The filtration of public water-supplies / Third edition, revised and enlarged.

by Allen Hazen

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 TOSULPHATE 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.