| Osmosis is the flow from a high concentration of | | | | Effect of Temperature |
| water to a low concentration of water. To help | | | | Temperature has a direct linear effect to production |
| understand the flow of water imagine a sealed filled | | | | rates. As temperature increase, water production |
| water balloon with a hole in it – what happens to | | | | increases almost linearly because of the higher |
| the water inside? The water quickly leaves balloon | | | | diffusion rates of water through the membrane. |
| because of the concentration of water inside the | | | | Rejection rates are actually lowered when |
| balloon is higher than outside which makes the water | | | | temperature rises. This is due to a higher diffusion |
| wants to equalize the concentration of water. | | | | rate of salt across the membrane. |
| Reverse osmosis is quite the opposite. The flow of | | | | Effect of Salt Concentration or TDS |
| water is from a low concentration to a high | | | | TDS inversely affects the pressure required for |
| concentration. Imagine an empty balloon – if | | | | reverse osmosis which in turn affects the production |
| you’re filling the water balloon with a hose then you | | | | rates. If feed water was constant and TDS |
| are using the water pressure and forcing water | | | | increases then the production rate decreases because |
| against its natural equalization tendencies. | | | | of the osmotic pressure difference. |
| A reverse osmosis (ro) membrane is simply a thin | | | | Osmotic pressure is the pressure and potential energy |
| semi-permeable layer that separates two solutions. | | | | required to force water to move against its natural |
| A ro membrane is a type of physical separation that is | | | | direction across a semi-permeable membrane. Every |
| capable of separating molecules down to 1/10,000 | | | | 100 ppm (parts per million) in TDS equals 1 psi (pounds |
| micron. Since the size of the pores on the | | | | per square inch). The higher the TDS, the more |
| membrane is so small, it requires pressure to force | | | | pressure required to force through the membrane. |
| water through. Most molecules are too large to pass | | | | Effect of Recovery Rates |
| through a reverse osmosis membrane but small | | | | Recovery rate refers to the amount of product water |
| enough for some salts, sugars and water molecules to | | | | being produced which is controlled by the flow |
| pass through. Rejection rates of ro membranes | | | | restriction on the waste line. Most reverse osmosis |
| average around 96-98% under ideal conditions (250 | | | | systems are sized with a sized flow restrictor will |
| ppm softened tapwater, 77°F (25°C), 50 psig (3.4 | | | | have a product to waste ratio of 1 to 4 which is a |
| bar), and 15% recovery). | | | | recovery rate of 25% this is made purposefully as a |
| TDS levels, temperature, pressure and recovery rates | | | | sales point to produce more product water but lower |
| are all things that affect the product water quality of | | | | the rejection rate. For example, the proper size for a |
| reverse osmosis membrane. | | | | 50 GPD membrane is a 15% recovery rate or a 1 to |
| Effect of Pressure | | | | 6.7 ratio. Lowering the recovery rates will increase |
| Feed water pressure affects both the product water | | | | the rejection rate and improve the quality of water. |
| production and the rejection rates of RO membranes. | | | | Raising the recovery rates will cause the quality of the |
| The increase of feed water pressure directly | | | | product water to decrease and will affect the required |
| increases the water production. | | | | driving pressure needed for reverse osmosis to take |
| Rejection rates also increase when pressure is | | | | effect. |
| increased but will plateau. | | | | |