56 SEWAGE AND ITS PURIFICATION 



oxygen absorbed, 2*o. Mersey and Irwell — albuminoid, 0*14 ; 

 oxygen absorbed, 1*40. Provisos as to amount of suspended 

 solids, acidity, alkalinity, metals, etc., are inserted in some, 

 and have special reference to manufacturing effluents. But in 

 all these arbitrary limits no account is taken of the volume of 

 the river into which the effluents are discharged, although 

 attention was long ago drawn to the purifying action of river 

 water. 



The Local Government Board have often been asked to lay 

 down a standard of purity for sewage effluents, but have 

 refused, on the ground that all the circumstances of each case 

 should be taken into consideration. 



The London County Council many years ago recognised 

 the fact that an oxidizing agent added to the effluent at the 

 time of contact with the river prevents any foulness. Provided, 

 therefore, a river is well aerated, or an effluent is well nitrated, 

 or an oxidizing agent is supplied in sufficient quantity at the 

 time of contact, an effluent may contain a larger quantity 

 of organic matter than has been sanctioned in the past, and 

 variations in such quantities are permissible under conditions 

 varied in the above way. The limits recommended in the 

 United States by R. Hering and the Massachusetts Board for 

 the amount of free ammonia that may be allowed in discharges 

 into a stream correspond to about 50 volumes of river water to 

 average sewage in this country. Such conditions are only 

 possible under very special circumstances, while the limit is 

 much greater than we have found necessary in England. In 

 other words, most experts now agree that the quality of the 

 stream, and not of the effluent, should be taken as a basis, and 

 that some fixed distance below the outfall in mid-stream should 

 be specified as the locality at which samples should be taken. 



Dibdin's Fish Test. — Mr. Dibdin describes this test as follows : 

 " He had long since adopted in his own mind a physiological 

 standard — viz., that the quality of an effluent should be such 

 that fish could live healthily in it. . . . Such a definition 

 involves necessarily the absence of poisons and the presence of 

 oxygen." But while an effluent which kills fish is obviously 

 unhealthy, it does not follow that one where fish will live is 

 therefore a good one. It is well known that fresh-water fish 

 are gross feeders, and fish in large numbers are often seen to 



bottle, all frothing should disappear in three seconds " (this relates to the colloids 

 in sewage). — Journal of the Royal Sanitary Institute, xxii., part ii., 112. 



