Effect of static magnetic field on the oxygen production of Scenedesmus obliquus cultivated in municipal wastewater

In vitro assessment of the effect of magnetic fields on efficacy of biosynthesized selenium nanoparticles by Alborzia kermanshahica

Cyanobacteria represent a rich resource of a wide array of unique bioactive compounds that are proving to be potent sources of anticancer drugs. Selenium nanoparticles (SeNPs) have shown an increasing potential as major therapeutic platforms and led to the production of higher levels of ROS that can present desirable anticancer properties. Chitosan-SeNPs have also presented antitumor properties against hepatic cancer cell lines, especially the Cht-NP (Chitosan-NPs), promoting ROS generation and mitochondria dysfunction. It is proposed that magnetic fields can add new dimensions to nanoparticle applications. Hence, in this study, the biosynthesis of SeNPs using Alborzia kermanshahica and chitosan (CS) as stabilizers has been developed. The SeNPs synthesis was performed at different cyanobacterial cultivation conditions, including control (without magnetic field) and magnetic fields of 30 mT and 60 mT. The SeNPs were characterized by uv-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), Dynamic light scattering (DLS), zeta potential, and TEM. In addition, the antibacterial activity, inhibition of bacterial growth, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC), as well as the antifungal activity and cytotoxicity of SeNPs, were performed. The results of uv-visible spectrometry, DLS, and zeta potential showed that 60 mT had the highest value regarding the adsorption, size, and stabilization in compared to the control. FTIR spectroscopy results showed consistent spectra, but the increased intensity of peaks indicates an increase in bond number after exposure to 30 mT and 60 mT. The results of the antibacterial activity and the inhibition zone diameter of synthesized nanoparticles showed that Staphylococcus aureus was more sensitive to nanoparticles produced under 60 mT. Se-NPs produced by Alborzia kermanshahica cultured under a 60 mT magnetic field exhibit potent antimicrobial and anticancer properties, making them a promising natural agent for use in the pharmaceutical and biomedical industries.

Optimization of Recombinant Protein Production in Synechococcus elongatus PCC 7942: Utilizing Native Promoters and Magnetic Fields

The cyanobacterium Synechococcus elongatus PCC 7942 holds significant potential as a biofactory for recombinant protein (RP) production due to its capacity to harness light energy and utilize CO2. This study aimed to enhance RP production by integration of native promoters and magnetic field application (MF) in S. elongatus PCC 7942. The psbA2 promoter, which responds to stress conditions, was chosen for the integration of the ZsGreen1 gene. Results indicated successful gene integration, affirming prior studies that showed no growth alterations in transgenic strains. Interestingly, exposure to 30 mT (MF30) demonstrated a increase in ZsGreen1 transcription under the psbA2 promoter, revealing the influence of MF on cyanobacterial photosynthetic machinery. This enhancement is likely attributed to stress-induced shifts in gene expression and enzyme activity. MF30 positively impacted photosystem II (PSII) without disrupting the electron transport chain, aligning with the "quantum-mechanical mechanism" theory. Notably, fluorescence levels and gene expression with application of 30 mT were significantly different from control conditions. This study showcases the efficacy of utilizing native promoters and MF for enhancing RP production in S. elongatus PCC 7942. Native promoters eliminate the need for costly exogenous inducers and potential cell stress. Moreover, the study expands the scope of optimizing RP production in photoautotrophic microorganisms, providing valuable insights for biotechnological applications.

Unraveling biological behavior and influence of magnetic iron-based nanoparticles in algal-bacterial systems: A comprehensive review

Magnetic iron-based nanoparticles have been found to stimulate algae growth and harvest, repair disintegrated particles and improve stability, and facilitate operation in extreme environments, which help improve the wide application of algal-bacterial technology. Nevertheless, up to now, no literature collected to systematically review the research progress of on the employment of magnetic iron-based nanoparticles in the algal-bacterial system. This review summarizes the special effects (e.g., size effect, surface effect and biological effect) and corresponding properties of magnetic iron-based nanoparticles (e.g., magnetism, adsorption, electricity, etc.), which is closely related to biological effects and algal-bacterial behaviors. Additionally, it was found that magnetic iron-based nanoparticles offer remarkable impacts on improving the growth and metabolism of algal-bacterial consortia and the mechanisms mainly include its possible iron uptake pathways in bacteria and/or algae cells, as well as the magnetic biological effect of magnetic iron-based nanoparticles on algae-bacteria growth. Furthermore, in terms of the mechanism for establishing the algae-bacteria symbiotic relationship, the most recent works reveal that the charge effect, material transfer and signal transmission of magnetic iron-based nanoparticles possess a large array of potential mechanisms by which it can affect the establishment of algal-bacterial symbiosis. This discussion is expected to promote the progress of magnetic iron-based nanoparticles, as an eco-friendly, convenient and cost-effective technology that can be applied in algal-bacterial wastewater treatment fields.

