Application of magnetic fields to wastewater treatment and its mechanisms: A review

Enhancement Effect of Static Magnetic Field on Bactericidal Activity

The biological effects of magnetic fields are pervasive in microorganisms, with significant attention given to alternating magnetic fields (AMFs). However, AMFs induce electrical and magnetothermal effects, which complicate the interpretation of magnetic field-induced biological effects and introduce uncertainties regarding cytotoxicity in practical applications. The static magnetic field (SMF) with few variables and high biocompatibility presents a promising alternative for both understanding biological mechanisms and ensuring safe applications, but has a remaining problem on weak interactions with microorganisms. Here we show that the combination of SMF with paramagnetic calcium-polypyrrole nanoparticles (Ca-PPy) remarkably enhances bactericidal activity. Our experiments indicate that the synergistic action of SMF and Ca-PPy significantly promotes the generation of reactive oxygen species (ROS), i.e., singlet oxygen and superoxide anion radicals, in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), coupled with the physical disruption of bacterial membrane, exhibiting the extraordinary bactericidal performance (the bactericidal rate is over 94%). The mechanism disclosed by computations is that the singlet-to-triplet transition of radical pairs can be increased by the introduction of magnetic fields. These findings offer new insights into the biological effects of magnetic fields and pave the way for their safe, highly effective use in bactericidal applications.

A novel micromagnetic carrier-modified integrated fixed-film activated sludge system for simultaneous efficient removal of tetracycline and mitigation of antibiotic resistance genes proliferation and dissemination

To address the challenge of antibiotic-containing wastewater, a novel micromagnetic carrier-modified integrated fixed-film activated sludge system (MC-IFAS) was developed for treating tetracycline (TC)-containing swine wastewater in this study. The magnetic effects of the MC significantly enhanced TC removal by improving TC biosorption and biodegradation in both the suspended activated sludge and the carrier-attached biofilm in the MC-IFAS. The increased electrostatic attraction and number of binding sites in both the activated sludge and the biofilm enhanced their TC biosorption capacities, particularly in the activated sludge. Additionally, the MC shifted microbial community assembly from stochastic to deterministic factors, amplifying the selection pressure induced by TC on the microbial community, thus enriching organic compound-degrading genera Dokdonella and TM7a; it also stimulated ammonia monooxygenase-mediated and cytochrome P450-mediated TC metabolisms and upregulated functional genes encoding lyases, transferases, hydrolases, and oxidoreductases- all of which enhanced TC biodegradation capacity in the MC-IFAS, particularly in the biofilm. While enhancing TC removal efficiency, the MC mitigated the proliferation and dissemination of antibiotic resistance genes (ARGs) by suppressing the abundances of ARGs hosts, the mobile genetic element intI1, and genes encoding ATP-binding cassette transporters and putative transposases. This study provides novel insights into the large-scale applications of magnetic field-enhanced TC removal strategies.

Augmented carbon utilization and ammonia assimilation in heterotrophic microorganism under magnetic field stimulation

Ammonia assimilation is crucial in microbial nitrogen metabolism, and researching the impact of magnetic field (MF) on heterotrophic ammonia assimilation (HAA) contributes to improving nitrogen utilization and environmental remediation. This study systematically investigated the profound effects of MF stimulation on carbon and ammonia assimilation mechanisms in heterotrophic microorganisms. The dynamic responses of microbial carbon source metabolic efficiency and nitrogen source assimilation rates were quantitatively analyzed by designing a multidimensional stimulation environment of different nutrient levels (C/N 20, 25, 30) and MF intensities (0, 1, 20 mT). The findings demonstrated that weak MF stimulation markedly enhanced carbon utilization efficiency and ammonia assimilation capacity, evidenced by accelerated metabolic flux, significant biomass augmentation and metabolic network reconfiguration. MF induced pronounced activation of key metabolic enzymes, uncovering coordinated regulatory mechanisms at the molecular level. Additionally, the MF stimulation enriched genera the Halomonas and Marinobacter, enhancing the stability of microbial community. These discoveries not only advance the theoretical understanding of MF-enhanced metabolic modulation but also offer cutting-edge insights and potential solutions for developing MF-assisted bioconversion and environmental remediation technologies.

