Effect of bubble size on microbial community in intermittently-aerated activated sludge process in wastewater treatment

Abstract

Although finer aeration bubbles improve the oxygen dissolution efficiency and activated sludge treatment performance, the effects of the changes in bubble size on the microbial community in activated sludge during intermittent aeration are often unknown. This study investigated the effect of aeration bubble size on the total microbial community, including prokaryotes (bacteria) and eukaryotes, during wastewater treatment at a food-processing plant with intermittent aeration in a single-tank reactor. Two types of diffusers were employed, showing distinctly different bubble size distributions, as confirmed by the Sauter mean diameter and bubble diameter histograms. Although the wastewater was well treated regardless of the bubble size, the microorganisms involved in the treatment process varied widely in terms of prokaryotes and eukaryotes. In prokaryotes, the genus Thiothrix characteristically appeared in the fine-bubble reactor, whereas the genus Kouleothrix appeared in the large-bubble reactor. In eukaryotes, osmotrophs of the phylum Cryptomycota, a fungus, were found to be dominant in the fine-bubble reactors, whereas phagotrophs of the genera Arcella, Euglypha, and Parachela were found to be dominant in the large-bubble reactors. The anaerobic time per day (dissolved oxygen concentration of less than 0.1 mg/L) differed depending on the bubble size, and this was thought to be reflected in the differences in the microbial communities.