Improving microbial production of value-added products through the intervention of magnetic fields

The magnetic field application is emerging as an auxiliary physical strategy to facilitate rapid biomass accumulation and intracellular production of compounds. However, the underlying mechanisms and principles governing the application of magnetic fields for microbial growth and biotransformation are not yet fully understood. Therefore, a better understanding of interdisciplinary technologies integration, expanded magnetic field application, and scaled-up industrial implementation is crucial. In this review, the magnetic field characteristics, magnetic field-assisted fermentation devices, and the working mechanism of magnetic field have been reviewed comprehensively from both physical and microbiological perspectives. The review suggests that magnetic fields affect the biochemical processes in microorganisms by mediating nutrient transport across membranes, electron transfer during photosynthesis and respiration, enzyme activity and gene expression. Moreover, the recent advances in magnetic field application for microbial fermentation and conversion in biochemical, food and agricultural fields have been summarized.

Biodegradation of human faecal sludge for photosynthetic bioelectricity generation and seawater desalination in a microbial desalination cell

ABSTRACTInaccessibility and expensiveness of vital infrastructures are the main problems in some urban and rural areas to supply fresh water, sustainable energy, and wastewater treatment. An effective solution is the integration of several systems in an environmentally friendly technology of the photosynthetic microbial desalination cell (PMDC). The aim of this study is to assess the process characterisation of an algae-based PMDC, which was loaded with a high-strength mixture of human feces and urine (HFS). The PMDC was also able to efficiently remove COD and total nitrogen of HFS by 50% and 94%, respectively. The maximum power density, voltage, and desalination efficiency of 362.5 mW/m², 175.2 mV, and 60% were accomplished. Adequate parameter adjustment led to a remarkable maximum of 2.25 g/L.d in the ion removal rate. In addition, an energy balance was governed showing that zero or positive net energy in PMDC is feasible by replacing the main energy consumers. Based on the results, this type of MDC had a high efficiency for simultaneous saline water desalination and HFS treatment, which makes it attractive for further studies of upscaling and its application in remote areas.

Mechanisms of magnetic sensing and regulating extracellular electron transfer of electroactive bacteria under magnetic fields

Electroactive bacteria can display notable plasticity in their response to magnetic field (MF), which prompted bioelectrochemical system as promising candidates for magnetic sensor applications. In this study, we explored the sensing and stimulatory effect of MF on current generation by Geobacter sulfurreducens, and elucidated the related molecular mechanism at the transcriptomic level. MF treatment significantly enhanced electricity generation and overall energy efficiency of G. sulfurreducens by 50 % and 22 %, respectively. The response of current to MFs was instantaneous and reversible. Cyclic voltammetry analysis of the anode biofilm revealed that the redox couples changed from -0.31 to -0.39 V (vs. Ag/AgCl), suggesting that MFs could alter electron transfer related components. Differential gene expression analysis further verified this hypothesis, genes associated with electron transfer were upregulated in G. sulfurreducens under MF treatment relative to the control group, specifically, genes encoding periplasmic c-type cytochromes (ppcA and ppcD), outer membrane cytochrome (omcF, omcZ, omcB), pili (pilA-C, pilM, and pilV2), and ribosome. The enhanced bacterial extracellular electron transfer process was also linked to the overexpression of the NADH dehydrogenase I subunit, the ABC transporter, transcriptional regulation, and ATP synthase. Overall, our findings shed light on the molecular mechanism underlying the effects of magnetic field stimuli on EAB and provide a theoretical basis for its further application in magnetic sensors and other biological system.

Influence of Cell Wall on Biomolecules Biosynthesis in Chlamydomonas reinhardtii Strains Exposed to Magnetic Fields

The application of magnetic fields (MF) has attracted the attention of researchers due to their efficiency to change cell metabolism. Chlamydomonas reinhardtii is a biotechnologically useful microalga with versatile metabolism that may be a valuable organism to study the effects of the MF in biology. Therefore, two C. reinhardtii strains, one with cell wall (2137) and other which lacks the cell wall (Wt-S1-cc4694), were evaluated that a new sensitivity factor in the analysis could be included. Comparative studies were undertaken with the two C. reinhardtii strains under the MF intensities of 0.005 mT (terrestrial MF - control), 11  and 20 mT. Results indicated that the physical cell wall barrier protected cells against the MF applied during the assays. Only with the highest MF applied (20 mT) a slight increase in lipid concentration in the cell wall strain was detected. The lowest growth of the strain that lacks cell wall (Wt-S1) indicated that these cells are under a negative effect. To cope with the two MF stresses conditions, Wt-S1 cells produced more pigments (chlorophylls and carotenoids) and lipids and enhanced the antioxidant defense system. The raise of these compounds under MF could potentially have a positive biotechnological impact on algal biomass.

