The strengthening effect of a static magnetic field on activated sludge activity at low temperature

Advances in bioelectrochemical systems for bio-products recovery

Bioelectrochemical systems (BES) have emerged as a sustainable and highly promising technology that has garnered significant attention from researchers worldwide. These systems provide an efficient platform for the removal and recovery of valuable products from wastewater, with minimal or no net energy loss. Among the various types of BES, microbial fuel cells (MFCs) are a notable example, utilizing microbial biocatalytic activities to generate electrical energy through the degradation of organic matter. Other BES variants include microbial desalination cells (MDCs), microbial electrolysis cells (MECs), microbial electrosynthesis cells (MXCs), microbial solar cells (MSCs), and more. BESs have demonstrated remarkable potential in the recovery of diverse products such as hydrogen, methane, volatile fatty acids, precious nutrients, and metals. Recent advancements in scaling up BESs have facilitated a more realistic assessment of their net energy recovery and resource yield in real-world applications. This comprehensive review focuses on the practical applications of BESs, from laboratory-scale developments to their potential for industrial commercialization. Specifically, it highlights successful examples of value-added product recovery achieved through various BES configurations. Additionally, this review critically evaluates the limitations of BESs and provides suggestions to enhance their performance at a larger scale, enabling effective implementation in real-world scenarios. By providing a thorough analysis of the current state of BES technology, this review aims to emphasize the tremendous potential of these systems for sustainable wastewater treatment and resource recovery. It underscores the significance of bridging the gap between laboratory-scale achievements and industrial implementation, paving the way for a more sustainable and resource-efficient future.

Synergistic effect of zero-valent iron and static magnetic field on wastewater purification and bioelectricity generation in electroactive constructed wetlands

This study investigated the enhancement effect of zero-valent iron and static magnetic field on the pollutant removal and power generation of electroactive constructed wetland. As demonstration, a conventional wetland was systematically modified by introducing zero-valent iron and then a static magnetic field, leading to progressive increases in pollutant (namely NH4+-N and chemical oxygen demand) removal efficiencies. By introducing both zero-valent iron and a static magnetic field, the power density increased four-fold to 9.2 mW/m2 and the internal resistance decreased by 26.7% to 467.4 Ω. Notably, static magnetic field decreased the relative abundance of electrochemically active bacteria (such as Romboutsia), while significantly enhancing species diversity. The permeability of the microbial cell membrane was improved, leading to a reduction in activation loss and internal resistance, thereby enhancing power generation capacity. Results showed that the addition of zero-valent iron and the applied magnetic field were beneficial to the pollutants removal and bioelectricity generation.

Research on microbial community structure and treatment of dye wastewater with the enhancement of activated sludge by magnetic field at low temperature

This study characterized the effect of different magnetic field (MF) intensities (10-40 mT) on the degradation of dye wastewater by activated sludge and the diversity of the microbial community at a low temperature (5 °C). The examined MF range promoted the degradation of dye wastewater by the microorganisms in the activated sludge at a low temperature. It was found that the optimal degradation performance was achieved at 30 mT. Additionally, the maximum degradation efficiency of COD and chromaticity (66.30% and 60.87%, respectively) were also achieved at 30 mT and the peak TTC-dehydrogenase activity (TTC-DHA) was 9.44 mg TF g^-1 SS. Furthermore, it was revealed that MF enhancement increased the richness and diversity of activated sludge microorganisms, thus promoting the growth and reproduction of activated sludge microorganisms at low temperatures. Bacterial taxa known to effectively participate in the degradation of pollutants by activated sludge were enriched at 30 mT. The dominant bacteria under 30 mT were Flavobacterium, Hydrogenophaga, Gemmatimonadaceae, Zoogloea, Saprospiraceae, Pseudomonas, and Geothrix.

