A municipality is currently operating a conventional waste activated sludge treatment system that receives two million gallons of wastewater per day with an average BOD concentration of 165 mg/L. The aeration basin has a volume of 100,000 ft. The mixed liquor suspended solids (MLSS) concentration is maintained at 2,800 mg/L and the effluent suspended solids concentration from the secondary clarifier is 25 mg/L. Assume that the secondary treatment system wastes 38,000 gal/day from the recycle line and that the MLSS concentration of the recycle flow is 9,000 mg/L. Determine the following process parameters: A. Hydraulic detention time of the aeration basin in hrs.
B. Volumetric BOD loading rate of the aeration basin in lb/1000 ft day
C. Food/Microorganism ratio in lb BOD/lb MLSS. D. Mean cell residence time in days.

Thermal stresses are developed in a metal when its a) initial temperature is changed b) final temperature is changed c) density is changed d) thermal deformation is prevented e) expansion is prevented f) contraction is prevented

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?

Aheavily insulated piston-cylinder device contains 0.02 m3 of steam at 300 kpa and 200 °c. 1.2 mpa. d this process. team is now compressed in a reversible manner to a pressure of etermine the entropy change and the work done on the steam during this process