3o8 SEWAGE AND ITS PURIFICATION 



When an apparatus is designed from the point of view of 

 overcoming these objections, it is obvious that the methods of 

 bringing about the contact between the sewage and the bacterial 

 surfaces must be radically different. 



In the filtration of hydrolysed effluents, whenever there is 

 a continual dripping upon a particular spot, growth is liable to 

 occur of a filamentous character allied to Crenothrix, but it 

 has been found that if a sufficient time is allowed to elapse 

 between the discharges of liquid on the upper surfaces, this 

 filamentous clogging is generally avoided. In a Whittaker bed 

 at Leeds in May, 1899, a falling off in the results was due to 

 the surface being covered by an abundant gelatinous growth of 

 Pylobolus, which prevented aeration and appeared to be pro- 



FiG. 56. — Distributing Channel, showing Flange at End. 



moted by the heating of the liquid. As the growth did not 

 penetrate more than a few inches, the surface was removed and 

 replaced by a foot of very coarse coke, which proved effectual. 



Mr. Dibdin states that some streaming filters were objection- 

 able on account of their smell, and at Carshalton relief had been 

 found by covering the beds with peat moss carried on wire 

 network. 



Continuous filter beds are frequently constructed for aeration 

 purposes with lower layers of very coarse material, but it is 

 found better to build them with a perforated base or "aerating 

 floor," arched or supported by girders, leaving an air space at 

 the base of the bed (see Chap. X.). 



Scott- Moncrieffs Sewage Testing Apparatus (Fig. 57) has been 

 in operation at Staines, Keighley, and elsewhere. It consists of 

 a box about 8 ft. high, 3 ft. wide, and i foot broad, filled to a 

 depth of exactly 6 ft. with the filtering material to be tested, 



