Removal of bacteriophages with different surface charges by diverse ceramic membrane materials in pilot spiking tests

This study examines mechanisms for removal of bacteriophages (MS2 and phiX174) by ceramic membranes without application of flocculants. The ceramic membranes considered included ultra- and microfiltration membranes of different materials. Phages were spiked into the feed water in pilot scale tests in a waterworks. The membranes with pore sizes of 10 nm provided a 2.5-4.0 log removal of the phages. For pore sizes of 50 nm, the log removal dropped to 0.96-1.8. The membrane with a pore size of 200 nm did not remove phages. So, the removal of both MS2- and phiX174-phages depended on the pore size of the membranes. But apart from pore size also other factors influence the removal of phages. Removal was 0.5-0.9 log higher for MS2-phages compared with phiX174-phages. Size exclusion seems to be the major but not the only mechanism which influences the efficiency of phage removal by ceramic membranes.     

Mg/Al layered double hydroxide for bacteriophage removal in aqueous solution

The objective of this study was to investigate the removal of bacteriophages in Mg/Al layered double hydroxide (LDH). Batch experiments were performed with bacteriophage MS2 in a powder form of Mg/Al LDH under various LDH doses. Column experiments were also performed under flow-through condition with bacteriophages MS2 and phiX174 in Mg/Al LDH immobilized on sand surfaces. Batch tests demonstrated that the powder form of Mg/Al LDH was effective in removing MS2 with the removal capacity of 2.2 × 10(8) plaque forming unit (pfu)/g under the given experimental conditions (LDH dose = 2 g/L; initial MS2 concentration = 4.61 × 10(5) pfu/mL). Column experiments showed that the log removal of phiX174 was 4.40 in columns containing 100% Mg/Al LDH-coated sand while it was 0.05 in 100% quartz sand. These findings indicated that Mg/Al LDH-coated sand was effective in removing bacteriophages compared with sand. A more than 4 log removal (=5.44) of MS2 was achieved in 100% Mg/Al LDH-coated sand. This study demonstrates the potential application of Mg/Al LDH for virus removal in water treatment.     

Optimization study of a hybrid alum coagulation-membrane filtration system for virus removal

Due to the intrinsically small sizes of enteric viruses (20-100 nm) and their relatively high resistance to most disinfectants, detection of viruses in treated drinking water is not a rare phenomenon. This study therefore evaluates various aspects involved in a hybrid alum coagulation-ultrafiltration (UF) system for virus removal. Coagulant doses (0, 1 and 10 mg Al(3+)/L) and pH conditions relevant to drinking water (pH 6-8) were investigated. With this hybrid system, removal was not attributable merely to MS2 adsorption to flocs and subsequent retention by UF membranes. MS2 removal comprises of inactivation by the effect of pH and coagulant and subsequently, rejection of virus-associated flocs by UF membrane. Coagulation with 1 mg Al(3+)/L at pH 6 and 7 resulted in an overall reduction brought about by an average of 0.62 log inactivation via the pH effect, 1.2 log inactivation by alum coagulant, and >5.4 log rejection by the 100 kDa polyethersulfone UF membrane. In contrast, negligible upstream inactivation was noted with a coagulant dose of 1 mg Al(3+)/L at pH 8, but 5.8 log rejection was attained with downstream UF filtration. By optimizing the conditions appropriate for upstream inactivation and subsequent membrane rejection, virus removal efficiencies can be enhanced.     

Efficiency of membrane processes for taste and odor removal.

The occurrence of tastes and odors (T&O) in drinking water is considered as one of the main problems by the drinking water companies. Thus, several treatment processes were developed over the years to control T&O including air stripping, activated carbon and oxidation using ozone. However, little information is available in the literature on the use of membranes for T&O removal. Therefore, the objectives of this paper are to present potential of membrane processes for removal of taste and odor causing compounds. Several membranes were tested including ultrafiltration (UF), UF combined with powdered activated carbon (PAC), nanofiltration (NF) and low pressure reverse osmosis (LP RO) membranes. The results of this study indicate that the combination of UF with PAC is effective for T&O control whereas the benefit of NF and LP RO remains unclear for T&O control.     

