Nanofiltration Membrane Bioreactor Research Articles

The nematode Caenorhabditis elegans enhances tolerance to landfill leachate stress by increasing trehalose synthesis.

The burgeoning issue of landfill leachate, exacerbated by urbanization, necessitates evaluating its biological impact, traditionally overshadowed by physical and chemical assessments. This study harnesses Caenorhabditis elegans, a model organism, to elucidate the physiological toxicity of landfill leachate subjected to different treatment processes: nanofiltration reverse osmosis tail water (NFRO), membrane bioreactor (MBR), and raw leachate (RAW). Our investigation focuses on the modulation of sugar metabolism, particularly trehalose-a disaccharide serving dual functions as an energy source and an anti-adversity molecule in invertebrates. Upon exposure, C. elegans showcased a 60-70% reduction in glucose and glycogen levels alongside a significant trehalose increase, highlighting an adaptive response to environmental stress by augmenting trehalose synthesis. Notably, trehalose-related genes in the NFRO group were up-regulated, contrasting with the MBR and RAW groups, where trehalose synthesis genes outpaced decomposition genes by 20-30 times. These findings suggest that C. elegans predominantly counters landfill leachate-induced stress through trehalose accumulation. This research not only provides insights into the differential impact of leachate treatment methods on C. elegans but also proposes a molecular framework for assessing the environmental repercussions of landfill leachate, contributing to the development of novel strategies for pollution mitigation and environmental preservation.

Removing refractory organic substances from landfill leachate using a nanofiltration membrane bioreactor: Performance and mechanisms

Membrane bioreactors (MBRs) are typically used to dispose landfill leachate, but they are challenged by the low removal of refractory organic substances. To address this challenge, in this study, we replaced the commonly used microfiltration (MF) membranes in conventional MBRs with nanofiltration (NF) membranes, i.e., MBRNF. We operated a one-step MBRNF for 127 days and benchmarked against a conventional MBRMF in terms of membrane fouling, pollutants removal, and bulk solution properties. The results showed that the NF membrane could effectively reject refractory organic substances, leading to a longer organic retention time (ORT) and a higher concentration of refractory organic substances in the bioreactor. Consequently, the MBRNF outperformed MBRMF by 20 %–30 % in removing of refractory organic substances, mainly by the enhanced biodegradation of refractory organic substances with low molecular weight. Further investigation suggested that the enhanced biodegradation in the MBRNF could be ascribed to 1) more biomass in the bioreactor; 2) higher concentration of refractory organic substances in the bioreactor; and 3) the enrichment of dominant bacteria such as Chloroflexi. These findings highlight the potential of MBRNF in removing refractory organic substances from landfill leachate and other wastewaters with poor biodegradability.

A novel loosely structured nanofiltration membrane bioreactor for wastewater treatment: Process performance and membrane fouling

A novel nanofiltration membrane bioreactor (NF-MBR) was constructed by integrating a loosely structured nanofiltration hollow fiber membrane into an aerobic activated sludge system. In order to verify the feasibility of loose NF membrane bioreactor, parallel experiments of conventional ultrafiltration membrane bioreactor (UF-MBR) and NF-MBR were conducted to investigate process performances, membrane fouling characteristics. The loose NF membrane showed a relatively high permeability at a level of around 10 L m-2 h-1 bar-1 (flux of 2.0 L m-2 h-1) under low operation pressure (10–30 KPa). The results showed that NF-MBR achieved a higher removal efficiency of chemical oxygen demand (CODCr) and dissolved organic carbon (DOC) due to high rejection of loose NF membrane for biopolymers and part of the humic substances. During long term operation in NF-MBR, loose NF membrane displayed low salt rejection, resulting in no obvious salts accumulation in bioreactor in comparison with UF-MBR. The average rising rates in TMP for the NF-MBR was 0.16 KPa/day, which was twice lower than that of UF-MBR. The results of fouling mechanism showed that reversible cake fouling was dominant for both NF and UF membranes, while the relatively small pore size of the NF membrane mitigated irreversible pore blockage. Further biofouling layer analysis demonstrated that humic substances, polysaccharides and proteins were the main organic foulants. The results of energy consumption revealed that NF-MBR had comparable total energy consumption compared with UF-MBR. The outcomes of this study show the feasibility of loose NF membrane bioreactor to provide a great potential as an advanced process for wastewater treatment.

