英文文献

摘要A novel oxidation ditch system using anaerobic tanks and innovative dual dissolved oxygen (DO) control technology is proposed for biological nitrogen and phosphorus removal from domestic sewage. A continuous bench-scale experiment running for more than 300 days was performed to evaluate the system. Monitoring and controlling the airflow and recirculation flow rate independently using DO values at two points along the ditch permitted maintenance of aerobic and anoxic zone ratios of around 0.30 and 0.50, respectively. The ability to optimize aerobic and anoxic zone ratios using the dual DO control technology meant that a total nitrogen removal efficiency of 83.2–92.9% could be maintained. This remarkable nitrogen removal performance minimized the nitrate recycle to anaerobic tanks inhibiting the phosphorus release. Hence, the total phosphorus removal efficiency was also improved and ranged within72.6–88.0%. These results demonstrated that stabilization of the aerobic and anoxic zone ratio by dual DO control technology not only resulted in a marked improvement of nitrogen removal, but it also enhanced phosphorus removal.关键词Biological nitrogen and phosphorus removal, dual DO control technology,oxidation ditch介绍Removal of biological nitrogen and phosphorus from domestic sewage is an important consideration for avoiding serious eutrophication problems in closed water ecosystem (Metcalf & Eddy 2003). Oxidation ditch (OD) technology is a modified activated sludge system that has been extensively applied for the removal of pollutants given the advantages associated with the process characteristics and ditch configurations. Typical oxidation ditches are completely mixed systems, and horizontally or vertically mounted aerators provide circulation and oxygen supply in the ditch simultaneously. The conventional oxidation ditch systems have been commonly operated with influent BOD loading (0.24 kg BOD/m3d) and hydraulic retention time (HRT) as long as 6–30 h (USEPA 2000).Since nitrogen removal potential is dependent upon the aerobic phase for nitrification and the anoxic phase for denitrification, the dissolved oxygen (DO) distribution in the ditch is an important control parameter for optimal nitrogen removal (Brouwer et al. 1998; Furukawa et al.1998;Ekman et al.2006). Surface aerators mentioned above hardly establish a stable anoxic zone under the daily variations of influent quality and water temperature due to the simultaneous change in circulation speed and oxygen supply. Hence, separation of aeration and mixing is effective for stabilizing the anoxic zone (Haoet al.1997). It was also reported that the efficiency of removing nitrogen could be increased by an oxidation ditch with the separation of the two functions of aeration (by flat flexible membranes) and mixing (by horizontal mixer) (Roustan et al.1993).Moreover, the combination of the aeration and mixing will cause high energy consumption and a perturbation of biological system without consideration the wastewater characteristics. The DO control system at one point maintains DO concentrations in the aerobic phase without consideration of the remaining DO subsequently entering the anoxic phase (Kiet al. 2008), limiting the rate of denitrification in anoxic phase and increasing the energy costs of municipal facilities (Ekmanet al.2006; Holenda et al.2008).In this study, the innovative dual DO control technology which was capable of controlling the aeration flow and recirculation rate independently was proposed for oxidation ditches with fine-bubble diffusers and submerged impellers.This novel system could effectively control the DO concentration at two points at the optimal level for the biological sewage treatment. In this research, the typical oxidation ditch was replicated by eight completely mixed tanks in series with huge inner recirculation rate similar to the previous studies (Furukawaet al. 1998; Henzeet al.2000). The objective of this research was to evaluate the novel oxidation ditch process employing dual DO control technology and anaerobic tanks prior to the ditch for the biological nitrogen and phosphorus removal.