This article is aimed towards an audience which has little if any knowledge of Reverse Osmosis and will make an attempt to explain the essentials in simple terms that will leave your reader using a better overall idea of Reverse Osmosis technology and its applications.
To understand the aim and process of reverse osmosis systems you should first know the natural procedure for Osmosis.
Osmosis is a naturally sourced phenomenon and probably the most important processes in nature. It is actually a process when a weaker saline solution will usually migrate to your strong saline solution. Instances of osmosis are when plant roots absorb water in the soil and our kidneys absorb water from the blood.
Below is a diagram which shows how osmosis works. An alternative that is less concentrated may have an organic tendency to migrate to a solution having a higher concentration. As an example, should you have had a container full of water with a low salt concentration and the other container filled with water with a high salt concentration and so they were separated with a semi-permeable membrane, then the water together with the lower salt concentration would start to migrate for the water container together with the higher salt concentration.
A semi-permeable membrane can be a membrane that will permit some atoms or molecules to pass although not others. An easy example can be a screen door. It allows air molecules to pass through through but not pests or anything greater than the holes in the screen door. Another example is Gore-tex clothing fabric that contains an exceptionally thin plastic film into which billions of small pores happen to be cut. The pores are large enough to allow water vapor through, but sufficiently small in order to avoid liquid water from passing.
Reverse Osmosis is the process of Osmosis in reverse. Whereas Osmosis occurs naturally without energy required, to reverse the process of osmosis you must apply energy to the more saline solution. A reverse osmosis membrane is really a semi-permeable membrane that permits the passage water molecules yet not the majority of dissolved salts, organics, bacteria and pyrogens. However, you should ‘push’ the water with the reverse osmosis membrane by using pressure that is greater than the natural osmotic pressure as a way to desalinate (demineralize or deionize) water during this process, allowing pure water through while holding back most contaminants.
Below is a diagram outlining the procedure of Reverse Osmosis. When pressure is used to the concentrated solution, the water molecules are forced through the semi-permeable membrane as well as the contaminants are certainly not allowed through.
Reverse Osmosis works using a high-pressure pump to boost the stress on the salt side in the RO and force water throughout the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind within the reject stream. The quantity of pressure required is determined by the salt concentration of the feed water. The more concentrated the feed water, the more pressure is necessary to overcome the osmotic pressure.
The desalinated water that may be demineralized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that failed to move through the RO membrane is referred to as the reject (or concentrate) stream.
Because the feed water enters the RO membrane under pressure (enough pressure to overcome osmotic pressure) water molecules move through the semi-permeable membrane as well as the salts as well as other contaminants are not able to pass and are discharged from the reject stream (also called the concentrate or brine stream), which goes toward drain or can be fed into the feed water supply in some circumstances to become recycled through the RO system to save water. The liquid which make it through the RO membrane is called permeate or product water and in most cases has around 95% to 99% of the dissolved salts removed from it.
It is essential to understand that an RO system employs cross filtration rather than standard filtration where the contaminants are collected within the filter media. With cross filtration, the remedy passes with the filter, or crosses the filter, with two outlets: the filtered water goes one way and the contaminated water goes another way. To prevent build-up of contaminants, cross flow filtration allows water to sweep away contaminant develop and also allow enough turbulence to maintain the membrane surface clean.
Reverse Osmosis can perform 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 viruses and bacteria). An RO membrane rejects contaminants based upon their size and charge. Any contaminant which has a molecular weight more than 200 is likely rejected by a properly running RO system (for comparison a water molecule features a MW of 18). Likewise, the higher the ionic control of the contaminant, the more likely it will likely be unable to move through the RO membrane. As an example, a sodium ion only has one charge (monovalent) which is not rejected from the RO membrane along with calcium by way of example, that has two charges. Likewise, that is why an RO system will not remove gases for example CO2 very well as they are not highly ionized (charged) when in solution and have a very low molecular weight. Because an RO system fails to remove gases, the permeate water can have a slightly below normal pH level dependant upon CO2 levels inside the feed water because the CO2 is converted to carbonic acid.
Reverse Osmosis is very good at treating brackish, surface and ground water for large and small flows applications. Examples of industries which use RO water include pharmaceutical, boiler feed water, food and beverage, metal finishing and semiconductor manufacturing among others.
There are a couple of calculations that are employed to judge the performance of any RO system plus for design considerations. An RO system has instrumentation that displays quality, flow, pressure and often other data like temperature or hours of operation.
This equation tells you how effective the RO membranes are removing contaminants. It will not let you know how every person membrane is performing, but alternatively just how the system overall normally is performing. A properly-designed RO system with properly functioning RO membranes will reject 95% to 99% of the majority of feed water contaminants (which are of your certain size and charge).
The better the salt rejection, the better the program has been doing. A small salt rejection often means that this membranes require cleaning or replacement.
This is merely the inverse of salt rejection described in the previous equation. This is the quantity of salts expressed as a percentage that are passing throughout the RO system. The less the salt passage, the better the program is performing. A higher salt passage can mean that this membranes require cleaning or replacement.
Percent Recovery is the amount of water which is being ‘recovered’ nearly as good permeate water. An alternate way to imagine Percent Recovery is the volume of water that is not delivered to drain as concentrate, but collected as permeate or product water. The better the recovery % means that you will be sending less water to drain as concentrate and saving more permeate water. However, when the recovery % is way too high for your RO design then it can lead to larger problems because of scaling and fouling. The % Recovery to have an RO method is established with the aid of design software bearing in mind numerous factors like feed water chemistry and RO pre-treatment ahead of the RO system. Therefore, the appropriate % Recovery where an RO should operate at is dependent upon what it was created for.
For example, if the recovery rate is 75% then this means that for each and every 100 gallons of feed water that go into the RO system, you will be recovering 75 gallons as usable permeate water and 25 gallons are likely to drain as concentrate. Industrial RO systems typically run any where 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 really a equation for RO system design. The greater number of water you recover as permeate (the higher the % recovery), the greater number of concentrated salts and contaminants you collect in the concentrate stream. This might lead to higher possibility of scaling at first glance from the RO membrane as soon as the concentration factor is simply too high for that system design and feed water composition.
The reasoning is no different than those of a boiler or cooling tower. They both have purified water exiting the device (steam) and end up leaving a concentrated solution behind. Because the standard of concentration increases, the solubility limits may be exceeded and precipitate on top of your equipment as scale.
For example, if your feed flow is 100 gpm as well as your permeate flow is 75 gpm, then the recovery is (75/100) x 100 = 75%. To get the concentration factor, the formula will be 1 ÷ (1-75%) = 4.
A concentration factor of 4 ensures that water going to the concentrate stream will likely be 4 times more concentrated compared to the feed water is. If the feed water with this example was 500 ppm, then your concentrate stream could be 500 x 4 = 2,000 ppm.
The RO system is producing 75 gallons each and every 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 possess in the RO system is a Dow Filmtec BW30-365. This particular RO membrane (or element) has 365 sq ft of surface.