Engineering application of membrane bioreactor for wastewater treatment in China: Current state and future prospect

China has been the forerunner of large-scale membrane bioreactor （MBR） application. Since the first large-scale MBR （≥ 10 000 m^3·d^-1） was put into operation in 2006, the engineering implementation of MBR in China has attained tremendous development. This paper outlines the commercial application of MBR since 2006 and provides a variety of engineering statistical data, covering the fields of municipal wastewater, industrial wastewater, and polluted surface water treatment. The total treatment capacity of MBRs reached 1× 10^6 m^3·d^-1 in 2010, and has currently exceeded 4.5 × 10^6 m^3·d^-1 with -75% of which pertaining to municipal wastewater treatment. The anaerobic/anoxic/aerobie-MBR and its derivative processes have been the most popular in the large-scale municipal application, with the process features and typical ranges of parameters also presented in this paper. For the treatment of various types of industrial wastewater, the configurations of the MBR-based processes are delineated with representative engineering cases. In view of the significance of the cost issue, statistics of capital and operating costs are also provided, including cost structure and energy composition. With continuous stimulation from the environmental stress, political propulsion, and market demand in China, the total treatment capacity is expected to reach 7.5 × 10^6 m^3·d^-1 by 2015 and a further expansion of the market is foreseeable in the next five years. However, MBR application is facing several challenges, such as the relatively high energy consumption. Judging MBR features and seeking suitable application areas should be of importance for the long-term development of this technology.     

膜生物反应器投加PAC处理生活污水效能的试验

在一体式MBR系统中投加少量的粉末活性炭，运行效果良好，并且可以很好地降低膜污染。粉末活性炭在形成生物活性炭后，对难降解有机物具有很好的降解能力；NH4^ -N的去除率得到进一步提高，NO3^-的含量升高；但反硝化作用不明显，致使总氮去除率不高；生物活性炭很好地吸附并降解了易引起膜污染的有机物，改变了污泥的性质，对膜组件起到了很好的保护作用。     

Excitation-emission matrix (EEM) fluorescence spectroscopy for characterization of organic matter in membrane bioreactors: Principles,methods and applications

• Principles and methods for fluorescence EEM are systematically outlined. • Fluorophore peak/region/component and energy information can be extracted from EEM. • EEM can fingerprint the physical/chemical/biological properties of DOM in MBRs. • EEM is useful for tracking pollutant transformation and membrane retention/fouling. • Improvements are still needed to overcome limitations for further studies. The membrane bioreactor (MBR) technology is a rising star for wastewater treatment. The pollutant elimination and membrane fouling performances of MBRs are essentially related to the dissolved organic matter (DOM) in the system. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy, a powerful tool for the rapid and sensitive characterization of DOM, has been extensively applied in MBR studies; however, only a limited portion of the EEM fingerprinting information was utilized. This paper revisits the principles and methods of fluorescence EEM, and reviews the recent progress in applying EEM to characterize DOM in MBR studies. We systematically introduced the information extracted from EEM by considering the fluorescence peak location/intensity, wavelength regional distribution, and spectral deconvolution (giving fluorescent component loadings/scores), and discussed how to use the information to interpret the chemical compositions, physiochemical properties, biological activities, membrane retention/fouling behaviors, and migration/transformation fates of DOM in MBR systems. In addition to conventional EEM indicators, novel fluorescent parameters are summarized for potential use, including quantum yield, Stokes shift, excited energy state, and fluorescence lifetime. The current limitations of EEM-based DOM characterization are also discussed, with possible measures proposed to improve applications in MBR monitoring.     

