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The radiotracer was chosen to trace the water phase of the sludge. As known, water and finesolids of a pulp or sludge have the same behavior in most of reactors, thus the radiotracer compoundused follows the sludge hydrodynamic behavior inside the digester system. Seventeen NaI 2” × 2”scintillation probes were installed around the digester walls to evaluate the flow behaviors inside thedigester (Figs. 59 and 60). After the radiotracer instantaneous (Dirac) injection the radiation wasmeasured every second during the first 10 minutes to record fast processes, and then measuringinterval was kept 10 minutes. It took 33 days from the injection to collect the whole radiotracersignals.(c) Discussion of resultsThe analysis of experimental results for the primary digester is shown in Fig. 61.Figure 61 shows several experimental responses at various locations around the primarydigester. D4 is the probe installed at the outlet of primary digester. Figure 61 b shows that theexperimental RTD curve fits better with a perfect mixer and the MRT results 7.4 days. The primarydigester as a whole behaves as a perfect mixer.Similar results were obtained for probes D8 and D9 located at the upper part of the primarydigester (Fig. 61, e &f). These detectors indicate that the digester zones in front of them are behavingas perfect mixers, with MRTs 7.5 and 7.1 days, respectively. Probe D3 located in front of therecirculation flow also indicates a perfect mixing zone in front of it (Fig. 61, a), with a MRT of 7 days.As shown above the parameters of flow dynamics provided by probes D3, D4, D8 and D9 are almostthe same. However, detector D6 and D7 located on the lower part of a digester showed different flowpatterns from those of probes in the upper part of digester (D8 and D9). Intensity of radiation detectedby probes D6 and D7 was substantially lower than those of the detectors in the upper part of theprimary digester. At the beginning (after radiotracer injection), D6 and D7 showed no radiationindication, and later on tracer appeared reaching a peak. After the peak, the curves decreasedexponentially with time having a long tail, which indicates the presence of stagnant zones in theseparts of the digester. Because of the stagnant zones, the MRTs of sludge in zones in front of probes D6and D7 were found, of 10.2 and 15.2 days, respectively (higher than the theoretical MRT of theprimary digester).The probe D5 placed at the bottom part of the digester did not show any tracer signal at allduring the experiment duration. This indicates the presence of a sludge scale layer in this part ofdigester (7~9 m above the ground level from the bottom). Using the signal of the detector D4 as aninflow a similar analysis was carried out for the secondary digester.The results of the secondary digester are shown in Fig. 62.The secondary digester has no mixing facility and functions only to separate the mixed sludgebeing delivered from the primary digester statically.Detector D11 installed at the bottom part of the secondary digester did not show any tracerindication during the experiment time (similar result with detector D5 in primary digester). DetectorD16 installed at the outlet of the secondary digester gave a MRT of 6.3 days (Fig. 62, b), which islower than the theoretical MRT of 8.5 days calculated for the secondary digester. The detector D12showed relatively low radiation counts and a long tail, giving a MRT of 11.2 days. This is apparentlycaused by stagnant zone in front of this detector.The total MRT calculated between the inflow of the primary digester and the outflow of thesecondary digester (D1-D16) was 13.5 days (Fig. 62, c). Compared with the added result of MRT (D1-D4) + MRT (D4 - D16) = 7.4 d+ 6.3 d = 13.7 days, it results almost the same. This confirms thecorrectness of the calculations.The results of the radiotracer test on the anaerobic digester are summarized in Table VIII.57
FIG.59. Radiotracer experimental design: position of detectors.FIG.60. Some NaI detectors installed around digester.58
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 56 and 57: 4.00E-033.50E-03ExperimentalModel3.
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 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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