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1.
Water Sci Technol ; 81(9): 2004-2010, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32666953

RESUMO

The goal of the present paper is to investigate the aeration process and the enhanced effect of baffles in a full-scale commercial membrane bioreactor (MBR) system configured with a flat sheet (FS) membrane module. Through a computational fluid dynamics (CFD) simulation, two aerated FS membrane modules for full-scale applications with 26 membrane sheets were simulated. The numerical results indicate that the presence of baffles and the distances between the baffle and the outmost membrane sheet have a minor influence on the area-weighted shear stress for full-scale MBRs. In addition, bubble size and the bottom distance between the aerator and membrane bottom do not affect the average shear stress of full-scale FS membrane modules much. However, an increase in air flow rate has a significant effect on the area-weighted shear stress. A large FS membrane module is recommended, as it could achieve the same cleaning effect as the small one with a lower specific aeration demand for membranes.


Assuntos
Hidrodinâmica , Eliminação de Resíduos Líquidos , Reatores Biológicos , Membranas Artificiais , Estresse Mecânico
2.
J Environ Manage ; 270: 110909, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32721343

RESUMO

This review summarizes the recent development and studies of anaerobic membrane bioreactor (AnMBR) to control fouling issues. AnMBR is an emerging waste water treatment technology mainly because of its low sludge residual, high volumetric organic removal rate, complete liquid-solid separation, better effluent quality, efficient resource recovery and the small footprint. This paper surveys the fundamental aspects of AnMBRs, including its applications, membrane configurations, and recent progress for enhanced reactor performance. Furthermore, the membrane fouling, a major restriction in the practical application of AnMBR, its mechanism and antifouling strategies like membrane cleaning, quorum quenching, ultrasonic treatment, membrane modifications, and antifouling agents are briefly discussed. Based on the review, the key issues that require urgent attention to facilitate large scale and integrated application of AnMBR technology are identified and future research perspectives relating to the prevalent issues are proposed.


Assuntos
Reatores Biológicos , Purificação da Água , Anaerobiose , Membranas Artificiais , Esgotos , Eliminação de Resíduos Líquidos , Águas Residuárias
3.
J Environ Manage ; 270: 110913, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32721347

RESUMO

Emerging contaminants (ECs) are synthetic organic chemicals that released into the environment, which pose a serious threat to the ecosystem and human health. Due to the high costs of physicochemical methods and the possibility of secondary pollution, and conventional biological treatment techniques are not efficient to remove ECs. Thus, there is a need to develop novel technologies to treat ECs. Anaerobic digestion (AD) is reported to degrade most ECs. Anaerobic membrane bioreactor (AnMBR) is an upgraded AD technology that has high system stability and microbial community abundance. The biogas production and EC biodegradation efficiency in the AnMBR system are markedly higher than those in the traditional AD system. In recent years, AnMBR is widely used to remove environmental ECs. This review analyzes the feasibility and challenges of AnMBR in the treatment of ECs and provides useful insights for improving the performance and efficiency of AnMBR to treat ECs.


Assuntos
Ecossistema , Águas Residuárias , Anaerobiose , Biocombustíveis , Reatores Biológicos , Membranas Artificiais , Eliminação de Resíduos Líquidos
4.
Environ Monit Assess ; 192(8): 543, 2020 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-32712819

RESUMO

Nitrate is among the important types of pollutant sources in drinking water worldwide, and there are a number of methods to remove it from water. New treatment methods are being developed as an alternative to traditional treatment methods. One of them is membrane capacitive deionization (MCDI). In this study, the removal of nitrate ions with MCDI system was investigated. Nitrate solutions were treated via MCDI at different operating conditions. The obtained nitrate removal efficiency reached 83.07% at a flow rate of 2.5 L/min and a potential of 0.8 V was applied. In addition, during the nitrate removal of the MCDI system, the environmental effects were evaluated by life cycle analysis. As a result of these analyses, MCDI system offered advantages of low energy demand and low-energy environmental effects during operation. The results showed that the improved MCDI technology holds a great potential to be an energy-efficient process for nitrate removal. Life cycle assessment was applied to the experimental study. According to the assessment, water consumption had the highest effect in all damage assessment categories.


