Post on 01-Nov-2014
Water Treatment Unit
For Hemodialysis machines
Fact
Inadequately purified water for hemodialysis treatments have led to many documented injuries and deaths.
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Municipal water
• Water arriving to faucets is acceptable for drinking but not acceptable for HD.
Why?
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Water and healthy people
• Water at faucets contains contaminants such as chloramines, chlorides, fluorides, etc.
• People drink an average of 2 L/day (14 L/week)
• However, the healthy kidney is capable of extracting and excreting the contaminants.
• Thereofre, it is considered good for drinking.
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• More than 90% of dialysate used in the machine is water
• Dialysis patient is exposed to about 300 L/week.• Renal Failure Patient no proper excretion of
contaminants.• This may lead to potential clinical symptoms and
complications as follows:
Water for hemodialysis patients
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Possible water ContaminantsSymptom
Al , chloramines, Cu, ZnAnemia
Al , FlBone Disease
Ca, NaHypertension
Bacteria, endotoxin, nitratesHypotension
Bacteria, Ca, CuNausea and Vomiting
Al, Fl, Bacteria, endotoxin, chloramineDeath
Table 1. Potential clinical symptoms due to water contaminants
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What is Needed?
• To have a water treatment system to:– Purify the water before entering the hemodialysis
machine– Achieve different water preparations that are
required for the optimum performance of different machine components.
• What is a water treatment system?– series of devices, each of which removes certain
contaminants.
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Water treatment unit components
• The design of a water treatment system is dependent on:– the quality of feed water and– local requirements of the purity standards.
• One typical scheme commonly used is shown next
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Detailed diagram of water treatment system
Feed Water comp. Pretreatment components
Post-treatmentDistribution
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Block diagram of water treatment system1. Feed Water components2. Pretreatment components3. Reverse Osmosis membrane4. Post treatment components5. Distribution system
Feed Water Components Pretreatment Components
RO
Post-treatment ComponentsDistribution System
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1 .Feed Water Components
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List of Feed Water Components & diagram
A. Back (Reverse) Flow Preventive Device
B. Temperature blending valve
C. Booster Pump
D. Bladder Tank
Temp Blending ValveBack-Flow Preventive
Device
Booster PumpBladder Tank
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1.A. Back (Reverse) Flow Preventive Device
• Function: In case of water main break down it:– prevents water in the water
treatment system from being drained out.
– Prevents chemicals added to the system from back flowing to the building piping system, thus, putting other people at risk of exposure to chemicals.
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Reason of backflow
• Backflow may be caused by numerous specific conditions, but basically the reverse pressure gradient may be due to by either:– a loss of pressure in the supply main called back
siphonage – the flow from the pressurized system through an
unprotected cross-connection, which is called back-pressure.
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RP device summary
• If the screen in RP is plugged up the water flow is reduced, thus, causing a drop in the baseline pressure.
• What to monitor?– Pressure drop across the device, annual testing
• What to look for?– Pressure drop of about 70 kN/m2 from baseline.
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1.B. Temperature blending valve
• Function:– The temperature blending
valve is a device that can be set to mix hot and cold water to achieve a specific water temperature.
• Objective (Why)?– To improve the of the RO membrane in purifying the water.
(Industry standard temperature of about 25°).
– If temp is 10° there is 40% decrease in RO water flow (At low temp and no blend valve use larger RO).
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Blending valve summary
• A defective blending valve will not endanger the patient but may damage the water treatment equipment.
• What to monitor?– Water temperature
• What to look for?– Appropriate water temperature (25 °C)
– Minimal temp fluctuation (2 °C).
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1.C. Booster Pump
• Function– To compensate for the
pressure loss in the back flow preventive device and blending valve by providing a constant supply of water flow and pressure required by RO.
• Pump is followed by a pressure gage and switch (or flow switch) to ensure working within set points (pressures or flow rate).
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Booster pump summary
• The pressure set points of the pump differ depending on the specific dialysis system.
• What to monitor?– Water pressure.
• What to look for?– Pump turning on and off at the appropriate
pressure (of flow rates).