Influence of nanofiltration concentrate recirculation on performance and economic feasibility of a pilot-scale membrane bioreactor-nanofiltration hybrid process for textile wastewater treatment with high water recovery

The membrane bioreactor-nanofiltration hybrid process has been proven to be promising for textile wastewater treatment. High water recovery could be achieved through the recirculation of nanofiltration concentrate to the membrane bioreactor. However, its influence on both the performance and economic feasibility of the membrane bioreactor-nanofiltration was not fully investigated, especially at larger scale. In this study, a pilot-scale membrane bioreactor-nanofiltration system was used for the on-site treatment of textile wastewater. The hydraulic retention time of membrane bioreactor was first optimized (Stage A), then the membrane bioreactor-nanofiltration system was operated at different water recovery rates (Stage B). The results showed that the sludge activity was relatively stable, but the nanofiltration concentrate recirculation significantly influenced the pollutants removal efficiencies of membrane bioreactor. The membrane bioreactor-nanofiltration effluent is suitable for reuse and the high water recovery could bring considerable benefits that enhance the economic feasibility of the process with a net income of 1.24 M USD/y and a payback period of 3.11 y.

Impact of salt accumulation in the bioreactor on the performance of nanofiltration membrane bioreactor (NF-MBR)+Reverse osmosis (RO) process for water reclamation

The impacts of salt accumulation, through adjusting the solid retention time (SRT), in the bioreactor on the bioprocess as well as membrane performance of a high retention nanofiltration membrane bioreactor (NF-MBR) and subsequent reverse osmosis (RO) process for water reclamation are addressed in this study. The build-up of salts (i.e., Ca, Mg, PO4) is a function of SRT, hydraulic retention time (HRT) and membrane rejection. Despite the accumulation of salts, both NF-MBRs at SRT of 30 and 60 days, achieved (i) similar biodegradation efficiency; (ii) excellent organic removal (> 97%); and (iii) excellent ammonia removal (> 98%). Extending the SRT could improve the microbial bio-flocculation capability, but did not influence the microbial activity, viability, and community structure. However, more severe membrane fouling was observed in the NF-MBR with elevated salt levels, which was attributed to the greater formation of calcium phosphate scale and Ca-polysaccharides complex (i.e., irreversible fouling layer) as well as the cake-enhanced-osmotic-pressure (CEOP) effect. Although both NF-MBRs produced comparable quality of permeate, a higher RO membrane fouling rate was observed when the permeate of NF-MBR with SRT at 60 days was fed to the RO system, implying organic compositions in NF-MBR permeate may influence RO performance.

Design and development of layer-by-layer based low-pressure antifouling nanofiltration membrane used for water reclamation

Recent studies have confirmed the advantages of low-pressure nanofiltration (NF) membranes in integrated nanofiltration membrane bioreactor system followed by the reverse osmosis (RO) process for high recovery water reclamation. However, fouling of low-pressure NF membranes restricts their application in providing high quality feed to subsequent RO process. In this study, an antifouling low-pressure NF membrane was designed and fabricated via rapid co-deposition of polydopamine (PDA)/polyethylenimine (PEI) on electrostatic layer-by-layer (LBL) assembled polyethersulfone (PES) flat sheet membrane followed by crosslinking with glutaraldehyde. The optimized resultant membrane (LBL-cPP) presented approximately 11 LMH/bar pure water permeability with more than 90% rejection divalent cations under 2 bar pressure. The newly developed selective layer exhibited excellent antifouling performance and chemical stability ascribing to the inherent hydrophilicity of PDA/PEI and dual covalent reaction of PDA with the LBL layer. By feeding real municipal wastewater, the LBL-cPP membrane also achieved superior permeate quality, leading to lower RO fouling rate in subsequent RO unit as compared to commercial NF 270 membrane. Further organic foulant analysis indicated that 96.8% of dissolved organic carbons were effectively removed by the LBL-cPP membrane. Specifically, the novel NF membrane demonstrated high removal rate (>93%) for foulants with low molecular weights which was largely responsible for RO fouling, while maintaining the desired flux recovery rate and reduced cleaning frequency. This study demonstrates the potential of PDA/PEI modified low-pressure NF membranes in designing efficient and sustainable water reclamation technology.

