufacturer’s specifications; overall system per-
cent rejection may be less.