By Peter Chawaga
As discharge requirements for nitrogen and phosphorus become stricter, wastewater utilities are in a no-win bind. Either investing in more advanced technology to treat influent or paying fines from regulatory bodies for failing to do so can cost a lot. For small and rural utilities that are already stretched thin budgetarily, this can prove to be an intractable problem. To help those facing this dilemma, new research is focused on a cost-efficient way to achieve nutrient removal.
Iowa State University researchers Dr. Martin Gross and Dr. Zhiyou Wen have developed a “revolving algal biofilm” (RAB) treatment system which removed nutrients from wastewater while producing a money-making byproduct.
“The RAB system uses a series of vertically oriented conveyor belts that rotate in and out of wastewater,” said the researchers. “Algae grows on the belts’ surface… Algae can be thought of as a microscopic plant so when it grows, it requires nitrogen and phosphorus. So, the mechanism for nutrient removal is through assimilation of nutrients into the algae cell.”
While the project is still currently at a pilot scale, the researchers project that a commercial-scale facility could process between 200,000 and 1 million gallons of wastewater per day.
The cost-saving angle lies in the ability to resell this algae and offset other costs around the plant. The RAB system can grow 10 times more algae in a given footprint than conventional raceway ponds, which are specifically designed to cultivate algae, can. This algae has the potential to be sold as fertilizer for agricultural operations.
“The algae fertilizer has been shown to be a better fertilizer than off-the-shelf organic fertilizers such as Milorganite,” the researchers said. “In addition to being an effective fertilizer, it also has slow-release properties so it will not contribute to nutrient leaching like other common fertilizers. This leaching is a major contributor to nutrient pollution in our nation’s waterways.”
Latching onto this earning potential, the Metropolitan Water Reclamation District of Greater Chicago (MWRD) has been one of several utilities to scale up the technology for testing. During a three-year pilot study, the utility has found it possible to produce 64 tons of algae per day and make $30 million a year by selling it, per The Des Moines Register.
“MWRD has a vision that algae will play an important role in nutrient recovery in the future,” said the researchers. “The testing is looking very good so far. The RAB system is able to effectively remove nitrogen and phosphorus from their wastewater. The focus now is to evaluate the economics of the system to verify that it will be a good investment for them.”
In 2011, Gross and Wen, who have turned this research into the startup Gross-Wen Technologies, originally sought to develop a system that could produce algae into biofuel. They developed a system that grew algae efficiently, but found that this alone would not yield a profitable product. So, they focused on wastewater treatment as the value driver and algae production became an added bonus.
In 2012 they received funding for the pilot-scale project at Iowa State’s BioCentury Research Farm and MWRD became interested soon after.
But the duo hasn’t lost focus on the technology’s potential to help small and rural utilities with their nutrient troubles. The RAB system is also being tested in small towns like Dallas Center, IA, with a population of about 1,600 in the center of the state.
“We have tested our system on three distinctly different wastewaters,” said the researchers. “Large communities like Chicago, small communities with lagoon systems, and industrial wastewater from food and feed manufacturing. Our system has been shown effective in treating all of these wastewaters.”
Gross-Wen Technologies plans to build its first full-scale facility this summer and is awaiting regulatory approval. Success on a full scale will mean rapid deployment and the chance for those struggling with nutrient removal to turn the expensive problem into a money-making solution.
 This is a brand of biosolids-based fertilizer produced by the Milwaukee Metropolitan Sewerage District.