238 



SEWAGE AND ITS PURIFICATION 



precipitated and sedimented before entering the filters. " The 

 quantity applied when the most satisfactory results were 

 obtained was at the rate of 263,780 gallons per acre per day, so 

 that at this rate the area required per 1,000,000 gallons of 

 effluent of the same impurity as that experimented upon would 

 be 3*8 acres. The dry- weather flow of the sewage experimented 

 upon is 16 gallons per head per day of the population, so that 

 the quantity treated at the most efficient rate is equal to that 

 from 16,486 persons per acre." 



The results are stated in October, 1895, as follows in parts 

 per 100,000 : — 



*' Calculated on the sewage, the results of the whole treat- 

 ment, tank and filter, would be a reduction of considerably over 

 go per cent. The Wolverhampton sewage is a most difficult 

 one to deal with, as it contains a large quantity of manufac- 

 turers' and acid waste." 



In the Lowcock filters constructed at Tipton in i8g6 the 

 sewage had also been preliminarily treated with lime and 

 alumino-ferric in precipitating tanks. The filters were 3J feet 

 deep, with a bottom of coarse coke, a body of coke breeze, and 

 a top layer of fine broken limestone and sand. The outlets of 

 the filters were open, and air was forced in at a pressure of 

 ^ inch of water, the rate of flow of the effluent being 240 gallons 

 per square yard per day. 



A purification of the tank effluent of y^'y per cent, calculated 

 on the organic ammonia, and 68*5 per cent, on the oxygen 

 absorbed, was obtained.^ 



On this filter Mr. Mansergh, in his report to the Baltimore 

 Sewage Commission, 1899, remarks : 



" It would seem that the supply of air into the filter enables the 

 bacteria to increase their activity, but the recent practice of resting 

 the filter for twelve hours each day tends to show that natural aeration 

 is necessary to the smooth working of the system. The original 



^ See further Lowcock's paper in Proc. hist. Civ. Engineers, vol. cxv. 



