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题名: 基于 ASM-CFD耦合模型的 MBR流场、传质及膜污染控制的模拟与优化研究
作者: 杨敏1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 樊耀波 ; 魏源送
关键词: 膜生物反应器 ; 计算流体力学 ; membrane bioreactor ; 膜污染 ; computational fluid dynamics ; 活性污泥模型 ; membrane fouling ; 耦合 ; activated sludge model ; coupling
其他题名: Simulation and Optimization for Flow Field, Mass Transfer and Membrane Fouling Control of Membrane Bioreactor (MBR) Based on ASM-CFD Coupling Model
学位专业: 环境工程
中文摘要: 膜生物反应器(Membrane bioreactor, MBR)及其组合工艺出水水质优良,占 地面积小、污泥产量低、操作简单灵活,广泛应用于污水处理与再生利用。但膜 污染及运行能耗高仍然是 MBR应用面临的两大难题。MBR的出水水质、膜污 染与运行能耗受水力条件和生化反应状况的共同影响,但 MBR水力学特征与生 化反应动力学过程的耦合研究仍然匮乏。本文通过耦合计算流体力学 (computational fluid dynamics, CFD)与活性污泥模型(activated sludge model, ASM),开展不同规模 MBR及其组合工艺流场、传质和膜污染的模拟与优化研 究,探讨污水脱氮除磷、污泥减量和膜污染的影响因素和作用机理。 以小试规模气升式外循环-膜生物反应器(airlift external circulation-membrane bioreactor, AEC-MBR)分散污水处理装置为对象,开发了包含氧传质子模型、简 化生物动力学子模型和污泥流变学子模型的耦合 ASM-CFD模型,并结合气液分 散高度和曝气强度,模拟和优化了 AEC-MBR的氧传递和消耗、脱氮效率和膜冲 刷。结果表明,当优化的气液分散高度为 300 mm、表观气流速率为 25 m3 h-1m -2, 可实现膜冲刷和脱氮协同优化,曝气量最高可降低约 50%,总氮去除率达 90%以 上。 小试 MBR装置(100 L d-1)膜组件结构和操作条件的模拟与优化研究结果 表明:曝气混合高度 hm、曝气管布置密度显著影响膜面剪切力和分布均匀性,而 膜组件整体高度对膜面剪切力影响较小,三者的优化值分别为 300 mm、40 mm 和 100 mm,膜面平均剪切力较优化前提高 85%以上。污泥浓度、气泡直径和曝 气对 MBR膜可逆污染的模拟和优化结果表明:影响膜面剪切力、膜面颗粒物反 向迁移速度的因素分别依次是污泥浓度>气泡直径>曝气强度、污泥浓度>曝气 强度>气泡直径。当膜面颗粒反向迁移速率权重大于膜面剪切力时,曝气量 2.0 m3 h-1、MLSS8820 mg L-1、气泡直径 4.88 mm,膜面剪切力和膜面颗粒反向迁移 速率较中心点均明显改善,分别提高了 12.4%和 51.1%。 为考察小试规模 MBR优化结果在工程规模 MBR的适用性,开展了工程规 模(500m3 d-1)MBR的结构和操作参数优化。模拟结果表明,不同规模MBR结 构参数敏感性存在差异,工程规模 MBR对水平结构参数(膜间距、曝气管间距) 更敏感;小试 MBR对竖直结构参数(曝气混合高度、膜组件安装高度、安全液 位高度)更敏感。优化的工程规模 MBR的膜间距、气水比、气水混合高度分别 为 25 mm~30 mm、20:1、100 mm。 采用流态、生化动力学模型以及微生物群落结构分析等多种方法考察小试 A2/O-MBR脱氮除磷、污泥减量和能量消耗的内在联系。流态分析结果表明,两 相模拟和三相模拟的 RTD曲线几乎完全重合,说明简化为两相流合理;Peclet数 (Per)随回流比增大而减小,内回流比分别为250%和350%时Per为0.98和0.75, 显著低于不存在回流时的 3.13。qPCR分析表明各单元微生物群落组成相同,但 相对丰度有所不同。 SRT显著影响污泥微生物群落结构的丰度和多样性 , SRT=25d时,厚壁菌门是优势菌门,SRT=50d时,变形菌门成为优势菌。 以工程规模(15万m3/d2)A /O-MBR污水处理厂为研究对象,历史数据分析 和现场调研的结果表明,采用曝气和推流搅拌的好氧池混合效果最好;曝气的膜 池混合效果次之,仅有搅拌的厌氧池和缺氧池混合效果最差。同一单元水质分布 较均匀,相对标准差不超过 50%(总磷除外),各单元上、下层 COD、氨氮、硝 酸盐、总氮和总磷的线性相关系数分别达 95.29%、98.79%、95.14%、97.14%和 81.03%;好氧池沿程氨氮和总氮浓度变化较小,说明曝气或池容富余,且单独设 立膜曝气池也不尽合理;尽管改用脉冲曝气后能量减低 42.39%,但沿程曝气量 和回流比仍具优化空间。RDA分析结果表明,可通过降低膜池和生化池的曝气 量、减少回流量、减少污泥停留时间和水力停留时间等多种方法降低运行能耗。
英文摘要: Membrane bioreactor (MBR) and its combined process produce effluent water with high quality witha small footprint, low sludge production, simple and flexible operation, so it is widely applied in sewage treatment and regeneration. But membrane fouling and high energy consumption are still two major challenges facing the MBR applications. In this study, an integrated model involving computational fluid dynamics (CFD) and activated sludge model (ASM) was developed and used for the simulation and optimization for flow field, mass transfer and membrane fouling control of different scale MBRs. The influencing factors and mechanism of nitrogen and phosphorus removal, sludge reduction and membrane fouling were investigated, and the corresponding control strategies in terms of configuration and operation were put forward. An ASM-CFD model with the sub-model of oxygen mass, a simplified biomechanical kinetics and the sludge rheology was developed for the oxygen transfer and consumption, nitrogen conversion and membrane scoring simulation for an airlift external circulation-membrane bioreactor (AEC-MBR) developed in this study. The gas-liquid dispersion height and aeration intensity for the optimization of membrane scouring and denitrification efficiency in the AEC-MBR were carried out then. The results showed that the optimum gas-liquid dispersion height is 300 mm and the aeration intensity is SAR (superficial aeration velocity) 25 m3 h-1 m-2 . The aeration energy consumption can be reduced by 50% at most and the total nitrogen removal ratio is more than 90%. Simulation and optimization for membrane module configuration and operations of the small-scale MBR device (100 L d-1 ) were carried out. The results showed that the intensity and evenness of shear force distributed on membrane were impacted by the mixing height of gas and liquid hm and the density of the aeration pipe sp