材料和方法反应器的安装和操作The bench-scale oxidation ditch system shown in Figure 1was specifically designed and operated to achieve simultaneous nitrogen and phosphorus removal from domestic sewage in Kochi Prefecture, Japan. The core reactor with a working volume of 300 L was divided into eight completely mixed tanks. For biological phosphorus removal, one or two anaerobic tanks (each tank was 37.5 L) were installed upstream from the main ditch. The tracer tests indicated that the core reactor consisting of the serial completely mixed tanks with huge inner recirculation rate replicated the flow characters and hydrodynamic characteristics of typical oxidation ditch. The grid chamber effluent was stored in a storage tank from where it was fed into the anaerobic tanks after filtration through a screen with 2 mm diameter. The mixed liquor then flowed through to a series of eight mixed tanks before entering the sedimentation tank (151 L). The return sludge was then pumped from the sedimentation tank into the anaerobic tanks to retain the biomass within the system.Continuous treatment of real domestic sewage wasconducted for the evaluation of the novel oxidation ditch from June 2007 to April 2008. The operational period was divided into several runs by different operating conditions as summarized in Table 1 in details. The huge inner recirculation ratios in the range of 45–78 suggested that the experimental set up was capable of replicating the typical oxidation ditches. Except for the fourth tank in RUN16, aeration was performed in the 5th tank in most experimental runs. HRT was maintained at approximately 11 h for the novel oxidation ditch process which was considerably shorter than the HRT employed in typicaloxidation ditch systems. Two anaerobic tanks were installed from RUN13-1 to RUN14, but other RUNs were operated with just one anaerobic tank. The mixed liquor suspended solids (MLSS) was maintained at approximately 3,000 mg/L and the solidretention time (SRT) ranged between 10 and 18 days during the operational period. The process was also operated at the range of 15–308C of water temperature.采样和分析方法Normal sampling involved the collection of 24-hours composite influent and effluent samples. Spot samples of the oxidation ditch, anaerobic tank and return sludge were directly collected on the sampling day. In addition, an intensive survey (from 14:00 on March 10 to14:00 on March 11, 2008 during RUN17) was conducted to evaluate the removal performanceof the system in response to daily influent fluctuations.The analysis of biochemical oxygen demand (BOD), total nitrogen (T-N), dissolved nitrogen (D-N), ammonium(NH4 +-N), nitrate (NO3--N), nitrite (NO2--N), total phosphorus (T-P), dissolved phosphorus (D-P) and MLSS were performed according to theStandardMethods(APHA 1998).On-line monitoring of DO at the 1st, 5th, 6th, 7th and 8th tanks was conducted using an automated sampling system,with DO values calibrated by a portable DO meter (Horiba OM51, Japan). The temperature of water was also measured using the portable DO meter. Water samples for the analysis of dissolved items were filtrated using 1-mm microfiber filters (Whatman GF/B, England).概念新颖的双溶解氧控制技术In this study, a novel strategy for dual DO control was developed for the oxidation ditch operation. The system enabled the maintenance and monitoring of defined DO values at two points along the system by independently controlling airflow and inner recirculation flow rates based on DO values in the 6th (DO6) and 8th (DO8) tanks. The DO6 was maintained at approximately 1.0 mg/L by continuous aeration of the 5th tank which effectively maintained theaerobic zone (DO.0.5 mg/L) ratio at levels above 30% of the total core reactor. The DO8 was maintained at approximately 0.2 mg/L to keep the DO concentration from the 1st to 4th tank below 0.1 mg/L by changing the inner recirculation flow rate. As a result, the anoxic zone (DO,0.1 mg/L) ratio was maintained at a level exceeding that of 50% of total core reactor (Fujiwara et al.2005). Importantly, application of the dual DO control technology was capable of maintaining the aerobic and anoxic zones in one ditch.Figure 2depicts the concept of the dual DO control strategy. An optimal DO inclination (a) is produced under conditions of normal influx loading. When influent loading is increased, the DO inclination becomes steeper due to the concomitant increase in the oxygen consumption rate as shown by the dotted line in (b). By employing dual DO control technology, the DO nclination recovers to the original gradient by increasing the aeration intensity and recirculation flow rate based on the set DO values at 6th and 8th tanks. On the other hand, the inclination of the DO curve becomes gentler due to the decrease in influx loading as shown by the dotted line in (c). The optimal DO inclination will also be recovered by the decrease in the aeration flow intensity and the recirculation flow rate. In other words, even when the system is operated under conditions with large fluctuations in influx loadings, the dual DO control technology responds dynamically to restore optimal conditions. In establishing a clear aerobic and anoxic zone through the independent control of airflow and recirculation flow rates,an optimal DO inclination is maintained in the ditch.