Influence of aeration intensity on the performance of A/O-type sequencing batch MBR system treating azo dye wastewater

Among the numerous parameters affecting the membrane bioreactor (MBR) performance, the aeration intensity is one of the most important factors. In the present investigation, an anoxic/aerobic-type (A/O-type) sequencing batch MBR system, added anoxic process as a pretreatment to improve the biodegradability of azo dye wastewater, was investigated under different aeration intensities and the impact of the aeration intensity on effluent quantity, sludge properties, extracellular polymeric substances (EPS) amount generated as well as the change of permeation flux were examined. Neither lower nor higher aeration intensities could improve A/O-type sequencing batch MBR performances. The results showed 0.15 m³·h^-1 aeration intensity was promising for treatment of azo dye wastewater under the conditions examined. Under this aeration intensity, chemical oxygen demand (COD), ammonium nitrogen and color removal as well as membrane flux amounted to 97.8%, 96.5%, 98.7% and 6.21 L·m^-2·h^-1, respectively. The effluent quality, with 25.0 mg·L^-1COD, 0.84 mg·L^-1 ammonium nitrogen and 8 chroma, could directly meet the reuse standard in China. In the meantime, the sludge relative hydrophobicity, the bound EPS, soluble EPS and EPS amounts contained in the membrane fouling layer were 70.3%, 52.0 mg·g^-1VSS, 38.8 mg·g^-1VSS and 90.8 mg·g^-1VSS, respectively, which showed close relationships to both pollutant removals and membrane flux.     

Comparison of CNT-PVA membrane and commercial polymeric membranes in treatment of emulsified oily wastewater

CNT-PVA membrane was fabricated and compared with polymeric membranes. The separation performance was evaluated by homemade and cutting fluid emulsions. The three membranes show similar oil retention rates. CNT-PVA membranes have higher permeation fluxes compared with polymeric membranes. CNT-PVA membrane shows higher fouling resistance. Membrane separation is an attractive technique for removal of emulsified oily wastewater. However, polymeric membranes which dominate the current market usually suffer from severe membrane fouling. Therefore, membranes with high fouling resistance are imperative to treat emulsified oily wastewater. In this study, carbon nanotube-polyvinyl alcohol (CNT-PVA) membrane was fabricated. And its separation performance for emulsified oily wastewater was compared with two commercial polymeric membranes (PVDF membrane and PES membrane) by filtration of two homemade emulsions and one cutting fluid emulsion. The results show that these membranes have similar oil retention efficiencies for the three emulsions. Whereas, the permeation flux of CNT-PVA membrane is 1.60 to 3.09 times of PVDF membrane and 1.41 to 11.4 times of PES membrane, respectively. Moreover, after five consecutive operation circles of filtration process and back flush, CNT-PVA membrane can recover 62.3% to 72.9% of its initial pure water flux. However, the pure water flux recovery rates are only 24.1% to 35.3% for PVDF membrane and 6.0% to 26.3% for PES membrane, respectively. Therefore, CNT-PVA membrane are more resistant to oil fouling compared with the two polymeric membranes, showing superior potential in treatment of emulsified oily wastewater.     

Metabolic uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide addition for sludge reduction and fouling control in a gravity-driven membrane bioreactor

• Effects of metabolic uncoupler TCS on the performances of GDMBR were evaluated. • Sludge EPS reduced and transformed into dissolved SMP when TCS was added. • Appropriate TCS increased the permeability and reduced cake layer fouling. • High dosage aggravated fouling due to compact cake layer with low bio-activity. The gravity-driven membrane bioreactor (MBR)system is promising for decentralized sewage treatment because of its low energy consumption and maintenance requirements. However, the growing sludge not only increases membrane fouling, but also augments operational complexities (sludge discharge). We added the metabolic uncoupler 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to the system to deal with the mentioned issues. Based on the results, TCS addition effectively decreased sludge ATP and sludge yield (reduced by 50%). Extracellular polymeric substances (EPS; proteins and polysaccharides) decreased with the addition of TCS and were transformed into dissolved soluble microbial products (SMPs) in the bulk solution, leading to the break of sludge flocs into small fragments. Permeability was increased by more than two times, reaching 60–70 L/m²/h bar when 10–30 mg/L TCS were added, because of the reduced suspended sludge and the formation of a thin cake layer with low EPS levels. Resistance analyses confirmed that appropriate dosages of TCS primarily decreased the cake layer and hydraulically reversible resistances. Permeability decreased at high dosage (50 mg/L) due to the release of excess sludge fragments and SMP into the supernatant, with a thin but more compact fouling layer with low bioactivity developing on the membrane surface, causing higher cake layer and pore blocking resistances. Our study provides a fundamental understanding of how a metabolic uncoupler affects the sludge and bio-fouling layers at different dosages, with practical relevance for in situ sludge reduction and membrane fouling alleviation in MBR systems.     

