PROTECTION OF RIVER AND HARBOR WATERS 



13 



Septic tank or modified sedimentation basin. Photograph of a model in the American 

 Museum 



day to dispose of, the task is far from simple. As a matter of fact this is 

 still a problem which awaits satisfactory solution. Cities on the seacoast 

 can carry their sewage sludge out to sea in tank steamers and dump it in 

 deep water with reasonable success and economy. For inland communities 

 there remain only the alternatives of burying or burning, both of which are 

 costly and unsatisfactory. Utilization seems theoretically promising, but 

 it has not been practically realized except with sewages like that of Brad- 

 ford. England, which contain an enormous proportion of fats from industrial 

 sources. 



THE SEPTIC TANK 



There is one form of the process of sedimentation which is specially 

 designed to minimize the sludge problem and which, to a limited extent, 

 does achieve that end. This is the septic tank, associated particularly with 

 the work of Cameron, but in its essential features dating far beyond the 

 year 1895, when he gave it that picturesque name. The septic tank is 

 indeed only a scientifically controlled and regulated cesspool, a sedimenta- 

 tion basin in which the suspended solids are removed by physical processes, 

 but in which they are afterward allowed to remain so that they may be 

 decomposed and reduced to the liquid form by the action of putrefactive 

 bacteria. 



The first septic tanks were tightly closed, in the opinion that this was 

 essential to the desired liquefaction. It has since been found, however, 

 that this is unnecessary. All that is essential is that the sewage, or the 

 sludge removed from the sewage, should be retained in a stagnant condition; 



