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Home arrow Blog arrow PETALUMA Green technology to make sewage a less dirty word

PETALUMA Green technology to make sewage a less dirty word PDF Print E-mail
Written by Glen Martin   
Tuesday, 01 August 2006
Petaluma residents soon will help local wildlife simply by flushing their toilets.
Green technology to make sewage a less dirty word
$110 million wetlands-based wastewater facility under construction

- Glen Martin, Chronicle Environment Writer
Tuesday, March 7, 2006
Petaluma residents soon will help local wildlife simply by flushing their toilets.

That may seem odd, given that sewage is more often viewed as an ecological bane than a boon. But officials say a new $110 million facility that will use wetlands to treat the city's sewage and storm runoff will benefit critters as well as people.

The idea, which has been tried in small towns but never in a city the size of Petaluma, promises to change sewage from a municipal liability to a valuable natural resource that can help restore wildlife habitat.

In a typical sewage plant, including Petaluma's current facility, wastewater is treated in giant tanks and ponds and ultimately discharged to a convenient river, bay or ocean. But in the city's new plant, under construction near the Petaluma River, wastewater will meander through a series of settling marshes, where bacteria and algae will remove nutrients, heavy metals and pathogens.

In addition to cleaning up sewage, the wetlands will provide rich habitat for a variety of waterfowl, shorebirds, raptors, fish, mammals, reptiles and amphibians. At the same time, the marshes will provide flood-control benefits by slowing down and dispersing runoff from winter storms.

Hiking and bike trails will allow visitors access to 221 acres of marsh, riparian thickets and uplands. Another bonus: The plant will yield about 4 million gallons of reclaimed water a day during summer months to keep a local golf course and city parks green.

The site, which is now being contoured by gigantic earthmoving machines, also addresses aesthetics. The configuration of the marsh was designed by New York "eco-artist" Patricia Johanson and roughly resembles the shape of a salt marsh harvest mouse, an endangered species that frequents Bay Area wetlands.

Begun last autumn and scheduled for completion in 2009, the facility expands on a concept first applied in the Humboldt County city of Arcata, which constructed a marshland sewage treatment facility on Humboldt Bay in the mid-1980s.

"But this takes it up to the next level," said Michael Ban, director of Petaluma's Department of Water Resources and Conservation. "It's about three times the size of Arcata's facility, and shows the technology can be used for larger cities, provided an appropriate site can be found."

Margaret Orr, engineering manager for Petaluma's water resources department, said the idea of using wetlands for wastewater treatment "is still considered a little radical by a lot of engineers. Typically, they'd be inclined to just build more tanks. But the technology is proven, and we've had tremendous support from the community. The town is really behind it."

Gerald Moore, the chairman for the Petaluma Wetlands Alliance, said the project wouldn't have happened without grassroots activism.

"When the plan for a new plant went before the City Council in 2001, they weren't very enthusiastic about the marshland component," Moore said. "But when we presented them with a petition with 3,600 signatures, they got behind it."

Still, said Moore, the council made its final imprimatur contingent on supporters finding funding for the purchase of the land required for the wetlands project.

"And we did it," Moore said. "We got $4 million (from the California Coastal Conservancy and the Sonoma County Agricultural Preservation and Open Space District). It was tremendously gratifying -- this was really our last opportunity to protect the upper reaches of the Petaluma River."

Most wastewater in the new plant will be treated passively by natural agents and will flow through the system via gravity.

When wastewater reaches the main plant -- which is also part of the project, replacing a facility built in 1938 -- it will be screened to remove large particulates and grit. The water will then languish for a spell in "oxidation ditches," where it will be infused with air to hasten the neutralization of pathogens and contaminants.

Solids, also known as sludge, will be dried, compressed and used either as fertilizer on local agricultural land or as a top dressing at landfills.

During the summer, about 65 percent of the water will then be finely filtered and sterilized with ultraviolet light, after which it will be reclaimed for golf course and park irrigation. The percentage of water filtered and sterilized will drop in winter, when demand for reclaimed water falls and high water inflows during storms can make such extensive treatment impossible.

The rest of the wastewater will be transferred to settling ponds that are already part of the city's treatment system. As the water slowly trickles through the ponds, algae will begin removing heavy metals; bacteria will start digesting nitrate and nitrite compounds, releasing water-fouling nitrogen as gas.

The decontamination process will continue as the water is pumped from the last pond to the top of the marshlands. By the time it flows out the bottom of the marsh, the water will be virtually pure, free of pathogens and any significant chemical contamination.

It is elegant and simple, but Ban said such a treatment facility isn't suitable for every municipality.

"This kind of project requires a lot of land, and it has to be the right kind of land," he said. "Even then it isn't easy - we're dealing with 14 different agencies, and each has to sign off on every step of the project. It's quite a dance."

For environmental advocates, however, the plant is a beacon pointing to a greener, cleaner future.

"You have to look at the larger context for this project," said Grant Davis, executive director of the Bay Institute, an advocacy group that promotes conservation of San Francisco Bay and the Sacramento-San Joaquin River Delta. The institute helped negotiate funding for the facility's land purchase and arranged the transfer of an adjacent 74 acres of tidal marsh from a private landowner to federal agencies.

"Right now, everyone is talking about integrated regional water planning," Davis said. "That's a driving force behind the infrastructure bonds the governor is pushing. This project is the best possible example of that concept. It has everything -- wastewater treatment, habitat restoration, flood control, reclaimed water and recreation."

From waste to wetlands
Petaluma's $110 million sewage treatment plant is being praised as an environmental model because the wastewater will be purified in a series of ponds and marshes that become a wetland for a variety of wildlife.

Treated water will be used to keep a nearby golf course and parks green during summer months.

1 Wastewater is delivered to the treatment plant, where solids are removed by screening.

2 The water is then transferred to "oxidation ditches," where it is mixed vigorously with air to begin the decomposition of pathogens and contaminants.

3 The water percolates through a series of treatment ponds, where algae remove heavy metals and bacteria degrade nitrogenous wastes.

4 At the bottom of the last pond, the water is pumped to the top of the "polishing" marshes, where algae and microorganisms complete the purification process.

Sources: Petaluma Department of Water Resources, ESRI, TeleAtlas

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©2006 San Francisco Chronicle
Last Updated ( Wednesday, 02 August 2006 )
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