Reverse Osmosis Water Treatment Systems

Reverse Osmosis Water Treatment Systems

Reverse osmosis, or RO, is the term used to describe the membrane filter process used to remove particles as small as one angstrom (one ten-thousandth of a micron) from water. It is a pressurized filtration system and is the finest filtering system that is sometimes used at the municipal water supply level.

1. Filtration System Classifications

o For municipal water treatment systems, the particle sizes removed determines the classification. Most systems use a settling tank process and filter water through layers of sand and carbon before final disinfection stages. Other systems pass the water through membrane filters to remove particles impacting water clarity as well as waterborne pathogens. They are rated as follows:

Microfiltration systems remove particles from less than 10 microns (100,000 angstroms) down to as small as one-hundredth of a micron. These systems can remove the most common waterborne pathogens tracked by the Safe Drinking Water Act, known as giardia and cryptosporidium. The systems also remove waterborne bacteria and the larger waterborne viruses as well as most colloidal metals.

Ultrafiltrations systems remove particles larger than one-tenth micron and as small as one-thousandth micron. In addition to the waterborne materials swept by microfiltration systems, these systems also will remove small viruses and some dissolved organics.

Nanofiltration systems remove particles from one-hundredth to one-thousandth of a micron, sweeping all viruses, most dissolved organics and larger metal ions from the water.

RO systems will remove particles from one-thousandth micron down to one ten-thousandth micron (one angstrom).

2. Costs

o Predictably, filters removing smaller particles cost more than less-fine filters. In addition, the finer the filter, the less flow passes through the filter. To match the volume of water treated by less-fine filters, more RO filters will be required operating in parallel.

For example, if a single microfilter passes 1,000 gallons of water an hour and a RO filter passes 200 gallons in an hour, four RO filters will be needed to match the single microfilter's output.
Also, while most other filtration systems may be able to operate using gravity flow of water, RO systems require a steady pressure from pumps and pressure regulators to work effectively.

3. Advantages

o Since RO systems remove all viruses, bacteria, cryptosporidium and giardia, the resulting water is effectively disinfected. Water passed through an RO system must still be tested for waterborne pathogens. Filters may tear, passing unfiltered water through, or other errors may occur.

Since RO removes colloidal metals, it rarely needs any form of softening. Additionally, since RO is not a chemical treatment, there are no trace treatment chemicals such as calcium carbonate, sulfates, alum or carbon added in the process.

For small municipalities or industrial sites, RO is cost-effective in that is a one-stage treatment with no chemical storage, ozone production or other costs.

4. Private RO systems

o For health-conscious families, a home RO system for the kitchen sink is practical. Water supplied by the city or county must meet clarity and disinfection standards, so the RO system will "polish" the water.

Not having to remove bulk organics or suspended metals will reduce the amount of particles the home RO must remove, adding to its service life while providing water of higher quality.

5. Rural RO systems

o For homes or small communities using well (groundwater) sources, an RO system offers a one-step source for drinking water that will meet or exceed most municipal standards.

As with small-town or industrial water treatment systems, the cost will be driven by the condition of the source water and the volume of processed water demand.

6. Professional Vs. Amateur

o A single-home kitchen-sink RO system is readily available and is easy to install. For a higher volume RO system such as a small community or industrial site, the most cost-effective and health-conscious approach is to go through a professional provider. It will properly scale the RO and pre-filter system to meet the demand and take into account the condition of the source water.

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