Effect of nanobubble application on performance and structural characteristics of microbial aggregates

Abstract Herein an investigation on the performance and structural properties with aspects of stability, composition, functional group, and three-dimensional distribution were approached to evaluate the influence of nanobubble aeration to the two most common microbial aggregates, activated sludge and biofilm. This study found that applying nanobubble effectively provided extra oxygen for microbial aggregates and achieved a 10.58% improvement in total nitrogen removal. The structure of microbial aggregates was enhanced, where extracellular protein and polysaccharides respectively increased as maximum as 3.40 and 1.70 times in biofilm and activated sludge, accompanied by the development of activated sludge floc size and the thickness of biofilm. Further investigation on extracellular polymeric substance and surface of microbial aggregates showed the composition of functional substances of microbial aggregates were shifted by the application of nanobubble, especially the oxygen-sensitive ones. Confocal laser scanning microscopy imaging visualized that the nanobubble changed the morphology of biofilm to a more evenly one. However, an adaptive process was more needed for activated sludge rather than biofilm, it suggested application of NB optimized the distribution of functional microorganisms in-depth and the metabolism pathway of them by accelerating the structure development of microbial aggregates, especially for biofilm.