Effects of attached and suspended biomass on the dynamics of the microbial community and wastewater characteristics in sewers

Various transformations in wastewater quality along sewers, such as that due to self-purification, have been reported. However, little is known about the contributions of the attached (sewer-wall) and suspended biomass originally existing in wastewater due to a lack of experimental fields. In this study, we examined the effects of attached and suspended biomass on the dynamics of the microbial communities in sewers by conducting recirculating batch tests in a pilot-scale sewer system equipped with sponge media and a lab-scale aerating batch test, respectively. The changes in the quantity and quality of organic matter indicated that the contribution of the attached biomass to self-purification was much larger than that of the suspended biomass, because the former was sufficiently acclimated to the wastewater. Moreover, the microbial community analysis by pyrosequencing suggested that there were two candidates responsible for self-purification: 1) Comamonadaceae and Rhodocyclaceae, which could immediately proliferate under attached conditions and become dominant (15% each) in the attached biomass, and 2) Pseudomonadaceae, which could proliferate under suspended conditions after a lag period of several hours and remain a small component (4%) of the attached biomass.