结果与讨论双溶解氧控制技术The average DO values in each tank during different RUNs are shown inFigure 3. Since aeration was performed in the 5th tank, the DO decreased from the 5th further downstream. As a result, the DO inclination was created clearly in the core reactor. The dual DO control system with high oxygen utilization rate ensured the development of welldefined aerobic and anoxic zones. A similar inclination in DO was also obtained by shifting the aeration point from tank 5 to tank 4 in RUN16 (data not shown).Dual DO control technology was evaluated using the results obtained from an intensive survey conducted during RUN17. As shown inFigure 4, although the influent BODMLSS loadings fluctuated during the 24 h of the investigation, the aeration rate and recirculation time were dynamically adjusted by the dual DO control technology. Figure 5 shows that DO6 and DO8 were stabilized at set points of around 1.1 mg/L and 0.2 mg/L, spectively,which maintained aerobic and anoxic zones at ratios of 0.38 and 0.50, respectively. Through affecting thesecontrols, the system was able to maintain very low levels of NH4+-N (0.45^0.39 mg N/L),NO3--N (0.32^0.19mg N/L) and NO2--N (0.07^0.04 mg N/L) in the effluent. Previous studies (Ekman et al.2006; Yang et al.2010)indicated that the management of DO level at a low level will not only save the aeration energy but also improve the denitrification rate. So the optimal DO for the simultaneous nitrification and denitrification should be the lowest DO answered for nitrification for which effluent ammonia concentration can meet with the discharge standards (Liuet al.2010). Distinctly, it should be pointed out that the dual DO control technology in this novel oxidation ditch was capable of responding to variations in influent loadings and tablishing aerobic and anoxic zones stably for nitrogen removal. The conflict between nitrification and denitrification was overcome almost completely. As a result, nitrite accumulated by incomplete nitrification was negligible during the experiments.一般的处理性能The general removal performance of each RUN is summarized in Table 2. The average effluent suspended solid (SS) concentration for each RUN ranged between 5 and 38 mg/L. The average total BOD (T-BOD) of the influent fluctuated from 151 to 217 mg/L and the removal efficiency of carbonaceous BOD ranged from 93.7 to 97.6% with the average effluent BOD in the range of 3.3 to 9.3 mg/L. Thus,the novel oxidation ditch was capable of reducing organic pollutants considerably.生物脱氮Average influent T-N concentrations fluctuated from 35 to 40 mg N/L during the operational period. Using the dual DO control technology, the ratios of the aerobic and anoxic zones were maintained at around 0.30 and 0.50, respectively, in most of RUNs. In RUN13-1, 3.0^1.9 mg N/L of T-N in effluent and 92.9^4.0% of T-N removal efficiency were obtained for 45 days. Furthermore, 91.9^2.3% of T-N removal efficiency was achieved over 79 days, with an SRT of 13.5 days in RUN13-2. Nitrogen removal (effluent T-N) amounting to 2.9^0.6 mg N/L (RUN14) and 6.5^1.4 mg N/L (RUN15) was achieved with an SRT of approximately 10 days.The aeration point was shifted upstream from mixing tank 5 to mixing tank 4 tank in RUN16, resulting in an increase in the aerobic zone ratio from 0.38 to 0.48 but a decrease of the anoxic zone ratio from 0.50 to 0.38. As a result, complete nitrification could occur and averageNH4-N removal ratio of 90.5% was obtained; however, the decrease in the anoxic zone meant that a concomitant decrease was observed in the denitrification efficiency of the system and average T-N removal decreased to 73.0%.In RUN17, the ratios of the aerobic and anoxic zones recovered to 0.31 and 0.55, respectively. Importantly, the average concentrations of T-N, D-N and NH4-N in the effluent were 5.0^1.1 mg N/L, 3.6^1.3 mg N/L and 2.0^1.2 mg N/L, respectively. In RUN18, the average water temperature decreased to 15.38C and the HRT of the core reactor increased to 14.3 h. Maintenance of stable aerobic (0.38) and anoxic (0.52) zone ratios meant that high T-N (90.0^3.1%), D-N (89.2^3.5%) and NH4-N (96.9^2.6%) removal was also achieved.Several studies pointed out that the nitrification and denitrification can occur simultaneously at low DO levels (Limet al. 2009; Liuet al. 2010). Haoet al. (1997) also reported that a maximum DO value of 1.0 mg/L or