Thallium-mediated NO signaling induced lipid accumulation in microalgae and its role in heavy metal bioremediation

Lipidomics analysis of microalgal lipid production and heavy metal adsorption under glycine betaine-mediated alleviation of low-temperature stress

Heavy metal pollution in the cold region is serious, affecting human health and aquatic ecology. This study investigated the ability of microalgae to remove heavy metals (HMs) and produce lipid at low temperature. The removal efficiency of different HMs (Cd2+, Cu2+, Cr3+ and Pb2+), cell growth and lipid synthesis of microalgae were analyzed at 15 °C. Moreover, addition of glycine betaine (GB) further enhanced the productivity of microalgae in treating HMs and lipid production, and simultaneously increased the antioxidant capacity of microalgae against environmental stresses. The results showed that the highest lipid productivity of 100.98 mg L-1 d-1 and the removal efficiency of 85.8 % were obtained under GB coupled with Cr3+. The highest glutathione content of 670.34 nmol g-1 fresh alga was achieved under GB coupled with Pb2+. In addition, lipidomics showed that GB was able to up-regulate the triglyceride and diglyceride content, influenced fatty acid composition to regulate the microalgal metabolism, and mediated lipid accumulation under 15 °C mainly through the regulation of glycerol ester metabolism. This study provided a new perspective on microalgal lipid production and the removal of HMs in cold regions and provided evidence for the use of phytohormones to improve the algal environmental resistance.

Biochemical transformation and bioremediation of thallium in the environment

Thallium (Tl) is a toxic element associated with minerals, and its redistribution is facilitated by both geological and anthropogenic activities. In the natural environment, the transformation and migration of Tl mediated by (micro)organisms have attracted increasing attention. This review presents an overview of the biochemical transformation of Tl and the bioremediation strategies for Tl contamination. In the environment, Tl exists in various forms and originates from diverse sources. The global distribution characteristics of Tl in various media are summarized here, while its speciation and toxicity mechanism to organisms are elucidated. Interactions between (micro)organisms and Tl are commonly observed in the environment. Microbial response mechanisms to typical Tl exposure are analyzed at both species and gene levels, and the possibility of microorganisms as bio-indicators for monitoring Tl contamination is also highlighted. The processes and mechanisms involved in the microbial and benthic mediated transformation of Tl, as well as its enrichment by plants, are discussed. Additionally, in situ bioremediation strategies for Tl contamination and bio-treatment techniques for Tl-containing wastewater are summarized. Finally, the existing knowledge gaps and future research challenges are emphasized, including Tl distribution characteristics in the atmosphere and ocean, the key molecular mechanisms underlying Tl transformation by organisms, the screening of potential Tl oxidizing microorganisms and hyperaccumulators, as well as the revelation of global biogeochemical cycling pathways of Tl.

Perspectives on nanomaterial-empowered bioremediation of heavy metals by photosynthetic microorganisms

Environmental remediation of heavy metals (HMs) is a crucial aspect of sustainable development, safeguarding natural resources, biodiversity, and the delicate balance of ecosystems, all of which are critical for sustaining life on our planet. The bioremediation of HMs by unicellular phototrophs harnesses their intrinsic detoxification mechanisms, including biosorption, bioaccumulation, and biotransformation. These processes can be remarkably effective in mitigating HMs, particularly at lower contaminant concentrations, surpassing the efficacy of conventional physicochemical methods and offering greater sustainability and cost-effectiveness. Here, we explore the potential of various engineered nanomaterials to further enhance the capacity and efficiency of HM bioremediation based on photosynthetic microorganisms. The critical assessment of the interactions between nanomaterials and unicellular phototrophs emphasised the ability of tailored nanomaterials to sustain photosynthetic metabolism and the defence system of microorganisms, thereby enhancing their growth, biomass accumulation, and overall bioremediation capacity. Key factors that could shape future research efforts toward sustainable nanobioremediation of HM are discussed, and knowledge gaps in the field have been identified. This study sheds light on the potential of nanobioremediation by unicellular phototrophs as an efficient, scalable, and cost-effective solution for HM removal.

