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ABSTRACT: A pilot-scale step-feed A/O system was used to treat low C/N municipal wastewater. To obtain high quality simultaneous nitrogen and phosphorus removal, a modified step-feed A/O system was developed and the nitrogen and phosphorus removal efficiency was evaluated between the original and modified system. The result showed that TN removal efficiency was 66.52% and TP removal efficiency was only 29.24% before the modified configuration was applied. When the modified system was adopted, the satisfied simultaneous nitrogen and phosphorus removal was achieved. TP removal efficiency increased to 89.81% and TN removal efficiency was 73.61% when the optimal feeding ratio (0.45:0.35:0.20) was applied. Compared to the original configuration, TN removal efficiency increased about 7.09% due to the enhanced denitrifying phosphorus removal, which saved the carbon source for denitrification. To evaluate the selection and dominance of polyphosphate-accumulating organisms (PAOs) and denitrifying polyphosphate-accumulating organisms (DNPAOs), batch test was explored to examine the anaerobic phosphorus release, aerobic and anoxic phosphorus uptake. The result showed that both PAOs and DNPAOs were accumulated gradually when the modified system was applied. The maximal aerobic P uptake rate [P/(MLSS x t)] was increased from 2.34 mg/(g x h) to 10.67 mg/(g x h) and the anoxic P uptake rate was increased from 0.33 mg/(g x h) to 2.81 mg/(g x h) when the modified system was operated.
Huan jing ke xue= Huanjing kexue / [bian ji, Zhongguo ke xue yuan huan jing ke xue wei yuan hui "Huan jing ke xue" bian ji wei yuan hui.] 10/2009; 30(10):2968-74.
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ABSTRACT: To obtain high quality drainage, external carbon source (ethanol) was used to enhance denitrification when low COD/N sewage was fed to a pilot-scale step-feed A/O system. To use carbon source sufficiently, five different external carbon addition control strategieswere proposed based on different control parameters, ORP and on-line nitrate, and dosing positions, D3 and D4. Control strategies were evaluated on investment, treatment efficiency and operation cost basis. The results showed that for the short hydraulic retention time in anoxic zone, the control parameter could not reach the set-point when control strategy I and II were applied. As a result, excessive feeding of external carbon source was occurred and the average COD concentrations in D4 were 192.8 mg/L and 158.9 mg/L for the insufficient usage of carbon. In this condition, effluent TN concentrations were 17.42 mg/L and 19.04 mg/L and the external carbon dosage rates were 92 mL/(m3 x d) and 84 mL/(m3 x d), respectively. Control strategies III, IV and V controlled the external carbon dosage in D3 and D4 simultaneously. The results indicated that the strategies had strong resistance to peak loadings and reduced the effluent TN concentration effectively. The average effluent TN concentrations, 7.30 mg/L, 8.2 mg/L and 7.49 mg/L and the external carbon dosage rates, 29 mL/(m3 x d), 45 mL(m3 x d) and 27 mL/(m3 x d), were achieved respectively. Finally, based on the amount of on-line sensors, reliability of treatment efficiency and cost of operation, the control strategies proposed in this paper were evaluated together. Compared to the other control strategies, the suggested external carbon addition strategy III was testified to be an optimal control strategy, which was characterized by good dynamic qualities, strong resistance to peak loadings, quick responding to loadings, and the lower external carbon addition amount.
Huan jing ke xue= Huanjing kexue / [bian ji, Zhongguo ke xue yuan huan jing ke xue wei yuan hui "Huan jing ke xue" bian ji wei yuan hui.] 04/2009; 30(3):792-7.
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ABSTRACT: To investigate the responding behavior of denitrifying bacteria to different carbon source (i.e., methanol, ethanol, sodium acetate, sodiumpropionate, glucose, domestic wastewater and endogenous carbon source), several batch experiments using the sludge from the Carrousel oxidation ditch were carried out at 15.4 degrees C +/- 0.8 degrees C. The results from sodium acetate feeding experiment show the highest maximum specific denitrification rate (MSDR), which is 6.51 mg/(g x h). However, the denitrificaion yield, which is 0.48, is at lowest level and an obvious accumulating of nitrite is observed. Compared to the other sole carbon source, a lower MSDR, 0.91 mg/(g x h) is shown when methanol is used as carbon source, which also suggests that the sufficient adaptation time should be promised for denitrifying bacteria. When the reactor is operated without exogenous carbon source, denitrifying bacteria can use the endogenous carbon source as electron donor for denitrification, but the specific denitrification rate is at lowest level accordingly. The MSDR value of 3.63 mg/(g x h) is obtained with fermented domestic wastewater feeding, which is equivalent to the MSDR attained from the test using VFAs as carbon source. Though the MSDR decreases a lot at low temperature, external carbon source addition improves the denitrification performance to some extent definitely.
Huan jing ke xue= Huanjing kexue / [bian ji, Zhongguo ke xue yuan huan jing ke xue wei yuan hui "Huan jing ke xue" bian ji wei yuan hui.] 02/2009; 30(1):108-13.
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ABSTRACT: In order to optimize the utilization of influent carbon source, a feeding pattern so-called "coefficient of influent flow rate" was adopted in a pilot-scale step-feed A/O process treating domestic wastewater. The effects of influent flow distribution ratio on nitrogen removal efficiency were investigated when the reactor was operated at different loading rates and COD/TKN ratio of 3, 5, 7, 9, 11, 13, respectively. The experiment results indicated that the wasting of nitrification capacity occurred when high loading rate and low C/N ratio (COD/TKN <5) were applied, while ammonia removal efficiency was decreased obviously at the same time. When the system was operated at high loading rate and high C/N ratios, the insufficient nitrification occurred in first stage, which resulted in the absence of electron accepter in the downstream anoxic zone. Consequently, the total nitrogen (TN) removal efficiency was decreased even though the COD/TKN was higher than 9. However, due to the unlimited nitrification, the increased C/N ratio led to an enhancement of TN removal efficiency when the system was operated at low influent loading rate. When the influent COD/TKN was kept at 13 around, relatively low effluent TN concentration less than 2 mg/L, and a highest TN removal efficiency of 97.6% were achieved, respectively. For the feeding pattern selected for the study, the conclusions obtained from the experiment results showed that the influent flow coefficient method could use carbon source sufficiently and decrease the influent flow rate of last stage when the wastewater with higher C/N(C/N > alpha) was fed. However, a completely nitrification should be promised in each stage during this period. When the wastewater with low C/N ratio (C/N < alpha), due to the limited carbon source, C/N is the key parameter for TN removal efficiency. From the point view to favor the growth of nitrifiers and satisfy the ammonia effluent standard, the balanced loading of nitrifiers in each stage strategy maybe substitute the feeding pattern proposed in this study as an optimal choice.
Huan jing ke xue= Huanjing kexue / [bian ji, Zhongguo ke xue yuan huan jing ke xue wei yuan hui "Huan jing ke xue" bian ji wei yuan hui.] 01/2009; 30(1):96-101.
