A study of the bubble column evaporator method for improved sterilization

• Improved bubble column sterilization rates were produced using high temperatures.
• This was shown to be about 7 times more energy-efficient than simple boiling.
• The bubble collision model for this novel sterilization process was verified.

A bubble column was used to study sterilization using bubbles of different sizes (mm to cm) produced via bubble coalescence or by inhibiting coalescence through the addition of NaCl. The rapid transfer of heat from small, hot (dry) gas bubbles to the surrounding water was used as an effective and energy efficient method of sterilizing contaminated water. It is shown that the continuous flow of (dry) hot gases, even at 250 °C, only heat the aqueous solution in the bubble column to about 58 °C and it was also established that coliforms are not significantly affected by even long term exposure to this solution temperature. Hence, the effects observed appeared to be caused entirely by collisions between the hot gas bubbles and the coliform particles close to the sinter, where the gas bubbles were still hot enough (i.e., within 5–10 cm of the sinter surface). It was also established that the use of high air inlet temperatures can reduce the thermal energy requirement to only about 14% (about 64 kJ/L) of that required for boiling (about 450 kJ/L).