Virus removal in a membrane separation process

Recently, membrane technology has been considered an alternative to conventional water purification. To study the fate of viruses in membrane processes, indigenous coliphages in pilot scale membrane processes located in the eastern part of Tokyo Metropolitan area have been surveyed for 6 months. This plant used river water as its resource and had two microfiltration membrane processes which had different pore sizes (0.2 µm and 0.1 µm) and one ultrafiltration process which had 13,000 nominal molecular weight cut off. To detect indigenous coliphages, E. coli K12 F⁺(A/λ) and E. coli C were used as host bacteria. E. coli K12 F+(A/λ) can detect both DNA and RNA phages and E. coli C can only DNA phage. The resource water contained E. coli K12 phages at 200–1500 PFU/100 mL and the removal ratio of these DNA and RNA phages was lower than that of DNA phage by E. coli C in both MF membrane processes through 6 months. It is thought to be caused by difference of phage size, because DNA phage is bigger than RNA phage in general. The removal ratio of E. coli K12 and E. coli C phages reached 100% in the UF membrane process. According to the comparison of the concentration of phages in solution and eluted from suspended solid in resource and drain, it is thought that most phages concentrated in the drain were absorbed in suspended solids. To make certain of the removal ratio in UF and NF (nanofiltration) processes, high concentrations of coliphage Qβ and poliomyelitis virus vaccine were fed into these processes. The removal ratio of coliphage Qβ in UF and NF processes are 10⁻⁸³ and 10^−6.3 respectively, and the ratio of poliomyelitis virus vaccine in UF and NF are µ10^−6.7 and µ10^−7.3 respectively.     

Pharmaceutical rejection by membranes for wastewater reclamation and reuse.

Various membranes, which have different materials and nominal molecular weight cut-offs (MWCO), were compared in terms of rejection of ibuprofen and removal of effluent organic matter (EfOM) from membrane bioreactor (MBR), because pharmaceutical compounds contain a potential risk and EfOM is the precursor of carcinogenic disinfection by-products when reusing for drinking water source. To provide equivalent comparison with respect to hydrodynamic condition, mass transfer parameter, J0/k ratio, was used. A tight-UF membrane with a molecular weight cut off of 8,000 daltons exhibited 25 approximately 95% removal efficiencies of ibuprofen with a molecular weight of 206 with and without presence of EfOM(MBR). EfOM(MBR) caused the reduction of ibuprofen removal efficiency for UF membrane. Rejection of EfOM(MBR) by UF and NF membranes ranged 29 approximately 47% and 69 approximately 86%, respectively. UF membrane could successfully remove ibuprofen at lower J0/k ratio range (< or = 1) in organic free water but could not efficiently reject ibuprofen with a relatively hydrophilic EfOM(MBR) (SUVA < or = 3).     

Organic and detergent degradation in combined O3/UF for domestic laundry wastewater reclamation.

This paper focuses on the evaluation of organic and detergent degradation in a combined Ozone/UF system for domestic laundry wastewater reclamation. Formation of by-product was investigated by GC/MS for the reclaimed water. Ozone was injected into the raw wastewater in a 10 L contact tank and the wastewater was circulated through the membrane module for inner pressurized cross-flow filtration. The concentrate was returned back to the contact tank. The membrane used in this experiment was hollow fiber polysulfone UF membrane with MWCO 10,000. It has an effective filtration area of 0.06 m2. The experiment was carried out with intermittent ozone injection, 5 min injection and 10 min idling. Ozone was dosed at the concentration of 1.5 mg/L. The flux of the UF could be maintained at 0.24 m/d under filtration pressure 40-45 kPa and water temperature, 20-22 degrees C. The organic removal efficiency by the system was 90% in terms of COD. Ozone was considerably effective to degrade organics in the wastewater. Molecular weight of organics in the raw waste was mostly greater than 10,000 (72% of 950 mgCOD/L). However 86% of effluent COD (94-100 mg/L) was composed of organics smaller than MWCO 500 by ozone injection. No harmful by-products by ozone contact were detected from the analysis of treated water using GC/MS. It was identified that residual organics in the treated water were 1,1'-Oxybisbenzene, Octadecanoic acid, Squalene and Benzenmethanol, etc., which were additives contained originally in the detergent. Consequently the reclaimed water quality could be estimated safe enough to recycle for the rinsing cycle in a washing machine.     

Fouling and its reversibility in relation to flow properties and module design in aerated hollow fibre modules for membrane bioreactors.

