Membrane bioreactors (MBRs) have been widely used in wastewater treatment and reclamation. Membrane cleaning is an essential part during the operation of MBRs since membrane fouling is an unavoidable ...problem. In past decades, with the in-depth understanding on membrane fouling, significant advances in membrane cleaning have been achieved. However, a comprehensive review on membrane cleaning in MBRs is still lacking. This paper attempts to critically review the recent developments of membrane cleaning. Firstly, the fouling and cleaning fundamentals are addressed, and then a comprehensive review on physical, chemical, and biological/biochemical cleaning is presented. The procedures of determining proper cleaning protocols for MBR systems are also proposed. Finally, the existing challenges and future research efforts are discussed in order to ensure the development of membrane cleaning toward a more effective and sustainable way in MBRs.
Display omitted
•A critical review on physical, chemical and biological cleaning in MBRs is presented.•The relations of cleaning methods, agents and factors to cleaning efficiency are addressed.•The procedures of determining proper cleaning protocols are proposed.•The challenges and future research efforts of membrane cleaning are discussed.
Membrane bioreactors (MBRs) suffer from high operational and cleaning costs due to biofouling. The biofouling begins when the adhesins (an anchor-type epitope made up of polar and charged amino ...acids) on microbial appendages bind to the surface. Two different compounds–dodecyl-β-D-maltoside (DDM) and methyl α-d-mannopyranoside (MeαMan)–were investigated as possible biofilm mitigation tools due to their documented anti-adhesin properties in the biomedical field. DDM prevented up to 56.3, 87.0, and 67.6% of the formation of Pseudomonas putida, Escherichia coli and wastewater culture biofilms, respectively, in microplate experiments. MeαMan increased biofilm in the microplates. In a biofilm reactor setting, DDM was then applied on typical membrane materials, polyvinylidene fluoride, polyamide, polyether-sulfone, and polyacrylonitrile and prevented 79.4, 62.5, 81.3, and 68.2% of the detectable wastewater culture biofilm formation, respectively. The mechanism of anti-adhesion was the binding of the polar head of the DDM to the polar amino acids of the microbial appendages in conjunction with the orientation of the DDM as it binds different membrane materials. If the anti-adhesins are effective at increasing the distance of the bacteria from the membrane materials, they will serve as a new method for delaying biofouling.
Display omitted
•Dodecyl-β-D-maltoside (DDM) is effective in biofilm prevention in well plates.•DDM mitigates biofilm formation on membrane materials in a biofilm bioreactor.•DDM prevents appendages from attachment by blocking adhesion protein.•Hydrophobic materials cause a polar-nonpolar repulsion of appendages with DDM.
Display omitted
•Comprehensive review of fouling control methods in membrane bioreactors.•Physically- and chemically based cleaning strategies of membrane fouling.•Recent progresses of fouling ...mitigation strategies and key challenges.•Nanomaterials, cell entrapment, biologically- and electrically-based methods.
The current research was an effort to critically review all approaches used for membrane fouling control in the membrane bioreactors treating water and wastewater. The first generation of antifouling methods tried to optimize operational conditions, or used chemical agents to control membrane fouling. Despite their positive impacts on the fouling mitigation, these methods did not provide a sustainable solution for the problem. Moreover, chemical agents may affect microorganisms in bioreactors and has some environmental drawbacks. The improved knowledge of membrane fouling mechanism and effective factors has directed the attention of researchers to novel methods that focus on disrupting fouling mechanism through affecting fouling causing bacteria. Employing nanomaterials, cell entrapment, biologically- and electrically-based methods are the latest efforts. The results of this review indicate that sustainable control of membrane fouling requires employing more than one single approach. Large scale application of fouling mitigation strategies should be the focus of future studies.
•The AnMBR plant was operated for more than 600 days at ambient temperature.•Effluent COD remained below effluent standards with average COD removal above 87 %.•Waste sludge reduced by between 9 and ...43 % less than CAS.•Methane yield ranged from 70 to 169 STP L CH4·kg−1 CODinf during the selected periods.·T, SRT, HRT and influent COD/SO42−-S are crucial parameters of AnMBR performance.