The best location for the application of static magnetic fields based on biokinetic coefficients in complete-mix activated sludge process

The use of the kinetic coefficients for the mathematical expression of the biochemical processes and the relationship between the effective parameters is importance. Change of the biokinetic coefficients in the complete-mix activated sludge processes were calculated for 1 month operation of the activated sludge model (ASM) in a Lab-scale in three series. 15 mT intensity of static magnetic fields (SMFs) applied on the aeration reactor (ASM 1), clarifier reactor (ASM 2) and, sludge returning systems (ASM 3) for 1 h, daily. During the operation of the systems, five basic biokinetic coefficients such as maximum specific substrate utilization rate (k), heterotrophic half-saturation substrate concentration (K_s), decay coefficient (k_d), yield coefficient (Y) and, maximum specific microbial growth rate (μ_max) were determined. The rate of k (g COD/g Cells.d) in ASM 1 was 2.69% and, 22.79% higher than ASM 2 and, ASM 3. The value of K_s (mg COD/L) was 54.44 and, 71.13 (mg/L) lower than the ASM 2 and, ASM 3. The rate of k_d ASM 1, ASM 2 and, ASM 3 was 0.070, 0.054 and, 0.516 (d^-1). The value of Y (kg VSS/kg COD) in ASM 1 was 0.58% and, 0.48% lower than ASM 2 and, ASM 3. The rate of μ_max (d^-1) in ASM 1 was 0.197, this value for ASM 2 and ASM 3 were 0.324 and 0.309 (d^-1). Related to the biokinetic coefficients analyses the best location for the application of 15 mT SMFs was the aeration reactor, where the present of oxygen, substrate and, SMFs have the greatest impact on the positive changes of these coefficients.

The use of the electromagnetic field in microbial process bioengineering

An electromagnetic field (EMF) has been shown to have various stimulatory or inhibitory effects on microorganisms. Over the years, growing interest in this topic led to numerous discoveries suggesting the potential applicability of EMF in biotechnological processes. Among these observations are stimulative effects of this physical influence resulting in intensified biomass production, modification of metabolic activity, or pigments secretion. In this review, we present the current state of the art and underline the main findings of the application of EMF in bioprocessing and their practical meaning in process engineering using examples selected from studies on bacteria, archaea, microscopic fungi and yeasts, viruses, and microalgae. All biological data are presented concerning the classification of EMF. Furthermore, we aimed to highlight missing parts of contemporary knowledge and indicate weak spots in the approaches found in the literature.

Insights into the potential application of magnetic field in controlling sludge bulking and foaming: A review

The formation of bulking and foaming in biological wastewater treatment could cause a series of operational issues with biomass and effluent quality, ultimately affect the treatment performance of the system. The essential parameters influencing the growth of bulking and foaming bacteria are comprehensively summarised in this paper. Existing bulking and foaming control approached are critically reviewed and addressed, as well as their drawbacks and limitations. Despite the abundance of information and implementation, a complete control technique for limiting filamentous sludge bulking and foaming remains insufficient. Magnetic field application is emphasised as a viable control strategy in this regard. The present review study provides new insight of this application by comparing the use of magnetic fields to conventional treatments. Future outlooks on the use of magnetic fields to prevent BFB proliferation were also highlighted.

Boosting microfluidic microbial fuel cells performance via investigating electron transfer mechanisms, metal-based electrodes, and magnetic field effect

The presented paper fundamentally investigates the influence of different electron transfer mechanisms, various metal-based electrodes, and a static magnetic field on the overall performance of microfluidic microbial fuel cells (MFCs) for the first time to improve the generated bioelectricity. To do so, as the anode of microfluidic MFCs, zinc, aluminum, tin, copper, and nickel were thoroughly investigated. Two types of bacteria, Escherichia coli and Shewanella oneidensis MR-1, were used as biocatalysts to compare the different electron transfer mechanisms. Interaction between the anode and microorganisms was assessed. Finally, the potential of applying a static magnetic field to maximize the generated power was evaluated. For zinc anode, the maximum open circuit potential, current density, and power density of 1.39 V, 138,181 mA m^-2 and 35,294 mW m^-2 were obtained, respectively. The produced current density is at least 445% better than the values obtained in previously published studies so far. The microfluidic MFCs were successfully used to power ultraviolet light-emitting diodes (UV-LEDs) for medical and clinical applications to elucidate their application as micro-sized power generators for implantable medical devices.

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.