Nowadays, most membrane bioreactors are using membranes submerged in the biomass and aeration in the concentrate compartment to limit or to control fouling. An important issue for the design of modules or membrane bundles in MBRs is to understand how the air/liquid flow is behaving and influencing fouling and its reversibility in relationship to the module properties. This paper focuses on an innovative and very specific process, in which HF membranes are put in a cartridge outside the activated sludge tank and a recycling loop is associated to the cartridge in order to decrease concentration of foulant species at the membrane surface and mass transfer resistance. Recycling operates with a very low liquid velocity in the module (a few cm.s(-1)) which constitutes a specificity of this process in terms of filtration operation. The aim of this study is to characterise two-phase flow and its effects on fouling and fouling reversibility at the scale of a semi-industrial bundle of outside/in hollow fibres, and as a function of bundle properties (packing density, fibre diameter), using specific methods to characterise the flow and fouling effects. Two modules were used showing a different packing density. Filtration was operated at constant permeate flux with clay suspension at 0.65 g.l(-1) in the same hydrodynamic conditions. Fouling kinetics and irreversibility were characterised by an adapted step method, and gas and liquid flows were characterised at global scale by residence time distribution analyses and gas hold-up. Fouling velocities are clearly influenced by gas velocity. The proportion of dead to total volume in the module is mainly affected by the liquid flow velocity and module design. The module with the higher fibre diameter and the lower packing density showed better performances in terms of fouling which was correlated with better flow properties.     

Addition of a magnetite layer onto a polysulfone water treatment membrane to enhance virus removal

The applicability of low-pressure membranes systems in distributed (point of use) water treatment is hindered by, among other things, their inability to remove potentially harmful viruses and ions via size exclusion. According to the USEPA and the Safe Drinking Water Act, drinking water treatment processes must be designed for 4-log virus removal. Batch experiments using magnetite nanoparticle (nano-Fe3O4) suspensions and water filtration experiments with polysulfone membranes coated with nano-Fe3O4 were conducted to assess the removal of a model virus (bacteriophage MS2). The membranes were coated via a simple filtration protocol. Unmodified membranes were a poor adsorbent for MS2 bacteriophage with less than 0.5-log removal, whereas membranes coated with magnetite nanoparticles exhibited a removal efficiency exceeding 99.99% (4-log). Thus, a cartridge of PSf membranes coated with nano-Fe3O4 particles could be used to remove viruses from water. Such membranes showed negligible iron leaching into the filtrate, thus obviating concern about coloured water. Further research is needed to reduce the loss of water flux caused by coating.     

Antibacterial properties of PES/CuCl(2) three-bore hollow fiber UF membrane

In this study, a three-bore polyethersulfone (PES) hollow fiber ultrafiltration (UF) membrane with antibacterial properties was prepared by phase inversion, using PES as the membrane material, N,N-dimethylacetamide (DMAC) as solvent, polyvinylpyrrolidone (PVP) and CuCl(2) as additives. The effect of CuCl(2) content on the water flux and rejection was studied and the antibacterial properties of PES hollow fiber UF membrane were also investigated. The water flux results indicated that the hydrophilic properties of PES UF membranes were improved after adding CuCl(2). The rejection of PVA-50000 was expected to drop slightly but remain high above 96%. The membranes showed good antibacterial activity against Escherichia coli (E. coli) after adding CuCl(2) and the antibacterial rate of PES/CuCl(2) UF membranes was close to 100% after running for 48 h. PES hollow fiber UF membranes with antibacterial properties were prepared through the formation of the water-soluble PVP/Cu(2+) complex with spatial network structure, which have good antibacterial and hydrophilic properties. Therefore, this study could provide an effective method for membrane antifouling.     

Performance of membrane bioreactors used for the treatment of wastewater from the chemical and textile industries.

Within the scope of the study, nine waste waters from the chemical and textile industries were treated in bench-scale (laboratory scale) and small-scale (pilot scale) membrane bioreactors. Depending on wastewater characteristics, the resulting performance varied significantly. It was observed that MBR effectiveness was determined primarily by the degree of biodegradability of the wastewater. In the course of several months of operation, no significant changes associated with the complete retention of the biomass by the membranes were observed. In some cases, it was possible to improve effluent quality by using smaller molecular separation sizes. The flux performance of the membrane modules was dependent on wastewater composition. Occasionally, non-degradable macromolecular substances concentrated in the bioreactor, resulting in strongly reduced filterability and flow performance of the membrane modules, consequently also reducing the economic viability of the process. The results demonstrate that wastewater-specific pilot tests are absolutely necessary, in particular if the technology is to be used for new applications.     