Assuntos
Purificação da Água , Adsorção , Eletrodos , Monitoramento Ambiental , Membranas Artificiais , Nitratos
5.
Water Sci Technol ; 81(10): 2127-2139, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32701491

RESUMO

Membrane fouling mechanisms of the filtration of a mixed-culture microalgal biomass grown in real wastewater were investigated using crossflow filtration experiments. The results of flux measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses for three membranes, two microfiltration (PES01 and PES003) and one ultrafiltration (UC030), showed that the UC030 membrane may be more appropriate for microalgae harvesting due to its higher steady flux rate and lower flux reduction during filtration compared to the initial flux (44% for UC030, compared to 86% for PES01 and 79% for PES003). It was also observed that the membrane resistance due to concentration polarization was the dominant membrane resistance in this study for all three membranes, constituting about 67%, 61% and 51% for PES01, PES003, and UC030, respectively. The next largest membrane resistance was provided by pore blocking, while the resistance provided by cake formation was found to be very small for all membranes (3%, 15% and 18% for PES01, PES003 and UC030, respectively), which were also supported by SEM and AFM analyses.


Assuntos
Microalgas , Biomassa , Filtração , Membranas Artificiais , Ultrafiltração , Águas Residuárias
6.
Water Sci Technol ; 81(7): 1354-1364, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32616688

RESUMO

The treatment of oily wastewater continues to pose a challenge in industries worldwide. Membranes have been investigated recently for their use in oily wastewater treatment due to their efficiency and relatively facile operational process. Graphene oxide (GO) and silica (SiO2) nanoparticles have been found to improve membrane properties. In this study, a polyethersulfone (PES) based GO-SiO2 mixed matrix membrane (MMM) was fabricated, using the phase inversion technique, for the treatment of oil refinery wastewater. The PES/GO-SiO2 membrane exhibited the highest water flux (2,561 LMH) and a 38% increase in oil removal efficiency by comparison to a PES membrane. Compared to PES/GO and PES/SiO2 membranes, the PES/GO-SiO2 MMM also displayed the best overall properties in terms of tensile strength, water permeability, and hydrophilicity.


Assuntos
Dióxido de Silício , Águas Residuárias , Grafite , Membranas Artificiais , Polímeros , Sulfonas
7.
Water Sci Technol ; 81(8): 1578-1587, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32644951

RESUMO

Optimal operation of membrane bioreactor (MBR) plants is crucial to save operational costs while satisfying legal effluent discharge requirements. The aeration process of MBR plants tends to use excessive energy for supplying air to micro-organisms. In the present study, a novel optimal aeration system is proposed for dynamic and robust optimization. Accordingly, a deep reinforcement learning (DRL)-based optimal operating system is proposed, so as to meet stringent discharge qualities while maximizing the system's energy efficiency. Additionally, it is compared with the manual system and conventional reinforcement learning (RL)-based systems. A deep Q-network (DQN) algorithm automatically learns how to operate the plant efficiently by finding an optimal trajectory to reduce the aeration energy without degrading the treated water quality. A full-scale MBR plant with the DQN-based autonomous aeration system can decrease the MBR's aeration energy consumption by 34% compared to other aeration systems while maintaining the treatment efficiency within effluent discharge limits.


