London Sewer Water (Letheby).
| Grains per gallon. | |||
| Day Sewage. | Night Sewage. | Storm Sewage. | |
| Soluble matters | 55·74 | 65·09 | 70·26 |
| Organic matters | 15·08 | 7·42 | 14·75 |
| Nitrogen | 5·44 | 5·19 | 7·26 |
| Mineral matters | 40·66 | 57·67 | 55·71 |
| Phosphoric acid | 0·85 | 0·69 | 1·03 |
| Potash | 1·21 | 1·15 | 1·61 |
| Suspended matters | 38·15 | 13·99 | 31·88 |
| Organic | 16·11 | 7·48 | 17·55 |
| Nitrogen | 0·78 | 0·29 | 0·67 |
| Mineral | 22·04 | 6·51 | 14·33 |
| Phosphoric acid | 0·89 | 0·64 | 0·98 |
| Potash | 8·08 | 0·04 | 0·16 |
Letheby states that the sewer water in towns with water-closets has the following average composition per gallon:
| Organic matter | 27·72 |
| Nitrogen | 6·21 |
| Phosphoric acid | 1·57 |
| Potash | 2·03 |
Sewer water placed under the microscope reveals various dead decaying matters, besides swarms of bacteria, ciliated infusoria, amœbiform bodies, and fungi, consisting of spores and mycelium. The rotifera, diatoms, and desmids are few in number.[151] That a fluid having a composition such as sewage water has been shown to possess, when mixed with solid excreta, would, from the decomposition that so soon takes place in it, seriously endanger the health of those in whose habitations it was allowed to remain, is so self-evident to the sanitarian and pathologist that it is no wonder every civilised community should endeavour to get rid of this refuse from their habitations as speedily and effectively as possible. But the removal of the home sewage is a proceeding as illogical as it is imperfect if we afterwards neglect so to dispose of it as to render it innocuous or devoid of danger to the public health. The old method of getting rid of sewage (even when deprived of the fæcal matter) by turning it into rivers and streams, has, more particularly since the Report of the Rivers Pollution Commissioners in 1870, been gradually abandoned. That when sewer water passes into a river it undergoes a great amount of purification from oxidation, subsidence, and the agency of water-plants is undeniable.
[151] Parkes.
Letheby considered that if sewage mixed with twenty times its bulk of water flowed for nine miles it would be perfectly oxidised. It appears, however, from the experiments of Frankland, that so far as sewage when mixed with twenty times its volume of water being oxidised during a flow of ten or twelve miles, scarcely two thirds of it would be so destroyed in the flow of 168 miles, at the rate of one mile per hour, or after the lapse of a week. The results of Frankland’s experiments led him to infer that there is no river in the United Kingdom of sufficient length to effect the destruction of sewage by oxidation; and he adds, “there is no process practicable on a large scale by which the noxious material (sewage matter) can be removed from water once so contaminated, and, therefore, I am of opinion that water which has been once contaminated by sewage or manure matter is thenceforth unsuitable for domestic use.”
The discharge of sewage water, whether with or without solid excreta, into our springs and rivers, was a practice so dangerous and prejudicial to health that it is no cause for wonder the Legislature should, during the
session of 1876, have passed a measure the object of which was after the lapse of one year to facilitate legal proceedings being instituted against persons who permitted sewage or other deleterious refuse to flow into rivers or streams. This measure, known as the “Rivers Pollution Prevention Act,” is now in force, and permits offenders to be proceeded against; but it still leaves unsolved the important hygienic problem—How are we ultimately and with safety to the community to dispose of our sewage?
The numerous processes (the chief of which will be brought under notice) proposed for the attainment of this end have been divided by writers and authorities on sanitary science into—