Abstract:

In this study, biochar (YF600) was prepared through the pyrolysis of sheep dung at 600 ℃ to cost-effectively mitigate water eutrophication, lower nitrogen, and phosphorus levels, thus addressing the efficient utilization of sheep manure as a valuable resource. Box-Behnken design was used to investigate the effects of impregnation ratio, pH, and temperature on the adsorption of NH₄⁺-N, PO₄³⁻-P and NO₃⁻-N in water by YF600. The optimal adsorption conditions were determined using response surface methodology. The adsorption processes for the targeted pollutants were modeled using Langmuir and Freundlich isotherm equations. Additionally, pseudo-first-order and pseudo-second-order kinetic equations were applied to characterize the adsorption kinetics. The adsorption mechanism was comprehensively characterized by BET, FTIR, SEM-EDS, XRD, and elemental analyzers. The results showed that the key factors influencing the adsorption of NH₄⁺-N, PO₄³⁻-P by YF600 were immersion ratio, pH, and temperature in turn. In the case of NO₃⁻-N adsorption, the immersion ratio was more influential than pH, with temperature was not significant. The optimal adsorption conditions were: immersion ratio of 0.004, temperature of 26.2 ℃, and a pH=6.77. Under these specified conditions, the respective adsorption capacities for NH₄⁺-N, NO₃⁻-N, and PO₄³⁻-P were found to be 14 mg∙g⁻¹, 2.08 mg∙g⁻¹, and 4.93 mg∙g⁻¹. These observations closely aligned with the predicted values, suggesting that YF600 effectively adsorbed nitrogen and phosphorus, supporting the feasibility of the model. Better fitness of the Langmuir equation suggested monolayer adsorption dominated. Meanwhile, the pseudo-second-order kinetic model better captured the adsorption efficiency of YF600. In addition, Our results revealed that YF600 possessed a specific surface area of 63.91 m²∙g⁻¹, featuring numerous folds on the surface and irregular micropores. The biochar was found to be rich in carboxyl, ester, hydroxyl, and other oxygen-containing functional groups, and it contained a variety of elements, including Mg, Ca, Fe, Al, Na, Si. Among these parameters, higher concentrations of Ca²⁺, Mg²⁺, and O/C ratio were observed. These physicochemical properties confer excellent nitrogen and phosphorus removal capabilities of YF600. The nitrogen and phosphorus adsorption mechanism of YF600 primarily involve ion exchange, electrostatic adsorption, and complex precipitation. This study demonstrated that YF600 effectively adsorbs various forms of nitrogen and phosphorus, offering a straightforward process with low production costs. The study provided a theoretical foundation for the resource utilization of sheep manure and optimization of sewage treatment processes through the application of sheep manure biochar.

Key words: biochar, sheep manure, ammonium nitrogen, phosphate, nitrate nitrogen, response surface

摘要：

为缓解水体富营养化，通过经济高效的方法降低水体氮磷含量，同时解决羊粪资源化利用问题，以羊粪球为原料在600 ℃下热解制备生物炭（YF600），利用Box-Behnken设计实验，研究浸渍比、pH、温度对YF600吸附水中NH₄⁺-N、NO₃⁻-N、PO₄³⁻-P效果的影响，运用响应面优化法确定最佳吸附条件。用吸附等温线中的Langmuir方程、Freundlich方程和吸附动力学的准一级方程、准二级方程对3种污染物的吸附过程进行拟合，并通过BET、FTIR、SEM-EDS、XRD、元素分析仪分析其理化性质和吸附机理。结果表明，对YF600吸附NH₄⁺-N、PO₄³⁻-P的影响显著性大小为：浸渍比>pH>温度，吸附NO₃⁻-N为：浸渍比>pH（温度影响不显著）。拟合出最佳吸附条件为浸渍比0.004，温度26.2 ℃，pH=6.77，此时NH₄⁺-N、NO₃⁻-N、PO₄³⁻-P的单位吸附量分别为14、2.08、4.93 mg∙g⁻¹，实验结果与预测值基本吻合，说明YF600复合吸附氮磷效果较好，该模型具有可行性。Langmuir方程拟合更好证明其以単分子层吸附为主；准二级动力学模型能更好地反映YF600的吸附效率。表征结果为YF600比表面积达63.91 m²∙g⁻¹，表面有大量褶皱且分布着不规则微孔，含丰富的羧基、酯基、羟基等含氧官能团和Mg、Ca、Fe、Al、Na、Si等多种元素，且Ca²⁺、Mg²⁺含量高，O/C高，以上理化性质使其具备良好的脱氮除磷性能，其氮磷吸附机理主要为离子交换、静电吸附和络合沉淀作用。研究结果表明，YF600复合吸附多种不同形式氮磷效果良好且工艺简单、生产成本低，对YF600氮磷吸附机理进行了解释分析，旨在为羊粪资源化利用与羊粪炭优化污水处理工艺提供理论依据。

关键词: 生物炭, 羊粪, 铵态氮, 磷酸盐, 硝态氮, 响应面