Sewage and the bacterial purification of sewage / by Samuel Rideal.

  • Rideal, Samuel, 1863-1929.
Date:
1906
Catalogue details

Licence: Public Domain Mark

Credit: Sewage and the bacterial purification of sewage / by Samuel Rideal. Source: Wellcome Collection.

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    339 principles. The screened sludge is acidified with sulphuric acid, heated to ioo° C. and pressed (the pressing requires 12 hours); dried by steam till the moisture is reduced to 15 per cent., and afterwards extracted three times by benzene. 300 to 450 tons of liquid sludge, containing about go per cent, moisture, are dealt with per week. From each charge of cake, some 800 kilos, of crude grease are obtained by the use of 1320 gallons of benzene (or petroleum spirit), 99 per cent, of which is recovered by distillation. The dry extracted residue con¬ tains 3 percent, of nitrogen, and fetches 30s. per ton as manure. The crude grease is treated by vacuum distillation, at a cost of 7s. to 10s. per ton : 7 tons crude grease yield 1 ton of water, 5 tons of distillate (valued for soap and candle making at £19 per ton), 1 ton of tar, and a little gas, which is burned under the boilers.1 X. The Smith-Leach Process, used at Bradford, consists in first driving off about four-fifths of the water in a Yaryan multiple evaporator, when the concentrated suds can be centrifuged into (1) mud, (2) concentrated potash soap solution, and (3) crude lanoline. At the Fieldhead Mills the potash soap is then further concentrated, and finally burnt in a revolving cylindrical incinerator to crude carbonate of potash, which is either sold, or used again for washing wool. No effluent remains, and the distilled water from the evaporator is utilized for wool-washing, and from its softness effects a saving of 15 to 30% in the quantity of soap required. The trials show a considerable profit, as the grease sells at nearly £20 per ton and the potash at £23. The Bradford sewage at the Frizinghall works is at present passed through a detritus tank of 260,000 gallons capacity and then treated by a modification of the Cassel process. The press-cake contains so much grease as to be unsuitable for manure. At Frizinghall a plant is being erected for extracting the grease by distillation, as it has been found that in this way practically all the grease can be extracted, and the cake left in a dry powder containing all the nitrogen. About 25 tons of sulphuric acid are required per day for 12,000,000 gallons of sewage, and 300 tons of sludge are pressed per day, producing 60 tons of cake. Paper Works. The process must vary with the materials used. Caustic liquors from esparto or straw are evaporated 1 For details of cost, and analyses of products, see Garfield’s paper, loc. cit. 22—2