膜振动过滤通量的实验研究

针对膜过滤过程中,因污染造成膜渗透通量下降等问题,提出了全新的将膜过滤与机械振动结合的膜振动过滤方式;用粘土悬浮液做正交实验,对比了在相同操作条件下,膜振动过滤及无振动膜过滤的膜过滤通量随时间的变化情况,表明膜振动过滤通量比无振动膜过滤通量大,并验证膜振动过滤方式的可行性;通过对影响因素的分析明确了振动频率适中、振动振幅较大时,膜过滤通量越大的原因。     

探究滤膜的振动过滤方法

借鉴大量国内外关于膜过滤分离先进技术研究成果并结合膜过滤生产实际,发现随过滤时间增加,膜污染加重导致过滤通量减小的问题。为此提出了一种新型的将膜过滤与机械振动相结合的膜振动过滤分离方式,即膜振动过滤,使之达到在保证膜过滤通量的基础上,又能有效防止膜阻塞的目的。从理论上分析证明膜振动过滤可行性,并应用自行设计、制造的具有控制振动振幅和频率的膜振动过滤装置进行过滤实验。通过实验测定膜过滤通量随过滤时间变化情况和过滤液体的透光值,证明了在合理操作条件下膜振动过滤的有效性和可行性。     

膜材料结构特性对污水深度超滤过程的影响

考察了聚砜(PS)、聚醚砜(PES)、聚偏氟乙烯(PVDF)、醋酸纤维素(CA)、聚丙烯腈(PAN)和聚酰胺(PA)等6种材质超滤膜的膜材料结构特性,分别以二级处理水为原水,研究了不同膜材料性质对污水深度超滤过程的影响.结果表明,在膜过滤过程中最初的通量衰减主要原因是表面污染而发生膜孔堵塞,造成膜孔密度下降,而过滤后期发生孔径窄化是其通量衰减的主要原因.膜的孔径分布越宽、孔形越规则越易发生膜孔堵塞污染,造成膜孔密度下降,其过滤初期通量衰减会越快;膜孔孔形越不规则越易发生膜孔内部污染,造成膜孔孔径窄化,在过滤末期通量衰减较快.     

改性PVDF膜在MBR中膜污染的研究

将聚偏氟乙烯膜磺化6 h,在TiO2胶体溶液中浸泡20 min,制得的TiO2改性膜纯水通量约为1 800L/m2·h,高出未改性膜250L/m2·h.通过膜生物反应器中膜阻力的测定,分析膜污染形成的原因,表明膜污染主要是浓差极化层及凝胶层引起的;通过活性污泥对膜污染机理的研究,判断出污泥的过滤过程严格符合沉积过滤定律.在膜生物反应器(MBR)中运行时,TiO2改性膜稳定通量高于未改性膜,总阻力低于未改性膜;通过扫描电镜分析,TiO2改性膜沉积层的厚度比未改性膜薄,表明TiO2改性膜的抗污染性能优于未改性膜.     

陶瓷膜过滤收获微藻的效能与膜污染特征

考察了平板陶瓷膜在次临界通量条件下多周期过滤收获小球藻细胞的效能以及跨膜压差、阻力构成、不可逆污染组分等膜污染特征。结果表明,次临界通量条件下,采用孔径100 nm的陶瓷膜多周期过滤能够有效收获普通小球藻。84%~98%的进水藻细胞以滤饼层方式被截留,通过物理清洗膜表面能够获得高浓度藻液,浓缩因子高于34。3个过滤周期内膜污染均呈现先缓慢增加后急剧升高的两阶段变化趋势。随过滤周期增加,膜污染急剧升高阶段显著加速,其主要原因是小球藻细胞及其EOM形成的协同污染效应以及水力不可逆污染的逐渐累积。水力不可逆污染组分的有机物分子量特征是100~1 000 Da的低分子酸以及1~10 kDa的蛋白类有机物,其中多种芳香族类蛋白和可溶性微生物产物是主要组分。     

动态膜的形成机理及其水处理性能研究

以陶瓷管为载体,对高岭土动态膜的形成及其污水处理性能进行了详细的研究.实验中采用错流过滤方式涂膜,考查了跨膜压差、涂膜液浓度、错流速度及涂制时间等对动态膜形成的影响.通过对实验数据分析可知,动态膜形成初期10～13 min,膜的形成过程可用标准过滤模型描述,在此期间颗粒堵塞载体膜管孔道,致使渗透液通量急剧减小;之后,膜的形成过程符合滤饼过滤模型,这一阶段颗粒主要在载体膜管内壁面沉积,渗透液通量缓慢下降直至基本稳定.制备的动态膜可用于处理城市污水厂二级出水,动态膜对浊度去除率基本上为100%,对COD也有一定的去除作用.     

