Marquette doctoral student Zihao Lu earns distinguished research assistantship for work on disinfectants and wastewater systems

When the world increased its use of disinfectants during the COVID-19 pandemic, few people considered what might happen after those chemicals washed down the drain. For Zihao Lu, a doctoral student in environmental and water resources engineering at Marquette University, that question became the focus of years of research which helped him earn the Richard W. Jobling Distinguished Research Assistantship for a second time.

Lu, now in his fifth year in the doctoral program in the Department of Civil, Construction and Environmental Engineering, studies how common disinfectants affect the microbial systems that keep wastewater treatment plants functioning.

"A wastewater treatment plant is like a giant living factory," Lu explained. "Inside, billions of helpful microbes work together like a team of tiny employees breaking down waste." These microscopic organisms play a critical role in turning sewage into cleaner water while also producing useful byproducts such as biogas and fertilizer. But the system depends on maintaining healthy microbial communities, something modern disinfectants may unintentionally disrupt.

Many disinfectant products contain chemicals called quaternary ammonium compounds, or QACs, which are widely used in cleaning sprays, soaps and personal care products. While these compounds are effective at killing harmful germs, Lu's research investigates how they may also affect beneficial microbes in wastewater treatment systems.

To study the problem, Lu and his research team built hundreds of small laboratory reactors designed to mimic a key wastewater treatment process known as anaerobic digestion. The experiments ran for up to three years and tested ten commonly used disinfectants along with several commercial mixtures.

Through this work, Lu identified chemical concentrations that begin to disrupt microbial activity and developed early warning indicators engineers can use to detect problems before treatment performance declines. "Not all disinfectants behave the same way," he said. "Some chemical classes are much more disruptive to wastewater microbes than others."

Understanding those differences is important not only for maintaining wastewater treatment systems but also for addressing the broader issue of antimicrobial resistance. By identifying which disinfectant structures are more harmful to treatment processes, the research can help guide the design of safer chemicals that protect public health without damaging environmental systems.

More recently, Lu has expanded his work beyond laboratory experiments into advanced computational modeling. He refined quantum chemistry workflows and built machine-learning models capable of predicting how chemical structures influence toxicity in wastewater systems. The modeling framework allows researchers to evaluate potential environmental risks far more quickly than running multi-year experiments for every new compound.

Ultimately, Lu hopes the research will guide engineers, regulators and product designers toward disinfectants that balance human health protection with environmental sustainability. "My work connects everyday consumer behavior with hidden environmental consequences," he said. "The goal is not to eliminate disinfectants, but to use them more wisely."

Lu's interest in environmental engineering began long before graduate school. He grew up in a small industrial town in northeastern China where a chemical fiber factory supported many local families-including his own. As a child, he noticed a stark difference in the river that ran through town. Upstream, the water was clear and calm. Downstream, after passing the factory's discharge, it became murky and foamy with a strong chemical smell.

"That contrast stayed with me," Lu said. "It showed me that environmental issues are rarely simple. They are connected to jobs, health and community needs." Those early observations inspired him to pursue research aimed at balancing economic development with environmental protection.

At Marquette, Lu works closely with faculty mentors including Dr. Patrick McNamara, his doctoral advisor, as well as Dr. Daniel Zitomer and Dr. Chris Marshall. He also collaborates with Dr. William Arnold at the University of Minnesota Twin Cities. Lu credits McNamara's mentorship with helping him develop independence as a researcher. "Instead of telling me exactly what to do, he encouraged me to identify research gaps and design my own experiments," Lu said. "That approach helped me grow into an independent scientist."

The Richard W. Jobling Distinguished Research Assistantship, awarded to three doctoral students in science and engineering disciplines, supports graduate research at Marquette University. For Lu, the fellowship has provided time and resources to advance his modeling framework linking chemical structure to environmental toxicity.

The work has already led to a first-author publication in the Journal of Hazardous Materials and opportunities to present his findings at national conferences, including the Water Environment Federation's Residuals and Biosolids Conference. Lu was also recognized with the Central States Water Environment Association's 2025 Academic Excellence Award, honoring outstanding graduate students across Wisconsin, Illinois and Minnesota.

Beyond research, the fellowship has allowed him to gain teaching experience through guest lectures in environmental engineering courses and mentoring undergraduate researchers in the laboratory. Lu hopes to continue developing tools that help engineers anticipate environmental risks before they become large-scale problems. "The systems that protect our water are often invisible to most people," he said. "But they are essential to public health and environmental sustainability."

For Lu, receiving the Jobling assistantship is both recognition of his work and motivation to keep pushing forward. "The doctoral journey is long," he said. "But if you stay curious and keep pursuing the questions that matter, the work becomes meaningful."

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