HOW TO CALCULATE ACTUAL PERFORMANCE FOR A REVERSE OSMOSIS MEMBRANE
- What Osmotic Pressure Is - The flow of water through a membrane in response to differing concentrations of solutes on either side generates a pressure across the membrane, which is called osmotic pressure. In other words, as the hardness of the tap water increases, greater tap water pressure is required to force the water through the membrane.
- Pressure and Temperature Compensation - In order to characterize a membrane, there must be common testing data. Industry standards for testing membrane performance are 60 PSI tap pressure with 77-degree water temperature.
Most locations will not have exactly 60 PSI or 77-degree water. Use the calculation below to determine what the membrane will do with your water conditions.
As you may know, the quality of tap water varies substantially from county to county and from state to state. A typical home measurement can be made with a TDS (total dissolved solids) meter. These are available at your local hardware store or online. While the TDS meter provides you with an idea of your water quality, it does not tell you the chemical content of your tap water. A sample of your water would need to be sent to a lab for analysis. This being said, purchasing and installing a SpectraPure water purification system will ensure that the water you drink, as well as the water that you produce for your aquarium, is pure.
99 percent of the time, the 0.5-sediment and 0.5-micron carbon filters work perfectly together, but there are a few water sources around the country that contain a high percentage of very fine sediment materials that are less than 0.5-microns, which could be the reason that you are experiencing this increase.
In these situations, the 0.5-micron carbon filters tend to become clogged with the smaller sediment before reaching the 0.5-micron sediment capacity. The solution is to substitute the 0.2-micron ZetaZorb® sediment filter for the 0.5-sediment filter.
In cases of extreme quantities of dirt in the tap water, another option is to add an additional 0.35-pleated sediment filter (in a new housing) before the 0.2-ZetaZorb® and the 0.5-carbon.
It can be difficult to diagnose the problem in terms of time, rather than in gallons produced during that time. The length of time that you have been experiencing this issue is not what is important. Instead, you should focus only on the gallons produced and the total gallons processed in order to determine the filter life. The gallons produced must include the brine volume in addition to the permeate volume.
To ensure a long pre-filter life, the ratio of brine to permeate should be checked to confirm that it is no greater than 5 to 1. The higher the ratio, the shorter the pre-filter life. This could also be part of the problem in a number of different situations.
In addition, if there is an automatic shut-off device on the system, make absolutely sure that the brine water completely stops flowing and stays off when the system shuts-off.
There are a few cases where customers incorrectly set up the systems by excluding the proper shut-off devices. For example, if a float is installed on a permeate line without an ASO valve or check valve, then the system will never shut off the brine flow. There have been cases where a customer has installed a solenoid backward, which allows the brine water to flow continuously down the brine tube. All of these possibilities must be tested and checked before a good solution can be determined.
Open up the wastewater line with the valve so that you can drain out the air that is trapped in the membrane housing. It takes a few minutes for the water to displace the air depending on the amount of production you have compared to the amount of the trapped air. Once all of the air is out, make sure to rebalance the product / waste water ratio in order to restore proper operation.
When it comes to drinking deionized (DI) water, there are many different opinions. The first thing that you need to understand is that DI water has had all of the minerals removed. If you drank only DI water and ate nothing, then it would be harmful. The cells in your body need electrolytes in order to stay active and produce more cells. If you do not replenish the electrolytes that are being used, your cells could not survive.
Imagine that you have two batteries. One battery is connected to a glass container filled with tap water, and the other is filled with DI water. Tap water is able to conduct electricity because of the minerals in it. DI water cannot conduct electricity because it completely lacks minerals. It is only when you add salt to the DI water that you would be able to conduct electricity.
DI water does not necessarily harm your health unless it is the only thing that you are putting into your body. We do not recommend drinking it because of its flat taste, and because DI resins are not made of food-grade-approved material.
Step 1 - mix together 1 tablespoon of bleach per gallon of water. You will need approximately 5 gallons of water.
Step 2 - Place the pleated filter in the water mixture and soak for 30 minutes.
Step 3 - Rinse the pleated filter until it no longer has a chlorine odor.
Type 1 strong-based anion resins release very low levels of amines (trimethylamine). A very low threshold of 5 PPB or greater will cause a noticeably fishy odor. The odor is most noticeable when the resins are new and when they are at or near the point of exhaustion.
NOTE: Trimethylamine is released by decomposing fish which results in a similar odor.