Growth alteration of Allium cepa L. roots exposed to 1.5 mT, 25 Hz pulsed magnetic field

The response of plants to magnetic fields (MF) is not fully understood. This work studies the effects of pulsed MF on the germination and growth of Allium cepa roots. Onions were exposed to 25Hz, 1.5mT, 33h. Pulsed MF was generated by a Helmholtz-type equipment that generated rectangular voltage pulses. The results showed that fewer roots grew in the specimens exposed to pulsed MF (14±6 roots on day 1 to 21±8 on day 4) than in the control groups (32±17 to 48±23) (p<0.05 Friedman). Control specimens showed a root mean length of 7±4 mm (day 1) and 24±10 mm (day 4). The specimens treated with pulsed MF showed a length of 4±2 mm (day 1), reaching 18±9 mm on day 4 (p<0.001 ANOVA). In conclusion, the exposure of Allium cepa specimens to 25Hz, 1.5mT pulsed MF during 33h produces a decrease in the germination and growth of roots.

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.

Equilibrium and Kinetic Modeling of Crystal Violet Dye Adsorption by a Marine Diatom, Skeletonema costatum

Significant efforts have been made to improve adsorbents capable of eliminating pollutants from aqueous solutions, making it simple and quick to separate from the treated solution. In the current study, the removal of Crystal Violet Dye (CVD) from an aqueous synthetic solution onto a marine diatom alga, Skeletonema costatum, was investigated. Different experiments were conducted as a function of different pH, contact time, adsorbent dosage, temperature, and initial CVD concentration. The highest adsorption efficiency (98%) was obtained at 0.4 g of S. costatum, pH 3, and a contact time of 120 min, at 25 °C. Furthermore, Fourier-transform infrared spectroscopy (FTIR) results display that binding of CVD on S. costatum may occur by electrostatic and complexation reactions. Moreover, the Brunauer-Emmett-Teller surface area analysis (BET) obtained was 87.17 m² g^-1, which, in addition to a scanning electron microscope (SEM), reveals large pores that could enhance the uptake of large molecules. However, the equilibrium adsorption models were conducted by Halsey, Langmuir, Freundlich, Henderson, and Tempkin isotherm. In addition, multilayer adsorption isotherm best described the uptake of CVD onto S. costatum. The maximum monolayer adsorption capacity (q_max) was 6.410 mg g^-1. Moreover, thermodynamic parameters of the adsorption studies suggested that the uptake of CVD onto S. costatum was endothermic and spontaneous. The pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic equations were applied to model the adsorption kinetic data. It was seen that the kinetics of the adsorption may be described using pseudo-second-order kinetic equations. Finally, the present work concluded that the marine diatom alga S. costatum is suitable as a natural material for the adsorption of CVD.

The Using of Nanoparticles of Microalgae in Remediation of Toxic Dye from Industrial Wastewater: Kinetic and Isotherm Studies

Batch adsorption experiments were carried out to study the removal of the toxic Methylene Blue Dye (MBD) from synthetic aqueous solutions using the nanoparticles form of Arthrospira platensis NIOF17/003. The adsorption capacity of the adsorbent for MBD was investigated using different amounts of A. platensis nanoparticles at different contact times, temperatures, pH, and MBD initial concentrations in the synthetic aqueous solution. In addition, A. platensis nanoparticles were characterized using Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), Fourier Transform Infrared (FTIR), and Ultraviolet spectra (UV) techniques. The optimum removal of MBD was found at a concentration of 0.4 g A. platensis nanoparticles. A. platensis nanoparticles remove 93% of MBD in 5 min (under agitation conditions at 150 rpm). The highest adsorption capacity was found by the Langmuir model to be 58.8 mg g⁻¹. It is an endothermic process with spontaneity increasing with temperature. The probable mechanism for the adsorption is chemisorption via surface-active charges in the initial phase, which is followed by physical sorption by occupying pores of A. platensis. MBD adsorption by A. platensis follows pseudo-second-order kinetics. The Freundlich and Langmuir models fit well with the experimental data. The adsorption experiments suggested that the regeneration of the adsorbents was possible for repeated use, especially regarding MBD up to 65.8% after three cycles, which proves it can be easily recycled. In conclusion, the nanoparticles of A. platensis have a significant adsorption potential in the removal of MBD from effluent wastewater.

Weak magnetic field intervention on outdoor production of oil-rich filamentous microalgae: Influence of seasonal changes

The weak magnetic field (MF) intervention on the semi-continuous system of filamentous algae Tribonema sp. during outdoor cultivation was investigated using starch wastewater. Results show that except for winter, MF in other seasons can effectively improve the algal biomass yield and oil productivity. In summer, the biomass concentration and oil productivity of Tribonema sp. could reach up to 14.7 g/L and 0.216 g/(L d) (130 mT), which increased by 9.8% and 35.8% respectively compared with the control group without MF intervention. By continuously shortening HRT to increase the nutrient load, the removal rate of COD, total nitrogen and total phosphorus all reached more than 87.9%. MF intervention not only weakened the bacterial diversity in open-photobioreactors system but also proved to be beneficial to the establishment of bacteria-algae symbiotic system. As a non-transgenic method, MF effectively up-regulated the growth of filamentous microalgae and promoted the biosynthesis productivity of high value-added compounds.

