CHAPTER XII 



DISTRIBUTION AND DISTRIBUTORS 



Intermittent — Continuous — Stationary Sprayers — Moving Distri- 

 butors — Tippers — Testing Apparatus. 



Choice of methods in great part depends on the character of 

 the site, as in many places the sewage has to be raised by 

 pumps, Hfts, or ejectors, and the problem becomes an engineering 

 one. A really anaerobic treatment in the first stage, like 

 Cameron's or MoncriefPs, requires no fall, the sewage simply 

 flowing in below and flowing out above. With terraced beds 

 fed from the top, the fall to be provided includes the sum of the 

 depths of the beds and of the distributing apparatus : increasing 

 the depth of material may economize surface area, but adds to 

 the expense of raising. 



Ordinarily, the sewage, owing to its fluctuations, has to be 

 controlled by penstocks and valves at the entrance and exit. A 

 restraint at the entrance involves storage. "Holding up" is 

 temporarily closing the outlet valve so that the filter fills with 

 fluid. In the Lowcock filter and others, the entrance is con- 

 trolled and the outlet always open. Variation in flow occasions 

 great difficulty where the admission is direct to bacteria beds, 

 but in septic tanks of sufficient capacity the irregularity isjnot 

 felt. In any case, the flow of sewage can be regulated by means 

 of '' modules." The first module, introduced in Piedmont, for 

 the purpose of giving a uniform discharge of water out of a 

 main channel or canal, was a chamber commanded by a sluice, 

 and with a square orifice of suitable size below. The sluice was 

 opened till the flowing water remained at a fixed level in the 

 chamber. 



Such a module, though giving for the purpose a sufficiently 

 uniform flow, would not adjust itself except within narrow 

 limits. A great number of self-acting modules were used on 

 the Indian canals, especially one devised by Lunt Jarrols. In 

 the Piedmont form a free fall is a necessity, but with self-adjust- 

 ing modules this is not required, those at Barrhead (Fig. 58, 



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