Coupling of sponge fillers and two-zone clarifiers for granular sludge in an integrated oxidation ditch
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Considering that aerobic granular sludge (AGS) exhibits a long granulation time in continuous flow and that the poor removal effects on N and P have severely restricted its large-scale application, a novel strategy was developed involving sponge fillers to construct an anoxic zone coupling two-zone clarifiers to promote granulation in an integrated oxidation ditch. The different pores in the sponge fillers were used to accelerate the accumulation and formation of aggregates under the impetus of water flow, meanwhile, the A/O operation mode and the formation of AGS were also improved the denitrification and phosphorus removal capacity of the reactor. The experimental results indicated that AGS was shaped in the anoxic and aerobic zones on day 30 and on day 43, respectively. When running for 90 days, the mixed liquor suspended solids (MLSS), sludge volume index (SVI5) and average particle size in the anoxic zone and aerobic zone were 5848 mg/L and 4812 mg/L, 31.2 mL/g and 35.8 mL/g, and 329.2μm and 362.3μm, respectively. During the granulation process, the EPS content in the anoxic zone was significantly higher than that in the aerobic zone, indicating that the sponge fillers played a dominant role in granulation. After the reactor reached steady conditions, the removal efficiencies of COD and N were 87.29%±2.61% and 60.11%±4.68%, respectively. The TP removal efficiency gradually increased from 26.90% on day 1 to 77.54% on day 90. Moreover, the microbial community transformed conspicuously throughout granulation, including an enrichment of microorganisms exhibiting EPS secretion and pollutants degradation.Keywords:
Granulation
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Oxidation ditch
Settling
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Settling is one of the processes occurring in waste stabilization ponds (WSP). Part of suspended solids (SS) is removed by sedimentation but very often the efficiency of WSP is presented without making a difference between settling and biological processes. In this way the WSP is seen as a black box process. This work presents an experimental approach to the study of the removal of wastewater suspended solids in a test column in order to improve our knowledge of the settling process in ponds. These results show that the settling test in columns can be used to estimate the half removal time (t 50 ) for the study of settling characteristics of suspended solids in wastewater stabilization ponds. The aim of this study was to determine the half removal time (t 50 ) in anaerobic, facultative and maturation ponds, and in the influent to these ponds, at the experimental wastewater treatment plant of CERTE (Recycling and Treatment Center of Wastewater in Tunisia), by a column settling test. The experiments lasted between 15 and 120 min. The column was 2 m high with sampling systems at various depths: 40, 80, 120, 160 and 200 cm. Half-removal suspended solids time t 50 was defined as the time at which 50% of SS was removed. Models derived from the scientific literature were used to interpret the experimental data. The experimental results demonstrated that higher suspended solids concentrations in the influent led to shorter t 50 values and better settling.
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Sedimentation
Total suspended solids
Decantation
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The 1140 m 3 /d (0.3 mgd) Grand Coulee, WA. oxidation ditch was modified to incorporate a computer-control anoxic/aerobic cycle operation to investigate SVI control and nitrogen removal. A directional mixer placed in the ditch is turned on and the aerators are turned off at selected times to create the anoxic cycle. The control system requires continuous ORP measurements in the ditch, with computer logging, data synthesis and decision making. An automated, single anoxic/aerobic control cycle was studied for a 5-month period. Diluted SVI values were maintained in a range of 70-110 mL/g for a 3-month period after chlorination was used to breakup a filamentous floc. Nitrogen removal averaged between 76 and 80 percent.
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Human activities and climate change are currently dominant processes that affect hydrological processes, resulting in alterations in water and sediment flows. Evaluation of the settling velocity of suspended solids is a critical parameter in modelling sediment transport. In this study, we investigated seasonal changes in suspended solids’ settling velocity and trapping capacity in the presence and absence of water turbulence on a dam reservoir. Using key parameters such as flow rate, mean settling velocity (V¯), critical velocity (vc), suspended solids concentration, ratio V¯/vc, and shape parameter ‘r’, the trapping capacity on the dam reservoir on the Lobo River in a tropical region was estimated. The results show that, considering the settling velocity of suspended solids, following the Gamma distribution law remains an innovative solution proposed to evaluate the trapping capacity in water reservoirs. The results show that the mean suspended solids settling velocity V¯ is well above the median rate V50%. For a parameter V¯/vc ≥ 4, there is an increase in the trapping capacity of the water retention. As established, a large proportion of the sediment is trapped. Furthermore, for a parameter V¯/vc ≤ 4, a decrease in the trapping capacity of the Lobo River water reservoir is observed.
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In this work, the separation of suspended solids from the Bor tank house acid solutions is presented. The investigation was performed by allowing the suspended particles to settle in a natural way, as well as by settling with the help of the flocculant FN-001 (polyacrylamide, product of Chemical industry Župa Krusevac). Natural settling was practically completed after three hours, and in this way 95 % of the suspended particles had settled. Settling with the help of the flocculant was practically completed after five minutes, whereby, also 95 % of the suspended particles had settled. Hence, the settling rate using the flocculant is 40 time faster than the natural settling rate. On the base of these results, it is possible to design a settler with smaller dimensions.
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Sedimentation
Polyacrylamide
Decantation
Settling time
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Granulation
Settling
Settling time
Sequencing batch reactor
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In order to improve the removal rate of phosphorus in the traditional oxidation ditch,three enhanced phosphorus removal measures were studied.The first measure is to add an anaerobic zone before the oxidation ditch,the second one is to add an anaerobic zone and an anoxic zone,and the third one includes an anaerobic zone,an anoxic zone and a pre-thickening tank of returned sludge.The results show that the third measure of sending 30% of thickened sludge to anaerobic zone can not only ensure the returned biomass but also avoid a negative effect of the excess nitrate in the returned sludge on anaerobic phosphorus release.A simulation study reveals that under the same influent conditions,the third enhanced measure has the best phosphorus removal efficiency with a final phosphorus concentration of 0.773 mg/L,while the other two with 1.52 mg/L and 1.73 mg/L respectively.Therefore,the third measure of including an anaerobic zone,an anoxic zone and a pre-thickening tank of returned sludge can greatly improve the efficiency of phosphorus removal.
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Ditch
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The initial settling behaviour of the low solids concentration suspensions is examined and analyzed to provide information on sedimentation characteristics and distribution of solids concentration profiles with time. The presence of surface-active forces, which participate in development of the suspended solids settling characteristics, does not always permit easy application of standard sedimentation models for calculating settling rates of the suspended solids. A simplified diffusion–convection model using the relative flux approach has been developed to predict the initial settling performance of the suspended solids. Experimentally determined fluid diffusion coefficients relative to diffused volumetric fluid contents are obtained to provide input to the calculations for prediction of actual test cases. Comparisons using laboratory settling test data, together with information from a field settling pond, are made with predictions obtained using the model. The comparative results show that the analyses obtained using the theoretical model can predict initial settling of the suspended solids. Key words: suspended solids, settling, sedimentation, diffusion, solids concentration, fines thickening.
Settling
Sedimentation
Decantation
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Influent with low BOD content leads to the ability of phosphorous removal with oxidation ditch process decreased.After extension of anoxic area,reduction of sludge returning and extension of anoxic area plus dissolved oxygen control are applied and compared,the third is favorable for 57%～82%TP removal under condition of low carbon,not being free from side-effect of NH3-N removal and MLss content within oxidation ditch dessending.
Oxidation ditch
Ditch
Carbon fibers
Oxidation process
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