Microbubble Application to Enhance Hydrogenotrophic Denitrification for Groundwater Treatment

Abstract

The physicochemical and biological characteristics of milli-microbubbles were compared to evaluate their performance on hydrogenotrophic denitrification (HD) for groundwater treatment in remote areas. The hydrogen supply was controlled at 1.14 L/d with 40 mgN/L of NO3-N. The microbial community structure in two bubble reactors was investigated by high throughput sequencing. Microbubbles enhanced biodegradation in the HD system, providing a maximum nitrogen removal efficiency of 99%. Approximately 50% of total hydrogen was utilized for biological nitrate removal with the highest hydrogen effectiveness achieved at 1.21 g N/g H2. In contrast, millibubbles achieved less than 10% efficiency and 9.9% of total hydrogen was consumed for biological nitrogen removal. Thaueraspp., Hydrogenophagaspp. and Rhodocyclaceaeof Proteobacteriaphylum were the dominant bacteria in the microbubble reactor, whereas Methyloversatilis spp.was dominant in the millibubble reactor, in which a relatively low amount of hydrogen (0.6 mg/L) was dissolved. The differences can be attributed to the higher hydrogen transfer efficiency (45×10-3s-1) and lower rising velocity (0.31 mm/s) of the microbubbles system than the millibubbles system (2×10-3s-1and 480 mm/s). The micro-hydrogen bubble technology affords increased hydrogen effectiveness, reduced energy consumption, and modified system design. Therefore, it is more appropriate for enhancing HD.

Keywords

• millibubble
• microbubbles
• mass transfer
• hydrogenotrophic denitrification
• nitrogen removal
• bacteria community