天然有机物引起的超滤膜污染研究进展

天然有机物(NOM)在多种地表环境介质中广泛存在。超滤(UF)膜有去除水体中胶体物质、部分细菌及病毒等优势,但NOM所带来的膜污染会限制UF技术广泛应用。在阐述天然有机物来源、特性及去除工艺的基础上,从亲疏水性能、分子量大小和表面荷电性能3方面,分析了NOM性质对超滤膜污染的影响。从优势污染物的确定、膜面有机污染物类型的解析、污染层形态特征的分析及微观相互作用力的表征4个层面,综述了天然有机物引起的超滤膜污染的研究现状,并对超滤膜污染机理研究的方向进行了展望。研究成果可为缓解NOM对UF膜的污染提供理论支撑。     

几种膜组件在管道直饮水处理系统中应用对比

膜处理是管道直饮水处理工艺的核心,介绍了微滤膜(MF)、超滤膜(UF)、纳滤膜(NF)、反渗透膜(RO)四种膜在管道直饮水处理系统中应用的对比,内容包括基本性能、去除杂质能力、工作压力以及出水电阻率等。结果显示,相比于其他三种膜,纳滤膜(NF)在直饮水处理工艺应用更具优势。     

Performance of ultrafiltration membrane process combined with coagulation/sedimentation.

Effects of coagulation/sedimentation as a pre-treatment on the dead-end ultrafiltration (UF) membrane process were studied in terms of membrane fouling and removal efficiency of natural dissolved organic matter, using Chitose River water. Two types of experiment were carried out. One was a bench scale membrane filtration with jar-test and the other was membrane filtration pilot plant combined with the Jet Mixed Separator (JMS) as a pre-coagulation/sedimentation unit. In the bench scale experiment, the effects of coagulant dosage, pH and membrane operating pressure on the membrane fouling and removal efficiency of natural dissolved organic matter were investigated. In the pilot plant experiment, we also investigated the effect of pre-coagulation/sedimentation on the membrane fouling and the removal efficiency of natural dissolved organic matter. Coagulation/sedimentation prior to membrane filtration process controlled the membrane fouling and increased the removal efficiency of natural dissolved organic matter.     

An integrated wastewater reuse concept combining natural reclamation techniques, membrane filtration and metal oxide adsorption.

In a Sino-German research project, a sustainable water reclamation concept was developed for different applications of municipal water reuse at the Olympic Green 2008 in Beijing, China. Results from pilot-scale experiments in Beijing and Berlin show that selective nutrient removal by adsorption onto granular ferric hydroxide (GFH) after a membrane bioreactor (MBR) can maintain a total phosphorus concentration of <0.03 microg L(-1) P, thus preventing eutrophication of artificial lakes. Operation time of GFH adsorption columns can be extended by regeneration using sodium hydroxide solution. A subsequent ultrafiltration (UF) membrane after bank filtration creates an additional barrier for pathogens and allows for further urban reuse applications such as toilet flushing. Short term bank / bio-filtration prior to UF is shown to effectively remove biopolymers and reduce membrane fouling.     

Membrane bioreactors for water reclamation.

Singapore has been using dual membrane technology (MF/UF RO) to produce high-grade water (NEWater) from secondary treated sewage. Membrane bioreactor (MBR) has very high potential and will lead to the further improvement of the productivity and quality of high-grade water. This study was focused on the technical feasibility of MBR system for water reclamation in Singapore, making a comparison between various membrane systems available and to get operational experience in terms of membrane cleaning and other issues. Three MBR plants were built at Bedok Water Reclamation Plant with a design flow of 300 m3/day each. They were commissioned in March 2003. Three different types of submerged membranes were tested. They are Membrane A, plate sheet membrane with pore size of 0.4 microm; Membrane B, hollow fibre membrane with pore size of 0.4 microm; and Membrane C, hollow fibre membrane with pore size of 0.035 microm. The permeate quality of all the three MBR Systems were found equivalent to or better than that of the conventional tertiary treatment by ultrafiltration. MBR permeate TOC was about 2 mg/l lower than UF permeate TOC. GC-MS, GC-ECD and HPLC scan results show that trace organic contaminants in MBR permeate and UF permeate were in the same range. MBR power consumption can be less than 1 kwh/m3. Gel layer or dynamic membrane generated on the submerged membrane surface played an important role for the lower MBR permeate TOC than the supernatant TOC in the membrane tank. Intensive chemical cleaning can temporarily remove this layer. During normal operation conditions, the formation of dynamic membrane may need one day to obtain the steady low TOC levels in MBR permeate.     

Analysing mass balance of viruses in a coagulation-ceramic microfiltration hybrid system by a combination of the polymerase chain reaction (PCR) method and the plaque forming units (PFU) method.

