SEWAGE DISPOSAL 159 



matter in solution in the sewage, so that such putrescible matter 

 appears in the effluent in a form which will not undergo any further 

 putrefactive change ; and thirdly, the removal of disease-producing 

 bacteria, which will be present in practically all crude town sewage. 



These results are not obtained equally by the various methods 

 employed, but it will be best to consider each of these separately. 



1. Disposal without Purification. 



Various antiquated forms of carrying out this mode have been 

 used. Seaside places have often been content to carry their un- 

 treated sewage out to sea. Towns situated on the banks of rivers 

 have frequently by means of a conduit conveyed sewage into the 

 running stream. There is nothing necessarily objectionable in this 

 mode of disposal, for both in the sea and in running river water the 

 sewage matter will become disintegrated and dissolved. Yet the 

 method is liable to give rise to very serious nuisance, unless the 

 conditions requisite for solution are carefully studied. Nuisances 

 may arise in respect to the pollution of bathing grounds, or actually 

 injurious effect upon the health of the population on the banks of 

 the river, or by injury to fish (by reducing the oxygen in the water, 

 destroying the food of fish, admitting poisonous matters into the 

 water, or by suspended matters clogging the gills of fish). In a 

 general way it may be said that before the admission of sewage into 

 any body of water is permissible, two points require consideration, 

 namely, the removal as far as practicable of the matters in suspension 

 in the sewage, and the sufficiency of dissolved oxygen in the water 

 completely to prevent any putrefaction. Broadly, also, it may 

 be said that for towns situated on non-tidal streams some form of 

 bacterial treatment is preferable. Towns on tidal rivers require as 

 a rule a chemical precipitation process.* 



* Foulerton has recently drawn attention to a modified chemical precipitation 

 process treatment of sewage which is to be discharged into a tidal water, which 

 may be carried out as follows : — The efiiuent from an ordinary chemical precipita- 

 tion process is distributed continuously over a coarse ' ' filter-bed " by means of a 

 sprinkler. In this way a thorough aeration of the effluent before its discharge into 

 the stream is ensured, and provision is made for the complete removal of all traces 

 of solid suspended matter. As the effluent from the sedimentation tanks trickles 

 slowly through the coarse Interstices of the filter-bed, any sohd suspended matter 

 which has escaped precipitation in the previous part of the process will be deposited, 

 and then dealt with by bacteria. And in the result an effluent, fully oxygenated, 

 free from the solid suspended matter of the crude sewage, and with the bacteria 

 originally present in the crude sewage considerably decreased in numbers, will be 

 discharged into the stream. The somewhat higher proportion of dissolved organic 

 putrescible matter in the effluent from such a chemical process, as compared with 

 the proportion which may obtain in a good bacterial process, is probably not a matter 

 of considerable importance in the case of tidal waters. — Report on Pollution of Tidal 

 Fishing Waters by Seioage, 1903, p. 8. 



