14 METHOD OF DESTROYING ALG^ IN WATER SUPPLIES. 



of obtainincT frequent agitation arc introduced wherever possible. 

 The pumping of air into water or aerating- it l)v means of a spraying 

 apparatus is often of considerable value in removing foul gases which 

 may be in solution, but the effect of aeration upon the growth of algte 

 in a reservoir has been very much overestimated, in some cases the 

 quantity being actually increased by this means. 



The filtration of water, both mechanically and by sand, which has 

 proved so effective for the removal of pathogenic bacteria, has been 

 recommended as a means of removing the odors and tastes caused by 

 algge, but the results obtained have not given promise of success. 

 Perhaps the most careful experiments to determine this point have 

 been conducted by those in charge of the Ludlow reservoir at Spring- 

 field, Mass. Here the annual trouble from alga? for the past fifteen 

 years has been so great that every possible means has been used which 

 offered any relief from the effects produced by these plants. On page 

 4 of the "Special Report on the Improvement of the Present Water 

 Supply and an Alternative New, Independent Supply," made by the 

 board of water commissioners to the city council of the city of Spring- 

 field, Mass., April 14, 1902, the following statement is made: 



We find, as the results of the experiments of filtration, made with the sanction of 

 your honorable body during the last fifteen months, that to purify the waters of this 

 source by filtration would be not only doubtful as to the degree of purification, but 

 so expensive in the cost of construction and perpetual maintenance thereafter as 

 to make it inexpedient to attempt improvement by such a method. Your board has 

 given constant and personal attention to the experimental work, and is convinced 

 that the excessive growths of obnoxious fresh-water organisms, notably the Ana- 

 baena, impart to the reservoir such rank and persistent tastes and odors as to make 

 uncertain entire removal by any method of filtration except that of the expensive 

 kind, applicable only to the filtering of extremely small quantities of water, and 

 requiring constant attention and adjustment. 



The State board of health, in a special report (p. 81) submitted at the 

 same time, say that the results of the experiments indicate, in the 

 opinion of the board, that by double filtration it will l)e possible to 

 purify the Ludlow reservoir; hence there seem to be differences of 

 opinion as to the value of this treatment for the removal of odors and 

 tastes, but on account of the expense involved there is not likely to be 

 any very extensive use of this method. 



DESIRABILITY OF OTHER METHODS. 



While each of the above-mentioned methods has been used with 

 some success, it is generally conceded by engineers that there is no 

 known remedy which is universally applicable. It is the practice 

 of some of the highest authorities to recommend that reservoirs fre- 

 quently polluted by alga? be abandoned, and steps taken to provide an 

 entirely new system of supply. This is, of course, the last resort, as 

 in all such cases a large loss of money is involved. One fact is certain. 