Assuntos
Reatores Biológicos , Eliminação de Resíduos Líquidos , Algoritmos , Membranas Artificiais
8.
Bioresour Technol ; 312: 123595, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32506043

RESUMO

In aerobic wastewater treatment, aeration is the most critical element of the treatment system. It supplies microorganisms with the required dissolved oxygen, maintains solids in suspension and, in membrane bioreactors, it controls fouling. However, conventional activated sludge is limited to the treatment of low strength wastewaters, as higher loadings require both higher biomass and higher dissolved oxygen concentrations. By replacing air with pure oxygen, oxygen transfer rates increase at lower flowrates. In this work, the potential and limitations of pure oxygen aeration are reviewed. The effect of the system's operational parameters and the mixed liquor characteristics on oxygen transfer, and vice versa, are determined. Pure oxygen treats higher loadings without compromising effluent quality. Fine bubbles are more efficient in oxygen transfer due to their increased contact area. However, pure oxygen is not always essential, so it is recommended to be restricted to applications where air is not adequate.


Assuntos
Eliminação de Resíduos Líquidos , Águas Residuárias , Reatores Biológicos , Membranas Artificiais , Oxigênio , Esgotos
9.
Bioresour Technol ; 312: 123612, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32526665

RESUMO

The feasibility of a novel bioflocculant (GemFloc™) for membrane fouling mitigation in membrane bioreactor (MBR) was investigated during real municipal wastewater treatment. When compared to the conventional MBR (CMBR), suspended sludge in the MBR with GemFloc™ (G-MBR) showed less soluble microbial products (SMP), higher ratios of proteins to polysaccharides in SMP (SMPP/SMPC) and loosely bound extracellular polymeric substances (LB-EPS). Adding GemFloc™ also enlarged floc size (> 200 µm), and increased tightly bound EPS levels, zeta potential and relative hydrophobicity of sludge flocs, further reduced cake layer and pore blocking resistances. Moreover, more diverse microbial community and enrichment of fouling reduction microbes such as Arenimonas and Flavihumibacter were observed in the G-MBR, together with less abundant microbes (e.g. Sphaerotilus and Povalibacter) which could aggravate membrane fouling. Therefore, GemFloc™ has high capability in improving sludge characteristics, mitigating membrane fouling and increasing diversity of special functional bacterial community in MBR.


Assuntos
Microbiota , Esgotos , Reatores Biológicos , Membranas Artificiais , Águas Residuárias
10.
J Contemp Dent Pract ; 21(4): 404-409, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32584277

RESUMO

AIM: The aim of this study was to analyze, by the aid of microbiological analysis and the field emission scanning electron microscopical (FE-SEM) analysis, the role of high-density polytetrafluoroethylene (d-PTFE) membranes in avoiding the microbial colonization of a nanocrystalline hydroxyapatite (nc-HA) bone graft and the involvement of this colonization in the healing process. MATERIALS AND METHODS: Six patients underwent extraction of unrecoverable teeth, and a socket preservation technique was carried out with nc-HA synthetic bone graft and then covered with a d-PTFE membrane. After 28 days from surgery, FE-SEM analysis and BioTimer assay technique to assess the microbiological count of streptococci species were carried out. Data were collected and analyzed by the Student's t test (confidence interval: 95%). RESULTS: The mean amount of bacteria measured on the upper side of the membrane was 6.52 ± 0.50 CFU, while on the lower side, it was 6.59 ± 0.40 CFU. Significant differences were not found between the two sides of the membrane or between the different sectors (p > 0.05). The FE-SEM analysis revealed structured biofilms on both sides of the membrane: species of cocci, bacilli, and fusobacteria were recognizable in occasional settled vegetations. CONCLUSION: Since the amount of bacteria found was low, the improved impermeability of the d-PTFE membrane permitted the healing process to proceed uneventful and without signs of infection or inflammation. CLINICAL RELEVANCE: The infection of the graft site could lead to a failure of the socket preservation technique which could delay or compromise the rehabilitation following procedures. The use of d-PTFE can improve the bone regeneration thanks to its antimicrobial properties.


