The microbial community composition has been surveyed in 50 WWTPs most years since 2006 by advanced DNA analyses, providing an enormous knowledge bank. Each WWTP now “know its microbes” and can use this information about key species involved in nitrogen removal, phosphorus removal, and settling properties to optimise the operation as changes in community composition are often reflected in plant performance. In order to have day-to-day information, Aalborg University has tested “online DNA analyses”, where hand-held DNA sequencers of the size of a smartphone are used for identification of the microbes in a few hours – directly at the WWTP. The results are very promising and day-to-day or week-to-week analyses are soon a reality for surveillance and control of microbes at many Danish WWTPs.