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1.D. Bladder Tank
• Function:– Maintains pressurized feed
water in case of extreme low or intermittent to no water flow.
• It cycles a diaphragm back and forth with pressurized water on the bottom side and an air charge on the top side
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2 .Pretreatment Components
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List of Pretreatment Components & diagram
A. Acid Injection Device
B. Multimedia Depth field
C. Softener
D. Carbon Filter
Multimedia Depth FilterAcid Injection Device
SoftenerCarbon Filter
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2.A. Acid Injection Device
• Function:– Only needed when pH water is
high to adjust pH between 5 and 8.5 for RO to operate properly and carbon filter to remove contaminants (chlorine and Chloramines) effectively.
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Acid feed pump summary
• It is important to consider the following points:– Acid injection before multimedia depth filter. Why?
Lower pH cause dissolved metals to precipitate
• What to monitor?– Online monitor of pH after the pump with audible
and visual alarms
• What to look for?– pH should be between 7 and 8.
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2.B. Multimedia Depth filter
• Function:– Removes large particulates such as
dirt, slit, suspended matter, and bacteria ≥ 10 microns that may cause water to be turbid.
• Filter contains layers of various sized rocks ranging from sand to gravel.
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Depth filter summary
• Pressure gauge on inlet and outlet to monitor a drop of ≥ 55 kN/m2 from baseline to backwash or replace the filter. Backwash timer; if present; should be set to perform backwash after working hours.
• What to monitor?– Pressure drop across filter, backwash timer
• What to look for?– Pressure drop of ≥ 55 kN/m2, timer set correctly.
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2.C. Water Softener & Brine Tank
• Function:– Removes Ca++ and Mg ++ from
water to avoid its build up on the RO membrane.
– Softener work on ion exchange basis (remove Ca & Mg and release Na).
• Softeners needs regenerating with concentrated sodium chloride salt (brine) in the Brine Tank.
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Water softener summary
• It is good to have regeneration timer to work when unit is not in operation.
• What to monitor?– Post softener hardness at end of day, amount of salt
in brine tank, pressure drop, timer settings.
• What to look for?– Hardness exceeding 1 Grain per Gallon (GPG) or
17.2 Parts per million (PPM).
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2.D. Carbon Filter
• Function:– Removes chloramines and
chlorine that destroy red blood cells and may damage the RO.
– Filters uses adsorption chemical process in which contaminants diffuse into the pores of the carbon and get attached.
• Filter is filled with Granulated Activate Charcoal (GAC or carbon) which absorbs chlorine and chloramines.
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2.D. Carbon Filter (contd.)• The filter is regularly acid washed (back flush) to
remove ash and to etch carbon to increase its porosity, thus, increase adsorbency of GAC.
• GAC is rated in terms of “iodine number” which measures adsorbabilty of substances to GAC.
• Iodine number of 900 or greater is recommended for the removal of chlorine & chloramines.
• Water must be exposed to carbon for at least 5 min’s in each tank (total 10 min’s). This time is called Empty Bed Contact Time (EBCT).
EBCT = V x 7.48 (gallons/cu. ft.)/Q
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Carbon filter summary
• What to monitor?– Chlorine & chloramines levels after tanks before
each patient, EBCT, pressure drop & backwash timer.
• What to look for?– levels within AAMI standards for chlorine and
cholramines are 0.5 and 0.1 mg/L respectively.
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Feed water and pretreatment components
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3.Reverse Osmosis membrane
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RO component and definition
• RO membrane is one of the most important component in water treatment system.
• RO is a process in which water is purified using ion exclusion semi-permeable membrane.
• Reverse Osmosis is the reversing the Osmosis process
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What is Osmosis• It is the transfer of water from regions of low
concentration to region of high one to equilibrate between concentrations.
• The process stops when hydrostatic pressure on the high solute side counter acts the osmotic pressure.
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Reverse Osmosis• The Osmosis process can be reversed by applying high
pressure to the high concentration (source water, reject) side through a selective semi-permeable membrane.