more appeared enough for nitrification in the Pasveer oxidation ditch. In our novel oxidation ditch, the control DO value in 6th tank was maintained around 1.0 mg/L and a long SRT in the range of 10–18 days was operated to keep the considerable nitrifying organisms in the system. As a result,with the optimal aerobic zone ratio, the average removal efficiency of TN and NH4-N in the experimental period amounted to83.2–92.9% and 84.6–99.2%, respectively,indicating that the significant nitrification results were obtained in this study.In order for denitrification to proceed optimally,adequate C/N ratio is required in influent to anoxic phase (Sakaiet al.2002; Penget al.2008; Liuet al.2010).Excessive aeration and it’s effect on increasing DO levels in the internal recycle liquor may adversely effect denitrification, in that organic compounds are oxidized by the surplus oxygen. It is therefore considered important to control DO levels and limit aeration as much as possible (Ingildsen et al. 2002; Ekmanet al. 2006). In this study,the application of dual DO control technology facilitated efficient control of DO in the ditch. Optimized control of aeration and recirculation flow rate resulted in the recycling of mixed liquor with a low DO concentration from the 8th tank to the anoxic zone (tanks 1 to 4). Almost no surplus oxygen remained in the anoxic zone to inhibit the denitrification. The T-N removal ratio was used to estimate the denitrification efficiency. The modified influent T-BOD/T-N ratio was calculated as Equation (1) by considering the residualDO recycled to the anoxic zone. The effect of the ratio on T-N removal efficiency was also discussed.TBODInf., Influent T-BOD concentration (mg/L); TN Inf.,Influent T-N concentration (mg N/L); DO8, DO concentration at 8th tank (mg/L); Q Inf, Influent flow rate (L/h);Q r, Inner recirculation flow rate (L/h).Theoretically, 2.86 mg BOD/mg N is required for denitrification.Sakaiet al. (2002) reported that influent BOD/N ratios exceeding 4.9 mg BOD/mg N were necessary for optimal denitrification using an oxidation ditch with intermittent aeration. As shown in Figure 6, most of the modified T-BOD/T-N ratios were higher than theoretical value of 2.86 in this study, and T-N removal ratios were approximately 90% when the anoxic zone ratio was larger than 0.50 (solid circles). It was confirmed that the organic compounds in the influent were effectively consumed for denitrification. Conversely, when the equilibrium between the aerobic and the anoxic zones was disrupted in RUN16, the T-N removal efficiencies (open circles) were unstable. The lowest T-N removal ratio in RUN16 was separately marked due to the high suspended solid (SS)concentration (114 mg/L) in effluent. These results demonstrate that the dual DO control technology described in this study is effective for managing DO in a way that is conducive to nitrogen removal by realizing the optimal anoxic zone ratio and modified T-BOD/T-N ratio.生物除磷Average influent T-P concentration fluctuated in the range 5.2 to 8.2 mg P/L during the operational period. In addition, an average T-P removal efficiency of 82.2% was achieved togive an average effluent T-P concentration of 1.3^0.8 mg P/L in RUN13-1. The average T-P removal ratio decreased to 73.7^12.7%, or 1.6^0.6 mg P/L, for an SRT of 13.5 days in RUN13-2.A decrease in the SRT to 10.0 days resulted in the phosphorus removal performance of 84.4^7.0% in RUN14. Although only one anaerobic tank was used for RUN15,T-P removal efficiency around 72.6^10.4% was possible. Disruption of the optimal aerobic and anoxic zone ratio occurred in RUN16, with the T-P removal ratio decreasing to 64.6^22.3% and the average effluent T-P concentration reaching 2.5^1.7 mg P/L. However, considerable phosphorus removal was achieved in RUN17 and RUN18 with 1.0^0.3 mg P/L and 0.6^0.1 mg P/L remaining in the effluent T-P, respectively. With the optimal conditions, the average removal efficiency of T-P and D-P in the experimental period amounted to 72.6–88.0% and 77.1–91.8%, respectively.It has been observed that phosphorus release is inhibited by the presence of nitrate in anaerobic phase (Kubaet al. 1994; Peng et al. 2008). The relationship between the T-P removalratio and effluent NO3-N concentration is presented in Figure 7. The NO3-N concentrations of less than 3.0 mg N/L in the effluent of most of RUNs were obtained in this experiment.Similarly, average T-P removal efficiencies of approximately 80% were achieved (solid dots). The deterioration of denitrification in RUN16 occurred because the balance of aerobic and anoxic zone