The Coast News Group

Wastewater treatment facility considers turning phosphorous into fertilizer

CARLSBAD — For the last several years, Encina Wastewater Authority has collaborated with several private companies to dispose of biosolids in a way that’s both environmentally friendly and profitable. 

And now the wastewater treatment facility is eyeing another green venture.

Encina, which serves more than 350,000 North County residents, is considering a project that would transform phosphorus and other harmful chemicals from biosolids into an environmentally friendly fertilizer to be sold commercially.

Phosphorus, a nonrenewable resource that’s increasingly in short supply, is an important ingredient in fertilizer. Consequently, it’s critical for farmers.

“The goal is to find a renewable source of phosphorus from our local facility that’s marketed to the food industry,” said Kevin Hardy, general manager of Encina.

Hardy said the technology is part of a growing trend of wastewater treatment facilities finding value in biosolids.

“Wastewater facilities are starting to see their purpose can go beyond treating wastewater,” Hardy said. “Environmental benefits that are profitable can be extracted onsite.”

Phosphorus and other chemicals from biosolids build up in pipes and valves at Encina, reducing flow and occasionally causing blockages. This increases maintenance costs. Last year, Encina partnered with Ostara Nutrient Recovery Technologies, a private company, for a one-month trial study to investigate whether it’s cost effective to remove the chemicals from the pipes and convert them into fertilizer.

The process involves running part of Encina’s waste stream through a holding tank, dousing it with magnesium chloride and passing it through a special type of reactor. Then the chemicals are transformed into fertilizer pellets for crops, plants and trees.

“The value proposition for ratepayers is reduced maintenance on the pipes, the money from Ostara to operate our facility and the sales from the fertilizer pellets that go back into the facility,” Hardy said. “For us, those three things have to add up to at least be cost neutral.”

“I’ll have to temper my enthusiasm because I can’t say definitively what we will do,” he added. “We have to look at the numbers closely. The test pilot program has been encouraging, though. We’ve proven we can do what we set out to do.”

Under the previous policy, most phosphorus-filled water would go through Encina’s wastewater treatment process several times instead of once, adding to costs.

Another advantage of recovering phosphorus for fertilizer: It’s less likely to end up in the ocean and surrounding environment, according to Hardy.

Hardy said it’s becoming more common for wastewater treatment facilities, which are generally publically owned and operated, to work with private companies.

“Funding from government sources are slowly going away,” Hardy said. “We can’t be so sure about the future. That’s why we’ll work with private companies to stay ahead of the curve and bring down costs.”

To fight rising costs, Hardy said Encina started experimenting with additional methods to dispose of biosolids about five years ago. One way that’s been successful: converting biosolids into biofuel. Cemex, a private cement producer, uses biofuel pellets from Encina as an alternative energy. Encina produces about 7,200 tons per year of biosolid pellets.

“The cement industry has diversified its fuel portfolio with alternative fuels,” Hardy said.

Encina also made producing its own power a major goal.

Thanks to large investments in a cogeneration facility, Encina generates 70 percent of its power onsite by using biogas byproduct from the facility’s wastewater treatment process, which earned it a spot alongside national companies on the Environmental Protection Agency’s “Top 20 Onsite Generation” list (there are two other wastewater treatment facilities in the U.S. on the list.)

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