The feasibility of nanofiltration membrane bioreactor (NF-MBR)+reverse osmosis (RO) process for water reclamation: Comparison with ultrafiltration membrane bioreactor (UF-MBR)+RO process

This study examines the feasibility of a novel nanofiltration membrane bioreactor (NF-MBR) followed by reverse osmosis (RO) process for water reclamation at 90% recovery and using an ultrafiltration MBR (UF-MBR)+RO as baseline for comparison. Both MBRs adopted the same external hollow fiber membrane configurations and operating conditions. The collected permeates of the MBRs were subsequently fed to the respective RO systems. The results showed that the NF-MBR (operated at a constant flux of 10 L/m2h) achieved superior MBR permeate quality due to enhanced biodegradation and high rejection capacity of the NF membrane, leading to lower RO fouling rates (∼3.3 times) as compared to the UF-MBR. Further analysis indicated that the cake layer fouling that caused the cake-enhanced osmotic pressure (CEOP) effect contributed predominantly to the transmembrane pressure (TMP) increase in the NF-MBR, while irreversible pore fouling was the major reason for UF membrane fouling. Furthermore, it was found that the biopolymers (i.e., organics with MW > 10 kDa) were the main components present in the foulants of the NF/UF membranes and RO membranes. The analysis indicated that the NF-MBR + RO system at recovery of 90% has comparable energy consumption as the UF-MBR + RO system at recovery of 75%. Our findings proved the feasibility of the NF-MBR + RO for water reclamation at a high recovery rate.

Coupling of nanofiltration with microfiltration and membrane bioreactor for textile effluent reclamation

ABSTRACTThis work investigates the application of a microfiltration–membrane bioreactor–nanofiltration hybrid process for textile effluent reclamation. The indigo blue dye was efficiently retained by the microfiltration membrane (100%), which allows its recovery from the concentrate stream. The membrane bioreactor resulted in chemical oxygen demand (COD) and ammonia removal of 73% and 100%, respectively. Nanofiltration technology was successfully applied to polish textile effluent. The principal cause of flux decline was determined to be concentration polarization. The nanofiltration permeate meets the quality requirements for all processes within the textile industry, while the nanofiltration concentrate can be used for less demanding purposes.

Biological performance and trace organic contaminant removal by a side-stream ceramic nanofiltration membrane bioreactor

This study evaluated the performance of a side-stream ceramic nanofiltration membrane bioreactor (NF-MBR) system with respect to basic water quality parameters as well as trace organic contaminant (TrOC) removal efficiency. The results show a stable biological performance of the continuous NF-MBR system with high effluent quality (total organic carbon < 4 mg L−1 and NH4+–N below the detection limit). Significantly higher performance by this NF-MBR in comparison to the conventional microfiltration/ultrafiltration MBR regarding the removal of a large number of TrOCs was observed. TrOC removal efficiency depended on their hydrophobicity and molecular features. All hydrophobic compounds (LogDpH=6 > 3) were well removed (>85%), except diazinon (59 ± 7%). Hydrophilic compounds containing electron donating groups were also well removed (>90%). By contrast, hydrophilic compounds containing electron withdrawing groups were poorly removed (8–54%). Most of the 40 TrOCs investigated in this study did not accumulate in the sludge. Only three hydrophobic compounds, namely amitriptyline, triclosan and triclocarban showed considerable accumulation in sludge (>500 ng g−1). Mass balance indicated biodegradation/transformation as the most significant TrOC removal mechanism by this NF-MBR.

