| Summary: | 碩士 === 崑山科技大學 === 環境工程研究所 === 97 === A kinetic model and empirical model for the EGSB reactor that take into account the inhibiting effect of free hydrogen sulfide (H2S) on bacterial groups is formulated and validated by experiments. Meanwhile, One ORP-based EGSB reactor (with internal oxygenation; operating temperature = 35C, superficial velocity us = 4.0 m/h) maintained at the influent COD/SO42- ratio of 0.5 and ORP of -410 mV as well as one conventional EGSB reactor (without adding SO42-; operating temperature = 35C, us = 4.0 m/h, ORP = -400 mV) were respectively used for the enrichment of sulfate-reducing bacteria (SRB) and methanogenic bacteria (MB) and thereby used for the determination of their intrinsic and apparent kinetic parameters. To investigate the treatment performance, granule characteristics, mass fractions of SRB and MB and reaction kinetics, two ORP-based EGSB reactors treating sulfate-laden organic wastewater were respectively maintained at the influent COD/SO42- ratios of 1.1 (reactor A) and 3.0 (reactor B) but with successive increasing organic loading rate from 4.0 to 6.0 and 9.0 kg COD/m3-d.
When the reactors A and B (organic loading rates of 4.0, 6.0, and 9.0 kg COD/m3-d) were respectively maintained at the operating ORP levels of -410, -420, -450 mV (corresponding to ORP values without internal oxygenation: -432, -446, -478 mV) and -390, -400, -425 mV (corresponding to ORP values without internal oxygenation: -411, -425, -450 mV), the H2S effluent concentration increased with increasing organic loading rate; the H2S effluent concentration in the reactor A (148–408 mg S/L) was remarkably higher than that in the reactor B (33–132 mg S/L); the COD removal efficiency still reached to 98.6% even at the organic loading rate of as high as 9.0 kg COD/m3-d, indicating that the ORP-based EGSB reactor can decrease H2S concentration and thereby benefit its operation at a high organic loading rate. In addition, the granule’s specific gravity, granule diameter, and microbial density increased with increasing organic loading rate; at the same organic loading rate, the granule diameter at the reactor A (influent COD/SO42- ratios of 1.1) was larger than that at the reactor B (influent COD/SO42- ratios of 3.0) whereas the granule’s specific gravity and microbial density at the reactor A were smaller than those at the reactor B. The organic loading rate did not affect the mass fractions of SRB and MB. The mass fraction of SRB determined from the reactor A ranged from 0.73 to 0.75, indicating that SRB out-competed MB for bacterial growth; the mass fraction of MB determined from the reactor B ranged from 0.75 to 0.77, indicating that MB out-competed SRB for bacterial growth.
The estimated intrinsic and apparent kinetic parameters kSR (2.1 mg acetate/mg VSS-d) and kSR’(1.79 mg acetate/mg VSS-d) were greater than kM (1.58 mg acetate/mg VSS-d) and kM’(1.38 mg acetate/mg VSS-d); Ks,M (10 mg acetate/L) and Ks,M’ (15 mg acetate/L) were smaller than Ks,a (32 mg acetate/L) and Ks,a’ (35 mg acetate/L), implying that the affinity of organics to MB was higher, compared with SRB; KI,M (266 mg H2S/L) and KI,M’ (476 mg H2S/L) were smaller than KI,SR (305 mg H2S/L) and KI,SR’ (591 mg H2S/L), indicating that H2S imposed a greater inhibiting effect on MB; apparent kSR’ and kM’ were smaller than intrinsic kSR and kM, showing that internal mass transfer resistance occurred in intact granules. By inserting operating conditions and physical and biological parameter values into the kinetic and empirical models, the calculated acetate removal efficiency and sulfate removal efficiency were ±1.0 and ±10.3% deviated from the experimental acetate removal efficiency and sulfate removal efficiency, respectively. The simulated removal efficiency by using the kinetic model was only 2.3% deviated from that by using the empirical model. Accordingly, the proposed kinetic and empirical models can be properly used for function design of the ORP-based EGSB reactor.
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