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Algae wastewater cleaning technology scores in Wisconsin

October 27, 2016

A series of interconnected plastic tubes

A series of interconnected plastic tubes lit by LED lights makes up the small-scale photobioreactor where photosynthesis has enabled algae to consume the phosphorus in Roberts’ wastewater for the past two weeks. Photo: Tom Lindfors

Tom Lindfors writes in the New Richmond News about how the Roberts, Wisconsin, wastewater treatment plant – considered a minor utility designed to treat an average flow of up to 465,000 gallons per-day – is working with a new algae technology from Clearas Water Recovery as one of the first communities to comply with the State’s new Phosphorus Water Quality Standard beginning in 2018.

The old limit for allowable phosphorus in treated water for Roberts was 1 mg/l with a cap of 880 pounds per-year. The new limit, using the same 800-pound annual cap, is .04 mg/l. Two months ago, finding a solution to meet the new standard, let alone the astronomical funding it would likely take to construct such a new technology, seemed a pipe dream.

Then at their Oct. 10 village board meeting, Roberts Public Works Director John Bond told board members the phosphorus removal pilot plant the village had been testing for two weeks had, so far, exceeded expectations in a big way. The samples tested from the pilot program had exceeded the DNR-mandated limits showing up as “zero detect,” according to Mr. Bond. Testing of additional samples were being sent to an independent third party lab to verify those results last week.

“Every batch that we have run through this plant, the final product has come back with zero detect for any nutrients. Another micro-filtration pilot program we ran, which was a mechanical process, got us to the limit for phosphorus, but nothing other than phosphorus and the cost was prohibitive. With this process, we are not only achieving ‘no detect’ on phosphorus, it’s taking care of nitrogens, the BODs, the suspended solids, and the trace elements, like copper,” said Mr. Bond.

Advanced Biological Nutrient Recovery (ABNR) could offer a long-term, cost-effective, sustainable recovery solution to meet or exceed the DNR-mandated limits for phosphorus and other nutrients. The technology developed by Clearas Water Recovery out of Missoula, Montana, uses algae grown by photosynthesis to feed on targeted nutrients like phosphorus and nitrogen present in the effluent of typical wastewater treatment facilities.

Clearas technician Kellen Triplett

Clearas technician Kellen Triplett tests water samples in a portable lab that accompanies the ABNR portable system when it travels to municipalities like Roberts. Photo: Tom Lindfors

The ABNR system starts by mixing phosphorus and nitrogen-loaded wastewater (effluent) with a “bio-diverse” blend of algae and other micro-biology. The liquid mixture is fed into a photobioreactor of plastic or glass tubing where it is circulates while being exposed to ultraviolet light sources causing photosynthesis to occur.

During photosynthesis, the algae feed on the phosphorus and nitrogen and other nutrients in the wastewater effluent. The effluent, now free of phosphorus, nitrogen and other nutrients, is separated from the algae using a sophisticated filter system generating oxygenated clean water for reuse and a biomass recycle stream which is returned to the mix stage to re-initiate the treatment process.

“Clearas systems work in three phases: a mixing phase, an actual recovery phase and then a separation phase,” says Clearas technician Kellen Triplett. “In the mixing phase, the wastewater effluent mixes with the algae culture, one part algae to one part wastewater. We use proprietary strains of algae, the strongest algae cells we can find that will eat up nutrients and the kind that are valuable to biomass companies. We then inject CO2 because the algae needs a carbon source, and also to regulate the pH level of the water.

“When the algae cells are in the recovery phase, they are creating oxygen in an enclosed environment – the photobioreactor tubes – which increases the pH level of the water.

“Depending on the size of the system, the algae effluent mixture either circulates or operates as a one-pass system. The algae cells pick up photons from sunlight during the day and from LED lighting at night so the system can operate 24 hours per day. As the algae cells grow, they ingest the nutrients in the effluent.

“The algae cell mixture is added to the effluent proportional to the nutrient level in the effluent. In the separation phase, the algae effluent mixture is pushed through a honeycomb-like filter, which allows clean water to pass through while the algae remains trapped in the filter. Then the clean water is pumped into one tank and the algae into another tank,” said Mr. Triplett.

The results from the third party testing came back and they confirmed “no detect” at all levels of effluent tested. Clearas executives are scheduled to meet with city officials from Roberts sometime the end of this year or beginning of next to discuss all of the possibilities.

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