Superior water disinfection via ozone micro-bubble aeration: Performance and mechanism

Ozone has been widely applied in water disinfection because of its high oxidation potential (2.07 V). However, slow ozone gas-liquid mass transfer results in high ozone requirements and operating costs. Micro-bubble aeration can effectively increase the ozone mass transfer efficiency while reducing ozone dose. Here, we used a ceramic ultrafiltration membrane for ozone micro-bubble aeration. The disinfection performance and mechanism of ozone micro-bubble aeration towards pathogenic microorganisms were studied. Micro-bubble aeration reduced the total ozone dose by > 60 % for 6-log inactivation of Escherichia coli and MS2 coliphage. It also improved the disinfection efficiencies for Gram-positive bacteria by 3-log. Both ozone and ^•OH oxidation was enhanced via micro-bubble aeration because of efficient gas-liquid transfer. The equilibrium aquatic ozone concentration increased by 1.38 times and the ^•OH yield increased by 2.40 times compared with those with milli-bubble aeration. Consequently, ozone micro-bubble aeration caused severe membrane damage to bacterial cells and fragmented the bacterial DNA, which caused a rapid decrease in the bacterial metabolic activity (> 80 %). This study demonstrates that ozone micro-bubble aeration can boost broad spectrum disinfection and effectively reduce the ozone dose, which will facilitate the application of ozonation with a lower cost and reduced environmental impact.