Modified biochars prepared from straw, pig manure, and chicken manure biogas residues were used to adsorb and remove ammonium nitrogen (NH₄⁺-N) and chemical oxygen demand (COD) in wastewater. The results showed that at 400–600°C, the adsorption performance of the biogas residue biochars increased with pyrolysis temperature, reaching the maximum at 550°C. Biochar from chicken manure biogas residue exhibited strong NH₄⁺-N (20.3%) and COD (28.1%) adsorption capacity. Through FeCl₃ modification, the Fe content on the surface of the biochar increased, and the adsorption data of the modified biochar conformed well to the pseudo-second-order kinetics and Langmuir model, and the reaction was dominated by chemical adsorption. The fitting calculation revealed that the FeCl₃-modified biochar from chicken manure biogas residue showed maximum NH₄⁺-N (55.29 mg/g) and COD (186.24 mg/g) absorption capacity. These results indicated that modified biochar from biogas residue could have potential application for the treatment and recycling of biogas slurry.

Graphical abstract

中文翻译：

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利用沼气残渣生产沼气及其对废水中氨氮和化学需氧量的吸附

由秸秆，猪粪和鸡粪沼气残渣制备的改性生物炭用于吸附和去除废水中的铵态氮（NH ₄ ⁺ -N）和化学需氧量（COD）。结果表明，在400–600°C下，沼气残渣生物炭的吸附性能随热解温度的升高而增加，在550°C时达到最大值。鸡粪沼气残渣中的生物炭表现出较强的NH ₄ ⁺ -N（20.3％）和COD（28.1％）吸附能力。通过FeCl ₃改性后，生物炭表面的Fe含量增加，改性生物炭的吸附数据与拟二级动力学和Langmuir模型很好地吻合，反应以化学吸附为主。拟合计算显示，来自鸡粪沼气残渣的FeCl ₃改性生物炭显示最大NH ₄ ⁺ -N（55.29 mg / g）和COD（186.24 mg / g）吸收能力。这些结果表明，利用沼气残渣制备的改性生物炭在沼气浆液的处理和循环利用方面具有潜在的应用前景。

图形概要