ratio was disrupted. Nearly the same amount of NO3-N as that in effluent was returned to the anaerobic tank. In the case, the surplus NO3-N would inhibit phosphorus release. The available carbon source was partly consumed by the denitrifying bacteria which utilize the nitrate as the elector acceptor. It was proposed that the denitrification organisms had a stronger capability of plundering the biological substrate which is easier than PAOs (Penget al. 2008). Indeed, when effluent NO3-N concentrations exceeded 4.0 mg N/L, the T-P removal ratio decreased around 60% (open dots). It can be concluded that the extraordinary biological nitrogen removal in the novel system supported the biological phosphorus removal by decreasing the transfer of nitrate into the anaerobic phase.As a result, the conflict on simultaneous nitrogen and phosphorus removal could be resolved by the novel DO control technology.In the presence of abundant carbon sources, such as acetate, which was easily assimilated by PAOs, was to support the stable phosphorus removal performance (Ohemenet al.2007). Simultaneously, the acetate was also utilized partly by denitrifying bacteria to reduce the nitrate which was transferred into the anaerobic phase. In order to evaluate the actual acetate utilization associated with phosphorus release, the modified acetate loadings of the influent were calculated using Equation (2). It is assumed that the nitrate concentration in the effluent was equal tothat in the return sludge.Modified influent acetate loading rate (mg COD/g VSS/h)QInf, Influent flow rate (L/h); CInf., Influent acetate concentration (mg COD/L); Cr, Nitrate concentration in return sludge (mg N/L); R, Return sludge ratio; X,MLVSS in anaerobic tank (g VSS/L);V, Volume of anaerobic tank (L).Figure 8shows the relationship between the rate of modified influent acetate loading and the phosphorus release rate during the intensive survey in RUN17.The linear correlation implied that higher influent acetate loading contributed to increased phosphorus release rates.In this study, fresh wastewater from the grid chamber was originally fed and completely mixed with activated sludge that had been returned to the anaerobic tank. Because the extraordinary denitrification was achieved by optimal aerobic and anoxic zone ratio in this novel oxidation ditch,the competition of denitrification to phosphorus release on carbon source utilization was weakened. Consequently, the biodegradable carbon source (e.g. acetate) could be selectively consumed by PAOs and converted to Polyb-hydroxyalkanoate (PHA). Then, in the subsequent anoxic and aerobic treatment stages, phosphorus uptake by PAOs would have occurred together with PHA consumption.As shown in Figure 9(solid dots), the modified influent acetate loading matched those of the actual values in the novel process. On the other hand, the conventionalAnaerobic-Anoxic-Oxic (A2O) process was normally operated with a 50% return sludge ratio and the NO3-N concentration in the return sludge was approximately 10 mg N/L(Metcalf & Eddy, 2003). If the A2O process were applied to the same sewage, the modified influent acetate loading would appear similar to that shown by the open circles in Figure 9. The distances between the line and the two kinds of data points demonstrate that almost all of the acetate was consumed during phosphorus release in the novel oxidation ditch. On other hand, more than 45% of the acetate would be used by denitrification in the A2O system. This calculation in Figure9revealed the advantage of the novel system over the A2O process for phosphorus removal. So stabilization of the aerobic and anoxic zoneratios therefore not only resulted in nitrogen removal, but it also enhanced the rate of phosphorus removal.In regard to other treatment process, Wang& Liu(2005) reported that the performance of T-N and NH4-N removal was disturbed by the unstable DO concentration in the mixed liquor when a bench-scale experiment using an integrated oxidation ditch with an anaerobic column was conducted to treat the raw wastewater. Moreover, the phosphorus removal efficiency was considered to be unstable in their process and the phosphorus removal ratio was only 77% even when acetic sodium was added to the influent.In our novel process, without the addition of any organic compounds, the carbon sources in the influent were effectively consumed by denitrification and effective phosphorus release. This success of the dual DO control technique presented here is considered to be due to the stable control of DO inclination and almost complete degradation of nitrate.