This information is aimed towards a crowd containing virtually no knowledge about Reverse Osmosis and can try to explain the essentials in simple terms which should leave your reader with a better overall knowledge of Reverse Osmosis technology and its applications.
To understand the purpose and process of backwashing systems you have to first know the naturally occurring procedure for Osmosis.
Osmosis is really a natural phenomenon and probably the most important processes in nature. It is actually a process wherein a weaker saline solution will often migrate into a strong saline solution. Samples of osmosis are when plant roots absorb water in the soil and our kidneys absorb water from our blood.
Below is really a diagram which shows how osmosis works. An answer that may be less concentrated will have an organic tendency to migrate to some solution having a higher concentration. As an example, should you have had a container full of water using a low salt concentration and another container full of water by using a high salt concentration plus they were separated with a semi-permeable membrane, then your water using the lower salt concentration would start to migrate towards water container together with the higher salt concentration.
A semi-permeable membrane is really a membrane that will allow some atoms or molecules to successfully pass however, not others. A simple example is a screen door. It allows air molecules to pass through although not pests or anything larger than the holes within the screen door. Another example is Gore-tex clothing fabric that contains an exceptionally thin plastic film into which vast amounts of small pores have been cut. The pores are large enough permit water vapor through, but small enough in order to avoid liquid water from passing.
Reverse Osmosis is the procedure of Osmosis in reverse. Whereas Osmosis occurs naturally without energy required, to reverse the whole process of osmosis you should apply energy to the more saline solution. A reverse osmosis membrane can be a semi-permeable membrane that enables the passage of water molecules but not virtually all dissolved salts, organics, bacteria and pyrogens. However, you must ‘push’ water from the reverse osmosis membrane by using pressure that is certainly higher than the naturally sourced osmotic pressure as a way to desalinate (demineralize or deionize) water at the same time, allowing pure water through while holding back most contaminants.
Below is a diagram outlining the whole process of Reverse Osmosis. When pressure is used towards the concentrated solution, this type of water molecules are forced with the semi-permeable membrane and also the contaminants are certainly not allowed through.
Reverse Osmosis works through a high pressure pump to increase pressure on the salt side of your RO and force water across the semi-permeable RO membrane, leaving nearly all (around 95% to 99%) of dissolved salts behind from the reject stream. The volume of pressure required is determined by the salt power of the feed water. The greater concentrated the feed water, the greater pressure is needed to overcome the osmotic pressure.
The desalinated water that is demineralized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that failed to pass through the RO membrane is called the reject (or concentrate) stream.
As the feed water enters the RO membrane under pressure (enough pressure to overcome osmotic pressure) this type of water molecules pass through the semi-permeable membrane and also the salts as well as other contaminants are certainly not allowed to pass and are discharged with the reject stream (also called the concentrate or brine stream), which would go to drain or can be fed into the feed water supply in certain circumstances to become recycled throughout the RO system to save water. Water which make it through the RO membrane is named permeate or product water and usually has around 95% to 99% from the dissolved salts taken off it.
It is important to recognize that an RO system employs cross filtration as opposed to standard filtration where contaminants are collected in the filter media. With cross filtration, the perfect solution passes throughout the filter, or crosses the filter, with two outlets: the filtered water goes a technique and also the contaminated water goes another way. To prevent increase of contaminants, cross flow filtration allows water to sweep away contaminant build-up as well as allow enough turbulence to keep the membrane surface clean.
Reverse Osmosis can perform removing up to 99% from the dissolved salts (ions), particles, colloids, organics, bacteria and pyrogens from the feed water (although an RO system ought not to be relied upon to eliminate 100% of viruses and bacteria). An RO membrane rejects contaminants depending on their size and charge. Any contaminant that includes a molecular weight higher than 200 is likely rejected with a properly running RO system (for comparison a water molecule includes a MW of 18). Likewise, the higher the ionic control of the contaminant, the more likely it will be struggling to move through the RO membrane. By way of example, a sodium ion only has one charge (monovalent) and is also not rejected through the RO membrane in addition to calcium for example, which has two charges. Likewise, for this reason an RO system will not remove gases such as CO2 well since they are not highly ionized (charged) while in solution where you can extremely low molecular weight. Because an RO system will not remove gases, the permeate water will have a slightly below normal pH level depending on CO2 levels inside the feed water because the CO2 is changed into carbonic acid.
Reverse Osmosis is extremely great at treating brackish, surface and ground water for large and small flows applications. A few examples of industries which use RO water include pharmaceutical, boiler feed water, food and beverage, metal finishing and semiconductor manufacturing for example.
You will find a handful of calculations that are utilized to judge the performance of your RO system as well as for design considerations. An RO system has instrumentation that displays quality, flow, pressure and quite often other data like temperature or hours of operation.
This equation tells you how effective the RO membranes are removing contaminants. It can not inform you how every individual membrane is performing, but just how the system overall generally has been doing. A highly-designed RO system with properly functioning RO membranes will reject 95% to 99% on most feed water contaminants (which are of a certain size and charge).
The better the salt rejection, the better the device is performing. A small salt rejection can mean how the membranes require cleaning or replacement.
This is simply the inverse of salt rejection described in the earlier equation. This is the level of salts expressed as a percentage that happen to be passing from the RO system. The reduced the salt passage, the greater the system is performing. A very high salt passage often means how the membranes require cleaning or replacement.
Percent Recovery is the amount of water that may be being ‘recovered’ pretty much as good permeate water. A different way to consider Percent Recovery is the quantity of water which is not brought to drain as concentrate, but collected as permeate or product water. The greater the recovery % means that you will be sending less water to empty as concentrate and saving more permeate water. However, in case the recovery % is simply too high for your RO design then it can cause larger problems because of scaling and fouling. The % Recovery for the RO product is established through the help of design software taking into consideration numerous factors for example feed water chemistry and RO pre-treatment prior to the RO system. Therefore, the right % Recovery where an RO should operate at is dependent upon just what it was created for.
For instance, in the event the recovery rate is 75% then which means that for each 100 gallons of feed water that enter into the RO system, you will be recovering 75 gallons as usable permeate water and 25 gallons are going to drain as concentrate. Industrial RO systems typically run between 50% to 85% recovery depending the feed water characteristics and other design considerations.
The concentration factor relates to the RO system recovery and is an important equation for RO system design. The better water you recover as permeate (the better the % recovery), the more concentrated salts and contaminants you collect within the concentrate stream. This may lead to higher possibility of scaling at first glance of the RO membrane when the concentration factor is way too high for that system design and feed water composition.
The idea is the same as that of a boiler or cooling tower. They both have purified water exiting the machine (steam) and turn out leaving a concentrated solution behind. As being the level of concentration increases, the solubility limits may be exceeded and precipitate on top in the equipment as scale.
For instance, if your feed flow is 100 gpm along with your permeate flow is 75 gpm, then your recovery is (75/100) x 100 = 75%. To find the concentration factor, the formula can be 1 ÷ (1-75%) = 4.
A concentration factor of 4 implies that the liquid going to the concentrate stream will be 4 times more concentrated in comparison to the feed water is. If the feed water in this particular example was 500 ppm, then your concentrate stream could be 500 x 4 = 2,000 ppm.
The RO system is producing 75 gallons each minute (gpm) of permeate. You may have 3 RO vessels with each vessel holds 6 RO membranes. Therefore you have a total of three x 6 = 18 membranes. The sort of membrane you might have in the RO method is a Dow Filmtec BW30-365. This type of RO membrane (or element) has 365 square feet of surface.