Assuntos
Perda do Osso Alveolar , Aumento do Rebordo Alveolar , Durapatita , Humanos , Membranas Artificiais , Microscopia Eletrônica de Varredura , Politetrafluoretileno , Extração Dentária , Alvéolo Dental/cirurgia
11.
Sci Total Environ ; 736: 139500, 2020 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-32479964

RESUMO

The polyamide reverse osmosis (RO) membrane was modified with graphene oxide (GO), followed by polymerization of acrylic acid (used as an antiscalant) for the reduction of both biofouling and mineral scaling. After functionalization, the water contact angle reduced from 41.7 ± 4.5° for unmodified RO membrane to 24.4 ± 1.3° for the modified RO membranes, which showed that membrane hydrophilicity was significantly enhanced, in addition to the improvement in surface smoothness. The modified membranes were tested for their anti-scaling and anti-biofouling characteristics. When the mineral scaling test was performed using CaSO4 solution as feedwater, the permeate flux was reduced by only 3% as compared to the unmodified RO membrane which encountered up to 22% decline in flux by the end of the experiment. After the scaling test, the membrane surface was characterized by Scanning electron microscopy - energy-dispersive X-ray spectroscopy, Fourier transform infrared, and X-ray diffraction techniques. The results showed that the unmodified RO membrane was fully covered with gypsum precipitates. Whereas, the precipitates were detected only at the highly saturated zones of the water channel i.e. towards the exit of water flow. Additionally, the anti-bacterial test was performed through bacteriostasis rate determination, which showed that the modified membranes inhibited the growth of nearly 95% of the bacterial cells. Further experiments were also performed to investigate the inhibition of both scaling and biofouling by modified RO membranes. Thus, it was found that the polymer-modified GO coated RO membranes were able to diminish both gypsum scaling and biofilm formation demonstrating their potential to control different types of membrane fouling.


Assuntos
Incrustação Biológica , Purificação da Água , Resinas Acrílicas , Grafite , Membranas Artificiais , Minerais , Osmose
12.
J Environ Manage ; 269: 110758, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32560988

RESUMO

Membrane separation technology is recognized as a competitive approach to remove Pb2+ from water system due to its high efficiency and low operating cost. In present study, a simple and facile approach was developed to fabricate covalent organic framework (COF) modified PVDF ultrafiltration membranes with comprehensive antifouling property and superior Pb2+ removal ability. Herein, COF was synthesised in a homogenous PVDF/DMAc solution to fabricate hydrophilic COF modified PVDF ultrafiltration membranes with the Pb2+ removal property. The filtration test demonstrated that the COF modified PVDF ultrafiltration membranes exhibited excellent antifouling property and high water flux. Moreover, the membranes showed remarkable potential for treating Pb2+-containing water. The removal efficiency was determined at 92.4%, and its removal efficiency was 87.5% at the fourth treatment cycle with Pb2+-containing water. The present work provides a valuable platform for further development of efficient composite membranes for the treatment of Pb2+-containing water.


Assuntos
Estruturas Metalorgânicas , Ultrafiltração , Chumbo , Membranas Artificiais , Polivinil
13.
Chemosphere ; 257: 127180, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32473407

RESUMO

Effect of sodium dodecyl sulfate (SDS) on the fouling of a commercial aquaporin based biomimetic forward osmosis (FO) membrane was investigated. Increasing draw solution (DS) concentration and decreasing the cross-flow velocity could aggravate the membrane fouling, and the effect of the latter was greater than the former. SDS as a surfactant could wash away some sodium alginate (SA) and calcium chloride (CaCl2) which were adsorbed on the surface of the membrane. However, SA and CaCl2 tended to form irreversible fouling when SDS had already been on the membrane. When SDS + SA + CaCl2 was used as the feed solution (FS), SDS was first adsorbed on the membrane surface and then SA and CaCl2 interact with SDS; irreversible fouling was formed when the hydrophobic tail of the SDS was adsorbed to the SA, and reversible fouling was formed while Ca2+ (bridged with SA) was bound with the hydrophilic head of the SDS. Afterwards, the cleaning effects of HCl and NaOH solutions on the membrane fouling caused by SDS were studied. The initial normalized flux could be recovered to 0.88 using both methods. Cleaning with HCl solution could slow down the formation of membrane fouling, while cleaning with NaOH solution could damage the aquaporin in the active layer of the membrane.