Enhanced anaerobic co-digestion performance by using surface-annealed titanium spheres at different atmospheres

A series of surface-annealed titanium spheres (Ti-A, Ti-B, and Ti-C) in different atmospheres were used as accelerants in anaerobic co-digestion (AcoD) systems under magnetic field (MF). Surface-annealed titanium spheres and MF exhibit remarkable coupling and promoting effects on the AcoD performance. The cumulative biogas yield (435.84-552.60 mL/g VS) and total chemical oxygen demand (COD) degradation efficiency (59.76%-71.28%) of the AcoD systems with Ti_MF, Ti-A_MF, Ti-B_MF, and Ti-C_MF were significantly higher than control (357.66 mL/g VS and 51.5%). The digestates of the AcoD system with surface-annealed Ti spheres delivered excellent stability (49.83%-59.90%) and fertilizer (4.21%-4.56%). This work clarifies the possible role of surface-annealed Ti spheres in enhancing methanogenesis.

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.

Bacterial survival strategies in sludge alkaline fermentation for volatile fatty acids production: Study on the physiological properties, temporal evolution and spatial distribution of bacterial community

This study investigated the dynamics of ATP synthase activity, phospholipid fatty acid (PLFA) profile, and temporal evolution and spatial distribution of bacterial community to analyze bacterial survival strategies in sludge alkaline fermentation (SAF) for volatile fatty acids (VFAs) production. The results revealed a significant increase in ATP synthase activity at pH 9 and 10 (p < 0.05), which could contribute to proton entry into cells and benefit bacterial survival. PLFA analysis indicated that the unsaturated fatty acids content increased with the increase of pH. Firmicutes were the dominant microorganisms in the running stage of the pH 10 reactor (35.81-62.34%) and might have been the key microbes that influenced VFAs production. Further analysis of the spatial distribution of microbial community suggested that Firmicutes mainly lived inside flocs during SAF. These findings provide an understanding for bacterial survival strategies in SAF, which could help to develop methods to further improve VFAs yield.

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

Magnetic field (MF) has been applied widely and successfully as an efficient, low-cost and easy-to-use technique to enhance wastewater treatment (WWT) performance. Although the effects of MF on WWT were revealed and summarized by some works, they are still mysterious and complex. This review summarizes the application of MF in magnetic adsorption-separation of heavy metals and dyes, treatment of domestic wastewater and photo-magnetic coupling technology. Furthermore, the mechanisms of MF-enhanced WWT are critically elaborated from the perspective of magnetic physicochemical and biological effects, such as magnetoresistance, Lorentz force, and intracellular radical pair mechanism. At last, the challenges and opportunities for MF application in WWT are discussed. For overcoming the limitations and taking advantages of MFs in WWT, fundamental research of the mechanisms of the application of MFs should be carried out in the future.

Static Magnetic Fields Effects on Polysaccharides Production by Different Microalgae Strains

Microalgae are able to produce many valuable biomolecules, such as polysaccharides, that presents a large diversity of biochemical structures and functions as antioxidant, antifungal, anticancer, among others. Static magnetic fields (SMF) influence the metabolism of microorganisms and has been shown as an alternative to increase microalgae biomass, yield and compounds production. Especially, some studies have highlighted that SMF application could enhance carbohydrate content. This study aimed to evaluate different conditions of SMF on Spirulina and Chlorella in indoor and outdoor conditions, in order to confirm the influence of SMF on polysaccharides production, evaluating which polysaccharidic fraction could be enhanced by SMF and highlighting a possible modification in EPS composition. Starch from Chlorella and exopolysaccharides (EPS) from Spirulina were quantified and characterized. SMF increased the starch content in Chorella fusca biomass. EPS productions from A. platensis and Spirulina sp. were not significantly increased, and global composition appeared similar to the controls (constituted basically of 80–86% neutral sugars and 13–19% uronic acids). However, the monosaccharide composition analysis revealed a significant modification of composition, i.e., the amount of fucose, arabinose, rhamnose, galactose and glucuronic acid was increased, while the glucose content was decreased. SMF application led to significant modification of polysaccharides production and this study demonstrate that combining the outdoor conditions with SMF, the starch content and EPS composition was positively affected.