Biochar-based composites for removing chlorinated organic pollutants: Applications, mechanisms, and perspectives

Chlorinated organic pollutants constitute a significant category of persistent organic pollutants due to their widespread presence in the environment, which is primarily attributed to the expansion of agricultural and industrial activities. These pollutants are characterized by their persistence, potent toxicity, and capability for long-range dispersion, emphasizing the importance of their eradication to mitigate environmental pollution. While conventional methods for removing chlorinated organic pollutants encompass advanced oxidation, catalytic oxidation, and bioremediation, the utilization of biochar has emerged as a prominent green and efficacious method in recent years. Here we review biochar's role in remediating typical chlorinated organics, including polychlorinated biphenyls (PCBs), triclosan (TCS), trichloroethene (TCE), tetrachloroethylene (PCE), organochlorine pesticides (OCPs), and chlorobenzenes (CBs). We focus on the impact of biochar material properties on the adsorption mechanisms of chlorinated organics. This review highlights the use of biochar as a sustainable and eco-friendly method for removing chlorinated organic pollutants, especially when combined with biological or chemical strategies. Biochar facilitates electron transfer efficiency between microorganisms, promoting the growth of dechlorinating bacteria and mitigating the toxicity of chlorinated organics through adsorption. Furthermore, biochar can activate processes such as advanced oxidation or nano zero-valent iron, generating free radicals to decompose chlorinated organic compounds. We observe a broader application of biochar and bioprocesses for treating chlorinated organic pollutants in soil, reducing environmental impacts. Conversely, for water-based pollutants, integrating biochar with chemical methods proved more effective, leading to superior purification results. This review contributes to the theoretical and practical application of biochar for removing environmental chlorinated organic pollutants.

Combined transcriptomic and metabolomic analyses of temperature response of microalgae using waste activated sludge extracts for promising biodiesel production

Waste activated sludge (WAS) as one of the major pollutants with a significant annual production, has garnered significant attention regarding its treatment and utilization. If improperly discharged, it not only caused environmental pollution but also led to the wastage of valuable resources. In this study, the microalgae growth and lipid accumulation using waste activated sludge extracts (WASE) under different temperature conditions were investigated. The highest lipid content (59.13%) and lipid productivity (80.41 mg L-1 d-1) were obtained at cultivation temperatures of 10 and 25 °C, respectively. It was found that microalgae can effectively utilize TN/TP/NH4+-N and other nutrients of WASE. The highest utilization rates of TP, TN and NH4+-N were achieved at a cultivation temperature of 10 °C, reaching 84.97, 77.49 and 92.32%, respectively. The algal fatty acids had carbon chains predominantly ranging from C14 to C18, making them suitable for biodiesel production. Additionally, a comprehensive analysis of transcriptomics and metabolomics revealed up-regulation of genes associated with triglyceride assembly, the antioxidant system of algal cells, and cellular autophagy, as well as the accumulation of metabolites related to the tricarboxylic acid (TCA) cycle and lipids. This study offers novel insights into the microscopic mechanisms of microalgae culture using WASE and approaches for the resource utilization of sludge.

New insights into rare earth element-induced microalgae lipid accumulation: Implication for biodiesel production and adsorption mechanism

