Corn cob biochar shows promise for removing ammonia and microplastics from contaminated water, offering a low cost, climate friendly tool for future treatment systems.
Researchers at the University of Delaware have transformed discarded corn cobs and other agricultural byproducts into high performance biochar filters that capture both ammonia and tiny plastic particles from water. In laboratory tests, optimized biochar removed up to 64 percent of dissolved ammonia and more than 97 percent of polystyrene micro and nanoplastics without leaching harmful chemicals back into the water. The study points to a practical way to clean polluted water while recycling agricultural waste and locking away carbon.
“We are taking something farmers usually throw away and turning it into a tool to protect water and public health,” said lead author Ruogu Tang from the Department of Animal and Food Sciences at the University of Delaware. “By carefully tuning how we make biochar, we can trap both dissolved pollutants like ammonia and particulate contaminants like microplastics in a single filtration step.”
Why ammonia and microplastics matter
Ammonia and micro or nanoplastics are two very different but increasingly common contaminants found in rivers, lakes, and wastewater around the world. Ammonia from fertilizer run off, livestock operations, and industry can harm fish at low concentrations and contribute to algal blooms, while microplastics have been detected in drinking water, seafood, and even human tissues. Existing treatment technologies often target one contaminant type at a time and can be expensive, difficult to regenerate, or prone to generating secondary waste.
From crop residues to engineered biochar
In the new study, the team produced biochar by heating corn cobs, cocoa husks, walnut shells, bamboo, and poultry litter under low oxygen conditions at temperatures between 350 and 700 degrees Celsius for up to two and a half hours. The process created highly porous, carbon rich solids whose surface chemistry and internal pore network depended strongly on the original feedstock and the exact heating conditions. Woody materials such as bamboo and walnut produced biochars with especially high surface areas, while corn cob biochar struck a balance of carbon content, pore structure, and functional groups that made it a strong candidate for detailed water filtration tests.
Among the corn cob samples, biochar made at 700 degrees Celsius for 2.5 hours, labeled CCB700, stood out. This material had the highest carbon content, well developed pore structure, and favorable surface charge, all of which helped it act as an efficient adsorbent in simple gravity driven filters.
How well the biochar filters performed
To test performance, the researchers packed ground biochar into funnel style filter units and passed water containing ammonia or fluorescent polystyrene micro and nanoplastics through the biochar layer. At an initial ammonia concentration of 10 parts per million, a 30 gram bed of CCB700 removed 63.95 percent of ammonia in a single pass, while still achieving more than 60 percent removal at lower loadings. At very low ammonia levels around 1 part per million, all tested corn cob biochars removed more than 65 percent of ammonia, but performance dropped for all materials at 100 parts per million as adsorption sites became saturated.
For plastic particles, the results were even more striking. High temperature corn cob biochars prepared at 550 and 700 degrees Celsius consistently removed around 90 percent or more of polystyrene particles across sizes from 0.10 to 2.10 micrometers and across a wide range of concentrations up to 20 million particles per milliliter. Even the lower temperature biochar, CCB350, could reach above 90 percent removal for larger microplastics when used at higher loadings, although its performance dropped for the smallest nanoplastic sized particles and at the highest particle concentrations.
Mechanisms and safety
Microscopy and surface analyses showed that the biochar captures pollutants through a combination of physical and chemical mechanisms. Scanning electron microscope images revealed that microplastics became trapped in surface layers and pores, while measurements of pore volume confirmed that internal pores filled with particles during filtration. Changes in surface charge and infrared spectra indicated that dissolved ammonia, present mainly as ammonium ions, binds through electrostatic attraction and interactions with oxygen containing functional groups on the biochar surface.
Crucially for real world use, the team saw no detectable release of any of the 16 priority polycyclic aromatic hydrocarbons regulated by the US Environmental Protection Agency in 24 hour leaching tests. All measured PAH levels in the solid biochar remained below the European Biochar Certificate safety limit, suggesting low risk of introducing new toxic compounds during water treatment.
Reuse and climate smart potential
The researchers also showed that corn cob biochar filters can be regenerated and reused. After treating 10 parts per million ammonia solutions, used biochar was dried and re pyrolyzed under the same conditions, then tested again across three regeneration cycles. CCB700 maintained more than 55 percent ammonia removal in the third cycle, with only modest declines from its initial performance, while lower temperature biochars also retained substantial capacity over repeated use.
“Biochar gives us a way to link water purification with climate smart agriculture,” said senior author Juzhong Tan. “By converting agricultural residues into reusable filters, we can cut waste, store carbon in a stable form, and tackle emerging contaminants in one integrated approach.”
Toward sustainable water treatment
Because biochar can be produced from locally available crop residues and animal wastes, the authors see strong potential for decentralized applications in rural communities, livestock operations, and small scale treatment systems. With further optimization of reactor design, filter configuration, and regeneration strategies, biochar based media could complement or partially replace more costly commercial adsorbents in removing both traditional pollutants and new threats such as micro and nanoplastics. The work underscores how engineering the structure and chemistry of a simple carbon material can unlock new tools for protecting water quality while advancing circular and climate conscious use of agricultural resources.
