【作者】 叶茂盛；

【导师】 杨凤林；

【作者基本信息】 大连理工大学 ， 环境工程， 2008， 博士

【摘要】 膜生物反应器（Membrane Bio-Reactors,MBRs）是污水处理和中水回用领域最有前途的工艺。它把膜分离过程与生物降解结合起来,取得高效的固液分离和出水效果。然而,膜组件昂贵的价格和其运行过程中难以控制的膜污染现象,导致MBR的投资和运行费用增加,最终限制了该技术的广泛应用。因此研究制备廉价的高抗污染性能的过滤膜对MBR在我国的推广应用具有重要的意义。近年,利用具有一定特性的颗粒物质在廉价的大孔径过滤介质的表面和内部形成动态膜的技术成为该研究的热点。本研究利用廉价易得的工业滤布作为膜基质,形成多种抗污染预涂动态膜,并对它们的制备、表征和性能进行了深入研究,同时利用气泡与平板的作用模型对平板膜组件的外形结构进行优化设计。首先,利用平均粒径为22.8μm的粉末活性炭（Powder Activated Carbon,PAC）作为预涂剂,在工业滤布表面形成预涂PAC动态膜。通过清水过滤和标准浊度溶液的截留实验,考察不同厚度PAC动态膜清水阻力和截留能力的变化,结果表明预涂PAC动态膜属于滤饼过滤型动态膜,其最佳厚度为0.3±0.05 mm。但是,浸没式膜生物反应器（Submerged Membrane Bio-Reactor,SMBR）中由下方曝气产生的膜面剪切作用能够在一定程度上破坏滤饼过滤型动态膜的稳定运行,研究发现MLSS低于8000 mg·L^-1时的活性污泥混合液可以近似看作牛顿流体,试验证明利用湍流边界层理论计算滤饼过滤型动态膜的稳定曝气量的实用性,因此PAC动态膜在SMBR中的稳定运行采用由供氧曝气量逐渐调节到稳定曝气量的操作方式。通过预涂PAC动态膜与自生生物动态膜（Self-Forming Dynamic Membrane,SFDM）,以及中空纤维膜（Hollow Fiber Membrane,HFM）组成的SMBR系统在处理模拟生活污水的对比试验,发现PAC动态膜具备较好的性能,其操作压力在43天内上升到42 kPa,出水效果和中空纤维膜相当,COD和氨氮的去除率分别为97.1%和76.1%。污染后的PAC动态膜只需进行干燥处理即可脱落,进行再生,无需消耗化学试剂,特别是PAC动态膜的造价不超过每平方米25元的价格优势,能保证其在实际应用中的潜力。另外,如果利用具有强负电性的阴离子表面活性剂或具有强亲水性的SiO₂和TiO₂等物质进一步吸附在预涂PAC动态膜表面和内部,将会取得更优质的运行效果。其次,本论文针对导致膜污染主要物质溶解性有机物（Soluble Microbial Products,SMP）和胞外聚合物（Extracellular Polymeric Substances,EPS）所具有的高疏水性和高电负性,制备一种新型的预涂剂——聚乙烯醇微球（Poly-Vinyl Alcohol Microsohere,PVA-MS）。通过PVA和戊二醛乳化交联所制备的PVA-MS具有良好的分散性,平均粒径为1.2±0.1μm。通过红外光谱分析和Zeta-电位测量结果发现PVA-MS表面富含羟基,具有很强的亲水性和电负性,其Zeta-电位受PH值得影响明显,在pH=11时最小为-87.25mV。随后,分别利用静电自组装和过滤预涂的方法在工业滤布表面和内部制备对称无滤饼标准型、不对称标准过滤型、对称完全堵塞型三种类型的PVA-MS动态膜。静态亲水接触角的测量证明PVA-MS动态膜均具有较好的亲水性,它们的清水过滤阻力分别为1.02×10¹⁰m^-1、2.76×10¹⁰m^-1、1.07×10¹¹m^-1,三种PVA-MS动态膜在浓度0.01 mol·L^-1的KCl电解质溶液中测量的相对流动电位分别为-26.2 mV、-35.3 mV、-65.1 mV。无滤饼标准型、标准过滤型以及完全堵塞型PVA-MS动态膜对上清液浊度为21.34NTU的截留率分别为78%、93.7%、98.9%,对上清液TOC为17.1 mg·L^-1的截留率分别为6.56%,37.16%,48.63%。对工业滤布以及三种PVA-MS动态膜不可逆污染的再生性能研究表明,化学清洗法均能完全去除膜的不可逆污染,物理反冲洗的效果随着PVA-MS预涂量的增加得到不断改善。综合对比,自组装和完全堵塞型PVA-MS动态膜显示出一定的竞争优势,前者利用化学清洗后能维持大部分PVA-MS的存在,可以经历多次运行清洗周期后再生,后者仅利用物理反冲洗即可去除不可逆膜污染,经再次预涂后即可应用。最后,对目前广泛应用的平板膜竖直结构提出改进,设计具有一定的倾斜角度θ的梯型平板膜结构,使其在保持膜面附近气泡错流速度的同时增加气泡与膜面弹性碰撞的强度与次数,提高曝气减缓膜污染的效率。通过对Vries建立的气泡与竖直平板相互碰撞的数学模型进行改进,利用计算机迭代运算技术得到不同曝气条件下的最佳倾斜角度θ。结合SMBR的实际应用,对膜组件和曝气的最佳设计方案如下:梯形膜组件间间隔为10～15mm,曝气位置为组件间5～7 mm,梯型膜设计角度在1.7°～2.5°之间。竖直结构和梯型结构的自组装PVA-MS动态膜组件在同一SMBR反应器中,同一曝气强度下的对比试验证实,梯型膜能够有效的控制膜表面的滤饼层污染,防止由于压力升高引起的滤饼层压缩和由于膜面缺氧而引起的阻力急速上升。但是活性污泥发生膨胀引起的沉降性变差和运动学粘度变化过大,将会使气泡及其尾流与膜面作用的消弱,导致膜阻力的急速上升。梯型组装PVA-MS动态膜组件保持通量在18.6 L·m^-2·h^-1下运行的120 d内压力仅上升到0.01 MPa,出水浊度约为1.34 NTU,COD,氨氮的去除率分别为90%和91.5%。更多还原

【Abstract】 Membrane bioreactors（MBRs） are the most promising processes used for wastewater treatment and water reclamation.The membrane filtration used in the bioreactor can retain the sludge flocs,and then improve the effluent quality significantly.However,the high cost of membranes and the severe fouling has been demonstrated as the major obstacle for the widespread application of MBRs.Therefore,development of anti-fouling and low-cost filtration medium is of great significance for the wide application of MBRs,especially in the developing countries.Recent