【作者】 仉春华；

【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（MBR）是将膜分离技术和生物反应器相结合的一个新型污水处理工艺。MBR以膜分离装置取代传统废水生物工艺中的二沉池，实现高污泥浓度运行，具有工艺流程简单、占地面积小、固液分离效率高、自动化程度好、剩余污泥产量少等优点。MBR作为一种新型高效的水处理技术，受到各国水处理技术研究者的日益关注。但是高造价的膜组件和膜污染问题成为当前限制MBR广泛应用的主要瓶颈。因此，有必要研究降低膜组件造价和减少膜污染的方法，这对扩大MBR的应用领域具有重要意义。本实验研究以国内企业生产的、价格低廉的过滤材料-无纺布代替目前MBR中通常使用的高分子膜材料；为了预防和减少膜污染，以聚乙烯醇（PVA）为改性材料，采用表面涂敷法对疏水性的无纺布表面进行亲水改性，制备了PVA改性无纺布复合膜，用于废水处理。本研究主要考察了制膜工艺和制备条件对PVA改性无纺布复合膜性能的影响以及复合膜的耐污染性能；并借助全反射红外光谱（ATR-FTIR）、X光电子能谱（XPS）以及扫描电子显微镜（SEM）等现代分析技术对复合膜的表面微观结构和表面化学结构进行了表征和分析。研究内容有：（1）考察了有／无亲合剂（聚乙二醇）预处理以及改变PVA浓度、催化剂浓度、涂膜时间、热处理温度和时间，复合膜的纯水通量和静态水接触角的变化。结果表明：亲水化预处理有利于PVA均匀地附着于无纺布的表面，但是复合膜纯水通量明显小于没有预处理的复合膜，而两者的静态接触角则没有显示出较大的差别。增加PVA和交联剂浓度以及涂膜时间、热处理温度和时间，均使复合膜的纯水通量降低。PVA改性使无纺布表面的亲水性能得到明显改善。（2）采用无亲合剂预处理的制膜工艺，考察了PVA浓度以及交联剂浓度、基膜（无纺布）公称孔径对复合膜的纯水通量、截留率、固定度以及拉伸强度和撕裂强度的影响。结果表明：增加PVA和交联剂的浓度以及减小基膜公称孔径，均使复合膜的纯水通量降低，对聚丙烯酰胺（分子量860万）的截留率提高。PVA在无纺布表面的固定度随着PVA浓度增大而增加，但交联剂浓度变化对固定度的影响不明显。PVA改性增强了无纺布的机械性能，复合膜的拉伸强度和撕裂强度均大于未改性无纺布，但受铸膜液中PVA浓度和交联剂浓度变化的影响。（3）ATR-FTIR、XPS以及SEM对复合膜的表面微观结构和表面化学结构的表征和分析结果表明：基于吸附、沉淀等物理化学作用的改性方法，改变了无纺布的表面性质和表面分子结构，在无纺布表面引入了基团-OH和C-O-C，且羟基以多种形式存在于改性无纺布的表面。通过化学交联作用增强了PVA薄膜分子间的相互作用，同时保留了无纺布的基本结构。改性后无纺布表面的组成元素中有C、O两种元素。C元素有三种结合形式，除了C-H外，增加了C-O和O-C-O两种结合形式。改性无纺布中由于含氧基团的引入，O元素的相对含量显著增加，C元素相对含量有所降低。PVA改性使无纺布的空隙率减小，表面变得更光滑。在断面扫描图中发现存在明显的界面层，说明在无纺布的表面复合了PVA薄膜，形成了复合膜结构。（4）通过静态吸附牛血清蛋白（BSA）实验和动态处理人工废水实验，研究了复合膜的耐污染性能。PVA浓度为0．8wt％时得到的改性无纺布，对BSA吸附量最小，与未改性无纺布相比，BSA吸附量降低了83．4％，说明无纺布经PVA改性后能有效抑制BSA的吸附，增加无纺布的耐污染性能。改性前后无纺布的膜污染指数（MFI）分别为0．9519和0．2238，改性无纺布显示了良好的耐污染性能。采用统计分析方法研究了MBR中的胞外聚合物（EPS）、溶解性EPS（EPS_S）组分中的P／C（蛋白质／多糖）、活性污泥的相对疏水性（RH）与膜污染阻力的相关性。结果表明：EPS_S以及其组分中的P／C、RH对膜污染阻力有明显影响，与改性无纺布／未改性无纺布膜污染阻力的皮尔逊相关系数r_p分别为：0．868／0．856、0．840／0．866、0．890／0．841。改性无纺布表面能有效抑制EPS_S的吸附，降低EPS_S中的P／C，减少活性污泥的吸附沉积，降低膜污染。（5）将PVA改性无纺布复合膜的膜组件置于处理人工废水的浸没式膜生物反应器（SMBR）中，实验结果表明：改性无纺布虽然能有效减少膜污染，降低膜污染阻力，但在过滤过程中仍存在膜污染现象。改性无纺布的过滤阻力主要为膜污染阻力。在引入比污染阻力概念的基础上，以描述压力驱动过滤过程中膜通量与阻力关系的Darcy定律为基础，建立了描述SMBR间歇方式运行时，滤饼阻力控制的过滤过程中的比污染阻力与时间关系的数学模型：R_stf（t）=a(1-e^-t/b),利用此模型能够预测运行过程中膜通量的衰减趋势，其数学表达式为：J（t）=TMP/μ[R_m+a(1-e^-t/b)]。将此模型用于预测SMBR处理制药废水的膜通量衰减趋势，与实测值比较的结果显示，当t>b时，相对误差<10％；当t>2b时，相对误差<5％。说明本文所建立的膜污染阻力模型在SMBR运行达到稳定状态后，能较好地预测膜通量衰减趋势，但是在运行初期非稳定状态（t<b）时，相对误差较大。更多还原

【Abstract】 In recent years, Membrane Bioreactors （MBRs） have been widely used in wastewater treatment to achieve higher effluent quality, which is often difficult to be effectively met by conventional activated sludge process. The advantages of MBR are a high mixed liquid suspended solids （MLSS） concentration, simple process flow, small space occupation, high efficient separation of solid-liquid, a higher automatization, a lower excess sludge production. As a new and high efficient wastewater treatment process, MBR is attracting attention of water treatment pursuers in the world. But the major obstacles for the application of MBRs are the high cost of membrane filtration module and the issue of membrane fouling. So it is necessary to investigate the methods of decrease of membrane