Asmall treatment plant with two filters operates at a filtration rate of 2 gpm/ft2 . the influent tss is 15 mg/l; the effluent tss is 0. (a) if each filter is square, 30 ft on a side, calculate the daily volume of water treated (in million gallons/d, mgd) assuming each filter is backwashed once per day in a process that takes 30 minutes. (b) if 3% of the treated flow is used for backwashing, calculate the backwash tss. (answers: 5.08 mgd, 500 mg/l)

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?