Energy reduction of a submerged membrane bioreactor using a polytetrafluoroethylene (PTFE) hollow-fiber membrane

The fiber length and packing density of the PTFE membrane element were increased. The MBR was stably operated under an SAD^m of 0.13 m³·m^-2·hr^-1. Specific energy consumption was estimated to be less than 0.4 kWh·m^-3. In this study, we modified a polytetrafluoroethylene (PTFE) hollow-fiber membrane element used for submerged membrane bioreactors (MBRs) to reduce the energy consumption during MBR processes. The high mechanical strength of the PTFE membrane made it possible to increase the effective length of the membrane fiber from 2 to 3 m. In addition, the packing density was increased by 20% by optimizing the membrane element configuration. These modifications improve the efficiency of membrane cleaning associated with aeration. The target of specific energy consumption was less than 0.4 kWh·m^-3 in this study. The continuous operation of a pilot MBR treating real municipal wastewater revealed that the MBR utilizing the modified membrane element can be stably operated under a specific air demand per membrane surface area (SAD_m) of 0.13 m³·m^-2·hr^-1 when the daily-averaged membrane fluxes for the constant flow rate and flow rate fluctuating modes of operation were set to 0.6 and 0.5 m³·m^-2·d^-1, respectively. The specific energy consumption under these operating conditions was estimated to be less than 0.37 kWh·m^-3. These results strongly suggest that operating an MBR equipped with the modified membrane element with a specific energy consumption of less than 0.4 kWh·m^-3 is highly possible.     

Ceramic membrane fouling mechanisms and control for water treatment

● The fouling is summarized based on ceramic membrane performance and pollutants. ● The current research methods and theoretical models are summarized. ● The membrane fouling control methods and collaborative technology are reviewed. Membrane separation, as an important drinking water treatment technology, has wide applications. The remarkable advantages of ceramic membranes, such as chemical stability, thermal stability, and high mechanical strength, endow them with broader prospects for development. Despite the importance and advantages of membrane separation in water treatment, the technique has a limitation: membrane fouling, which greatly lowers its effectiveness. This is caused by organics, inorganic substances, and microorganisms clogging the pore and polluting the membrane surface. The increase in membrane pollution greatly lowers purification effectiveness. Controlling membrane fouling is critical in ensuring the efficient and stable operation of ceramic membranes for water treatment. This review analyzes four mechanisms of ceramic membrane fouling, namely complete blocking, standard blocking, intermediate blocking, and cake filtration blocking. It evaluates the mechanisms underlying ceramic membrane fouling and summarizes the progress in approaches aimed at controlling it. These include ceramic membrane pretreatment, ceramic membrane surface modification, membrane cleaning, magnetization, ultrasonics, and nanobubbles. This review highlights the importance of optimizing ceramic membrane preparation through further research on membrane fouling and pre-membrane pretreatment mechanisms. In addition, combining process regulations with ceramic membranes as the core is an important research direction for ceramic membrane-based water treatment.     

Enhanced cross-flow filtration with flat-sheet ceramic membranes by titanium-based coagulation for membrane fouling control

• Ceramic membrane filtration showed high performance for surface water treatment. • PTC pre-coagulation could enhance ceramic membrane filtration performance. • Ceramic membrane fouling was investigated by four varied mathematical models. • PTC pre-coagulation was high-effective for ceramic membrane fouling control. Application of ceramic membrane (CM) with outstanding characteristics, such as high flux and chemical-resistance, is inevitably restricted by membrane fouling. Coagulation was an economical and effective technology for membrane fouling control. This study investigated the filtration performance of ceramic membrane enhanced by the emerging titanium-based coagulant (polytitanium chloride, PTC). Particular attention was paid to the simulation of ceramic membrane fouling using four widely used mathematical models. Results show that filtration of the PTC-coagulated effluent using flat-sheet ceramic membrane achieved the removal of organic matter up to 78.0%. Permeate flux of ceramic membrane filtration reached 600 L/(m²·h), which was 10-fold higher than that observed with conventional polyaluminum chloride (PAC) case. For PTC, fouling of the ceramic membrane was attributed to the formation of cake layer, whereas for PAC, standard filtration/intermediate filtration (blocking of membrane pores) was also a key fouling mechanism. To sum up, cross-flow filtration with flat-sheet ceramic membranes could be significantly enhanced by titanium-based coagulation to produce both high-quality filtrate and high-permeation flux.     

