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4.00E-033.50E-03ExperimentalModel3.00E-032.50E-032.00E-031.50E-031.00E-035.00E-040.00E+00151101151201251301351401E(t)451501551601651701751801851901Time (min)FIG.42. Experimental and model RTD curves of the aeration tank.FIG.43. Model of the aeration tank. V1 = 80 m 3 , V2 = 101 m 3 , V3 = 100 m 3 , V4 = 100 m 3 ,V5 = 97.7 m 3 , V6 = 106.7 m 3 .The model consists of five perfect mixers in series with back mixing and connected with a plugflow reactor at the beginning. After the injection point, the incoming wastewater passes through anarrow duct before it enters into the series of tanks through small holes. Because of this reason, a plugflow reactor is used between node no. 1 and node no. 2. Back mixing ratio of the tanks connected inseries is found to be 2.7.The volume of the aeration tank was 567.5 m 3 and the volumetric flow rate during theexperiment was 2.08 ± 0.08 m 3 /min. It gives the theoretical mean residence time of 272.8 min. Theexperimental mean residence time of the unit was estimated as 271.9 min with a very small deadvolume (0.32%). Therefore, almost negligible amount of dead volume was estimated in the aerationtank. This is due to the vigorous mixing process inside the aeration tank.Due to high gas flow rate, tracer experiments conducted in aeration tank have shown that waterand sludge have generally similar flow behavior. Radiotracer investigation in aeration tank has shownthat the fluid flow can be modeled either by perfect mixing cells in series or by perfect mixing cells inseries with back mixing. The number of mixing cells found by RTD modeling was J=5, in fact numberJ is a function of both gas and water flowrates as well as of the geometrical configuration. The resultsof this experiment showed that the aeration tank was achieving the designed residence time and wasworking efficiently as far as residence time is concerned.(c) Secondary clarifierThe experimental RTD curve obtained at the output of the secondary clarifier is given in theFig. 44. Figure 45 shows the best model found using RTD software simulation.47
8.00E-037.00E-03ExperimentalModel6.00E-035.00E-034.00E-033.00E-032.00E-031.00E-030.00E+00154107160213266319372E(t)425478531584637690743796849902955Time (min)FIG.44. Experimental and model RTD curves of the secondary clarifier.FIG.45. Model of the secondary clarifier.Where: V1 = 29 m 3 , V2 = 230.2 m 3 , V3= 374 m 3 , V4 = 314.1 m 3 , V5 = 315 m 3 .In the model, node no. 1 is the inlet and tracer input, node no. 7 is the outlet; V 1, V 3and V 5arethe perfect mixing cells and V 2, V 4are the plug flow reactors. From the inlet node, the flow goesthrough a small perfect mixing cell in the center of the clarifier. From node no. 2 to node no. 4, theflow is through the perfect mixing cell connected with the plug flow reactor. Then, there is a recyclebetween node no. 2 and node no. 4 (with ratio 2.3) through the perfect mixing cell connected with theplug flow reactor.Experimental and model output responses of the secondary clarifier (Fig. 44) show a sharp highpeak at 27 min indicating that an important portion of the tracer passes away due to the shortcircuitingcausing a significant reduction in the removal efficiency of the settling tank. There isanother peak appearing at 124 min, which is representing the main flow of the secondary clarifier. Themean residence time of the model curve is calculated from the moment of first order of the modelcurve and it is 260.2 min that is close to the experimental value of the mean residence time.The total volume of the secondary clarifier was 2790 m 3 which is almost double that of theprimary clarifier. The volumetric flow rate during the experiment was 4.16 ± 0.15 m 3 /min giving thetheoretical mean residence time of 670.6 min. The experimental mean residence time of the secondaryclarifier was estimated as 284.7 min. The dead volume of the system was estimated as 57.5%. Thisshows that the working efficiency of the unit is very poor because more than half of the systemvolume was not taking part in the process. All final results are summarized in Table 6.TABLE 6. SUMMARY OF RESULTS OBTAINED BY RADIOTRACERS.System underinvestigationVolume(m 3 )Flow rate(m 3 /min)TheoreticalMRT (min)Exp. MRT(min)Primary clarifier 1387 4.83 287 164 43Aeration tank 567.5 2.08 272 271 0.2SecondaryclarifierDead Volume(%)2790 4.17 670 285 5748
Page 1 and 2:
Radiotracer Applications inWastewat
Page 3 and 4:
The following States are Members of
Page 5 and 6: TRAINING COURSE SERIES No. 49RADIOT
Page 7 and 8: EDITORIAL NOTEThe use of particular
Page 9 and 10: PRACTICAL RECOMMENDATIONS .........
Page 11 and 12: The success of radiotracer applicat
Page 13 and 14: skimmed out. Flotation, as currentl
Page 16 and 17: 1.3.3. Primary clarifiersA clarifie
Page 18 and 19: esidence times of phases, mixing ch
Page 20 and 21: FIG.8. Secondary clarifier: periphe
Page 22 and 23: processes that occur in natural env
Page 24 and 25: The RTD and MRT are parameters that
Page 26 and 27: (b) Perfect mixers in series modelA
Page 28 and 29: and practically it has better sense
Page 30 and 31: The experimental RTD curve gives ma
Page 32 and 33: FIG.18. Experimental and CFD calcul
Page 34 and 35: Optical tracers can be divided in t
Page 36 and 37: Table 1b. Liquid tracers.- Field of
Page 38 and 39: TABLE 2. SOME WATER RADIOTRACERSIso
Page 40 and 41: The detection efficiency (ϕ) is de
Page 42 and 43: Since on-line radiotracer technique
Page 44 and 45: source. The dose received is direct
Page 46 and 47: 4. CASE STUDIESWastewater from indu
Page 48 and 49: FIG.26. Scheme of equalizer-clarifi
Page 50 and 51: FIG.29. Exp. RTD of S2 and S3 jet m
Page 52 and 53: FIG.33. Experimental RTD curves mea
Page 54 and 55: 1. Radiotracer testsRadiotracer Br-
Page 58 and 59: 3. Conclusions• The aeration tank
Page 60 and 61: FIG.50. Experimental response curve
Page 62 and 63: 4.8. DIAGNOSIS OF A CYLINDRICAL TWO
Page 64 and 65: FIG.56. RTD simulation for experime
Page 66 and 67: The radiotracer was chosen to trace
Page 68 and 69: (a) D1 - D3 (b) D1 - D4(c) D1 - D6
Page 70 and 71: (d) ConclusionsThe diagnosis of dig
Page 72 and 73: • average gamma energy of 400 keV
Page 74 and 75: To estimate the MRT of the mud insi
Page 76 and 77: FIG.71. Experimental RTD curve and
Page 78 and 79: FIG.75. Biological aeration tank.FI
Page 80 and 81: 4.12.2. Radiotracer experiment(a) L
Page 82 and 83: FIG.80. The experimental RTD curve
Page 84 and 85: FIG.84. Experimental RTD curve of l
Page 86 and 87: FIG.88. Characteristic curves of se
Page 88 and 89: tracer background level detection.
Page 90 and 91: As seen from Fig. 94, the tanks-in-
Page 92 and 93: FIG.99. Experimental RTD curves wit
Page 94: The experimental RTD curves obtaine
Page 98: BIBLIOGRAPHYBORROTO J.I., DOMINGUEZ
Page 102: CONTRIBUTORS TO DRAFTING AND REVIEW
Page 106:
I S S N 1 0 1 8 - 5 5 1 8
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