222 ASPHALT. 



18th, 1917, and the photo taken on March 31st, 1917. The 

 difference in blooms and foliage is noticeable. 



The process has been very extensively adopted in England and 

 America, and during the war plants were installed by the Ministry 

 of Munitions, by the United States Red Cross, by the Admiralty, 

 and others. In England plants are installed at Baguley, Davy- 

 hulme, Worcester, Stamford, Aintree, Blackpool, Withington, St. 

 Albans, Tunstall, Moreton, Harpenden, Witney and Birmingham. 

 Also abroad they are installed at Holte and Burmeister, Denmark; 

 Jamshedpur and Sibpur, India; and last, but not least, De Beers, 

 Kimberley, South Africa. At Milwaukee, in America, they are 

 spending £1,000,000 to instal the new process, which will treat 

 eighty-five millions gallons per twenty-four hours d.w.f. I might 

 mention that the Royal Sanitary Institute have just granted their 

 Silver Medal, their highest award, to Activated Sludge, Ltd. 



Before concluding, I think the paper would be incomplete 

 without comparing the question of cost, both capital and working 

 charges, and I will take the figures given by Mr. W. M. Makepeace, 

 Borough Sewage Engineer, Stoke-on-Trent, in his report of April, 

 1920. For comparison he has taken a population of 50,000 with 

 a dry weather flow of one and a half million gallons. The cost 

 of a Bacteria Plant to deal with this population where pumping 

 would be necessary is £125,000, and the working charges for the 

 year would be £6,800. The capital cost of an activated sludge 

 plant on the same basis would be £85,000, and the working charges 

 calculated from the air consumption required to deal with three 

 times the d.w.f. as sewage, and three to six times as storm water, 

 together with making provision for dealing with the sludge and 

 without taking any credit for its market value as fertiliser, is 

 £4,372. You will note that there is a saving capital expenditure 

 of £40,000 and an annual saving on working costs of £2,427. 

 Then you have the revenue from the sale of sludge, which has not 

 been taken into account. 



The following is a comparison analysis of a raw sewage and 

 final effluent, one treated by activated sludge and the other treated 

 on first and second contact beds. Both processes were supplied 

 from the same sewer. 



Results in Grains per Gallon. 



First and Secoud 

 Activated Contact, 

 . Sludge Process. Bed Treatment. 

 Sewage. Effluent. Sewage. Effhient. 

 Four Hours' Oxygen Absorp- 

 tion 6.83 



Percentage Purification — 



Free and Saline Ammonia ... 1.98 



Albuminoid Ammonia 0.59 



Nitrite and Nitrate — 



(In terms NH 3 ) 