A critical review on thermodynamic mechanisms of membrane fouling in membrane-based water treatment process

● Fundamentals of membrane fouling are comprehensively reviewed. ● Contribution of thermodynamics on revealing membrane fouling mechanism is summarized. ● Quantitative approaches toward thermodynamic fouling mechanisms are deeply analyzed. ● Inspirations of thermodynamics for membrane fouling mitigation are briefly discussed. ● Research prospects on thermodynamics and membrane fouling are forecasted. Membrane technology is widely regarded as one of the most promising technologies for wastewater treatment and reclamation in the 21st century. However, membrane fouling significantly limits its applicability and productivity. In recent decades, research on the membrane fouling has been one of the hottest spots in the field of membrane technology. In particular, recent advances in thermodynamics have substantially widened people’s perspectives on the intrinsic mechanisms of membrane fouling. Formulation of fouling mitigation strategies and fabrication of anti-fouling membranes have both benefited substantially from those studies. In the present review, a summary of the recent results on the thermodynamic mechanisms associated with the critical adhesion and filtration processes during membrane fouling is provided. Firstly, the importance of thermodynamics in membrane fouling is comprehensively assessed. Secondly, the quantitative methods and general factors involved in thermodynamic fouling mechanisms are critically reviewed. Based on the aforementioned information, a brief discussion is presented on the potential applications of thermodynamic fouling mechanisms for membrane fouling control. Finally, prospects for further research on thermodynamic mechanisms underlying membrane fouling are presented. Overall, the present review offers comprehensive and in-depth information on the thermodynamic mechanisms associated with complex fouling behaviors, which will further facilitate research and development in membrane technology.     

Transparent exopolymer particles (TEPs)-associated protobiofilm: A neglected contributor to biofouling during membrane filtration

• Bacteria could easily and quickly attached onto TEP to form protobiofilms. • TEP-protobiofilm facilitate the transport of bacteria to membrane surface. • More significant flux decline was observed in the presence of TEP-protobiofilms. • Membrane fouling shows higher sensitivity to protobiofilm not to bacteria level. Transparent exopolymer particles (TEPs) are a class of transparent gel-like polysaccharides, which have been widely detected in almost every kind of feed water to membrane systems, including freshwater, seawater and wastewater. Although TEP have been thought to be related to the membrane fouling, little information is currently available for their influential mechanisms and the pertinence to biofouling development. The present study, thus, aims to explore the impact of TEPs on biofouling development during ultrafiltration. TEP samples were inoculated with bacteria for several hours before filtration and the formation of “protobiofilm” (pre-colonized TEP by bacteria) was examined and its influence on biofouling was determined. It was observed that the bacteria can easily and quickly attach onto TEPs and form protobiofilms. Ultrafiltration experiments further revealed that TEP-protobiofilms served as carriers which facilitated and accelerated transport of bacteria to membrane surface, leading to rapid development of biofouling on the ultrafiltration membrane surfaces. Moreover, compared to the feed water containing independent bacteria and TEPs, more flux decline was observed with TEP-protobiofilms. Consequently, it appeared from this study that TEP-protobiofilms play a vital role in the development of membrane biofouling, but unfortunately, this phenomenon has been often overlooked in the literature. Obviously, these findings in turn may also challenge the current understanding of organic fouling and biofouling as membrane fouling caused by TEP-protobiofilm is a combination of both. It is expected that this study might promote further research in general membrane fouling mechanisms and the development of an effective mitigation strategy.     

