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Residue biochar can be utilized as an adsorbent for ammonium nitrogen (NH4+-N) to prevent non-point source pollution. However, the limited adsorption capacity has restricted its extensive application. In this study, biochar was modified with hydrogen peroxide (H2O2), potassium permanganate (KMnO4), and sodium hydroxide (NaOH) to enhance its adsorption performance. A comparative analysis of the biochar surface characteristics was used to investigate the adsorption systems. The results indicated that the adsorption capacities of the modified biochar (MB) were significantly enhanced compared with the raw biochar (RB). At the highest NH4+-N concentration of 150 mg L−1, the adsorption capacities of RB-H2O2, RB-NaOH, and RB-KMnO4 increased to 3.0, 3.2, and 4.0 times that of RB, respectively. As predicted by the Langmuir isotherm model, the maximum adsorption capacities of these three MB were 13.93, 41.00, and 68.15 mg g−1, respectively. Ammonium adsorption on the MB surfaces was affected by surface adsorption, liquid membrane diffusion, and intra-particle diffusion. The specific surface area and pore volume of RB-KMnO4 were significantly enhanced, with an increase in active sites on the pore surfaces, thereby strengthening its adsorption capacity for NH4+-N. In contrast, the adsorption of NH4⁺-N by RB-H2O2 and RB-NaOH primarily relied on the substantial increase in –C–O functional groups, with additional contributions from other oxygen-containing functional (e.g. –OH, –COOH, and Fe–O). In conclusion, RB-KMnO4 exhibited the highest adsorption efficiency, with pore-based adsorption playing a dominant role over functional group-based adsorption. These findings highlight the critical role of pore structure optimization in enhancing the biochar adsorption capacity for NH4+-N. Highlights The biogas residue biochar was modified using H2O2, KMnO4 and NaOH. RB-KMnO4 created a superior ammonium adsorption capacity because of its exceptional pore structure. RB-H2O2 and RB-NaOH showed an enhanced adsorption performance attributed to its increased surface –C–O functional groups. Enhancing the pore structure of biochar more effectively boosted ammonium ion adsorption capacity.
Details
Surface properties;
Comparative analysis;
Biogas;
Rubidium;
Ammonium;
Hydrogen peroxide;
Nitrogen;
Liquid membranes;
Adsorption;
Surface chemistry;
Agricultural land;
Nonpoint source pollution;
Functional groups;
Particle diffusion;
Sodium hydroxide;
Potassium permanganate;
Point source pollution;
Carbon;
Charcoal;
Porous materials;
Residues;
Ion adsorption
; Song, Wenjing 1 1 Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Key Laboratory of Tobacco Biology and Processing, Ministry of Agriculture and Rural Affairs, Qingdao, China (GRID:grid.418524.e) (ISNI:0000 0004 0369 6250)
2 South Subtropical Crops Research Institute, Chinese Academy of Tropical Agricultural Sciences, Key Laboratory of Tropical Crops Nutrition of Hainan Province, Ministry of Agriculture and Rural Affairs, Zhanjiang, China (GRID:grid.509157.f)
3 Honghe Prefecture Branch of Yunnan Tobacco Company, Mile, China (GRID:grid.509157.f)
4 Honghe Prefecture Branch of Yunnan Tobacco Company, Mile, China (GRID:grid.418524.e)