Water Treatment UnitFor Hemodialysis machines
FactInadequately purified water for hemodialysis treatments have led to many documented injuries and deaths.
Municipal water Water arriving to faucets is acceptable for drinking but not acceptable for HD. Why?
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.4
Water for hemodialysis patients 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:
Table 1. Potential clinical symptoms due to water contaminantsPossible water Contaminants Al , chloramines, Cu, Zn Al , Fl Ca, Na Bacteria, endotoxin, nitrates Symptom Anemia Bone Disease Hypertension Hypotension
Bacteria, Ca, Cu Al, Fl, Bacteria, endotoxin, chloramine
Nausea and Vomiting Death
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.7
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
Detailed diagram of water treatment systemFeed Water comp. Pretreatment components
Block diagram of water treatment system1. 2. 3. 4. 5. Feed Water components Pretreatment components Reverse Osmosis membrane Post treatment components Distribution systemFeed Water Components Pretreatment Components
1. Feed Water Components
List of Feed Water Components & diagramA. B. C. D. Back (Reverse) Flow Preventive Device Temperature blending valve Booster Pump Bladder TankBack-Flow Preventive Device
Temp Blending Valve
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.13
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.
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.15
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).16
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).17
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).18
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 appropriatepressure (of flow rates).
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 side20
2. Pretreatment Components
List of Pretreatment Components & diagramAcid Injection Device Multimedia Depth Filter
A. B. C. D.22
Acid Injection Device Multimedia Depth field Softener Carbon Filter
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.
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 8.24
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.
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.26
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.27
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).28
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.29
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 mins in each tank (total 10 mins). This time is called Empty Bed Contact Time (EBCT). EBCT = V x 7.48 (gallons/cu. ft.)/Q30
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 andcholramines are 0.5 and 0.1 mg/L respectively.
Feed water and pretreatment components
3.Reverse Osmosis membrane
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 process34
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.
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 .
Reverse Osmosis vs. Osmosis
Pre-filters in RO systemsPrefilter RO Pump RO Membranes
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.39
Comparing RO membranesMembrane
Advantages Little higher reject ratio Operate at wider pH range
Thin film membrane (TF)
Chlorine sensitive, requires carbon pretreatment
Lower reject ratio Cellulose Tri