214 REPORT— 1870. 



Tuming- from sewage ■works to the utilization of sewage by irrigation, which 

 the Rivers Pollution Commissioners have recommended as the only plan of dealing 

 with the sewage difficulty at present known, a very strong opinion has prevailed, 

 and has been acted upon up to the present time, that it is only necessary to run 

 the sewage over a surface of land covered with growing vegetation to extract from 

 it all that is fertilizing, and to render the effluent liquid perfectly harmless. It has 

 not been considered necessai-y that sewage shoidd pass through, as well as over, 

 the soil. The Rivers Pollution Commissioners themselves appear to have con- 

 sidered filtration, both downward and upward, separately from irrigation, and to 

 have reported upon each as distinct operations ; for, after advising a trial of inter- 

 mittent downward filtration on a large scale, they add that in all practicable cases 

 they would strongly recommend " the adoption of irrigation in preference to filtra- 

 tion," evidently considering that irrigation can be properly adopted without filtra- 

 tion. It is to this very important recommendation, as one likely to mislead if 

 not at once set right, that attention is called ; for by those who have made agricul- 

 ture a study, and have traced the effects of irrigation in England, Lombardy, and 

 elsewhere, it is considered that no irrigation is perfect unless it be accompanied by 

 filtration, and that if purification of the sewage is to accompany its profitable 

 application to land, it is absolutely necessary that no liquid whatever should pass 

 ort' the surface, but that the whole should go through the soil as well as over it. 

 In no case where the sewage has uniformly filtered through a sufficient depth of 

 soil has failure occurred. In one case (Walton Convalescent Hospital) within my 

 own practice, the effluent water from a small area of land receiving the sewage of 

 iipwards of 300 people, having been subjected last year to a properly devised mode 

 of natural filtration, in conjunction with irrigation, was analyzed by Dr. Odling, 

 and declared to be " unexceptionable potable water." In this case the soil is free 

 and porous, though it was excessively wet before it was drained. The sewage 

 having satisfied the growing vegetation is absorbed by the soil, and passing down- 

 wards by filtration (naturally incident to under-draiuage) is mixed with a constant 

 and copious flow of subsoil-water, the level of which is maintained by the imder 

 drains. At Briton's Farm, near Romford, Mr. William Ilope, A^.C, has dealt 

 with a somewhat different description of land, though of similar porosity. Ho 

 has had the whole drained at a minimum depth of 5 feet, and the effluent water 

 from the imder drains, though not equal in purity to that just referred to, shows 

 very distinctly the supei-iority of irrigation in connexion with filtration over irri- 

 gation simply. At Briton's (as at Walton) not a drop of water passes oft' the land. 

 Though the instances are few in which irrigation and natural filtration have 

 been associated in executed works of sewage utilization, they are sufficient to sup- 

 port the conclusion that no irrigation should be adopted in which filtration docs 

 not form a part of the system. At Penrith, Carlisle, and Bedford, the whole of 

 the sewage is absorbed at the sm-face and discharged in diftcrent ways from the 

 subsoil, and the amount of nitrogen and ammonia existing in the effluent water is 

 stated, in the report of the Rivers Pollution Commission, to be as follows : — 



In the first two cases there appears to be no nitrogen as nitrates and nitrites, 

 but in the last they are represented as •505. With complete pulverization of soil 

 sewage farms may be established with secxu'ity in any part of the countn^ inas- 

 much asnatm-al downward filtration, which is only another term for subsoil-drain- 

 age, is not only a sure means of purifying liquid sewage, as shown by the Rivers 

 Pollution Commissioners, but it is equally sure to free the atmosphere of those 

 noxious gases which several high medical authorities have feared may be evoh'ed 

 fvom the surfaces irrigated with sewage matter. 



