140 SEWAGE AND ITS PURIFICATION 



Osier beds are often planted, and act partly as strainers ; 

 watercress and many aquatic plants have been found useful. 



With careful management the sale of produce from a sewage 

 farm may be made to yield a small balance over working 

 expenses, but not sufficient to repay the capital, which is 

 estimated to be about five times that required for an ordinary 

 farm. There is a better prospect where a large area of vacant 

 seashore is available, as in the case of Dantzig, where a daily 

 sewage flow of over 3J million gallons (in 1894) was disposed 

 of by irrigation on **dune sand." The liquid sank rapidly, 

 leaving the suspended matter on the surface and in the pores 

 of the soil. The land, originally let at 4jd. per acre, was sub- 

 sequently leased to a contractor for thirty years at £1 lis. 6d. 

 per acre, and the scheme is said to have been in every way 

 successful. The depth of humus or vegetable soil was increased 

 by the continued irrigation of about 5,500 gallons per acre per 

 day, and the effluent would have satisfied the requirements of 

 our Rivers Pollution Commissioners.^ 



In America, especially in Massachusetts, where there is 

 sufficient area of sandy soil, the sewage is successfully treated 

 by intermittent filtration at the rate of 50 to 90 thousand 

 gallons per day. In a great number of localities the treatment 

 is screening, sedimentation, and filtration through land which 

 is prepared by removing the loam and levelling. The land is 

 ploughed and harrowed, and planted with corn or other crops 

 every spring. 



Some statistics of sewage farms are given on p. 141. The first 

 series was published in 1896 ; the Berlin figures are dated 1890 ; 

 and the subsequent ones are of 1900, from the Fourth Report 

 of the Royal Commission on Sewage, 1904, vol. iv., part i., p. 7. 

 In each of the latter cases only a fraction of the irrigable area 

 (one-sixth to one-half) is sewaged at one time, in order to allow 

 the remaining land a resting period. 



' Proceedings of the Institute of Civil E^igineers, vol. xliv. 





