When Sewage Is Not a Dirty Word
Algae can purify wastewater and provide electricity.
Venture capitalists can chase the holy grail all they want, trying to convert algae into bio-diesel. The City of Santa Rosa, Calif., has hit on a more practical way to turn green slime into green power.
On May 10, the city's Laguna Wastewater Treatment Plant will inaugurate a small pilot project that relies on native algae and marsh plants to purify sewage and produce methane. The gas will run a generator that charges a fleet of four electric maintenance vehicles.
"It's a totally cool thing," said Dell Tredinnick, project development manager for the city's Utilities Department. "It's a real-life demo project in a real-life sewage treatment plant that can show you what you can do."
Nationwide, there's a rush to extract more energy from wastewater treatment, but Laguna boasts that it is the only operation in the U.S. harvesting algae for fuel. The city has published a coloring book about its "F.A.B" (Fuel from Aquatic Biomass) project, featuring Algae, a smiley, if scummy, little fellow.
Under the direction of Sonoma State University biologists, six algae channels or ponds at Laguna clean a small portion of the wastewater stream, meeting state standards for nitrates and phosphates. The algae, marsh plants and associated bacteria "eat" these contaminants, bringing to mind the words of Buckminster Fuller, the futurist: "Pollution is nothing but the resources we are not harvesting."
As the algae proliferate, the floating mats are harvested and fed into an airtight tank, along with invasive vegetation from nearby creeks. As the plants decompose in the tank, they produce methane that will fuel a generator for the electric vehicles. The plant leftovers will be spread as fertilizer on an acre of strawberries.
"You can make progress in little ways by closing loops and using waste products," said Cat Hare, a graduate student at Sonoma State. "I can get a 35 percent decrease of the level of nitrates in one day in the water coming through the channels, which is really good."
Laguna serves a population of 250,000 people, and it would require more than 100 acres of algae ponds to purify the entire waste stream of nitrates. The current project measures only 800 square feet. Treddinick plans to scale up the project to an acre, thinking that perhaps a smaller plant might want to copy the technology.
"What we're doing is advancing the science," he said.
Algae-to-fuel is a side operation at Laguna, but it has garnered top honors from the Association of California Water Agencies. In addition, Laguna has won state and federal awards for recycling and quality control. Ninety-nine percent of its biosolids — treated, nutrient-rich sewage sludge — are spread on the land, either as fertilizer on fodder or as compost on city parks and playgrounds. Only 1 percent is trucked to a landfill. Apart from the algae operation, 25 percent of the plant's electrical bill is offset by methane from biosolids.
Last year, Laguna became one of only 25 sewage plants in the country to be certified for high standards by the National Biosolids Partnership, made up of the U.S. Environmental Protection Agency and two nonprofit advocacy groups, the National Coalition of Clean Water Agencies and Water Environment Federation.
"When you look at the whole system, it's really quite phenomenal," Tredinnick said. "It's a cradle-to-cradle approach."
Recycling, not 'disposal'
In California, on average, 70 percent of biosolids are spread on farmland or used as compost, compared to 55 percent nationwide, said Greg Kester, a spokesman for the California Association of Sanitation Agencies, a nonprofit government group.
"We never use the term 'disposal' anymore," Kester said. "Everyone views biosolids as a renewable resource."
Well, not everyone. A number of agricultural counties in Southern California have tried to ban or limit the use of biosolids even for fodder because they view the practice as "rural dumping." Kern County banned it, was sued by the city of Los Angeles, and lost. In 2007, a federal court found "no evidence at all" of environmental harm to Kern County from biosolids.
"To me, it's the ultimate act of recycling," Kester said. "It's putting it back on the soil from which it came."
But rural reluctance in California, manifested in local ordinances requiring hard-to-get permits, has forced urban areas to convert more sewage into fuel. Last year, Ventura Regional Sanitation District, serving Ventura County, began converting biosolids into dried pellets for fuel. And in a pilot project, the city of Los Angeles started injecting some of its biosolids into wells a mile under the ocean floor at Terminal Island, where they will degrade into methane for fuel.
In northern San Diego County, the Encina Wastewater Authority now converts its biosolids into dried pellets for sale to a cement manufacturer in Victorville. The Encina treatment plant, like Laguna, is certified by the National Biosolids Partnership.
"We've gotten our ratepayers out of the game of paying millions of dollars to haul biosolids more than 200 miles to Yuma, Ariz.," said Kevin Hardy, the general manager. "Instead of five trucks to Yuma, we're sending one truck a day to Victorville. That's half the distance. And we're getting to beneficially use the product as fuel."
Similarly, Los Angeles and Orange counties are hoping to recycle a third of their biosolids as pellets at the Rialto SlurryCarb Facility, which opened last June. The plant is designed to produce twice as much energy as it consumes. It has hit some technical hurdles and is operating only at 20 percent capacity, but it will be fully up and running by the end of this year, said Brian Dooley, vice president of marketing.
"It's a longer start-up process than we were anticipating," he said.
In the Bay Area, a coalition of 16 wastewater treatment agencies, including San Francisco, will put out a request for proposals later this spring for a biosolids-to-energy project.
"To date, facilities have found it easier to truck their biosolids a sizable distance, but it's beginning to turn around," said Lauren Fondahl, an environmental engineer at EPA headquarters in San Francisco. "They're starting to look at the overall carbon footprint and the cost of trucking biosolids a long way out."
A quixotic quest?
At the Laguna plant in Santa Rosa, scientists couldn't resist trying to extract oil from sewage-fed algae, though they were skeptical it would be worth it. Some algae has more lipids, or fats, per pound, than any other crop, but it's a tough proposition to get the oil out, said Michael Cohen, the Sonoma State biologist who oversees the algae operation.
"Algae have tough cell walls, so extraction is really difficult," he said. "They don't give up their oil so easily."
Hare, who is Cohen's student at Sonoma State, stuffed a trash bag full of algae into a giant duffle bag, got past airport security without incident, and flew to a U.S. Department of Agriculture lab in Philadelphia to see what she could do. After four months and two trips, she extracted a cup of oil, but it was not suitable for bio-diesel production.
"We knew going in that we were going to be fighting a losing battle, but we thought we would see if we could make it work," Hare said. "I proved I could do it, but it's not cost-effective. It looks like methane gas is going to be our best bet."
Are you on Facebook? Become our fan.
Follow us on Twitter.