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General Reverse Osmosis Questions

How do I determine the flow rate in my home?

If you need to figure out the flow rate in gallons per minute of a steady flow in to a holding tank, or open discharge: To estimate the flow rate of water into your home:

  • Make sure no water is running in the house
  • Use the faucet closest to the water source (pump, tank or pipe)
  • Open the faucet completely and measure the time it takes to fill a one US gallon container
  • Divide 60 seconds by the time it took to fill the container flow rate
    EXAMPLE: If it takes 20 seconds to fill a 1 gallon container, the flow rate is 3 gallons per minute.

Can an RO System achieve 100% recovery or 100% separation?

No, 100% separation is not possible with thin film composite membranes. Also, 100% recovery is not possible with thin film composite membranes. With thin film composite membranes, there are always three streams (feed, concentrate, and permeate). As the permeate water is being produced, the feed water is being concentrated, but it can not be separated 100%. Also, since there is always a concentrate stream, 100% recovery is not possible. Percent recovery is defined by permeate flow rate divided by feed flow rate x 100%.

 What is the difference between NF & RO?

Nanofiltration is a membrane liquid separation technology that is positioned between reverse osmosis and ultrafiltration. While RO can remove the smallest of solute molecules, in the range of 0.0001 micron in diameter and smaller, nanofiltration (NF) removes molecules in the 0.001 micron range.

NF is a poly piperazine amide membrane and is essentially a lower-pressure version of reverse osmosis where the purity of product water is not as critical as pharmaceutical grade water, for example, or the level of dissolved solids to be removed is less than what is typically encountered in brackish water or seawater. As such, nanofiltration is especially suited to treatment of well water or water from many surface supplies.

Nanofiltration is used where the high salt rejection of reverse osmosis is not necessary, and yet NF is still capable of removing hardness elements such as calcium or magnesium. Sometimes referred to as "membrane softening", nanofiltration is an attractive alternative to lime softening or sodium chloride zeolite softening technologies. And since NF operates on lower pressure than does RO, energy costs are lower than for a comparable RO treatment system.

 Is there a minimum daily run time on RO membranes to keep the membrane healthy?

No, but it is better not to let membranes sit stagnant for long periods of time to avoid possible microorganism growth. If a system is going to be down for more than a week, then the membranes must be cleaned and system stored in a preservative solution. See the articles about RO & NF System Shutdown and RO Membrane Preservation & Storage. Running it for a few minutes every day accomplishes the same thing, but if it is down for less than a week, it should be fine.

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All Content on this site is  intended for informational purposes for experienced water treatment professionals only.  Applied Membranes, Inc. does not assume any liability for any damages caused by the misapplication or misinterpretation of any of the information contained on this website.
Applied Membranes, Inc. 2007