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27.4 Reaeration. The data below are from an experiment that attempted to relate the rate of disso-
lution of an organic chemical to the reaeration rate (y) in a laboratory model stream channel.
The three experimental factors are stream velocity (V, in m/sec), stream depth (D, in cm), and
channel roughness (R). Calculate the main effects and interactions and interpret the results.

Run V D R y (Triplicates) Average
1 0.25 10 Smooth 107 117 117 113.7
2 0.5 10 Smooth 190 178 179 182.3
3 0.25 15 Smooth 119 116 133 122.7
4 0.5 15 Smooth 188 191 195 191.3
5 0.25 10 Coarse 119 132 126 125.7
6 0.5 10 Coarse 187 173 166 175.3
7 0.25 15 Coarse 140 133 132 135.0
8 0.5 15 Coarse 164 145 144 151.0

27.5 Metal Inhibition. The results of a two-level, four-factor experiment to study the effect of zinc
(Zn), cobalt (Co), and antimony (Sb) on the oxygen uptake rate of activated sludge are given
below. Calcium (Ca) was added to some test solutions. The (−) condition is absence of Ca,
Zn, Co, or Sb. The (+) condition is 10 mg/L Zn, 1 mg/L Co, 1 mg/L Sb, or 300 mg/L Ca (as
CaCO 3 ). The control condition (zero Ca, Zn, Co, and Sb) was duplicated. The measured
response is cumulative oxygen uptake (mg/L) in 20-hr reaction time. Interpret the data in
terms of the main and interaction effects of the four factors.

Uptake
Run Zn Co Sb Ca (mg/L)
1 −1 −1 −1 −1 761
2 +1 −1 −1 −1 532
3 −1 +1 −1 −1 759
4 +1 +1 −1 −1 380
5 −1 −1 +1 −1 708
6 +1 −1 +1 −1 348
7 −1 +1 +1 −1 547
8 +1 +1 +1 −1 305
9 −1 −1 −1 +1 857
10 +1 −1 −1 +1 902
11 −1 +1 −1 +1 640
12 +1 +1 −1 +1 636
13 −1 −1 +1 +1 822
14 +1 −1 +1 +1 798
15 −1 +1 +1 +1 511
16 +1 +1 +1 +1 527
1 (rep) −1 −1 −1 −1 600
Source: Hartz, K. E., J. WPFC, 57, 942–947.
27.6 Plant Lead Uptake. Anaerobically digested sewage sludge and commercial fertilizer were
applied to garden plots (10 ft × 10 ft) on which were grown turnips or Swiss chard. Each
treatment was done in triplicate. After harvesting, the turnip roots or Swiss chard leaves were
washed, dried, and analyzed for total lead. Determine the main and interaction effects of the
sludge and fertilizer on lead uptake by these plants.

Exp. Sludge Fertilizer Turnip Root Swiss Chard Leaf
1 None None 0.46, 0.57, 0.43 2.5, 2.7, 3.0
2 110 gal/plot None 0.56, 0.53, 0.66 2.0, 1.9, 1.4
3 None 2.87 lb/plot 0.29, 0.39, 0.30 3.1, 2.5, 2.2
4 110 gal/plot 2.87 lb/plot 0.31, 0.32, 0.40 2.5, 1.6, 1.8
Source: Auclair, M. S. (1976). M.S. thesis, Civil Engr. Dept., Tufts University.
© 2002 By CRC Press LLC