Advancements in magnetic catalysts: Preparation, modification, and applications in photocatalytic and environmental remediation

Owing to their widely available source materials, simple magnetic separation, and low cost, magnetic catalysts have demonstrated considerable application potential in modern photocatalysis technologies and environmental remediation. This review summarizes the synthesis and modification methods of magnetic catalysts and describes recent advances using different synthesis methods. Several key problems still need to be solved in the existing progress, such as the fact that the catalytic activity of magnetic catalysts decreases over time. Under an external magnetic field, magnetic catalysts exhibit satisfactory energy bandgaps and charge transfer rates for photocatalysis, enabling wide and comprehensive photocatalytic applications. In addition, they are strong candidate materials for wastewater treatment and new-energy applications. In summary, the review provides future directions for the development of novel magnetic catalysts, contaminant removal, and even large-scale practical applications.

Performance of a novel Built-in Static Magnetic Field - Biological Aerated Filter (BSMF-BAF) for treating high-salt textile dyeing wastewater

High-salt textile dyeing wastewater is difficult to treat. Magnetic fields can enhance the biodegradation capacity and extreme environmental adaptabilities of microorganisms. Thus, magnetically enhanced bioreactors are expected to improve the treatment efficiency and stability of high-salt textile dyeing wastewater. Accordingly, a novel Built-in Static Magnetic Field - Biological Aerated Filter (BSMF-BAF) was constructed and investigated for treating actual high-salt textile dyeing wastewater in this study. Two other BAFs packed with traditional and magnetic ceramsite carriers, respectively, were simultaneously operated for comparison. The removal of color, chemical oxygen demand (COD), suspended solid (SS) and acute toxicity were monitored. The activities of key enzymes and microbial community structure were analyzed to reveal possible mechanisms for improving the treatment efficiency of traditional BAF using the BSMF. The results showed that the BSMF-BAF possessed the highest removal efficiencies of color, COD, SS and acute toxicity among the three BAFs. The BSMF induced significant increases in the activities of azoreductase and lignin peroxidase, which were responsible for the degradation of azo compounds in the wastewater and the detoxification of toxic intermediates, respectively. Additionally, the BSMF induced the relative enrichment of potentially effective bacteria and fungi, and it maintained a relatively high abundance of fungi in the microbial community, resulting in a high treatment efficiency.

Wastewater Treatment: Functional Materials and Advanced Technology

With accelerated advancements in various industries, water pollution has emerged as a significant issue characterized by two features: (1) the rapid increase in population and corresponding demands, leading to a sharp rise in wastewater discharge, and (2) the development of new technologies, contributing to a significant increase in the variety of emerging contaminants, resulting in a more complex wastewater composition [...].

Recent advances in the application of magnetic materials for the management of perfluoroalkyl substances in aqueous phases

Perfluoroalkyl substances (PFASs) are a class of artificially synthesised organic compounds extensively used in both industrial and consumer products owing to their unique characteristics. However, their persistence in the environment and potential risk to health have raised serious global concerns. Therefore, developing effective techniques to identify, eliminate, and degrade these pollutants in water are crucial. Owing to their high surface area, magnetic responsiveness, redox sensitivity, and ease of separation, magnetic materials have been considered for the treatment of PFASs from water in recent years. This review provides a comprehensive overview of the recent use of magnetic materials for the detection, removal, and degradation of PFASs in aqueous solutions. First, the use of magnetic materials for sensitive and precise detection of PFASs is addressed. Second, the adsorption of PFASs using magnetic materials is discussed. Several magnetic materials, including iron oxides, ferrites, and magnetic carbon composites, have been explored as efficient adsorbents for PFASs removal from water. Surface modification, functionalization, and composite fabrication have been employed to improve the adsorption effectiveness and selectivity of magnetic materials for PFASs. The final section of this review focuses on the advanced oxidation for PFASs using magnetic materials. This review suggests that magnetic materials have demonstrated considerable potential for use in various environmental remediation applications, as well as in the treatment of PFASs-contaminated water.

