332 SEWAGE AND ITS PURIFICATION 



portions, according to the standard solution adopted by Nobbe, 

 which contained in parts per 100,000 : — 



By experiments on plants I have found these effluents to give 

 great fertility. While some plants (Leguminosse) can assimi- 

 late free nitrogen, others organic compounds, and still others 

 nitrogen in the form of ammonia, nitrates appear to be the 

 form in which nitrogen is taken up with the greatest readiness 

 by most plants. The change of sewage into a fertilizing effluent 

 is favoured by a higher temperature. In India a report of 1901 

 states that at Bombay, Poona and Calcutta septic tanks and 

 bacteria beds produced an effluent that gave much better crops 

 than the poudrette manure and irrigation wath canal water 

 previously employed, and that at the Matunga Asylum farm, 

 Bombay, irrigation with the septic tank effluent alone gave a 

 gross profit of over £60 per acre per annum. 



As regards the mineral constituents of different sewage 

 effluents not much information is recorded. An average 

 sample of the final fiow from the Sutton beds showed : — 



Fixed mineral matter ... 

 Volatile and organic matter 

 Actual sodium chloride... ... 



Soda in other forms (sulphate, carbonate, etc.), calculated 



as Na20 

 Total soda as Na.jO 

 Total potasti as K^O 

 Phosphate as P0O5 

 Nitrogen as nitrate 

 Total nitrogen 



100 parts of total solids would correspond to — 



Total N 4-25 : KjO 3*48 : P2O5 0-32 

 Mineral matters 77*93 : Organic 22*07 



Probably coke in the filters absorbs much of the phosphorus 

 as phosphate of iron, and accounts for the small amount of 

 phosphoric acid. Polarite and other highly ferruginous mixtures 

 would have a still greater effect. Disused filtering materials 

 must consequently contain a large proportion of phosphate. 



The difficulty of utilizing any of the valuable constituents of 

 sewage resulting from their extreme dilution, prevents evapora- 

 tion, distillation, or any of the ordinary chemical methods 