Assuntos
Membranas Artificiais , Dodecilsulfato de Sódio/química , Purificação da Água/métodos , Adsorção , Alginatos , Cloreto de Cálcio , Interações Hidrofóbicas e Hidrofílicas , Osmose
14.
Chemosphere ; 257: 127144, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32473409

RESUMO

Polyvinylidene fluoride (PVDF) membrane was coated with polyvinyl alcohol (PVA)/titanium dioxide (TiO2) solution using dip-coating method. The effect of PVA loading (0-12 wt%) at a fixed TiO2 concentration (1 wt%) was investigated through physical and morphological characterization of the membranes. The experimental results showed that increasing the PVA content from 0 to 12 wt% in the coating solution increased the hydrophilicity and tensile strength as well as the young's modulus of the coated membranes. It also increased the thickness of the thin film coating which enhanced the removal of dyes but affected the permeate flux adversely. Larger the molecular weight of the dye, higher the rejection and lower the permeate flux obtained. The antifouling performance of the membrane was studied using Bovine Serum Albumin (BSA) solution and the fouling was measured using the irreversible fouling factor. The results indicated that the PVA/TiO2 coated PVDF membrane had lower irreversible fouling factors compared to plain PVDF membrane. The PVDF membrane with a thin film coating containing 3 wt% of PVA and 1 wt% of TiO2 showed high photocatalytic degradation for the three dyes studied under UV irradiation due to uniform dispersion of TiO2 nanoparticles over the membrane surface. Further, smaller the molecular weight of the dye, larger the photodegradation that was observed.


Assuntos
Corantes/química , Álcool de Polivinil/química , Polivinil/química , Eliminação de Resíduos Líquidos/métodos , Interações Hidrofóbicas e Hidrofílicas , Membranas Artificiais , Nanopartículas , Fotólise , Soroalbumina Bovina , Têxteis , Titânio , Raios Ultravioleta
15.
Environ Sci Pollut Res Int ; 27(23): 29433-29440, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32436092

RESUMO

Membrane fouling is still the main obstacle that hinders the development and implementation of anaerobic membrane bioreactor (AnMBR). In conventional upflow anaerobic reactors, sludge at different height usually presents certain differences in characteristics in terms of particle size, etc. The immersion depth of membrane modules in anaerobic reactors can also influence the fouling of membrane. Thus, it is of great interest to investigate the fouling mechanism with the membrane installed at different heights in reactors. The filtration performance and sludge properties were investigated at different heights of AnMBR. The fouling of membrane in the middle position was severer than that in the top and bottom positions. The total resistance of membrane in the top, middle, and bottom positions was 27.31 × 1011 m-1, 34.67 × 1011 m-1, and 25.29 × 1011 m-1, respectively. By comparing the characteristics and structure of bulk sludge and cake layer at three heights, the bulk sludge in the middle position presented higher content of soluble microbial products (SMP) and finer flocs, and the cake layer was also denser. The results obtained in this study indicated that small size of sludge flocs as well as adhesion of SMP might be the major factors governing membrane fouling at different height in the AnMBR.


