Woodchips and biochar combined to clean pharmaceutical wastewater

The study, published in the Journal of Hazardous Materials, took place at the University of Illinois Urbana-Champaign.

“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,” study author Hongxu Zhou said in a statement.

Zhou and his collaborators knew woodchip bioreactors - woodchip-filled tanks or trenches through which water flows - efficiently remove excess nitrogen in water. This is due to microbes living in and on the woodchips that ‘eat’ nitrate, turning it into nitrogen gas.

The team developed a novel designer biochar - sawdust pretreated with lime sludge and then slow-burned into a charcoal-like material – that could bind phosphorus and certain PPCPs. The large surface area and composition of the designer biochar cause chemical compounds to strongly adhere to it.

The researchers then tried a so called treatment-train approach in the lab to see how well the two treatments worked together. They collected water from a local stream 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 per cent of the nitrate, 99 per cent of the phosphorus, and about 70 per cent of the ibuprofen, 74 per cent of the naproxen, 91 per cent of the sitagliptin, and 97 per cent 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 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,” said Zhou. “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 modelled the B2 system’s efficacy at larger scales, showing potential for industrial applications.