新型聚芳醚砜酮超滤膜污染与膜阻力研究

采用新型聚芳醚砜酮(PPESK)超滤膜为分离介质,以炼油污水为研究对象,测定了膜污染和膜阻力.结果表明,PPESK超滤膜在100 kPa下的初始通量为480 L·m-2·h-1,自身阻力为0.78mm-1;在超滤膜运行过程中,溶液通量随运行时间呈指数衰减,通量衰减由60%增加到95%时,膜污染阻力由0.69nm-1增大到5.68 nm-1,膜污染阻力占总阻力的分数从43.95%增大到86.72%,其中不可逆膜污染阻力大小为0.20nm-1.PPESK超滤膜对迭标炼油污水过滤时,因膜污染造成通量衰减,经化学清洗能够得到较大程度的恢复.     

陶瓷膜强化过滤技术的应用

陶瓷膜在过滤过程中,因浓差极化和膜污染会导致膜通量下降而影响陶瓷膜的过滤效果。通过对陶瓷膜污染进行径向分层分析,结合工程实践和相关试验研究,总结了现有相关的陶瓷膜强化技术,为陶瓷膜过滤强化技术的工业应用提供参考。     

二氧化钛动态膜在油水乳化液分离中的应用研究

以多孔管式炭膜为载体制备二氧化钛动态膜并开展动态膜分离油水乳化液的研究,考察了载体孔径对动态膜的截留率和稳定渗透通量的影响。实验结果表明,动态膜处理油水乳化液的截留率在98%以上,渗透液浓度低于8.3mg·L-1,达到国家环保排放要求;稳定渗透通量随载体孔径的增大先减小后增大。在实验基础上,提出了动态膜稳定渗透通量衰减率(FDR)的概念,并将FDR的变化趋势与动态膜类型进行关联研究。分析发现,FDR随载体孔径的增大先增大后减小,动态膜由完全堵塞过滤型过渡为中间堵塞过滤型;用中间堵塞过滤型动态膜过滤油水乳化液时,随着载体孔径的增大,渗透通量衰减变缓。     

自组生物动态膜在污泥截留中的应用研究

在膜生物反应器基础上的自组生物动态膜反应器有其独特的性能。试验研究了 200 目不锈钢丝网为基材在曝气池内形成的生物动态膜的过滤性能,在普通混合液悬浮固体(MLSS)浓度约2200±200mg/L下,采用自流出水,考察了不同水头(Water Head)及初始通量对出水流量和SS的影响。结果表明:水头和初始通量对动态膜的形成具有关键作用,但同时对膜的堵塞也有相当大的影响。30cm是较好的操作水头,而初始通量小于0.62m/h时,基材上未形成有效的生物动态膜。试验中的通量高于0.1m/h,远远超过微滤膜生物反应器。     

倾斜振动过滤膜通量实验研究

根据膜过滤过程中存在的膜污染、膜通量不理想的问题,研究了一种可改变滤膜倾斜角度与振动相结合的新型过滤实验方式,以酵母悬浮液为物料,过滤实验测定在不同滤膜倾斜角度与振动频率条件下的相关数据,绘制出不同状态下的膜通量随过滤时间变化曲线,分析了原因.得到了在本实验范围内可获得理想膜通量的最佳滤膜倾斜角度和振动频率的操作条件.     

