From Lab to Field: Using Biochar to Clean Watersheds

Protecting watersheds across the state is crucial to ensuring water stays clean and safe for drinking and recreation, while also keeping aquatic habitats healthy. However, human activities, particularly wastewater from rural treatment plants, can introduce harmful nutrients into these systems. 

Liz Riedel, a graduate student in NC State University’s Department of Biological and Agricultural Engineering, is investigating a low-cost solution to improve water quality in rural wastewater systems by using biochar as a filtration device.

Biochar is a charcoal-like substance produced by heating plant materials, such as pine bark, in an environment absent of oxygen. In Riedel’s research, she uses biochar to absorb pollutants like nitrogen and phosphorus from wastewater before it enters a watershed. This reduces the risk of eutrophication, a process that can disrupt aquatic ecosystems by causing excessive algae growth. The health of watersheds, a land area where surface and underground water flows to a specific outlet, determines the quality of the water draining into rivers, lakes and streams.

Riedel says she was drawn to this project because it is connected to NC State’s Extension work. 

“I liked the aspect of having an impact and helping other people, especially because we’re working with rural towns, that often have limited budgets to develop low-cost alternatives for improving wastewater treatment,” she says. 

The project, funded by North Carolina’s Water Resources Research Institute, strives to implement cost-effective technology to create the biochar in such a way that small towns can apply it to their treatment facilities, no matter the size. 

The study requires a lot of time at research sites collecting samples, but it involves even more time in the lab. When she’s not in class, Riedel dedicates 20-25 hours a week to conducting experiments and making biochar.

She focuses on creating two types of biochar: Magnesium-doped biochar and Hydrogen peroxide-doped biochar. Magnesium-doped biochar absorbs phosphate, while Hydrogen peroxide-doped biochar absorbs ammonium from wastewater. 

To make Magnesium-doped biochar, Riedel follows a very specific process. She soaks pine bark nuggets in a concentrated magnesium chloride solution for six days. Then, the saturated nuggets are put in a kiln (an insulated oven) at 600 degrees Celsius for two hours. Next, the biochar is sieved to an appropriate size for use in laboratory experiments. Hydrogen peroxide-doped biochar is made by putting pine bark nuggets in the kiln at 400 degrees Celsius for four hours, sieving the resulting biochar to the necessary size, and then soaking it in a hydrogen peroxide solution for six hours. After it is dried in an oven, the biochar is ready to be added to the laboratory scale column study. 

Riedel designed the experiments to provide insights into the biochar’s ability to adsorb ammonium and phosphate in a flow-through configuration. Different flow rates, nutrient concentrations and biochar doses are being tested in the biochar-packed columns. These tests will help determine the best parameters for nutrient removal with biochar in constructed treatment wetlands.

At this point in her research, Riedel is preparing to apply the biochar filter on a larger scale at bigger wastewater treatment wetland facilities. 

The journey has involved a lot of living and learning. 

“It was definitely a lot of trial and error, reading literature and going back to what other people have done while also keeping our ideas in mind,” Riedel says. She values the balance of building from previous research on biochar production and applying new formulations. 

“Even if other people have done this before and you try to do the exact same thing, there are little parameters that can always throw things off,” she says. 

The smallest deviations can lead to variations in results. But it’s the frustrating aspect of needing to get things just right that has made Riedel appreciate how water treatment works.

And seeing everything take shape gives her a rush. “If I’m in the middle of an experiment and the pollutant removal rates appear promising, that gets me really excited,” she says.  

Ultimately, her research aims to protect both humans and wildlife by keeping watersheds healthy. After graduation, she plans to work in the ecological engineering field and continue working on the design and implementation of nature-based solutions for water treatment.

“I want to show that it’s possible to use nature-based solutions, and they can be the same price, or maybe even cheaper than [traditional water treatment solutions] like concrete or mechanical options, ” says Riedel. “It might seem untraditional because there’s not a lot of information or research on it yet, but I think people just need to give it a chance.”

This post was originally published in College of Agriculture and Life Sciences News.