Study of the aeration intensity effect in a bioreactor on the pressure head

Summary

The design of a bioreactor with vertically arranged anoxic and aerobic zones is described. The bioreactor is designed for wastewater biological treatment at the facilities ranging from ultra-small to low-capacity ones. It is shown that the given bioreactor type is characterized by the ease of operation owing to the lack of circulation pumps and mixers. The pressure head dependence on the aeration intensity and gas filling coefficient in the aerobic zone of the bioreactor is presented. It has been established that the gas filling coefficient in the aerobic zone of a bioreactor operating under static conditions eliminating liquid overflow into the anoxic zone can be calculated as the ratio of the aeration intensity to the average air bubble rise rate. It has been determined that air bubbles generated in industrial pneumatic fine-bubble aerators rise in a turbulent mode at a rate proportional to the bubble diameter raised to the power of minus 0.4. The results obtained in this investigation will be used in the second part of the experimental and theoretical studies that will provide for determining the dependence of the circulation flow rate on the aeration parameters, and developing a mathematical model of the fluid flow in a bioreactor with the vertical arrangement of aerobic and anoxic zones.

Key words

wastewater , biological treatment , aeration , bioreactor , anoxic zone , aerobic zone , gas filling coefficient

Comparison of the results of calculating aeration tanks according to different methods (for discussion)

Summary

The calculation results are compared according to the method described in the book by D. A. Danilovich and A. N. Epov «Calculation and technological design of processes and facilities for the removal of nitrogen and phosphorus from municipal wastewater», and the method given in the book «Wastewater technology. Processing and recovery of resources» (fifth edition, Metcalf & Addy), in a model unit, for which earlier in the article by V. N. Shvetsov, S. V. Stepanov and O. V. Khar’kina «Comparison of the calculation results for aeration tanks using the NII VODGEO/SamGTU and ASM2d models» calculations had been made according to the method of NII VODGEO/SamGTU and following the model developed by ASM2d. It is shown that calculations based on the equations of enzymatic kinetics and microbial growth (NII VODGEO/SamGTU, ASM2d and Metcalf & Addy) give similar results in terms of the volume of aeration tanks with the «tabular» method based on the German standard ATV-DVWK-A131E and revised taking into account the growth kinetics of nitrifying microorganisms. The difference in approaches gives different results as for the age of activated sludge; however, the final results of the volumes of aeration tanks and zones in them have discrepancies that do not exceed 15–20%. Simulation of the operation of aeration tanks in BioWin-3 program, designed on ASDM model that is essentially close to the ASM group of activated sludge models, with zone volumes calculated using different methods, showed a similar calculated quality of effluent. This confirms the possibility of any of the considered methods to adequately calculate the volumes of aeration tanks. The choice of the calculation method for each specific case depends on the availability and ease of use of the methodology, as well as on the personal preferences of the designer.

Key words

nitrification , denitrification , aeration tank , wastewater biological treatment , anaerobic zone , theoretical and empirical mathematical models , comparative calculation of the biological treatment facilities , technological calculation methods , anoxic zone