WATER FILTRATION. 



XLI. 



Change in hardness. — "The following table gives a com- 

 parison of the average hardness of the river and the filtered 

 waters: — 



River Water 



Filtered Water 



Temporary 

 Alkalinity 



Permanent 

 Incrusting 



Constituents 



Total Hardness 



Temporary 



Permanent 



Total Hardness 



23 



12 



35 



15 



19 



34 



Effect of rate of filtration. — "The rate of filtration, as 

 far as the quality of the filtered water is concerned, does 

 not seem to be a factor of significance. If the applied water 

 is well coagulated, satisfactory results will follow with a 

 rate of filtration at least as high as 185,000,000 gallons per 

 acre per 24 hours; and, with an inadequately coagulated 

 water, good results cannot be obtained at rates of 80,000,000 

 gallons per acre per 21 hours, or much less. That the num- 

 ber of bacteria in the filtered water is not materially 

 affected by the rate of filtration, is shown by the following 

 tables : — 



Average Eesults Showing Eemoval oe Bacteeia by Filters 



Operating at Different Rates. 



Average for 20 weeks. 



Rate of 

 Filtration 



Rate of Filtration 



Bacteria per Cubic 

 Centimetre 



Percetages 



of 

 Eemoval 



of 

 Bacteria 



Gallons per Acre 

 Daily 



Gallons per nq. 

 ft. per Minute 



River Water 



Filtered Water 



High ... 



Normal .. 

 Low 



1 85,000,000 



125,000,000 



80,000,000 



30 

 2-0 

 1-2 



3,500 

 3,500 

 3.500 



100 

 90 



80 



97-1 

 97-4 



97-7 



Average Results, Showing the Effect of the Rate of Filtration 



on Period of Service and Percentage of Wash Water. 



Average for 20 weeks. 



Rate of Filtration 



Period of Service 

 Hours 



Volume of Water 

 Filtered per Run 



Percentage of 

 Wash Water 



High 

 Normal 

 Low ... 



7-52 

 10-18 

 12-93 



470.000 

 425,000 

 258,000 



3-8 



4-1 

 4-4 



"The larger yield of filtered water between washings by 

 the high-rate filters, apparently is explained by the deeper 



