Advancing aerobic digestion efficiency using ultrafine bubbles in wastewater treatment
Tatek Temesgen, Mooyoung Han
Abstract
The application of ultrafine/nanobubbles (NBs) was tested as an aeration mechanism in a laboratory scale, semi-batch, biological wastewater treatment unit and compared with a similar scale, conventional bubbling supported aerobic digestion unit. The results showed that the oxygen utilization rate (OUR) and volumetric oxygen mass transfer coefficient ( kla ) were doubled from 0.075 to 0.159 mg O 2 /min and 0.07 to 0.13 respectively, through the application of NBs compared to the use of conventional bubbles (CBs). This was achieved by exploiting the sufficient residence time NBs can have in the aqueous system along with its capacity of high mass transfer surface area to volume ratio. The twofold increment in the OUR and kla due to the application NBs improved the biodegradation rate of the organic matter from 5.83 to 17.5 mg/l.hr compared to the application of CBs. Thus, 60 % of the hydraulic residence time reduction was achieved by the application NBs compared to CBs to achieve a similar amount of organic waste degradation. Moreover, the membrane filtration results also showed a reduction in the sludge load and fouling rate for aerobic membrane bioreactors supported by NB systems. A possible mechanism for sludge reduction was also proposed based on the results achieved.