1917) RUBAL ENGINEERING. 489 



series. lu this way a filter 4 ft. in depth was constructed in which the 

 sewage in order to reach tlie bottom had to flow over a very large surface of 

 filter. Air could enter from all sides and the top through the regular channels 

 provided. . . . 



" Sedimented sewage was allowed to trickle over the surface of this lath 

 filter. In less than a month the filter was mature, and the results obtained 

 thereafter exceeded all expectations. Where the standard type of stone filter, 

 operatetl side by side with it as a control, treated 2,000,000 gal. of sewage per 

 acre per day, the lath filter treated 6,000.000 gal. and yielded a nonputres- 

 cible efliuent. This lath filter has now been In continuous use for 3.5 years and 

 has never failed to give satisfactory results." 



SatLsfactory results were also obtained with a brushwood filter which withiu 

 two months was treating sewage at the rate of 6,000,000 gal. per acre per day. 



Brushwood as a medium for sewage filters, G. Phelps (Canad. Engin., 52 

 (1917), No. 6, pp. in-120, figs. 6; Surveyor, 51 (lUll), No. 1312, pp. 254, 255).— 

 Experiments using brushwood and washed and graded steel slag as filter 

 media are reported. The depth of medium in each case was 5.5 ft., both filters 

 being 50 ft. in diameter. 



"After two months' working, the brushwood had become thickly coated with 

 gray slime and a very satisfactory effluent was obtained, and from that time 

 on the flow to the filter has been periodically incieased up to the present 

 average rate of 7,2.50,000 gal. per acre per day. . . . Witch-hazel was found 

 to be the best material for making up, but almost any kind of brush is suitable 

 provided no dead wood is used. It requires to be cut in the fall or early 

 spring when no leaves are on." 



The slag filter " was started at a rate of 1,250,000 gal. per acre per day and 

 worked up to 2,500,000 in sis months. The rate was increased for a short 

 time to 3,000,000, but this resulted in clogging and ponding on the surface 

 and the rate had consequently to be reduced. The effluent from this filter 

 has always been satisfactory, but Its capacity is limited to about 2,000,000 gal. 

 per acre per day, the rate at which the sewage will pass through without 

 clogging. 



" The effluent from both filters contains usually from 0.1 to 0.2 cc. of 

 sediment per liter. This is a fine humus which is settled out by a half-hour 

 retention in tanks. It Is liable to increase with sudden rushes of storm water 

 but is easily got rid of." 



Analyses of samples of effluent from both filters "show that nitrates are 

 not formed in the brushwood as readily as in the slag filter, which is no 

 doubt due to the rapidity with which the sewage pa.sses through the brush- 

 wood. . . . The open nature of the brush allows good aeration, and it is 

 very efficient when working at a high rate of flow. The rotary distributor also 

 seems well adapted for this type of filter. It gives a good distribution, does 

 not require a great deal of attention, and requires only about a foot of head 

 for its operation. . . . 



" Brushwood shows it.self to be particularly suitable as a medium for inducing 

 the slimy growth characteristic of sewage filters. The thick coating of this 

 slime over every particle of the brush is in marked contrast to anything that 

 can be seen on a medium such as stone or slag. ... To engineers constructing 

 filters of this type, it is recommended that they be made at least 7 ft. deep if 

 possible, and made up to this depth again when the bed has been in work 

 for 12 or 18 months, In which time it will have shrunk down considerably." 



EegTilations respecting hig-hways, 1916, F. G. Macdiarmid {Ann. Rpt. Dept. 

 Pith, Hightoays Ontario, 1916, App., pp. 11). — The text of the regulations Is 

 given. 



