膜法处理腈纶厂废水

本文主要研究了用聚砜超滤膜对腈纶厂热牵伸废水、水洗机废水处理回用以及用超滤膜及反渗透膜处理腈纶厂污水的情况。并从工艺可行性上作了探讨。同时，本文还对用膜法处理脯纶厂永经济效益作了估算。     

An experimental study of UF membrane fouling by humic acid and sodium alginate solutions: the effect of backwashing on flux recovery

One of the critical issues for the successful application of ultrafitration in water treatment is membrane fouling due to dissolved organic matter, which negatively affects productivity, product quality and process cost. The aim of the present study is to contribute to the understanding of fouling phenomena by organic matter and the efficiency of the backwashing technique, which is applied in practice to restore membrane flux. In this experimental study commercial humic acid and sodium alginate have been used as model substances representative of natural organic matter and extracellular organic matter, respectively. All fouling experiments were carried out in a special single fiber apparatus. An important parameter considered in the study of both model substances is the concentration of calcium ions, which promote their aggregation and influence the rate of flux decline, the reversibility of fouling and rejection. Membrane fouling by humic acid appears to be the outcome of simultaneous action of several fouling mechanisms. Initially, a relatively rapid irreversible fouling takes place due to internal pore adsorption; however, progressively pore blocking becomes important and a fouling layer develops on the membrane. Sodium alginate fouling on the other hand is apparently due to two consecutive mechanisms; i.e. a rapid irreversible fouling due to internal pore constriction, followed by cake development on the membrane surface which becomes the dominant mechanism. Comparing fouling in both cases it can be inferred that even though sodium alginate fouling is more severe than the one caused by humic acids, it is to a large extent reversible by backwashing. On the contrary, fouling caused by humic acid is characterized by greater and increasing with calcium addition irreversibility, which is not remedied by the periodic backwashing. The different fouling propensity of the two types of macromolecules is apparently due to differences of their physical–chemical characteristics.     

Effect of cake layer structure on colloidal fouling in reverse osmosis membranes

A series of reverse osmosis (RO) membrane filtration experiments was performed systematically in order to investigate the effects of various hydrodynamic and physicochemical operational parameters on a cake layer formation in colloidal and particulate suspensions. Bench-scale fouling experiments with a thin-film composite RO membrane were performed at various combinations of trans-membrane pressure (TMP), cross-flow velocity (CFV), particle size, pH, and ionic strength. In this study, silica particles with two different mean diameters of 0.1 and 3.0 μm were used as model colloids. Membrane filtration experiments with colloidal suspensions under various hydrodynamic operating conditions resulted that more significant permeate flux decline was observed as TMP increased and CFV decreased, which was attributed to the higher accumulative mass of particles on the membrane surface. Results of fouling experiments under various physicochemical operating conditions demonstrated that the rate of flux decline decreased significantly with an increase of the ionic strength as well as particle size, while the flux decline rate did not vary when solution pH changed. The experimentally measured cake layer thickness increased with a decrease in particle size and solution ionic strength. Furthermore, the model estimation of cake layer thickness by using a cake filtration theory based on the hydraulic resistance of membrane and cake layer was performed under various ionic strength conditions. The primary model parameters including accumulated mass and specific cake resistance were calculated from the cake layer resistance. This result indicated that the formation of cake layer could be closely related with solution water chemistry. The model estimated cake layer thickness values were in good agreement with the experimentally measured values.     