filtration module cost and reduction of membrane fouling. Thus, it can broaden its application fields if the crucial problems to be resolved.In this experiment, a low cost filtration material- hydrophobic nonwoven fabric （NWF） was used to replace high molecular membrane materials. The NWF is a local product. In order to reduce membrane fouling, the hydrophobic NWF surface was modified by polyvinyl alcohol （PVA） dip coating to prepare hydrophilic PVA-NWF that was used for wastewater treatment. In this work, the influence of membrane preparation processes and conditions on performance of PVA-NWF was investigated, anti-fouling characteristics of PVA-NWF was identified. Chemical structures and morphological changes of the NWF surface were characterized in detail by modern analysis technics i.e. attenuated total reflectance Fourier Transform Infrared （FTIR/ATR） spectroscopy, X-ray Photoelectron Spectroscopy （XPS）, Scanning Electron Micrograph （SEM）. This work includes:（1） To investigate the changes of pure water flux and static water contact angles with non hydrophilic pretreatment and hydrophilic pretreatment by PEG, and with the changes of the PVA concentrations, crystal concentration, dip coating time, heat treatment temperature and time. The results show that PVA can be equably coated on the NWF surface after hydrophilic pretreatment. But pure water membrane flux of pre treatment surface is obviously less than the flux of non pretreatment. Static contact angles of them are not big different. Pure water flux is decreased with the increase of PVA concentration, crosslink concentration, coating time, heat treatment temperature and time. PVA modification makes the contact angles of NWF surface decreased from 86°±1°（before modification） to 40°±1°（pretreatment） and 43°±3°（non pretreatment）. The hydrophilicityof NWF surface is improved greatly.（2） To prepare membrane without hydrophilic pretreatment to investigate the influence of PVA concentration, crosslink concentrations, nominal size of NWF on pure water flux, rejection, immobilization, tensile strength and tear resistance. The results show that increasing the concentration of PVA and crosslinking, as well as decreasing nominal size of NWF, pure water flux is enhanced, and rejection of PAM （molecular weight 8.6 million） is increased. PVA immobilization on the NWF surface increases with increasing PVA concentration. The influence of variety of crosslinking concentration on immobilization is not obviously. In addition, Mechanical performance of NWF is increased after PVA modification. Both tensile strength and tear resistance are increased after modification, and they are influenced by PVA and crosslinking concentrations in coating solution.