152 ENVIRONMENTAL, ENGINEERING7.2 An engineer suggests the following design parameters for a city's proposed
rapid sand filter: flow rate = 0.6 m3/s, and loading rate to filter = 125.0 m3/day-m2.
How much surface area is required for the filter? Select the number of equally sized
filters, and size these filters assuming a width-to-length ratio of 1.0 to 2.5 with a
maximum surface area of each filter tank being 75 m2.
7.3 A flocculator is designed to treat 25 mgd. The flocculator basin is 100 ft long,
50 ft wide, and 20 ft deep and is equipped with 12-in. paddles 48 ft long. The paddles
are attached to four horizontal shafts, two paddles per shaft, their center line is 8.0 ft
from the shaft, and they rotate at 2.5 rpm. Assume the velocity of the water is 25%
of the velocity of the paddles, the water temperature is 5OoF, and the drag coefficient
is 1.7.
Calculate (1) the time of flocculation, (2) the velocity differential between the
water and the paddle, (3) the hydraulic power (and subsequent energy consumption),
and (4) the values of G and GF.
7.4 Propose some use and disposal options for water treatment sludges collected
in the settling tanks following flocculation basins.
7.5 For the house or dormitory where you live, suggest which water uses require
potable water and for which a lower water quality would be adequate.