BASIS OF DESIGN AND TREATMENT SCHEME
Monitoring the Temperature Blending Valve:
Often, water treatment systems will require that the feed water temperature be raised to a certain degree. For example, reverse osmosis systems operate most efficiently (produce the largest volume of dialysis quality water for the number and type of membranes) - at a feed water temperature of 77°F. This is accomplished through the use of a heater in conjunction with a temperature blending valve. A common problem comes from the water heater not being large enough to keep up with the facility’s needs. The temperature blending valve is a device that can be set to mix hot and cold water to achieve a specific water temperature. There are various designs for this important piece of equipment, but some are more appropriate for use in a dialysis setting – specifically ones with an incorporated temperature indicator or thermometer. A common type seen today uses a spring-loaded thermostat. This is important because these tend to fail hot meaning that when they go out, the output water temperature rises, and rises quickly. For this reason, it is necessary to monitor and record the output temperature at least daily.
When working properly, with an appropriately sized water heater, the blending valve output temperature will rarely vary more than plus or minus 2 to 3 degrees F. If, during your daily recording, you note a temperature fluctuation out of this acceptable range, immediately bring it to the attention of the facility’s maintenance person or your supervisor. A defective blending valve will not necessarily endanger your patients (dialysis machines have a bypass mechanism for overheated water/dialysis), but it can damage the heart of your dialysis clinic, your water treatment equipment.
Blending Valve Summary
What to monitor: Water temperature
What to look for: Appropriate water temperature, minimal temperature fluxuation
Monitoring the Back Flow Prevention Device:
It is required by building codes that dialysis water treatment equipment be connected to the source water through a Backflow Prevention Device (also known as a Reverse Flow Prevention Device), or RP. The purpose of this is to prevent water from the water treatment equipment being pulled backward through the building’s water supply piping. As an example, if a water main broke at the bottom of a hill, gravity would cause the water in the pipe feeding the dialysis unit to drain down. The RP device would prevent the draining back of water from the treatment system. If there were not backflow prevention, this suction would pull water out of the treatment system. The Backflow Prevention Device also prevents the backflow of chemicals into the building water main during the process of chemical disinfection of the water treatment system, thus eliminating the risk of chemical exposure to the other parts of the building. If the system was being disinfected, the chemical would be pulled into the water main as well. Once the break was fixed, water that had been in the RO machine, and is now in the water main could be diverted to any other uses on the main water line. The screen on the RP device can get plugged up thus reducing the water flow through it. Therefore, the RP device needs to be monitored for fouling of the internal screen. This is done by monitoring the pressure going into and out of the device. There is normally a significant reduction in pressure across an RP device, often as much as 20 Pounds Per Square Inch (PSI). It is important to have a baseline pressure drop established which would be the normal pressures for the device. After that, if the pressure difference between pre and post RP device increases by 10 PSI, the internal screen should be cleaned, or the RP device may need servicing.
RP devices must also be checked for proper function at least annually by someone who
has been properly trained and certified. Most facilities use a plumber for this, though you
can get certified by taking a class specifically for this purpose.
RP Device Summary
What to monitor: Pressure drop across the device, annual testing
What to look for: A pressure drop change of 10 PSI from baseline
Monitoring the Booster Pump:
In order to maintain the necessary minimum pressure and flow to the treatment system,
booster pumps are often used on the feed water line. The on/off cycle of booster pumps are controlled by either a pressure switch or flow switch, which turns the pump on when the pressure drops below a specific set point, and turns it off once the pressure recovers to the baseline (above the set point). These set points vary depending on the needs of an
individual dialysis facility. Once the proper set points are established, the pump should be
monitored periodically to ensure its proper functioning and that the booster pump cycles
on and off as needed.