RO water is produced at a very slow rate, which is dependent on the water temperature, water pressure, and the size of the membrane. The water trickles into the DI housing, located on the outside of the DI cartridge, and is forced up through the center as it leaves the DI housing.
There are two reasons that this housing will not completely fill with water. The first possibility is that air trapped in the housing, which prevents it from filling. The second possibility is that the product line leaving this housing might be sloped downward, which means that you are using gravity to drain the water out of the housing. In either case, no harm is done to the quality of the water or the DI cartridge.
Procedures for aeration of RO product water and
CO2 removal in well water and other sources of water with low pH
One of the most common reasons for low DI cartridge life is high carbon dioxide content in low pH waters. CO2 levels in low pH waters, like well water, can be as high 50 to 100 ppm. Since carbon dioxide is a small, gaseous molecule, it passes right through the reverse osmosis membrane. Carbon dioxide is weakly ionized and is not detected in conductivity measurements. Since it occupies the anion-exchange sites in the deionization cartridge, it significantly reduces their expected lifetime. Therefore, CO2 removal from RO product water significantly enhances the lifetime of the deionization cartridges.
Procedure for determination of CO2 level
CO2 levels in your water can be measured in a variety of ways:
1. Use a test kit from either the Hach Company or the LaMotte Company.
2. Use the nomogram below (pH and bicarbonate alkalinity measurements are required. Fig. 1).
3. Follow this link to determine your CO2 level: ww.fishfriend.com/aquarium_co2_calculator.html
Procedure for aeration for CO2 removal
RO product water is collected in a PVC column that is three feet tall and has an air stone resting at the bottom. Air is pumped into the column containing the RO product water. Degassed water (almost free of CO2) is collected from the top of the column and then fed into the deionization cartridge using gravity (Fig. 2).
The noise is caused by the location of the drain saddle with an air-gap faucet.
- The air-gap faucet inherently makes a noise that is amplified when the water running from the drain saddle splashes into the water in the sink trap. The noise is most commonly heard upon start-up and after filter changes when air is being purged from the system. Once all of the air is expelled, which usually takes five minutes, the noise should subside.
- To purge air, rotate the system so the product and waste ports of the membrane are pointing up. Let the system run in this manner for 10 to 15 minutes. Rotating the membrane housing this way allows the air bubble to escape through the waste line.
- You can reduce the noise if you relocate the drain saddle to a greater height and make sure that the waste line is as straight as possible.
The product water production rate is dependent on the pressure across the membrane, while the wastewater production rate is mostly dependent on tap water pressure. As a bladder tank fills with water, its back pressure quickly starts to reduce the working pressure across the membrane.
There is some confusion on RO membrane GPD ratings that we would like to explain.
We have been testing our RO membranes against the industry standard of 60psi for more than 20 years. This provides a significant amount of data for us to draw upon when we share performance characteristics with our customers, help them troubleshoot production problems, or back up our ratings claims.
For example, the popular Filmtec 75GPD membrane is rated 75 GPD at 50psi. When we test it at the industry standard of 60 psi, the rating is 90 GPD. The production rate of RO membranes is directly proportional to the applied pressure, which explains the rating difference. It is for this reason that we sell our membranes and systems as 90 GPD (at 60 psi and 77 F).
Unfortunately, most of our customers in America have less than 60 psi or 50 psi available. They also lack the ability to maintain a water temperature at 77, which is used in the rating
process. The average water temperature across most parts of the country is around 50. In these cases, a pressure-boosting pump can obtain higher production rates.
Even more astounding, is that with the membranes that we hand-select and test to ensure rejection greater than 98 percent, we typically see production rates exceeding 100 GPD at 60 psi and 77 F. When you purchase our hand selected and proprietary tested Filmtec 75 GPD membranes, you can rest assured that you are purchasing greater than 98 percent rejection.
Here is a listing of Nominal Rejection Characteristics of a (TFC) Membrane:
Why is a difference of one to two percent so important? A two percent increase in rejection can double the life of your DI cartridge, which will save you a lot of money. This is why our hand selection and proprietary testing is worth the extra cost.
It's believed that mineral water helps to supply the elements that your body needs to support metabolic functions. There is scientific proof, however, to suggest that most of these minerals are in an inorganic, or dead, form. While they may enter the body’s circulatory system, they cannot be used in the physiological process of building new cells. These inorganic minerals interfere with the delicate and complex biology of the body. "The body's need for minerals is largely met through foods, not drinking water". - The American Medical Journal. One glass of orange juice contains more beneficial minerals than thirty gallons of untreated tap water.
