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[Article Title]Optional features in RO system design
[Artical Suimmary] They may not be critical, but they can save much time and expense.
[Article Contect]
However, at pH 7, H2S is mostly (75 percent) ionic and only 25 percent gas, so you will get precipitation on the membrane in the form of ionic sulfur that will eventually foul the membrane. The flush system will help lower the fouling potential by pushing it from the membrane at higher flows.
Why not just remove H2S before the unit as you would hardness or iron?
Recall the pH. Even conventional treatments will not get all H2S, and then it will enter the RO as ionic sulfur and foul the inlet feed spaces more rapidly. But why add the extra cost to treat a gas? It抯 better to allow it to pass through, because once the membrane lowers bicarbonate levels, the permeate pH will drop, the H2S will reconvert to 80-90 percent gas, and it can be aerated in the storage tank.
With brackish or seawater systems, the flush cycle is activated typically upon shutdown of the RO and is done with clean permeate to lower the salt content on the membrane during dormant stages. (It抯 not a bad idea to do this with any well application.)
Storage tank
When choosing a tank, determine first where the tank will be located and whether it will fit through building openings to get it there. Most tanks are polyethylene and have a minimum 16-inch manway on top.
You want to size the tank for peak usage of daily requirements. The average home will require 15 gallons per minute service flows, but only for short periods ?usually between 6 and 8 a.m. and 5 and 8 p.m. However, on the weekends all bets are off. I've seen my family go through five loads of laundry on a Saturday while also running the dishwasher and giving baths to kids.
Nevertheless, if you estimate an average of 100 gallons per person per day, you can size the tank accordingly. The distribution pump should be sized for the 15 gpm usage at a 50-60 psi discharge. When determining the discharge, you need to look at elevation, pipe size and friction loss so you dont end up with a dribble at the furthest point of use.
I have been using submersible pumps (1/2 horsepower) inside a 4-inch sleeve. I rest the sleeve on a saddle I make, making sure water flow comes from the end with the motor so that it remains cool during operation. The pump should be made of non-corrosive materials such as Noryl or stainless steel.
After storage, you can add on the distribution line post-treatment in the form of calcium carbonate to raise pH, ultraviolet disinfection, or chlorine if required by regulations.