Booster Pump Summary
What to monitor: Water pressure
What to look for: Pump turning on and off at the appropriate pressures or flow
Rates
Monitoring the Acid Feed Pump:
Though this is not needed in all water treatment systems, adding an acidic solution to the raw water is indicated in areas where the pH of incoming feed water is high. Some municipalities add a base such as sodium hydroxide into the water system to increase the pH of the water. This minimizes leaching of metals from the pipes. Carbon filtration and Reverse Osmosis devices will not work as effectively at a pH of >8.5. In these municipalities, adding an inorganic acid to lower the feed water pH may be required for the proper functioning of water treatment system. Organic acids are discouraged because they encourage bacterial growth. To assure that the acid is fed in at the appropriate rate, pH must be monitored from a sample port just downstream from the acid feed pump. This monitoring should be The expected range for pH should be between 7.0 and 8.0. Some important points to consider:
- Place the acid feed system before the multi-media since the lower pH can cause
aluminum to precipitate.
- Online monitoring of pH is required with both audible and visual alarms in place
- An independent test of pH is required daily
Note: Sometimes as an alternative pretreatment, weak acid cation tanks are used to lower
pH by adding hydrogen ions.
Acid Feed Pump Summary
What to monitor: pH post acid feed pump
What to look for: pH should be between 7.0 and 8.0
Monitoring Depth Filtration Devices:
Depth filters are used to remove particulate matter from the water. They range from large multi-media filters and cartridge filters which remove dirt from the incoming water to ultra filters that remove bacteria from product water. Monitoring of depth filters is the same, regardless of their size or configuration. The pressure should be measured both
pre and post filter, and a baseline pressure drop established when they are fresh. From this point, there should not be more than a 10 PSI pressure drop from this baseline. If the
pressure drop change is greater than 10 PSI, the filter should be replaced or back flushed to restore unrestricted flow of water. The back flush timer (if present) should be set to perform the back flush operation after facility operation hours.
Depth Filtration Summary
What to monitor: Pressure drop across the device, back flush timer
What to look for: Pressure drop of 10 PSI or more from baseline operating
pressures, timer set correctly
Monitoring the Water Softener:
Water softeners are an important part of most water treatment systems. Their use, however, is primarily in protecting and prolonging the life of the RO membrane. Water softeners are used primarily to remove calcium and magnesium from the water, which an
RO will do easily as well. (Softeners remove Ca++ and Mg++ by exchanging these for Na+.) The problem resolved by softening is that the calcium would otherwise build up on
the RO membrane and cause a significant decrease in water quality as well as RO membrane life. To assure that your softener will perform appropriately, you need to monitor:
- Total hardness post softener
Measured in either Grains per Gallon (GPG) or Parts per Million (PPM). The Association for the Advancement of Medical Instrumentation (AAMI) RD52 recommends a limit of 1GPG, which is equal to 17.2 PPM. PPM can be converted to GPG by multiplying by 0.058. GPG can be converted to PPM by dividing by 0.058.
- Pressure Drop
The pressure should be monitored before and after the softener. Softeners vary in how much pressure is lost across them, and you need to establish a baseline when it is working properly. The device may require back flushing if the pressure drop changes by more than 10 PSI. A breakdown of the resin can occur (from chlorine) which can also cause increased pressure drops.
- Salt level in the brine tank
There should always be an adequate amount of salt in the tank to allow the resin beads to be regenerated by the softener. Monitor the brine tank for a “Salt Bridge”- where salt at the top of the tank solidifies, making it appear as though the tank is full when it is actually empty underneath.
- Regeneration Timer
The system should be set to regenerate the resin beads often enough to provide exchange ions for the calcium and magnesium. The timer should be set to activate when the facility is not operating, and monitored daily to make sure it will not go into a regeneration cycle during a patient treatment. The timer should always be visible.
Water Softener Summary
What to monitor: Post softener hardness at the end of the day, amount of salt in
the brine tank, “salt bridge” in the brine tank, pressure drop across the device,
settings on regeneration timer.
What to look for: Hardness not exceeding 1 GPG (17.24 PPM), adequate amount
of salt with no salt bridge, pressure drop change from baseline of 10 PSI or more,
Monitoring the Carbon Tanks:
One of the most critical tasks regarding patient safety in the day of a dialysis technician is checking the water treatment system for chlorine and chloramines.
