164 BACTERIAL TREATMENT OF SEWAGE 



Moncrieff introduced his cultivation beds filled with flint, coke, and 

 gravel. In this system the crude sewage passes into the bottom of 

 the bed, the liquid portion rises through the bed, and the suspended 

 matter is kept back at the bottom, where it undergoes solution by the 

 action of bacteria present upon the surfaces of the flints, etc. In order 

 to complete the process highly oxygenated water was added to the 

 effluent, which was then passed down a " nitrification channel," where 

 further oxidation was secured. The results of this process were 

 superior to anything previously obtained in this country. 



Between the years 1891-95 Mr Dibdin experimented with sewage 

 from which solid organic matter, had been previously removed by 

 screens or chemical sedimentation. Such sewage he passed through 

 filter-beds of coke breeze, and was able by intermittent filtration 

 through such beds (i.e. allowing rest periods between charging the 

 filters) to obtain a purification of more than 70 per cent. 



Dr Clowes has carried on this work on behalf of the London 

 County Council, and he reports that the sewage is allowed to flow 

 into large tanks which contain fragments of coke about the size of 

 walnuts. As soon as the level of the liquid has reached the upper 

 surface of the coke-bed, its further inflow is stopped, and it is 

 allowed to remain in contact with the bacteria coke surface for about 

 three hours. It is then allowed to flow slowly away from the 

 bottom of the coke-bed. After an interval of about seven hours, the 

 processes of emptying and filling the coke-bed are repeated with a 

 fresh portion of sewage. The coke-bed is usually filled in this way 

 twice in every twenty-four hours. The aeration of even the lowest 

 portions of a deep coke-bed seems to be satisfactory in the above 

 method of working, since the air present in the interstices of the 

 coke, between two fillings with sewage, usually contains 75 per cent, 

 of the amount of oxygen present in the open air. 



In dealing with the sewage of the metropolis, Dr Clowes holds 

 that it is best to allow the roughly-screened raw sewage to undergo a 

 somewhat rapid process of sedimentation, in order to permit these 

 matters to subside ; and then to pass the sewage direct into the coke- 

 beds. The dissolved matters and the small amount of suspended 

 matters which are still present in the sewage are then readily dealt 

 with by the bacteria of the coke-bed, and practically no choking of 

 the bed occurs. The sewage effluent from the coke-bed is entirely 

 free from offensive odour, and remains inoffensive and odourless even 

 after it has been kept for a month. 



The chemical character of this effluent may be briefly indicated 

 by stating that on an average 51 '3 per cent, of the dissolved matter 

 of the original sewage, which is oxidisable by permanganate, has 

 been removed by the bacteria, and that the portion which has 

 been removed is evidently the matter which would become rapidly 



