450 REPORT— 1873. 



competent, and necessarily so, to effect more than a separation of a small part 

 of the valuable ingredients of sewage, and that only a partial purification is 

 effected by them. Some of them may, however, be useful as methods of 

 effecting a more rapid and complete separation of the sewage-sludge. 



The upward-filtration process only effects a clarification of the sewage, and 

 is therefore no solution of the question. 



Weare's charcoal-filtration process, as carried on at Stoke-upon -Trent 

 Workhouse, did not give satisfactory results, the effluent water being in effect 

 weak sewage ; an opportunity will, however, soon be given for an examina- 

 tion of this process in a modified form on a much larger scale at Bradford, 

 and under more favourable conditions. 



Intermittent downward filtration through soil has been shown at Merthyr 

 Tydfil to afford a means of purifying the sewage under favourable conditions ; 

 but it cannot be said to be a method of utilization except to a very partial 

 extent, as the investigations made by the Committee showed that the effluent 

 water contained as much nitrogen as was originally in solution in the sewage, 

 but mainly as nitric acid instead of as ammonia and organic nitrogen. _ There 

 can be no doubt that the process would prove useful as an adjunct to irrigation, 

 or where a sufficient amount of laud for irrigation cannot conveniently be got. 

 By properly conducted sewage-irrigation a solution is afforded to the ques- 

 tion of sewage utilization ; it has already been stated that a precipitation- 

 process, or some clarifying process, may be found useful. If such process, 

 however, removes the phosphates from the sewage, it wiU, if employed for 

 irrigation, require to be supplemented either by the use of the precipitate 

 produced in the settling-tanks, or by that of some other manure supplying 

 phosphoric acid. 



In all instances it is essential that the land should be well underdrained, 

 and that the sewage should all pass through the soil and not merely over it ; 

 otherwise, as has been shown, it will only occasionally be satisfactorily 

 purified. 



The catchwater, or, as the Committee has termed it, the supersaturation 

 principle, is not defensible either on agricultural, chemical, or sanitary 

 principles. 



An irrigation-farm should therefore carry out intermittent downward fil- 

 tration on a large scale, so that the sewage may be always thoroughly puri- 

 fied, while at the same time the maximum of utilization is obtained. 



It is certain that all kinds of crops may be grown with sewage, so that the 

 farmer can grow such as he can best seU ; nevertheless, the staple crops must 

 be cattle-food, such as grass, roots &c., with occasional crops of kitchen vege- 

 tables and of corn. 



And it is also certain, from the analysis of the soil, that it becomes very 

 much richer under sewage-irrigation, and that some of the manurial consti- 

 tuents of the sewage accumulate in it. 



Cattle should be fed on the farm. The result would be a vast increase in 

 the production of meat and milk, the great desiderata of the populations pro- 

 ducing the sewage. 



Thus the system of farming must be specialized and capital concentrated, 

 the absence of which conditions has proved a great barrier to the satisfactory 

 practical solution of the sewage question. 



The Committee has not been able to trace any ill effects to the health of 

 the persons living around sewage-farms, even when badly conducted ; nor is 

 there any proof whatever that vegetables grown thereon are in any way in- 

 ferior to those grown with other manure. On the contrary, there is plenty 