Assuntos
Reatores Biológicos , Membranas Artificiais , Anaerobiose , Filtração , Esgotos
16.
Chemosphere ; 256: 127118, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32460162

RESUMO

Dye wastewater is harmful to the ecological environment because of its potential biological toxicity, teratogenicity, carcinogenicity, and mutagenicity. We fabricated a layered graphene oxide (GO) membrane through layer-by-layer (LBL) self-assembly. We used borate to crosslink with GO on a polyethyleneimine (PEI)-coated hydrolyzed polyacrylonitrile (hPAN) support. Fourier transform infrared (FTIR) spectrometry, Raman spectra, and x-ray photoelectron spectroscopy (XPS) confirmed the presence of a crosslinking reaction. The dynamic thermomechanical analysis (DMA) results indicated that the introduction of borate can significantly improve the mechanical properties of the membrane. The Young's modulus, ultimate tensile strength, and proportional limit of borate that was assembled twice as the outermost layer were increased by 110.81%, 62.37%, and 53.72%, respectively, as compared to those of a single-layered GO membrane. Moreover, the pure water fluxes of the layered GO membrane did not obviously decrease with an increase in the number of layers. The flux of the membrane with an outermost layer of borate was greater than that of the previous GO layer. The salt and dye rejection of the membranes was augmented with an increase in the number of layers. For the GO membrane assembled three times, rejection to methyl orange (MO), methylene blue (MB), NaCl, MgCl2, and MgSO4 reached 74.02%, 88.56%, 14.55%, 27.50%, and 41.95%, respectively. The use of borate as an inorganic crosslinker can avoid the environmental pollution caused by organic agents, and improve the mechanical properties as well as the filter capability of the layered GO membrane. Therefore, this study presents a novel method of membrane preparation for dye removal.


Assuntos
Compostos Azo/análise , Boratos/química , Grafite/química , Membranas Artificiais , Azul de Metileno/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Resinas Acrílicas/química , Filtração , Polietilenoimina/química , Propriedades de Superfície , Águas Residuárias/química
17.
J Environ Manage ; 269: 110720, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32425175

RESUMO

The use of the anaerobic membrane bioreactor (AnMBR) process for domestic wastewater treatment presents an opportunity to mitigate environmental, social, and economic impacts currently incurred from energy-intensive conventional aerobic activated sludge processes. Previous studies have performed detailed evaluations on improving AnMBR process subcomponents to maximize energy recovery and dissolved methane recovery. Few studies have broadly evaluated the role of chemical use, membrane fouling management, and dissolved methane removal technologies. A life cycle assessment was conducted to holistically compare multiple AnMBR-based domestic wastewater treatment trains to conventional activated sludge (CAS) treatment. These treatment trains included different scouring methods to mitigate membrane fouling (gas-sparging and granular activated carbon-fluidizing) with consideration of upstream treatment (primary sedimentation vs. screening only), downstream treatment (dissolved methane removal and nutrient removal) and sludge management (anaerobic digestion and lime stabilization). This study determined two process subcomponents (sulfide and phosphorus removal and sludge management) that drove chemical use and residuals generation, and in turn the environmental and cost impacts. Furthermore, integrating primary sedimentation and a vacuum degassing tank for dissolved methane removal maximized net energy recovery. Sustainability impacts were further mitigated by operating at a higher flux and temperature, as well as by substituting biological sulfide removal for chemical coagulation.


Assuntos
Reatores Biológicos , Águas Residuárias , Anaerobiose , Membranas Artificiais , Metano , Esgotos , Eliminação de Resíduos Líquidos
18.
Water Res ; 181: 115843, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32422450