A semi-industrial scale AnMBR plant was operated for more than 600 days to evaluate the long-term operation of this technology at ambient temperature (ranging from 10 to 27 ○C), variable hydraulic retention times (HRT) (from 25 to 41 h) and influent loads (mostly between 15 and 45 kg COD·d−1). The plant was fed with sulfate-rich high-loaded municipal wastewater from the pre-treatment of a full-scale WWTP. The results showed promising AnMBR performance as the core technology for wastewater treatment, obtaining an average 87.2 ± 6.1 % COD removal during long-term operation, with 40 % of the data over 90%. Five periods were considered to evaluate the effect of HRT, influent characteristics, COD/SO42−-S ratio and temperature on the biological process. In the selected periods, methane yields varied from 70.2±36.0 to 169.0±95.1 STP L CH4·kg−1 CODinf, depending on the influent sulfate concentration, and wasting sludge production was reduced by between 8 % and 42 % compared to conventional activated sludge systems. The effluent exhibited a significant nutrient recovery potential. Temperature, HRT, SRT and influent COD/SO42−-S ratio were corroborated as crucial parameters to consider in maximizing AnMBR performance.
Display omitted
Display omitted
•The removal of AOX was improved in a biochar-amended AnMBR.•Fouling mitigation was achieved in ‘TMP jump’ stage with biochar addition.•The major foulant EPS-protein was sharply ...reduced with biochar addition.•High Mw EPS-proteins in cake layer were degraded into low Mw proteins.•The relative abundance of bio-foulant Arcobacter decreased obviously.
Anaerobic membrane bioreactor (AnMBR) is an advanced technology in treating pharmaceutical wastewater, but the membrane fouling limits its development. In this study, the biochar with adsorption capacity of biopolymers was added in AnMBR to investigate its potential in treating pharmaceutical wastewater and alleviating membrane fouling. In the biochar-amended AnMBR, adsorbable organic halogen (AOX) was removed effectively, and more COD was biotransformed into CH4. Membrane fouling mitigation was achieved in the third stage with a 56% decrease of average transmembrane pressure difference (TMP) rising rate. The predominant culprit, proteins of extracellular polymeric substance (EPS-proteins) in sludge mixture and cake layer, was reduced significantly. Particularly, the proportion of micromolecular (0.1–0.15 kDa) EPS-proteins in cake layer was 1.5-folds that of the control group. The important bio-foulant genus Arcobacter aggregating on the membrane had less and almost half the relative abundance (16.5%) than that of the control group (30.7%).
Concentration gradients that occur in large industrial‐scale bioreactors due to mass transfer limitations have significant effects on process efficiency. Hence, it is desirable to investigate the ...response of strains to such heterogeneities to reduce the risk of failure during process scale‐up. Although there are various scale‐down techniques to study these effects, scale‐down strategies are rarely applied in the early developmental phases of a bioprocess, as they have not yet been implemented on small‐scale parallel cultivation devices.
In this study, we combine mechanistic growth models with a parallel mini‐bioreactor system to create a high‐throughput platform for studying the response of Escherichia coli strains to concentration gradients. As a scaled‐down approach, a model‐based glucose pulse feeding scheme is applied and compared with a continuous feed profile to study the influence of glucose and dissolved oxygen gradients on both cell physiology and incorporation of noncanonical amino acids into recombinant proinsulin. The results show a significant increase in the incorporation of the noncanonical amino acid norvaline in the soluble intracellular extract and in the recombinant product in cultures with glucose/oxygen oscillations. Interestingly, the amount of norvaline depends on the pulse frequency and is negligible with continuous feeding, confirming observations from large‐scale cultivations. Most importantly, the results also show that a larger number of the model parameters are significantly affected by the scale‐down scheme, compared with the reference cultivations.
In this example, it was possible to describe the effects of oscillations in a single parallel experiment. The platform offers the opportunity to combine strain screening with scale‐down studies to select the most robust strains for bioprocess scale‐up.
Concentration gradients that occur in large industrial‐scale bioreactors due to mass transfer limitations have significant effects on process efficiency. Hence, it is desirable to investigate the response of strains to such heterogeneities to reduce the risk of failure during process scale‐up.
