| Summary: | 碩士 === 國立成功大學 === 環境工程學系 === 87 === Characteristics of Tapered Upflow Anaerobic Sludge Bed Reactors
ABSTRACT
A kinetic model of upflow anaerobic sludge bed (UASB) reactors, which involves characteristic parameters of sludge granules, is proposed. Also, one conventional and three tapered UASB reactors (angle = 0o, 2.5o, 5o, and 10o) were used to treat synthetic wastewater containing the inhibitory substrate phenol. Once each of the four UASB reactors reached steady state, sludge granules removed from the UASB reactor were used to measure granule sizes and to determine activity coefficients of methanogens (by independent experiments). The existence of multiple steady states in UASB reactors treating the inhibitory substrate phenol was also verified by experiments. Finally, the steady-state-granule kinetics was used to analyze the kinetic behavior of UASB reactors treating the inhibitory substrate phenol and thereby the analyzed results were compared to experimental results. Also, the proposed kinetic model of upflow anaerobic sludge bed reactors was verified by twelve sets of experimental data.
At the volumetric loadings ranging from 2.03 to 20.5 kg COD/m3-d (based on sludge bed volume) or F/M ratios ranging from 0.11 to 0.42 kg COD/kg VSS-d, the COD removal efficiencies of the four UASB reactors do not vary significantly. With an increase in volumetric loading, the average equivalent diameter of granules (dp, avg) increases but the equivalent diameter of granules (dpi) in the lower-, middle-, and upper-part of sludge bed are nearly the same. In addition, from tracer tests the flow regimes of the four UASB reactors with recycle ratios of 12, 16.3 and 25 are close to complete-mix.
In the conventional UASB reactor, the activity coefficients of methanogens in the lower-, middle-part of sludge bed (0.18 — 0.63) are larger than those in the upper-part of sludge bed (0.14 — 0.50). In the tapered UASB reactors (angle = 2.5o and 5o), larger activity coefficients appear to shift from the lower- and middle-part of sludge bed at lower volumetric loadings to the upper-part of sludge bed at higher volumetric loadings. However in the tapered UASB reactor (angle = 10o), the activity coefficients of methanogens do not vary significantly with different parts of sludge bed at the high volumetric loading.
By using suspended-growth batch reactors (35 C; disrupted granules), the Haldane-type intrinsic biokinetic constants k, Ks and Ki (of anaerobic degradation of phenol) determined by Levenberg-Marquardt algorithm (nonlinear regression) are 0.69 mg phenol/mg VSS-d, 46.2 mg phenol/L, and 66.4 mg phenol/L, respectively. The Monod-type intrinsic biokinetic constants k and Ks (of acetate methanogenesis with enriched culture) determined by the Halwachs method (linear regression) are 4.68 mg acetate/mg VSS-d and 117 mg acetate/L, respectively.
From the relationship between the specific phenol utilization rates (obtained from either the kinetic model or treatment performance of UASB reactors) and the phenol concentration in bulk liquid, the kinetic behavior of UASB reactors treating the inhibitory substrate phenol is typical substrate-inhibited kinetics. In addition, the simulated results obtained from the kinetic model of UASB reactors, which involves the characteristic parameters of sludge granules, show that the calculated phenol removal efficiencies are only 5% deviation from all actual experimental data of the four UASB reactors. Also, the simulated results obtained from the kinetic model based on uniform granule size are closed to those based on granule size distribution.
Finally, three other findings are briefly described as follows: (1) The true growth yield YT determined from the four UASB reactors are nearly the same (0.043 — 0.050 g VSS/g CODu); (2) Multiple steady states do occur in the UASB reactor treating the inhibitory substrate phenol; and (3) In batch reactors containing distrupted granules, the enriched methanogens appear to be stimulated by phenol if (i.e. compared to that of the control) the adsorbed phenol onto disrupted granules reaches to 8.47 — 8.90 mg phenol/g VSS; however, the enriched methanogens appear to be remarkably inhibited by phenol if the adsorbed phenol onto disrupted granules reaches to 10.64 mg phenol/g VSS.
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