Department of Environmental Sciences and Biotechnology, Hallym University, Chuncheon, Gangwon-do 24252, Republic of Korea.
Civil and Environmental Engineering Department, United Arab Emirates University, Al Ain 15551, UAE; National Water Center, United Arab Emirates University, Al Ain 15551, UAE.
J Contam Hydrol. 2020 Jan;228:103563. doi: 10.1016/j.jconhyd.2019.103563. Epub 2019 Nov 4.
Aqueous solutions of micro-nano bubbles (MNBs) containing ozone gas were injected through a NAPL-contaminated glass bead column. The glass column (15 cm × 2.5 cm) was packed with glass beads: the first 12 cm was packed with coarse glass beads while much finer glass beads were used to pack the remaining 3.0 cm of the column. Decane was used as the representative NAPL, to which an oil-soluble fluorescence tracer was added. The fluorescence tracer was considered as a constituent of the NAPL that readily reacts with ozone. Air and ozone-containing oxygen were used to generate MNB solutions, and injected through the column. In addition, HO was introduced to the O-containing MNB (O-MNB) solution to investigate the effect of hydroxyl free radicals on the NAPL removal. An ozone gas sparging experiment was also conducted for comparison. After 72 h of O-MNB application, a significant mass of n-decane (27.6% of the initial mass applied) was removed from the column. HO injection into the column during O-MNB application was effective in increasing the n-decane mass removal by 22%, compared to the O-MNB experiment. The rate of NAPL removal during O-MNB flushing was significant, although slower than ozone sparging. During O-MNB application, fast decay of fluorescence was observed; whereas, during co-injection of HO and O-MNB solutions, only a slight change in the fluorescence was observed. This indicates that oxidative degradation of NAPL during HO and O-MNB injection takes place only at the NAPL-water interface due to the reactivity of hydroxyl free radical, whereas ozone diffusion into NAPL induced the decay of the fluorescence tracer in the bulk NAPL. The removal characteristics during MNB application and ozone gas sparging were investigated based on the analysis of NAPL using mass spectrophotometer. When O-MNB and HO were co-injected, only n-decane was detected in the NAPL; while when O-MNB was used for flushing, oxidative products were found in the NAPL. More hydrophilic compounds were found in the NAPL after ozone sparging. This implies different removal mechanisms depending on the kind of oxidation agent, and the state of oxidizing fluid. Based on the findings in this study, the application of O-MNB could be a feasible option for cleaning up NAPL-contaminated aquifers.
含臭氧气体的微纳米气泡（MNB）水溶液通过NAPL 污染的玻璃珠柱注入。玻璃柱（15cm×2.5cm）用玻璃珠填充：前 12cm 用粗玻璃珠填充，而剩余的 3.0cm 用更细的玻璃珠填充。癸烷被用作代表性的 NAPL，并添加了一种油溶性荧光示踪剂。荧光示踪剂被认为是 NAPL 的一种成分，它很容易与臭氧反应。空气和含氧臭氧用于生成 MNB 溶液，并通过柱注入。此外，将 HO 引入含 O 的 MNB（O-MNB）溶液中，以研究羟基自由基对 NAPL 去除的影响。还进行了臭氧气体曝气实验进行比较。在应用 O-MNB 72 小时后，柱中大量的正癸烷（初始应用质量的 27.6%）被去除。在 O-MNB 应用过程中向柱中注入 HO 可有效提高正癸烷的去除率，比 O-MNB 实验提高了 22%。尽管比臭氧曝气慢，但 O-MNB 冲洗过程中的 NAPL 去除率是显著的。在 O-MNB 应用过程中，观察到荧光快速衰减；而在 HO 和 O-MNB 溶液的共注入过程中，仅观察到荧光的轻微变化。这表明，由于羟基自由基的反应性，HO 和 O-MNB 注入过程中 NAPL 的氧化降解仅发生在 NAPL-水界面处，而臭氧向 NAPL 中的扩散导致了 NAPL 中荧光示踪剂的衰减。基于质谱仪对 NAPL 的分析，研究了 MNB 应用和臭氧气体曝气过程中的去除特性。当 O-MNB 和 HO 共注入时，仅在 NAPL 中检测到正癸烷；而当 O-MNB 用于冲洗时，在 NAPL 中发现了氧化产物。在臭氧曝气后，NAPL 中发现了更多的亲水化合物。这意味着根据氧化剂的种类和氧化流体的状态，去除机制不同。根据本研究的结果，O-MNB 的应用可能是清理 NAPL 污染含水层的可行选择。
