According to a study published in the Journal of Water Process Engineering by Hongxu Zhou, Haribansha Timalsina, and their research team, a high-performance treatment train has been developed to address the significant challenge of agricultural nutrient pollution. In many farming regions, underground drainage pipes carry excess water away from fields to improve crop growth, but this water often contains high levels of nitrogen and phosphorus. These nutrients can lead to harmful algal blooms and degraded water quality in downstream rivers and lakes. The researchers tested a combined system known as a woodchip bioreactor-biochar system, or B2, which pairs a traditional woodchip-filled trench with secondary channels containing designer biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More pellets.

The findings from the one-year field trial show that this integrated approach is remarkably effective at purifying drainage water. During the study, the woodchip bioreactor acted as the primary engine for nitrogen removal, reducing nitrate-nitrogen loads by 58 percent. By converting these nitrates into inert nitrogen gas through a natural microbial process, the system prevented nearly two kilograms of nitrogen from entering the watershed during the pilot period. While woodchip bioreactors are excellent for nitrogen, they often struggle with phosphorus and can even leak it into the environment. The B2 system solved this problem by adding biochar sorption channels, which captured dissolved phosphorus with efficiencies ranging from 20 percent to 94 percent. Beyond its cleaning power, the economic analysis revealed that this system is a highly practical solution for widespread agricultural use. When scaled up to treat a typical ten-hectare field, the estimated cost of removing nitrogen dropped to approximately $4.70 per kilogram per year. This makes the B2 system one of the most competitive edge-of-field technologies available today, especially when compared to more expensive practices like constructed wetlands or standard stormwater control structures. The researchers noted that the system is most cost-effective when placed in nutrient hotspots where drainage flows are consistent throughout the year. This strategic deployment ensures that the investment by landowners results in the greatest possible environmental benefit for the surrounding community.

The success of the biochar pellets used in the second stage of the system is largely due to their unique chemical makeup. These designer pellets were manufactured by mixing sawdust with lime sludge, a common byproduct from drinking water treatment plants. This combination created a material that could trap twenty times more phosphorus than lime sludge alone. The high alkalinity of the biochar facilitates a chemical reaction that turns dissolved phosphorus into solid minerals that stay locked inside the pellets. This mechanism not only cleans the water but also creates a valuable byproduct. Once the biochar pellets are saturated with phosphorus, they do not need to be discarded. Instead, they can be applied back to farm fields as a slow-release fertilizer that enhances plant growth, completing a sustainable cycle of nutrient management.

The environmental implications of this study are significant for water quality policies in major agricultural regions like the Midwestern United States. By providing a scalable and low-barrier enhancement to existing woodchip bioreactor technology, the B2 system offers a way to meet ambitious nutrient reduction goals without sacrificing farm productivity. The researchers emphasized that the societal benefits of clean water, such as reduced damage from algal blooms and lower water treatment costs for cities, far outweigh the implementation costs of these bioreactors. As the technology moves toward broader adoption, it represents a major step forward in creating a more resilient and sustainable agricultural landscape that protects vital water resources for future generations.

Source: Zhou, H., Timalsina, H., Cooke, R., Bhattarai, R., & Zheng, W. (2026). Performance, stability, and cost-effectiveness of a bioreactor-biochar (B2) system for nutrient removal from agricultural drainage. Journal of Water Process Engineering, 81, 109258.