NOTES ON THE PURIFICATION OP 1 SEWAGE. XXI. 



are practically the same, the question naturally arrises. Is this 

 the best we can do 1 or are any of the other too numerous to 

 mention processes in vogue likely to give a better result? 



To answer such a question it must be borne in mind that both 

 of these systems are primarily anaerobic, and the much argued 

 question as to whether the preliminary breaking up of the solids 

 and preparation for the final oxidation is necessarily anaerobic has 

 not yet been settled. 



From the investigations of Dr. Clowes at Crossness, on a 13 

 feet deep coke bed and on the coarse grain bed at Sutton — both of 

 which receive the sewage intermittently, the action upon the organic 

 matter retained in it, was found to be purely aerobic, and the 

 effluents have frequently reached the nitrifying stage. It there- 

 fore appears to the writer that apart from any question of 

 expediency, equal results can be attained by either. In practice, 

 however, the use of a tank, be it septic tank or a Scott-Moncrieff; 

 lias much to recommend it. 



In the first place such a tank as either of the foregoing is able 

 to contend with any rush of sewage and the nature of such incom- 

 ing sewage can be to a certain extent somewhat equalised, and a 

 smoothing influence exerted on the sewage leaving the tank, which 

 of itself is most important. Then again no screening is necessary 

 as in the case of the coarse grain filter, where if not screened most 

 of the solids remain on the surface. For these reasons a pre- 

 liminary tank seems to be desirable, nor is it essential that such 

 tank should be covered in, since air and light are sufficiently 

 excluded naturally, to enable the anaerobic organisms to perform 

 their functions; but the possibility of nuisance arising from an 

 open tank is another question which can only be settled by time 

 and experience. From the writer's acquaintance with open tanks 

 or carriers containing sewage the conviction is forced upon him 

 that they are not above suspicion. 



Through the courtesy of Mr. W. M. Hamlet, Government 

 Analyst, I am able to give you the percentage of purification 



