Studies of Bacterial Population During Sludge Digestion

Bacterial population studies on digesting sludge mixtures have been carried out in the laboratory of the Sanitary District of Chicago during the past three years. The purpose of these studies was to determine the importance and relationship of the bacterial numbers and groups present to the rates of digestion. It was desired to compare the bacterial numbers present in various sludge mixtures digesting at different rates on the basis of the digestible substrate rather than on the volume of the liquor and also to determine the approximate bacterial rates of reduction of the digestible substrate. REVIEW OF BACTERIAL WORK ON SEWAGE SLUDGE Fresh solids and Imhoff sludge The object of anaerobic sludge digestion is, briefly, to convert the putrescible sewage solids through the agency of bacterial activities to a relatively inert humus of reduced volume which can be easily air dried. The bacteriology of the digestion proc-esses has not been studied so extensively as the chemical changes involved (Buswell, 1928). Many strains of bacteria have been isolated from sewage and their biochemical functions determined (Clark and Gage, 1905). However, the r6le and importance of the various biochemical groups in digestion is not well known. Correlation be,tween any such groups and the course of digestio