集成膜技术深度回用处理精对苯二甲酸废水研究

近两年来,膜法回用石化废水备受重视,利用集成膜技术对炼油和乙烯化工废水进行深度回用处理,目前已有相对成熟的经验,但集成膜技术用于精细化工产品精对苯二甲酸废水回用处理的研究尚少。在试验基本工况为超滤系统采用全量过滤方式,运行周期30min,内压式超滤运行通量不大于75L/(m2.h),超滤系统前加入絮凝剂PAC(投加量为5mg/L),低污染反渗透膜运行通量不大于19L/(m2.h),试验中系统回收率为70%,反渗透进水的COD含量小于40mg/L的条件下,精对苯二甲酸达标废水深度回用处理稳定运行,产水水质稳定可靠。     

A Review of Membrane Fouling in MBRs: Characteristics and Role of Sludge Cake Formed on Membrane Surfaces

Abstract

Membrane bioreactor (MBR) has been deemed to be a promising technology for wastewater treatment and reclamation; however, the MBR filtration performance inevitably decreases with filtration time attributed to the deposition of soluble and particulate materials onto and into the membrane under the interactions between activated sludge components and the membrane. Cake layer formation on membrane surfaces has been a major challenge in the operation of MBRs under supra-critical flux operation, and/or caused by uneven distribution of aeration intensities, etc.; however, it was argued that a thin cake layer might improve filtration operation by some researchers. This paper provides a critical review on the formation mechanisms, properties, the role of sludge cake in membrane filtration, and the corresponding strategies of controlling cake fouling in MBRs. Drawbacks and benefits of the formation of sludge cake were also discussed in order to better understand the characteristics and role of sludge cake formation in MBRs.     

Tubular Membrane Filtration with A Side Stream and its Intermittent Backwash Operation

The tubular membrane filtration system is widely applied to solid-liquid separation processes. Any improvements to the filtration module would increase separation efficiency, thus reducing operating costs. In this experiment, PMMA powder with an average particle diameter of 0.8 µm was filtered by a ceramic tubular membrane with an average pore size of 0.2 µm, and the impacts of the operating variables, such as suspension concentration, the filtration pressure, and the crossflow velocity on the permeate flux were discussed. In order to understand the increased permeate flux, the proposed module is comparable to the tubular membrane filtration module, but with an additional side stream under the same filtration mass flow rate. In addition, variations of shear force on the membrane surface are analyzed by CFD simulation, and the influence of backwash operations on the permeate flux is discussed. The results show that the side stream membrane filtration increased the shear force on the membrane surface, reduced fouling on the membrane surface, and increased the permeate flux. Furthermore, a backwash operation with a side stream flow channel could effectively clean the particles deposited in the module, thus, increasing the permeate flux.     

动态膜在错流微滤系统中的应用

利用6000目的高岭土作为动态膜涂膜材料,在相同的条件下过滤活性污泥和二级出水.实验结果显示,动态膜过滤在出水水质和通量方面明显优于直接过滤,而处理二级出水在膜通量方面没有优势.清洗实验结果表明动态膜能有效降低膜内部污染,并能恢复到新膜通量的90%.污泥浓度越大,通量越小.提高膜面流速和增加压力都能有效的提高膜通量,但提高膜面流速更经济.     

Fouling Control in a Submerged Flat Sheet Membrane System: Part I – Bubbling and Hydrodynamic Effects

Abstract

Submerged flat sheet membranes are mostly used in membrane bioreactors for wastewater treatment. The major problems for these modules are concentration polarization and subsequent fouling. By using gas‐liquid two‐phase flow, these problems can be ameliorated. This paper describes a study of the use of gas‐liquid two‐phase flow as a fouling control mechanism for submerged flat sheet membrane bioreactors. The effect of various hydrodynamic factors such as airflow rate, nozzle size, intermittent filtration, channel gap width, feed concentration, imposed flux, and the use of membrane baffles were investigated. Experiments conducted on model feeds showed that fouling reduction increased with air flow rate up to a given value and beyond this flowrate no further enhancement was achieved. The effect of bubbling was also found to increase with nozzle size at constant airflow. Using intermittent filtration as an operating strategy was found to be more effective than continuous filtration and it also reduced energy requirements. The study showed the importance of the size of the gap between the submerged flat sheet membranes. As the gap was increased from 7 mm to 14 mm, the fouling became worse and the degree of fouling reduction by two‐phase flow decreased by at least 40% based on suction pressure rise (dTMP/dt). This is the first study which has reported the effects of baffles in improving air distribution across a flat sheet submerged membrane. It was found that baffles could decrease the rate of fouling by at least a factor of 2.0 based on the dTMP/dt data, and significantly increase critical flux.     

