Excel is required for full credit on 12.38. Complete the following problems from the textbook. Partial solutions given. 12.28 (E18 first stage = 67%; E18 second stage = 56%; total E = 91%) 12.31 (Peak hourly flows 1.93 cfs = 3.29 m³/min = 4730 m³/day, BOD = 248 mg/L, SS = 218 mg/L) 12.33* (check hydraulic & BOD loading! Each filter same size with A≈2,310 ft², first stage E15 = 60%; second stage E15 = 52%; effluent BOD = 31 mg/L) 12.34 (Se/Sp=0.143; soluble effluent BOD = 14.3 mg/L; total BOD = 28.8 or 29 mg/L) 12.38 Use Excel! (n = 0.4; C = 1.53) Plot log Q, log t; insert straight-line trendline, show equation. Slope is -n, y-intercept is log(CD) 12.44* (RBC area corrected for temperature = 433,000 ft²; use 12 shafts, give area per stage and arrangement) *Design problem Textbook Questions: 12.28 Determine the NRC BOD removal efficiency for a two-stage trickling-filter plant based on the following: primary clarification with 35% BOD reduction, first-stage filters loaded at 80 lb/1000 ft³/day, intermediate settling, second-stage filters sized identical to the first- stage units, an operating recirculation ratio of 1.0 for all filters, final clarification of the effluent, and a wastewater temperature of 18°C. 12.31 The following are design data for the town of Nancy, with a sewered population of 7600. Design flows are as follows: the average daily flow is 0.84 mgd, the peak hourly flow is 1.25 mgd, and the minimum hourly flow is 0.12 mgd. Design average BOD equals 1740 lb/day and average suspended solids equal 1530 lb/day. Calculate the following: equivalent popu- lation based on 0.20 lb of BOD per capita; design flows in units of gpm, ft³/sec, m³/min, and m³/d; mean BOD and SS concentrations in mg/l. 12.33 Consider the feasibility of treating the wastewater from the town of Nancy (Problem 12.31) in a two-stage stone-media trickling-filter plant with intermediate clarification. The treated wastewater is required to meet the effluent standards of 30 mg/l of BOD and 30 mg/l of suspended solids at a wastewater temperature of 15°C. Assume a primary BOD removal efficiency of 35%. Calculate the volume of filter media required at a BOD load- ing of 35 lb/1000 ft³/day and divide the resulting volume equally between the first-stage and second-stage filters. Use a filter media depth of 7.0 ft. Assuming a recirculation ratio of 0.5 for both filters, determine the effluent BOD concentration using the NRC formulas. 12.34 Consider the feasibility of treating the wastewater from the town of Nancy (Problem 12.31) in a single-stage trickling-filter plant, as diagrammed in Figure 12.21, using high- density cross-flow media with a specific surface area of 42 ft²/ft³. Use the same filter sur- face area as calculated for stone-media filtration in Problem 12.31 (A = 4600 ft²) and a recirculation ratio of 0.5. The design wastewater temperature is 15°C. As determined from laboratory testing, the soluble (filtered) BOD of the primary effluent is 100 mg/l or less, compared to the unsettled unfiltered BOD of 160 mg/l. The soluble effluent BOD concen- tration of trickling-filter plants treating similar wastewaters is approximately 50% of the unfiltered BOD concentration. From pilot-plant studies and full-scale experience, the manufacturer of the cross-flow media recommends a reaction-rate coefficient at 20°C of 0.0030 (gpm/ft²)05 for a media depth of 6.6 ft (2.0 m). From these data, calculate the solu- ble effluent BOD and double this value for the estimated effluent BOD. 12.38 A tracer analysis was performed on a pilot trickling filter packed with a 10-ft depth of plastic media. The time to the appearance of the peak of the tracer concentration was recorded as a function of the hydraulic loading rate. The following data were collected: Hydraulic loading rate (Q) gpm/ft² 0.2 0.6 0.9 1.2 Time to peak of tracer conc., min 28 21 15 14 Find the coefficients C and n in the model shown in equation 12.46. 12.44 Calculate the RBC surface area required for secondary treatment of wastewater for the town of Nancy (Problem 12.31). Assume 35% BOD removal in the primary, a required effluent quality of 30 mg/l of BOD, and wastewater temperature of 50°F.