Effective treatment of aquaculture wastewater with mussel/microalgae/bacteria complex ecosystem: a pilot study

The discharge of aquaculture wastewater increased significantly in China. Especially, high content of nitrogen and phosphorus in wastewater could destroy the receiving water environment. To reduce the pollution of aquaculture wastewater, farmed triangle sail mussel (Hyriopsis cumingii) was proposed to be cultivated in the river. This was the first time that bacteria (Bacillus subtilis and Bacillus licheniformis) and microalgae (Chlorella vulgaris) were also used and complemented ecosystem functions. The pollutants in wastewater were assimilated by Chlorella vulgaris biomass, which was then removed through continuous filter-feeding of Hyriopsis cumingii. While, Bacillus subtilis and Bacillus licheniformis enhanced the digestive enzyme activities of mussel. It demonstrated that approximately 4 mussels/m³ was the optimal breeding density. Under such condition, orthogonal experiment indicated that the dose of Bacillus subtilis, Bacillus licheniformis, and Chlorella vulgaris should be 0.5, 1, and 2 mL respectively. Compared with mussel, mussel/microalgae, mussel/bacteria system, treatment ability of the mussel/microalgae/bacteria system in batch experiment was better, and 94.67% of NH₃-N, 92.89% of TP and 77.78% of COD were reduced after reaction for 6 days. Finally, 90 thousand mussels per hectare of water were cultivated in Kulv river in China, and the field experiment showed that water quality was significantly improved. After about 35 days of operation, NH₃-N, TN, TP and COD concentration were maintained around 0.3, 0.8, 0.3, and 30 mg/L respectively. Therefore, the mussel/microalgae /bacteria system in this study showed a sustainable and efficient characteristic of aquaculture wastewater bioremediation.

Magnetic Field Action on Limnospira indica PCC8005 Cultures: Enhancement of Biomass Yield and Protein Content

The effects of a magnetic field (MF) on the cyanobacteria Limnospira indica PCC 8005 growth rate and biomass composition were investigated. A device to apply the MF during the cultivation was built and the cyanobacteria were exposed to a steady 11 mT transverse MF. The growth increased with MF application, and when it was applied for 1 h per day, 123% more biomass was produced than in the control group. The protein content in the biomass cultured under this condition increased, achieving 60.4 w/w, while the Chl-a increased by 326%. The MF application for 1 h per day was found to be more efficient than when applied continuously for 24 h per day, in addition to being more economical and sustainable. This study showed an inexpensive and non-toxic way to enhance biomass concentration, leading to amounts more than 100% higher than those obtained in the control group. Furthermore, the high protein content in the biomass gave us several possibilities to increase the nutritional value of food.

Fatty Acid Profile of Microalgal Oils as a Criterion for Selection of the Best Feedstock for Biodiesel Production

Microalgae are considered to be potentially attractive feedstocks for biodiesel production, mainly due to their fast growth rate and high oil content accumulated in their cells. In this study, the suitability for biofuel production was tested for Chlorella vulgaris, Chlorella fusca, Oocystis submarina, and Monoraphidium strain. The effect of nutrient limitation on microalgae biomass growth, lipid accumulation, ash content, fatty acid profile, and selected physico-chemical parameters of algal biodiesel were analysed. The study was carried out in vertical tubular photobioreactors of 100 L capacity. The highest biomass content at 100% medium dose was found for Monoraphidium 525 ± 29 mg·L−1. A 50% reduction of nutrients in the culture medium decreased the biomass content by 23% for O. submarina, 19% for Monoraphidium, 13% for C. vulgaris and 9% for C. fusca strain. Nutrient limitation increased lipid production and reduced ash content in microalgal cells. The highest values were observed for Oocystis submarina, with a 90% increase in lipids and a 45% decrease in ash content in the biomass under stress conditions. The fatty acid profile of particular microalgae strains was dominated by palmitic, oleic, linoleic, and linoleic acids. Nutrient stress increased the amount of saturated and unsaturated fatty acids affecting the quality of biodiesel, but this was determined by the type of strain.

