| The anaerobic baffled reactor(ABR)with the advantages of stable process,energy saving,simple operation and so on,therefore it has been developed rapidly to treat medium and high-strength wastewater in recent years.The biogas flow is reduced,the mass transfer efficiency between the substrate and the sludge is low and the microbial activity can not play well owing to low concentration of municipal wastewater and many industrial wastewater(COD concentration<2000mg/L)which has limited the application while treating the low-strength wastewater by the ABR,and thus the modified anaerobic baffled reactor(m ABR)with improved baffles design for the opposite folded plates style to promote the contact between the microorganisms and their substrate achieves the turbulence pattern,high mass transfer efficiency and favourable conditions for increasing the removal rate of organics.In addition,providing the best growth environment for different bacterial community,and enhancing the bacterial activity taking place per unit of reactor volume through the proper volume ratio of compartment desigh which makes the reactor has the characteristics of high microbial activity,mixing degree and impetus of substrate degradation.The residence time distribution(RTD)studies on the plane folded plate reactor(PFPR)and the opposite folded plate reactor(OFPR)were performed to investigate hydraulic characteristics for comparative analysis of the mixing pattern and dead space between the different structures of two ABRs,and the influence of special section area on the mixing pattern was also discussed,so as to provide theoretical guidance for rational design of the folded plate in ABR.As the results shown,the values of Peclet number(Pe)and theoretical stirred tanks(N)for the OFPR were greater than the PFPR at the same HRT under clean and inoculation condition.It is assumed that the overall mixing pattern of the OFPR moved closer to plug flow.The dead space of the OFPR was lower than the PFPR regardless of whether the reactors were inoculated at the same HRT,because the structural change of the ABR by converting plane folded plates to opposite folded plates could strengthen the turbulence effect and improve the mass transfer.The turbulence degree of OFPR was superior to that of PFPR because the change of velocity and Reynolds number(Re)due to alternative variation of special section area in the up-flow compartments,which was helpful to improve the rate of degradation.The influent wastewater strength was maintained and improved the organic loads gradually by decreasing the HRT at 35±0.5 centigrade when the m ABR which was constructed based on the hydraulic characteristics of OFPR starting-up.The COD,VFA and p H value were monitoring researched,and the fractal characteristics of granular sludge culture by using fractal geometry theory was also image analysed.As the results shown,the COD removal,VFA concentration and p H value of the reactor presented a short fluctuation after the organic loading increased,but it would soon be restored without any measures a few days later which indicated the special structure of m ABR has strong anti-shock loading capability.A lot of granular sludge with good properties was formed in the four compartments of m ABR,the sequence of average particle size from high to low was the first compartment,the third compartment,the second compartment and the fourth compartment,whereas the sequence of settleability and fractal dimension from high to low was the third compartment,the second compartment,the fourth compartment and the first compartment.The running effect at different HRT were studied by using the m ABR to treat the wastewater at 35±0.5 centigrade,and the mixing pattern and dead space were also analyzed.As the results shown,the total biogas flow and effluent VFA concentration increased and the effluent p H value decreased as HRT reducing when the influent wastewater strength was maintained.The COD removal increased and the effluent TSS concentration decreased as the HRT increased when the HRTs were in the range of 8 to 20 h,but the COD removal decreased when the HRT was further increased.The first and second compartments of m ABR played a major role in matrix degradation,thus,the biogas flow and VFA concentration in the former two compartments were higher than the subsequent compartments,and the p H value along the compartment gradually increased.It could be inferred from all test HRTs that the mixing pattern was in the “intermediate state”,i.e.,between plug flow and completely mixed,the longer the HRT,the mixing pattern of the m ABR was closer to plug flow.However,there was a negative correlation between dead space and the mixing patter,the longer the HRT,the more the dead space.Considering the mass transfer impetus and the volume utilization for the removal rate,the optimal HRT to treat the wastewater by the m ABR was 16~20h.For the mABR mathematical model,through analysis on influent characteristics and determination of kinetic parameters and stoichiometric coefficients,the effluent COD concentration,effluent TSS concentration,biogas flow and effluent p H values were simulated.As the results shown,the biogas flow,COD and TSS concentration were predicted with high accuracy at low organic loading conditions,also,effluent p H was predicted quite well at all test conditions.The results show that the model was found to closely predict the biomass characteristics,in this instance it was able to simulate the performance of the m ABR.In terms of benefits the established mathematical model has the ability to be a useful tool in the analysis on the performance of m ABR,that is,seeking the optimal running conditions,so as to further improve the efficiency of the reaction. |
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