Application of Microbubbles toward Repression of Biofilm Formation and Removal of Biofilm Formed inside Aluminum Brass Pipes with Iron Film Used for Heat Exchangers

Abstract

The effectiveness of seawater that contains air and nitrogen (N₂) microbubbles was examined for its ability to repress biofilm formation and remove biofilm formed inside an aluminum brass pipe covered with iron film. As a result, biofilm formation was effectively repressed by the injection of N₂ microbubbles into a continuous seawater flow running through the pipe. After three weeks, the fouling factor of the pipe was 9.0×10^－5 m²・K W^－1, while the value was 15.0×10^－5 m²・K W^－1 when seawater alone was delivered. The most effective result was obtained by using seawater after removal of injected N₂ microbubbles. The value was 5.2×10^－5 m²・K W^－1. To remove biofilm already formed inside the pipe, a seawater flow containing N₂ microbubbles reduced biofilm to 0.4 mg cm^－2, as dry weight, from 0.9 mg cm^－2 of the control. While the value was reduced to 0.6 mg cm^－2 when seawater, from which injected N₂ microbubbles had been removed, was delivered into the pipe. Formation of iron film on the inner surface of an aluminum brass pipe was confirmed even when Fe^2＋ was supplied to the seawater flow with injected N₂ microbubbles. These results indicate that the seawater flow containing N₂ microbubbles has the potential to remove biofilm formed inside the pipes. Seawater from which N₂ microbubbles had been removed is applicable for the repression of biofilm formation during operation of machinery.