It's a byproduct of Petaluma?s new $115 million wastewater treatment plant, which will process up to 2 billion gallons of the city?s raw sewage each year, converting about a quarter of it to recycled water for parks and crop irrigation.

It also produces about 20 tons a day of sludge ? known in the industry as bio-solids ? which get trucked to area landfills and are available as fertilizer.

?This is beautiful,? said Orr, the plant?s engineering manager, as she held the loamy material to the sunlight. ?You can put it on a farm field and it augments the soil.?

After nearly four years of construction, the Ellis Creek Water Recycling plant opened this summer without major complications, officials said.

The project near Lakeville Highway was completed on time and with a 4.4 percent cost overrun, replacing the 70-year-old facility on Hopper Street that had fallen into disrepair.

The new plant, financed by water and sewer rates, could serve the city of 56,000 for the next 100 years, said Mike Ban, director of the city?s Water Resources and Conservation Department.

An additional $10 million pipeline system installed over the next three years will carry tertiary treated water to points throughout the city, including parks, athletic fields and farms, he said.

?Recycled water is the only new water in California,? Ban said. ?It allows us to save our potable water for homes and businesses.?

Despite the successful construction, the plant is dogged by critics who said it is too expensive.

Petalumans for Fair Utility Rates, which sponsored a failed water and sewer rate rollback initiative in November, will try again in 2010.

Organizer Jim Fitzgerald said he will ask voters to return sewer rates to 2006 levels. Since the City Council approved hikes three years ago to pay for the plant, rates have gone up three time for a total of 60 percent, he said.

?It?s just far too much money,? Fitzgerald said. ?This idea of raising the rate to the point where its outstripping the income of people on pension is just silly.?

Like before, city officials said a reversal of the rates could jeopardize their ability to repay a low-interest state loan for the plant. The money would come out of the city?s operating budget, threatening city services, Ban said.

City Councilwoman Tiffany Renee said the city has begun a rate study to see if there is another way to repay the loan.

The ?Son of Measure K,? as she calls it, seeks to exploit an inherent distrust in the way government spends money.

?We?ve already saved the ratepayers millions in how this was financed,? Renee said. ?If we can do more through a restructuring, we will.?

By many accounts, the plant itself is a model of efficiency and green technology.

Methane gas from sewage holding tanks fuel its boilers. Water treated on premises irrigates its landcaping. Rooftop grasses insulate its administration offices.

The dirtiest job is done by microscopic organisms that feed off dissolved solids, leaving behind only their nutrient-rich shells.

About 15 employees oversee the plant, monitoring its functions with a state-of-the-art computer system and laboratory.

Even the design ? with trails connecting to nearby Shollenberger Park ? pays tribute to the environment. When viewed from the sky, a cluster of treatment ponds and polishing wetlands takes the shape of a harvest mouse, an indigenous species in the area near the Petaluma River.

Officials will stage an opening ceremony Friday morning.

?It?s really one of the best kinds of projects we can fund,? said Maxene Spellman, a project manager with the California Coastal Conservancy, which put up about $2.2 million. ?It combines habitat enhancement and public access with serious water quality improvement.?