314 SEWAGE AND ITS PURIFICATION 



120 million gallons daily of Manchester sewage would involve 

 works similar to waterworks as an adjunct to the sewage works, 

 but six times the size of the waterworks already existing. 



With contact beds, Mr. Dibdin considered "it was not a 

 question of whether they had more or less water, it was the 

 amount of the organic matter that was put on the bed, and if 

 that was not materially increased 'it mattered not how much 

 storm-water was put upon it. They had been able (at Sutton) 

 to put three or four times the quantity of storm-water on to a 

 bed than the volume of sewage they had put previously." As 

 a matter of fact, an occasional flush of storm-water through a 

 bacterial system is advantageous, as it removes some of the 

 products, and so stimulates the bacteria to fresh activity. 



The present regulations of the Local Government Board 

 have been already given (p. 148), and several towns have now 

 provided special storm -filters of sufficient extent to allow a rate 

 of filtration of 500 gallons per square yard per diem for the 

 balance of three times the dry weather flow in excess of that 

 required to be fully treated. Lloyd-Davies^ has described in 

 detail the design of the storm-water overflow chambers at 

 Birmingham, and discusses the various discharge formulae 

 which have been suggested by Santo Crimp (the one preferred), 

 Burkli-Ziegler, McMath, Kuichling, and others. 



A. J. Martin- remarks on the wide difference between the 

 dry-weather sewages of different towns, so that if a hard and 

 fast relation of volumes be prescribed as above, " the diluted 

 sewage which one public body may discharge without treat- 

 ment will be considerably stronger than that which another 

 authority will be called upon to purify." 



The Local Government Board insists that fixed weirs shall 

 be used, which will only come into operation when the sewage, 

 as mentioned above, has been diluted with five times its volume 

 of storm-water, that is, when a certain rate of flow in the sewer 

 is reached. But Martin proves that the amount of dilution 

 secured by a fixed weir is variable, and will at times be con- 

 siderably less than the works are intended to secure. 



Among the advantages of the bacterial processes involving a 

 large anaerobic preliminary chamber, is the ease with which 

 the works can be adapted for dealing with storm-water. In 

 such systems provision is made for the subsidence of solids, as 

 well as for their liquefaction, as a tank constructed to hold the 



^ Proc. I.C.E., 1905-6. '^ J. San. hist., xx., 4, p. 624. 



