Nanofiltration and reverse osmosis of model process waters fromthe dairy industry to produce water for reuse

In dairy plants the process waters generated during the starting, equilibrating, interrupting and rinsing steps contribute to the production of effluents. They correspond to milk products (milk, whey, cream) diluted with water without chemicals. The treatment of these dairy process waters by nanofiltration (NF) or reverse osmosis (RO) operations was proposed to concentrate dairy matter and to produce purified water for reuse in the dairy plant. The study reports one-stage and two-stage (NF + RO and RO + RO) spiral-wound membrane treatments with five model process waters representative of the main composition variations observed in dairies. Performances (permeate flux, milk components rejection, purified water characteristics) of the different operations were compared. Discussion was focused on the comparison between quality of produced waters and vapour condensates (from product drying and evaporation processes) reused in dairy plants. Accordingly, both total organic carbon (TOC) and conductivity of water treated by a single RO or NF + RO operations were convenient for reuse as heating, cooling, cleaning and boiler feed water. With the two-stage RO + RO process, a more purified water complying with the TOC drinking water limit was achieved.     

Critical flux analyses on differently pretreated olive vegetation waste water streams: Some case studies

One of the main disadvantages of batch membrane processes is the increase of the pollutant concentration in the feedstock throughout the operation. Operating the plant at constant process conditions leads in many cases to weaker performances and, moreover, to heavy fouling on the membranes. Critical flux-based methods are one of the most used approaches to overcome fouling problems. Within critical flux conditions, only reversible fouling can occur, which can be periodically soft-cleaned.This work studies the relationship between particle size distributions in the feed stream and critical flux values when different pretreatment processes are applied to an olive vegetation waste water stream. The considered pretreatment processes were: coagulation (with aluminum hydroxide and aluminum sulphate), aerobic biodigestion (by means of fungi) and photocatalytic organic matter reduction (by means of nanometric titanium dioxide anatase powders irradiated by UV light). The study was carried out at pilot plant scale (100 L batch capacity).These results were compared with performances and effects on the critical flux value for MF, UF and NF membranes. The different pretreatment on the same waste water stream shifts differently the particle size distribution mainly by organic matter degradation, and this influences heavily the critical flux value and thus the filtration outcome.Finally, the purification of the olive vegetation waste water stream can be performed with a MF, UF, NF and RO membrane system in series, being very careful in choosing the correct operating conditions to avoid the quick formation of an unsustainable fouling.     

A comprehensive review of nanofiltration membranes:Treatment, pretreatment, modelling, and atomic force microscopy

Nanofiltration membranes (NF) have applications in several areas. One of the main applications has been in watertreatment for drinking water production as well as wastewater treatment. NF can either be used to treat all kinds of water including ground, surface, and wastewater or used as a pretreatment for desalination. The introduction of NF as a pretreatment is considered a breakthrough for the desalination process. NF membranes have been shown to be able to remove turbidity, microorganisms and hardness, as well as a fraction of the dissolved salts. This results in a significantly lower operating pressure and thus provides a much more energy-efficient process. Similar to other membrane processes, a major problem in NF membrane applications is fouling. Several studies have investigated the mechanisms of fouling in NF membranes and suggested methods to minimize and control the fouling of NF membranes. For NF membrane characterizations and process prediction, modeling of NF processes and the use of atomic force microscopy (AFM) are very important. The ability to predict the performance of NF processes will lead to a lower number of experiments, saving of time and money, and help to understand the separation mechanisms during NF. A comprehensive review of NF in water treatments is presented including a review of the applications of NF in treating water as well as in the pretreatment process for desalination; the mechanism as well as minimization of NF membrane fouling problems; and theories for modelling and transport of salt, charged and noncharged organic compounds in NF membranes. The review will also address the application of AFM in studying the morphology of membrane surfaces as part of the NF membrane characterization.     