膜生物反应器中污泥特性对膜污染的影响研究

膜生物反应器(MBR)是膜技术与污水生物技术的组合工艺，与传统污水处理工艺相比具有许多优点，但膜污染目前仍是限制MBR广泛应用的突出问题。有效的膜污染防治技术，可以增加膜通量，增强系统稳定性，减少系统维护和运行费用。在膜过滤过程中，污泥混合液的特性对于膜污染具有重要作用。近年来围绕污泥特性对膜污染的防治问题取得了许多研究成果，膜污染的数学模型研究也得到了很大发展。     

Recovery of Water from Sewage Effluents using Alumina Ceramic Microfiltration Membranes

Abstract

This work highlights the recovery of water from sewage effluents using alumina ceramic membranes with pore sizes of 0.2 and 0.45 µm respectively in dead‐end filtration mode. The work demonstrates the ability and advantages of alumina‐based microfiltration (MF) membranes in filtering microbes and other harmful pollutants normally present in sewage effluents in dead‐end filtration mode. The fouling behavior of the membranes in the filtration cycle is identified, which in turn helped to regenerate the fouled membranes for subsequent usage. Regeneration studies of fouled membranes also suggest that though chemical cleaning was effective in recovering membrane performance, the fouling had still been progressed slowly and the membranes showed the ability to perform at least five filtration cycles of highly‐contaminated sewage effluents. As expected, the filtration efficiency and flux characteristics at various transmembrane pressure (TMP) of the membranes varies with the pore size of the membrane and is explained in light of Darcy's and Poiseuille's laws of filtration. The results show that alumina ceramic membrane with disc geometry having a pore size of 0.2 µm is more effective in filtering the total suspended solids, turbidity and microbes of the sewage effluents as compare to that of 0.45 µm membrane to a level in which the permeate water appears to be benign for discharging into the surface thereby offering the possibility of recycling or reusing the recovered water from the sewage effluents for suitable purposes.     

A comparison of hydrodynamic methods for mitigating particle fouling in submerged membrane filtration

Hydrodynamic methods are used for mitigating particle fouling and for enhancing the filtrate flux in submerged membrane filtration. In the comparison membrane blocking-cake formation filtration system, the effects of filtration pressure, aeration intensity, backwash duration and stepwise increasing pressure on the filtration resistances and filtration flux are measured and discussed. Aeration is helpful for reducing particle deposition on the membrane surface, while stepwise increasing pressure can mainly mitigate internal fouling of the membrane. Periodic backwash can significantly reduce both the resistance caused by the membrane internal fouling and by cake formation; consequently, it can effectively recover the filtrate flux. In contrast, increasing the pressure in constant pressure filtration leads the flux to be decreased due to more severe membrane blockage. According to the comparison of the long-term flux and the received filtrate volume, among these hydrodynamic methods, the periodic backwash with longer duration is the optimal strategy for the filtration.     

Sustainable Flux Fouling in a Membrane Bioreactor: Impact of Flux and MLSS

Abstract

The long term sustainable flux behavior of a submerged membrane bioreactor operated under a steady state conditions at a range of mixed liquor suspended solids (MLSS) concentrations has been examined. Comparison of fouling rates at a number of imposed fluxes has been made between long term filtration trials and short term tests using the flux step method. Results indicate an exponential relationship between fouling rate and flux for both long and short term trials, although the value was an order of magnitude lower during long term tests. Moreover, operation during long term trials is characterised by a period of pseudo stable operation followed by a catastrophic rise in TMP at a given critical filtration time (t_filt) during trials at 6 g · L^?1. This time of stable operation, t_filt, is characterised by a linear relationship between fouling rate and flux. Results have been compared with the literature. Data for membrane fouling prior to the end of t_filt yielded a poor fit with a recently proposed model. Trends recorded at t>t_filt revealed the fouling rate to follow no definable trend with flux, contrary to the notion that fouling beyond the critical filtration time relates to solids deposition.