| Summary: | 博士 === 國立中興大學 === 環境工程學系所 === 101 === The autothermal thermophilic aerobic treatment (ATAT) system is a biological process in which the operating temperature can be spontaneously maintained at 45 - 65oC. Comparing with the activated sludge process (ASP), the ATAT produces significantly less wasted sludge. Although, full-scale ATAT or autothermal thermophilic aerobic digestion (ATAD) systems have been well documented in literature, the technology is not widely used due to the scarcity of documentation relating to spontaneity and feasibility. There is no effective technique to evaluate the feasibility of an ATAT system. Therefore, it is necessary to develop evaluation tools for the specific biological heat potential (hb) and kinetic analysis for the ATAT system. This study also verifies the two-phase kinetic model algorithm of respirometer serial dilution kinetic and estimates microbial kinetic parameters.
Based on the two-phase model for analyzing a batch OUR vs. Ou respirogram was analyzed. For this verification study, results showed that the maximal growth rate (μm), half-saturation constant (Ks), decay coefficient (Kd) and gross growth yield (Yg) had lower coefficients of variation (Cv value was 2.5% to 15.9%) than that from the transient method. Because the oxygen uptake estimation variability of substrate was only 2.5%, therefore, respirometer is an advantageous tool to estimate kinetic parameters in microbial systems. Then, it is suggested that the ratio of S0/X0 must be higher 15 for two phase kinetic model algorithm of respirometer. The algorithm was illustrated by a respirometric test on glucose of 2,500 mg/L COD at 55oC. The result shows the μm of 5.16±0.1 1/d, Yg of 0.46±0.04 mg BOD of X/mg BOD of S, Ks of 401.7±15.2 mg/L BOD, and Kd of 0.39±0.05 1/d for the ATAT system. Also, these microbial kinetic parameters had the tendency showing that an increase in temperature also increased these paramenters. The temperature effect constants (Φ) of van’t Hoff-Arrhenius law for μm, Ks, Kd and Yg were 1.040, 1.028, 1.019 and 1.033, respectively. This result demonstrated the ATAT system has successfully competed the traditional active sludge with better microbial kinetic parameters and higher potential treatment efficiency for high concentration organic wastewaters.
Then, this study focuses on the calculation of hb of wastewater in an ATAT system. The treatment system was daily fed with realistic and artificial wastewater at 11,250 and 17,420 mg COD/L, respectively. The wastewater was rich in oil and grease (O&G) at 1,220 and 600 mg/L, respectively. The sludge retention time (SRT) was controlled at 5 days. The results showed that the COD removal efficiency was as high as 88 to 93% for the realistic and artifical wastwaters, respectively. The O&G reduction was 69 to 72%. These two systems could maintain reactor operating temperatures at 43 oC and 48oC, respectively. The average values of hb were 3.7 and 3.1 kcal/g-COD-removed and the observed growth yield (Yo) were 0.10 and 0.13 mg MLSS/mg COD for realistic and artificial wastewater, respectively. Next, this system was daily fed with oily and artificial wastewater at 21,460 mg/L COD. The SRT was controlled at 5 days and tank temperature was controlled at 35, 45, 55, and 65oC. The results showed that the COD removal efficiency was 77% to 91%. However, the O&G removal efficiency was 50% to 69%. These results might indicate that oil and grease become more soluble and accessible to microorganisms at high temperatures. The average values of hb were 3.25 to 3.63 Kcal/g-COD-removed for the artificial wastewater. The values of Y0 were 0.08 to 0.19 mg-MLSS m/L-COD for the wastewater at different temperatures. The temperature effect constant (Φ) of van’t Hoff-Arrhenius law for Yo was 0.958 with ATAT pilot study, which explained typical characteristics showed in the low sludge yield of an ATAT process. The high organic matter removal capacity with low sludge yield of ATAT process have been demonstrated.
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