' CHAPTER XI 



BACTERIAL PURIFICATION {continued) 



Unaided bacterial processes — Scott-Moncrieff's tank — Conditions of 

 hydrolysis — The Exeter septic tank — Tank and filter deposits — 

 Statistics of septic tank plants — Ames Tank — Hydrolytic Tank 

 — Separate Zones — Moncrieff's trays — Nitrogen and Oxygen 

 relations — Caterham — Manchester experiments — Birmingham 

 — Sheffield — Leeds — American experience. 



We next come to processes that rely for purification on the 

 natural action of bacteria without extraneous aid. This idea 

 had been indicated in the '' Automatic Scavenger " of Mouras 

 (p. 205), and could also be gathered from the Massachu- 

 setts investigations ; but prior to the latter,^ in 1890, Scott- 

 Moncrieff made a number of experiments with regard to the 

 observed rapid liquefaction of organic matter in sewers. As he 

 has expressed it, ''unless an actively liquefying process was at 

 work it would be impossible for the solid organic matter thrown 

 into a long sewer, with accretions going on more or less all the 

 way, ever to reach its destination along so slight a declivity b}^ 

 any flushing that was available." If this action, which was 

 soon shown to be due to liquefying bacteria, could be intensified 

 and regularly conducted within a small area, it promised to 

 eliminate the sludge difficulty. 



It had long been known that in the slow filtration of sewage, 

 more particularly when the direction was upwards, so that little 

 or no mixing with air occurred, very considerable changes in 

 the organic matter were brought about, entirely unconnected 

 with oxidation. Thus in one of Frankland's experiments in 

 1870, when a strong London sewage was made to traverse, 

 " continuously upwards so as to exclude aeration," a layer of 

 sand, the analysis of sewage and effluent given is the more in- 

 structive as the meaning of it was not understood at the time. 



^ The Lawrence, Mass., Experiment Station has been in continuous service 

 since the autumn of 1887, but the earlier results related to mechanical and 

 chemical treatment. 



249 