RESUMO

In this study, a coupled system of algal-sludge and membrane bioreactor (AS-MBR) was established for fouling control, and meanwhile the performance of wastewater treatment was enhanced. Results indicated that the AS-MBR increased the COD, NH4+-N, TN and PO43- -P removal efficiencies from 91.7% to 95.9%, 90.8%-96.9%, 22.0% to 34.3% and 18.4%-32.6%, respectively. Further analysis suggested that in the AS-MBR, the total specific oxygen utilization rate (SOUR), the SOUR of ammonia oxidizing bacteria and the SOUR of nitrite oxidizing bacteria were 26.6%, 58.5% and 52.4% higher than the control, respectively, indicating the improvement of microbial activities in AS-MBR. Additionally, the membrane fouling rates in the AS-MBR were 52.6% and 32.2% lower than the control in the slow and rapid fouling processes, respectively. A further mechanism investigation demonstrated that the concentrations of extracellular polymeric substance (EPS) were decreased by 19.8% and 22.1% in the mixed liquid and the fouling layer, respectively, after the inoculation of algae, which was expected to have a positive effect on the higher permeability and longer operation cycle of the membrane in the AS-MBR. More regular floc morphology was observed for the fouling layer on the membrane of AS-MBR, with the polysaccharides and proteins forming large clusters and channels in the fouling layer that likely decreased the filtration resistance. Consequently, high-throughput sequencing analysis revealed that the microbial community in the AS-MBR had higher abundances of bacteria and algae related to nutrients and organic matters degradation, which was beneficial for the improvement of wastewater treatment and alleviation of membrane fouling.


Assuntos
Matriz Extracelular de Substâncias Poliméricas , Esgotos , Reatores Biológicos , Membranas Artificiais , Águas Residuárias
19.
Water Res ; 181: 115881, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32438119

RESUMO

This study investigated the efficiency of intensive membrane cleaning for membrane bioreactors (MBRs) using a combination of mechanical scouring with granules and chemically enhanced backwashing (CEB). The implementation of such intensive cleaning was possible with ceramic flat-sheet membranes. Experiments were carried out using bench-scale MBRs at an existing wastewater treatment plant. First, CEB with NaClO was investigated in terms of the CEB frequency, duration, and concentration of the chemical reagent. CEB carried out for 60 min every 6 h, with 50 ppm of NaClO, was found to be effective, and it enabled an MBR to operate at 50 LMH, two to three times higher than the flux of full-scale MBRs. However, these CEB conditions were insufficient when the temperature was low (i.e. in winter), when an adhesive gel layer formed on the membrane surface. Its high resistance to cleaning might be explained by the increased levels of soluble microbial products and/or the presence of algal cells. Alkaline-assisted CEB, with NaClO (pH 12) and an increase in the volume of granules in the membrane tank, solved this problem. With the modified cleaning method, the fouling could be almost perfectly controlled at low-temperature conditions, such as 13 °C. MBRs may be regarded as fouling-free MBRs when the proposed cleaning method is used with ceramic flat-sheet membranes. Most real-world MBR operations operate with lower fluxes than the flux examined in this study, and at higher temperatures.


Assuntos
Eliminação de Resíduos Líquidos , Águas Residuárias , Reatores Biológicos , Cerâmica , Membranas Artificiais , Temperatura
20.
Water Res ; 181: 115932, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32454321

RESUMO

Though sludge foaming often occurs and thus causes serious membrane fouling in membrane bioreactors (MBRs), the fouling mechanisms related with the foaming phenomenon have not been well addressed, hindering better understanding and solving foaming problem. In this work, it was interestingly found that, the foulants during the foaming period possessed extremely high specific filtration resistance (SFR) (over 1016 m kg-1) and strong adhesion ability to membrane surface. Chemical characterization showed that the proteins (178.57 mg/L) and polysaccharides (209.21 mg/L) in the foaming sample were about 6.4 times and 5.4 times of those in the supernatant sample, suggesting existence of a mechanism permitting continuous production of these foulants in the MBR during the foaming period. It was revealed that the fouling caused by foams was associated with gel layer filtration process, and the extremely high SFR can be interpreted by chemical potential change in the gel filtration process depicted in Flory-Huggins theory. Meanwhile, analyses by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed that the strong adhesion ability stemmed from the high interaction energy between the foaming foulants and membrane surface. In addition, 16S rDNA gene sequencing identified that the abundance of the foaming related bacteria species in the sludge suspension during the foaming period was more than 10 times of that during the non-foaming period. This study offered new mechanism insights into foaming fouling in MBRs.


Assuntos
Reatores Biológicos , Membranas Artificiais , Bactérias , Filtração , Esgotos
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