New progress in the deep understanding of the biocake layer property: Combined effect of neglected protein secondary structure, morphology, and mechanism

The application of magnetic fields (MFs) and magnetic particles (MPs) in water treatment has attracted widespread attention due to their stability, strong biological compatibility, and less chemical consumption. This study introduced MPs and MFs to GDM and probed their effects on filtration performance. Predeposited large MPs (P-large) and batch-added little MPs (B-little) intervened biocake layer development, forming more open and porous structures, they also reduced biomass secretion, resulting in flux increases of 13 % in P-large and 40 % in B-little than P-little, respectively. Besides, MFs controlled MPs distribution on the biocake layer, resulting in forming of more rough and open structures. A relatively lower magnetic field of 20 mT facilitated biomass secretion, while a higher magnetic field of 50 mT decreased biomass. Furthermore, applying magnetic fields decreased the ratios of α-helix and β-sheet, and increased random coil percentage. Thus, applying magnetic field mediation would contribute to the flux improvements in I-20 and I-50 by 29 % and 32 % relative to I-0. Economic analysis suggested introducing MPs and MFs to GDM was economically feasible, synergy of MPs and MFs had more economic advantages on the community scale and MPs-assisted GDM had significant economic advantages on both community and household scales. Future works should focus on developing new technologies for the recycling of MPs and membranes. This study provided new insight into the protein secondary structures associated with GDM performance and would encourage new sustainable MFs and MPs-assisted GDM technological developments.

Weak magnetic carriers reduce nitrite accumulation and boost denitrification at high nitrate concentrations by enriching functional bacteria and enhancing electron transfer

Biological denitrification is the dominant method for NO3- removal from wastewater, while high NO3- leads to NO2- accumulation and inhibits denitrification performance. In this study, different weak magnetic carriers (0, 0.3, 0.6, 0.9 mT) were used to enhance biological denitrification at NO3- of 50-2400 mg/L. The effect of magnetic carriers on the removal and mechanism of denitrification of high NO3- was investigated. The results showed that 0.6 and 0.9 mT carriers significantly enhanced the TN removal efficiency (>99%) and reduced the accumulation of NO2- (by > 97%) at NO3- of 1200-2400 mg/L 0.6 and 0.9 mT carriers stimulated microbial electron transport by improving the abundances of coenzyme Q-cytochrome C reductase (by 4.44-23.30%) and cytochrome C (by 2.90-16.77%), which contributed to the enhanced elimination of NO3- and NO2-. 0.6 and 0.9 mT carriers increased the activities of NAR (by 3.74-37.59%) and NIR (by 5.01-8.24%). The abundance of narG genes in 0.6 and 0.9 mT was 1.47-2.35 and 1.38-1.75 times that of R1, respectively, and the abundance of nirS genes was 1.49-2.83 and 1.55-2.39 times that of R1, respectively. Denitrifying microorganisms, e.g., Halomonas, Thauera and Pseudomonas were enriched at 0.6 and 0.9 mT carriers, which benefited to the advanced denitrification performance. This study suggests that weak magnetic carriers can help to enhance the biological denitrification of high NO3- wastewater.

Inactivation of antibiotic-resistant bacteria Escherichia coli by electroporation

Introduction

In modern times, bacterial infections have become a growing problem in the medical community due to the emergence of antibiotic-resistant bacteria. In fact, the overuse and improper disposal of antibiotics have led to bacterial resistance and the presence of such bacteria in wastewater. Therefore, it is critical to develop effective strategies for dealing with antibiotic-resistant bacteria in wastewater. Electroporation has been found to be one of the most promising complementary techniques for bacterial inactivation because it is effective against a wide range of bacteria, is non-chemical and is highly optimizable. Many studies have demonstrated electroporation-assisted inactivation of bacteria, but rarely have clinical antibiotics or bacteria resistant to these antibiotics been used in the study. Therefore, the motivation for our study was to use a treatment regimen that combines antibiotics and electroporation to inactivate antibiotic-resistant bacteria.

Methods

We separately combined two antibiotics (tetracycline and chloramphenicol) to which the bacteria are resistant (with a different resistance mode) and electric pulses. We used three different concentrations of antibiotics (40, 80 and 150 µg/ml for tetracycline and 100, 500 and 2000 µg/ml for chloramphenicol, respectively) and four different electric field strengths (5, 10, 15 and 20 kV/cm) for electroporation.