废水处理系统中生物聚集体胞外多聚物研究进展

胞外多聚物(Extracellular polymeric substances,EPS)是废水生物处理系统中生物聚集体(包括絮体污泥、生物膜、颗粒污泥等)的重要组成部分,直接包裹于微生物细胞壁外,其理化性质及所处的特殊位置决定了它在生物聚集体中的重要作用.综述了EPS对废水生物处理系统污泥沉降性能、脱水性以及膜生物反应器膜污染影响的相关研究,分析认为EPS组成与结构特性改变污泥表面电位、疏水性等,进而影响污泥沉降与脱水性能、膜污染程度;以好氧颗粒污泥为典型的生物聚集体代表,总结了EPS组分含量与分布对颗粒污泥的形成与结构稳定性的影响,并在EPS提取方法标准化、现代理化技术与分子生物学技术综合分析等方面进行了展望,进一步的研究有望揭示生物絮凝体形成过程EPS的产生与调控机制.     

Fate of microplastics in a coastal wastewater treatment plant: Microfibers could partially break through the integrated membrane system

• Fate of microplastics in integrated membrane system for water reuse was investigated. • Integrated membrane system has high removal efficiency (>98%) for microplastics. • Microplastics (>93%) were mainly removed through membrane bioreactor treatment. • Small scale fiber plastics (<200 μm) could break through reverse osmosis (RO) system. • The flux of microplastics maintained at 2.7 × 10¹¹ MPs/d after the RO treatment. Rare information on the fate of microplastics in the integrated membrane system (IMS) system in full-scale wastewater treatment plant was available. The fate of microplastics in IMS in a coastal reclaimed water plant was investigated. The removal rate of microplastics in the IMS system reached 93.2% after membrane bioreactor (MBR) treatment while that further increased to 98.0% after the reverse osmosis (RO) membrane process. The flux of microplastics in MBR effluent was reduced from 1.5 × 10¹³ MPs/d to 10.2 × 10¹¹ MPs/d while that of the RO treatment decreased to 2.7 × 10¹¹ MPs/d. Small scale fiber plastics (<200 μm) could break through RO system according to the size distribution analysis. The application of the IMS system in the reclaimed water plant could prevent most of the microplastics from being discharged in the coastal water. These findings suggested that the IMS system was more efficient than conventional activated sludge system (CAS) for the removal of microplastics, while the discharge of small scale fiber plastics through the IMS system should also not be neglected because small scale fiber plastics (<200 μm) could break through IMS system equipped with the RO system.     

曝气强度对膜生物反应器运行特性的影响

以膜生物反应器（MBR）处理模拟生活废水为研究体系,考察曝气强度对系统污染物去除效果、脱氢酶活性、胞外聚合物（EPS）组分和含量、Zeta电位、污泥粒径及跨膜压差等的影响.结果表明,随着曝气强度降低,COD去除率变化不大,均大于94.0%,脱氢酶活性明显降低,VSS/SS比值下降;污泥LB-EPS增加,Zeta电位降低,污泥平均体积粒径减小,膜通量下降速率增大.曝气强度为800—400 L.m-.2h-1的条件下,曝气产生的水力剪切力不是影响污泥粒径大小的主导因素,污泥Zeta电位则起着决定作用,但水力剪切力有利于缓解膜污染.     

改进型膜生物反应器处理洗浴污水的试验研究

在大量试验研究的基础上提出了一种改进型膜生物反应器 (MBR) ,并对其处理洗浴污水的效果进行了试验 ,结果表明 :利用改进型MBR处理洗浴污水出水水质良好 ,COD <40mg/L ,LAS <0 .2mg/L ,符合国家建设部颁布的生活杂用水回用水质标准。     

Aggravation of membrane fouling and methane leakage by a three-phase separator in an external anaerobic ceramic membrane bioreactor