Only after they have passed through the roots of plants do these inorganic minerals become organic minerals that are capable of being assimilated into our tissues. Pure water removes the inorganic mineral deposits in your body. Organic minerals are fully absorbed and remain in your tissues. According to many nutritionists, minerals are much easier to assimilate when they come from foods.
There is frequent confusion between Zero-Indicated TDS and the common misnomer Zero TDS. There is quite a bit of difference between the two when talking about ultra-pure water. Ultra-pure water is about 18.2 megohm or about 0.05 micro-siemens. Most aquarists want this level of ultra-pure water. If there were such a thing as Zero TDS, then it might be more appropriately measured around 0.05 micro-siemens. Unfortunately, most inexpensive TDS meters can resolve only about 5 micro-siemens.
While 5 micro-siemens conductivity is very reasonable for break-through detection to signal that cartridge replacement is required, it is clearly not sufficient to measure Zero TDS.
- Pre-Filters (Sediment & Carbon-Block Filters)
Pre-Filters do not have a shelf life.
- Reverse Osmosis Membrane (RO)
Purchase an RO membrane as needed. If you would like to keep one on hand, then you can store it in the refrigerator for up to one year. Make sure that you keep the filter sealed in its original packaging. If the membrane dries out, it will not produce water.
- De-Ionizing Cartridges (DI)
Replacement DI cartridges come shipped in a Mylar® Bag. Keep it sealed in its original packaging until use. You can store it for approximately six months.
Put the sediment in the left housing and the carbon in the second housing. Put the DI-MC-10 in the third housing, and run water through the fourth, empty housing and allow it to drain until the right meter “in” probe reads 000. Once you reach this number, put in the DI-SB-10 and let it run to drain until the right meter “out” probe reads 000.
Here is a chart of the areas that are known to have the most contaminants of arsenic, lead, halo-acetic acids, total trihalomethanes, which have been linked to cancer, and total coliform bacteria.
Perhaps you believe that the standard filter in your refrigerator will be sufficient to remove these harmful contaminants, but this simply isn’t true. The filter in your refrigerator is meant to remove only the contaminants that cause foul tastes and chlorine. It does not reduce total dissolved solids (TDS) such as calcium and magnesium, nor does the refrigerator filter remove arsenic.
If you feel that your water tastes fine when it is cold try tasting it again once it is at room temperature, and you’ll taste the difference!
The RO membrane is the workhorse of the water purification system. It uses a thin film (membrane) technology to reject impurities. RO membranes are especially good at rejecting large atoms, molecules, and other items that exhibit a relatively strong electron charge. It is less effective in rejecting small atoms, molecules smaller than water, and those with relatively weak electron charge. RO membranes will allow all dissolved gases, including ammonia and carbon dioxide to pass through. The percent rejection rating for a membrane is an indication of how many of these impurities will pass through the membrane and on to the DI cartridge.
A membrane that has a 98 percent rejection rating will pass about half of the impurities that a membrane with a rating of 96 percent will pass. The direct result of using a 98 percent rejection membrane as opposed to a 96 percent membrane, is that the life of your DI cartridge will be doubled. It is important to note that all membrane manufacturers adhere to a lower percent rejection limit for small membranes, which means that you need to purchase your membranes from a source that screens for higher rejection rates to ensure that you are getting the quality you need.
Our experience has been that not all RO membranes are the same. SpectraPure's membranes are treated with a proprietary process to enhance percent rejection and production characteristics. We have been testing our RO membranes for more than 20 years, using the industry standard of 60psi. We have a significant amount of data to draw upon when sharing performance characteristics with our customers.
Rejected membranes are sold to another, far less demanding market. The difference in price reflects some of our investment to perform necessary testing. The price difference between a membrane that is tested and a membrane that is untested becomes insignificant when you obtain a one or two percent improvement in rejection and the life of your DI cartridge is extended. Even our untested membranes are subjected to a proprietary process which increases their rejection ratio over units purchased by other vendors from the same supplier. Those who claim that all membranes from a particular vendor are exactly the same may not be aware of the intensive testing processes we use to increase our rejection rates.
Critical products like membranes, DI cartridges, filters, housings, gauges, valves, and pumps are exhaustively tested and analyzed in the lab and field, to make sure they meet our performance standards before you make your purchase.
