ACTIVATED SLUDGE PROCESS. 217 



attempted. In giving a description of a plant working with 

 activated sludge, I will take as an example the sewage disposal 

 works of the city of Worcester, in England, which, owing to the 

 kindness and courtesy of the former Engineer of the city, Mr. 

 Thomas Caink, I had the pleasure of inspecting. I was also per- 

 mitted to take some photographs, which have been converted into 

 slides. I select the city of Worcester because the first complete 

 installation on the continuous flow type was erected there. The 

 plant was designed and installed by Messrs. Jones and Attwood, 

 Ltd., under special agreement with the Worcester Corporation, 

 whereby the payment for the installation was conditional on the 

 successful operation of the process so as to comply with certain 

 requirements in regard to the character of the effluent obtained, 

 and the volume of sewage treated. The installation was designed 

 to deal with 750,000 gallons dry weather flow. The tank placed 

 at the disposal of the firm was 80 feet long by 72 feet wide and 

 18 feet deep. It was divided longitudinally into nine bays eight 

 feet wide, which was subdivided by three transverse walls, thus 

 forming 36 compartments. In the adoption of this tank for the 

 trial of the process, five bays were used for aeration, and the other 

 four for settlement purposes. 



The five aeration bays are arranged as follows: The first bay, 

 though eight feet broad at the top, is only five feet broad at the 

 bottom, due to the batter of the outside wall. The bottom of the 

 first bay is arranged with ridge and furrows at five feet centres, 

 the furrows each containing five air diffusers, each one foot square 

 over all. These are, of course, placed transversely to the flow of 

 the sewage. The lower part of each transverse wall is cut away, 

 making an opening three feet deep right across the tank above the 

 top of the ridge. The ratio of total diffuser area to tank area 

 in this bay is 1 : 5, or 1 : 7, if the actual diffusion area is considered. 

 The other four aeration bays are arranged in pairs, each pair 

 making a circulating tank. The bottoms of these bays are formed 

 with ridges and furrows, saw-tooth form, at ten feet pitch, with 

 eighty diffusers in each furrow, so that the ratio of diffuser area 

 to tank area is 1 : 10, or 1:14 for actual diffusion area. Advantage 

 is taken of the transverse walls which are used as baffles, and 

 these, together with intermediate wooden baffles, gives a baffle 

 alongside each side of diffusers which checks the back flow, and 

 allows the rising current of sewage to flow forward. In this way 

 a much more rapid horizontal circulation is secured than would 

 be obtained by the natural flow of sewage. The mixture of 

 purified effluent and sludge leaving the aeration chamber enters 

 the settlement tanks underneath a timber baffle eight feet below 

 the surface. The settled sludge is removed from a series of col- 

 lecting sumps through a system of pipes to the inlet sewage 

 chamber. 



The settlement tanks have been partiallv reconstructed since 

 the plant was brought into operation, as will be seen later. An 

 overhead system of air pipes is provided, and the air is admitted 

 to the diffuser through a series of down pipes which are arranged 

 so that one pipe serves two diffusers, each one foot square. Valves 