超滤膜和反渗透膜联用处理苦咸水

介绍了将超滤膜和反渗透膜联用的水处理工艺,并对此种方法进行了研究。结果表明,在原水为苦咸水、含盐量在4010～4500mg／L的情况下,经预处理超滤膜和反渗透膜联用的水处理工艺对CODMn、总硬度、Cl^-的去除率分别达到了95％、98％、97％以上,脱盐率也达到97％以上,连续运行稳定,出水水质优于中华人民共和国饮用水标准。在实验基础上研究并探讨了超滤膜和反渗透膜联用的水处理工艺特性,为其在中水回用和小型饮用水装置等水处理应用提供实验依据。     

The use of RO to remove emerging micropollutants following CAS/UF or MBR treatment of municipal wastewater

The removal of various organic micropollutants (OMPs), including six antibiotics (ERY, ROX, CLA, SMX, SMZ, and TMP), three pharmaceuticals (ibuprofen, salicylic acid, and diclofenac), one industrial product (BPA), and one hormone (cholesterol), was investigated in two pilot plants treating the same raw sewage of the Tel-Aviv WWTP. The effluent production by CAS-UF was 45 m³/h while that of MBR was 40 L/h. Each system's effluent constituted the feed for its RO, which comprised three RO steps after the CAS/UF and a semi-batch RO system after the MBR. Despite significant molecular differences between the selected OMPs, high removal rates were achieved after the RO stage (> 99% for macrolides, pharmaceuticals, cholesterol, and BPA, 95% for diclofenac, and > 93% removal of sulfonamides). However, low antibiotics concentrations and 28–223 ng/L residuals of ibuprofen, diclofenac, salicylic acid, cholesterol, and BPA in the MBR/RO and CAS-UF/RO permeates showed that although RO is an efficient removal solution, it cannot serve as an absolute barrier to OMPs. Therefore, additional treatment techniques should be considered to be incorporated aside the RO to ensure complete removal of such substances.     

Investigations of the coupled effect of cake-enhanced osmotic pressure and colloidal fouling in RO using crossflow sampler-modified fouling index ultrafiltration

The aim of this study was to investigate the potential of using the resistivity and deposition rate data from Crossflow Sampler-Modified Fouling Index Ultrafiltration (CFS-MFI_UF) measurements to determine the coupled effects of colloidal fouling and cake enhanced osmotic pressure (CEOP) effect. Cake filtration derived from CFS-MFI_UF was combined with a CEOP model to predict the crossflow RO fouling profile under constant flux filtration. The prediction based on resistivity, I′ from CFS-MFI_UF measurement alone was found to underestimate the RO fouling for high salinity solutions. However, when incorporating the mass information from the CFS-MFI_UF test to account for the CEOP effect, the prediction showed good agreement with the TMP profile of the RO system. The results indicated that the CFS-MFI_UF test which includes the CEOP effect is a very promising technique to provide an estimation of the RO colloidal fouling profile. When the changes of cake thickness and porosity throughout the filtration were considered, the predicted TMP profile based on the model clearly indicated a two-stage of fouling profile which agreed well with the experimental data. Additional studies on the effects of cake thickness and porosity on CEOP highlighted the important influence of cake structure on CEOP.     

Effect of hydrophilic/hydrophobic fractions of natural organic matter on irreversible fouling of membranes

Natural organic matter (NOM) has been identified as a major factor affecting membrane processes performances, but its impact is difficult to quantify from global parameters such as organic carbon content. The extent of fouling due to the different fractions of NOM from surface water has been examined in dead-end ultrafiltration using criteria such as flux decline and irreversibility in regard with organic matter rejection. The most important flux decline was observed during the filtration of the hydrophilic acids fraction whereas fulvic acids led to the most irreversible fouling. Furthermore, the hydrophilic fraction lost its fouling character when mixed with other fractions underlining that interactions between numerous components are possibly more important than the composition itself.     

Performances of RO and NF processes for wastewater reuse: Tertiary treatment after a conventional activated sludge or a membrane bioreactor

Wastewater reclamation requires processes and technologies having the ability to reduce the presence of micropollutants which are not wholly treated in conventional WWTP. Due to the complexity of membrane-solute interactions and the diversity of secondary treatment effluent (STE) matrices, deeper investigations are required to identify the major foulant species and more specifically their behaviour at high concentration in real waters. This study investigates the rejection and fouling potential of nanofiltration (NF) and low-pressure reverse osmosis (RO) membranes with two STEs sampled from i) a conventional activated sludge process coupled with ultrafiltration (CAS-UF) and from ii) a membrane bioreactor MBR (AquaRM^®, SAUR (France)). Whatever the origin of the effluent, RO seems to be the best solution to prevent pollution of tertiary effluents (expected result) but also to obtain low fouling levels. The different composition and molecular weight distribution of MBR and CAS-UF effluents can explain the different fouling behaviours that were observed.     

