Campus: Sonoma - August 14, 2007

Biology professor uses algae to scrub wastewater for toxins at treatment plant

A Sonoma State University biology professor and his graduate student has teamed up with the City of Santa Rosa to investigate the potential use of algae to remove excess nutrients and other contaminants from municipal wastewater effluent.

Early this month treated wastewater began flowing through two parallel 400 foot experimental scrubbers on the grounds of the city’s Laguna Treatment Plant. The three-tiered, flow-through devices built by R.S. Duckworth Construction of Sebastopol are based on a smaller pilot scrubber design in operation since October 2006 under the supervision of SSU Assistant Professor of Biology Dr. Michael Cohen.

A presentation on the experimental scrubber system will be given to the City of Santa Rosa Board of Public Utilities on Aug. 16.

Like plants, algae remove nitrogen and phosphorus from their surroundings as they grow, sequestering these elements into their cells. “Our goal,” says Cohen, “is to remove nutrients that would otherwise support unwanted growth of algae and aquatic plants in waterways that receive the effluent.”

The scrubbers are designed to hold a standing crop of floating algal mats, termed metaphyton, that are harvested daily to maintain the algae in a constant growth phase and, thus, continuously remove nutrients from the water.“The flow rate will determine the concentration of nutrients removed,” adds Cohen.

Algae are also able to bind other problem components in the wastewater effluent, such as copper, lead and nickel, and some algae have the capacity to breakdown complex organic molecules including pharmaceutical drugs.

Algae harvested from the scrubbers are fed to on-site anaerobic digesters that produce methane, which is burned to generate electricity that helps to power the treatment plant.

City Project Development Manager Dell Tredinnick sees potential for this project to integrate with the city’s other renewable energy programs. “Should experimental results demonstrate the viability of a larger system,” says Tredinnick, “prior to feeding algae to the digesters, we would like to extract oils to produce biodiesel for fueling part of the city’s vehicle fleet.” Production of biodiesel from algal oils is an active area of research.

Catherine Hare, who helped to establish the wastewater scrubbing project in Cohen’s laboratory, graduated magna cum laude from Sonoma State this spring and will be continuing to work on the project as a Master’s student.

“Having a parallel system will allow us to change experimental conditions in one scrubber while keeping the other constant as a control,” she says.

“Careful monitoring and analysis of scrubber performance will provide us with information necessary to determine whether scaling up is feasible. It’s an exciting time to be involved in this research.”

Given the go-ahead, project builder Bob Duckworth says he’d be ready to scale-up. “Algal scrubbers could be a relatively low-cost, low-tech solution to a 21st century problem,” he says.

Contacts: Michael Cohen at (707) 664-3413


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