In the winter of 2008, Orange County, CA turned on the world’s largest, most modern reclamation plant — a facility that can turn 70 million gallons of treated sewage into drinking water every day. The Los Angeles Times reports that the new purification system at the Orange County Water District headquarters cost about $490 million and includes a labyrinth of pipes that extend across 20 acres. The plant took over four years to build.
From Sewage to Kitchen Faucet?
Does the sewage get treated and then end up directly in the public water supply? Not exactly, according to the New York Times:
The finished product, which district managers say exceeds drinking water standards, will not flow directly into kitchen and bathroom taps; state regulations forbid that. Instead it will be injected underground, with half of it helping to form a barrier against seawater intruding on groundwater sources and the other half gradually filtering into aquifers that supply 2.3 million people, about three-quarters of the county. The recycling project will produce much more potable water and at a higher quality than did the mid-1970s-era plant it replaces.
Only about a dozen water agencies in the United States, and several more abroad, recycle treated sewage to replenish drinking water supplies, though none here steer the water directly into household taps. They typically spray or inject the water into the ground and allow it to percolate down to aquifers.
Namibia’s capital, Windhoek, among the most arid places in Africa, is believed to be the only place in the world that practices “direct potable reuse†on a large-scale, with recycled water going directly into the tap water distribution system, said James Crook, a water industry consultant who has studied the issue.
How Does it Work?
The process works by employing filters, screens, chemicals and ultraviolet light and mother nature herself–the passage of time underground. Again, from the New York Times:
The Groundwater Replenishment System, as the $481 million plant here is known, is a labyrinth of tubing and tanks that sucks in treated sewer water the color of dark beer from a sanitation plant next door, and first runs it through microfilters to remove solids. The water then undergoes reverse osmosis, forcing it through thin, porous membranes at high pressure, before it is further cleansed with peroxide and ultraviolet light to break down any remaining pharmaceuticals and carcinogens.
The result, Mr. Markus said, “is as pure as distilled water†and about the same cost as buying water from wholesalers.
Recycled water, also called reclaimed or gray water, has been used for decades in agriculture, landscaping and by industrial plants.
Cost
With drought and growing populations, cities are looking for creative ways to either create new water sources or reduce demand through conservation. Many coastal cities are looking at the benefits of desalinization plants; however, large-scale desalination typically uses extremely large amounts of energy as well as specialized, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater. Is reclamation more cost effective? From the NY Times:
Although originally estimated at $10 million for the pilot study in San Diego, water department officials said the figure would be refined, and the total cost of the project might be hundreds of millions of dollars. Although the Council wants to offset the cost with government grants and other sources, Mr. Sanders predicted it would add to already escalating water bills.
“It is one of the most expensive kinds of water you can create,†said Fred Sainz, a spokesman for the mayor. “It is a large investment for a very small return.â€
San Diego, which imports about 85 percent of its water because of a lack of aquifers, asked residents this year to curtail water use.
Related Articles
From Sewage, Added Water for Drinking, New York Times, Nov 27, 2007
From Toilet to Tap, Discover Magazine, May 23, 2008
Sewage becomes Drinking Water at CA Facility, LA Times, Jan 11, 2008
