Temperature Dependency of Granule Characteristics and Kinetic Behavior in Mesophilic UASB Reactors

• Main Authors: Weng-Feng Hong, 洪文豐
• Other Authors: Ju-Sheng Huang
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/59123743197067933113

碩士 === 國立成功大學 === 環境工程學系 === 88 === ABSTRACT A kinetic model of upflow anaerobic sludge bed (UASB) reactors, which involves a distributed fraction of methanogens (f) and characteristic parameters of sludge granules, is proposed. Meanwhile, four identical UASB reactors (superficial velocity us = 0.5, 1.0, 2.0, and 4.0 m/h), which were operated under mesophilic temperatures of 35oC, 40oC, 30oC, and 25oC (Run 1, 2, 3, and 4), were used to treat synthetic wastewater containing the inhibitory substrate phenol. Once each of the four UASB reactors reached steady state, not only the flow regime and effluent water quality of the UASB reactor were determined but sludge granules were also removed from the UASB reactor to measure granule sizes and to determine the f values (by independent batch experiments). Finally, the proposed kinetic model of UASB reactors was verified by sixteen sets of experimental data. Under the volumetric loading of 10.6 kg COD/m3-d, the COD removal efficiencies (96.3% — 99.4%) of the four mesophilic UASB reactors treating the inhibitory substrate phenol did not vary significantly. In each of the four steady-state UASB reactors, the average equivalent diameter of granules in the lower-, middle-, and upper-part of sludge bed (dpi) tended to increase with an increase in us; the dpi was the largest under the operating temperature of 30oC but sludge granules were somewhat disintegrated under the operating temperature of 25oC. A larger dpi was found in the middle-part of sludge bed, which can be attributed to the differences in us and bed porosity, especially the UASB reactors operated at 30oC — 40oC. With the use of sludge granules taken from each of the four steady-state UASB reactors, the f values determined by independent batch experiments were 0.21 — 0.45. A higher operating temperature tended to give a larger f value, and the f value in the lower-part of sludge bed was larger than that in the upper-part or middle-part of sludge bed. In addition, from tracer tests and calculated results of dispersion number, the flow regimes of the four steady-state UASB reactors were close to complete-mix. By using suspended-growth batch reactors (25oC — 40oC; disrupted granules), the Haldane-type intrinsic biokinetic constants k, Ks, and Ki (phenol degradation with mixed culture) determined by Levenverg-Marquardt algorithm (nonlinear regression) were 0.60 — 0.76 mg phenol/mg VSS-d, 92 — 362 mg phenol/L, and 48 — 190 mg phenol/L, respectively. The Monod-type intrinsic biokinetic constants k2 and Ks2 (acetate methanogenesis with enrichment culture) determined by the Halwachs method (linear regression) were 2.9 — 5.1 mg acetate/L and 190 — 270 mg acetate/L, respectively. By performing linear regression (Arrhenius equation) of the intrinsic biokinetic constants k and k2 versus reaction temperatures (25oC — 40oC), the obtained activation energy (Ea) were 2960 and 6200 cal/mole, respectively; the obtained temperature coefficients (q) were 1.016 and 1.041, respectively. By performing linear regression (Arrhenius equation) of the specific phenol utilization rates (of the four steady-state UASB reactors) versus operating temperatures (30oC — 40oC), the obtained Ea and q were 2050 cal/mole and 1.012, respectively. By using the kinetic model, that accounts for the f and characteristic parameters of sludge granules, the calculated phenol and COD removal efficiencies were only ± 10% deviated from the experimental data. This implies that the proposed kinetic model can be used to predict the treatment performance of the UASB reactor treating the inhibitory substrate phenol. In addition, the calculated phenol and COD removal efficiencies basing on granule size distribution were nearly the same as those basing on uniform granule size. Accordingly, to predict phenol and COD concentrations in bulk liquid, one would rather choose the calculation basing on uniform granule size. Key words: upflow anaerobic sludge bed, inhibitory substrate phenol, operating temperature, superficial flow velocity, granule characteristics, Arrhenius equation, flow pattern, kinetic model, phenol degradation, acetate methanogenesis, distributed fraction of methanogens, model verification.