Results and discussion

Our results show that electroporation effectively enhances the effect of antibiotics and inactivates antibiotic-resistant bacteria. The inactivation rate for tetracycline or chloramphenicol was found to be different and to increase with the strength of the pulsed electric field and/or the concentration of the antibiotic. In addition, we show that electroporation has a longer lasting effect (up to 24 hours), making bacteria vulnerable for a considerable time. The present work provides new insights into the use of electroporation to inactivate antibiotic-resistant bacteria in the aquatic environment.

Membrane processes enhanced by various forms of physical energy: A systematic review on mechanisms, implementation, application and energy efficiency

Membrane technologies in water and wastewater treatment have been eagerly pursued over the past decades, yet membrane fouling remains the major bottleneck to overcome. Membrane fouling control methods which couple membrane processes with online in situ application of external physical energy input (EPEI) are getting closer and closer to reality, thanks to recent advances in novel materials and energy deliverance methods. In this review, we summarized recent studies on membrane fouling control techniques that depend on (i) electric field, (ii) acoustic field, (iii) magnetic field, and (iv) photo-irradiation (mostly ultraviolet or visible light). Mechanisms of each energy input were first reported, which defines the applicability of these methods to certain wastewater matrices. Then, means of implementation were discussed to evaluate the compatibility of these fouling control methods with established membrane techniques. After that, preferred applications of each energy input to different foulant types and membrane processes in the experiment reports were summarized, along with a discussion on the trends and knowledge gaps of such fouling control research. Next, specific energy consumption in membrane fouling control and flux enhancement was estimated and compared, based on the experimental results reported in the literature. Lastly, strength and weakness of these methods and future perspectives were presented as open questions.

Exposure of the static magnetic fields on the microbial growth rate and the sludge properties in the complete-mix activated sludge process (a Lab-scale study)

BACKGROUND

In this study, the effect of static magnetic fields (SMFs) on improving the performance of activated sludge process to enhance the higher rate of microbial growth biomass and improve sludge settling characteristics in real operation conditions of wastewater treatment plants has been investigated. The effect of SMFs (15 mT), hydraulic retention time, SRT, aeration time on mixed liquor suspended solids (MLSS) concentrations, mixed liquor volatile suspended solids (MLVSS) concentrations, α-factor, and pH in the complete-mix activated sludge (CMAS) process during 30 days of the operation, were evaluated.

RESULTS

There were not any differences between the concentration of MLSS in the case (2148.8 ± 235.6 mg/L) and control (2260.1 ± 296.0 mg/L) samples, however, the mean concentration of MLVSS in the case (1463.4 ± 419.2 mg/L) was more than the control samples (1244.1 ± 295.5 mg/L). Changes of the concentration of MLVSS over time, follow the first and second-order reaction with and without exposure of SMFs respectively. Moreover, the slope of the line and, the mean of α-factor in the case samples were 6.255 and, - 0.001 higher than the control samples, respectively. Changes in pH in both groups of the reactors were not observed. The size of the sluge flocs (1.28 µm) and, the spectra of amid I' (1440 cm-1) and II' (1650 cm-1) areas related to hydrogenase bond in the case samples were higher than the control samples.

CONCLUSIONS

SMFs have a potential to being considered as an alternative method to stimulate the microbial growth rate in the aeration reactors and produce bioflocs with the higher density in the second clarifiers.

Enhancement of organics and nutrient removal and microbial mechanism in vertical flow constructed wetland under a static magnetic field

Low and unstable pollutant removal is regarded as the bottleneck problem in constructed wetlands (CWs) for wastewater treatment. This study investigated the effect of static magnetic field (MF) on enhancing the purification efficiency and microbial mechanism in vertical flow CW systems for treating domestic wastewater. The results showed that MF-CWs outperformed control systems in terms of treatment performance, with average removal efficiencies of COD, NH₄⁺-N, TN, and TP reaching 92.58%, 73.58%, 72.53%, and 95.83%, respectively. The change of malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD) activity indicated that MF application was beneficial for plant health. Additionally, higher ammonia monooxygenase (AMO) activity in MF-CWs suggested the removal of NH₄⁺-N was facilitated. The high-throughput sequencing results demonstrated that MF application could enrich the functional bacteria such as Patescibacteria phylum, mainly, including Gammaproteobacteria, Betaproteobacteria, and Alphaproteobacteria, which further accelerated pollutants transformation. These findings would be beneficial in understanding pollutant removal processes and their mechanism in CWs with MF application.