The existence of three-phase separator did not affect COD removal in the EAnCMBR. The existence of three-phase separator aggravated methane leakage of EAnCMBR. The existence of three-phase separator aggravated membrane fouling rate of EAnCMBR. Start-up of EAnCMBR equipped three-phase separator was slightly delayed. The three-phase separator is a critical component of high-rate anaerobic bioreactors due to its significant contribution in separation of biomass, wastewater, and biogas. However, its role in an anaerobic membrane bioreactor is still not clear. In this study, the distinction between an external anaerobic ceramic membrane bioreactor (EAnCMBR) unequipped (R1) and equipped (R2) with a three-phase separator was investigated in terms of treatment performance, membrane fouling, extracellular polymers of sludge, and microbial community structure. The results indicate that the COD removal efficiencies of R1 and R2 were 98.2%±0.4% and 98.1%±0.4%, respectively, but the start-up period of R2 was slightly delayed. Moreover, the membrane fouling rate of R2 (0.4 kPa/d) was higher than that of R1 (0.2 kPa/d). Interestingly, the methane leakage from R2 (0.1 L/d) was 20 times higher than that from R1 (0.005 L/d). The results demonstrate that the three-phase separator aggravated the membrane fouling rate and methane leakage in the EAnCMBR. Therefore, this study provides a novel perspective on the effects of a three-phase separator in an EAnCMBR.     

Co-application of energy uncoupling and ultrafiltration in sludge treatment: Evaluations of sludge reduction,supernatant recovery and membrane fouling control

• Effects of metabolic uncouplers addition on sludge reduction were carried out. • TCS addition effectively inhibited ATP synthesis and reduced sludge yield. • The effluent quality such as TOC and ammonia deteriorated but not significantly. • Suitable dosage retarded biofouling during sludge water recovery by UF membrane. Energy uncoupling is often used for sludge reduction because it is easy to operate and does not require a significant amount of extra equipments (i.e. no additional tank required). However, over time the supernatant extracted using this method can deteriorate, ultimately requiring further treatment. The purpose of this study was to determine the effect of using a low-pressure ultrafiltration membrane process for sludge water recovery after the sludge had undergone an energy uncoupling treatment (using 3,3′,4′,5-tetrachlorosalicylanilide (TCS)). Energy uncoupling was found to break apart sludge floc by reducing extracellular polymeric substances (EPS) and adenosine triphosphate (ATP) content. Analysis of supernatant indicated that when energy uncoupling and membrane filtration were co-applied and the TCS dosage was below 30 mg/L, there was no significant deterioration in organic component removal. However, ammonia and phosphate concentrations were found to increase as the concentration of TCS added increased. Additionally, due to low sludge concentrations and EPS contents, addition of 30–60 mg/L TCS during sludge reduction increased the permeate flux (two times higher than the control) and decreased the hydraulic reversible and cake layer resistances. In contrast, high dosage of TCS aggravated membrane fouling by forming compact fouling layers. In general, this study found that the co-application of energy uncoupling and membrane filtration processes represents an effective alternative method for simultaneous sludge reduction and sludge supernatant recovery.     

Ozonation as an efficient pretreatment method to alleviate reverse osmosis membrane fouling caused by complexes of humic acid and calcium ion

Humic acids (HA) didn’t cause obvious reverse osmosis (RO) membrane fouling in 45 h. Osmotic pressure (NaCl) affected slightly the RO membrane fouling behavior of HA. Ca²⁺ promoted aggregation of HA molecules and thus aggravated RO membrane fouling. Ozonation eliminated the effect of Ca²⁺ on the RO membrane fouling behavior of HA. The change of the structure of HA was related to its membrane fouling behavior. Humic acid has been considered as one of the most significant sources in feed water causing organic fouling of reverse osmosis (RO) membranes, but the relationship between the fouling behavior of humic acid and the change of its molecular structure has not been well developed yet. In this study, the RO membrane fouling behavior of humic acid was studied systematically with ozonation as a pretreatment method to control RO membrane fouling. Furthermore, the effect of ozone on the structure of humic acid was also explored to reveal the mechanisms. Humic acid alone (10–90 mg/L, in deionized water) was found not to cause obvious RO membrane fouling in 45-h operation. However, the presence of Ca²⁺ aggravated significantly the RO membrane fouling caused by humic acid, with significant flux reduction and denser fouling layer on RO membrane, as it was observed by scanning electron microscope (SEM) and atomic force microscope (AFM). However, after the pretreatment by ozone, the influence of Ca²⁺ was almost eliminated. Further analysis revealed that the addition of Ca²⁺ increased the particle size of humic acid solution significantly, while ozonation reduced the SUVA₂₅₄, particle size and molecular weight of the complexes of humic acid and Ca²⁺ (HA-Ca²⁺ complexes). According to these results and literature, the bridge effect of Ca²⁺ aggregating humic acid molecules and the cleavage effect of ozone breaking HA-Ca²⁺ complexes were summarized. The change of the structure of humic acid under the effect of Ca²⁺ and ozone is closely related to the change of its membrane fouling behavior.     

