We humans manage to foul up our planet’s vital water supply in countless ways. Although we have found some reliable strategies to clean up the abundant mess, a few among us are determined to find better answers to a serious and growing problem. Tyler Radniecki, an assistant professor of environmental engineering, is one of those individuals. He’s spent his entire career cleaning up dirty water.

“The overall quality of water in our country is deteriorating,” Radniecki said. “Is it in crisis mode? I don’t know, but it’s getting worse, and we need practical, affordable solutions.”

Radniecki has explored how titanium dioxide nanoparticles interact with sunlight and generate a reactive form of oxygen, creating molecular cannonballs that destroy waterborne toxins. He’s studied the effects of using a giant magnifying lens to supercharge sunlight and beam it through water brimming with dangerous pollutants, thereby intensifying the photocatalyst’s power to decontaminate water previously untreatable using titanium dioxide nanotechnology. Now, he’s researching a pair of promising wastewater treatment systems that rely on complex microbial processes.

The anammox (anaerobic ammonium oxidation) process enlists special bacteria that combine the ammonia and nitrite already present in wastewater to form harmless nitrogen gas. If treated wastewater still contains excessive ammonia or nitrite (and therefore nitrogen) when it’s released, the potent nutrient overstimulates algae growth in rivers and streams, threatening fish and other aquatic life.

“The conventional way to remove nitrogen from wastewater is to bubble air through it continuously so bacteria can turn ammonia into nitrate,” Radniecki explained. “Adding a carbon source, like methanol, enables bacteria to convert nitrate into nitrogen gas.”

That aeration process is expensive, accounting for about 60 percent of a treatment facility’s energy costs. And methanol can cost millions of dollars each year. Anammox reduces the need for aeration and eliminates methanol from the equation. It works best when ammonia concentrations are high, but not so well in more dilute wastewater that typifies municipal sewage. Anammox also demands a lot of technical expertise and continuous monitoring, making it financially nonviable for many smaller communities.

Radniecki sees a possible solution: integrate anammox with constructed wetlands and let the chemistry kick in and run on cruise control. In partnership with Clean Water Services, a water resources management utility in Hillsboro, Oregon, he’s testing the idea in his lab. If everything falls into place, he envisions a full-scale anammox wetland going up one day.

“It’s a passive system. To work, it has to pretty much run on its own,” Radniecki said. “It requires a strong understanding of how an anammox wetland responds to a wide variety of complex and real-world conditions to ensure that it won’t be overwhelmed. The system I want to create will be affordable and make sense for smaller communities that have abundant land but not a lot of money or technical expertise.”

FOG (fats, oils, grease) co-digestion is another promising development. It starts with the anaerobic digester, a sealed silo used by many wastewater treatment plants to process sludge, the solid constituents in the waste stream. Inside, bacteria gobble up pathogens and neutralize organic contaminants to produce nutrient-rich solids (that can be used as fertilizer) and methane gas, which is usually flared off.

Adding FOG sources to the digester (such as restaurant fryer grease and other high-energy byproducts of the food industry) can boost methane output so dramatically that the excess biogas becomes an economically viable source of renewable energy. The Gresham Wastewater Treatment Plant (GWTP) in Gresham, Oregon, began using the process in 2012. By 2015, it achieved energy self-sufficiency, saving the town a half million dollars in electricity costs annually.

Curious about how the plant determines the amount of FOG to feed into the digester, Radniecki asked the plant’s chief engineer to explain it. His answer was surprisingly arbitrary: “He said, ‘well, we add a little, which seems to work,’ but they’re wary of overdoing it and upsetting the chemical balance,” Radniecki said. “Adding too much FOG could harm the digester and possibly cause millions of dollars in damage.”

Radniecki saw an opportunity to help the GWTP solve the problem and offered to build a model digester in his lab to analyze the impact of various FOG sources and quantities on methane production.

“Anaerobic digesters are picky eaters, and there’s a lot we don’t know about how FOG affects their microbial ecologies,” he explained. “If you shift the microbial environment too quickly, methane production can decline rapidly. Also, different FOG sources result in higher methane production than others, though the reasons remain unclear. This leads to a trial and error approach to FOG co-digestion.”

Radniecki posits that a thorough understanding of how the anaerobic digester’s resident bacteria interact with FOG will lead to a framework by which engineers can accurately control the reactions and enhance methane production. There’s even some evidence that FOG co-digestion can be used to produce alternative by-products, such as hydrogen gas and
bioplastic precursors.  

“Methane production is the low-hanging fruit,” Radniecki said, “but I see other applications, and to get there, we need a much better understanding of what’s happening within these complex biochemical communities.”

By STEVE FRANDZEL

Published Date: 
Friday, April 13, 2018