164 



DONALD W. STRASBURG 



structed and a number of experiments were 

 performed. Attention was focused on var- 

 iations in dissolved oxygen resulting from 

 different numbers and spacings of trays, 

 while perforation size and number were 

 lield constant. Flow rate was necessarily 

 low because of the miniature size of the 

 equipment, but it was essentially constant 

 at 182 to 193 milliliters per second (3 gal- 

 lons per minute). Water temperature 

 was also approximately constant, the range 

 being 74.2° to 77.8° F. over the test period 

 but with a fluctuation of less than 1 degree 

 on any one day. 



The apparatus assembled for a test is 

 shown in figure 4; it consisted of the fol- 

 lowing parts : an open-faced wooden cabi- 

 net with a bottom drain and valve; an 

 11 14 -inch square wood and plastic inlet 

 tray (actually an "under-gravel" filter) 

 having 289 perforations and a brass nip- 

 ple for attaching a hose; a number of 111/2- 

 inch square wooden trays having 144 per- 

 forations and no nipple; an ordinary %- 

 inch plastic garden hose ; a supply of metal 

 C-clamps for positioning the trays in the 

 cabinet ; several sheets of thin vinyl plastic 

 which were stretched across the face of 

 the cabinet to prevent splashing; a short 

 length of siphon tubing (not shown) ; and 

 chemical equipment for determining dis- 

 solved oxygen by the Winkler method. In 

 practice the flow rate, temperature, and 

 amount of oxygen in the unaeratecl water 

 were first measured, followed by the collec- 

 tion of samples from beneath varying num- 

 bers of equally spaced trays. The water 

 samples were drawn from the bottom valve 

 or by siphon ; the drain was stoppered un- 

 til 1 inch of water had accumulated in the 

 cabinet's base, at which time a sample was 

 taken. 



Figure 5 shows the relations between 

 tray spacing, tray number, and dissolved 

 oxygen obtained from experiments with 

 the model aerator. All oxygen values are 

 shown in terms of percentage saturation 



289-'/^" HOLES 



\ HOSE NIPPLE 



C CLAMPS 



HOLES 



I '/j' DRAIN PIPE 



'/4"GATE VALVE 



Figure 4. — Model aeration device used to deter- 

 mine effects of tray spacing and number on 

 amount of dissolved oxygen in water. Water 

 was supplied to the topmost tray by a hose at- 

 tached to the nipple. 



for the particular salinity and tempera- 

 ture prevailing at the time of the test (the 

 percentage saturation was obtained from 

 data presented by Sverdrup et al., 1942, 

 p. 188). The curves were fitted by eye to 

 coincide with the maximum number of 

 points. Not shown in the crowded upper 

 left portion of the figure are data from 

 tests using 10 to 15 trays; the curves from 

 these tests lay between those for 9 and 16 



