Degradation mechanism of organic contaminants in complex contaminated groundwater in landfill sites with oxygen micro-nano-bubbles aeration

Complex contaminated groundwater in landfill sites poses a significant health threat. Oxygen micro-nano-bubbles (MNB O 2 ) aeration shows promise for remediation of such complex contaminated groundwater, while its mechanism for degradation contaminants remained unclear. This study investigated the degradation mechanism of organic contaminants in complex contaminated groundwater in landfill sites with MNB-O 2 aeration by contaminants degradation process and efficiency, dissolved organic matter (DOM) transformation as well as enzyme activity and microorganism. The test results indicated that after 105th day of MNB-O 2 aeration, the removal efficiencies of 5-day biological oxygen demand, chemical oxygen demand and α(254) in the water sample were 92.64 %, 50.56 % and 77.03 %, respectively. Additionally, the refractory DOM increased by 3 % to 11 %, while biodegradable DOM decreased by 57.63 %. MNB-O 2 aeration enhanced the activity of aerobic microorganisms but reduced the diversity, evenness and richness of microbial species in the soil sample. Moreover, it altered the microbial community of the soil sample and enhanced oxidation of organic substance in the water sample. MNB-O 2 aeration enhanced the biodegradation of the water sample, and its enhanced volatilization and strong chemical oxidation also contributed to organic contaminants degradation in the water sample. Collectively, the finding of this work will provide theoretical support for the practical application of MNB-O 2 aeration in remediation of complex contaminated groundwater in landfill sites.