Bubble Generation by Micro-Orifices with Application on Activated Sludge Wastewater Treatment

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 30 µm to 200 µm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with rubber membrane diffusers bubbles generated from the micro-orifices transfer up to 82% more oxygen content into the continuous phase at up to 75% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency. Therefore, we also expect an improvement in the oxygen transfer coefficient KLa and standard oxygen transfer efficiency SOTE compared to commercial rubber membrane diffusers