• Membranes develop from natural pig bladder to synthetic materials (polyamides-PA) membranes highly efficient at rejecting contaminants.
• Membranes are made tough enough to withstand the greater pressures necessary for efficient operation .
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Reverse Osmosis vs. Osmosis
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Pre-filters in RO systems
• RO systems require a carbon pre-filter for the reduction of chlorine (as mentioned before), which can damage an RO membrane
• A sediment pre-filter is required to ensure that fine suspended materials in the source water do not permanently clog the membrane.
RO Pump Prefilter RO Membranes
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Comparing RO membranes
MembraneAdvantagesDisadvantages
Thin film membrane (TF)
• Little higher reject ratio
• Operate at wider pH range
• Chlorine sensitive, requires carbon pretreatment
Cellulose Triacetate membrane (CTA)
• Lower reject ratio
• Operate on less pH range
• Not sensitive to chlorine
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RO membrane performance
• RO membrane performance is measured by percent rejection.
• Final product water quality can be measured by either conductivity in micro-siemens/cm or total dissolved solids (TDS) displayed as mg/L or parts per million (PPM).
• AAMI recommends both percent rejection and water quality monitors be used
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4. Post-treatment Components
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Deionization
• Required when RO alone cannot reduce contaminants to within AAMI standards.
• Many times used as backup to RO.
• DI contains resin beads that remove both cations and anions from water in exchange for hydroxyl (-OH) and hydrogen (+H) ions. The ions released combine to form pure water (H2O).
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De-ionizer summary
• AAMI and FDA dictate that:– DI should be monitored continuously with an
audible and visual resistivity alarm that should be heard in the patient care area.
– What to monitor? • Resistivity should continuously read above 1
meg-ohm/cm and be recorded at least daily.
• Pre and post tank pressures be recorded at least daily.
– What to look for?• A change in pressure of 70 kN/m2 from baseline.
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5. Distribution system
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Stages of Distribution system
• Four stages of distribution systemA. Storage tanksB. UV irradiatorC. Submicron and ultra filtrationD. Piping system
UV irradiator
Submicron & ultra filtration
Piping System
Storage tanks
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5.A. Storage Tanks
• Storage tanks are required in an indirect feed system to accumulate the product water and delivers it to the distribution loop.
• Unused portions of the product water are re-circulated back into the storage tank.
• The RO unit will stop and start filling the tank by receiving signals from the high and low level switches on the storage tank.
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Storage tanks requirements
• According to AAMI and FDA, storage tanks should:– be made of inert materials that do not contaminate
the purified water.– bottoms should be conical shaped for complete
emptying.– size of the tank should be in proportion to meet
the facilities peak demands, no larger.
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5.B. Ultraviolet Irradiator
• It is a low pressure mercury vapor lamp enclosed in a quartz sleeve that emits a germicidal 254 nm wavelength.
• It is required to provide a dose of radiant energy of 30 milliwatts sec/cm2 in order to kill bacteria.
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Maintenance of the UV device
• Regular maintenance of the UV device includes:– continuous monitoring of radiant energy output.– an audible and visual alarm.– replacing the lamp at least annually. – routine cleaning of the quartz sleeve
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Problem with UV Irradiator
• There are 2 problem with UV– It is possible for some species of bacteria to
become resistant to UV irradiation.– UV does not destroy endotoxin, and it may even
increase the level as a result of the destruction of the bacteria cell wall where endotoxins harbor.
• Therefore, other filtrations are required after this stage.
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5.C. Submicron and Ultra-filtration
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Functions of Submicron filter & Ultra-filtration
• Both are membrane filters.
• The housing should be opaque to inhibit algae growth.
• A submicron filter reduces the level of bacteria.
• Ultr-afilter removes both bacteria and endotoxin
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Monitoring of submicron & UF
• Submicron and ultrafilters, even though they remove microbes, are targets for bacterial infestation. Therefore, it is required to routinely be disinfected or replaced.
• The pressure differentials should be monitored continuously and documented at least daily
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This completes the water treatment system which may look as follows
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Water treatment system
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• F1 to F4 are filters with tighter pores