The influence of a static magnetic field on a Chlorella vulgaris - Bacillus licheniformis consortium and its sewage treatment effect

In this study, the influence of a static magnetic field (SMF) on a Chlorella vulgaris-Bacillus licheniformis consortium and the subsequent effect of this algal-bacterial consortium on sewage treatment were explored. Accordingly, the algal density, Fv/Fm, algal aggregation percentage, extracellular polymeric substances (EPS) content, dissolved organic matter distribution, enzymatic activity, metabolites, microbial community diversity and nutrient removal were investigated. For the treatment group exposed to an SMF of 150 mT, the total phosphorus removal rate reached 82.21%, which was 19.10% higher than the control group. On the last day, the algal density of the 150 mT group was the highest, being 56.01% greater than the control group. The high intensity SMF promoted the anti-oxidative stress response in C. vulgaris. It also affected EPS secretion, subsequently influencing the algal aggregation percentage and bacterial growth. Bacillus accounted for the largest proportion of the overall microbial community in the 150 mT group, which was conducive to rapid formation of the C. vulgaris-B. licheniformis consortium. In short, the SMF was conducive to the rapid formation of a C. vulgaris-B. licheniformis consortium. The use of an SMF can promote the efficiency of the algal-bacterial consortium, thereby shortening the processing time.

Response to Static Magnetic Field-Induced Stress in Scenedesmus obliquus and Nannochloropsis gaditana

Magnetic fields in biological systems is a promising research field; however, their application for microalgae has not been fully exploited. This work aims to measure the enzymatic activity and non-enzymatic activity of two microalgae species in terms of superoxide dismutase (SOD), catalase (CAT), and carotenoids, respectively, in response to static magnetic fields-induced stress. Two magnet configurations (north and south) and two exposure modes (continuous and pulse) were applied. Two microalgae species were considered, the Scenedesmus obliquus and Nannochloropsis gaditana. The SOD activity increased by up to 60% in S. obliquus under continuous exposure. This trend was also found for CAT in the continuous mode. Conversely, under the pulse mode, its response was hampered as the SOD and CAT were reduced. For N. gaditana, SOD increased by up to 62% with the south configuration under continuous exposure. In terms of CAT, there was a higher activity of up to 19%. Under the pulsed exposure, SOD activity was up to 115%. The CAT in this microalga was increased by up to 29%. For N. gaditana, a significant increase of over 40% in violaxanthin production was obtained compared to the control, when the microalgae were exposed to SMF as a pulse. Depending on the exposure mode and species, this methodology can be used to produce oxidative stress and obtain an inhibitory or enhanced response in addition to the significant increase in the production of antioxidant pigments.

Unveiling the induced lipid production in Chlorella vulgaris under pulsed magnetic field treatment

The pulsed magnetic field (PMF) was adopted for the enhancement of lipid in Chlorella vulgaris. The average biomass and lipid content in outdoor conditions were found to be 0.315 g.L^-1 and 20-25% respectively. The effect of magnetic flux density in the range of 600-900 mG on biomass production and lipid content was studied. A magnetic flux density of 700 mG at 1Hz for 4 h per day was found to be optimum, which yielded a maximum dry cell weight of 0.61 g.L^-1, two-fold than the normal condition, with a lipid content of 55.2%. FTIR analysis evidenced that the PMF treatment increased the active oxygen, which could be attributed to the enhancement of growth and lipid of C. vulgaris.

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 fields exhibit a positive impact on lipid and biomass yield during phototrophic cultivation of Spirulina sp

This study aimed to investigate the effects of magnetic field (MF) application (1, 12 and 24 h day ^-1) to Spirulina sp. LEB 18 in different photosynthesis cycles (dark and/or light) during short (15 days) and long periods (50 days) of cultivation. MF application was performed via two sources: ferrite magnets and solenoids. At the end of cultivation, the biomass was characterized in terms of lipids, proteins, and carbohydrates. In the 15 day cultures, the highest maximum biomass concentrations (2.06 g L^-1 and 1.83 g L^-1) were observed when 30 mT was applied for 24 h day ^-1 or 12 h day ^-1 (on the light cycle), respectively. MF application throughout cultivation (24 h day ^-1) for more than 30 days is not recommended. In all conditions, there was an increase in the lipid concentration (from 14 to 45%). The protein profile suggested important changes in photosystems I and II due to MF application. Cell morphology was not altered by MF application. In conclusion, the effects on the metabolism of Spirulina sp. are directly related to the photosynthesis cycle and time period in which the MF was applied.

Magnetic field as promoter of growth in outdoor and indoor assays of Chlorella fusca

This study aimed to evaluate the influence of a magnetic field (MF) intensity of 25 mT on Chlorella fusca cultivation in outdoor and indoor conditions, and evaluate the changes in the macromolecules, pigment content and protein profile. C. fusca was cultivated for 15 d in raceway photobioreactor. MF was applied for 24 h d^-1 and 1 h d^-1. In outdoor cultivation, MF applied for 24 h d^-1 increased 23% in the biomass concentration, while indoor assays resulted in an increase in both modes, with biomass production increasing between 70 and 85%. Biomass composition was altered when MF was applied for 1 h d^-1 in indoor assays; the highest protein content was achieved (32.7%). Nitrate consumption was higher in outdoor assays, while MF application did not alter the protein profile. The results showed that combining the outdoor conditions with MF is advantageous, as higher biomass concentration can be achieved with lower energy expenditure.

