CONTACT BEDS 171 



furnish a report as to the system best adapted for Manchester. 

 Various points demanded elucidation which had previously escaped. 

 These were chiefly (1) whether trade-refuse in the sewage impaired 

 the efdciency of bacterial purification ; (2) whether a portion, at any 

 rate, of the sludge can be destroyed by laacterial agency ; (3) whether 

 chemical precipitation, as in Dibdin's first method, before bacterial 

 treatment could be dispensed with ; (4) whether an aerobic process 

 alone or a combination of anaerobic and aerobic processes is the more 

 effective. With these objects in view a septic-tank (Cameron) 

 method and a filter-bed method were installed, and under the super- 

 intendence of Dr Gr. J. Fowler, the superintendent and chemist of 

 the Corporation Sewage Works, the observations were carried out.* 



That the experts' view of the bacterial treatment of sewage was 

 similar to that set forth above may be gathered from a preliminary 

 note : " The bacteria already existing in the sewage," they state, 

 "are brought by it on to the bacteria beds, or into the septic tank. 

 The former, by providing an enormously extended surface for the 

 development of bacterial growths, furnish an ideal habitat for the 

 aerobic micro-organisms which require air for the display of their 

 powers, whilst the septic tank, by confining a large volume of liquid 

 which is but superficially in contact with air, enables the anaerobic 

 micro-organisms to work to great advantage. It will be understood 

 that some time must elapse before the bacterial life attains its 

 maximum, either in the bacteria bed or in the septic tank, and 

 consequently the amount of sewage which can be purified therein 

 will gradually increase as time goes on."-f- 



The contact beds at Manchester were five in number, and of different 

 area. In principle they were of similar construction to those described 

 already. The filtering medium was clinkers laid to a depth of 3 feet, 

 and of varying size in the five beds, but uniform in each bed. 

 Clinkers which passed |-inoh mesh, rejected by ^-inch mesh, were 

 found to be the best grade.J 



Arrangements are made by which it is possible to admit sewage 

 to the beds in three different conditions, namely, raw, screened 

 sewage ; sewage which has undergone settlement in a small settling 

 tank; sewage which has undergone both settlement and anaerobic 

 action. Eventually a plan was adopted by which the sewage was 



* A full record of the work done at Manchester will be found in the Rivers 

 Department Reports for 1901, 1902, 1903, and 1904. 



t City of Manchester, Rivers Department. Experts' Report on Treatment of 

 Manchester Sewage, 1899, p. 12. (Mr Baldwin Latham, Professor Percy Frankland, 

 F.R.S., and Professor W. H. Perkin, Junr., F.R.S.). 



X It appears that the initial capacity of a contact bed is uninfluenced by the 

 grade of clinker. At first there is a rapid decrease in capacity, due in part to 

 sinking of the surface and in part to bacterial growth on the clinkers, which must 

 necessarily occupy some space, even though relatively little. In a comparatively 

 short time the beds acquire a constant average capacity. 



