PROTECTION OF RIVER AND HARBOR WATERS 23 



for the suspended matter conies through trickling beds in the long run in 

 about the same amount in which it goes on at the top, changed only in 

 its chemical nature. The effluent is far less well purified than that of a 

 sand filter. It is more turbid even than contact effluent and in appear- 

 ance may not even seem very different from untreated sewage; however, 

 the essential changes have been brought about. The more unstable 

 organic bodies have been oxidized and the effluent contains a sufficient 

 excess of oxygen so that succeeding changes will he nitrifications and 

 not putrefactions. At Birmingham, England, where the trickling process 

 has been most ably and exhaustively studied, a sewage How of 30 million 

 gallons a day is treated first in sedimentation and septic tanks and then 

 on trickling beds, having a total area of about thirty acres; and in dis- 

 missing an injunction granted against the city by a lower court the 

 Master of the Rolls has recently decided that the effluent from the Birm- 

 ingham works actually improves the character of the river into which it is 

 discharged. The large plants recently constructed in the Inited States at 

 Columbus. Ohio (twenty million gallons), at Washington, Pa. (one million 

 gallons^, at Reading, Pa. (two million gallons) and at Mt. Vernon, X. Y. 

 (three million gallons' are all of the trickling type. The trickling filter is 

 indeed an ideal mechanism for solving the essential problem of sewage dis- 

 posal. It exhibits the simplicity of all scientific applications, which are 

 merely intelligent intensifications of natural processes. A pile of stones 

 on which bacterial growth may gather and a regulated supply of air and 

 sewage are the only desiderata. We meet the conditions resulting from 

 an abnormal aggregation of human life in the city by setting up a second 

 city of microbes. The dangerous organic waste material produced in the 

 city of human habitations is carried out to the city of microbes on their hills 

 of rocks, and we rely on them to turn it over into a harmless mineral form. 



SEWAGE DISINFECTION 



So far nothing has been said about the problem of bacterial removal. 

 In general this is a subsidiary question in sewage purification. Frequently 

 the elimination of offensive organic decomposition is all that is necessary 

 and bacteria can be allowed to pass with the effluent into the stream, to 

 be removed by the quite distinct processes of water purification from any 

 water taken out for human consumption. Sand filtration effects a very 

 considerable purification in living and lifeless constituents alike; but the 



