UCLA environmental engineer Sanjay Mohanty adds iron filings and biochar to topsoil to facilitate natural water treatment
Growing up in arid eastern India in a family of farmers, water was always on Sanjay Mohanty’s mind. And it still is: Mohanty, an assistant professor of civil and environmental engineering who joined the UCLA faculty in 2016, is studying how to remove contaminants from stormwater to ensure a good supply of clean water. Mohanty and his team are experimenting with using low-cost waste materials such as iron filings and biochar—a manmade type of charcoal—to help soil naturally filter water. Mohanty is also involving local high school students and UCLA undergraduate and graduate students in real-world research experiences.
Most of our water comes from rain, which fills lakes and rivers and percolates through the soil to replenish groundwater. However, rapid urbanization has reduced both the quality and quantity of these bodies of water.
“As soon as rain water hits the ground, it picks up contaminants like oil, pesticides, and heavy metals from developed areas such as parking structures, roads, and buildings,” said Mohanty. Contaminants naturally decay over time, he explained, but we’re adding so many contaminants to the environment that nature can’t treat them as fast as they’re accumulating.
Mohanty and his collaborators are investigating how to remove these contaminants by enriching topsoil with substances typically thought of as waste products, like biochar, a type of charcoal produced by burning biomass such as wood, grass, or manure in a low-oxygen environment. They’ve conducted laboratory experiments showing that biochar boosts the growth of some contaminant-eating bacteria and fungi. Fungi grow naturally in soil in very tough conditions such as droughts and can degrade many contaminants, Mohanty said. “Our team is exploiting this biological process to clean stormwater.”
One of the key challenges facing Mohanty and his team is that their natural biofilters have limited lifetimes, like any filter. The researchers are working on methods to recharge the filter materials in the ground. “Using fungi, bacteria, and principles of electrochemistry, we hope to engineer rechargeable biofilters,” said Mohanty.
The science of stormwater decontamination uses principles of geochemistry, microbiology and hydrology to engineer better and more resilient stormwater treatment systems, explains Mohanty, a blending of science that appeals to the astrophysicist-turned-environmental engineer. Mohanty completed his first master’s degree in physics with a specialization in astrophysics before choosing to study civil and environmental engineering.
Lots of research has focused on how climate change affects water quantity. However, we don’t have a good understanding of how climate change affects water quality, Mohanty said. He and his team are studying how longer periods of drought might affect how effectively soil removes contaminants in stormwater, which could result in changes in groundwater quality.
Mohanty and his team enjoy sharing their work with the larger Los Angeles community. “We’re working with students in Southern California, teaching them how to collect soil samples from public areas to check for contaminants,” he said. We’re looking to increase awareness about stormwater treatment systems, Mohanty explains. “It’s not that we’re looking for a problem. We want to engage members of the public at a grassroots level so they’re aware of their surroundings.”
Mohanty is excited by recent initiatives in California, particularly in Los Angeles, to supply 25 percent of our water locally by 2025. “People understand the value of water now,” he said.
By Katherine Kornei
Featured image: Sanjay Mohanty holding petri dishes of iron filings and biochar.