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Integrated systems up to 50 gallons per minute can occupy a space of approximately 6 feet by 15 feet by 6 feet high without storage tanks. A 30 minute holding tank after the system is usual and if recycling is used, a 10 minute storage tank to feed the reverse osmosis pump is used.
Small systems will have to shut down but in larger (>10 gpm) systems, the individual portions of the plant can be isolated and cleaned one at a time and only part of the flow will be lost.
There are various pretreatment configurations that will work on the front of an reverse osmosis water system. Part of the selection is based on the capabilities and experience of you maintenance staff. The better preventative maintenance you have, the easier it will be to maintain a chemical addition system. Chemical metering systems require more daily maintenance and calibration to insure consistant operation. Fixed bed systems such as softeners and carbon beds require little daily maintenance.
Water must have a very low silt (solids) content to keep the membranes from plugging up. This can be accomplished by removing the solids or keeping them in suspension while passing through the system. Chemicals can be added to the incoming water to keep the solids in suspension or efficient filtration can be used. We prefer to remove all solids before the system which results in the lowest rate of membrane plugging.
As the water passes through the reverse osmosis system, the ionic content of the reject stream increases as water permeates the membranes. This increase in TDS can results in calcium and magnesium (the hardness ions) precipitating out in the system and plugging the membranes. Again, either the Calcium and Magnesium can be removed or a chemical can be added to keep them in solution. We prefer using a water softener to remove the hardness ions and replace them with sodium.
Chlorine must be removed for thin film membranes and should be minimal for CTA membranes. Either it can be removed by carbon treatment or reduced with a chemical addition of sodium metabisulfite. The carbon is preferred because the chemical addition can enhance bacterial growth in the system which can plug the membranes.
The amount of reject water will vary with the configuration of the system. Up to 6 membranes(RO) can be connected in series and the theoretical capture rate is about 84% (rejecting 16%). We have use oversized systems and redirected the reject to the front of the system for a multiple pass system and have gotten recovery's of about 92% (half or the reject to drain, half to the system feed tank). This does require oversizing the pumps and system size to get the required flow rate. Reject water is discharged directly to drain. Usually the TDS is less than 1500 ppm and there are no contaminants. If a system is used to recycle some water after a plating application, monitoring of the reject may be necessary.