Magnetic MBR technology: from the fabrication of membrane to application in wastewater treatment

The aim of this study is to synthesize a magnetic nanocomposite membrane using iron oxide and alumina nanoparticles and employing it in magnetic membrane bioreactors (MBRs) for oily wastewater treatment. Al₂O₃ and Fe₃O₄ nanoparticles with approximate sizes of 20 and 30 nm respectively, were settled into a polysulfone (PSf) membrane matrix via magnetic casting method. The concentration of alumina and iron oxide nanoparticles were 0-0.25 wt% and 0.03 wt%, respectively. Compared with the blank membrane, an increase in the concentration of Fe₃O₄ up to 0.2 wt%, led to the flux as much as 70% and mitigated total resistance by 70%. The presence of the magnetic field around the bioreactor increased the flux significantly and reduced the cake resistance by 93%. Moreover, by applying the static magnetic field to MBR, the Chemical Oxygen Demand (COD) removal rate was increased to 93%, while in the MBR without the magnetic field the COD removal rate was 80%. Our investigation illustrated that the magnetic casting is an effective method to improve the flux and mitigate the fouling of the magnetic nanocomposite membrane. The output of this research indicates that the magnetic casting method enhance the magnetic MBRs performance for wastewater treatment.

Effect of Fe3O4 nanoparticles exposure on the treatment efficiency of phenol wastewater and community shifts in SBR system

Increasing magnetic Fe₃O₄ nanoparticles (Fe₃O₄ NPs) application has aroused concern about its potential environmental toxicity. During acute and chronic exposure, key enzymes involved in phenol biodegradation were promoted at 0-600 mg/L Fe₃O₄ NPs, while were inhibited at 800 mg/L Fe₃O₄ NPs, correspondingly affected phenol degradation efficiency. Lactic dehydrogenase (LDH) increased when Fe₃O₄ NPs exceeded 600 mg/L, indicated the more severe cell rupture at high Fe₃O₄ NPs concentration. At the same Fe₃O₄ NPs concentration, the removal of EPS further inhibited key enzymes, decreased phenol degradation, and increased LDH, indicating that the existence of EPS relieved the adverse effects on microorganisms. Spectroscopic analysis showed that protein and polysaccharide associated bonds in EPS decreased at 0-600 mg/L Fe₃O₄ NPs, while increased when Fe₃O₄ NPs exceeded 600 mg/L, which was in accordance with EPS content. Biopolymer-degrading and phenol-degrading genera increased at 0-600 mg/L Fe₃O₄ NPs, while decreased at Fe₃O₄ NPs exceeded 600 mg/L, which conformed to EPS content and phenol degradation efficiency.

Role of weak magnetic strength in the operation of aerobic granular reactor for wastewater treatment containing ammonia nitrogen concentration gradient

Weak magnetic field (WMF) and aerobic granular sludge (AGS) technology were both robust technologies in wastewater treatments. In this study, the AGS characteristics and nutrient removal performances were all estimated at the load of 20 to 40 mg/L ammonia nitrogen (NH₄⁺-N) and 0 to 40mT magnetic field. Results showed that 10mT was beneficial for keeping stable structure of granules when increasing NH₄⁺-N load, accompanied with increasing protein (PN) secretion in EPS. Besides, all the total nitrogen (TN) removal rate under 10mT reached above 90%, while they were all less than 80% under other WMF strength when loading with 40 mg/L NH₄⁺-N. Moreover, the simultaneous nitrification and denitrification (SND) efficiency could be enhanced by WMF of 10mT. Illumina MiSeq sequencing showed that NH₄⁺-N load changed the bacterial richness and diversity when the magnetic strength was 10mT. And Candidatus_Competibacter was identified as the main functional genes for effective operation in this system.

