Department of Water Resources
A daily compilation of significant news articles and comment
February 28, 2008
4. Water Quality
From sludge to fertilizer
By Emily Vizzo, staff writer
FALLBROOK – Thousands of gallons of warm, muddy-looking sludge bubbled away in a tank below a gangway at the Fallbrook Public Utility District wastewater treatment plant, looking like something lifted from Willy Wonka's Chocolate Factory.
But sludge it was, and destined to be slurped through a new processing system that went on line last month at the sewage treatment plant on
The system filters out the wastewater, treats the sludge and bakes it so the final product is crumbly, dry fertilizer that can be bagged and sold to growers.
“It's a class-A biosolid, which can be used for agriculture, your garden, your own lawn, because 100 percent of the pathogens have been killed,” said Mike Page, the district's engineering manager. “You can put your hands on it to no ill effect.”
Four years ago, the utility district began brainstorming for a different way to dispose of the sludge that remains when sewage is treated. Trucking it out was expensive, at least $150,000 per year. It also seemed inefficient because up to 90 percent of sludge cargo is water weight, Page said.
“The real issue is places to dispose of sludge. With this technology, it's not going to a landfill.”
The U.S. Environmental Protection Agency defines biosolids as nutrient-rich, organic materials left over from treating domestic sewage. The biosolids can be used as fertilizer, burned or buried.
People living near the treatment plant were invited to observe the process and offer their opinions. Positive feedback prompted the district's board of directors to approve a plan in 2006 to install the system.
The next year, the district bought a processing unit for $1.13 million. Construction began in February 2007, and workers fired up the machinery last month.
In the treatment process, chemicals thicken the sludge so it begins to separate into solids and liquids. Pipes funnel both into a 250,000-gallon holding tank, where air bubbles make the sludge pop and fizz like a giant, muddy hot tub.
After a legally mandated 15-day detention period, the thickened sludge passes through a rotating drum, where wastewater is filtered out for treatment.
Pumps move batches of clumpy sludge to a centrifuge, and its 35,000 revolutions-per-minute wring out more wastewater. A dryer bakes the solid sludge at about 460 degrees Fahrenheit, and the remaining wastewater is heated, cooled and filtered.
Finally, the dried biosolids are sorted, bagged and sold for $4 per cubic yard, or $8 per bag. The process takes about three hours, said Gary Pitts, who handles maintenance and operations. In a roughly nine-hour workday, the district can create three batches of fertilizer.
“It's totally automated, and there's less and less maintaining time involved,” Pitts said. “Computers set the temperatures, the feeding time, the drying time.”
A history of wastewater treatment published on the EPA's Web site says local governments have been treating wastewater for about 30 years. About 50 percent of all biosolids are recycled back to less than 1 percent of the country's agricultural land.
Although the EPA and the National Academy of Sciences have declared the use of biosolids as fertilizers safe for humans, some consumer groups such as the nonprofit advocacy group Center for Food Safety, lobby against the practice.
In 2001, the EPA slapped a
Fallbrook utility district representatives say their project should pay for itself through saved shipping costs by 2014.
Revenues will be greater once more customers come aboard.
“It's going to be great,” said David Deem, the chief plant operator. “When we had those sludge trailers coming in and out all the time, we had massive problems with scheduling. Now we feel there's a controlling of our future, which is a good aspect.” #
http://www.signonsandiego.com/uniontrib/20080228/news_1mc28sludge.html
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