1900.] on Bacteria and Sewage. 323 



The results obtained by the experimental bacterial treatment of 

 sewage at Manchester during the last two or three years bear out 

 generally those which have been obtained in London. The treat- 

 ment has differed in some details from that adopted in London. The 

 particles of coke constituting the coke-berls have been smaller. The 

 coke-beds have been subjected to a larger number of intermittent 

 fillings per day ; and the preliminary treatment in an open anaerobic 

 tank has been carried out with advantageous results. The scientific 

 experts who have suggested and watched the experiments state their 

 conviction that bacterial treatment is the treatment which is most 

 suitable for Manchester sewage, but that in order to secure the most 

 effective purification, the coke-beds must have sufficiently frequent 

 and prolonged periods of rest, and must be fed with sewage as free 

 as possible from suspended matter, and as uniform in quality as may 

 be. Preliminary anaerobic treatment is referred to as the best means 

 of securing uniformity in quality of the sewage, and of adapting it 

 to rapid subsequent aerobic purification. Four fillings in twenty- 

 four hours have been found suitable, if one day's rest in seven is 

 given to each coke-bed ; the number of fillings, however, may exceed 

 this without detriment to the bed or to the character of the effluent. 



Town sewage is found to arrive at the outfalls at an almost con- 

 stant temperature throughout the year. It rarely falls below 13° C. 

 And this temperature not only prevents the possibility of the coke- 

 beds being stopped by the freezing of the sewage, but also secures to 

 the bacteria one condition favourable to their action. When a bed is 

 too freely aerated by the passage of frosty air constantly through the 

 interstices of the coke this favourable condition is, however, seriously 

 interfered with, and the bed may even become stopped by the freez- 

 ing of the sewage. 



In the more recent experiments carried out in America by the 

 State Board of Health, Massachusetts, the tendency has been to use 

 fine coke, and to allow the effluent from the coke to pass through 

 sand. The passage of the liquid has either been allowed to take 

 place with the outflow widely opened, so that the bed never fills, or 

 the sewage has been allowed to fill the bed and to remain quiescent 

 in contact with the coke for a time, as in the English experiments. 

 The conclusions arrived at seem to be that the degree of purification 

 obtained by the use of fine coke and sand is very satisfactory, but 

 that the volume of sewage dealt with in a given time is smaller than 

 when larger coke fragments are used, and the tendency seems to be 

 to adopt the larger coke in order to expedite the more rapid drainage 

 away of the effluent. 



It will be seen from what has already been said that it is well 

 not to speak of this system of treatment as one of filtration. Filtra- 

 tion ordinarily implies a process of mechanical separation of material 

 suspended in a liquid. The fact that the coke-beds only commence 

 their purifying action after they have been " primed " by repeated 

 contact with sewage, and that this purifying action keeps increasing 



