2. Bench studies have determined that aluminurn sulfote (alum) promotes acceptai
ID: 580110 • Letter: 2
Question
2. Bench studies have determined that aluminurn sulfote (alum) promotes acceptaite floc formation at a dose Of 23 mg/L when applied to a surface water source. Design standards for chemical flocculation require flash mixing at a minimum velocity gradient (G) of 900/s for 120 sec onds. Alun is available at 17% pírity for B234/1000 kg and electrical power costs $0.05/kW-h. The water demand is 19000 m'/d. The water temperature is 20°O. 31.1. What is the total tank volume required for flash mixing? (A)27 (B) 16 (C) 27 (D) 160 m 31.2. If four tanks are desired, what are the dimen- sions of each tank? (A) 1-5.4 m, w= 1.9 m,3.0 ml (B) 1-1.9 m,=1.9 m, d= 1.0 m (C) l-3.0 m, w=3.0 m, d= 3.0 m (D) 1-5.4 m, n' = 5.4 m, d= 5.4 m | 3.0 m. 3.0 m,Explanation / Answer
for the first one we have to get the water demand per second so we have the demand per day, 1 day has 24 hours 1 hour has 3600 segs
24 * 3600 = 86 400 segs in 1 day
19000 / 86 400 = 0.2199 m3/seg
multiply this by the 120 seconds from the statement
apply the formu Volume = volumetric flow rate * time
Volume = 0.2199 * 120 = 26.388 m3
b) volume divided by 4 tanks
Volume = 26.388 / 4 = 6.597 m3
We have been given choices, option b is the most suitable choice
volume ?= lenght * heith * d
Volume = 1.9 * 1.9 * 1.9 = 6.859, answer is B, it is important to notice that the calculation for the volume of tanks are considering the idea that the tanks are rectangular
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