CEE 330 Homework 7 Problem 1 8 8 ETextbook A mechanical rapid mix tank is to be designed to treat 50 m3 d of water at a temperature of 12oC Using typical design values in the text determine the tank volume and power requirement Solution Assume 60 seconds of detention time m3 day V Q 50 60 s 0 035 m3 day 86400s Using table 10 13 select a G value of 900 sec At 12oC 1 2388x10 3 N sec m2 P G2 V N s kN m 1 kN 2 900 s 1 2388 10 3 2 0 0347 m3 0 035 35 W s m 1 000 N Problem 2 8 16 etextbook Calculate the settling velocity of a 100 m diameter particle with a specific gravity of 2 4 in 10oC water Solution Find settling velocity using Stoke s law Table 10 15 Particle density specific gravity x water density at 4 oC 2 4 x 1000 kg m3 2400 kg m3 vs g p d p2 18 2 9 81 m s2 2400 999 7 kg m3 1 0 10 4 m 3 600 s m 21 3 2 h h 18 1 307 10 N s m Check Reynolds number d p vs 1 0 10 4 m 21 m h 1h 3600 s Re 0 45 1 306 10 6 m 2 s Since Re is less than 1 the flow is laminar and Stoke s law is valid Problem 3 8 15 etextbook Water contains 7 0 mg L of soluble ion Fe2 that is to be oxidized by aeration to a concentration of 0 25 mg L The pH of the water is 6 0 and temperature is 12oC Assume the dissolved oxygen in the water is in equilibrium with the surrounding atmosphere Laboratory results indicate the pseudo first order rate constant for oxygenation of Fe2 is 0 175 min Assuming steady state operations and a flow rate of 40 000 m3 d calculate the minimum detention time and reactor volume necessary for oxidation of Fe2 to Fe3 Perform the calculations for both a CMFR and PFR You should be able to work this out from information provided in previous chapters 1 Solution For the CMFR at steady state dm 0 min mout mrxn QCin QC VkC dt m3 mg 1000 L m3 mg 1000 L 0 40000 7 40000 0 25 3 day L day L m m3 0 175 1440 min mg 1000 L V 0 25 min day L m3 V 4 286 m3 V 4285 7 m3 So minimum detention time is 0 11 day 2 6 h m3 Q 40000 day For PFR dm dC min mout mrxn 0 0 V dt dt 0 175 Ct Co e kt mg mg min t 0 25 7 e L L Solve for t t 19 min V 40000 m3 day 19 min 528 m3 day 1440 min Problem 4 8 25 etextbook Given the following data graph the data for the Poliomyelitis virus using hypobromite as a disinfectant Determine the Chick s law rate constant and the time required for 99 99 percent 4 log removals inactivation of this virus Time sec s 0 0 2 0 4 0 6 0 8 0 10 0 12 0 Solution First add N No and ln N No to the table Time sec N L N org L number 1 000 of organisms L 350 78 20 6 2 1 N No 2 ln N No 0 2 4 6 8 10 12 1 000 350 78 20 6 2 1 1 0 35 0 078 0 02 0 006 0 002 0 001 0 1 04982 2 55105 3 91202 5 116 6 21461 6 90776 Plot log N No as a function of time The slope 0 6092 is the Chick s law rate constant k 0 6092 second 1 For 99 99 removal ln 0 0001 0 6092 t t 15 s Problem 5 solution Process Grit Chamber Bar Rack and Screen Waste product Sand and fine Plastic paper gravel rags Waste Landfill Landfill disposal 3 Sludge Disposal Dewater stable sludge Recycle landfill incinerate Anaerobic Digester Methane Disinfection Burn Lake river land application Clean water Problem 6 solution Unit Process Removes ammonia Bar screen Grit chamber Primary clarifier Aeration basin X nitrification Removes phosphorus X particulate P P is changed from dissolved to particulate Removes suspended solids X X X X X only particulate P X Anaerobic digester Belt filter press removes water from solids X particulate X 4 Removes nitrate NO3 X particulate X Trickling filter X Secondary clarifier Disinfection Destroys pathogens Removes BOD Only if part of basin is operated as anoxic denitrification X if operated to do this
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