结论A continuous bench scale experiment for the novel oxidation ditch system was conducted for more than 300 days in this study. The experimental results demonstrated that stabilization of the ration between the aerobic and anoxic zones by the dual DO control system presented here not only achieved considerable nitrogen removal, but the technique also enhanced phosphorus removal. The concept is expected to be applied to a full-scale plant employing fine-bubble diffusers and submerged impellers, which is capable of controlling the aeration intensity and recirculation flow rate independently参考APHA1998Standard Methods for the Examination of Water andWastewater, 20th edition. Edited by American Public HealthAssociation/American Water Works Association/WaterEnvironment Federation, Washington, DC.Brouwer, H., Bloemen, M., Klapwijk, B. & Spanjers, H.1998Feedforward control of nitrification by manipulating the aerobicvolume in activated sludge plants. Water Sci. Technol.38(3),245–254.Ekman, M., Bjorlenius, B. & Andersson, M.2006Control of theaeration volume in an activated sludge process usingsupervisory control strategies. Water Res.40(8), 1668–1676.Furukawa, S., Tokimori, K., Hirotsuji, J. & Shiono, S.1998Newoperational support system for high nitrogen removal inoxidation ditch process. Water Sci. Technol.37(12), 63–68.Fujiwara, T., Kitasaki, S., Yoshino, M., Ohtoshi, K., Nishimura, F. &Tsuno, H.2005A novel technique for effective nitrogenremoval through control of dissolved oxygen in OxidationDitches.IWA Specialized Conference Nutrient Management inWastewater Treatment Process and Recycle Stream.Hao, X., Doddema, H. & Van Groenestijn, J.1997Conditions andmechanisms affecting simultaneous nitrification anddenitrification in a Pasveer oxidation ditch. Bioresour.Technol.59(2–3), 207–215.Henze, M., Gujer, W., Mino, T. & Loosdrecht, M. v.2000ActivatedSludge Models ASM1, ASM2, ASM2d and ASM3.IWA,London.Holenda, B., Domokos, E., Redey, A. & Fazakas, J.2008Dissolvedoxygen control of the activated sludge wastewater treatmentprocess using model predictive control. Comput. Chem. Eng.32(6), 1270–1278.Ingildsen, P., Olsson, G. & Yuan, Z.2002A hedging point strategybalancing effluent quality economy and robustness in thecontrol of wastewater treatment plants.Water Sci. Technol.45(4–5), 317–324.Ki, H., Duk, C., Sung, W., Joon, M., Sang, B. & Young, S.2008Effect of cycle length and phase fraction on biologicalnutrients removal in temporal and spatial phase separatedprocess. J. Ind. Eng. Chem.14(4), 520–525.Kuba, T., Wachtmeister, A., van Loosdrecht, M. C. M. & Heijnen, J. J.1994Effect of nitrate on phosphorus release in biologicalphosphorus removal systems.Water Sci. Technol.30(6), 263–269.Lim,E.,Jeong,G.,Bhang,S.,Park,S.&Park,D.2009Evaluation ofpilot-scale modified A2O processes for the removal of nitrogencompound from sewage.Bioresour. Technol.100(24), 6149–6154.Liu,Y.,Shi,H.,Xia,L.,Shi,H.,Shen,T.,Wang,Z.,Wang,G.&Wang,Y.2010Study of operational conditions of simultaneous nitrificationand denitrification in a Carrousel oxidation ditch for domestic wastewater treatment.Bioresour. Technol.101(3), 901–906.Metcalf & Eddy Inc2003Wastewater Engineering: Treatment and Reuse, 4th edition. McGraw-Hill, Inc., Singapore.Oehmen,A.,Lemos,P.,Carvalho,G.,Yuan,Z.,Keller,J.,Blackall,L.& Reis, M.2007Advances in enhanced biological phosphorus removal: frommicrotomacroscale.Water Res.41(11), 2271–2300.Peng, Y., Hou, H., Wang, S., Cui, Y. & Yuan, Z.2008Nitrogen and phosphorus removal in pilot-scale anaerobic-anoxic oxidationditch system. J. Environ. Sci.20(4), 398–403.Roustan, M., Chatellier, P., Lefevre, F., Audic, J. M. & Burvingt, F. 1993Separation of the two functions aeration and mixing in oxidation ditches: application to the denitrification byactivated sludge. Environ. Technol.14(9), 841–849.Sakai, Y., Wakayama, M. & Miyake, H.2002The proposal of operating methods to deal with influent fluctuation for OD plants.J. Jpn. Sewage Works Assoc.31(379), 16–33 (in Japanese).USEPA2000US Environmental Protection Agency, Office of Water, EPA 832-F-00-013 Wastewater Technology Fact Sheet:Oxidation Ditches. US Environmental Protection Agency,Office of Water, Washington, DC, USA.Wang, S. & Liu, J.2005Enhanced biological nutrients removalusing an integrated oxidation ditch with vertical circle from wastewater by adding an anaerobic column.J. Environ. Sci.17(6), 894–898.Yang, S., Yang, F., Fu, Z., Wang, T. & Lei, R.2010Simultaneous nitrogen and phosphorus removal by a novel sequencing batch moving bed membrane bioreactor for wastewater treatment.J. Hazard. Mater.175(1–3), 551–557。