Frequently Asked Questions About Advanced Water Purification
To help provide a solid foundation for solutions that can help sustain our natural resources, water reuse and desalination facts and terminology have been provided. By understanding the facts and the terminology along with the existing misconceptions, one can begin to understand the needs and benefits of water reuse and desalination.
The Silicon Valley Advanced Water Purification Center (SVAWPC), which opened in March of 2014, receives secondary-treated wastewater and uses microfiltration, reverse osmosis, and ultraviolet light disinfection to produce highly purified water that meets all California Primary and Secondary Drinking Water Standards. The purified water produced by the SVAWPC is not currently used for potable (i.e., drinking) purposes, but instead is blended with tertiary-treated recycled water and used for a variety of non-potable purposes such as landscaping, agriculture and industry.
The district is evaluating additional uses for the purified water similar to what is being done by other water districts in the state. For example, Orange County Water District in Southern California recharges its groundwater supply with purified recycled water. The water purified at their Groundwater Replenishment System is the purest water source available, and actually improves groundwater quality.
In this initial filtration process, treated effluent is forced through filtration membrane modules made up of thousands of hollow fibers, similar to straws. These fibers have very fine pores in the sides that are 0.1 micron in diameter, or about 1/300th the width of human hair. As the water is drawn through the pores into the center of the fibers, solids, bacteria, protozoa and some viruses are filtered out of the water.
During the reverse osmosis (RO) process, water is forced under high pressure through membranes with holes so small that a water molecule is essentially the only substance that can pass through. The process removes constituents such as salts, viruses and most contaminants of emerging concern, such as pharmaceuticals, personal care products and pesticides.
Now the water is very clean, but as a further safety back-up, the water is sent through chambers that emit strong ultraviolet light to inactivate any remaining viruses and break down some of the remaining trace organic compounds. Ultraviolet light is a powerful disinfection process that creates water of very high quality. The technique is often used to sterilize medicines, food and fruit juices.
Direct Potable Reuse (DPR) – is the delivery of purified water to a drinking water plant or a drinking water distribution system without an isolating environmental buffer.