932 EXPERIMENT STATION RECORD. 



liquefying power of bacteria are described, with discussions of the accuracy of these 

 methods and the application of biochemical methods to the study of sewage and the 

 effluents from sewage filters. 



"The chemical changes which take place in the sewage in the process of purifica- 

 tion may be divided into three groups: (1) putrefaction — that is, the breaking down 

 of the complex organic matter into simpler forms; (2) nitrification and oxidation — 

 that is, the oxidation of the nitrogenous matter into nitrites and nitrates, and of 

 carbonaceous matter into carbonates; (3) denitrification — that is, the breaking down 

 of nitrates and nitrites into ammonia and free nitrogen. 



"These three processes probably all go on to a greater or less extent in sewage 

 filters of all the various types. If a filter is so constructed and operated that oxidiz- 

 ing processes are active throughout the entire depth, the reduction of nitrates is pre- 

 vented and practically all the nitrogen in the applied sewage will appear in its 

 effluent. If, however, the construction and operation of a filter is such that both 

 oxidizing and reducing actions occur, much nitrogen will be lost. The effluents of 

 intermittent continuous filters in good operation contain practically all the nitrogen 

 applied, while the effluents of contact filters in good operation show a large disap- 

 pearance of nitrogen. From these results we should conclude just what is shown by 

 the biochemical examination of the effluents of these various classes of effluents. It 

 was found that the effluents from the contact filters, in which a considerable amount 

 of reducing action takes place, showed denitrifying and nitrogen-liberating coeffi- 

 cients many times greater than those obtained for the effluents of the tricklim: filters 

 in which conditions are always favorable for oxidation and nitrification. 



"The effluents of intermittent sand filters in good operation also contain a large 

 portion of the nitrogen applied. During the cold weather, however, nitrification 

 may become inert in filters of this type, and while the effluents may remain fairly 

 good in appearance, free ammonia and low nitrates will be given, combined with a 

 considerable loss of nitrogen. In the biochemical examination of the effluents from 

 sand filters located out of doors it was found that during the winter those filters 

 which were giving unsatisfactory purification, as shown by small amounts of nitrates 

 in the effluents, showed, as would be expected, great power to reduce nitrates and 

 to liberate nitrogen, whereas in summer, when nitrification is active, these powers 

 are very slight or entirely absent from these filters. 



"Studies of sands from filters in which nitrification was active and from others in 

 which nitrification was not active show that the sands from the latter filters are able 

 to induce a rapid and complete reduction of large amounts of nitrates, while sands 

 from filters which are actively nitrifying do not cause this denitrification, and, 

 further, studies of the bacteria in these sands and in the effluents from these filters 

 show that a very considerable portion of the bacteria in the filters in which nitrifi- 

 cation is not active are able to reduce nitrates to nitrites and ammonia quite readily, 

 while the reverse is true of the bacteria from filters in which nitrification is active. 



"The ordinary methods of bacterial analysis do not yield information concerning 

 the part which the various types of bacteria play in the process of purification. The 

 present studies have been devoted to finding methods by which these functions may 

 be determined and to the expression of these functions in such a manner that they 

 may yield this information. In order to be of the most value it has been found that 

 the determination of these functions must be approximately quantitative. Methods 

 have been devised for the determination of the total power of the bacteria in a sample 

 to produce ammonia from organic matter (ammonifying coefficient) ; of their power 

 to reduce nitrates (denitrifying coefficient), and of their power to liberate nitrogen 

 (nitrogen-liberating coefficient. ) So far the methods have been applied only to sew- 

 age and to the effluents of sewage filters, but they are also directly applicable to the 

 study of the conditions of bacterial life in the material of the filters themselves." 



