By Jennifer Lance
The Orange County [California] Water District is purifying wastewater into drinking water at a $481 million recycling plant. The plant uses microfiltration, reverse osmosis, ultraviolet light, and hydrogen peroxide disinfection. 70 million gallons of sewer water is treated a day in Orange County, California meeting the drinking needs of over $500,000 people, including visitors to Disneyland.
Some call the process "toilet to tap", but county officials prefer the term "Groundwater Replenishment System". Wastewater treatment is more economical than desalination, but there is definitely a negative public perception to consider with treated sewage water. Steve Gorman explains the process:
The plant takes pre-treated sewer water that otherwise would be discharged to the ocean and runs it through a three-step cleansing process—essentially the same technology used to purify baby food and bottled water.
Orange County, CA turning wastewater into drinking water; photo by pvsbond
Thousands of microfilters, hollow fibers covered in holes one-three-hundredth the width of a human hair, strain out suspended solids, bacteria and other materials.
The water then passes to a reverse osmosis system, where it is forced through semi-permeable membranes that filter out smaller contaminants, including salts, viruses and pesticides. Reverse osmosis also is the main process used in desalination.
Finally, the water is disinfected with a mix of ultraviolet light and hydrogen peroxide.
The resulting product exceeds all U.S. drinking standards but gets additional filtration when it is allowed to percolate back into the ground to replenish the aquifer.
Trying to build public support, waste managers have launched a campaign to inform residents of Southern California that they are already drinking treated wastewater. Large amounts of heavily treated waste is discharged from cities upstream that also tap into the Colorado River, like Las Vegas.
Orange County's wastewater recycling system currently produces water for $600 an acre foot, and experts predict the price of imported water will rise to $800 an acre foot in just three years. An acre foot provides a year supply of water to two families. Southern Californians are going to have to accept wastewater recycling if they are going to continue to provide water for all residents in times of drought.
Additional Video: http://www.youtube.com/watch?v=6bk6PEz2QF8