While flow-electrode capacitive deionization (FCDI) is a potential alternative to brackish and/or sea water desalination, there is limited understanding of both the fate of ions following migration ...across the ion exchange membranes and the mechanisms responsible for ion separation. In this study, we investigate the desalting performance of an FCDI system operated over a range of conditions. Results show that although ion transport as a result of electrodialysis is inevitable in FCDI (and is principally responsible for pH excursion in the flow electrode), the use of high carbon content ensures that a high proportion of the charge and counterions are retained in the electrical double layers of the flowing carbon particles, even at high charging voltages (e.g., 2.0 V) during the deionization process. Estimation of the portions of sodium and chloride ions adsorbed in the flow electrode after migration through the membranes suggests that the ongoing capacitive adsorption exhibits asymmetric behavior with the anodic particles demonstrating better affinity for Cl− (than the cathodic particles for Na+) during electrosorption. These findings provide an explanation for the change in electrode properties that are observed under imperfect adsorption scenarios and provide insight into aspects of the design and operation of flow electrode pairs that is critical to achieving effective desalination by FCDI.
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•Desalting mechanisms evaluated in an FCDI with composite current collectors.•Electrodialysis associated with ion transport and pH excursion is inevitable.•High carbon content ensures the coupling of the charge and counterions.•Ongoing capacitive adsorption in FCDI exhibits asymmetric behavior.
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.
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•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.
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•Less than 150 ppm water product can be obtained by one-time-continuous charge process in batch mode.•The removal efficiency is up to 95.5% for single-continuous batch-mode ...treatment.•An unlimited salt removal capacity was demonstrated.•A relatively low average energy consumption down to 8.34 kJ mole−1 salt removed is achievable.•No electrode regeneration is required to realize the full continuous desalination.
Low-energy desalination technologies capable of continuous throughput at reasonable operating and maintenance cost are now critically needed. Herein, we present a continuous desalination process with average energy consumption as low as 2.14 kJ mole−1 salt removed achievable when using a 10 mM/10 mM ferri-/ferrocyanide solution that flows continuously between anode and cathode chambers. The salt feed at ~3000 ppm can be continuously desalted to a potable level of less than 150 ppm during the desalination process. At the anode, ferrocyanide is oxidized with electrons released to the external circuit and cations captured to achieve charge balance. Ferricyanide is reduced at the cathode, resulting in the constant transfer of anions from the dilute stream to the concentrate stream. The recycling of the redox mediators maintains an extremely low operating potential (~100 mV) and continuous salt extraction with unlimited removal capacity. Comparison of the use of ferri-/ferrocyanide, pure ferricyanide and ferrocyanide solutions indicate that the ultra-low energy consumption can be ascribed to the excellent electrochemical properties of the ferri-/ferrocyanide couple and the extremely low overpotential of the redox reactions owing to the synergistic effect of sufficient simultaneous ferrocyanide oxidation and ferricyanide reduction in the flow electrolyte streams. Our research provides a route for ultra-low energy desalination based on voltage suppression via use of facile redox couple mediators.
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•A g-C3N4/TiO2 floating photocatalyst was prepared via a facile sol-gel method.•M. aeruginosa and Microcystin-LR were simultaneously removed under visible light.•Photoinduced holes ...and OH are the reactive species involved in photocatalysis.•Microcystin-LR was gradually degraded with oxidation of the Adda chain occurring.•The floating photocatalyst can be readily recovered for reuse.