（3） After characterization and analysis of surface morphological and chemical structures by ATR-FTIR、XPS and SEM, the results show based on physical and chemical modification methods, i.e. absorption and sedimentation etc, the surface character and molecular structure of NWF are changed. The bases -OH and -C-O-C- are introduced to the NWF surface, and -OHs are on the surface in various forms. Interaction between molecules of PVA film is increased by chemical crosslinking. Basic structure of NWF is kept. There are two atoms （C, O） on the modified NWF surface, and three forms of C atom consist of C-H, C-O, O-C-O. Since O base is introduced on the NWF surface, relative content of O atom is enhanced obviously, and relative content of C atom is decreased. PVA Modification makes the pore size rate of NWF smaller and the surface smoother. An obvious interphase layer can be found in cross section of SEM, it reveals that NWF surface is coated by PVA film to form composite membrane.（4） Anti-fouling performance of composite membrane is investigated through static absorption of BSA and dynamic treatment of man-made wastewater. The results show that the prepared NWF at 0.8wt% of PVA can absorb least quantity of BSA. Compared with original NWF, the absorption of BSA is decreased by 83.4%. It reveals that PVA modification can restrict BSA absorption. Anti-fouling performance is enhanced. Membrane Fouling Index （MFI） of original and modified NWF is 0.9519 and 0.2238, respectively. Modified NWF has better anti-fouling performance. Correlation between EPS, P/C in soluble EPS （ESPs） composite, RH in activated sludge and fouling resistance is investigated by statistic analysis. The results show that the influence of EPSs, P/C in EPSs and RH on fouling resistance is very obvious. Pearson Correlation coefficients of original and modified NWF are 0.868/0.856, 0.840/0.866, 0.890/0.841. The modified surface can effectively restrict the absorption of EPSs, decrease P/C in EPSs, reduce sedimentation of activated sludge, and decrease fouling resistance.（5） PVA-NWF model is immerged in SMBR to be used for man-made wastewater treatment. The results show that PVA-NWF can reduce membrane fouling, can decrease the resistance of membrane fouling, but membrane fouling is still occurring during filtration. Filtration resistance is mainly from membrane fouling resistance. Based on the concept of specific fouling resistance and Darcy law that describes the relationship between flux and resistance during filtration driven by pressure, a module is established to explain therelationship between specific fouling resistance and time during filtration controlled byake resistance in SMBR of periodic operation:R_stf（t）=a(1-e^-t/b).The decline trend offlux can be predicted by this model, the expression is below J（t）=TMP/μ[R_m+a(1-e^-t/b)].This model is used to predict the decline trend of flux during pharmaceutical wastewater treatment. Compared with experimental data, the relative error is less than 10% at t>b, the relative error is less than 5% at t>2b. It shows that the model can predict the decline trend of flux during stable operation of SMBR. But the relative error is bigger during unstable operation at initial stage （t<b）.更多还原