Treatment of Oily Wastewaters Using the Microfiltration Process: Effect of Operating Parameters and Membrane Fouling Study

This work focuses on the treatment of oily wastewater using the cross-flow microfiltration (MF) process to determine the effect of different operating parameters such as transmembrane pressure (TMP) and cross-flow velocity on the separation performance and to study the mechanism of membrane fouling during microfiltration of oil in water emulsions. In this regard, the permeation flux and oil rejection of a polyvinylidene fluoride (PVDF) membrane in a flat-frame MF module for separation of 3000 ppm oil/water emulsions were measured. The results indicated that the permeate flux increased by an enhancement in both TMP and cross-flow velocity, while the oil rejection decreased. The analysis of variance (ANOVA) showed that the individual effect of TMP and cross-flow velocity is more important than the interactional effect of these operating parameters on the permeate flux and oil rejection. The results of fouling modeling revealed that the membrane fouling mechanism was affected by the applied TMP. The cake filtration model dominates the fouling mechanism at lower operating pressures. The fouling mechanism was changed from the cake formation to intermediate pore blocking and then to standard pore blocking as the TMP varied from 1 to 3 bar. Finally, a five-step procedure was used for cleaning the oil/water fouled membranes.     

陶瓷膜污染的超声波辅助清洗

膜污染的控制和膜的清洗再生是膜应用的关键,研究了采用超声波辅助清洗被乳化液污染的氧化锆陶瓷膜。结果表明：超声波的功率、超声清洗时间及膜污染程度等对清洗效果均有影响,超声功率越高,清洗后水通量的恢复率越高,超声清洗时间在20 min左右比较适宜。超声波对膜表面的污染清洗效果较好,对膜孔内堵塞清洗效果相对较弱,超声辅助化学清洗可有效恢复膜通量。     

One-step cleaning method for flux recovery of an ultrafiltration membrane fouled by banknote printing works wastewater

A method was developed to clean ultrafiltration (UF) membranes fouled by banknote printing works wastewater.The cleaning agent was comprised of 0.7 wt.% NaOH, 0.8 wt.% Na₂EDTA, 0.3 wt.% Turkey red oil and 98.2 wt.% de-ionized water. Membrane flux recovered adequately when the cleaning agent was circulated for 20–30 min at 1.5 m/s and 50–60°C. The membrane surfaces before and after cleaning were characterized by SEM/EDX. The spent cleaning agent was analyzed by TOC and ICP. The results showed foulants were removed from the fouled membrane by the cleaning. Pilot-scale experiments were also conducted to validate the efficiency of the cleaning method. This one-step cleaning method replaced an existing four-step cleaning method and was employed to clean OF units in banknote printing works wastewater plants.     

Effect of Casting Solution on Morphology and Performance of PVDF Microfiltration Membranes

The effects of preparation‐influencing parameters such as polymer concentration, thickness of casting solution, and type of solvent on morphology and performance of poly(vinylidene difluoride) (PVDF) microfiltration membranes for the treatment of emulsified oily wastewater were investigated. Flat‐sheet membranes were prepared from a casting solution of polymer and additive in various solvents by immersing the prepared films in nonsolvent‐containing mixtures of water and 2‐propanol. The membranes were characterized using scanning electron microscopy. Increasing the polymer concentration and membrane thickness significantly affected the pore size, leading to permeate flux decrease. An attempt was made to correlate the effect of the solvent on membrane morphology and performance employing solubility parameters between solvent and nonsolvent).     

