effective phosphorus removal. An alum dose of 25 mg/L or more is needed to
achieve effective phosphorus removal. There did not seem to be any correlation of
flow rate with treatment efficiency at the flow rates studied. Considering that
flocculation is slower in the cold hypolimnion waters, this represents satisfactory
operation for phosphorus removal.
Based upon WDNR Table 7.1, the depth of the thermocline on September 20 was
estimated to be at 13 m. Thus, at this time the volume of water in the hypolimnion
was relatively small. However, the results of the phosphorus content of the inlet to
the treatment system showed that hypolimnetic water was consistently used during
this study. From the contour map of the lake (Fig. 7.5), the volume of the lake at its
normal level would be 13,641 million m
3 (481,660 million ft
3 or 3,602,817 MG).
The volume below 13 m depth was only 83,040 MG. Nevertheless, at an average
pumping rate of the treatment system of 50 gpm, it would take 1,153 days to deplete
Table 7.4. Results of DAF pilot studies of phosphate removal from Devils Lake
Chemical addition
mg/L
Date
mo/d/yr
Influent TP
mg/L
Effluent TP
mg/L
Flow rate
gpm
Percent
removal %
49.5 Alum
092596
0.496
<0.007
40
99
47.6 Alum
092596
–
<0.007
40
99
23.0 A/C
092596
–
<0.007
40
99
20.8 Ferric
092696
0.495
0.036
35
93
13.2 Ferric
092696
–
0.045
35
93
19.8 Ferric
092696
–
0.058
30
88
15.8 Ferric
092696
–
0.204
50
59
5.0 Ferric
092796
0.436
0.130
35
70
9.4 Ferric
092796
–
0.222
35
49
10.2 Ferric
092796:
–
0.326
52
25
32 Ferric
092796
0.411
0.096
45
77
29 Ferric
092796
–
0.082
50
80
26.4 Alum
092896
0.492
0.007
45
99
17.6 Alum
092896
–
0.016
45
97
13.2 Alum
092896
–
0.013
45
97
14.4 Alum
093096
0.575
0.087
55
83
22.8 Alum
093096
–
0.019
55
96
20.4 Alum
093096
–
0.022
65
96
6.6 A/C
100196
0.588
<0.007
60
98
8.8 A/C
100196
–
0.008
60
98
7.5 A/C
100196
–
0.011
55
98
35 Ferric
100396
–
0.028
55
95
50 Ferric
100396
–
<0.007
55
99
40 Ferric
100396
–
<0.007
55
99
40 Ferric
100396
0.516
<0.007
55
99
38.1 Ferric
100396
–
<0.007
45
99
Note: alum as aluminum sulfate, ferric as ferric chloride, and A/C as aluminum chlorohydrate
276
L. K. Wang et al.
achieve effective phosphorus removal. There did not seem to be any correlation of
flow rate with treatment efficiency at the flow rates studied. Considering that
flocculation is slower in the cold hypolimnion waters, this represents satisfactory
operation for phosphorus removal.
Based upon WDNR Table 7.1, the depth of the thermocline on September 20 was
estimated to be at 13 m. Thus, at this time the volume of water in the hypolimnion
was relatively small. However, the results of the phosphorus content of the inlet to
the treatment system showed that hypolimnetic water was consistently used during
this study. From the contour map of the lake (Fig. 7.5), the volume of the lake at its
normal level would be 13,641 million m
3 (481,660 million ft
3 or 3,602,817 MG).
The volume below 13 m depth was only 83,040 MG. Nevertheless, at an average
pumping rate of the treatment system of 50 gpm, it would take 1,153 days to deplete
Table 7.4. Results of DAF pilot studies of phosphate removal from Devils Lake
Chemical addition
mg/L
Date
mo/d/yr
Influent TP
mg/L
Effluent TP
mg/L
Flow rate
gpm
Percent
removal %
49.5 Alum
092596
0.496
<0.007
40
99
47.6 Alum
092596
–
<0.007
40
99
23.0 A/C
092596
–
<0.007
40
99
20.8 Ferric
092696
0.495
0.036
35
93
13.2 Ferric
092696
–
0.045
35
93
19.8 Ferric
092696
–
0.058
30
88
15.8 Ferric
092696
–
0.204
50
59
5.0 Ferric
092796
0.436
0.130
35
70
9.4 Ferric
092796
–
0.222
35
49
10.2 Ferric
092796:
–
0.326
52
25
32 Ferric
092796
0.411
0.096
45
77
29 Ferric
092796
–
0.082
50
80
26.4 Alum
092896
0.492
0.007
45
99
17.6 Alum
092896
–
0.016
45
97
13.2 Alum
092896
–
0.013
45
97
14.4 Alum
093096
0.575
0.087
55
83
22.8 Alum
093096
–
0.019
55
96
20.4 Alum
093096
–
0.022
65
96
6.6 A/C
100196
0.588
<0.007
60
98
8.8 A/C
100196
–
0.008
60
98
7.5 A/C
100196
–
0.011
55
98
35 Ferric
100396
–
0.028
55
95
50 Ferric
100396
–
<0.007
55
99
40 Ferric
100396
–
<0.007
55
99
40 Ferric
100396
0.516
<0.007
55
99
38.1 Ferric
100396
–
<0.007
45
99
Note: alum as aluminum sulfate, ferric as ferric chloride, and A/C as aluminum chlorohydrate
276
L. K. Wang et al.