木屑生物炭对填料土的氮磷吸附及雨水持留改良影响

现阶段生物滞留系统的填料土存在氮磷营养盐净化效果不稳定、雨水持留能力下降等问题.为评估木屑生物炭作为生物滞留系统填料土添加剂的改良效果,选用对照填料土和施用了木屑生物炭的改良填料土进行对比研究,通过理化性质测试、等温吸附实验、土柱实验和土水特征曲线测定,研究木屑生物炭对填料土的改良影响与优化机制.结果表明,木屑生物炭孔隙率大、比表面积大、饱和含水率高和CEC高,可优化填料土的结构,提升填料土的离子交换能力;木屑生物炭对填料土的氮磷吸附改良效果突出,对NH4+-N的最大吸附量提高了 2.80倍,去除率由31.30％提高至64.10％,对PO43--P的最大吸附量提高了 1.28倍,去除率由61.90％提高至90.00％;经木屑生物炭改良后,填料土的饱和含水率提高1.63倍,渗透系数提高2.43倍,在各含水率下的基质吸力明显增加.木屑生物炭的添加可优化生物滞留系统填料土的性能,加强对雨水径流中氮磷营养盐的吸附,提高系统的渗透性和雨水持留能力.

Improvement of Nitrogen and Phosphorus Adsorption and Stormwater Retention Capacity by Hardwood Biochar as an Additive Material in Filler Soil

The additive materials in bioretention facilities play a leading role in stormwater treatment to purify polluted runoff. Currently, the traditional additive materials have several problems, such as unstable purification effects of nitrogen and phosphorus and decreasing rainwater retention capacity. It has been demonstrated that hardwood biochar has the ability to retain nutrients and improve soil water retention in some soils. Here, physicochemical property tests, isothermal adsorption experiments, column experiments, and soil water characteristic curve tests have been conducted on control and hardwood biochar modified filler soil to assess the feasibility of hardwood biochar as an additive material in filler soil. The results showed that the hardwood biochar with porosity, large specific surface area, high saturated water content, and high CEC could optimize the structure of the filler soil and improve the ion exchange capacity of the filler soil. Hardwood biochar had a remarkable improvement effect on ammonium and phosphorus adsorption in the filler soil. The maximum adsorption capacity of NH₄⁺-N increased by 2.80 times, and the removal rate increased from 31.30% to 64.10%. The maximum adsorption capacity of PO₄^3--P increased by 1.28 times, and the removal rate increased from 61.90% to 90.00%. After the addition of hardwood biochar, the saturated water content of the filler soil increased by 1.63 times, and the permeability coefficient increased by 2.43 times. The matric suction of hardwood biochar modified filler soil at each water content increased significantly. In conclusion, the addition of hardwood biochar can optimize the performance and grading of the filler soil, enhance the adsorption of ammonium and phosphorus in rainwater runoff, and improve the bioretention systems'' permeability and rainwater retention capacity.