(30d) Enhanced Mixing and Oxygen Transfer Using Air Pulsing

Aerobic biological treatment systems play a critical role in the management of wastewaters and sludges. However, the systems are costly to operate because the mass transfer rate of oxygen into the water phase is rather low and can be reduced still further by constituents in wastewater. The most common approach for improving mass transfer is to introduce smaller bubbles and/or improve mixing. The overall objective of this study was to determine if the transfer of air from conventional diffusers could be improved by altering the hydraulic currents about the rising bubbles with pulses of air from a newly patented device. Both pilot-scale (17,000 L) and full-scale (380,000 L) tests were conducted in which the novel, pneumatic-mixing system was used in combination with conventional aeration systems. Oxygen transfer rates and energy consumption were evaluated at different airflow rates and for different diffusers. Our hypothesis that the new system would enhance the oxygen transfer rate, as well as reduce energy consumption, was substantiated for activated sludge (1.2% solids) aerated at lower airflow rates (70 L/min). Tests with thickened activated sludge (4.9% solids) seemingly demonstrated an enhancement in oxygen transfer rate, as well. However, due to data variation and the high oxygen demand of the thickened sludge, the differences could not be shown to be statistically significant.