Harmful algal blooms (HABs) have increasingly occurred worldwide causing human and ecological health risks. In this study, we report on an effective alternative to inactivating Microcystis aeruginosa under visible light irradiation with the use of a floating heterojunction photocatalyst. The photocatalyst (CTAE for short) is made of graphitic carbon nitride (g-C3N4) and TiO2 that are loaded on Al2O3-modified expanded perlite via a facile sol-gel method. The N/C doping in TiO2 and the interaction between TiO2 and g-C3N4 enhanced the generation of h+ and OH independent of O2 activation, which could facilitate applications in oxygen-deficient waters. Consideration was given to the impacts of different mass ratios of g-C3N4 to TiO2. The photocatalysts were characterized by XRD, N2 adsorption/desorption isotherms, FESEM/EDS, TEM, XPS, UV–vis absorption and Photoluminescence spectroscopy. Results showed that different contents of g-C3N4 had an influence on the crystal structure, specific surface area and pore volumes of the photocatalysts. The use of 2 g/L of 0.03CTAE (i.e., the theoretical mass ratio of g-C3N4 to TiO2 = 0.03) photocatalyst could simultaneously remove 88.1% of M. aeruginosa at an initial concentration of 2.7 × 106 cells/mL and 54.4% of Microcystin-LR at an initial concentration of 50 μg/L following 6-h of visible light irradiation. Microcystin-LR was gradually degraded with oxidation of the Adda chain occurring. Following each treatment, the floating g-C3N4/TiO2 photocatalyst could be readily recovered from the solution, demonstrating a great potential for in situ remediation of eutrophic waters.
For understanding of the microbial community structure and composition under different aeration intensities, 454 high-throughput pyrosequencing was applied to analyze the 16S rRNA gene of bacteria in ...two submerged membrane bioreactors (MBRs) under low (RL) and high aeration (RH) conditions. In total, 7818 (RL) and 9353 (RH) high-quality reads were obtained, and 1230 (RL) and 924 (RH) operational taxonomic units (OTUs) were generated at 3% cutoff level, respectively. 454 pyrosequencing could also reveal the minority bacteria that were hardly detected by the conventional molecular methods. Although the core populations were shared with highly functional organization (>80%), clear differences between the samples in the two MBRs were revealed by richness–diversity indicators and Venn analyses. Notably, microbial diversity was decreased under high aeration condition, and the evolution of the populations was observed mainly in the shared OTUs. Moreover, specific comparison down to the class and genus level showed that the relative abundances of β-Proteobacteria and γ-Proteobacteria in the RH community were respectively decreased by 41.5% and 66.6%, consistent with the observed membrane fouling mitigation during the reactor operation. It was also found that Nitrospira and Nitrosomonas, being nitrite oxidizing bacteria (NOB) and ammonium oxidizing bacteria (AOB), were the dominant phylogenetic groups at the genus level of both reactors, and that the high ratio of NOB to AOB populations well supported the complete ammonium oxidation performance in the two reactors. Although some populations of NOB and AOB decreased with the increase of aeration intensity, the functional stability of the nitrification process was less affected, probably due to the low influent substrate concentration and the high level of functional organization.
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► Microbial compositions of SMBRs with varied aeration intensity were studied. ► The evolution mainly occurred in the shared operational taxonomic units (OTUs). ► β-Proteobacteria and γ-Proteobacteria reduction was consistent with fouling mitigation. ► The number of nitrifiers decreased under high aeration while nitrification was less affected.
Sodium hypochlorite (NaClO) is a commonly used reagent for membrane cleaning in membrane bioreactors (MBRs), while it, being a kind of disinfectant (oxidant), may impair viability of microbes or even ...totally inactivate them upon its diffusion into mixed liquor during membrane cleaning. In this study, we systematically examine the effects of NaClO on microorganisms in terms of microbial cell integrity, metabolism behaviours (key enzymes), and intracellular reactive oxygen species (ROS) under various NaClO concentrations. Different proportions of microbial cells in activated sludge were damaged within several minutes dependent on NaClO dosages (5–50 mg/g-SS), and correspondingly organic matters were released to bulk solution. Inhibition of key enzymes involved in organic matter biodegradation, nitrification and denitrification was observed in the presence of NaClO above 1 mg/g-SS, and thus organic matter and nitrogen removal efficiencies were decreased. It was also demonstrated that intracellular ROS production was increased with the NaClO dosage higher than 1 mg/g-SS, which likely induced further damage to microbial cells.
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•Cell lysis occurred within initial several minutes at NaClO dosages of 5–50 mg/g-SS.•Heterotrophic metabolism was inhibited when NaClO concentration was above 1 mg/g-SS.•Key enzymes for nitrogen removal were lowered at NaClO dosage higher than 1 mg/g-SS.•Increased production of intracellular ROS was observed in the presence of NaClO.
