The study showed that the engineered material, named BC5-500, achieved strong adsorption performance, especially for phosphate, and maintained useful activity even after repeated reuse cycles and in real swine wastewater.
Nitrogen and phosphorus pollution remains a major environmental challenge because large inputs from fertilizers, domestic discharge, and industrial and agricultural wastewater can destabilize aquatic ecosystems and trigger eutrophication. Adsorption has become a widely studied treatment route because it is simple, fast, and efficient, while biochar is especially attractive due to its porous structure, surface functional groups, and tunable chemistry. Previous studies have improved nutrient capture by modifying biochar with metals such as magnesium, iron, and aluminum, but adsorption performance still varies widely with feedstock and modification method. In this context, calcium-based modification is especially promising because calcium is abundant, relatively safe, inexpensive, and has strong affinity for ammonium and phosphate. At the same time, the rapidly expanding Camellia oleifera industry generates large volumes of shell waste that are difficult to dispose of, creating a practical need to convert this residue into higher-value materials.
A study (DOI:10.48130/bchax-0026-0002) published in Biochar X on 30 January 2026 by Anping Wang’s & Jie Wang’s team, Guizhou Normal University & Qiandongnan Agriculture Science Institute, reports that Ca(OH)2-modified shell biochar can effectively remove ammonium and phosphate through different but complementary chemical pathways.
To create the adsorbent, the team first cleaned, dried, ground, and pyrolyzed Camellia oleifera shells at 500 °C to obtain the base biochar BC-500, then mixed it with calcium hydroxide, washed and dried the product, and subjected it to a second pyrolysis step to produce BC5-500. They screened nine modified biochars and found BC5-500 to be the best performer, reaching adsorption capacities of 26.66 mg·g−1 for ammonium and 186.18 mg·g−1 for phosphate in preliminary tests. The material was then characterized by SEM, BET surface area analysis, FT-IR, XRD, and XPS. These analyses showed that calcium modification roughened the biochar surface, increased pore volume and average pore diameter, introduced calcium-containing active phases, and created more reactive sites for nutrient capture. Adsorption tests further showed that ammonium uptake was favored under alkaline conditions, peaking at pH 11.0, while phosphate uptake was strongest in acidic conditions, peaking at pH 2.0. Kinetic modeling showed that both adsorption processes followed the pseudo-second-order model, indicating chemisorption-dominated behavior. Isotherm analysis suggested that ammonium adsorption involved both monolayer and multilayer behavior, whereas phosphate adsorption was better described by the Freundlich model, consistent with multilayer adsorption on a heterogeneous surface. Temperature experiments showed that phosphate adsorption declined as temperature increased, while ammonium adsorption first decreased and then rose at higher temperatures. Mechanistic evidence from FT-IR, XRD, and XPS indicated that ammonium removal was driven mainly by ion exchange, whereas phosphate removal relied on both ion exchange and, more importantly, calcium-phosphate precipitation, including formation of hydroxyapatite-like products. Reuse tests showed that the biochar still retained substantial adsorption after five cycles. In actual swine wastewater, ammonium removal was limited, likely because of low concentration and competition from coexisting contaminants, but phosphate removal remained highly effective, reaching 97.73%, demonstrating particular promise for phosphorus-rich waste streams.
Overall, the study presents a practical example of waste-to-resource engineering: an abundant agricultural by-product was converted into a functional adsorbent capable of targeting two problematic nutrients in polluted water. Although its phosphate removal was much stronger than its ammonium performance in complex real wastewater, the material combined affordability, reusability, mechanistic clarity, and applicability to livestock effluents. The work therefore offers a useful foundation for developing biochar-based nutrient management technologies that link agricultural residue utilization with cleaner water and more sustainable resource recovery.
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References
DOI
10.48130/bchax-0026-0002
Original Source URL
https://doi.org/10.48130/bchax-0026-0002
Funding information
This work is supported by the project of the Guizhou Provincial Department of Science and Technology (Grant Nos Qiankehe Zhicheng [2023] 078, Qiankehe Jichu-ZK [2024] zhongdian 055, and Qiankehe Pingtai-KXJZ [2025] 023), and Projects of Forestry Research in Guizhou Province (Grant No. GUI[2022] TSLY07).
About Biochar X
Biochar X is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.