Effects of returning NF concentrate on the MBR-NF process treating antibiotic production wastewater.

The optimization of the nanofiltration (NF) concentrate backflow ratio (R cb) and the influence of the NF concentrate on the performance of membrane bioreactor-nanofiltration (MBR-NF) process treating antibiotic production wastewater were investigated on a laboratory scale. The R cb was optimized at 60% based on the removal rates of chemical oxygen demand (COD) and NH4 (+)-N by MBR. Data analyses indicated that salinity brought by NF concentrate is the major driver leading to the decrease of sludge activity, especially at a high R cb. EPS analysis showed that electric conductivity (EC), proteins in soluble microbial products (SMP), and SMP brought by NF concentrate are the dominant factors causing the severe membrane fouling in MBR. Furthermore, undegradable substances including fulvic acid-like and humic acid-like compounds accumulated in NF concentrate showed significant influence on fouling of NF. MBR could well degrade small MW compounds in NF concentrate, which confirmed the enhancement of organic removal efficiency by recycling the NF concentrate to MBR. The MBR-NF process showed a relatively stable performance at the R cb of 60% (volume reduction factor (VRF) = 5), and the NF permeate could satisfy the water quality standard for fermentation process with a water recovery rate of 90.9%.

Effect of powdered activated carbon on integrated submerged membrane bioreactor–nanofiltration process for wastewater reclamation

The aim of this study was to determine the effect of powdered activated carbon (PAC) on the overall performance of a submerged membrane bioreactor (SMBR) system integrated with nanofiltration (NF) for wastewater reclamation. It was found that the trans-membrane pressure of SMBR increased continuously while that of the SMBR with PAC was more stable, mainly because water could still pass through the PACs and membrane even though foulants adhered on the PAC surface. The presence of PAC was able to mitigate fouling in SMBR as well as in NF. SMBR–NF with PAC obtained a higher flux of 8.1 LMH compared to that without PAC (6.6 LMH). In addition, better permeate quality was obtained with SMBR–NF integrated process added with PAC. The present results suggest that the addition of PAC in integrated SMBR–NF process could possibly lead to satisfying water quality and can be operated for a long-term duration.

Pretreatment of concentrated leachate by the combination of coagulation and catalytic ozonation with Ce/AC catalyst.

A raw concentrated leachate produced from membrane bioreactor-nanofiltration (MBR-NF) was taken from Chengdu Chang'an Waste Landfill Site, China. The major fraction of this concentrated leachate was large refractory humic substances. A coagulation-ozonation process was applied to treat this leachate, aiming at enhancing chemical oxygen demand (COD) removal efficiency and increasing its biodegradability. Meanwhile the molecular size distribution of the leachate, before and after coagulation and ozonation treatment, was analyzed by using ultrafiltration membrane separation. Coagulation pretreatment effectively removed varieties of large molecules in the raw concentrated leachate. The addition of Ce/AC greatly improved the oxidative ability of O3 in COD removal in the ozonation of coagulated leachate. The biochemical oxygen demand (BOD5)/COD ratio increased from 0.011 for the untreated concentrated leachate to 0.30 for the effluent of the coagulation-catalytic ozonation process, which indicated that a subsequent biological treatment could be readily conducted. The stability test demonstrated that the Ce/AC catalyst was effective and stable in the catalytic ozonation process. According to the results of molecular size distribution analysis, a direct correlation was observed between the increase of BOD5/COD and the decrease of apparent molecular weight.

