MICROBIOTA OF SEWAGE TREATMENT PLANTS IN STREAMS 5 



tion in a standard counting cell. By this means a direct relationship is 

 established between the quantity of growth and the number of organisms 

 present therein. The vertical series of samples from the filter rock were 

 collected at 6-inch intervals over a distance of 5 feet, where a filter had 

 been opened for repair. In order to determine the microbiotic composition 

 of the film and solids removed by backwashing a filter, samples were col- 

 lected near the beginning and near the end of the operation. Before the 

 backwashing started, however, a sample for control was collected from the 

 combined filter effluent as it emptied into the final clarifier. 



Reaction of Microbiota to Changes in the Operation of a 

 Trickling Filter 



The sewage treatment plant at Owatonna, Minnesota, was investigated 

 5 times from March 18 to April 24, 1942, to determine the effects of changes 

 in plant operation upon the microbiota of the trickling filters. This sewage 

 plant was designed to handle a large volume of waste from a canning fac- 



Fig. 1. Effect of changes in the operation of the sewage plant at Owatonna, Minn, 

 upon the microbiota in the upper part of the second stage trickling filter. 



tory in the fall in addition to the normal flow of sanitary sewage from the 

 community of nearly 9,000 population. Provision was made in the design 

 for coping with the wide variation in strength and volume of sewage. Among 

 other devices for absorbing ''shock loads," the design called for two trickling 

 filters placed in series with an intermediate clarifier between. The microbi- 

 ota in the secondary filter only will be discussed. 



Analytical data obtained from earlier tests on this plant showed that 

 during the 9 months of the year when the cannery is inoperative, the primary 

 filter does most of the work and the secondary filter operates on a strictly 



