This information is aimed towards viewers that has little or no experience with Reverse Osmosis and definately will attempt to explain the basics in simple terms which should leave your reader with a better overall understanding of Reverse Osmosis technology and its particular applications.
To know the purpose and procedure for backwashing systems you must first know the naturally occurring process of Osmosis.
Osmosis can be a naturally occurring phenomenon and one of the more important processes naturally. It is actually a process when a weaker saline solution will usually migrate to a strong saline solution. Types of osmosis are when plant roots absorb water in the soil and our kidneys absorb water from your blood.
Below is a diagram which shows how osmosis works. An alternative that is certainly less concentrated may have a natural tendency to migrate to a solution using a higher concentration. For example, if you have a container filled with water having a low salt concentration and the other container filled with water by using a high salt concentration and they were separated from a semi-permeable membrane, then a water together with the lower salt concentration would set out to migrate towards the water container with all the higher salt concentration.
A semi-permeable membrane is a membrane that will allow some atoms or molecules to pass through yet not others. A basic example is a screen door. It allows air molecules to pass through yet not pests or anything larger than the holes inside the screen door. Another example is Gore-tex clothing fabric that contains a very thin plastic film into which billions of small pores have already been cut. The pores are adequate enough to allow water vapor through, but sufficiently small to prevent liquid water from passing.
Reverse Osmosis is the procedure of Osmosis in reverse. Whereas Osmosis occurs naturally without energy required, to reverse the entire process of osmosis you should apply energy up to the more saline solution. A reverse osmosis membrane is actually a semi-permeable membrane that enables the passage water molecules however, not the vast majority of dissolved salts, organics, bacteria and pyrogens. However, you should ‘push’ water with the reverse osmosis membrane by making use of pressure which is more than the natural osmotic pressure to be able to desalinate (demineralize or deionize) water in the process, allowing pure water through while holding back a majority of contaminants.
Below is actually a diagram outlining the process of Reverse Osmosis. When pressure is applied to the concentrated solution, the water molecules are forced through the semi-permeable membrane as well as the contaminants usually are not allowed through.
Reverse Osmosis works by using a high-pressure pump to improve the stress around the salt side in the RO and force the liquid across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind within the reject stream. The amount of pressure required is dependent upon the salt power of the feed water. The greater number of concentrated the feed water, the more pressure is needed to overcome the osmotic pressure.
The desalinated water that is demineralized or deionized, is known as permeate (or product) water. This type of water stream that carries the concentrated contaminants that failed to move through the RO membrane is referred to as the reject (or concentrate) stream.
As the feed water enters the RO membrane under pressure (enough pressure to beat osmotic pressure) this type of water molecules pass through the semi-permeable membrane and also the salts and also other contaminants usually are not capable to pass and are discharged from the reject stream (also referred to as the concentrate or brine stream), which would go to drain or might be fed into the feed water supply in some circumstances being recycled through the RO system to save water. Water that makes it throughout the RO membrane is called permeate or product water and usually has around 95% to 99% of your dissolved salts taken off it.
It is important to realize that an RO system employs cross filtration rather than standard filtration where the contaminants are collected inside the filter media. With cross filtration, the perfect solution passes through the filter, or crosses the filter, with two outlets: the filtered water goes one of many ways and also the contaminated water goes yet another way. To prevent develop of contaminants, cross flow filtration allows water to sweep away contaminant build-up as well as allow enough turbulence to maintain the membrane surface clean.
Reverse Osmosis is capable of removing approximately 99% of the dissolved salts (ions), particles, colloids, organics, bacteria and pyrogens from the feed water (although an RO system really should not be relied upon to remove 100% of bacteria and viruses). An RO membrane rejects contaminants based upon their size and charge. Any contaminant which has a molecular weight more than 200 is likely rejected from a properly running RO system (for comparison a water molecule has a MW of 18). Likewise, the higher the ionic control of the contaminant, the more likely it will be unable to go through the RO membrane. For example, a sodium ion only has one charge (monovalent) which is not rejected by the RO membrane in addition to calcium for instance, which includes two charges. Likewise, that is why an RO system is not going to remove gases for example CO2 adequately because they are not highly ionized (charged) when in solution where you can extremely low molecular weight. Because an RO system is not going to remove gases, the permeate water will have a slightly less than normal pH level dependant upon CO2 levels from the feed water as the CO2 is converted to carbonic acid.
Reverse Osmosis is extremely great at treating brackish, surface and ground water for large and small flows applications. Some situations of industries that utilize RO water include pharmaceutical, boiler feed water, food and beverage, metal finishing and semiconductor manufacturing for example.
There are a few calculations that are used to judge the performance of an RO system and also for design considerations. An RO system has instrumentation that displays quality, flow, pressure and in some cases other data like temperature or hours of operation.
This equation tells you how effective the RO membranes are removing contaminants. It can not tell you how every person membrane is performing, but rather just how the system overall generally is performing. A properly-designed RO system with properly functioning RO membranes will reject 95% to 99% on most feed water contaminants (that happen to be of a certain size and charge).
The better the salt rejection, the better the system has been doing. A low salt rejection can mean that the membranes require cleaning or replacement.
This is simply the inverse of salt rejection described in the last equation. This is the volume of salts expressed as a percentage that are passing throughout the RO system. The low the salt passage, the greater the machine is performing. A higher salt passage could mean the membranes require cleaning or replacement.
Percent Recovery is the amount of water that may be being ‘recovered’ as good permeate water. An alternate way to imagine Percent Recovery is the quantity of water which is not shipped to drain as concentrate, but instead collected as permeate or product water. The greater the recovery % means that you are currently sending less water to drain as concentrate and saving more permeate water. However, in the event the recovery % is just too high for that RO design then it can cause larger problems because of scaling and fouling. The % Recovery on an RO product is established with the aid of design software bearing in mind numerous factors for example feed water chemistry and RO pre-treatment ahead of the RO system. Therefore, the appropriate % Recovery at which an RO should operate at is determined by exactly what it was designed for.
For instance, if the recovery rate is 75% then which means that for every single 100 gallons of feed water that enter in the RO system, you might be recovering 75 gallons as usable permeate water and 25 gallons will certainly drain as concentrate. Industrial RO systems typically run anywhere from 50% to 85% recovery depending the feed water characteristics and also other design considerations.
The concentration factor relates to the RO system recovery and is a vital equation for RO system design. The greater water you recover as permeate (the higher the % recovery), the greater number of concentrated salts and contaminants you collect from the concentrate stream. This may lead to higher prospect of scaling on top of your RO membrane once the concentration factor is too high for your system design and feed water composition.
The concept is no different than that from a boiler or cooling tower. Both of them have purified water exiting the system (steam) and turn out leaving a concentrated solution behind. Because the degree of concentration increases, the solubility limits may be exceeded and precipitate at first glance from the equipment as scale.
As an example, in case your feed flow is 100 gpm and your permeate flow is 75 gpm, then the recovery is (75/100) x 100 = 75%. To find the concentration factor, the formula would be 1 ÷ (1-75%) = 4.
A concentration factor of 4 ensures that the liquid coming to the concentrate stream will be 4 times more concentrated than the feed water is. When the feed water with this example was 500 ppm, then your concentrate stream can be 500 x 4 = 2,000 ppm.
The RO product is producing 75 gallons each minute (gpm) of permeate. You might have 3 RO vessels with each vessel holds 6 RO membranes. Therefore you do have a total of three x 6 = 18 membranes. The particular membrane you may have within the RO technique is a Dow Filmtec BW30-365. This kind of RO membrane (or element) has 365 sq . ft . of surface.