Study combines woodchips and biochar to clean water of pharmaceuticals, nutrients

In a new University of Illinois Urbana-Champaign study, researchers show how a simple system using woodchips and a bit of glorified sawdust can dramatically reduce nitrogen, phosphorus, and multiple common drugs in wastewater.

"Even at low concentrations, pharmaceuticals and personal care products (PPCPs) can degrade water quality, disrupt ecosystems, promote antibiotic resistance, and lead to bioaccumulation in wildlife. While nutrients like nitrogen and phosphorus cause visible problems like harmful algal blooms, PPCPs pose potential risks, particularly through long-term exposure in vulnerable populations. Both issues highlight the need for better wastewater management," said study author Hongxu Zhou, who completed this study as a doctoral student in the Department of Agricultural and Biological Engineering (ABE), part of the College of Agricultural, Consumer and Environmental Sciences and The Grainger College of Engineering at U. of I.

Zhou and his collaborators knew woodchip bioreactors -- woodchip-filled tanks or trenches through which water flows -- efficiently remove excess nitrogen in water. This is thanks to microbes living in and on the woodchips; they "eat" nitrate, turning it into harmless nitrogen gas. The team developed a novel designer biochar -- in this case, sawdust pretreated with lime sludge and then slow-burned into a charcoal-like material -- could bind phosphorus and certain PPCPs. The large surface area and composition of the designer biochar cause chemical compounds to stick and not let go.

With these principles in mind, the researchers tried a "treatment-train" approach in the lab to see how well the two treatments worked together. They collected water from a local creek and loaded it with nitrogen, phosphorus, ibuprofen, naproxen, the diabetes drug sitagliptin, and a derivative of estrogen. This water entered small woodchip bioreactors, then flowed "downstream" through tubes filled with biochar. On the other end of the system, which they called B² (bioreactor-biochar), the researchers measured the remaining compounds in the water.

"On average, the B² system removed 77% of the nitrate, 99% of the phosphorus, and about 70% of the ibuprofen, 74% of the naproxen, 91% of the sitagliptin, and 97% of the estrone," said study co-author Wei Zheng, principal research scientist at the Illinois Sustainable Technology Center (ISTC), part of the Prairie Research Institute at U. of I. "The biochar acted like activated carbon to efficiently remove pharmaceutical residues from the contaminated water."

The results varied a bit when the research team changed the speed at which the water moved through the system, with slower speeds leading to greater nitrogen removal. They also tested the role of biochar format -- granules or pellets -- finding the granules picked up more pharmaceuticals and phosphorus.

Because microbes are responsible for the nitrogen removal in woodchip bioreactors, the researchers wondered whether the pharmaceuticals could impact the microbial community. They found changes in the abundance of certain bacterial groups, but the main function of the microbial community was unaffected.

"For me, the most exciting aspect of our findings is the confirmation that the woodchip bioreactor's nitrate efficiency remains unaffected by PPCPs, despite the changes in microbial composition," Zhou said. "This suggests that the bioreactor system is robust enough to maintain its performance under challenging conditions, which has significant implications for its application in real-world scenarios."

Although the study was conducted on the lab bench, the researchers modeled the B² system's efficacy at larger scales, showing strong potential for industrial applications.

"We believe that through regular maintenance and optimizing system design, many of the challenges associated with scaling can be addressed. For example, clogging in continuous flow-through systems can reduce overall performance and longevity; therefore, periodic replacement of biochar is needed," said co-author Rabin Bhattarai, associate professor in ABE.

"These design and operational considerations are critical to ensuring both performance and service life in relevant applications, ultimately enhancing the effectiveness of B² systems in addressing environmental challenges," he added.

Zhou is now a postdoctoral research associate in ISTC. Zheng is also an adjunct faculty in ABE.