A treatment plant has two oxidation-ditch activated-sludge systems, as illustrated in Figure 12.36. Each ditch has a liquid volume of 35.000 ft3 and is equipped with two horizontal-rotor aerators with capacity to transfer 1150 lb of oxygen per day at normal submergence. Each system has a clarifier of the type illustrated in Figure 10.12 with a diameter of 30 ft, a 9.0 ft side-water depth, and a single weir set on a diameter of 30 ft. The effluent chlorination tank has a volume of 2200 ft’. The design flow is 0.54 mgd: 0.35 domestic and commercial, 0.02 industrial, and 0.17 infiltration and inflow. The design BOD and suspended solids aie both 740 lb/day. During heavy rains, the peak hydraulic loading anticipated is 800 gpm for 2-3 hr. Calculate
(a) the BOD concentration at design flow and
(b)at design flow, the aeration period, volumetric BOD loading, and F/M at 2500 mg/l. How do these compare with values listed in Table 12.3?
(c) How many pounds of oxygen can be transferred to the mixed liquor per pound of BOD aeration tank loading?
(d) Calculate the overflow rate and weir loading at the peak hydraulic loading. How do these values compare with recommended design values?
(e) What is the detention in the chlorination tank at peak hydraulic flow? At twice the design flow? How do these values compare with the recommended detention time for chlorination of wastewater effluent?
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