Ice makers usually need at least 30 Psi to operate. If you are supplying RO water to your ice maker, then you may have a problem.
The pressure of the RO water as it leaves a pressurized storage tank is dependent on the pressure of the incoming tap water. The pressurized tank will have about 1/2 to 2/3 as much pressure when compared with the pressure of the incoming tap water. For example, if your tap water pressure is at 50 Psi, then the tank pressure will be about 25 Psi. Make sure when you supply water to an ice maker that you have sufficient pressure for the ice maker to function.
If you have a problem with your ice maker due to low pressure, then please call for an alternative solution.
Flushing the membrane helps to prevent membrane scaling and plugging. When a system is used in an area with particularly high TDS, or hard water, you are more likely to experience these types of problems. A system run at a low ratio 2:1 will greatly benefit from employing a flush mechanism, especially in cases where there is high TDS. For more information on why it is beneficial to flush the membrane, be sure to read this article from DOW.
Years ago, vendor specs for the best membrane were at 96 percent minimum, with 98 being typical. SpectraPure® tested each of these membranes individually to select the ones that had the best performance. These membranes were sold as our SpectraSelect™ greater than 98 percent rejection guaranteed. Those membranes that did not make the grade were used in less critical applications or simply returned to the supplier.
Around this time, SpectraPure also developed an in-house, proprietary treatment process to enhance rejection, increase production, and decrease rinse time. We still use this process today, regardless of the source material as the benefits are substantial for high-purity water production.
These original SpectraSelect membranes could easily provide a customer with a two percent rejection increase over the bottom end of the specification of the leading membranes of the time. 96 percent rejection was the bottom end of the spec, and greater than 98 percent rejection was our treated, individually tested, and verified guarantee.
You may ask why 98 percent rejection is so much more important than 96 percent rejection. How does a small, two percent increase save money in operation costs? In this case, going from 96 percent to 98 percent rejection increase cuts the ionic load passed on to the Di section of your RODI system in half! Cutting the load in half doubles the life of the DI section, which cuts your costs in half.
Case#1 Impact of going from 96% to 98% rejection on typical feed
|Raw Water TDS||96% rejection||98% rejection||Improvement||DI Life|
Our newest membrane is treated with our in-house, proprietary process to enhance rejection, and increase production. Each membrane is individually tested to guarantee a minimum of 98 percent rejection with an average rejection of 99 percent. Our new 99 percent rejection SpectraSelectPlus™ membrane blows away the competition! It is simply the best available membrane for the money.
Is a one percent increase over our old SpectraSelect membrane really worth it? See the chart below, which shows that a one percent increase at these high levels of rejection still doubles the life of your DI!
Case #2 Impact of going from 98% to 99% rejection on typical feed
|Raw Water TDS||98% rejection||98% rejection||Improvement||DI Life|
|270||8.1||5.4||150%||One and a half|
What if I currently have 97 percent rejection and I upgrade to 99 percent with the SpectraSelectPlus? The chart below shows that if you go from the minimum competitor rejection spec of 97 percent to our typical SpectraSelectPlus™ 99 percent rejection, you can expect to see an increase in the life of your DI membrane by triple!
Case #3 Impact of going from 97% to 99% rejection on typical feed
|Raw Water TDS||97% rejection||99% rejection||Improvement||DI Life|
If I currently have 96 percent rejection now, what will 99 percent rejection do for my operating costs? A 99 percent rejection membrane will quadruple the life of your DI membrane. The information in the chart below makes a strong case for using the best membrane in your system. Improved rejection performance pays huge dividends in the life of your DI membrane!
Case #4 Impact of going from 96% to 99% rejection on typical feed
|Raw Water TDS||96% rejection||99% rejection||Improvement||DI Life|
With the life of my DI membrane being extended to such great lengths, when should I change the membrane? See the chart below which shows the impact of your rejection degrading from 98 percent to 95 percent, which is when the life of your DI membrane is cut in half.
Case #5 Impact of going from 98% to 95% rejection on typical feed
|Raw Water TDS||98% Rejection||95% Rejection||Increase in Ionic Load||DI Life|
Please note that these calculations make the assumption that no CO2 is present, since it is not removed by your RO membrane. CO2 can significantly degrade the life of your DI membrane. High pH, which includes contaminants such as chloramines will also affect performance. The typical calculation charts shown reflect the IONIC load improvements relative to each rejection improvement.