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.

Magnetic Field (MF) Applications in Plants: An Overview

Crop yield can be raised by establishment of adequate plant stand using seeds with high germination ratio and vigor. Various pre-sowing treatments are adopted to achieve this objective. One of these approaches is the exposure of seeds to a low-to-medium level magnetic field (MF), in pulsed and continuous modes, as they have shown positive results in a number of crop seeds. On the basis of the sensitivity of plants to MF, different types of MF have been used for magnetopriming studies, such as weak static homogeneous magnetic fields (0–100 μT, including GMF), strong homogeneous magnetic fields (milliTesla to Tesla), and extremely low frequency (ELF) magnetic fields of low-to-moderate (several hundred μT) magnetic flux densities. The agronomic application of MFs in plants has shown potential in altering conventional plant production systems; increasing mean germination rates, and root and shoot growth; having high productivity; increasing photosynthetic pigment content; and intensifying cell division, as well as water and nutrient uptake. Furthermore, different studies suggest that MFs prevent the large injuries produced/inflicted by diseases and pests on agricultural crops and other economically important plants and assist in reducing the oxidative damage in plants caused by stress situations. An improved understanding of the interactions between the MF and the plant responses could revolutionize crop production through increased resistance to disease and stress conditions, as well as the superiority of nutrient and water utilization, resulting in the improvement of crop yield. In this review, we summarize the potential applications of MF and the key processes involved in agronomic applications. Furthermore, in order to ensure both the safe usage and acceptance of this new opportunity, the adverse effects are also discussed.

Screening of seaweeds for sustainable biofuel recovery through sequential biodiesel and bioethanol production

The present study evaluated the sequential biodiesel-bioethanol production from seaweeds. A total of 22 macroalgal species were collected at different seasons and screened based on lipid and carbohydrate contents as well as biomass production. The promising species was selected, based on the relative increase in energy compounds (REEC, %), for further energy conversion. Seasonal and annual biomass yields of the studied species showed significant variations. The rhodophyte Amphiroa compressa and the chlorophyte Ulva intestinalis showed the highest annual biomass yield of 75.2 and 61.5 g m^-2 year^-1, respectively. However, the highest annual carbohydrate productivity (ACP) and annual lipid productivity (ALP) were recorded for Ulva fasciata and Ulva intestinalis (17.0 and 3.0 g m^-2 year^-1, respectively). The later was selected for further studies because it showed 14.8% higher REEC value than Ulva fasciata. Saturated fatty acids (SAFs) showed 73.4%, with palmitic acid as a dominant fatty acid (43.8%). Therefore, biodiesel showed high saturation degree, with average degree of unsaturation (ADU) of 0.508. All the measured biodiesel characteristics complied the international standards. The first route of biodiesel production (R1) from Ulva intestinalis showed biodiesel recovery of 32.3 mg g^-1 dw. The hydrolysate obtained after saccharification of the whole biomass (R2) and lipid-free biomass (R3) contained 1.22 and 1.15 g L^-1, respectively, reducing sugars. However, bioethanol yield from R3 was 0.081 g g^-1 dw, which represented 14.1% higher than that of R2. Therefore, application of sequential biofuel production using R3 resulted in gross energy output of 3.44 GJ ton^-1 dw, which was 170.9% and 82.0% higher than R1 and R2, respectively. The present study recommended the naturally-grown Ulva intestinalis as a potential feedstock for enhanced energy recovery through sequential biodiesel-bioethanol production.

Bioeffect of static magnetic field on photosynthetic bacteria: Evaluation of bioresources production and wastewater treatment efficiency

Photosynthetic bacteria (PSB) technology is a promising method for biomass, protein, pigments, and other value-added substances generation from wastewater. However, the above bioresources production efficiency is relatively low. In this work, a static magnetic field (SMF) was used to promote bioresources production. Results showed that SMF had positive effects on value-added substances production. With 0.35 Tesla (T) SMF, the PSB biomass, protein, carotenoids, and bacteriochlorophyll concentration were promoted by 31.1%, 22.6%, 56.7%, and 73.1% compared with the control group, respectively. Biomass yield finally reached 0.58 g biomass/g COD removal, which was promoted by 37.1%. The doubling time was shortened by 37.9% in 0.35 T group, showing that SMF can promote cell growth. With 0.35 T SMF, the intracellular NADH dehydrogenase and ATP synthase activities concentration increased by 23.4% and 29.1%, respectively, thus increased the ATP content by 38.0%. Succinic dehydrogenase activity concentration greatly increased by 609.0% at 48 hr, which potentially accelerated the tricarboxylic acid cycle and COD degradation as well as enhanced biomass production. PRACTITIONER POINTS: SMF promoted PSB bioresource production during wastewater treatment processing. Biomass, protein, carotenoids, and Bchl concentration were promoted by 31.1%, 22.6%, 56.7%, and 73.1%, respectively. PSB yield of 0.35 T group was promoted by 37.1% compared with the control group. SDH concentration of 0.35 T was promoted by 609.0% compared with the control group. Increased NADH and ATP synthase activity concentration by SMF enhanced energy metabolism.

