缓释氧钝化剂对滇池底泥磷地球化学形态转化的作用机制

Dianchi Lake, located in the central of Yunnan-Guizhou Plateau, has had a long history of water eutrophication problem. Phosphorus (P) is one of the most limiting nutrients for the eutrophication. At present, the external P loading has been controlled effectively. However, the P in the sediments plays a major role in the total amount of P present in the water column. In situ passivation technology has been shown to be one of the most fast, cost-effective and highly efficient approach for the control of P releasing from sediments to water body, and the research on passivation focuses on the release mechanism of sediment P and it influence factors, deactivator development, and the mechanism of passivation. At present, many researches have elucidated the release mechanism of sediment P and its influencing factors and have achieved accordant conclusions (i.e. Fe-P is the main releasing speciation and the dissolved oxygen (DO) is the intensive influencing factor). However, there are still many problems in the aspects of passivator selction, accurate analysis of P speciation, action mechanism of passivator and co-influencing by environmental factors. This research takes improving passivation environment DO value as the breakthrough point, selects Dianchi as research subject, and uses oxygen slow-releasing passivator. Through a series of environment controlled experiments, discusses passivation efficiency and kinetics characteristics of oxygen slow-releasing passivator under various environmental conditions, analyzes the concentrations of anion and cation in interstitial water before and after passivation and predicts P speciation in sediments by applying MINTEQ geochemical model, adopts a combination of SEP and 31P NMR technique to find out the key environment factor that influences passivation efficiency and to clarify its mechanism, discusses the comprehensive influencing mechanism of multiple factors that affect sediment P geochemical speciation transformation. This research also employs a combination analysis of SEP, 31P NMR and XANES, to identify the distribution and proportion of P speciation (especially Fe-P and Org-P) under conditions of anaerobic, aeration and oxygen slow-release by different passivator during different period in different layer to clarify the passivation mechanisms of oxygen slow-releasing passivator on molecule/atom scale. Research findings will provide scientific basis and theoretical support for the application of in situ passivation technique in eutrophication remediation of Dianchi Lake.

原位钝化技术可控制湖泊底泥磷的释放，但钝化时的环境因素严重影响着钝化效率和时效。目前，多因素对钝化效率的综合影响机制、磷赋存形态的详细信息、不同钝化剂在不同环境下对磷形态转化的作用机制等问题尚不十分清楚。本研究拟采用缓释氧钝化剂，以改善钝化环境中水体DO值为突破口，选取滇池作为研究对象，通过一系列环境条件控制实验，研究不同外界环境条件下，缓释氧钝化剂的钝化效率和钝化动力学特征；应用MINTEQ模型对底泥磷形态进行预测，采用SEP和31P NMR相结合的手段查明影响钝化效率的关键环境因子并厘清其影响机制，研究在改善水体DO值条件下，多环境因子对底泥磷地球化学形态转化的综合影响机制；采用SEP、31P NMR和XANES相结合的研究手段，从分子/原子尺度深入研"缓释氧"特性对底泥磷形态转化的作用机制，阐明缓释氧钝化剂的钝化原理。研究成果可为钝化技术在湖泊富营养化治理中的成功应用提供理论支持。

原位钝化技术具有生态、经济、快速有效等特点，但由于缺乏环境友好、廉价、高效的钝化剂，环境因素对钝化效率和时效性的综合影响机制尚不十分清楚等问题，限制了其应用。本项目对钢渣、缓释氧剂、黏土矿物、粘合剂的配比进行研究，研发出释氧速率慢、钝化效率高的缓释氧钝化剂；选取滇池入湖河口区沉积物为研究对象，对研究区各形态磷的分布及“源”、“汇”特征进行研究；通过室内钝化实验研究，研究缓释氧钝化剂在钝化过程中对沉积物磷形态转化的作用机制。项目预期研究任务已按期完成，通过研究，获得如下结果：. 1）对钢渣、过氧化物、粘土矿物、粘合剂等进行了筛选和复配研究，成功的制备出环境友好、释氧速率慢，时效长、钝化效率高的湖泊沉积物磷钝化剂复配配方，钢渣︰过氧化钙︰蒙脱土︰水泥（质量百分比）=45%︰25%︰20%︰10%；. 2）目前，盘龙江河口区、古城河河口区和观音山、白鱼口区沉积物中的磷依然是滇池上腹水体中磷的“源”，而捞鱼河和淤泥河入湖河口区沉积物中的磷则暂时与上腹水体之间维持相对的平衡状态；. 3）温度、DO值、pH值和扰动频率等环境因子对研究区沉积物中磷的释放量的影响最大的是“泥-水”微环境中的DO值；. 4）缓释氧钝化剂对改善“泥-水”微环境中的DO值的效果要优于人工曝气方式；. 5）缓释氧钝化剂的钝化机理是：一方面通过调节“泥-水”微环境的DO值，控制了沉积中Fe/Al-P的释放。另一方面，钝化剂中的铁盐和钙盐可使沉积物中的部分Ex-P转化为Fe/Al-P和Ca-P，进而降低了沉积物中磷释放的潜在风险。. 目前，由于“外流域引水工程”的实施，滇池水体的富营养化状况暂时得以缓解，但滇池沉积物内源磷释放的风险依然存在。随着滇池水质的逐步改善，沉积物中磷的释放风险正在逐渐凸显。因此，本项目的研究结论可为目前滇池内源治理的“靶区”选择提供理论支持。后续应继续对各入湖河口区沉积物中磷的“源”和“汇”特征进行跟踪研究，为滇池富营养化治理方案的制定提供科学依据。