A coupling technology for lipid production and adsorption of rare earth elements (REEs) using microalgae was studied in this work. The microalgae cell growth, lipid production, biochemical parameters and lipid profiles were investigated under different REEs (Ce3+, Gd3+and La3+). The results showed that the maximum lipid production was achieved at different concentrations of REEs, with lipid productivities of 300.44, 386.84 and 292.19 mg L-1 d-1 under treatment conditions of 100 μg L-1 Ce3+, 250 μg L-1 Gd3+ and 1 mg L-1 La3+, respectively. Moreover, the adsorption efficiency of Ce3+, Gd3+ and La3+exceeded 96.58 %, 93.06 % and 91.3 % at concentrations of 25-1000 μg L-1, 100-500 μg L-1 and 0.25-1 mg L-1, respectively. In addition, algal cells were able to adsorb 66.2 % of 100 μg L-1 Ce3+, 48.4 % of 250 μg L-1 Gd3+ and 59.9 % of 1 mg L-1 La3+. The combination of extracellular polysaccharide and algal cell wall could adsorb 25.2 % of 100 μg L-1 Ce3+, 44.5 % of 250 μg L-1 Gd3+ and 30.5 % of 1 mg L-1 La3+, respectively. These findings indicated that microalgae predominantly adsorbed REEs through the intracellular pathway. This study elucidates the mechanism of effective lipid accumulation and adsorption of REEs by microalgae under REEs stress conditions. It establishes a theoretical foundation for the efficient microalgae lipid production and REEs recovery from wastewater or waste residues containing REEs.

Effects of environmental microplastic exposure on Chlorella sp. biofilm characteristics and its interaction with nitric oxide signaling

Microalgal biofilm is promising in simultaneous pollutants removal, CO2 fixation, and biomass resource transformation when wastewater is used as culturing medium. Nitric oxide (NO) often accumulates in microalgal cells under wastewater treatment relevant abiotic stresses such as nitrogen deficiency, heavy metals, and antibiotics. However, the influence of emerging contaminants such as microplastics (MPs) on microalgal intracellular NO is still unknown. Moreover, the investigated MPs concentrations among existing studies were mostly several magnitudes higher than in real wastewaters, which could offer limited guidance for the effects of MPs on microalgae at environment-relevant concentrations. Therefore, this study investigated three commonly observed MPs in wastewater at environment-relevant concentrations (10-10,000 μg/L) and explored their impacts on attached Chlorella sp. growth characteristics, nutrients removal, and anti-oxidative responses (including intracellular NO content). The nitrogen source NO3--N at 49 mg/L being 20 % of the nitrogen strength in classic BG-11 medium was selected for MPs exposure experiments because of least intracellular NO accumulation, so that disturbance of intracellular NO by nitrogen availability could be avoided. Under such condition, 10 μg/L polyethylene (PE) MPs displayed most significant microalgal growth inhibition comparing with polyvinyl chloride (PVC) and polyamide (PA) MPs, showing extraordinarily low chlorophyll a/b ratios, and highest superoxide dismutase (SOD) activity and intracellular NO content after 12 days of MPs exposure. PVC MPs exposed cultures displayed highest malonaldehyde (MDA) content because of the toxic characteristics of organochlorines, and most significant correlations of intracellular NO content with conventional anti-oxidative parameters of SOD, CAT (catalase), and MDA. MPs accelerated phosphorus removal, and the type rather than concentration of MPs displayed higher influences, following the trend of PE > PA > PVC. This study expanded the knowledge of microalgal biofilm under environment-relevant concentrations of MPs, and innovatively discovered the significance of intracellular NO as a more sensitive indicator than conventional anti-oxidative parameters under MPs exposure.

Microalgae cultivation with recycled harvesting water achieved economic and sustainable production of biomass and lipid: Feasibility assessment and inhibitory factors analysis

This study was conducted to achieve economic and sustainable production of biomass and lipids from Chlorella sorokiniana by recirculating cultivation with recycled harvesting water, to identify the major inhibitory factors in recirculating culture, and to analyze accordingly economic benefits. The results showed that recirculating microalgae cultivation (RMC) could obtain 0.20-0.32 g/L biomass and lipid content increased by 23.1 %-38.5 %. Correlation analysis showed that the extracellular polysaccharide (PSext), chemical oxygen demand (COD) and chromaticity of recirculating water inhibited photosynthesis and induced oxidative stress, thus inhibiting the growth of C. sorokiniana. In addition, the economic benefits analysis found that circulating the medium twice could save about 30 % of production cost, which is the most economical RMC solution. In conclusion, this study verified the feasibility and economy of RMC, and provided a better understanding of inhibitory factors identification in culture.

