| Modified Sequencing Batch Reactor(MSBR) is one of the widely used process in municipal wastewater treatment plants(WWTPs) for simultaneous phosphorus and nitrogen removal. But this process exits some contradictions and deficiencies, such as: the contradiction between carbon source competition and SRT, low post-denitrification efficiency, which means it difficult to make the good removal efficiency of nitrogen and phosphorus at the same time. So improving the efficiency and stable biological nutrient removal rate becomes the difficult points of operation regulation and upgrading reconstruction in MSBR process. In this study, the combination of numerical simulation, full-scale and lab-scale SBR test were adopted. The effect of process parameters on MSBR process system effectiveness and the reasonable value ranges of the parameters were analyzed. Moreover, viable optimization strategy and improvements to enhance biological nutrient removal in the MSBR process were systematically and deeply researched. In order to compensate the deficiency of numerical simulation research, the effects of the dissolved oxygen concentration and sludge concentration on post denitrification and phosphorus removal were studied systematically in a lab-scale SBR reactor. The conclusion of this study could be provided theoretical guidance to optimization and upgrading reconstruction for MSBR, A2/O and JBH process.The mathematical models of the 7-tank MSBR process were established and the model parameters checked. A novel construction scheme of ‘a series of 4 completely mixed reactors + plug flow reactor + sedimentation tank’ was proposed to represent the MSBR reactors. The mathematical models were built with ASM2 d as simulation mechanism. Then model parameters sensitivity and identifiability analysis showed that parameters subsets of YPAO, YH aerobic, YH anoxi,YPO4, μAUT, bAUT, KNH4, bH, ηNO3, μPAO, bpp, bPAO, qpp of the integrated model had significant impact on the performance of the system. The estimated results with optimal solution are as follows: YPAO=0.075, YH aerobic=0.60, YH anoxia=0.55, YPO4=0.3, μAUT=1.15, bAUT=0.16, KNH4=1.2, bH=0.45, ηNO3=0.65, μPAO=1.15, bpp=0.30, bPAO=0.15, qpp=0.75. The relative deviation between the simulated and measured results for average effluent COD, NO3--N and TN were less than 10%. The average absolute errors between the simulated and measured results for effluent NH4+-N and TP were only 0.21 mg/L and 0.13 mg/L. Verification results showed that the model has better forecast precision.Process regulating method and characteristics for nitrogen and phosphorusremoval in MSBR process was studied using model. The results showed the order of the primary and secondary factors of nitrogen removal is mixed-liquor recirculation ratio> SBR tank anoxic time> concentrated sludge recirculation ratio> dissolved oxygen concentration> sludge retention time in MSBR process. And the order of the primary and secondary factors of phosphorus removal is sludge retention time> concentrated sludge recirculation ratio> SBR tank anoxic time> dissolved oxygen concentration> mixed-liquor recirculation ratio. Adjusting these process parameters could enhance the adaptability of the system to resisting water quantity and quality change, control the effluent quality. Nitrogen and phosphorus removal performance of MSBR process were less effect by temperature when it changes between 21~15 ℃. When the temperature decreases to 12 ℃,the effluent of NH4+-N can meet the requirement by improving the system of sludge concentration(>3500 mg/L). MSBR process has a characteristics of post-denitrification and phosphorus removal. And shortage of carbon source for post-denitrification in SBR tank is one of the reasons that nitrogen efficiency is low. Transitional endogenous denitrification or insufficient denitrification in pre-anoxic can decrease the phosphorus removal efficiency of the system.Optimal operation strategies for nitrogen and phosphorus removal in MSBR process were studied in a full-scale WWTP. Based on the basis of the dynamic variation characteristics of the influent flow, the whole year were divided into dry and rainy season period. According to simulation analysis, optimal process parameters for biological nitrogen and phosphorus removal were put forward. The study presented an optimized control strategy of improving removal nitrogen and phosphorus such as: the adjustments of sludge retention time, dissolved oxygen concentration, SBR tank anoxic time, mixed-liquor recirculation ratio and concentrated sludge recirculation ratio. And a discrete control scheme based on the adjustment of the aeration system was built, which intended to implement of the strategy followed the fluctuation of influent quantity. A full-scale experiment was conducted to examine this control strategy from march to july 2012. The results showed that the effluent quality was effectively improved by using this control method, and the effluent of COD and N index met the requirement of first-A wastewater discharge standards of China well. The feasibility of this scheme was proved by numerical simulation and the microbial population variation analysis.In the view of the problem low post-denitrification rate in SBR tank or existing invalid phosphorus release in pre-anoxic tank, enhanced nitrogen and phosphorus removal technology with step feed were investigated in a full-sacle WWTP. Both of the model and test results showed that phosphorus removal performance increasedfirstly and then decreased with the increase of the two feed rato of pre-anoxic(from 0 to 0.2). When the two feed rato of pre-anoxic was 0.15, the performance of nitrogen and phosphorus removal efficiency could improve and the TP removal efficiency up to 76.1%. It was found that phosphorus removal performance increased, and nitrogen removal performance increased firstly and then decreased with the increase of the two steps feed ratio for SBR tank(from 0 to 0.4). When the two step feed ratio for SBR tank was approximately 0.30, both the integrated nitrogen and phosphorus removal efficiency of MSBR process were higher.In the view of the problem shortage of carbon source in post denitrification and simulation analysis of existing issues, the effect of different dissolved oxygen, sludge concentration and pre-anoxia time on nitrogen and phosphorus removal was investigated in a lab-scale SBR which was operated as post denitrification. The utilization efficiency of internal carbon source and the nitrogen and phosphorus removal efficiency decrease with the dissolved oxygen increasing. Both of post denitrification efficiency and nitrogen removal performance increased with the increase of the sludge concentration. So the system should run in a high sludge concentration condition when high nitrogen removal efficiency is required only. If the sludge concentration was controlled at 4300 mg/L, the contradiction between substrate competition and SRT were alleviated, and it had the high removal efficiency of the total phosphorus. So it is conducive to enhance the removal efficiency of nutrient if the dissolved oxygen and sludge concentration are managed appropriately. The relationship among invalid phosphorus release, anaerobic phosphorus release and aerobic phosphorus uptake was investigated. The experiment’s results showed that the quantity of the invalid phosphorus release was caused by the change of pre-anoxia time and mixed liquor volatile suspended solids(MLVSS) in pre-anoxia tank. More, there is good linear relationship between invalid phosphorus release and anaerobic phosphorus release and also the phosphorus removal, and the correlation coefficient R2 is 0.86 and 0.98, respectively. So, the invalid phosphorus release had adverse effect on anaerobic phosphorus release and phosphorus removal. |
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