Positive effects of magnetic Fe3O4@polyaniline on aerobic granular sludge: Aerobic granulation, granule stability and pollutants removal performance

The magnetic material has been determined to have a positive effect on sludge granulation and wastewater treatment performance. In this study, the effect of magnetic Fe₃O₄@polyaniline (Fe₃O₄@PANI) on aerobic granulation, granule stability, and pollutants removal performance was evaluated by adding it into a sequencing batch reactor to cultivate aerobic granular sludge (AGS). The results indicated that the composite combined the advantages of PANI and Fe₃O₄ to promote the formation of AGS during the granulation period. The Fe₃O₄@PANI stimulated the granules to secrete extracellular polymeric substances with a higher proteins/polysaccharides ratio, thus enhancing the stability of the AGS. In addition, microbial community analysis revealed that the great performance of the AGS on denitrification and phosphorus removal could be attributed to the enrichment of denitrifying bacteria, phosphorus accumulating organisms (PAO), and denitrifying PAO by Fe₃O₄@PANI. Thus, Fe₃O₄@PANI has been demonstrated to have a positive effect on the formation and stability of AGS.

IoT-Based Fish Farm Water Quality Monitoring System

Typhoons in summer and cold snaps during winter in Taiwan often cause huge aquaculture losses. Simultaneously, the lack of human resources is a problem. Therefore, we used wireless transmission technology with various sensors to transmit the temperature, pH value, dissolved oxygen, water level, and life expectancy of the sensor in the fish farm to the server. The integrated data are transmitted to mobile devices through the Internet of Things, enabling administrators to monitor the water quality in a fish farm through mobile devices. Because the current pH sensors cannot be submerged in the liquid for a long time for measurements, human resources and time are required to take the instrument to each fish farm for testing at a fixed time. Therefore, a robotic arm was developed to complete automatic measurement and maintenance actions. We designed this arm with a programmable logic controller, a single chip combined with a wireless transmission module, and an embedded system. This system is divided into control, measurement, server, and mobility. The intelligent measurement equipment designed in this study can work 24 h per day, which effectively reduces the losses caused by personnel, material resources, and data errors.

Recent advances in starch-based magnetic adsorbents for the removal of contaminants from wastewater: A review

Considerable concern exists regarding water contamination by various pollutants, such as conventional pollutants (e.g., heavy metals and organics) and emerging micropollutants (e.g., consumer care products and interfering endocrine-related compounds). Currently, academics are continuously exploring sustainability-related materials and technologies to remove contaminants from wastewater. Magnetic starch-based adsorbents (MSAs) can combine the advantages of starch and magnetic nanoparticles, which exhibit unique critical features such as availability, cost-effectiveness, size, shape, crystallinity, magnetic properties, stability, adsorption properties, and excellent surface properties. However, limited reviews on MSAs' preparations, characterizations, applications, and adsorption mechanisms could be available nowadays. Hence, this review not only focuses on their activation and preparation methods, including physical (e.g., mechanical activation treatment, microwave radiation treatment, sonication, and extrusion), chemical (e.g., grafting, cross-linking, oxidation and esterification), and enzymatic modifications to enhance their adsorption properties, but also offers an all-round state-of-the-art analysis of the full range of its characterization methods, the adsorption of various contaminants, and the underlying adsorption mechanisms. Eventually, this review focuses on the recycling and reclamation performance and highlights the main gaps in the areas where further studies are warranted. We hope that this review will spark an interdisciplinary discussion and bring about a revolution in the applications of MSAs.