Chlorine and its combined form, chloramine, are high-level oxidative chemicals. They are added to municipal water systems to kill bacteria—but they also destroy red blood
cells. For this reason they must be removed from water to be used for dialysis. Unfortunately the R/O system is not very effective at removing chlorine and chloramines. In fact, many membranes are destroyed by them. Chlorine is removed from the incoming water by running it through tanks filled with Granulated Activated Charcoal (GAC, or carbon), which absorbs it. Carbon tanks are part of the pre-treatment section of a water treatment system and normally are arranged where water will flow first through one tank and then directly into another. This is called a “series” configuration. The first tank in the series (Primary Carbon Tank) is referred to as the “worker” tank and second is called the “polisher.” Knowing the flow arrangement of your carbon tanks will help you understand how and where to test them. The amount of carbon in your tanks must be adequate to allow the chlorine to be absorbed in the amount of time the water is flowing through it. The water must be exposed to the carbon for 5 minutes in each tank, for a total of 10 minutes for both the worker and polisher. This residence time is known as Empty Bed Contact Time, or EBCT. It is calculated using the formula EBCT=V/Q, where V= the Volume of Carbon (in cubic feet) and Q= the water flow rate, in cubic feet per minute. To calculate the volume of carbon needed, use the formula V= (Q * EBCT) / 7.48 (this is the number of gallons in one cubic foot of water). For example, if you know that you have a flow rate of 10 Gallons per Minute (GPM), and you want an EBCT of 5 minutes, your calculation would be:
V = (Q * EBCT) / 7.48
V = (10 * 5) / 7.48
V = 6.69
You need a 6.69 cubic foot carbon tank for each working and polishing tank
To calculate your EBCT from a known carbon tank volume and flow rate (assume a 6 cubic foot tank and a 12 GPM flow rate), your calculation would be:
EBCT = V/Q
EBCT = 6 / (12/7.48)
EBCT = 6 / 1.6
EBCT = 3.75 minutes per 6 cubic foot tank
The objective of your chlorine/chloramine testing is to verify that chlorine has been removed from the water entering the RO. Your sample should be taken at the point where
the water leaves the first tank (worker) and before entering the second (polisher). If the
results show any chlorine leaving the first tank, a second sample should be taken immediately after the water leaves the second tank. If there is chlorine leaving the second
tank, dialysis should be discontinued in the facility. If there is no breakthrough, the
chlorine level should continue to be monitored after the second tank on an hourly basis
until the primary tank is replaced. This is because you no longer have redundant
protection.
It is very important that the water system be in full operation for at least 15 to 20 minutes
before you take your first test. If you take your sample as soon as you start up the system,
you will be testing water that has been sitting in the tank overnight, and it will not give
you a representative sample of the carbon tank’s capability at normal flow rates.
There are various ways to test water for chlorine/chloramine but the most widely used are
colorimeters, color comparators, and test strips. Because the results of this test (and
others) are determined by comparing colors, it is important that the person performing
them has passed a color blindness test.
The limit for chlorine is 0.5 PPM, and the limit for chloramine is 0.1 PPM. There is no
method to test directly for chloramine, so you must perform two separate tests: one for
Total Chlorine, and one for Free Chlorine. The chloramine level is the difference between
the two tests.
Example:
Your Measured Total Chlorine is 1.2 PPM
Your Measured Free Chlorine is 0.8 PPM
1.2 - 0.8 = 0.4 PPM
Therefore your Chloramine Level is 0.4 PPM
It is acceptable, according to the AAMI, to just test for total chlorine so long as the test is
of appropriate sensitivity and the result does not exceed 0.1 PPM. The rationale being if
you have a zero reading for total chlorine then there is no chloramine present.
Most commonly, chlorine/chloramine testing is done before each patient shift. In most
clinics, it would be difficult to find times during the day when there are no patients on the
dialysis machine, so one strategy is to test before the first patient treatment at the
beginning of the day, again at 9:00 am or 10:00 am, followed by a third and last test
between 2:00 pm and 5:00 pm depending on your patient schedule. You will probably
find that the best plan would specify exact times rather than a time frame, approximately
every four hours. If any of your tests indicates the presence of chlorine/chloramine, you
must immediately notify the person responsible for maintaining the water treatment
system.
