162 BACTERIAL TREATMENT OF SEWAGE 



so separated would not be sufficiently free from noxious matters to 

 allow of its being discharged at the present outfalls as a permanent 

 measure. It would require further purification, and this, according 

 •to the present state of knowledge, can only be done effectually by its 

 application to the land." 



The present Eoyal Commission has recorded its view in a pre- 

 liminary report on land treatment, " that peat and stiff clay lands are 

 generally unsuitable for the purification of sewage, that their use for 

 this purpose is always attended with difficulty, and that where the 

 depth of top soil is very small, say six inches or less, the area of such 

 lands which would be required for efficient purification would in cer- 

 tain cases be so great as to render land treatment impracticable." On 

 the subject of effluents they state in the same preliminary report : — 



" We may, however, even at this stage, point out that as a result 

 of a large number of examinations of effluents from sewage farms and 

 from artificial processes, we find that while in the case of effluents 

 from land of a kind suitable for the purification of sewage, there are 

 fewer micro-organisms than in the effluents from most artificial pro- 

 cesses, yet both classes of effluents usually contain large numbers of 

 organisms, many of which appear to be of intestinal derivation, and 

 some of which are of a kind liable, under certain circumstances at 

 least, to give rise to disease. 



"We are of opinion, therefore, that such effluents must be 

 regarded as potentially dangerous, and we are considering whether 

 means are available and practicable for eliminating or destroying 

 such organisms, or, at least, those giving rise to infectious diseases." . 



Until comparatively recent years, the above methods of treating 

 sewage were the only ones available, or, at all events, practised. But 

 now, as is well known, some new applications of the biological treat- 

 ment of sewage have been introduced, which call for consideration. 

 Their popularity has been due to it being possible to adopt them 

 where suitable soil did not exist for the other biological methods, and 

 to the fact they have been on the whole less expensive to work. 

 These new departures depend upon bacteria contained ia the sewage. 

 The process may depend mainly upon anaerobes (Cameron's Septic 

 Tank or Scott-Moncrieff's process) or aerobes (Duckett's filter or 

 Dibdin's filter). These may be conveniently dealt with in more or 

 less chronological order. 



The Bacterial Treatment of Sewage 



In 1872 the Berlin Sewerage Commission reported that sewage 

 matter was converted into nitrates, not simply by molecular processes 

 but by organisms present in sewage and soil. Muntz, Mueller, and 

 others demonstrated this in various ways. Mueller, indeed, had shown 



