I9 6 SCIENCE PROGRESS 



Dibdin's Slate Beds 



Dibdin has now modified the system of coarse contact beds 

 of coke or clinker (Sutton system) by the introduction of slate 

 beds. This new system has been tried at Devizes, where the 

 sewage is exceptionally foul and strong owing to the bacon 

 factories, slaughter-houses, etc., which exist in this town. The 

 slate beds are constructed of refuse from slate quarries, 65 ft. 

 by 45 ft. and 4 ft. deep ; the slates are laid in horizontal layers 

 2J inches apart, and there is a 6-inch space between the last 

 layer and the floor of the tank. 



The crude, unscreened sewage is allowed to fill the beds 

 and to remain for two hours. The beds are then emptied, given 

 two hours' rest, and filled again. Enough air remains in the 

 beds to allow of aerobic action going on while the sewage is at 

 rest therein. It emerges in a fresh condition properly liquefied, 

 and is then found to be more suitable for subsequent treatment 

 on land or secondary filter beds. The Royal Commission 

 inspected these beds at Devizes, and came to the tentative 

 conclusion that they must be regarded as preliminary settling 

 or septic tanks rather than as contact beds. The slate beds alone 

 will give a purification of twenty-five to thirty per cent., which is 

 practically very much the same figure as is ordinarily attained 

 by septic tank treatment. The results obtained at Devizes 

 are, on the whole, very favourable ; but further experience is 

 required before this method of treatment can be definitely 

 pronounced upon. 



Finally, one may say that from the foregoing statement it 

 is clear that in sewage we are dealing with a highly complex 

 liquid, the nature of which must vary within very wide limits 

 depending upon many factors. The problem of purification 

 therefore is exceedingly difficult in some instances, and it may 

 be safely said that each particular case requires special study if 

 a successful result is to be attained. 