Performance and fate of organics in a pilot MBR–NF for treating antibiotic production wastewater with recycling NF concentrate

A double membrane system comprising a membrane bioreactor (MBR) combined with a nanofiltration (NF) membrane was investigated on a pilot scale for the treatment of antibiotic production wastewater over a three-month period at a pharmaceutical company in Wuxi, China. By recycling the NF concentrate, the combined MBR–NF process was shown to be effective for the treatment of antibiotic production wastewater, resulting in excellent water quality and a high water yield of 92±5.6%. The water quality of the pilot-scale MBR–NF process was excellent; e.g., the concentrations of TOC, NH4+-N, TP were stable at 5.52, 0.68, 0.34mgL−1, respectively, and the values of turbidity and conductivity of the NF permeate were 0.15 NTU and 2.5mScm−1, respectively; these values meet China’s water quality standard requirements for industrial use (GB21903-2008). Not only were the antibiotic removal rates of spiramycin (SPM) and new spiramycin (NSPM) over 95%, the acute toxicity was also drastically reduced by the MBR–NF pilot system. The main organics in the MBR effluent were proteins, polysaccharides, and humic-like substances; they were almost completely retained by the NF membrane and further biodegraded in the MBR because the NF concentrate was recycled. The microbial community of the MBR did not significantly change with the recycling of the NF concentrate.

Comparison in reduction of solids, turbidity and EC between nanofiltration membrane bioreactor and activated sludge

Hospital wastewater has special importance since having pathogens, radioactive materials, pharmaceutical wastes and heavy metals. Removing them into environment without any treatment may cause serious problems for the public health. Membrane Biological Reactor is the combination of the activated sludge and membrane filters. This research has investigated the performance of the Nano-Filtration in a Membrane Biological Reactor (NF-MBR) in the pilot scale in comparison to the activated sludge system which is very common in

Fate of organic pollutants in a pilot-scale membrane bioreactor-nanofiltration membrane system at high water yield in antibiotic wastewater treatment

A double membrane system combining a membrane bioreactor (MBR) with a nanofiltration (NF) membrane at the pilot scale was tested to treat real antibiotic wastewater at a pharmaceutical company in Wuxi (China). The water yield of the pilot system reached over 92 ± 5.6% through recycling the NF concentrate to the MBR tank. Results showed that the pilot scale system operated in good conditions throughout the entire experiment period and obtained excellent water quality in which the concentrations of chemical oxygen demand and total organic carbon were stable at 35 and 5.7 mg/L, respectively. The antibiotic removal rates of both spiramycin (SPM) and new spiramycin in wastewater were over 95%. Organics analysis results showed that the main organics in the biological effluent were proteins, soluble microbial by-product-like, fulvic acid-like and humic-like substances. These organics could be perfectly rejected by the NF membrane. Most of the organics could be removed through recycling NF concentrate to the MBR tank and only a small part was discharged with NF concentrate and permeate.

Municipal wastewater reclamation and reuse in the leather industry

In the present work, an integrated pilot-scale membrane system (membrane bioreactor–nanofiltration [MBR–NF]) was applied to the treatment of municipal wastewater to produce reclaimed water. Its performance was evaluated and designed to meet the requirements of the water quality to use in the tanning process. The feasibility of using reclaimed wastewater in the different wet phases of the tanning process (beamhouse, tanning, re-tanning, dyeing, and fatliquoring) was investigated on a pilot scale for manufacturing chrome-tanned leathers. The results showed that the combination of MBR and NF processes applied to municipal wastewaters was adequate for recovering water with low hardness, very low Fe, Mn, and ammonium levels as required by tanneries. The pilot-scale tanning tests demonstrated that there were no significant differences between the wet-blue (chrome-tanned) leathers produced using treated wastewater and those produced using softened tap water in terms of physical and sensorial properties. Hence, the suitability of the treated water for use in the tanning was verified and validated.

Nanofiltration membrane bioreactor for removing pharmaceutical compounds

The application of a nanofiltration membrane bioreactor (NF-MBR) has been investigated for the treatment of two pharmaceutical compounds (cyclophosphamide and ciprofloxacine). A new type of ceramic nanofiltration (NF) membrane has been employed for the filtration of acclimated activated sludge artificially doped by these antibiotics. The performance of the NF-MBR was monitored during approximately 4 months, in order to evaluate the long term operational stability of the system and the potential effect of the high sludge retention time on antibiotics degradation. The hypothesis of this study lies in the development of NF membrane and its cut-off support in order to (i) retain micropollutants and (ii) increase micropollutant concentration in the bioreactor. The two antibiotics are weakly degraded even with acclimated sludge, and only a small fraction of these compounds was retained when the fouling of the membrane increased. COD, total suspended solids (TSS) and colour were effectively removed. No unclogging operation was necessary (4 months of operation without chemical cleaning). The biodegradability, retention and adsorption mechanisms have been also studied.

