BACTERIAL PURIFICATION 



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The anaerobic cultivation tank, and Cameron's septic tank, 

 which followed it, do similar work, and both processes to a 

 great extent obviate the sludge difficulty of the precipitation 

 method, and also the choking up of the open downward contact- 

 beds of Dibdin. Kenwood and Butler point out that an upward 

 cultivation has advantages over a septic tank in which there 

 are "no surfaces provided for the organisms. They say, " while 

 upward filtration offers a better prospect of effecting the separa- 

 tion and solution of the suspended matters of sewage, it, at the 

 same time, reduces the pollution of the effluent better than any 

 system which aims at their removal by digestion in a hollow 

 chamber, such as the septic tank." Cultivation tanks on these 



Fig. 26.— Filter House at Caterham. 



lines were constructed at Finchley, and are alluded to later. 

 At Maltham, Yorks, as a result of a Local Government Board 

 inquiry in igoi, upward filtration was permitted to be sub- 

 stituted for the scheme sanctioned in 1899, which had included 

 chemical precipitation, settling, filtration through coke and 

 magnetite, and finally through land. The new system was in 

 triple series, with detritus tanks 43 feet by 5 J feet by 4 feet, hold- 

 ing 21,000 gallons or 4 hours' flow, from which the sewage, 

 after passing over a weir into a supply chamber, flowed upwards 

 through the cultivation tanks, 43 feet by 43 feet by 4 feet, con- 

 taining stone or hard clinker riddled to between 2 inches and 

 5 inches in size. The effluent was collected above by perforated 

 troughs 3 feet apart, and at the rate of 200 gallons per square yard 

 per day rapid liquefaction and hydrolytic change is reported. 

 In 1895 Mr. Cameron introduced his '* septic tank " process 