Application of Static Magnetic Fields on the Mixotrophic Culture of Chlorella minutissima for Carbohydrate Production

Magnetic field (MF) can interact with the metabolism of microalgae and has an effect (positive or negative) on the synthesis of molecules. In addition to MF, the use of pentose as a carbon source for cultivating microalgae is an alternative to increase carbohydrate yield. This study aimed at evaluating the MF application on the mixotrophic culture of Chlorella minutissima in order to produce carbohydrates. MF of 30 mT was generated by ferrite magnets and applied diurnally for 12 days. The addition of 5% pentose, MF application of 30 mT, and nitrogen concentration reduced (1.25 mM of KNO₃) was the best conditions to obtain higher carbohydrate concentrations. MF application of 30 mT increased biomass and carbohydrate contents in 30% and 163.1%, respectively, when compared with the assay without MF application. The carbohydrate produced can be used for bioethanol production.

Enhanced lipid production by Chlorella pyrenoidosa through magnetic field pretreatment of wastewater and treatment of microalgae-wastewater culture solution: Magnetic field treatment modes and conditions

The cultivation of microalgae in municipal wastewater not only purifies the wastewater but also transforms nutrients into biomass that contains high-value lipids. In this study, conventional static bottom-magnetic field (bottom-MF) equipment and cost-effective bypass-magnetic field (bypass-MF) equipment were designed and independently coupled with a microalgae-wastewater system in different positions to evaluate the effect of magnetic field (MF) on microalgae biomass production and lipid accumulation. When the MF equipment was applied in the wastewater pretreatment unit, the bottom-MF pretreatment mode exhibited a more beneficial effect on subsequent biomass and lipid accumulation. However, when the MF equipment was applied in the microalgae-wastewater culture unit, there was no significant difference between the bottom-MF and bypass-MF modes. The results of the orthogonal experiment suggested the optimum conditions for lipid production were wastewater pretreatment by bottom-MF at 5000 Gs for 1 h, followed by microalgae-wastewater culture treatment by bypass-MF at 5000 Gs for 3 h.

Magnetic field intervention on growth of the filamentous microalgae Tribonema sp. in starch wastewater for algal biomass production and nutrients removal: Influence of ambient temperature and operational strategy

This paper investigated the effects of temperature and cultivation methods (batch or semi-continuous culture) on the filamentous microalgae Tribonema sp. biomass production and nutrients removal in starch wastewater under low intensity magnetic field (MF) intervention. The MF significantly promoted algal growth in the late logarithmic-phase of batch cultivation, and the effect was even more obvious at lower temperatures. The MF treated group at 30 °C accumulated the highest biomass of 4.44 g/L of batch culture, an increase of 15.0% compared with the control group. The oil content of Tribonema sp. was enhanced with the MF intervention, especially for the batch culture. In the semi-continuous culture under MF intervention, Tribonema sp. reached the high biomass of 18.45 g/L after 25 days. When gradually reducing hydraulic retention time (HRT) to 1 day, the average removal rates for COD, TN, NH₃-N and TP were all more than 90% in the semi-continuous cultivation.

Use of magnetic fields and nitrate concentration to optimize the growth and lipid yield of Nannochloropsis oculata

Microalgae produce increased lipid content accompanied by a significant decrease in cell density with decreasing nitrate concentration. Magnetic fields (MF) have been reported as a factor that could accelerate metabolism and growth in microalgae culture. Thus, this study aimed to optimize the influence of MF and nitrate concentration (sodium nitrate, N) on the growth and lipid productivity of Nannochloropsis oculata. A single-factor experiment integrated with response surface methodology (RSM) via central composite design (CCD) was performed. The results showed that the maximum specific growth rate (0.24 d^-1) and maximum lipid productivity (38 mg L^-1 d^-1) obtained in this study were higher than those of the control culture (by 166% and 103%, respectively). This study also found that the two-way interaction term MF × N had a significant effect on cell growth but not on lipid production. It was concluded that to design appropriate MF for enhanced lipid productivity due to cell growth, further research must focus on developing an understanding of the relationship between the bioeffects of the magnetic field and the proteomic changes involved in lipid accumulation strategies. This approach would enable the design of conditions to obtain inexpensive high-value products from N. oculata.