The Effect of Static Magnetic Field on Methanogenesis in the Anaerobic Digestion of Municipal Sewage Sludge

The present study aimed to determine the effect of a 17.6 mT static magnetic field (SMF) on the efficiency of anaerobic digestion (AD) of municipal sewage sludge (MSS). The SMF had a significant impact on methane (CH4) production efficiency, the levels of fermentation rate (ηFMSS) vs. removal rate (ηVS), and the structure of the anaerobic bacteria consortium, but it did not affect cumulative biogas production. The highest CH4 yield (431 ± 22 dm3CH4/kgVS) and the highest methane content in the biogas (66.1% ± 1.9%) were found in the variant in which the SMF exposure time was 144 min/day. This variant also produced the highest ηFMSS and ηVS values, reaching 73.8% ± 2.3% and ηVS 36.9% ± 1.6%, respectively. Longer anaerobic sludge retention time in the SMF area significantly decreased AD efficiency and caused a significant reduction in the number of methanogens in the anaerobic bacteria community. The lowest values were observed for SMF exposure time of 432 min/day, which produced only 54.8 ± 1.9% CH4 in the biogas. A pronounced reduction was recorded in the Archaea (ARC915) and Methanosaeta (MX825) populations in the anaerobic sludge, i.e., to 20% ± 11% and 6% ± 2%, respectively.

Effect of magnetic powder on nitrous oxide emissions from a sequencing batch reactor for treating domestic wastewater at low temperatures

Low temperatures can lead to an increase of N₂O generation and emission from the nitrogen removal process in wastewater treatment plants. This study investigated the effect of the addition of magnetic powder on N₂O generation and emission from a sequencing batch reactor treating domestic sewage at low temperatures. The results showed that the magnetic powder simultaneously inhibited N₂O generation and emission and improved the removal of NH₄⁺, total nitrogen (TN), and chemical oxygen demand at low temperatures. Furthermore, the conversion rate of N₂O (N₂O generation to TN removal) was reduced. The efficacy of the magnetic powder depended on its concentration, which could be ordered as 1 mg/L > 2 mg/L > 4 mg/L. With the addition of magnetic powder, especially at the 1 mg/L level, the activities of nitrification and denitrification enzymes in activated sludge were significantly improved and the growth of ammonium and nitrite oxidizing bacteria was also promoted.

Employing magnetism of Fe3O4 and hydrophilicity of ZrO2 to mitigate biofouling in magnetic MBR by Fe3O4-coated ZrO2/PAN nanocomposite membrane

The aim of this research is benefiting from the synergistic effect of the simultaneous presence of Fe₃O₄ and ZrO₂ in the form of Fe₃O₄-coated ZrO₂ (Fe₃O₄@ZrO₂) nanoparticles within the structure of PAN membrane to reduce membrane fouling. The role of Fe₃O₄ nanoparticles in increasing the pore size and magnetic saturation as well as the role of ZrO₂ in decreasing surface roughness and hydrophobicity can mitigate membrane fouling in magnetic-assisted membrane bioreactors. For this purpose, Fe₃O₄, ZrO₂, and Fe₃O₄@ZrO₂ nanoparticles were embedded into PAN membrane structure and magnetic (M _nM), hydrophilic (H _nM), and magnetic-hydrophilic (HM _nM) membranes were synthesized. H ₁M (1ZrO₂/PAN) membrane with a contact angle of 31 degrees, M ₁N (1Fe₃O₄/PAN) with a pore size of 90 nm, and H ₃M (3ZrO₂/PAN) membrane with an RMS roughness of 13.5 nm were the most hydrophilic, porous, and smoothest membranes, respectively. High sensitivity to magnetic field along with high porosity, high hydrophilicity and low surface roughness simultaneously exist within the structure of MHMs membranes, such that MH ₁M (1Fe₃O₄@ZrO₂/PAN) indicated 116% greater flux, 121% greater flux recovery, and 85% less total filtration resistance in comparison with the blank membrane in magnetic membrane bioreactor, at a magnetic field intensity of 120 mT and MLSS = 10,000 mg/l. As an overall conclusion, the output of this research was compared with other research in term of normalized flux. Results reveal that at MLSS = 10,000 mg/l, HRT = 8 h and TMP = 0.3 bar, MH ₁M membrane has normalized flux equal to 1.56 g/m² h bar which is an acceptable value compared to normalized flux reported by other researchers.

