Gwyneth Perseveranda

A team of researchers from the University of Illinois-Urbana Champaign developed biochar pellets that seize phosphorus from drainage systems, which then turns into a slow-release fertilizer.

Photo Courtesy of Architect Magazine.

The study, published on November 4, titled “Exploring the engineering-scale potential of designer biochar pellets for phosphorus loss reduction from tile-drained agroecosystems” investigates the effectiveness of engineered biochar pellets in reducing phosphorus loss from agricultural lands which utilize tile drainage systems.

Phosphorus is an essential nutrient for the formation of bone and teeth for humans, as well as a vital element for plant growth and agricultural productivity.

However, it becomes an environmental problem when it leaches from agricultural fields, reaching bodies of water.

The excess phosphorus can lead to Eutrophication, a process that causes excessive growth of algae and other aquatic plants.

When these algae die and decompose, it causes oxygen depletion in water, leading to “dead zones” in which aquatic life cannot survive.

It also affects water quality, making the water not potable and be used for other purposes.

"Phosphorus removal structures have been developed to capture dissolved phosphorus from tile drainage systems, but current phosphorus sorption materials are either inefficient or they are industrial waste products that aren't easy to dispose of,” said Hongxu Zhou, the lead author of the study.

“This motivated us to develop an eco-friendly and acceptable material to remove phosphorus from tile drainage systems," said Zhou.

Zhou and his colleagues used sawdust and lime sludge, both byproducts from milling and water treatment plants.

They mixed these two ingredients together and slowly burned the mixture under low-oxygen conditions to create a product with high-phosphorus binding capacity.

The process of burning materials under low-oxygen conditions is called pyrolysis and this is used to create biochar, which has a high-phosphorus binding capacity.

Once these engineered biochar pellets bind all the phosphorus with all their thresholds, they can be spread on fields to release the nutrient slowly, making it a fertilizer and preventing pollution.

For two years, they tested these biochar pellets in Fulton County, Illinois, as the fields had drainage water pipes that are connected with structures filled with biochar pellets.

During the first year, larger pellets measuring two to three centimeters were used, while smaller pellets measuring one centimeter were used in the second year.

It was found out that smaller pellets were more effective, removing 38 to 41% of phosphorus, compared to just 1.3 to 12% for the larger pellets.

"If we put powder-form biochar in the field, it would easily wash away," Zhou said.

 "This is why we have to make pellets, as we have to sacrifice some efficiency to ensure the system will work under field conditions," he said.