INFLUENCE OF AMOUNT OF SULPHATE OF ALUMINA ON BACTERIAL EFFICIENCY OF MECHANICAL FILTERS.

The number of bacteria passing a mechanical filter is dependent principally upon the amount of sulphate of alumina used; and by using a larger quantity of sulphate of alumina than was actually used in the experiments the bacterial efficiency could be considerably increased. To investigate this point, the results obtained each day with each of the mechanical filters were arranged in the order of the sulphate of alumina quantities used, and averaged by classes. In this and the following tables a few abnormal results were omitted.[44] A summary of the results is as follows:

SUMMARY OF RESULTS WITH WARREN MECHANICAL FILTER, ARRANGED ACCORDING TO SULPHATE OF ALUMINA QUANTITIES.
Number
of Days
Represented.		 Turbidity. Bacteria. Per cent
remaining.		 Per cent
removed.		 Sulphate of
Alumina
used Grains
per Gallon.
Raw Water. Effluent.
  7 0.05   4,773 1713 35.89 64.11 0.00
  2 0.08   2,785   850 30.52 69.48 0.12
  4 0.10   5,109   726 14.21 85.79 0.26
  2 0.20   8,713   214   2.45 97.55 0.36
  8 0.06   3,224   112   3.47 96.53 0.44
19 0.06   3,488   123   3.53 96.47 0.55
11 0.06   5,673   154   2.71 97.29 0.64
10 0.10   6,100   112   1.84 98.16 0.74
  8 0.09   8,647   148   1.71 98.29 0.85
  5 0.16   5,645   142   2.52 97.48 0.93
13 0.12 10,397   200   1.92 98.08 1.07
10 0.08 12,778   121   0.95 99.05 1.13
13 0.14 13,397   164   1.22 98.78 1.25
19 0.13 10,462   160   1.53 98.47 1.34
10 0.12 12,851   107   0.83 99.17 1.46
  4 0.27 16,015     77   0.48 99.52 1.57
  7 0.53 12,262   191   1.18 98.82 1.64
  4 0.58 26,950   347   1.29 98.71 1.74
  5 0.29 14,570     86   0.59 99.41 1.84
  3 0.23 13,833   153   1.11 98.89 1.92
19 0.40 18,222     92   0.50 99.50 2.48
  5 0.45 29,300 1119   3.82 96.18 3.37
  5 1.06 33,030   535   1.62 98.38 8.06
SUMMARY OF RESULTS WITH JEWELL MECHANICAL FILTER, ARRANGED ACCORDING TO SULPHATE OF ALUMINA QUANTITIES.
Number
of Days
Represented.		 Turbidity. Bacteria. Per cent
remaining.		 Per cent
removed.		 Sulphate of
Alumina
used Grains
per Gallon.
Raw Water. Effluent.
  6 0.03 14,037 6217 44.29 55.71 0.00
  5 0.07   4,267   680 15.93 84.07 0.24
14 0.06   2,613   170   6.50 93.50 0.35
10 0.06   2,446   113   4.62 95.38 0.44
  9 0.11   7,303 234   3.20 96.80 0.55
20 0.09   6,979   220   3.15 96.85 0.65
  9 0.08   5,191   130   2.50 97.50 0.75
16 0.12   8,504   242   2.84 97.16 0.83
22 0.16   8,506     99   1.16 98.84 0.96
12 0.11 11,998   246   2.05 97.95 1.05
14 0.18 18,982   423   2.23 97.77 1.16
  5 0.14 13,981   224   1.60 98.40 1.23
  9 0.27 19,806   325   1.64 98.36 1.34
14 0.27 16,549   324   1.96 98.04 1.45
  9 0.29 12,194     96   0.79 99.21 1.54
  6 0.25 13,483     51   0.38 99.62 1.65
  7 0.53 24,243   220   0.91 99.09 1.72
  3 0.90 20,953   602   2.88 97.12 1.90
  5 0.43 25,958   307   1.19 98.81 2.19
  4 0.84 21,017   228   1.09 98.91 3.71

These results are shown graphically by Fig. 21.

Fig. 21.—Bacterial Efficiencies of Mechanical Filters.