平板膜在中药废水处理MBR系统中的应用

采用平板膜MBR工艺处理高浓度中药废水,介绍了MBR膜系统的工艺设计参数和运行情况,近1 a半的实际运行结果表明,平板膜可以处理中药废水,出水水质达到设计要求。同时,通过分析膜池水质和膜垢情况后认为,膜垢主要由钙离子和多糖类物质组成。经试验确定先用盐酸,再用次氯酸钠对平板膜进行清洗,可以取得良好的效果。     

无机陶瓷微滤膜处理含油乳化液废水的污染机理探讨

讨论了用陶瓷微滤膜处理含油乳化废水过程的膜污染情况，初步探讨了此分离过程的污染机理；给出了阻力的大致分布，为采用有效方法控制污染提供了依据。     

MBR污水处理工艺长期运行中的膜强化清洗方式

基于上海城镇污水处理厂AAO-MBR膜工艺长期运行中膜不可逆污染严重、离线化学清洗难以恢复理想通量的问题,对其清洗方式进行改进。在原清洗方式的基础上增加草酸二次清洗,探究污染膜产水能力恢复情况,并通过中试试验进行验证。结果表明：膜清洗方式改进后,离线清洗对膜污染物的去除更加彻底,清水通量可恢复至新膜的95.1%,较原清洗方式提高了27.2%。在相同通量下中试运行24 d后,膜运行压力比原清洗方式低18.2 kPa,膜污染速率明显减慢。研究通过改进MBR长期运行平板膜的污染物清洗方法,为今后MBR污水厂膜清洗提供参考,具有较好的工程指导意义。     

含油污水处理方法研究

综述了含油污水的来源及危害,较系统地介绍了盐析法、絮凝法、气浮法、粗粒化法、膜分离法、吸附法和生物法等处理含油污水的方法。最后介绍了微波法这种新型的含油污水处理方法。     

陶瓷膜微滤骨架镍催化剂的膜污染机理分析

用孔径为0.2μm的陶瓷膜过滤骨架镍催化剂悬浮液,研究膜污染机理。结果表明,膜污染主要是骨架镍催化剂在膜表面上形成的滤饼层,当操作压力循环变化时滤饼层表现出不可逆性。工业上用过的污染膜和滤饼层的组分分析表明,污染物主要是骨架镍催化剂。应用结果也表明了膜污染原因是骨架镍催化剂在膜表面形成了不可逆性滤饼层。     

丝厂废水中的丝胶蛋白在超滤过程中的膜污染和膜清洗

采用十种不同的膜清膜方法对超滤丝厂废水后被污染的中性聚砚中空纤维超滤膜进行了研究。结果表明：０．１％ＮａＯＨ、０．５％ＮａＣｌＯ、０．１％渗透剂等组成的碱性溶液对丝胶蛋白造成的膜污染具有最佳清洗效果。     

阳离子型有机絮凝剂处理含油乳化废水的研究

对阳离子型有机絮凝剂处理含油乳化废水进行了试验研究,试验结果表明单独投加阳离子有机絮凝剂对含油乳化废水没有处理效果;阳离子有机絮凝剂与聚合氯化铝复合使用可使絮凝体大而密实,同时使聚合氯化铝的用量降低30%,气浮产生的浮渣量少,含水率低。     

Some observations on the chemical cleaning of fouled membranes

Multi-photon microscopy, a fluorescence based technique, was used to image in-situ the fouling and cleaning of a 0.22 μm microfiltration membrane fouled by bovine serum albumin and ovalbumin. Imaging of the cleaning was possible for two of the three cleaning regimes used. The free chlorine cleaner bleached the fluorescence labelling on the proteins and so visualisation of the process, whilst using this cleaner, could not be undertaken. However, during the use of solutions of either sodium hydroxide or Ultrasil 53, appropriate fluorescent labelling of the proteins allows the foulant species to be clearly identified. Cleaning with sodium hydroxide was less effective resulting in only 50% flux recovery. The cleaning mechanism was different and large aggregates remained on the membrane surface even after 1 h of cleaning. Images correlated well with filtration data and clearly show re-fouling of the membrane during the second half of the cleaning cycle by ovalbumin alone. The discussion includes observations on the need for one to be aware of the potential for this to occur and on the need for some studies to involve repeated cycles of fouling and cleaning.     

