Bacterial communities in samples of wastewater and biofilms were analysed using terminal-restriction fragment length polymorphism in order to assess the level of variation found in bacterial communities in combined sewers. Samples were collected between November and July at two sites in the sewer system in Nantes, France. Biofilms were collected both from the part of the pipe wall that is only submerged during rain events and from the daily flow variation zone. In addition wastewater samples were collected. High variation in the bacterial communities were found in the wastewater samples when comparing sampling time and site. In the biofilm samples, evidence of seasonal variation was detected when comparing communities in samples from November with the samples collected between April and July. The study starts to identify the timescale at which changes happen in the bacterial communities in sewer biofilms, which may over time become important in the further development of in-sewer process models.