Nanofiltration for drinking water treatment: a review

In recent decades, nanofiltration (NF) is considered as a promising separation technique to produce drinking water from different types of water source. In this paper, we comprehensively reviewed the progress of NF-based drinking water treatment, through summarizing the development of materials/fabrication and applications of NF membranes in various scenarios including surface water treatment, groundwater treatment, water reuse, brackish water treatment, and point of use applications. We not only summarized the removal of target major pollutants (e.g., hardness, pathogen, and natural organic matter), but also paid attention to the removal of micropollutants of major concern (e.g., disinfection byproducts, per- and polyfluoroalkyl substances, and arsenic). We highlighted that, for different applications, fit-for-purpose design is needed to improve the separation capability for target compounds of NF membranes in addition to their removal of salts. Outlook and perspectives on membrane fouling control, chlorine resistance, integrity, and selectivity are also discussed to provide potential insights for future development of high-efficiency NF membranes for stable and reliable drinking water treatment.     

Application of hybrid coagulation–microfiltration process for treatment of membrane backwash water from waterworks

A coagulation–microfiltration (MF) system was studied to treat the discharged membrane backwash water (MBW) to meet the drinking water quality requirements. The values of dissolved organic carbon (DOC) and trihalomethanes formation potential (THMFP) in MBW were higher than those in Luan River water (LRW, the raw water for a pilot-scale membrane plant, which produced MBW used in this study), and organic matter enriched in MBW distributed mainly in molecular weight (MW) > 10k Da. When 15 mg FeCl₃/L and 15 mg/L powdered activated carbon (PAC) were added into the system, the average concentration of DOC was reduced from 5.731 mg/L in MBW to 3.377 mg/L in the treated water, and the average UV₂₅₄ was reduced from 0.047 to 0.030 cm⁻¹. The removal of organic matter was main in the range of MW > 30k Da. Efficient organic removal by the hybrid coagulation–MF system resulted in significant reduction of THMFP in the treated water. Concentrations of trihalomethanes, turbidity, bacteria and coliforms in the treated water were below the limit value of the drinking water standards. The results show that the treated water from MBW is with satisfactory organic and microbiological quality.     

长江下游原水臭氧-生物活性炭深度处理效果及有机物特性变化

以长江下游镇江征润洲段为原水,利用中试装置研究臭氧-生物活性炭(O3-BAC)组合工艺优化运行及其对有机物特性变化的影响。结果表明:当调整主臭氧投加量为2.5 mg/L时,深度处理工艺对CODMn、NH4^+-N和两类消毒副产物前体物(TTHMFP、THAAFP)的去除率分别为68.5%、86.7%、57.3%和48.9%;同时,从净水过程中有机物特性变化对消毒副产物影响的角度,提出应将强疏水性小分子有机物作为镇江市饮用水处理的控制主体。     

Nanofiltration flux, fouling and retention in filtering dilute model waters

Fouling of membranes decreases the applicability of the nanofiltration (NF) process, and thus a deeper understanding of membrane fouling is needed. Fouling and retention of different NF membranes by model feed waters was investigated in a laboratory-scale filtration unit. The model waters were composed so as to imitate the characteristics of chemically pre-treated surface water. No differences were seen in membrane flux declines when filtering feed waters containing the studied organic compounds of different characteristics. However, organic matter containing feed waters resulted in remarkably lower flux than the metal ions containing feed waters. An additional decrease in flux was seen when both organic matter and metal ions,especially silica, were present in the feed water. An increased feed water organics concentration increased the retention of organic matter, but the addition of metal ions to organics containing feed water caused a decrease in the retention of both organic matter and conductivity. The different behaviour is most probably caused by the differences in the fouling layers and foulant characteristics as well as by the electroneutrality effect. Generally, it is difficult to change feed water composition to non-fouling, but the operating pH can be used to some extent in optimising membrane performance.     

天然沸石与纳滤组合工艺处理铜突发污染的应用

纳滤工艺被广泛应用于分散式饮用水深度处理,能解决饮用水苦咸化,盐碱化或微污染等常规水处理工艺无法规避的用水风险,在长时间运行过程中还能有效应对重金属等突发污染风险。但重金属污染易加重纳滤膜污染,需要增设预处理装置加以缓冲,实现纳滤装置的长久稳定运行。而天然沸石具有良好的筛分性能和吸附性能,能够有效缓冲重金属对纳滤装置的冲击。试验以重金属铜为例,证明水中铜离子会造成纳滤不可逆污染比例增加,不利于系统稳定运行;天然沸石对铜离子有很好的吸附效果,静态吸附试验表明天然沸石对水中铜离子的最大吸附量为3.03 mg/g,通过正交试验合理设计吸附预处理,能够有效为纳滤工艺提供安全进水,保证纳滤进水铜离子浓度低于10 mg/L。实践工艺中,吸附预处理能有效缓解纳滤膜不可逆污染,而且吸附-纳滤组合工艺对铜离子及部分其他重金属离子表现出良好的处理效果。     