RO membrane solute rejection behavior at the initial stage ofcolloidal fouling

This study investigated the rejection of salt and inert organic compounds by reverse osmosis membranes during the initial stage of colloidal fouling. Results of laboratory-scale experiments showed that colloidal fouling caused a marked decrease in flux, salt rejection and rejection of organics with molecular weight (MW) smaller than about 100 g/mol. Removal of neutrally charged organics was mainly by size or steric exclusion. Rejection of xylose, which has MW >100 g/mol, was not affected much by colloidal fouling. The decrease in salt and low MW organic rejections during the initial stage of colloidal fouling was attributed to cake-enhanced concentration polarization, whereby the colloidal cake layer hindered back diffusion of solutes from the membrane surface to the bulk solution, resulting in higher solute concentration gradient across the membrane. At higher channel wall shear rate, the rates of colloidal deposition, flux decline, decrease in salt rejection, and decrease in low MW organic rejection were lower.     

干熄焦除盐水装置的应用与探讨

酒钢焦化厂3#、4#焦炉干熄焦除盐水装置以反渗透(RO)系统、混床系统为核心设备,全自动过滤器、超滤系统(UF)为预处理单元,采用高分子分离膜加混床的制水方式,生产的除盐水品质高,膜前压力保持在0.02～0.06MPa的低水平,超滤进水流量可稳定在70t/h左右。介绍了除盐水装置在实际应用中出现的问题和采取的各项改进措施。     

Pilot-scale testing of reverse osmosis using conventional treatment and microfiltration

In order to meet the growing needs of its consumers, the Metropolitan Water District of Southern California is looking for ways to desalt water from the relatively hard Colorado River. This study evaluated conventional treatment as the pretreatment step for reverse osmosis (RO) desalting. Other pretreatment options studied include microfiltration (MF) and conventional treatment with ozone and biologically active filters. Each of three pretreatment scenarios produced effluent waters generally considered appropriate for use with RO [median turbidity of less than 0.1 Nephelometric turbidity unit (NTU) and median silt density index of less than 3]. Both microfiltered and ozonated/ biofiltered waters gave steady RO performance over 3 months of testing. However, conventional treatment left the RO system vulnerable to organic and biological fouling. Despite maintaining a 2-2.5 mg/L chloramine residual, pretreatment using conventional treatment required more frequent cleanings than either MF or ozonation/biofiltration (O₃/BF). The good performance for biofiltered water may have resulted from the stabilization of the natural organic matter through the O₃/BF process. Microfiltration, with its superior particle and bacteriological removal characteristics, provided the best RO pretreatment technology.     

超滤膜污染指数模型及其在工程设计中的应用

本文提出了超过滤的模型,通过对苯二甲酸悬浮液的超滤浓缩数据的线性回归,提出了对该体系的污染方程系数,利用此模型计算了操作参数变化对超滤通量的影响曲线,求出了最佳操作条件。本模型对类似体系的超滤工程设计有参考价值。     

Interaction mechanisms associated with organic colloid fouling of ultrafiltration membrane in a drinking water treatment system