Coupling Magnetic Field and Salinity Upshock To Improve Polyhydroxyalkanoate Productivity by Haloferax mediterranei Feeding on Molasses Wastewater

Low polyhydroxyalkanoate (PHA) volumetric productivity from wastewater limits low-cost PHA production. To resolve this problem, an external magnetic field (MF) coupled with upshock salinity was applied to PHA production by Haloferax mediterranei (family Halobacteriaceae). Elevating the fermentation salinity over the optimal growth salinity (200 g/L) increased the PHA cell content while inhibiting cell proliferation, decreasing volumetric productivity. When a MF of 50 mT in 300 g/L salinity was applied, H. mediterranei proliferation and PHA cell content were promoted, leading to a 7.95% increase in PHA volumetric productivity in synthetic molasses wastewater and a 13.82% increase in glucose feeding compared with those in 200 g/L salinity. Under the MF, osmotic pressure regulation was activated by accumulating K⁺ and increasing betaine synthesis. The maximum betaine content increased by 74.33% in 300 g/L salinity with a 50-mT MF compared with that in 200 g/L salinity. When a 50-mT MF in 300 g/L salinity was applied, the malondialdehyde (MDA) content decreased by 32.66% and the activity of superoxide dismutase (SOD) increased by 46.89%, which reduced the oxidative damage. This study provides a new solution to enhance PHA volumetric productivity by MF and an insight into the magnetic effects of H. mediterranei. IMPORTANCE The obstacle to replacing petroplastics with PHA is its high production cost. To increase the fermentation economy, a novel strategy of coupling a MF with salinity upshock was applied, which enhanced the PHA volumetric productivity of H. mediterranei in fermenting molasses wastewater. The magnetic effect of H. mediterranei was found at a MF of 50 mT, which improved the salt tolerance of H. mediterranei and reduced the oxidative damage induced by the elevated salinity, thereby promoting proliferation and PHA cell content. This is the first time a technical method for enhancing PHA volumetric productivity by means of a MF has been proposed. Such a strategy can advance the utilization of H. mediterranei for the industrial production of PHA using organic wastewater.

Modification of expanded clay carrier for enhancing the immobilization and nitrogen removal capacity of nitrifying and denitrifying bacteria in the aquaculture system

In aquaculture systems, the treatment of nitrogen pollution has always been a center of attention due to its impact on productiveness. The bioremediation method based on simultaneous nitrification and denitrification was often used to effectively remove ammonium, nitrite, and nitrate compounds. In addition, the attachment and biofilm formation of the nitrogen-converting bacteria on carriers had superior removal efficiency over the suspended bacteria. Thus, this study focused on the fabrication of a porosity floatable expanded clay (EC) carrier that provided the basic structure for the immobilization of the nitrifiers Nitrosomonas sp., Nitrobacter sp., and the denitrifier Bacillus sp. The EC was also coated with alginate and essential nutrient to support the cohesion and growth of bacteria. Especially, the selected Bacillus sp. previously proved was able to reduce nitrite/nitrate in aerobic conditions. The co-immobilization of these three aerobic bacteria on the prepared carrier would simply the treatment process in practical use. Initial results showed that the integration of essential nutrients (N, P, K) on alginate coated EC (EC_Alg_N) increased bacterial density to (57 ± 3) × 10⁷ - (430 ± 30) × 10⁸ CFU/g, which then led to the enhancement of removal efficiency up to 91.62 ± 0.67% in the medium containing initial nitrogen content of 60 mg-N/L. The nitrogen removal efficacy of bacterial immobilized EC_Alg_N remained at 83.95 ± 0.15% after being reused for 6 cycles. In conclusion, the bacterial immobilized EC_Alg_N could be a potential material for nitrogen polluted wastewater treatment in aquaculture systems.

