Acompletely mixed activated-sludge plant is being designed for a wastewater flow of 5.0 mgd. the soluble bod concentration of the influent to the aeration basin is 200 mg/l. the effluent soluble bod requirement is 10 mg/l. the mean cell residence time is to be 8.0 days at an mlss concentration of 2500 mg/l. from pilot plant data, y = 0.6 lb vss/lb bod, kd = 0.06 day–1 , and 80% of the mlss are vss. calculate:

a) the volume of the aeration basin, in gals.
b) the dry mass of excess solids in the waste sludge in lb/day.
c) the aeration period, q in hours.
d) food-to-microorganism ratio, f/m.
e) bod loading, lb/day-1000 ft3 .

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?

The higher the astm grain size number, the finer the gran is. a)-true b)-false

Find the kinematic pressure of 160kpa. for air, r-287 j/ kg k. and hair al viscosity of air at a temperature of 50°c and an absolute (10 points) (b) find the dynamic viscosity of air at 110 °c. sutherland constant for air is 111k