Removal of Manganese(II) from Acid Mine Wastewater: A Review of the Challenges and Opportunities with Special Emphasis on Mn-Oxidizing Bacteria and Microalgae

Many global mining activities release large amounts of acidic mine drainage with high levels of manganese (Mn) having potentially detrimental effects on the environment. This review provides a comprehensive assessment of the main implications and challenges of Mn(II) removal from mine drainage. We first present the sources of contamination from mineral processing, as well as the adverse effects of Mn on mining ecosystems. Then the comparison of several techniques to remove Mn(II) from wastewater, as well as an assessment of the challenges associated with precipitation, adsorption, and oxidation/filtration are provided. We also critically analyze remediation options with special emphasis on Mn-oxidizing bacteria (MnOB) and microalgae. Recent literature demonstrates that MnOB can efficiently oxidize dissolved Mn(II) to Mn(III, IV) through enzymatic catalysis. Microalgae can also accelerate Mn(II) oxidation through indirect oxidation by increasing solution pH and dissolved oxygen production during its growth. Microbial oxidation and the removal of Mn(II) have been effective in treating artificial wastewater and groundwater under neutral conditions with adequate oxygen. Compared to physicochemical techniques, the bioremediation of manganese mine drainage without the addition of chemical reagents is relatively inexpensive. However, wastewater from manganese mines is acidic and has low-levels of dissolved oxygen, which inhibit the oxidizing ability of MnOB. We propose an alternative treatment for manganese mine drainage that focuses on the synergistic interactions of Mn in wastewater with co-immobilized MnOB/microalgae.

Enhancement of Spirulina biomass production and cadmium biosorption using combined static magnetic field

The effect of static magnetic field (SMF) on Spirulina platensis growth and its influence on cadmium ions (Cd²⁺) removal efficiency were studied. Application of 6 h day^-1 SMF resulted in the highest significant biomass productivity of 0.198 g L^-1 day^-1. However, 10 and 15 mg L^-1 of Cd²⁺ resulted in significant reduction in biomass productivity by 8.8 and 12.5%, respectively, below the control. Combined SMF showed 30.1% significant increase in biomass productivity over the control. On the other hand, increase of initial Cd²⁺ concentration resulted in significant reduction of Cd²⁺ removal efficiency, representing 79.7% and 61.5% at 10 and 15 mg L^-1, respectively, after 16 days. Interestingly, application of SMF for 6 h day^-1 enhanced Cd²⁺ removal efficiency counted by 91.4% and 82.3% after 20 days for cultures with initial Cd²⁺ concentration of 10 and 15 mg L^-1, representing increase by 6.3 and 25.3%, respectively, over the SMF-untreated cultures.

Effect of lipid-free microalgal biomass and waste glycerol on growth and lipid production of Scenedesmus obliquus: Innovative waste recycling for extraordinary lipid production

In the present work, a novel approach of using growth medium with different substitutions of lipid-free algal hydrolysate (LFAH, 0, 5, 10 and 15%) and/or waste glycerol (WG, 0, 5, 10 and 20 g L^-1) for enhanced biodiesel production from Scenedesmus obliquus was studied. Combination of different concentrations of WG with 15% LFAH showed the maximum significant biomass productivity, which represented 27.4, 30.5 and 28.9% over the control at combined 5, 10 and 20 g L^-1 WG, respectively. The combinations of different LFAH with 20 g L^-1 WG showed the maximum significant lipid accumulation, where lipid productivity showed its maximum significant value of 59.66 mg L^-1 d^-1 using LFAH15-WG10. In addition, LFAH15-WG10 significantly enhanced total FAMEs yield by 21.2% over the control. Moreover, it reduced polyunsaturated fatty acids (PUFAs) ratio from 52.1% to 47.8% of total FAMEs, and increased monounsaturated fatty acids (MUFAs) ratio from 26.6% to 31.3% of total FAMEs.

Magnetic treatment of microalgae for enhanced product formation

Static or modulated magnetic fields (MF) may interact with the biological system and affect the metabolism of microorganisms, such as their photosynthetic capacity or synthesis of carbohydrates. Their effects on microorganisms, which can be classified into inhibiting, stimulating and null, may be interpreted as the result of stress that cells undergo, thus, leading to responses through the same mechanisms. Biological effects of exposure to magnetic forces depend on magnetic intensity, frequency and exposure time. Modifications in these parameters may enhance product formation. Effects differ according to the form and application of MF characteristic parameters. Magnetic treatments have the advantages of being convenient and non-toxic, having low running cost, emitting no secondary pollution, enabling wide application and being easily shielded. MF application to the cultivation of microalgae, to improve the production of finished biomolecules, is a simple, inexpensive and powerful process. However, bioeffects of MF on microalgae need to be further investigated because there have currently been very few available reports in the literature. Thus, studies which aim at optimizing parameters involved in MF application must be developed in order to obtain the best conditions for the production of molecules with high economic potential.