The relationship between biodiversity and ecosystem stability is poorly understood in microbial communities. Biofilm communities in small bioreactors called microbial electrolysis cells (MEC) contain ...moderate species numbers and easy tractable functional traits, thus providing an ideal platform for verifying ecological theories in microbial ecosystems. Here, we investigated the resilience of biofilm communities with a gradient of diversity, and explored the relationship between biodiversity and stability in response to a pH shock. The results showed that all bioreactors could recover to stable performance after pH disturbance, exhibiting a great resilience ability. A further analysis of microbial composition showed that the rebound of Geobacter and other exoelectrogens contributed to the resilient effectiveness, and that the presence of Methanobrevibacter might delay the functional recovery of biofilms. The microbial communities with higher diversity tended to be recovered faster, implying biofilms with high biodiversity showed better resilience in response to environmental disturbance. Network analysis revealed that the negative interactions between the two dominant genera of Geobacter and Methanobrevibacter increased when the recovery time became longer, implying the internal resource or spatial competition of key functional taxa might fundamentally impact the resilience performances of biofilm communities. This study provides new insights into our understanding of the relationship between diversity and ecosystem functioning.
A bench-scale anaerobic membrane bioreactor (AnMBR) equipped with submerged flat-sheet microfiltration membranes was operated at psychrophilic temperature (15 °C) treating simulated and actual ...domestic wastewater (DWW). Chemical oxygen demand (COD) removal during simulated DWW operation averaged 92 ± 5% corresponding to an average permeate COD of 36 ± 21 mg/L. Dissolved methane in the permeate stream represented a substantial fraction (40–50%) of the total methane generated by the system due to methane solubility at psychrophilic temperatures and oversaturation relative to Henry's law. During actual DWW operation, COD removal averaged 69 ± 10%. The permeate COD and 5-day biochemical oxygen demand (BOD5) averaged 76 ± 10 mg/L and 24 ± 3 mg/L, respectively, indicating compliance with the U.S. EPA's standard for secondary effluent (30 mg/L BOD5). Membrane fouling was managed using biogas sparging and permeate backflushing and a flux greater than 7 LMH was maintained for 30 days. Comparative fouling experiments suggested that the combination of the two fouling control measures was more effective than either fouling prevention method alone. A UniFrac based comparison of bacterial and archaeal microbial communities in the AnMBR and three different inocula using pyrosequencing targeting 16S rRNA genes suggested that mesophilic inocula are suitable for seeding psychrophilic AnMBRs treating low strength wastewater. Overall, the research described relatively stable COD removal, acceptable flux, and the ability to seed a psychrophilic AnMBR with mesophilic inocula, indicating future potential for the technology in practice, particularly in cold and temperate climates where DWW temperatures are low during part of the year.
Display omitted
► Psychrophilic anaerobic membrane bioreactors (AnMBRs) can treat domestic wastewater. ► Permeate dissolved methane is a substantial portion of total methane production. ► Membrane fouling can be managed using biogas sparging and permeate backflushing. ► Combining biogas sparging and permeate backflushing is important for fouling control. ► Mesophilic inocula are suitable for psychrophilic AnMBR seeding.
Display omitted
•Current advancements in at-line and in-line analytical tools have enabled the refinement of existing tools.•Spectroscopic methods continue to be promising tools for monitoring cell ...culture performance and product quality attributes.•Further refinements in data processing have allowed for monitoring of additional parameters than previously reported.
Real-time and near real-time monitoring of cell culture processes are critical to the evolving process analytical technology (PAT) paradigm for upstream bioprocessing. The responses measured from these analytical instruments can enable rapid feedback to perturbations that can otherwise lead to batch failures. Historically, real-time monitoring of bioreactor processes has been relegated to parameters such as pH, dissolved oxygen, and temperature. Other analytical results, such as cell growth and metabolites, are provided through manual daily sampling. In order to reduce sample error and increase throughput, real-time and near real-time instruments have been developed. Here we discuss recent advances in these technologies. This article aims to focus on other developing at-line and in-line technologies that enable monitoring of bioreactor processes, including dielectric spectroscopy, NIR, off-gas spectrometry, integrated at-line HPLC, and nanofluidic devices for monitoring cell growth and health, metabolites, titer, and product quality.
The use of new technologies for micropropagation such as temporary immersion systems (TISs) is important, because it reduces costs by 40% lowering labor, agar and containers. TISs are containers ...designed for large-scale, semiautomatic production of plants in a liquid medium, which has been used in propagation of commercial orchids. This tool has high potential for application in micropropagation of medicinal and endangered orchids for conservation and commercial purposes. In this chapter, we describe a detailed protocol for propagation and development of Encyclia cordigera to be used in research projects for small-scale production. This protocol comprises all steps from explant preparation to the establishment orchids plantlets.
PDF
