Advancing aerobic digestion efficiency using ultrafine bubbles in wastewater treatment

• Published in: Journal of water process engineering 2023-10, Vol.55, p.104072, Article 104072
• Main Authors: Temesgen, Tatek, Han, Mooyoung
• Format: Article
• Language: English
• Subjects: Aerobic digestion; Mass transfer; Nanobubbles; Sludge reduction; Ultrafine bubbles
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2023.104072

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 O2/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. [Display omitted] •NBs bubbles enhance volumetric mass transfer rate up to two-fold compared to CBs.•NBs facilitate the aerobic digestion of organic matter better than CBs.•The application of NBs improves the sludge volume reduction compared to CBs.•Application of NBs reduce the fouling rate of membranes compared to CBs systems.•The time for conventional aerobic digestion can be reduced by 1/3 by using NBs.