72 Sewage Disposal and River Pollution. 



can be manufactured from sewage, but simply that an honest 

 attempt can be made to recover that amount of natural value 

 which sewage undoubtedly has. In former systems the more 

 volatile and evanescent of these elements have been allowed to 

 pass away, or have been simply neutralised. I would go farther 

 — retain them. In the apparatus before me there are three, or 

 indeed four, sections, for I propose to perform in detail what 

 other systems do all together, and so fail to accomplish either. 

 In the first section I apply the natural process which is to be seen 

 at the mouth of the Blackstaff — i.e., to allow the solid matter to 

 settle by quiescence to the bottom. In the second section the 

 liquid, freed from the grossest of this, flows between and through 

 filter boxes filled with, let us say, coarse lime or chalk. These 

 operate in a twofold manner — they serve both as a mechanical 

 filter and as a chemical neutraliser for such acids as exist more 

 or less in all sewage. In the third section the liquid, having 

 gone through these preliminary stages of purification, falls to a 

 lower level, one foot, or two or three feet, as the case may be, 

 but falling by means of spray plates in a highly divided form 

 through which a current of air passes. This is aeration, and is 

 the system nature applies in every river or running stream. 

 Then in the fourth section the highly aerated and oxidised 

 liquid passes through a second series of filter boxes containing 

 charred and earthy matter whose natural affinity for ammonia 

 takes up more or less of this valuable constituent of manures. 

 The final stage of this is subsidence, in the last tank, of all the 

 remaining sediment, chiefly the finer organic particles. The 

 fully purified effluent then passes away at any, even if necessary 

 at a dead level — it is clear water, no longer sewage. Each part 

 of the system is in duplicate, each may be of any convenient 

 size, and any number can be placed side by side, so as to be 

 applicable either to one central area, to a series of drainage 

 areas scattered over one large town, or to a separate institution, 

 workhouse, a hospital, or to a private house, or group of houses. 

 The chief difficulty in all sewage questions has been the disposal 

 of the " sludge." In the system I propose the sludge is not the 

 manurial element in which I rely— for that purpose it may be 



