Researchers are developing cost-efficient waste water treatment methods that are set to be deployed in major cities.

Across the U.S., wastewater treatment plants are looking for cost-efficient solutions to meet new state and federal water quality requirements. This includes lower thresholds for the amount of nitrogen and phosphorous that can be discharged into rivers and lakes.

All organisms need nitrogen and phosphorous to grow. But high concentrations of these nutrients in waterbodies can cause certain types of algae to grow faster than normal. “Harmful algal blooms” create dead zones and some species of algae also release toxins that can sicken or kill wildlife, pets and people.

Algal blooms pose serious environmental and public health risks and threaten economies dependent on fishing and tourism. Ironically, algae can also be part of the solution.

“‘Algae’ includes a large and very diverse group of organisms, somewhere between 5,000 and 10,000 species that range from single-cell diatoms to giant kelp,” says Zhiyou Wen, director of Iowa State’s Center for Crops Utilization Research. He’s also a professor in the department of food science and human nutrition.

Over the last two decades, Wen has investigated the use of certain species of algae as food ingredients, and more recently, as an “effective, reliable, and economical” way to treat wastewater.

The researcher and one of his former students, Martin Gross, developed a novel system called Revolving Algal Biofilm (RAB) to grow algae and remove nitrogen and phosphorous. After a successful pilot project at Iowa State’s BioCentury Research Farm, they co-founded Gross-Wen Technologies in 2014. They attracted state and federal grants and investors, and licensed the patented revolving algal biofilm system through ISURF.

With the RAB system, algae grow on a series of large, vertical conveyor belts that rotate in and out of a wastewater reservoir. “Like skyscrapers, you can fit a lot more into a space by going up rather than out,” says Wen.

The microorganisms absorb nitrogen and phosphorus from the wastewater, and sunlight and carbon dioxide from the air. A greenhouse encloses the RAB system, which Wen says is more cost-efficient than artificial light. An adjustable blade scrapes off the algae once it reaches a certain thickness.

“It’s like mowing the lawn. We just cut the top, and it keeps growing,” says Wen, adding that harvest may happen every two to three days in summer compared to once a week in winter.

Gross-Wen Technologies has experimented with turning harvested algae into slow-release fertilizer pellets for gardens and lawns. The founders say this, along with other potential applications like bioplastics, could give wastewater treatment facilities additional revenue streams.

Cost efficient and versatile

Data from at least 10 pilot projects across Iowa, Illinois, Kansas and Washington show the RAB system uses less energy than traditional wastewater systems. It’s also 10 times more efficient than other algae treatment options, largely due to its compact design. Taking up less than a tenth of a football field, the RAB system can recover one ton of nitrogen, half a ton of phosphorous and 16 tons of carbon dioxide each year.

Wen says the RAB system is also more cost-efficient than many alternatives, especially if it’s added to existing infrastructure. The central Iowa town of Slater estimates it will save roughly $1 million by choosing the RAB system for an upgrade to its municipal wastewater treatment plant. The current unit in Slater treats about one-third of the town’s wastewater needs. But later this year, Gross-Wen Technologies will expand the RAB system to serve the whole population, around 1,500 people.

Wen adds that the RAB system is highly versatile to meet the needs of clients. Like Legos, more units can be added to treat higher volumes of wastewater or placed at different stages of treating wastewater.

“In Slater, the RAB system is treating wastewater before it’s discharged into a river. The pilot project in Chicago is treating a different wastewater stream; the RAB system is pulling out nutrients from water before it goes into the metro’s facility,” explains Wen.

Along with all of the household and commercial wastewater, the Metropolitan Water Reclamation District of Greater Chicago serves many large-scale food and beverage manufacturers. Coca Cola and Kellogg Company are just a few that produce high volumes of nutrient-rich wastewater. Wen says being part of the pre-treatment solution could reduce the burden on Chicago’s water district and help industries avoid higher surcharge rates.

Across the food supply chain, Iowa State researchers are striving to help protect the health of animals, people and the environment.