The effects of performance and cleaning cycles of new tubular ceramic microfiltration membrane fouled with a model yeast suspension

The efficiency of crossflow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The experiments that were carried out in the laboratory were conducted to determine and investigate the performance, behaviour and the fouling susceptibility of new ceramic tubular microfiltration membranes during the crossflow filtration of yeast suspensions. The tubular membranes of nominal pore size 0.5 microns were fouled over a varied range of concentration, temperatures, pH, crossflow velocities and system pressures. The typical filtration conditions were at a temperature of 25°C, a system pressure of 1.5 bar and a concentration of 0.03 g/L yeast suspension. These parameters varied during subsequent investigations. After each experiment, the membrane and the rig were cleaned using a three stage cleaning process and was reused in order to replicate industrial filtration conditions. The effects of repeated fouling and cleaning cycles upon membrane flux over time and cleaning efficiency are investigated and their influence over time is also documented. For every experiment, the flux data was recorded over a 50 min period and the membrane was changed after the PWF declined considerably due to excessive fouling over time. Chemical cleaning consisted of a sequential application of a 1% caustic solution through the rig followed by a 2% hypochlorite solution and a 2% nitric solution, all at 50°C. The permeate flux was shown to decrease with filtration time during the development of the fouling layer. Once the fouling layer was developed and established, there appeared to be a leveling of permeate flux. The experimental results are presented in the report and the flux values at different conditions are presented.     

Ozone Cleaning of Fouled Poly(Vinylidene) Fluoride/Carbon Nanotube Membranes

This research demonstrates for the first time that ozone is an effective cleaning agent for polyvinylidene fluoride (PVDF) membranes fouled by natural organic matter (NOM). Bare PVDF membranes as well as PVDF impregnated with CNTs (pristine (CNTs–P) and oxidized (CNTs–O)) at 0.3% mass membranes were used. Three different methods were investigated for cleaning the fouled membranes including; A: 10-min cleaning by pure water, B: 5-min water followed by 5-min ozonated water, and C: 10-min fully ozonated water. It was found that the application of fully ozonated water for 10 min was very effective to reinstate the flux to almost its original value of unfouled membrane. The CNTs–P/PVDF membrane exhibited the highest fouling with a total fouling ratio of 81%, while for the bare PVDF and the CNTs–O/PVDF membranes, the fouling ratios were 76% and 74%, respectively. The full ozonated water cleaning method gave the highest removal of fouling leaving the lowest irreversible fouling on the membrane as compared to the other cleaning methods. On the other hand, the highest removal of NOM fouling was obtained for CNTs–O/PVDF membranes indicating that fouling on CNTs–O/PVDF membrane was less bound than the other membranes. Contact angle measurements of the fouled membranes showed that all membranes exhibited increased contact angles due to the NOM deposition but after cleaning, particularly with ozonated water, the membrane contact angles returned to almost their original values. FTIR analysis of the membranes corroborated the results obtained.     

渗透模式影响纳米涂层修饰陶瓷微滤膜分离性能的研究

研究了膜分离技术处理含油废水存在因油滴变形引起的膜堵塞问题。为减少膜污染,使用在市场上销售氧化铝微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,具有良好的效果。考虑其工业应用条件,重点研究了循环模式（模拟大量废水处理）和浓缩模式（模拟少量废水处理）对膜渗透通量的影响。结果表明：循环模式下料液的油浓度为恒定的,纳米涂层能有效提高微滤膜的渗透通量。膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显。当膜面流速为7m／s时,修饰陶瓷膜的最大渗透通量为280L／（m^2·h）,油截留率为96．4％。在浓缩模式下,料液的油浓度随渗透液的排出呈指数性增加,随着油浓度的增加,渗透通量持续衰减,油截留率持续上升。当油浓度达到一定程度后,修饰陶瓷微滤膜不能有效地实现稳定含油废水的油水分离。     