Membrane performance in combined processes including ozonation or advanced oxidation, powdered activated carbon and coagulation — Investigations in pilot scale

In Luxembourg the largest drinking water production plant treating reservoir water with conventional technology including ozonation is in operation since 1969. Its maximum capacity is 64,000 m³/d. After 40 years of operation the need for both modernizing and extension of capacity to 100,000 m³/d emerged. Nowadays, due to new developments in technology and research it is possible to assess the water treatment processes more effectively with regard to current and future requirements. Against this background, membrane processes combined with conventional and advanced processes were identified as potential option and long term pilot-scale tests were started in June 2008. Different treatment process schemes all including membranes are investigated in a one year pilot plant period. Various treatment steps such as different pre- and post-treatment steps, various membranes and membrane materials and also conventional treatment steps are compared and assessed.     

磁性离子交换树脂强化水源中有机物去除性能研究

在调查某水厂水源水质及传统工艺处理效能的基础上,对比探讨了粉末活性炭和磁性离子交换树脂分别以预吸附、预吸附-混凝、混凝沉淀-吸附等不同工艺对水源水中溶解性有机物的去除效能,确定了最佳工艺。该水源存在季节性有机物污染,亲水性有机质占比80%。水厂传统工艺对有机物的去除能力约20%~30%。与其他工艺相比,树脂预吸附-混凝对有机物的去除功效最好,DOC和UV254的去除率分别达到41.48%和80.0%,与单独强化混凝相比,该工艺可将DOC和UV254的去除效率分别提高17.7和35.49个百分点,且可减少86.67%的混凝剂投加量。Langmuir等温线模型和拟二级动力学方程可定量描述树脂吸附有机物平衡和动力学。磁性离子交换树脂预吸附可作为该水厂强化去除水源中溶解性有机物的可靠技术。     

天然有机物对国产纳滤膜的污染及清洗效果研究

为考察水体中天然有机物(NOM)对纳滤膜性能产生的影响,以腐殖酸(HA)、牛血清蛋白(BSA)和海藻酸钠(SA)分别模拟水中常见NOM,腐殖质、蛋白质和多糖,对国产NF-1812纳滤膜进行单组分及其混合物定性定量有机污染及清洗实验。结果表明,有机污染造成膜通量下降,膜污染程度为SA>HA>BSA;NOM截留率可稳定在99.2%~99.6%;膜污染阻力主要为浓差极化阻力,其次是凝胶层阻力和内部污染阻力,有机污染液综合黏度和综合含量越大,浓差极化阻力的比例越高;对多组分有机污染膜进行错流速度9 cm/s的物理水力清洗和pH=10.0的质量分数分别为0.1%的NaOH+0.025%Na-SDS化学药剂清洗,膜通量、NOM截留率、苦咸水截留率、SEM成像均恢复至原膜状态,纳滤膜清洗效果良好,适用于中国西北苦咸水地区。     

膜生物反应器用于微污染地表水处理的中试研究

引言 地表水作为主要的饮用水源水,其日益严重的污染问题给传统的水处理工艺带来巨大挑战.将膜生物反应器(MBR)应用于微污染水处理,进行饮用水制备是解决上述问题的一项新技术[1].向MBR内投加粉末活性炭(PAC)所形成的MBR-PAC组合工艺集物理吸附、生物净化和膜分离于一体,具有良好的污染物去除能力.目前,将MBR作为微污染水处理主体工艺的研究并不多见.香港大学的李晓岩等[2]研究证实MBR组合工艺处理微污染水效果良好.清华大学的莫罹等[3]也进行了类似的研究.但均限于小试试验,并且对相应的膜污染问题关注不多.     