Enhanced aerobic granular sludge by static magnetic field to treat saline wastewater via simultaneous partial nitrification and denitrification (SPND) process

Saline wastewater poses a threat to biological nitrogen removal. This study investigated whether and how static magnetic field (SMF) can improve the salt-tolerance of aerobic granular sludge (AGS) in two simultaneous partial nitrification and denitrification (SPND) reactors. Results confirmed that the SMF improved the mean size and settleability of granules, stimulated secretion of extracellular polymeric substances with high protein content, in turn enhancing the aerobic granulation. Although high salt stress inhibited functional microorganisms, the SMF maintained better SPND performance with average COD removal, TN removal and nitrite accumulation ratio finally recovering to 100%, 72.9% and 91.1% respectively. High throughput sequencing revealed that functional bacteria evolved from Paracoccus to halotolerant genera Xanthomarina, Thauera, Pseudofulvimonas and Azoarcus with stepwise increasing salinity. The enhanced salt-tolerance may be because the SMF promoted the activity of these halotolerant bacteria. Therefore, this study proposes an economic, effective and environmental biotechnology for saline wastewater treatment.

Research and Application of Supersaturated Dissolved Oxygen Technology Combined with Magnetization Technology in the Improvement of Water Quality: Taking the South-to-North Water Diversion Project of China as a Pilot Project

Supersaturated dissolved oxygen and magnetization (SDOXM) technology is a composite technology that combines supersaturated dissolved oxygen with water magnetization technologies. Compared with conventional water purification technology, the advantages introduced by such technology include obvious and efficient improvement in purified water quality without adding any chemicals, removing sludge and changing the original function of the river. In this study, taking the Middle-Route (MR) of the South-to-North Water Diversion Project of China (SNWDPC) as a pilot project, the effects of the SDOXM composite process on microbial activity, phytoplankton community structure, and removal efficiency of the main nutritional indexes in the canal of the MR were evaluated. Aiming at static and flowing water bodies, this study was divided into two parts: static and dynamic experiments (two groups: a group with artificial aquatic plants and another group without artificial aquatic plants). The performance of the SDOXM system was assessed by monitoring the organic matter removal as well as the relative light unit (RLU) of ATP, changes in the community structure of phytoplankton, and the effects of artificial aquatic plants as a biofilm carrier on organic matter removal and microbial activity. During the study period, SDOXM technology was able to increase the concentration of dissolved oxygen (DO) in water and maintained the state of supersaturation for more than three days. The removal effect of organic matter from water was obvious. The community structure of phytoplankton changed from the Bacillariophyta-Cyanophyta type to the Bacillariophyta-Cyanobacteria type. Finally, the introduction of artificial aquatic plants has contributed to the improvement in water quality. Therefore, SDOXM technology can be used as a new water quality improvement technology to enhance the self-restoration ability of a river natural ecology.

Revealing the effects of static magnetic field on the anoxic/oxic sequencing batch reactor from the perspective of electron transport and microbial community shifts

The effects of static magnetic field (SMF) on an anoxic/oxic sequencing batch reactor were investigated from the perspective of electron transport via determining the variations of reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD⁺) ratio, NADH concentration, electron transport system activity (ETSA), poly-β-hydroxybutyrate (PHB), extracellular polymeric substances (EPS), as well as the gene expression under different conditions. Moreover, the shifts of microbial community were also analyzed. The application of SMF with an appropriate intensity significantly improved the performance of the process, the abundance of the anoxic denitrifiers, and the activity of the aerobic denitrifiers. The NADH content, as well as ETSA were also enhanced, therefore, the total nitrogen removal efficiency of the process was increased. However, the overhigh SMF intensity resulted in the change of microbial community, meanwhile, had negative effects on the metabolism of microorganisms. Selecting a proper intensity is crucial for the SMF-enhanced biological wastewater treatment process.

Efficient degradation of naproxen in a three dimensional biofilm electrode magnetism reactor (3DBEMR): Removal performance and microbial community

A three-dimensional biofilm electrode magnetism reactor (3DBEMR) was constructed to removal naproxen (NPX). This study evaluated 3DBEMR performance in removal of refractory NPX, while also discussing the effect of the electro-magnetic superposition on microbial community by high throughput sequencing. Results indicated that 3DBEMR's average removal rate for NPX stood at 88.36%, representing an increase by 75.24%, 65.03% and 12.36%, respectively, compared to 3DBR (Three-Dimensional Biofilm Reactor), 3DBMR (Three-Dimensional Biofilm Magnetism Reactor) and 3DBER (Three-Dimensional Biofilm Electrode Reactor). This was attributed to the influence of electro-magnetic adsorption, electro-oxidaton/catalysis, and electro-magnetic biodegradation. Another major contributing factor to NPX removal was the presence in 3DBEMR of high-abundance genera such as Rhodobacter, Porphyrobacter, Methyloversatilis, Sphingopyxis,Bosea, Singulisphaera, Sphingomonas. Therefore, the 3DBEMR was successfully demonstrated to be a flexible and effective technique in NPX degradation, which would help to better understand the effect of superposition of electric and magnetic fields on microbial community.