significantly. The optimum hm,sp and overall height of the membrane module is about 300 mm, 40 mm and 100 mm, respectively, the average shear force on the membrane is improved by 86%. The main operating parameters (MLSS, bubble diameter and aeration) of MBR The influence of the main operating parameters (MLSS, bubble diameter and aeration) on the membrane shear stress and the rate of reverse migration of the particles are MLSS> bubble diameter> aeration intensity and MLSS> aeration intensity> bubble diameter, respectively; Membrane surface shear stress and the migration rate of the particles are improved by 12.4% and 51.1% compared with the center point case, respectively at the optimum operating conditions of aeration rate = 2.0 m3 h-1 , MLSS = 8820 mg L-1 , and the bubble diameter = 4.88 mm. To test the applicability of model and the conclusions in small-scale MBR, industrial-scale (500 m3/ d) MBR was simulated and optimized using the same framework. The simulation results showed that the sensitivity of structural parameters on different scale MBRs is quite different. The horizontal structure parameters (membrane spacing and aeration spacing) have the same effect on the shear stress of different sizes while full-scale MBR is more sensitive. Vertical structural parameters (aeration mixing height, membrane module installation height, safety level height) have the impact of inconsistency with small-scale MBR more sensitive. The optimal conditions for the membrane spacing, gas-water ratio and gas and water mixing height of this industrial MBR is of 25 mm ~ 30 mm, 20: 1and 100 mm, respectively. Based on the analysis of flow analysis, biochemical dynamics model analysis and microbial community structure analysis, the foundmental reasons and correlations of nitrogen and phosphorus removal, sludge reduction and operation energy consumption for A2/O-MBR were comprehensively investigated. The results showed that the two- /O-MBR and the RTD curve of the three-phase simulation phase simulation of the A2 are almost completely coincident, indicating that the two-phase flow was reasonable; Peclet number decreased with the increase of internal recycle ratio (IRR), Perwere 0.98 and 0.75 at an IRR of 250% and 350, respectively. These Peclet numbers were much smaller than that of A2 /O-MBR without internal recycling (Per=3.13). The qPCR analysis showed the abundance and diversity of the microbial community structure of different SRTs changed significantly: for SRT = 25d, the dominate bacteria is Firmicuteswhile for SRT = 50d, the Proteobacteria bacteria became the dominant bacteria. Taking the A2 /O-MBR sewage treatment plant with the engineering scale (150,000m3/ d) as the research object,the historical data and field survey data analysis showed that the mixing were best in aerobic tank due to the energy put by aerators and impellers,and followed the membrane tank mixed by only aeration, and the mixing in anaerobic and anoxic, which were mixed by agitators and impellers only, respectively, were worst. The water quality in a same tank was even with a specific standard deviation less than 50% (except for TP). The linear correlation coefficients of concetrations of COD, ammonia, nitrate, total nitrogen and total phosphorus at upper and lower layers were 95.29%、98.79%、95.14%、97.14% and 81.03%, respectively. The concentrations of ammonia and TN along the aerobic tnak didn’t vary much indicating that the aeration intensity or tank volume can be reduced and it is not necessary to have a separate membrane tank for the save of energy. Despite the excellent water quality of the plant and energy consumption decreased by 42.39% after upgrading, the aeration along the channel and sludge refluxcan be optimized. The RDA analysis showed that the operation energy consumption can be reduced by reducing the membrane pool and biochemical pool aeration, reducing the return flow, reduce SRT, increasing HRT and other methods.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38729
Appears in Collections:水污染控制技术研究室_学位论文

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作者单位: 1.中国科学院生态环境研究中心
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