Electrodialysis in an Integrated NF/ED Process for Water Recovery in the Leather Industry

Electrodialysis (ED) was assessed for integration in a nanofiltration NF/ED sequence for water reuse in the leather industry. Two ED feeds composed of different model solutions were used: Model Solution FED1, which is a surrogate of a nanofiltration permeate generated by the NF processing of a biologically treated leather effluent, and Model Solution FED2, which has the same salt concentration as FED1 but with an organic matter content that is approximately ten times higher. The electrodialysis experiments were carried out in a five-compartment bench cell using cationic and anionic membranes HDX 100 and HDX 200. The final product water, with a conductivity ranging from 3.28 to 3.67 mS cm^?1, can be reused as process water for beamhouse operations. With respect to chloride and COD parameters, the ED product water meets the requirements of process water, even for dyeing operations. An alkaline membrane cleaning process for fouling removal was also tested for the membranes using Model Solution FED2. The cleaned membranes were evaluated in terms of visual aspect, polarization curves, TGA, and SEM/EDS analysis. The results obtained with the cleaned membranes were very similar to those obtained with the new ones in ED experiments with Model Solution FED2.     

Direct drinking water treatment by spiral-wound ultrafiltration membranes

This paper presents the results of a research on direct drinking water treatment through an ultrafiltration pilot plant unit using spiral-wound membranes (3500 MWCO). The source of water is the Guarapiranga Reservoir, an eutrophicated water body located in the metropolitan region of São Paulo, Brazil. The data were collected during a period of almost 3400 h, from August 2005 to January 2006. The main objective of the study was to evaluate the membrane production capacity and contaminant removal efficiency. It was verified that the system was able to produce a high quality permeate with a flow close to the specified by the membrane manufacturer. The average permeate flow was 19.7 L.h⁻¹.m⁻², at 467 kPa and 25°C, with a global water recovery of almost 85%. The removal efficiencies for TOC, UV light absorption, and turbidity were 85%, 56%, and 95%, respectively. The results provide substantial evidence of the technical feasibility of spiral-wound UF membranes for direct drinking water treatment from euthrophicated sources, as an alternative for conventional drinking water treatment systems.     

Huangpu River water treatment by microfiltration with ozone pretreatment

With the promulgation of more stringent regulations to guarantee the quality of drinking water, low pressure membrane processes are nowadays considered for surface water treatment. But these membranes are sensitive to fouling. In this study ozone is introduced to pretreatment for membrane filtration to get a high quality permeate and improve membrane performance. The organic matter characteristics, such as AMWD of organic matter, hydrophilic/hydrophobic fractions were studied with ozone oxidation. Results show that for Huangpu River water, ozone oxidation offers high percentage of UV absorbance removal than DOC removal. Highest removal of DOC and UV₂₅₄ of 10% and 71% respectively were observed. The dominant organic matter oxidized by ozone was 2-7.0 kDa in terms of molecule distribution investigation. Ozone oxidizes more hydrophobic fraction to hydrophilic one. Changes of organic matter composition improved membrane flux. There is the optimal dosage with ozone of 1.5 mgO₃/L made membrane flux maximum during 0.5-3.0 mgO₃/L ozone dosage. Ozone oxidization provided degradation of macromolecule organic matter, which is responsible to membrane fouling, to small molecule organic substance. Study about the chemical cleaning of the fouled membrane also supports the point that membrane fouling is produced by the organic substance with high molecule weight.     

Optimization of Chemical Cleaning for Improvement of Membrane Performance and Fouling Control in Drinking Water Treatment

A pilot-scale study using a ZeeWeed^® 1000 membrane pilot plant was conducted to optimize the use of sodium hypochlorite (NaClO) and citric acid for membrane permeability recovery and membrane fouling control in drinking water treatment. Backwash was the most effective strategy for permeability recovery and under the same NaClO dose, a lower concentration combined with a longer soak time achieved a higher permeability recovery. Organics were the major foulants responsible for permeability decrease. Inorganic foulants surprisingly increased after NaClO cleaning. Similarly, a lower pH was more effective in permeability recovery than a higher concentration of citric acid.     

