168 



SCIENCE. 



[N. S. Vol. XVI. No. 396. 



periods of rest as required by the intermit- 

 tent and contact-bed methods, as the only 

 object of periods of rest in these methods 

 is to supply sufficient air to the bacteria. 



The continuous supply of air and the 

 continuotis retention of air in the filter, 

 the advocates of continuous filters claim 

 can be accomplished by applying the clar- 

 ified sewage in the form of fine spray, so 

 that each drop of liquid will be surrounded 

 by air as it enters the filter, and that air 

 can be retained in the filter by making the 

 filter of so open a construction and so thor- 

 oughly underdrained that the liquid can- 

 not fill up the void spaces between the par- 

 ticles of the filling material. 



There is much to be said in favor of 

 these ideas, for there seems to be no reason 

 why if air is always present the bacteria 

 should not act continuously and thus pu- 

 rify a much greater amount of sewage 

 than is possible in those methods where 

 sewage is only run on the filter six or 

 seven hours each day. 



Theoretically it would not seem difficult 

 to construct a filter answering the condi- 

 tions required. Practically, however, it is 

 just otherwise. It has been found no easy 

 problem to devise automatic apparatus to 

 convert successfully large volumes of sew- 

 age into the form of spray, or to build 

 filters sufficiently open to ensure air al- 

 ways being present, and at the same time to 

 contain sufficient filling material so that the 

 sewage will be retained in the filter the 

 length of time required for the bacteria to 

 remove the organic matter. The contin- 

 uous filters now being tried in England 

 are attempts to solve this problem. 



Such filters are the Scott-Moncrieff, the 

 Ducat, the "VVhittaker & Bryant, the Stod- 

 dart, apd what may be called the Sal ford 

 filter. Of these filters I consider the Whit- 

 taker-Bryant, the Stoddart, and the Sal- 

 ford filters as the most important, and these 

 three different continuous filters are the 



only ones that I shall at the present time 

 try to describe. They are all merely dif- 

 ferent methods of applying septic tank or 

 chemically treated sewag'e in the form of 

 spray to a filter bed of very open con- 

 struction. 



The Whittaker & Bryant filter is a cir- 

 cular or polygonal chamber, about sixty-one 

 feet in diameter and nine feet high, con- 

 taining a central air shaft. The bottom is 

 made of cement with a collecting drain run- 

 ning along one diameter, connecting with 

 which are tile drains set herring-bone-wise. 

 The pigeon-hole walls of the chamber and 

 air shaft are supported on short brick col- 

 umns, so that there is an air space between 

 the walls and the concrete floor. The filling 

 material between the outside walls and the 

 air shaft consists of coke one and one half 

 inches or over in diameter. 



The sewage is distributed on the surface 

 of the filter by an automatic sprinkler, into 

 the delivery pipe of which is placed a steam 

 pipe, so that a small jet of steam can be 

 blown into the sewage just before it is dis- 

 tributed on the filter in order to raise the 

 temperature of the sewage to about 70°. 

 The heat, according to Mr. Whittaker, 'not 

 only keeps the bacteria at their fullest 

 activity, but raises the temperature of the 

 air in the filter, thereby causing it to rise 

 through the filter, and fresh air to enter, 

 rendering the filter self-ventilating and 

 self -aerating. ' 



A filter like the one described is calcu- 

 lated to treat sewage at the rate of over one 

 million gallons per acre per daj^ 



The largest Whittaker & Bryant plant is 

 at Church, near Aecrington. A very inter- 

 esting small plant has been erected at Hyde, 

 and is being tested by Mr. Scudder, of the 

 Mersej^ and Irewell Commission. 



The Whittaker & Bryant filter does treat 

 satisfactorily a very large amount of sew- 

 age on a given area, at least one million 

 gallons per acre. It removes the putres- 



