Green with Algae: Mercury removal tech trials
WLSSD has focused its pollution prevention programs to address several pollutants of concern. However, mercury has been a high priority of WLSSD’s pollution prevention program since 1989, following reports of high levels in fish in the St. Louis River. We’ve made a lot of progress toward preventing mercury from ending up in our dirty water and trash in the past 30 years, including the amount of mercury present in the cleaned-up effluent we return to the St. Louis River each day. Learn more about our nationally-recognized pollution prevention programs at wlssd.com.
Like all water dischargers, WLSSD has a permit that limits the amount of mercury contained in the clean water we return to the St. Louis River; we have been challenged over the years to meet one of the nation’s most stringent mercury limits. We currently have a variance that allows an interim limit as we seek solutions. It’s a challenge we’ve embraced—mercury can have harmful effects on the people and wildlife that depend on the water resources we serve to protect.
WLSSD has studied dozens of potential mercury reduction technologies, and even tested some of the technologies on site—to no avail. In 2020, WLSSD partnered with a company called Clearas to experiment with their technology in a way never before studied. Could their algae-based system, known as Advanced Biological Nutrient Recovery (ABNR), remove the elusive last bit of mercury remaining after our treatment process?
The Clearas ABNR system was set up in a greenhouse structure at WLSSD designed to provide the algae everything it needed for optimal growth—sunlight and wastewater that contains nutrients like nitrogen and phosphorus. As the algae grows, it consumes nutrients, removing them from the wastewater. The algae can be harvested and repurposed by a company that converts it into products like plastics and foam.
Our groundbreaking study found the algae also slurped up mercury, reducing the “total mercury” content in the wastewater by 84%! In theory, this technology would help us reduce mercury levels below the looming permit limits, but it has never been implemented in a context like ours.
Our next step is to team up with Clearas and a consulting firm to examine feasibility and viability for a large scale system (35 million gallons a day) at WLSSD, to include cost, infrastructure, and site integration. While ultimately it may not be possible to implement, WLSSD is pleased to continue our research contributions toward mercury elimination in wastewater.