Cobalt(III) EDTA complex removal from aqueous alkaline borate solutions by nanofiltration

At the PWR Paks diluted low-level radioactive waste water (LLW) contains the long-lived ⁶⁰Co isotope in EDTA complex form, which has no simple separation procedure. In this research nanofiltration(NF) was studied for selective removal of the cobalt(III) EDTA complex from a drain waste water model solution, which contains mainly sodium borate at an alkaline pH. A suitable NF membrane was chosen to separate the cobalt complex from the borate solution. The NF experiments were performed at constant temperature (25°C) and pressure range 1-10 bar. The cobalt complex and the borate ion rejection (R) as well as the permeate flux of the membrane was investigated as a function of pH. The rejection of the cobalt(III) EDTA complex ion and especially the borate were strongly pH dependent. The rejection of the complex ion and the borate was increased at alkaline pH (at pH 8, R = 73%; at pH 11.5, R = 96% for the cobalt complex; at pH 8, R = 7%; at pH 11.5, R = 59% for borate). NF seems to be a suitable separation method for the removal of the Co(III) EDTA complex from nuclear power plant waste streams. The removal of the cobalt complex ion from an alkaline borate solution by NF is possible in two ways: at slightly alkaline pH by a two-step separation, or at a more alkaline pH (pH > 9.5) by a one-step separation.     

纳滤膜的制备与应用

目前,纳滤膜应用于饮用水处理行业已引起业界广泛的关注与研究。纳滤膜是一种介于反渗透膜与超滤膜之间的水处理膜,有着较高的渗透和截留性能;纳滤膜一方面能截留水体中大部分的微量污染物质,另一方面保留水体中对人体有益的矿物质。文中主要讨论了纳滤膜的制备方法、分离机理、表征方法、污染以及在饮用水方面的应用和所面临的瓶颈,并探讨了纳滤膜技术今后的发展工作。可以看出,纳滤膜在饮用水处理领域有着广阔的应用前景。     

COD Removal from Concentrated Wastewater Using Membranes

Membranes can be used for wastewater treatment. The selection of the appropriate membrane depends on a number of factors, such as waste characteristics, nature of materials present in the wastewater, concentration, temperature, pH, etc. If the wastewater contains low molecular weight organics, reverse osmosis (RO) is the best treatment process. RO membranes allow solvent (water) to pass and prevent the transport of organics, either completely or partially. In this study, raw wastewater from an alcohol manufacturing plant was treated using a RO process. The chemical oxygen demand (COD) of the wastewater was between 35000-40000 mg/l due to the presence of organic components. Eight polymeric membranes (e.g. FT30, PVD, DSII, DS, BW30, 37100, 3750 and NF45) were used in total. None of the membranes were able to reduce COD to a desirable level (i.e. less than 200 mg/l) in one step. However a two-step process could be designed for wastewater treatment. Based on data obtained for flux and rejection, the NF45 nanofiltration membrane exhibited the best performance. A high volume of fluid can pass through the NF45 membrane because of its high porosity. The flux of this membrane (i.e. 15 kg/m².h) was higher than the reverse osmosis membranes tested. The NF45 membrane decreased COD to a greater extent than the other membranes tested (52%). While the PVD membrane showed better efficiency compared to the other reverse osmosis membranes, probably because of its material of construction and configuration.     

Ultrafiltration and nanofiltration membranes applied to the removal of the pharmaceuticals amoxicillin,naproxen, metoprolol and phenacetin from water

BACKGROUND: In the removal of pharmaceuticals present in aquatic systems by membrane processes, some important issues must be explored in order to obtain a better knowledge of the global process. Among these issues, a better understanding of the influences of the operating parameters on the membrane flux, an analysis of membrane resistances and fouling, and determination of the removal of specific substances, must be studied. RESULTS: Four selected pharmaceuticals (amoxicillin, naproxen, metoprolol and phenacetin) were subjected to ultrafiltration (UF) and nanofiltration (NF) processes for their removal from several water matrices. The determined permeate fluxes at the steady state were affected by the main operating conditions: molecular weight cut‐off (MWCO) of the membrane, transmembrane pressure TMP, cross‐flow velocity and temperature. The retention coefficients with the UF membranes followed the sequence naproxen > metoprolol > amoxicillin > phenacetin, and with the NF membranes, followed the trend: amoxicillin > naproxen > metoprolol > phenacetin, due to the role of other mechanisms such as size exclusion and electrostatic repulsion. In the case of the selected water matrices, the retention coefficient was referred to some quality parameters (total organic carbon, chemical oxygen demand and absorbance at 254 nm), leading to moderate (UF) or high (NF) removals of the organic matter content. CONCLUSIONS: The NF CK membrane achieved the highest retention of these pharmaceuticals (excepting phenacetin), and provided retentions for quality parameters around 80% in the four water systems tested. Copyright © 2011 Society of Chemical Industry