纳滤回收头孢拉定母液的实验研究

考察了NF270、NF90、DL纳滤膜对头孢母液脱盐浓缩的性能,NF270适合头孢母液的脱盐浓缩。考察了直接浓缩、预浓缩-渗滤-浓缩的方式对NF270膜浓缩头孢过程的影响,并用不同的清洗方法对膜进行通量恢复,而且用2-萘酚对浓缩母液和原始母液进行螯合回收进行了比较。实验结果表明,直接浓缩将导致膜通量迅速衰减,达不到理想的浓缩效果。采用预浓缩-渗滤-浓缩的方式能有效的对头孢母液进行脱盐浓缩,而且采用含NaOH的清洗剂能有效的回复膜的通量。用2-萘酚对浓缩母液进行螯合回收头孢的得率大于原始母液。     

陶瓷膜微滤凹凸棒土过程中膜污染的控制和再生

采用阻力系列模型分析了膜污染主要来自凹土在膜表面的沉积,通过Darcy定律过滤模型计算,确定过滤过程的阻力主要来自滤饼层阻力Rg,约占总阻力的85%。实验结果表明,单一的物理、化学清洗方法不能达到理想的清洗效果,采用化学方法和反冲技术相结合的清洗方法,可使膜的纯水通量恢复至新膜的89 %以上,且多次的清洗效果稳定。考察了反冲压力、反冲时间和反冲周期等因素对陶瓷膜微滤凹土浆液强化过程的影响,确定合适的反冲操作条件：反冲压力0. 5 MPa、时间10 s、周期20 min。反冲技术在陶瓷膜微滤过程的膜污染控制和再生环节上起了重要作用,并具有广阔的应用前景。     

Cross-Flow Microfiltration of Industrial Oily Wastewater: Experimental and Theoretical Consideration

Microfiltration of industrial oily wastewater was performed using polyamide membrane. A rectangular cross flow membrane cell was used for the experiments. Effects of different operating parameters such as transmembrane pressure drop and Reynolds numbers on the steady state permeate flux and oil rejection was investigated in detail. Initial oil concentration in the industrial oil-water emulsion was found to be 192 mg/L with average oil droplet range size 0.01 to 47 µm. The treated industrial oily water was characterized in terms of electrical conductivity, total dissolved solids (TDS), and chemical oxygen demand (COD). It was observed that the steady state permeate flux increased with transmembrane pressure drop and Reynolds numbers. The oil concentration in permeate was found to be around 4.5 mg/L, after treatment, which was lower than the permissible discharge limit. The results showed that microfiltration was an efficient and ecologically suited technology for the treatment of industrial oily wastewater. The cross flow velocity was considered in both laminar and turbulent regimes. A model was proposed by combining of Brownian diffusion and shear-induced diffusion to predict the steady state permeate flux data at different Reynolds numbers and different transmembrane pressure drops.     

陶瓷微滤膜在回收矿浆工业废水中的应用与再生性能研究

对陶瓷微滤膜在矿浆工业废水中的应用及陶瓷膜的再生性能进行了研究。针对矿浆悬浮液中的固液相性质,选择陶瓷微滤膜对已经经过预处理的矿浆进行过滤与脱水。经多次过滤后的陶瓷膜用正、反冲洗法进行冲洗并考察膜再生性能。研究认为对某些已经经过预处理的矿浆用陶瓷微滤膜过滤,效果明显;用水正反冲洗后再生性能良好,膜的使用寿命长。     

不溶性阳极电解气浮法处理含油废水的试验研究

采用石墨作阳极对含油废水进行电解气浮处理研究,对电解法处理乳化含油废水的作用机理进行了初步探索,考察了电流强度,电解时间,极间距和pH值对废水中油去除率的影响。正交实验表明,电解时间是影响废水除油率的最显著因素。在电流强度为0.38A,电解时间为28min,极间距为1.5cm,原水pH值为7.1的条件下进行电解气浮实验,废水除油率达到93.59%。