Enhanced anaerobic mono- and co-digestion under mesophilic condition: Focusing on the magnetic field and Ti-sphere core-shell structured additives

Enhancing anaerobic digestion performance is highly desired for its large-scale application. In the present work, magnetic fields (0-30 mT) and Ti-sphere core-shell structured additives (Ti-1 and Ti-2) are simultaneously introduced in anaerobic mono-digestion and co-digestions. Compared with the control group, the Ti-sphere core-shell structured additives increase the biogas yield by 27.12%-65.53% for mono-digestion and 8.47%-35.89% for co-digestion systems under the optimized magnetic field intensity (5 mT), respectively. Meanwhile, the degradation rate of total chemical oxygen demand is 54.68%-69.14% for anaerobic mono-digestion and 53.03%-78.25% for anaerobic co-digestion with Ti-sphere core-shell structured additives, respectively. The digestate with Ti-sphere core-shell structured additives exhibits the remarkable stability (45.24%-53.17%) and fertility (4.85%-4.97%). This work clarifies the effect of magnetic field in AD system, and proposes a possible mechanism for understanding the enhanced methanogenesis pathways induced by Ti-sphere core-shell structured additives.

Enhanced azo dye biodegradation performance and halotolerance of Candida tropicalis SYF-1 by static magnetic field (SMF)

Enhancing Acid Red B (ARB) decolorization by growing cells of a halotolerant yeast Candida tropicalis SYF-1 with static magnetic field (SMF) was investigated. Activity of key enzymes and membrane phospholipid fatty acids (PLFAs) were analyzed for estimating the change of metabolic activity and membrane salt-stress response, respectively. Possible enhancement mechanisms were revealed through comparative transcriptome analysis. The results showed that 95.0 mT SMF enhanced ARB decolorization by growing cells of a yeast SYF-1, as well as cell growth and halotolerance capability. Activity of intracellular lignin peroxidase (LiP) and laccase (Lac) was 1.51- and 1.47-fold higher with 95.0 mT SMF than that without SMF, respectively. Unsaturation degree and chain length of dominant PLFAs was increased by 95.0 mT SMF treatment. Several functional protein encoding unigenes related to organics biodegradation, cell growth and halotolerance were 1.17- to 4.19-fold up-regulated in response to 95.0 mT SMF.

Effect of temperature on the characterization of soluble microbial products in activated sludge system with special emphasis on dissolved organic nitrogen

Previous research has focused on dissolved organic carbon (DOC) as a surrogate for soluble microbial products (SMPs) and found that temperature has a significant influence on the production of SMP-based DOC (SDOC) during biological processes. Little is known about the SMP-based dissolved organic nitrogen (SDON), although some nitrogenous organic matter has been identified as an important part of SMPs. This study investigated the effect of temperature (8 °C, 15 °C and 25 °C) on the characterization of SMPs in an activated sludge system with special emphasis on SDON. Results showed the positive effect of reduced temperature on SDON production. Fluorescence spectroscopy and ultrahigh-resolution mass spectrometry showed the produced SDON at 8 °C and 15 °C exhibits more lability than at 25 °C. This was also supported by the algal bioassay, indicating the SDON produced at low temperature is highly bioavailable and prone to stimulate algae and microorganisms. In addition, principal component analysis demonstrated that the effect of temperature on the chemical characterization of SDON is different from that of SDOC. Overall, this study highlights the importance of SDON control during biological processes at a low temperature to reduce the potential impact of effluent SMPs on receiving waters or wastewater reuse.

Effect of microbial activity and microbial community structure on the formation of dissolved organic nitrogen (DON) and bioavailable DON driven by low temperatures

Dissolved organic nitrogen (DON) formed by microbial metabolism in wastewater treatment processes adversely impacts wastewater reuse and receiving waters quality, and microbial metabolism is greatly influenced by temperatures. However, little is known about the effect of microorganisms on DON and bioavailable DON (ABDON) formation under low temperatures. In this study, six reactors were operated at low (8 °C and 15 °C) and room (25 °C) temperatures to evaluate the relationship between microbial activity, microbial communities, and DON and ABDON. Results showed that DON and ABDON concentrations significantly increased at low temperatures (p < 0.05, t-test). DON formation was significantly correlated to microbial activity only, with adenosine triphosphate (negative, r = -0.64) and polysaccharide (positive, r = 0.61) as key indicators; however, ABDON formation was influenced by both microbial activity (polysaccharide > triphenyltetrazolium chloride-dehydrogenases > adenosine triphosphate) and microbial community structure. Short-term tests using the biomass from six reactors were performed at room temperature to further validate the relationship. The distinct differences between these results provide a basis for different strategies on reducing effluent DON and ABDON under low temperatures.