The Extended Derjaguin Landau Verwey Overbeek (XDLVO) approach was introduced to predict organic colloid fouling of membranes in an initial ultrafiltration (UF) phase. Two polymeric UF membranes, made of polyvinylchloride (PVC) and polyvinylidene fluoride (PVDF) respectively, were selected to investigate membrane fouling by filtering water samples with different organic colloid compositions. The experiment was performed to determine the fouling contributions of van der Waals (LW) interactions, electrostatic (EL) interactions, as well as double layer and short-range acid–base (AB) interactions, to the total interaction energy caused by organic colloids attaching to UF membrane surfaces. The results showed that LW interaction energy predominated when the distance between the membrane surface and organic colloid was > 5 nm, while AB accounted for a key contribution to total interaction energy over short distances (< 2.5 nm). The influence of EL interaction energy was ignored in the total interaction energy composition. The surface energy, among all characteristics of membrane material, was a dominant factor affecting membrane fouling. The experimental results of initial ultrafiltration of raw water from the actual water source were in accordance with the predictions based on XDLVO theory, indicating that it was a feasible option for predicting membrane fouling during the initial ultrafiltration phase.     

Pretreatment of seawater: Results of pilot trials in Singapore

In this paper, performance ofdifferent pretreatment systems used in the seawaterreverse osmosis desalination process is presented. The different pretreatment techniques analyzed included conventional media-filtration technique and non-conventional membrane filtration techniques. For the membrane filtration techniques, two ultrafiltration and one microfiltration pilot plants were used in the experimental study. During the experiments, the silt density index (SDI) of the filtrate samples was regularly measured to quantify the performance of pretreatment systems in rejecting colloidal particles. Measurements of other important parameters included filtrate flux, transmembrane pressure, total suspended solids, colloidal silica, total organic carbon, etc. According to the experimental findings, the quality of the filtrate produced by the conventional media-filtration technique was inferior and highly inconsistent. SDI of filtrate varied from 2.8 to 3.8 and spikes as high as 6.3 were frequently observed. Membrane pretreatment produced filtrate of a better quality. SDI ofthe filtrate produced was consistently below 3.0, a prerequisite for proper operation of a RO desalination plant. The ease of operation of the membrane pretreatment processes was also noted. Together with improved maintenance procedures such as filtrate backwashing and air scouring, complete flux and pressure recoveries were achievable with minimal use of chemicals during the experiments.     

An experimental assessment of centrifugal membrane separation using spiral wound RO membrane elements

The influence of the rotating environment created in a centrifugal membrane separation (CMS) system on the performance of commercial spiral wound RO membrane elements has been examined. In CMS the membrane elements are located at the periphery of a centrifuge rotor. The spinning action develops the process pressure and alters the fluid flow pattern within the element due to Coriolis and centripetal acceleration. CMS has been shown to improve performance of a small-scale plate and frame element by reducing concentration polarization and fouling. The current study probes the benefits of spinning commercial spiral wound RO membrane elements in a radial orientation. Mechanical element stability at over 3000 `g' has been demonstrated as well as concentration polarization reduction and fouling alleviation. Results also indicate that rotation induced secondary flows are more effective in reducing concentration polarization than increasing cross-flow velocities for the non-rotating condition.     

Feasibility study for reclamation of a secondary treated sewage effluent mainly from industrial sources using a dual membrane process

A feasibility study for reclamation of a secondary treated sewage effluent mainly from industrial sources (60%) in Singapore has been conducted using a dual membrane UF-RO process. The pilot system had a treatment capacity of 2 m³/h. The UF unit and RO unit were operated at 70–80% and 40% water recovery, respectively. Six-month run for the pilot was carried out to study the stability and fouling tendency of membranes.

The characteristics of the raw feed indicated that ammonia-N was consistently high at 30–50 mg/L. Very high fluctuations in iron (0.3–3.7 mg/L), turbidity (1–27.1 NTU) and TOC (3.2–56.7 mg/L) were observed. Nitrate was low at <0.2 mg/L. The results of the study showed that dosage of alum in the UF process significantly reduced organic foulants and phosphate scalants. The polymeric RO membrane could tolerate organics from industrial wastewater and performed >96% salt rejection at the end of the study after 6 months. The study concluded the dual membrane process was capable of reclaiming the sewage effluent mainly from industrial sources for industrial use.