Virus removal experiments using river water spiked with bacteriophages were conducted by an in-line coagulation-ceramic microfiltration hybrid system to investigate the effects of filtration flux (62.5 and 125 L/(m2 x h)) and type of virus (Qbeta and MS2) on virus removal. In addition, the mass balance of viruses through the hybrid system was analysed by quantifying the infectious and inactive viruses by a combination of the polymerase chain reaction (PCR) method and the plaque forming units (PFU) method. Even when the system was operated at high filtration flux (125 L/(m2 x h)), high virus removal (> 6 log) with short coagulation time (2.4 s) was successfully achieved by dosing polyaluminium chloride (PACI) at more than 1.08 mg-Al/L. Removal performances were different between Qbeta and MS2, although their diameters are almost the same: greater virus removal was achieved for MS2 at PACI dosing of 0.54 mg-Al/L, and for Qbeta at PACI dosing of more than 1.08 mg-Al/L. The combination of the PCR and PFU methods revealed that two phenomena, adsorption to/entrapment in aluminium floc and virucidal activity of PACI, partially account for the high virus removal in the coagulation-MF hybrid system.     

Drinking water production by coagulation-microfiltration and adsorption-ultrafiltration

Microfiltration (MF) and ultrafiltration (UF) pilot plants were operated to produce drinking water from surface water from 1992 to 1996. Microfiltration was combined with pre-coagulation by polyaluminium chloride and was operated in a dead-end mode using hollow fiber polypropylene and monolith type ceramic membranes. Ultrafiltration pilot was operated in both cross-flow and dead-end modes using hollow fiber cellulose acetate membrane and was combined occasionally with powdered activated carbon (PAC) and granular activated carbon (GAC) adsorption. Turbidity in the raw water varied in the range between 1 and 100 mg/L (as standard Kaolin) and was removed almost completely in all MF and UF pilot plants to less than 0.1 mg/L. MF and UF removed metals such as iron, manganese and aluminium well. The background organics in the river water measured as KMnO₄ demand varied in the range between 3 and 16 mg/L. KMnO₄ demand decreased to less than 2 mg/L and to less than 3 mg/L on the average by the coagulation-MF process and the sole UF process, respectively. Combination of PAC or GAC adsorption with UF resulted in an increased removal of the background organics and the trihalomethanes formation potential as well as the micropollutants such as pesticides. Filtration flux was controlled in the range between 1.5 and 2.5 m/day with the trans-membrane pressure less than 100 kPa in most cases for MF and UF. The average water recovery varied from 99 to 85%.     

Membrane fouling and selectivity mechanisms in effluent ultrafiltration coupled with flocculation.

Membrane filtration is adequate for producing disinfected clear water suitable for various kinds of applications. However, fouling of membranes is the main limitation. The scope of the present study is to examine the effect of iron coagulation of primary wastewater effluent on membrane filtration, in parallel to fouling characterization of the iron itself. The fouling of ultrafiltration membranes by colloidal iron hydroxide-oxide has been studied by measuring the pore streaming potential of PES UF membrane. pH 5.5 (charge neutralization zone) provided better removal and lower fouling intensity than pH 7.8 (sweep coagulation zone), but the internal clogging at acidic pH was higher. Fouling of the membrane as measured by flux reduction was usually accompanied by a positive change in zeta potential and iso-electric point (IEP) of the membrane. An initially large change in zeta potential (without charge reversal) was seen even after relatively small amounts of iron solution were filtered through the membrane. A control experiment showed this is not due to iron adsorption equilibrium, but should probably be attributed to fouling. Change in zeta potential, can be used as an indicator for commencement of fouling even for small flux reductions. UF membrane critical flux after iron filtration can be evaluated more accurately by zeta potential than pressure drop or change in iron concentration.     

不同孔径平板膜对景观水体水质控制效果的试验研究

为研究平板膜处理景观水体的特性,采用孔径为0.1 μm、0.2μm和0.3μm平板膜处理景观水体用水.结果表明,三种膜对悬浮物和藻类有很好的去除效果,去除率都在95％以上,对于溶解态的N、P去除效果不好;三种膜处理效果相比较,孔径最小的0.1μm膜对各种污染物去除效果最好;在过滤不同污染物配水时,0.1μm膜的膜通量下降速率最慢,稳定后较0.2μm和0.3μm膜的膜通量大;通过对污染物的粒径分析和膜表面污染物分析认为,景观水体中,主要污染物对膜通量的影响顺序为:腐殖酸＞藻＞悬浮物;150 nm是景观水体中污染物质粒径的分界点,污染物质粒径主要集中在150 nm以上;与0.2μm、0.3μm膜相比,0.1μm膜抗污染能力更强,更适合用来处理景观水体用水.