340 SEWAGE AND ITS PURIFICATION 



and the soda-ash recovered by incineration. The wash waters 

 are economized by being used over and over again and finally 

 are precipitated and filtered as above. Wood - pulp works 

 introduce much less pollution : the whole of the pulp, which is 

 usually prepared abroad, is of value, and is kept back by a 

 variety of "save-alls" (revolving sieves of fine gauze), and 

 settling tanks. 



At Chorley Paper Mill, Lancashire, it was decided in August, 

 1900, to try the effect of bacterial treatment on their waste, 

 with highly satisfactory results, the turbidity being removed 

 by the coagulating effect of the sewage. In almost all mills 

 where esparto grass is used, much difficulty is experienced in 

 obtaining a clear effluent, even after filtration through very 

 fine ashes. After admixture with sewage, however, and sprink- 

 ling, the final effluent contains much less suspended matter 

 than that from brewery waste. ^ 



Tanners' and Fellmongers' Waste is generally admitted to the 

 sewers after deposition of the grosser solids. If precipitation 

 is practised, the tanks require to be cleaned out frequently in 

 warm weather, and suitable land or double filtration is resorted 

 to afterwards. 



Breweries. A large quantity of water is used for cooling ; 

 this does not require treatment. The washings of barrels, vats, 

 and tanks are precipitated and filtered, but in many breweries 

 they are discharged direct into the sewers. All these wastes 

 are preferably treated by bacterial methods.- 



Sewage consisting largely of brewery waste was singularly 

 intractable under the old methods of purification, and neither 

 chemical precipitation nor the most favourable land treatment 

 effected much improvement. At Burton-on-Trent (pop. 40,000, 

 sewage for 24 hours 5 to 6 million gallons) the sewage was first 

 precipitated, then filtered through 450 acres of land — less than 

 90 persons per acre — yet the farm had never been able to pro- 

 duce a good efiluent.^ But it has been found amenable to 

 bacterial treatment by septic tanks and filters that have been 

 properly managed and matured, and a successful instance is 

 given by Anson and Shenton'^ at Ash in Kent using a septic 

 tank and triple contact. 



^ '* Bacterial Treatment of Trade Waste," W. Naylor, p. 223. 



'^ J. Soc. Client. Inci., June, 1901. 



^ Dr. S. Barwise, Royal Commission on Sewage, vol. ii., 1902, p. 240. See also 

 Mr. Chatterton's evidence, ihid., p. 354. 



^ " Purification of Sewage and Brewery Refuse," published by Davis, Epping, 

 1903. 



