[Quantitative studies of heterotrophic bacteria from two purification plants in Schleswig-Holstein].

Saprophytic bacteria have been analysed as to their quantity during a one year period in all clarification steps of the sewage treatment plants of Plön and Kiel. The numerical amount of the bacteria varied between 10(5) and 10(10) per ml. They show extreme variations in the in- and outflow of the primary settling tanks. From the activated sludge tanks on the highest bacterial counts could be found. During July and August a distinct maximum appeared in the biological treatment, followed by a tremendous decrease in September and October. During this period bulking sludge appeared in the Kiel plant.