再生水地下储存系统微纳米曝气过程解析及其对溶解性有机物迁移归趋的影响

In recent years, increased attention has being given to the subsurface storage and subsequent utilization of treated sewage effluent (reclaimed water) through aquifer storage and recovery (ASR) to meet growing demands for water particularly in seasonally arid regions. During ASR, water quality problems may arise when refractory dissolved organic matter (DOM) is introduced into the anoxic subsurface environment. Several studies have been performed to investigate the limited natural attenuation efficiency of soil-aquifer systems in specific sites or cases. However, research on in-situ enhanced attenuation is quite insufficient. To solve this problem, the micro-nano bubble (MNB) technology is introduced in this work to develop a long-effective method for the deep treatment, which is based upon the tiny bubbles’ mobility and oxidization characteristics. With the combination of experimental and theoretical analysis, the impact of reclaimed water quality on bubbles characteristics will be revealed, and the water purification mechainsm induced by MNBs will be elucidated in single liquid system. Then, columns experiments will be conducted to simulate the transport and fate of bubbles in saturated porous media (liquid-solid phases). At this point, the interactions between MNBs and DOM will be also examined and major impact factors will be identified through comparisons of batch experiments. Based upon these experimental data, numerical modelling that couples the multi-phase flow, attachment/deattchment and free radical oxidation will be built to quantify the evolution mechainsms of both MNBs and DOM during ASR. In addition, the feedbacks of application of MNBs to ASR project will be also evaluated by considering the hydraulic conductivity and the facilitated transport effect. Knowledge from this research will provide useful insights on the mechanism of MNB technology application to ASR system (especially the DOM purification ) and its environmental responses, which also support effective engineering design, operation & regulation and risk management in terms of theoretical analysis.

残余溶解性有机物在地下缺氧环境中难衰减是制约再生水地下储存水质安全的关键，已有研究多聚焦于土壤含水层系统有限的天然净化过程，其原位衰减效能的强化研究相对不足。本项目首次引入新兴微纳米曝气技术，旨在建立基于微气泡迁移-氧化特性的再生水地下储存系统有机物长效深度处理方法。通过地表入渗池单一水相及地下储水区固液两相体系的模拟实验和理论模型，分析再生水水质特征对微纳米气泡产生特性的影响规律，揭示液相体系微纳米气泡对再生水的净化机理，进而从达西尺度、孔隙尺度及界面尺度对微纳米气泡随流迁移过程及其对溶解性有机物的影响进行监测分析，揭示其控制因子和影响规律，建立数学模型定量刻画对流弥散、多相吸附阻滞、自由基氧化等过程的耦合作用机制，并评估微纳米气泡在降低渗流效率及污染物易化迁移方面的潜在影响。项目成果将为解析微纳米曝气用于再生水地下储存的机制、优化工程方案以及评估该过程的环境风险奠定理论和实践基础。

针对再生水中残余溶解性有机物带来的水质风险问题，本项目引入新兴的微纳米气泡技术，旨在建立基于微气泡迁移-氧化特性的再生水地下储存系统有机物长效深度处理方法。所取得的成果包括：.（1）研发了流控微气泡曝气技术，获批了3项发明专利，设计加工了相应的元件及设备，能够在无需加压驱动水相循环的条件下使普通微孔板产生的气泡尺寸更小，提高气相传质及复氧效能，提升率达到15-40%。.（2）对微气泡粒度、上升速度、自由基产生及复氧效能等特性进行了研究，结果发现：所产生的微气泡平均直径约1-7μm，上升速度远低于普通毫米级气泡，氧传质系数是传统曝气的6倍，溶解氧含量是后者的1.32倍，且微气泡溃灭过程能够产生羟基自由基，具有氧化分解有机污染物的潜能。.（3）开展微纳米气泡技术深度处理污水厂二级出水实验研究，分别探索了空气微气泡曝气、微气泡耦合光催化、臭氧微气泡等技术处理污水厂二级出水，对二级出水COD、TOC及UV254的去除率达到25-85%，也显著改变了出水有机物组成结构，提高了可生物降解性。.（4）开展再生水回灌渗滤一维土柱模拟实验，分析发现再生水中的溶解性有机物主要以色氨酸类蛋白质和溶解微生物代谢产物为主，回灌过程中土壤淋溶释放腐殖酸类有机物，这些释放的土壤腐殖酸类物质促进了共存有机污染物（四环素）的迁移扩散。.（5）开展了增溶剂及稳定剂添加强化臭氧微纳米气泡技术研究。液相臭氧浓度是不添加时的4-18倍，半衰期延长了3-36倍，相同条件下强化微纳米臭氧曝气去除水中4-CP的效率提高了1.5-3.6倍。添加剂-臭氧微气泡耦合大幅提升臭氧氧化的强度和寿命，有利于地表臭氧处理后继续将臭氧微气泡稳定输送到地下储存区。.（6）微气泡水地下回灌柱试验表明，再生水经地表微纳米曝气处理后回灌至地下。气泡水不会引起明显的渗流堵塞，多孔介质渗透系数及弥散度均为发生明显改变。. 项目成果将为解析微纳米曝气用于再生水地下储存的机制、优化工程方案以及评估该过程的环境风险奠定理论和实践基础。