NT 4-1. A tank with a volume (of 15,000 gal contains salt solution at an initial concentration (Co of 55,000 mg/L, but the concentration in the tank (C) needs to be reduced to 1,000 mg/L. Two approaches are being considered as indicated below (Alternatives 1 and 2). Alt. l: Flush tank with clean tap water while tank is mixed. Flowrate into the tank (Qin) and flowrate out of tank (Qou) are each 60 gpm (both flows are limited by the drain pipe capacity). You do not need to derive the equations (but you can if you wanti: Define all variables used Alt. 2: First decant a portion of the salt solution at a flowrate (Qoa) of 60 gpm, then replace the decanted volume with clean tapwater at a flowrate into the tank (Qin) of 130 gpm Required: a) Determine which method will accomplish the job in the shortest time. 2 pts. b) Determine the difference in clean water used wastewater gencrated (gal.) by cach method. I pt. c) Of course our time is valuable and the importance of accomplishing the task quickly is obvious. Rather than discussing time, discuss, from the standpoint of sustainability, the importance of: 1) conserving (not wasting) clean water, and 2) minimizing the gencration of waste brine (salty water) in the Central San Joaquin Valley Be thoughtful; Simplistic answers will not receive much credit. Include in your discussion: the long-term outlook of groundwater reserves in the Central Valley I pt ethe challenges we face with respect to disposal of waste brine solution; what are the legal ways of doing this in the Valley? Note that it would not be legal to put brine in the sewer or percolate it into the ground due to the negative impact both would have on the groundwater. I pt
For Alt 1 60gpm is being flushed out but at the same time
60 gpm is being replaced. Thus the amount of water leaving the tank is equal to the amount of water entering the tank hence it will take (15000/60)min to refill the tank and that is 250 min = 4 hr 10 min.
Alt 2- if we assume that the tank is decanted for a minute and we lost 60g of water, but it next second we get 130 g of clean water,which is almost twice the rate with which it\'s leaving thus it might take almost half the time to decant the full tank
Which should be around( 4hr10min)/2= 2 hr 5 min.
Thus part a is solved.
b. In alternative 1 60g of salt water leaves the tank and then 60 g of clean water is flushed into it, thus the ratio of clean water used and waste water generated is 1:1.
In alt 2 , 60g of waste water is flushed out and that\'s replaced by 130g of clean water the next minute , here clean water used is almost twice the amount of salt water lost, thus here twice the amount of waste water is generated.
c. Although alternative 1 takes more time than alternative 2, in the long run that\'s a betterprocess because of the factors explained in part b. In alternative 1, less amount of clean amount of clean water is wasted.
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