Electro/magnetic superposition effects on diclofenac degradation: Removal performance, kinetics, community structure and synergistic mechanism

Electric and magnetic fields characterized by high efficiency, low consumption and environment-friendly performance have recently generated interest as a possible measure to enhance the performance of the biological treatment process used to remove refractory organics. Few studies have been carried out to-date regarding the simultaneous application of electric and magnetic fields on biofilm process to degrade diclofenac. In this study, 3DEM-BAF was designed to evaluate the electrio-magnetic superposition effect on diclofenac removal performance, kinetics, community structure and synergistic mechanism. The results show that 3DEM-BAF could significantly increase the average removal rate of diclofenac by 65.30 %, 57.46 %, 9.48 % as compared with that of BAF, 3DM-BAF, 3DE-BAF, respectively. The diclofenac degradation kinetic constants and dehydrogenase activity of 3DEM-BAF were almost 6.72 and 2.53 times higher than those of BAF. Microorganisms of 3DEM-BAF in the Methylophilus and Methyloversatilis genera were distinctively enriched, which was attributed to the screening function of electric field and propagation effect of magnetic field. Moreover, three processes were found to contribute to diclofenac degradation, namely electro-magnetic-adsorption, electro-chemical oxidation and electro-magnetic-biodegradation. Thus, the simultaneous application of electric and magnetic fields on biofilm process was demonstrated to be a promising technique as well as a viable alternative in diclofenac degradation enhancement.

Performance evaluation and mechanism of nitrogen removal in a packed bed reactor using micromagnetic carriers at different carbon to nitrogen ratios

Advanced nitrogen removal of effluent discharged from secondary treatment systems can avoid eutrophication. However, the lack of biodegradable organics limits biodenitrification. Packed bed reactors filled with carriers with different micromagnetic field (MMF) strengths were used to perform tertiary denitrification. The results showed that MMF significantly improved the denitrification performance, especially at low C/N ratios. Total nitrogen (TN) removal was increased by 4.12% with 0.6 mT MMF when C/N = 4 and increased by 7.06% and 8.06% with 0.3 mT and 0.9 mT MMFs when C/N = 3, respectively. Zooglea, Flavobacterium, and Denitratisoma contributed to the advanced denitrification performance under MMF. In addition, 0.6 mT MMF enhanced nitrogen metabolism and ABC transporter protein and two-component system activities of microorganisms under C/N = 4; 0.3 mT and 0.9 mT MMFs increased nitrogen, carbohydrate, and amino acid metabolism and ABC transporter protein activities under C/N = 3. These findings indicate that MMF has great potential for advanced denitrification from secondary effluent.

Up-concentration processes of organics for municipal wastewater treatment: New trends in separation

Carbon neutrality is a pressing goal for the whole society. Over 20% of municipality electrical energy on public utilities was consumed by the operation of wastewater treatment plants (WWTPs). Up-concentration of organic matters and maximum energy recovery is essential for a more sophisticated municipal wastewater management. Chemical coagulation and biological adsorption have been used to achieve efficient carbon capture, while separation is an overlooked step. It may lead to poor effluent quality, as well as consume most of the time and volume. The introduction of new driving forces, such as pressure and magnetism, significantly improved the retention rate and speed, respectively. In this paper, recent works were comprehensively reviewed and a horizontal comparison was conducted from aspects of separation speed, retention rate, concentrate characteristics and economic costs. This review also discussed the selection of technologies under different conditions. Finally, the practical application, fouling mitigation with considering the value of the concentrate, identification of unique concentrate characteristics, and the establishment of an evaluation system was suggested as core issues for future researches. This review will promote the development of an energy-efficient wastewater treatment system with up-concentration processes.