1、PDF外文：http:/ - 1 - Performance of an oxidation ditch retrofitted with a membrane bioreactor during the start-up ABSTRACT The objective of this study is to elucidate the full-scale characteristics of an oxidation ditch (OD) retrofitted with a membrane bioreactor (MBR). Domest
2、ic wastewater entering an oxidation ditch at a flow rate of 86 m3/d was directed to a MBR retrofitted into the original secondary sedimentation tank. The MBR contained flat sheet membranes. The data collected for 2 months during the start-up of the system showed that pH was maintained at 7.2 and 6.7
3、 in OD and MBR, respectively. Dissolved oxygen (DO) in MBR remained stable at 7.8 mg/L, while fluctuated in OD. The mixed liquor suspended solids (MLSS) in the OD remained steady at a concentration about1000 mg/L, but it was gradually building up from 500 mg/L to 2400 mg/L in the MBR during this per
4、iod.Measurements of carbohydrate and protein were made by extracting the extra cellular polymeric substances (EPS)with sodium hydroxide (NaOH) from the mixed liquor obtained from both OD and MBR. Carbohydrate was predominant in the EPS and the ratios between carbohydrate and protein converged to fix
5、ed values from the fourth week； in this case the ratio was 4.5 for OD and 5 for MBR. The variation in EPS contents showed similar trends in both OD and MBR. The integrated treatment facility removed ammonia, COD and BOD at 100、 91.6 and 97.0%, respectively. However, efficiency of nitrate and phospha
6、te removal has not been realized yet. KEYWORDS: Oxidation ditch； Submerged flat sheet membrane； Extracelluler polymeric substance； Nutrient removal - 2 - INTRODUCTION An oxidation ditch is a modified activated sludge treatment process that is comparatively similar to wastewater treatmen
7、t in a sequential batch reactor. But the oxidation ditch provides aerobic and anaerobic treatment in the same circular basin. The first full scale plant of oxidation ditch installed in Voorschoten, Holland, in 1954. There have been more than 9200 municipal oxidation ditch installations in the United
8、 States .Many oxidation ditches were operating around Australia during 1788 1988 and especially, more than 50 of these plants were in New South Wale . A typical process flow diagram of an oxidation ditch is shown in Fig. 1. Influent passing through a bar screen flows straight into an oxidation ditch
9、 (see Fig. 1a). Oxygen is added to the mixed liquor in the oxidation ditch using brush aerator which increases the surface area of the wastewater and creates waves and movement within the ditch . The aeration in oxidation ditch sharply increases the dissolved oxygen (DO) concentration but the DO dec
10、reases as the biomass uptake the oxygen when the mixed liquor travels through the ditch . After biodegradable organics or BOD is removed, mixed liquor will flow out of the oxidation ditch and sludge will usually be settled and removed in the secondary clarifier. Tertiary filtration after clarificati
11、on may be necessary, depending on the effluent requirements. The specific advantages of oxidation ditches include the following: long hydraulic retention time and complete mixing minimize the impact of a shock load, produces less sludge than the other biological treatment processes, energy eff
12、icient operations result in reduced energy costs compared to other biological treatment processes 4. On the other hand, oxidation ditch has some disadvantages such as high effluent suspended - 3 - solids concentrations and requires large land area 4. Nu0ria Vidal and co-workers (2002) compare
13、d the difference among three wastewater treatment processes including； (1) activated sludge process, (2) Ludzack Ettinger (anoxic process followed by aeration process) and (3) Oxidation ditch 5. For each of the three scenarios, the emissions and the use of natural resources due to their operation an
14、d transportation of sludge were evaluated. Consumption values for all energy resources were higher for the Ludzack Ettinger configuration, while the values from the oxidation ditch configuration did not differ significantly from the activated sludge. Major environmental impact by eutrophication due
15、to NH4+ /NO3-was reduced by 68% in the Ludzack Ettinger configuration and 75% in the oxidation ditch configuration with respect to the reference activated sludge process 5. However, the quality of effluent from oxidation ditch is not sufficient enough for higher standards that are required for unlim
16、ited irrigation and reuse of the water. Membrane bioreactor (MBR) technology has been applied to provide high quality effluent by constructing a membrane system into the existing clarifier.The benefits of using the MBR technology for retrofiting are no extra land requirement, produces high quality e
17、ffluent for reuse, no odor, and allows treatment of much higher capacity of wastewater 6. A full scale oxidation ditch retrofitted with a membrane bioreactor is in operation in Kilkenny Ireland since 1999 to treat 9000 m3/d of dairy farm wastewater 6. The purpose of this study is to characterize the performance of a full-scale OD retrofitted with a MBR during the start-up. The study will show the attributes of treatment from raw wastewater to final effluent namely； COD, BOD, ammonia, nitrate, phosphate, EPS, soluble protein, carbohydrate, MLSS
