Revolutionizing Farming Practices: Harnessing Biochar for Sustainable Phosphorus Recycling

If farmers could not only prevent excessive phosphorus pollution in downstream waterways but also recycle these nutrients as slow-release fertilizers without incurring significant costs, what would that mean? In a groundbreaking field study, researchers from the University of Illinois in the United States have shown that this concept is indeed achievable.

The researchers utilized sawdust and lime sludge, byproducts respectively from a mill and a drinking water treatment plant. They combined these two components to create granules, which were then slowly burned under low oxygen conditions to produce a "designed" biochar. Compared to standalone lime sludge or biochar, this designed biochar demonstrated significantly higher phosphorus binding capacity. Crucially, once these granules have absorbed all the phosphorus they can hold, they can be spread onto fields, gradually releasing the captured nutrients over time.

Leveraging the numerous sustainable attributes of designed biochar, the team conducted field tests for the first time under real working conditions and monitored the phosphorus removal effects in fields for two years, with underground drainage pipes installed in the experimental plots. These wastewater flows passed through structures filled with two different sizes of designed biochar granules. The team tested 2-3 cm biochar granules in the first year of the experiment and switched to 1 cm granules in the second year.

Both sizes of granules were effective in removing phosphorus, but the 1 cm granules proved far more efficient, achieving phosphorus removal rates of 38% to 41%, compared to only 1.3% to 12% for the larger granules.