FREQUENTLY ASKED QUESTIONS Index
| What is osmosis? | Go to Top | |
| Osmosis refers to the passage of water through a thin semipermeable membrane from the side with low salt concentration to the side with higher salt concentration. This can happen even when the water level is higher on the high salt side and the water must move against a pressure difference. The bottom line is that osmosis refers to a concentration difference manifesting itself as a pressure difference. | ||
| What is reverse osmosis (RO)? | ||
| The other side of the coin is reverse osmosis. A difference in pressure is used to cause a difference in salt concentration. It is as though the pressure is being used to force the water molecules through the membrane while retaining the larger salt. Salt means any inorganic compound dissolved in water. When water is processed by reverse osmosis a large fraction of dissolved material is removed. The cleaner the input water the cleaner the output water will be. Conversely, if your input water is clean enough, you may not need an RO unit. | ||
| What are the alternatives to RO? | Go to Top | |
| Distillation | ||
| produces clean water by evaporating the water from the input and condensing the steam. It is highly energy-intensive and expensive unless you have a free source of waste heat. Distillation systems tend to be low capacity. | ||
| Ion-exchange | ||
| systems work by exchanging cations such as calcium and magnesium for the cation on the resin, usually sodium, potassium or hydrogen. They also exchange anions like carbonate and sulfate for the anion on the resin, usually chloride or hydroxyl. These systems can be recharged and should be as the resins are very expensive. The recharging may be just a small annoyance (as with sodium chloride resins) or potentially hazardous (as with hydrogen/hydroxyl resins). | ||
| How do I know what is in my drinking water? | ||
| If you are on city water, your local water must meet very strict Federal and State standards for purity. However, many areas use ground water (well water) high in minerals and salts. This can affect taste. All municipally treated water is chlorinated, and this can also affect taste and create odors in the water. If you are on a private well or spring, you should have your water tested. Contact AWS for specific recommendations. | ||
| Will RO's remove hardness minerals or help cut down on scale build-up in coffee pots, etc.? | Go to Top | |
| Yes! Most water contains "total dissolved solids" (TDS), which is roughly the total inorganic mineral content of the water, and these are removed. The reverse osmosis membrane separates these dissolved solids, or salts and flushes them down the drain. | ||
| Will these systems remove lead? | ||
| Yes. Both the RO membrane and the carbon block filter will reduce the lead. Carbon block filters use a lead-specific filter media combined with the carbon to reduce lead. | ||
| Will these systems remove parasites or cysts? | Go to Top | |
| Yes. The RO systems are certified for cyst removal. | ||
| Are bacteria a problem with reverse osmosis systems? | ||
| Yes and no. We have tested many of our systems for total bacteria counts over the years and have not found higher levels after the systems unless the systems sat for several days in between uses. However, in some cases, bacteria can grow, particularly when the source water is high in bacteria and/or low in chlorine residual. We also have Ultra-Violet Sterilizer Systems that disinfect water after it leaves the filter system, insuring water low in bacteria. The manufacturers state in their warranty information that the RO systems are designed to be installed on water that is disinfected or does not have dangerous bacteria such as e.coli. | ||
| Are RO systems difficult to install? | Go to Top | |
| No. The RO systems come complete with tubing, fittings and items required to install it. In some cases you may need to drill a new hole in your sink, or you can use an existing hole to install the RO faucet. Typically a plumber will take 20 minutes to read the installation instructions and 1 to 1-1/2 hours to do a professional installation, but many homeowners have installed these themselves. | ||
| How often should I change the filters in an RO system? | ||
| The filters should be changed once a year. The membrane should be changed every 3 to 5 years depending on the TDS levels in the purified water. | ||
| What does mean by 'Recovery' of RO system? | Go to Top | |
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'Recovery' of RO system is defined as ratio of Permeate Flow to the Feed Flow. % Recovery = Permeate Flow/Feed Flow X 100 For e.g. : If feed Flow is 100 m3/hr and Permeate Flow is 60 m3/hr Then Recovery of RO System is 60 %. Recovery = 60 m3/hr/100 m3/hr X 100 = 60 %. |
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| What is meaning of 'Salt Passage'? | ||
| Theoretically no salt should pass through RO membrane. But no membrane is 100% perfect. Hence some salt does pass through imperfections on the membrane. Passage of this salt is called 'Salt Passage'. % Salt Passage = Permeate TDS/Feed TDS X 100 | ||
| What is meaning of 'Salt rejection'? | Go to Top | |
| The percentage of Solute concentration removed from system feed water by the membrane is called 'Salt rejection'. % Salt rejection = (1 - Salt Passage) X 100 | ||
| What does it mean by 'Permeate water'? | ||
| Purified product water produced by membrane is called 'Permeate water' of RO system. | ||
| What is meaning of 'Reject water'? | Go to Top | |
| Concentrated high TDS water is rejected by membrane is called 'Reject water' of RO system. | ||
| What does mean by 'Flux'? | ||
| The rate of Permeate water transported per unit membrane area is called 'Flux' of RO system. | ||
| What is MOC for RO membrane? | Go to Top | |
| Polyamide and Cellulose acetate are the MOC for RO membrane. | ||
| Does RO system require cleaning? | ||
| Yes, RO system needs cleaning frequently, to remove scaling and fouling from the membrane surface, to improve system performance. | ||
| What factors affect RO performance? | Go to Top | |
| Pressure, temperature, recovery and feed water salt concentration are the factors which mainly influence the RO performance. | ||
| Can I use RO reject water for other applications? | ||
| If RO reject TDS is 1000 ppm, we can use it for gardening purpose and toilet flushing purpose. RO reject water having TDS 1000 ppm to 2000 ppm can also be selectively used for plantation as some plants survive and grow on High TDS water. | ||
| Is pH correction required for RO system? | Go to Top | |
| In some process application where neutral pH (pH 7) is desired, pH correction is required for RO permeate water. pH of RO permeate water is slightly acidic in nature. It is around 5.5 to 6.4. Normally pH correction is carried out by caustic or Soda ash solution or by using degasser system. Degasser system removes CO2 (Carbon dioxide) from water and raise pH of water up to 7 (neutral pH). | ||
| What is feed water limiting condition for RO system? | ||
| Following are the feed water limiting condition for RO system. | ||
| a) Chlorine | : Nil | |
| b) Suspended solids | : < 1 ppm | |
| c) Turbidity | : < 1 NTU | |
| d) SDI | : < 4 | |
| e) BOD and COD | : Nil ( In some cases 10 ppm tolerable ) | |
| f) Heavy metals | : Nil | |
| g) Oil and grease | : Nil | |
| h) pH (for cellulose acetate membrane) | : 4 - 6 | |
| (for Polyamide membrane) | : 3 - 11 |
| Does chlorine affect RO membrane? | Go to Top | |
| Yes, if chlorine is present in RO feed water, it will oxidize RO membrane and will increase the pore size of RO membrane. It will deteriorate RO permeate water quality. Hence chlorine should be Nil in RO feed water. Activated carbon filter and SMBS dosing system are provided in pretreatment to prevent chlorine from entering RO membrane. | ||
| What is tolerable limit for iron for RO system? | ||
| Iron in feed water should be less than 0.3 ppm for trouble free and safe operation of RO system. Fouling will take place on RO membrane and it will reduce RO permeate flow, if iron is more than 0.3 ppm. | ||
| What is the life of reverse osmosis membrane? | Go to Top | |
| RO membrane will last for at least 3 years with proper operation and maintenance of RO plant and with proper pretreatment system. | ||