i8 SEWAGE AND ITS PURIFICATION 



in the past, with the proviso usually required that by screening, 

 sedimentation, or precipitation, the suspended solids should be 

 prevented from forming mud-banks and deposits of black sludge 

 on the river bed. 



Exeter, for example, a city which first gave a name to the 

 septic tank system, has also the historical position of being the 

 first to be sewered, and to discharge the combined sewage, 

 untreated, into a river. As the volume of the Exe is about 

 forty times that of the sewage, at the Local Government Board 

 inquiries no chemical evidence of pollution a few miles below 

 the city was obtainable. 



Composition of River Exe, 1894. 



TS Cl NH ^^^- Oxygen 



i.b. L.1. iNiig. ^jj^ absorbed. 



Above Exe Bridge ... 9*1 i'i9 0*007 o-oi6 0-29 



Below the town at Trew's 



Weir ... ... ... io'85 ^"^^ 0*025 0*023 0*30 



But in countries thickly populated there is no such opportunity 

 for the recovery of the river. Given even twenty-four hours for 

 the completion of the natural process, the river would arrive at 

 the next town denuded of its oxygen and in an unfit state for the 

 reception of more sewage. The result has been such a condition 

 as I have already mentioned in connection with the Seine and 

 Irwell. 



Even in America the distance between the cities and the 

 volume of the waterways has not prevented the discharge of 

 unpurified sewage from causing evils, which became specially 

 acute in periods of drought, as the resulting concentration of 

 refuse in their beds has made some of the rivers nothing better 

 than neglected sewers. Partly as a result of this, and partly 

 because recent court decisions have given encouragement to 

 many persons who are injured by the pollution of streams. 

 State Commissions have been in most places appointed to 

 consider the methods of purification. The longer the delay in 

 taking up this matter, the more expensive it will be when it 

 becomes imperative.^ As a rule it is everywhere necessary for 

 sewage to be prepared before it is discharged, and the methods 

 for so doing constitute our present subject. 



There can be no doubt that on the efficiency with which 

 refuse matters, and especially human excretal refuse, are 

 removed, the health of towns largely depends, and that im- 



^ Report, State of Connecticut, 1901. 