years,precoating the low-coat filtration medium（i.e., non-woven,mesh and filter cloth） by using some special particles（i.e.,powder activated carbon） has been proved as an interesting and potential alternative for MBRs.The powder activated carbon（PAC） with particle size of 22.8μm was used as precoating reageat to develop a dynamic membrane on the commercially used filter cloth.The impacts of the developed dynamic membrane thickness on membrane resistance and rejection ability were studied by measuring the distilled water permeation and the rejection of standard turbidity solution.The results indicate that the optimum thickness of the precoated PAC daynamic membrane was determined to be 0.3±0.05 mm.But,it was found that the aeration used in the submerged MBR could damage the precoated PAC dynamic membrane.As MLSS was lower than 8000 mg·L^-1,the activated sludge suspension featured non-newtonian fluid.In addition,according to the theory of boundary layer,the steady aeration intensity was estimated and optimized in this study.The results indicate that the optimized aeration intensity can guarantee the steady and sustainable operation of the precoated dynamic membrane bioreactor.Compared with self-forming dynamic membrane and hollow fiber membrane,it was found that the precoated dynamic membrane（PDM） could keep high permeation,the TMP of PDM rose up to 42 kPa after 43 days of the stable operation of PDMBR,and the removal efficiency of effluent COD（97.09%） and NH₄⁺-N（76.13%） were as good as traditional hollow membrane bioreactor（THFMBR）.Furthermore,the flux of the fouled membrane could recover totally just after being cleaned by brushing,and it didn’t consume any chemical reagent.Moreover,it was also found that PDM could prevent the biomass contaminations diffusing from the surface to the internal.The application of filter cloth is much attractive since it commercial price is only 25 RMB per square meter.Lastly,the PAC precoated filter cloth will become a more and more reliable and cost-saving when some more hydrophilic substances（i.e.,YiO2,SiO2） can be introduced into PAC precoated filter cloth.Since the major membrane foulants of EPS/SMP featured higher hydrophobicity and negative charge,a novel coating reagent,polyvinyl alcohol microsphere（PVA-MS）,was prepared and was coated onto the surface of filter cloth.The PVA-MS was prepared by PVA and glutaraldehyde after acetal reaction.The PVA-MS prepared featured an excellent dispersal with a mean particle size of 1.2±0.1μm.The analysis of FTIR and zeta potential shows that the PVA-MS had several solar groups and behaved negative charge.It also was found that the pH value had significant influence on zeta potential and at pH=11 there was a lowest zeta potential of-87.25 mV.Subsequently,Three dynamic membranes of symmetric Standard blockage filtration type without filter cake、asymmetric Standard blockage filtration type、symmetric full blockage filtration type were prepared successfully by