Enhancement of mixture pollutant biodegradation efficiency using a bacterial consortium under static magnetic field

One of the main challenges of bioremediation is to define efficient protocols with low environmental impact and high removal rates, such as static magnetic field (SMF). The aim of this study was to evaluate the effect of SMF exposure on the biodegradation rate of a mixture of pollutants using three bacterial strains which were isolated and identified from the Bizerte lagoon: Pseudomonas stutzeri LBR (KC157911), Cupriavidus metallidurans LBJ (KU659610) and Rhodococcus equi LBB (KU743870). To recognize the improvement role of SMF, the culture was submitted to a pre-treatment with SMF with an induction equal to 200 mT for 5 hours, after that the degradation experiment was followed with individual strains and with a consortium. Results showed an increase by 20% in the growth of the exposed bacterial population compared to controls, and 98% of biodegradation of DDT and 90% for BaP after 30 days of follow-up. This encouraging data opens new perspectives for a bioremediation bioprocess using SMF.

Linking microbial respiratory activity with phospholipid fatty acid of biofilm from full-scale bioreactors

Deficiency of researches on biotic community-driven biofilm activity makes biofilm regulation lack of quantitative response for decades. Based on three full-scale aerobic bioreactors in wastewater treatment plants, this study for the first time linked microbial respiratory activity with phospholipid fatty acid (PLFA) of biofilm developed on fixed and suspended carriers. Results showed that C16:00, C18:00, C16:1, ω7c, C18:1, ω7c, C12:00 and C18:1ω9c were top six biomarkers of PLFA among different sources of samples and Gram-negative bacteria (G-) was more abundant than Gram-positive bacteria (G+) with average G-/G+ of 2.98. It's interesting to find defective revealing of PLFA-based biofilm activity by specific oxygen uptake rate (SOUR). Further modeling indicated that C16:00 achieved the optimal quantitative response to STOUR with the best model of composite, growth, or exponential curve (R² = 0.416, p = 0.005). This research was promising to provide important reference for biofilm regulation and accurate control of biofilm-based process.

Factors affecting the efficiency of a bioelectrochemical system: a review

The great potential of bioelectrochemical systems (BESs) in pollution control combined with energy recovery has attracted increasing attention.

Cell membrane characteristics and microbial population distribution of MBBR and IFAS with different dissolved oxygen concentration

This paper investigated the influences of different dissolved oxygen (DO) concentration (0.71-1.32, 2.13-3.02 and 4.31-5.16 mg/L) on cell membrane characteristics and microbial population distribution of moving biofilm reactors. Two representative reactors, i.e., moving bed biofilm reactors and integrated fixed-film activated sludge were operated. Results indicated that both DO concentration of 0.71-1.32 mg/L and 4.31-5.16 mg/L could increase membrane lipid mobile fraction (49.4%-67.4%) of the microbes, however, through prompting the synthesis of branched fatty acids and unsaturated fatty acids, respectively. For the biofilms, the abundance of Bacteroidetes decreased and Actinobacteria increased with the increase of DO levels. The lowest EfOM content and the highest microbial diversities (1.14-1.52) was observed at DO of 2.13-3.02 mg/L. Redundancy analysis showed that changes of DO levels could alter cell membrane properties and bacterial community structures, and subsequently significantly influenced effluent organic matter composition of moving biofilm reactors.

Impact of a static magnetic field on biodegradation of wastewater compounds and bacteria recombination

The current study presents results concerning the effect of a static magnetic field (SMF) on synthetic wastewater biodegradation by activated sludge and on dehydrogenase activity of microorganisms of activated sludge. The highest process efficiency was obtained for a SMF of 0.0075 T among the tested magnetic flux density values of 0.005-0.14 T. Decrease in COD was 25% higher for the bioreactor exposed to SMF compared with control experiments. The positive effect of SMF 0.0075-0.0080 T was confirmed in experiments on the dehydrogenase activity of activated sludge. It was also shown that a SMF of 0.007 T increased p-nitroaniline removal from wastewater and influenced the recombination frequency in a streptomycin-resistant bacteria strain of Eschercihia coli.