Pre and post pressures must also be monitored on the carbon tanks to assure consistent
flow of water. If the carbon is fouled by particulate matter, the pressure drop will
increase, indicating a need to backflush the tank to remove the particulates.
On larger tanks in particular, it is important to periodically backflush the tank to prevent
channeling, which causes the water to flow quickly through established channels
reducing the expected EBCT.
Carbon Tank Summary
What to monitor: Chlorine and chloramine levels after the worker tank before
each patient shift, pressure drop across each tank, backflush timer. EBCT
calculated and at the minimum 10 minutes for both tanks.
What to look for: Chlorine levels within AAMI standards (0.5 PPM chlorine, 0.1
PPM chloramine), pressure drop change of 10 PSI or greater, back flush timer set to activate when facility is not in operation.
Monitoring the Reverse Osmosis (RO) Device:
The primary concerns in monitoring your RO for quality are discussed below in their own sections on Chemical Contamination and Microbiological Monitoring. However, it is important to monitor the operation of the RO system to maintain its efficiency. Every RO will have its own specific parameters that indicate whether it is operating correctly.
Water pressure is measured in several places. Incoming water pressure needs to be adequate to maintain flow through the RO, generally 30-40 PSI. Pre and post pressure should be monitored on any incorporated depth filter as well. There is usually a safety switch that shuts down the RO if the pressure is too low to prevent damage to the RO
pump. The pump pressure is monitored, as this pressure is what pushes water through the membrane, and is generally 200-250 PSI. The reject pressure is usually 50-75 PSI less than the pump pressure. The pressure of the product water is also monitored, and it will vary greatly depending on whether it is a direct or indirect (holding tank) system.
Water flow is also measured in several places using flow meters. Product flow indicates
the amount of purified water that is getting through the membrane. Waste flow indicates
the amount of concentrated water being flushed down the drain. Direct systems often
measure the amount of product water recalculated through the system, and being blended
with the incoming water.
The amount of dissolved solids is monitored in the incoming and product water, and is
discussed in detail in the Monitoring Chemical Contamination section.
Reverse Osmosis Summary
What to monitor: Water pressure and flow at various locations throughout the
system.
What to look for: Pressure and flow in an RO system are inter-related. For example, if you reduce the RO pump pressure, you will have a decrease in product water flow, and an increase in waste water flow. If the product water flow drops without a change in pump pressure, the RO membrane may be getting plugged up. A change in the delta pressure between the pump and reject pressures can indicate fouled membranes. It is therefore very important to establish appropriate baseline values for all pressures and flows, and then investigate any deviations. Use a trend analysis so that even minor changes can be seen over time.
Monitoring the De-Ionization (DI) System:
The primary concerns in monitoring your DI for quality are discussed below in the
sections on Chemical Contamination and Microbiological Monitoring. However, it is
important to monitor the pressures of the DI system to maintain its efficiency.
Water pressure should be monitored before and after each DI tank you are using.
Baseline pressure drops should be established when the system is operating
correctly. Changes of 10 PSI or greater indicate that the tanks are becoming plugged with particulate matter, or potentially the resin is breaking down, and restricting the flow of water. Flow rates in DI systems are determined by product water usage. They do not generate a waste stream like an RO. If a holding tank is used, the flow velocity in the distribution loop should be a minimum of 3 ft/sec.
DI System Summary
What to monitor: Pressure before and after each tank.
What to look for: A change in pressure of 10 PSI or more from baseline.
Chemical Contaminant Standards
Monitoring Microbiological Contamination:
Microbiological contamination of water is a serious health concern for patients on dialysis. High levels of bacteria and/or end toxin can harm patients by causing phylogenic
reactions or even systemic infections if a dialyzer membrane ruptures. If the bacterial
contamination is severe enough, there can be a release of toxins that can adversely affect
dialysis patients. It is essential that dialysis facilities monitor both bacteria and end toxin
levels in the water used for dialysis and dialyzer reprocessing.
Water Treatment Monitoring Summary
Monitoring Your Water Treatment System