Simply expressed, water is pressurized and forced through an extremely thin sheet of specially formulated plastic sheet. The higher the pressure, the more water passes through. The thin sheet (membrane) passes water and traps a high (95% plus) percentage (rejection) of everything (dissolved solids) in the water. The trapped items exit the membrane as a waste (concentrate) stream and the balance (permeate) stream is collected. The permeate stream normally represents 50% to 80% (recovery) of the water entering the membrane
There are basic steps in processing water with a commercial reverse system that must be considered in the design and application of the systems. They are:
1. PRETREATMENT. Often overlooked or poorly designed, this step determines system life cycle, maintenance requirements and overall performance. The following must be addressed —
- Turbidity (undissolved solids) reduction to at least 5 microns. The porosity of the membrane down to 0.0002 microns makes it an excellent filter, but unaddressed turbidity will plug membranes in as little as hours.
- Iron and manganese removal to nondetectable or trace amounts. Both severely lower membrane life and/or cause frequent membrane cleaning.
- Hard water scale prevention. Hard water scale rapidly stops treated water flow. There are alternative prevention methods less costly and more environmentally friendly than water softeners. These include our ESF, Aquafer, Maxi-Cure and chemical feed systems.
- Chlorine and organics removal. Both shorten membrane life.
- Biologics removal. Like turbidity, biomasses plug membranes. Chemical feed (chlorine, hydrogen peroxide), ozone or Ultra Violet needs to be employed
2. HIGH-PRESSURE PUMP. It should be selected so that during system operation, the pump motor is not maxed out and is operating near the highest efficiency point.
3. MEMBRANE SELECTION. This should be tailored to your specific needs of optimizing water quality, water use efficiency, specific contaminant removal, etc. There is no universal type.
4. ELECTRICAL CONTROLS. Ultimately, they all do the same thing, so simplicity, cost and serviceability are primary considerations. Being able to by-pass controls while producing water in an emergency is important.
5. DUTY CYCLE. It should not be a surprise that something running 24/7 will require more frequent service and parts replacement than one operating 1/3 to ½ the time. Selecting a larger system also provides business increase wiggle room.
6. TREATED WATER STORAGE. R.O. units seldom deliver treated water at a required flow rate. To overcome this, storage with re-pressurization is needed. Tanks should be sized in anticipation of occasional system downtime.