Optimization of submerged depth of surface aerators for a carrousel oxidation ditch based on large eddy simulation with Smagorinsky model

This paper is concerned with the simulation and experimental study of hydraulic characteristics in a pilot Carrousel oxidation ditch for the optimization of submerged depth ratio of surface aerators. The simulation was based on the large eddy simulation with the Smagorinsky model, and the velocity was monitored in the ditches with an acoustic Doppler velocimeter method. Comparisons of the simulated velocities and experimental ones show a good agreement, which validates that the accuracy of this simulation is good. The best submerged depth ratio of 2/3 for surface aerators was obtained according to the analysis of the flow field structure, the ratio of gas and liquid in the bottom layer of a ditch, the average velocity of mixture and the flow region with a velocity easily causing sludge deposition under the four operation conditions with submerged depth ratios of 1/3, 1/2, 2/3 and 3/4 for surface aerators. The research result can provide a reference for the design of Carrousel oxidation ditches.

Study of the Oxygen Supply, Propelling and Mixing Performance Optimization Conditions of an Improved Carrousel Oxidation Ditch

The oxygen supply, propelling and mixing performance optimization conditions of a reactor are studied by adopting a pilot-scale system and a production test system for an improved Carrousel oxidation ditch, including the influence of flow velocity on the mass transfer of DO, the influence of the flow state on the denitrification and energy conservation of the oxidation ditch, and the influence of the particle sizes of floc inactivated sludge on simultaneous nitrification and denitrification (SND). The results indicate that as the flow velocity increases, the mass transfer of DO is better. The appropriate operating condition is regulated and controlled so that the denitrification efficiency of the system can be improved. The starting number of aeration wheels is reduced from 5 to 2, the particle sizes of large-ratio floc in the activated sludge are increased from 20 to 130 μm, and the removal rate of total nitrogen is improved from 44%-49% to 69%-75%.

Application and Development of Oxidation Ditch Process in Wastewater Treatment

The structure and the techniques of carrousel oxidation ditch process on nitrogen and phosphor removal are introduced in this paper. The problems in running and their corresponding resolve are also pointed. At last, the author showed the up to date research improvement and the mainly future research direction.

Research on Intensive Nutrients Removal of the Low C/N Sewage

This paper was based on Carrousel oxidation ditch, which was common in the urban sewage treatment plants. With the effect of SND in the oxidation ditch, it was accomplished the effective removal for nitrogen and phosphorus of urban sewage with low C/N, while adopting point-aeration and brush flow, combining with the operation parameters adjustment. Under the condition of low dissolved oxygen (DO), the phenomenon of simultaneous nitrification and denitrification was obvious in macro and micro environments. And compared with the traditional process, this process increased the proportion of organics up to 51% in the ditch, which raised utilization rate of organics. Based on this to establish the kinetics model of TN removal, it could control the concentration of TN in the effluent effectively by adjusting HRT, MLSS and other parameters in the oxidation ditch, which would provide effective theory basis for optimization and adjustment of the process

Impact of SRT on Simultaneous Nitrification and Denitrification in a Carrousel Oxidation Ditch for Sewage Treatment

The impact of SRT on simultaneous nitrification and denitrification (SND) in the Carrousel Oxidation Ditch was carried out based on pilot-scale to treat low COD/TN municipal sewage. The impact factor, sludge retention time (SRT), was investigated on the occurrence of SND. The experiment results showed that in the oxygen-deficient environment whose DO was 0.3 mg/L, R of 50%, MLSS of 4000 mg/L, the treatment efficiency achieved the best with SRT of 20 d, the COD, ammonia nitrogen, total nitrogen (TN) of effluent were lower than 32 mg/L, 5 mg/L, 13 mg/L, respectively, which was observed efficient phenomenon of SND. Overall, these results demonstrated that the Carrousel Oxidation Ditch with the occurrence of SND could have the potential to treat low C/N sewage.