Effects of DO levels on surface force, cell membrane properties and microbial community dynamics of activated sludge

In this paper, we employ atomic force microscopy (AFM), fluorescence recovery after photobleaching (FRAP) technique, phospholipid fatty acids (PLFA) and MiSeq analysis to study the effects of traditional dissolved oxygen (DO) levels (0.71-1.32mg/L, 2.13-3.02mg/L and 4.31-5.16mg/L) on surface force, cell membrane properties and microbial community dynamics of activated sludge. Results showed that low DO level enhanced the surface force and roughness of activated sludge; the medium DO level decreased cell membrane fluidity by reducing the synthesis of branched fatty acids in the cell membrane; high DO level resulted in the highest protein content in the effluent by EEM scanning. Abundance of Micropruina, Zoogloea and Nakamurella increased and Paracoccus and Rudaea decreased with the increase of DO levels. RDA analysis suggested that saturated fatty acids (SFA), anteiso-fatty acids (AFA) and iso-fatty acids (IFA) were closely related to effluent quality as well as some genera.

Effect of static magnetic field on the performances of and anode biofilms in microbial fuel cells

The electricity production and substrate removal rate of microbial fuel cells (MFCs) could be improved by the application of a static magnetic field (SMF).

Enhanced reduction of waste activated sludge at a low temperature by locally isolated strains Pseudomonas sp. VNT and Aeromonas sp. VNT

Appropriate control of waste activated sludge (WAS) is required to solve the annual increment of WAS volume. The low bacterial activity at low temperatures poses a difficulty in reducing or utilizing WAS in cold weather regions and/or during the winter season. This study reveals a practical method to enhance sludge reduction at a low temperature using isolated strains of Pseudomonas and Aeromonas species. The effect of inoculating each strain into WAS was examined at different temperatures (4°C, 10°C, 12°C, 15°C, 20°C, and 30°C) and under an aerobic condition. Sludge reduction showed 2- to 8-fold improvement at the temperature range from 4°C to 15°C. Both strains are psychrophilic and can produce protease and lipase for sludge degradation even at low temperatures. Thus, biological WAS treatment at a psychrophilic temperature can be enhanced by inoculating these promising strains.

Effects of a static magnetic field on phenol degradation effectiveness and Rhodococcus erythropolis growth and respiration in a fed-batch reactor

The aim of this study was to evaluate the impact of short-term repeated exposure to a static magnetic field (induction 370 mT) on the Rhodococcus erythropolis cells. Specifically, it was ascertained the magnetic field's potential to influence degradation of a phenol substrate, cell growth and respiration activity (oxygen consumption) during substrate biodegradation. The experiment took place over 3 days, with R. erythropolis exposed to the magnetic field for the first day. During the experiment, different recirculation rates between the reactor and the magnetic contactor has been tested. Use of the magnetic field at higher recirculation rates (residence time in contactor was less than 7 min) stimulated substrate (phenol) oxidation by around 34%; which, in turn, promoted R. erythropolis growth by around 28% by shortening the lag- and exponential-phases and increasing bacterial respiration activity by around 10%.

Enhancement of activated sludge activity by 10-50 mT static magnetic field intensity at low temperature

Effects of different static magnetic field (MF) intensities (10-50 mT) on the activity of activated sludge were compared at low temperature (5°C). The TTC dehydrogenase activity (TTC-DHA) achieved the maximum of 8.12 mg TF/gSS at the MF intensity of 40 mT. MF intensity enhanced from 20 mT to 40 mT could promote microorganisms to produce more unsaturated fatty acids (UFAs) to stimulate the TTC-DHA and adapt to low temperature. At 30 mT, the Gram-negative bacteria with better cold adaptability were greatly enriched, which ensured the cold resistance of low-temperature reactor. The PLFA diversity strengthened by MF was higher than that of control when MF intensities changed from 20 mT to 50 mT and reached the maximum of 1.31 at 20 mT. Optimal MF intensity is supposed to be a potential pathway to strengthen the activity and cold resistance of activated sludge microorganisms in biological wastewater treatment under low temperature.