2o8 SEWAGE AND ITS PURIFICATION 



also greatly limited the amount of sewage treated. Moreover, 

 the " thin film " oxidation of Massachusetts requires large 

 filtering areas with great labour to keep them in order — there- 

 fore is exceedingly costly when applied to sewage — it is also 

 attended with certain dangers from " channelling " of the beds 

 by careless or too rapid working, or by frost, whereby it arises 

 that the effluent escapes almost unpurified. In the Massa- 

 chusetts Report of 1890,^ the process is compared to a com- 

 bustion, and was found to be most rapid in the summer 

 months. It must be remembered that sewage in America is 

 usually weaker and of greater volume than it is in Europe, on 

 account of the more abundant supply of water. ^ 



In Ohio State there were in 1903 eleven plants for inter- 

 mittent sand filtration without any previous treatment. 

 R. W. Piatt reports in 1905 that the best of these, at Mans- 

 field Reformatory, treated 70,000 gallons per diem (from only 

 700 persons) on seven beds of crushed sandstone, I'l acres 

 total area. There was considerable trouble in winter, and 

 the results were poor, owing to frost, even when the surface 

 was ploughed with deep or with shallow furrows. Sand treat- 

 ment alone is inadequate over most of this great region, and 

 preliminary processes have had to be adopted.^ Barbour finds 

 that in the Middle West U.S. sand filters usually cost from 

 £400 to ;f 500 per acre per foot in depth. Ten years' experi- 

 ence in Massachusetts^ proves that their cost averages 43 cents 

 per capita per annum, divided about equally between capital 

 charges at 5 per cent, and maintenance. Over the glacial; 

 drift area, where porous sand and gravel are available at low 

 cost, intermittent sand filters are used with a measure of suc- 

 cess, and when operating at low rates require little attention. 

 The maximum rate in practical design is that possible at the 

 time of lowest temperature. About double the area necessary; 

 for summer is required for maintenance of filters in Newj 

 England after some years' use. It is suggested that mechanical 

 filters could be used as " finishers." 



The work of the Massachusetts State Board still left un- 



1 Mills, pp. 578, 586. 



2 The daily consumption of water per head in New York is 92 U.S. gallons; 

 in New Jersey, 92 gallons ; in Philadelphia, 143 ; in Los Angeles, California, 200 ; 

 in Alleghany, Pennsylvania, as much as 247 gallons. (Ten U.S. gallons = 7 

 imperial.) — Mason. See also p. 16. 



3 See Ohio Sanitary Bulletin, ix., 177 ; Eighteenth Attntial Report of the Ohio State 

 Board of Health; Transactions of the American Society of Civil Engineers, liv. , E, 

 1905. 



■^ Report of State Board for igo^. 