Using loose nanofiltration membrane for lake water treatment: A pilot study

• A pilot study was conducted for drinking water treatment using loose NF membranes. • The membranes had very high rejection of NOM and medium rejection of Ca²⁺/Mg²⁺. • Organic fouling was dominant and contribution of inorganic fouling was substantial. • Both organic and inorganic fouling had spatial non-uniformity on membrane surface. • Applying EDTA at basic conditions was effective in removing membrane fouling. Nanofiltration (NF) using loose membranes has a high application potential for advanced treatment of drinking water by selectively removing contaminants from the water, while membrane fouling remains one of the biggest problems of the process. This paper reported a seven-month pilot study of using a loose NF membrane to treat a sand filtration effluent which had a relatively high turbidity (~0.4 NTU) and high concentrations of organic matter (up to 5 mg/L as TOC), hardness and sulfate. Results showed that the membrane demonstrated a high rejection of TOC (by>90%) and a moderately high rejection of two pesticides (54%–82%) while a moderate rejection of both calcium and magnesium (~45%) and a low rejection of total dissolved solids (~27%). The membrane elements suffered from severe membrane fouling, with the membrane permeance decreased by 70% after 85 days operation. The membrane fouling was dominated by organic fouling, while biological fouling was moderate. Inorganic fouling was mainly caused by deposition of aluminum-bearing substances. Though inorganic foulants were minor contents on membrane, their contribution to overall membrane fouling was substantial. Membrane fouling was not uniform on membrane. While contents of organic and inorganic foulants were the highest at the inlet and outlet region, respectively, the severity of membrane fouling increased from the inlet to the outlet region of membrane element with a difference higher than 30%. While alkaline cleaning was not effective in removing the membrane foulants, the use of ethylenediamine tetraacetate (EDTA) at alkaline conditions could effectively restore the membrane permeance.     

Effect of iron addition on the performance of anoxic-oxic membrane process and biological phosphorus removal北大核心CSCD

In order to solve the problem of poor treatment of phosphorus in membrane bioreactor (MBR) with long sludge retention time (SRT), a ferric salt was added to enhance phosphorus removal; FeCl36H2O (Fe/P = 2.0) was added to the reactor. The removal efficiency of nitrogen, organic matters, and phosphorus in the MBR was investigated systematically. Moreover, this study focused on the membrane performance, the change of active sludge flora, and the effect of adding a ferric salt on membrane fouling before and after the addition. It was seen that adding the ferric salt could not affect the removal of COD and NH4 +-N and the removal rate of COD and NH4 +-N reached over 90%. However, the average removal rate of phosphorus was 52%, while the removal rate increased by nearly 40% after adding the ferric salt. The effects of adding ferric salts on the dominant bacteria and biological phosphorus removal of activated sludge were further studied. The results showed that the addition of ferric salt (Fe/P = 2.0) decreased the diversity of active sludge flora and relative abundance of some phosphorusaccumulating organisms and had a negative effect on biological phosphorus removal. The analysis of transmembrane pressure difference (TMP) recording revealed that the concentration of iron salts did not exacerbate membrane fouling. The results showed that the concentration of iron salts entering the membrane bioreactor would reduce the relative abundance and phosphorus removal efficiency of the activated sludge in the system to a certain extent, but it had no obvious effect on membrane fouling. It allowed the effluent to attain acceptable standards, especially with respect to phosphorus removal efficiency. © 2018 Science Press. All rights reserved.