北京市北运河沉积物对氮、磷的吸附/解吸动力学特征

选取北运河土沟、榆林庄及和合站3个典型河道断面,进行河道0~60 cm深度沉积物对氨氮、磷酸盐的吸附/解吸批平衡静态试验研究,采用多种动力学模型分析北运河沉积物对氮、磷的吸附/解吸动力学特性,提出适用于北运河沉积物吸附/解吸特性的动力学模型,并对模型参数的主要影响因素进行探讨.结果表明:1)北运河典型断面各深度的沉积物对氨氮和磷酸盐的吸附/解吸过程总体呈现3个阶段:快反应阶段—慢反应阶段—平衡阶段;在0~0.5 h的快反应阶段可完成吸附或解吸总量的60%,且对氮、磷的吸附速率大于解吸速率.2)北运河各断面对氨氮与磷酸盐的平衡吸附量表现为S(榆林庄)S(土沟)S(和合站);对氨氮的平衡解吸量表现为S(土沟)S(榆林庄)S(和合站),对磷酸盐的平衡解吸量表现为S(和合站)S(土沟)S(榆林庄),沉积物对氨氮和磷酸盐的吸附以化学吸附为主,平衡吸附与解吸量随断面深度的增加而减小,0~20 cm表层沉积物对氮、磷的吸附能力较强.3)Lagergren二级动力学模型对各深度沉积物的吸附/解吸过程拟合最优,模型参数公式为k2=S-0.369max+0.163;qe=0.022 Smax+18.077 Kf+41.947.通过模拟得出在400 mg/L氮、磷浓度下吸附于沉积物中的氮、磷污染物会随着解吸过程释放52%~80%的氨氮和6%~42%的磷酸盐,可能不仅二次污染上覆水体,还随河水下渗从而对地下水质形成潜在污染风险.

Adsorption/desorption dynamic characteristic of sediments on nitrogen and phosphorus in the north Grand Canal of Beijing

Typical sections of north Grand Canal in Beijing (Tugou, Yulin Village and Hehe Station) were selected, and the upper 0-60 cm sediments were collected to operate batch equilibrium static experiment on adsorption and desorption of nitrogen or phosphorus. Adsorption/desorption dynamic characteristic analysis was developed combing the experiment result and several dynamics models. Based on that, we aimed to provide a suitable dynamics model to describe the adsorption/desorption dynamic characteristic of sediments on nitrogen and phosphorus in the north Grand Canal, as well as figure out the influence aspects of the model parameters. The research showed that:1) Three typical stages, which were quick reaction stage, slow reaction stage and equilibrium stage, were obviously showed in adsorption and desorption curves of nitrogen or phosphorus on sediments in the north Grand Canal; 60% of the total adsorption and desorption amount occurred in the first stage (0-0.5 h), and the adsorption rate is higher than the desorption rate. 2) equilibrium adsorption/desorption quantity of every typical sections in the north Grand Canal were difference, the order of equilibrium adsorption quantity is:S_{(Yulin Village)} > S_(Tugou) > S_{(Hehe Station)}, the order of equilibrium adsorption quantity for ammonia nitrogen is:S_(Tugou) > S_{(Yulin Village)} > S_{(Hehe Station)}, for phosphate:S_{(Hehe Station)} > S_(Tugou) > S_{(Yulin Village)}; and chemical adsorption was the main interaction; with the depth increasing, the adsorption rate and desorption rate were decreased, and the upper 0-20 cm has a higher adsorption ability. 3) Lagergren second-order kinetic model performed the best fitting result with the experiment data, and the regression equations are k₂=S_max^-0.369+0.163;q_e=0.022 S_max+18.077 K_f+41.947. Through the simulation solution, we obtained that there would be 6%-42% of phosphate and 52%-80% of nitrogen detaching from the sediments by desorption process at 400 mg/L nitrogen and phosphate concentrations, which will probably cause recontamination to the overlying water and pollution risk to ground water through river water percolation.