using self-assembly coating and pre-coating methods.It shows that the water contact angle of the coated PVA-MS membrane was determined as 0,and their filtration resistances were calculated to be 1.02×10¹⁰ m^-1、2.76×10¹⁰ m^-1、1.07×10¹¹ m^-1.The zeta potential of the dynamic membrane prepared was also monitored by measuring streaming potential with 0.01 mol·L^-1 KCl solution,and the zeta potentials were calculated to be -26.2 mV,-35.3 mV and -65.1 mV after corrected with membrane resistance. The coated PVA-MS on the filter cloth was found to be effective in the rejection of small particles.The symmetric Standard blockage filtration type without filter cake、asymmetric Standard blockage filtration type、symmetric full blockage filtration type could reject 78%, 93.7%and 98.9%turbidity of the sludge supernatant with 21.34 NTU.Their rejection abilityes on TOC were 6.56%,37.16%and 48.63%,respectively,when the sludge supernatant with 18.3 mg·L^-1 TOC was filtered.The results suggest that chemical cleaning can eliminate the irreversible fouling of uncoated filter cloth,self-assembly coated filter cloth and pre-coated cloth filter.The efficiency of physical cleaning would increase with increasing coated MS on the filter cloth. By comparing,the self-assembly coated MS are not readily shatter even after frequent chemical cleaning;however,regarding the pre-coated MS,physical cleaning could eliminate the irreversible fouling completely,but it needs a repeated precoating to maintain the MS layer on the surface of the filter cloth.The cross flow shear stress induced by aeration is an effective approach to control membrane fouling.In this study,a novel flat sheet membrane module,ladder-type flat membrane structure,was developed.In this way,the aeration bubbles near the membrane surface can be held,at the same time the intensity and times of elastic collision between bubbles and membrane surface will be increased.According to the mathematics model of collision between bubble and vertical flat developed by Vries,the inclination angle of the ladder-type was calculated and optimized by using computer iterative calculation technology. In view of the real application of SMBR,the design of membrane and aeration was optimized as following:the interval distance of membrane modules is 8～15 mm,and aeration will be operated at 5～7 mm among membrane modules,besides the optimal design angle of trapeziform membrane is 1.7°～2.5°.To confirm the role of ladder-type flat membrane structure in fouling control,a vertical and a ladder-type flat PVA-MS module were submerged in the bioreactor and operated in parallel.By comparing,it confirms that the ladder-type flat module can control membrane fouling effectively,but after long-term operation the TMP increased suddenly due to the compress of the cake layer.The effluent quality of ladder-type PVA-MS module was determined as turbidity 1.34 NTU,and the removal efficiency of effluent COD and NH₄⁺-N were 90%and 91.5%respectively.更多还原