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In this study, Electro-Fenton (E-Fenton) reactions at pH 3.0 were initiated by cathodic generation of H2O2, with subsequent production of OH following the addition of Fe(II) or ...Fe(III) ions into the system. The variation in concentrations of H2O2, Fe(II), total Fe and OH following addition of Fe ions into the E-Fenton system was investigated over a range of conditions. A kinetic model incorporating the key processes operating in the E-Fenton system was developed with particular attention given to (i) cathodic generation of H2O2 and anodic formation of OH, (ii) production of OH via homogeneous Fenton reactions, and (ii) surface reactions including electro-sorption of Fe ions and cathodic reduction of Fe(III) to Fe(II) species resulting in the enhancement of production of OH via surface-located Fenton reactions.
While microalgae have been suggested as a promising substitute to conventional fossil fuels, their cost effective cultivation and harvesting constitutes a major challenge. In the work described here, ...a novel photosynthetic microbial fuel cell (PMFC) in which a stainless steel mesh with biofilm formed on it serves as both the cathode and filtration material has been developed. Results of this study reveal that, in addition to inducing oxygen reduction reactions under illumination, the biocathode is effective in preventing the washout of algae during continuous operation, resulting in retained biomass concentrations reaching 3.5–6.5 g L−1. The maximum output current density reached ∼200 mA m−2 under irradiation, which is comparable with recent PMFC studies. Microbial diversity analyses targeting 16S and 18S rRNA genes indicated that the eukaryotic species belonging to the genus Chlorella was able to sustain its community dominance (>96%) over other competing species over the course of the studies. In the absence of catalysts such as Pt, a consortium of photosynthetic organisms including plant growth-promoting bacteria such as Azospirillum and Rhizobium were overrepresented in the biofilm, with these organisms most likely contributing to cathodic electron transfer. Energy flow analysis suggested that the PMFC system held the potential to achieve theoretical energy balance in simultaneous algae production and wastewater treatment.
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•A novel PMFC was developed for cost-effective Chlorella biomass production.•High concentrations (3.5–6.5 g/L) of algae were obtained during continuous operation.•Chlorella sustained its community dominance over other competing species.•A consortium of photosynthetic organisms may relate to cathodic electron transfer.•Energy flow analysis shows this PMFC holds the potential to achieve energy balance.
The status of maritime features is one of the core issues in the South China Sea Arbitration. The essence of this issue is territorial sovereignty and maritime delimitation disputes between China and ...the Philippines. Based on the interception of certain facts and evidence, the Tribunal did not interpret the China’s diplomatic position as it wanted, and it had an intensely subjective interpretation of Article 121(3) of the United Nations Convention on the Law of the Sea of 1982. Combined with the Chinese government’s positions before and after the publicity surrounding the Award, this paper, which takes the logical approaches of the Award as the main line, focuses on chapter 6 of the Award, raising questions about disputes on the status of maritime features, analyzing the treaty interpretations related to the status of maritime features, and clarifying the defections.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, PRFLJ, SAZU, UILJ, UKNU, UL, UM, UPUK
► Pyrosequencing reveals high microbial diversity in the bulk sludge and cake layer. ► Colonizers of the cake layer were mainly originated from the bulk sludge. ► Microbial evolution occurred due to ...the selective pressure and environmental stress. ► Bacteroides, Clostridia and δ-proteobacteria were the pioneers of colonization on membranes.
454 high-throughput pyrosequencing was employed to investigate microbial communities in bulk sludge (BS) and cake layer (CL) in an anaerobic dynamic membrane bioreactor (AnDMBR). Pyrosequencing produced 7402 and 7026 high-quality V1–V3 tags of the 16S rRNA-gene for the BS and CL samples, and the number of total OTUs estimated by Chao1 was 2906 (BS) and 2532 (CL) at a 3% distance. Phylogenetic spectrum and Venn diagrams revealed that the bacterial phyla in the two samples were nearly identical, and that the predominant microorganisms of them exhibited a high homology. Nevertheless, population distribution was different between them. Proteobacteria were the most dominant in the BS, while Bacteroidetes, Firmicutes and Spirochaetes were highly enriched in the CL, accounting for 57.6% of the total microbes. The main microbial groups in the CL were highly functionally organized. Bacteroides, Clostridia and Delta-proteobacteria were likely the pioneers for surface colonization on membranes in the AnDMBR.
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