Evaluation of a membrane bioreactor and nanofiltration for municipal wastewater reclamation: Trace contaminant control and fouling mitigation

A membrane bioreactor (MBR) and nanofiltration (NF) membrane processes were developed for municipal wastewater reclamation, and their performances, in terms of trace contaminant control and fouling mitigation, were evaluated and designed to meet water quality criteria and minimize flux decline. The dissolved contaminants in wastewater were poorly degraded by MBR but the microbial nitrification in MBR could greatly contribute to nitrogen removal in the MBR permeate through the addition of a NF membrane. Furthermore, most dissolved contaminants were efficiently removed by the NF membrane. However, the NF membrane was ineffective in the removal of boron. The org-N/C molar ratio was inversely correlated to SUVA and directly corresponded to the 3D FEEM, structural analysis, and IR spectra of organic matter in raw and treated water, and desorbed foulants. The observations obtained from rigorous characterization revealed that the hydrophilic fractions, which were comprised of polysaccharides and amino groups, played a major role in fouling formation of the MBR–NF system. In addition, strong amide IR peak in the NF-base supported the notion that amino groups were primarily responsible for the fouling formation of the NF membrane relative to the polysaccharides groups.

Fractionation of organic matters in sludge rejected by NF membrane

Nanofiltration membrane bioreactor (NF-MBR) was proposed to provide quality effluent free of virus and most large organic substances. The dissolved organic matter (DOM) in soluble microbial products (SMP), loosely bound extracellular polymeric substances (LBEPS) and tightly bound extracellular polymeric substances (TBEPS) of wastewater sludge before and filtered through nanofiltration membrane were fractioned using size exclusion chromatography, characterized with ultraviolet absorbance at 230, 254 and 280 nm, dissolved oganic carbon (DOC) content, and excitation-emission-matrix (EEM) spectra. Except for long-chain organic acids, the membrane rejected most organic matters in SMP and LBEPS fractions. However, the membrane failed to reject fluorescent DOM from TBEPS at molecular weight of 3000–7000 Da. The content of TBEPS in the mixed liquor affected significantly the effluent quality in NF-MBR application.

Comparison of sludge characteristics and PCR–DGGE based microbial diversity of nanofiltration and microfiltration membrane bioreactors

The objective of this study was to compare the sludge characteristics and microbial community diversity between the submerged nanofiltration membrane bioreactor (NF MBR) and microfiltration membrane bioreactor (MF MBR) treating the same municipal wastewater. The influence of a higher concentration of organic matter and salt was investigated. The results of water qualities showed that the dissolved organic carbon (DOC), total phosphorus (T-P) and salt concentrations of the supernatant in the NF MBR were three, four and two times as high as those in the MF MBR, respectively. The specific oxygen uptake rate of the NF MBR (2.9+/-0.4 mg O(2)g(-1)MLSSh(-1)) was lower than that of the MF MBR (4.3+/-1.1 mg O(2)g(-1)MLSS h(-1)). Result of extractable extracellular polymeric substances showed that the NF MBR sludge had more protein and less polysaccharide compared to the MF MBR sludge, whereas specific amount of total organic carbon were the same in both MBRs. The median floc diameters of the NF MBR and the MF MBR were 72+/-12 microm and 59+/-12 microm, respectively, which could be attributable to the different polysaccharide concentrations between both MBR mixed liquor. A higher concentration of materials (DOC, T-P and salt) in the bioreactor, determined by the high rejection rate of the NF membrane, did not significantly affect the microbial diversity under similar operation conditions.