Melatonin, a phytohormone for enhancing the accumulation of high-value metabolites and stress tolerance in microalgae: Applications, mechanisms, and challenges

High-value metabolites, such as carotenoids, lipids, and proteins, are synthesized by microalgae and find applications in various fields, including food, health supplements, and cosmetics. However, the potential of the microalgal industry to serve these sectors is constrained by low productivity and high energy consumption. Environmental stressors can not only stimulate the accumulation of secondary metabolites in microalgae but also induce oxidative stress, suppressing cell growth and activity, thereby resulting in a decrease in overall productivity. Using melatonin (MT) under stressful conditions is an effective approach to enhance the productivity of microalgal metabolites. This review underscores the role of MT in promoting the accumulation of high-value metabolites and enhancing stress resistance in microalgae under stressful and wastewater conditions. It discusses the underlying mechanisms whereby MT enhances metabolite synthesis and improves stress resistance. The review also offers new perspectives on utilizing MT to improve microalgal productivity and stress resistance in challenging environments.

Pollution characteristics and potential health effects of airborne microplastics and culturable microorganisms during urban haze in Harbin, China

In this study, active sampling technology was used to collect microplastics (MPs) and microorganisms simultaneously on haze days in Harbin, China. Airborne MPs concentrations in Junior high school (162.4 ± 44.6 particles/m3) with high vehicular and pedestrian traffic was higher than those in University (63.2 ± 21.8 particles/m3) and Park (12.8 ± 5.5 particles/m3). More airborne MPs were detected in the night samples than in the morning and noon samples. The majority (69.06 %) of airborne MPs measured less than 100 μm, with fibers (69.4 %) being the predominant form. Polyesters and polyethylene were the dominant polymers. In addition, airborne MPs concentrations were positively correlated with microorganisms and PM10 concentrations, and the health hazards associated with microorganisms and MPs exposure via inhalation far exceeded those associated with skin contact, which can serve as a theoretical foundation for considering MPs as indicators of air quality in the future.

Influence mechanism of sludge bed position on microalgal-bacterial granular sludge process

Sludge bed position in the reactor is one of the key parameters for microalgal-bacterial granular sludge (MBGS) process, which lacks of study. To fill this gap, this study investigated the influence of sludge bed position on MBGS. The sludge bed located closer to the bottom of the bioreactor demonstrated the optimal pollutant removal performance due to a close synergistic effect between microalgae and bacteria, resulting in the high growth rate as well as agglomeration rate of MBGS. Specifically, organics and ammonia removals were closely related to the sludge bed position. For the bottom bed position, the removals of organic matter, ammonia, and phosphate were 75.1 %, 73.1 %, and 82.5 %, whereas for the top bed position, they were only 13.2 %, 9.6 %, and 68.9 %, respectively. Additionally, a significant correlation between the position of the sludge bed and the relative abundance of Rotifera (R2 = 0.931) and Chlorophyta (R2 = 0.733) was observed, while the microbial communities at the lower sludge bed positions underwent rapider succession. It can be inferred that that a sludge bed located closer to the bottom of the bioreactor ensures that the light source and substrate matrix are transmitted in the same direction, thereby resulting in a close synergistic effect between microalgae and bacteria for achieving the excellent performance of MBGS. These results can provide basis knowledge for engineering application of MBGS process.

Microalgal-bacterial biofilms for wastewater treatment: Operations, performances, mechanisms, and uncertainties

Microalgal-bacterial biofilms have been increasingly considered of great potential in wastewater treatment due to the advantages of microalgal-bacterial synergistic pollutants removal/recovery, CO2 sequestration, and cost-effective biomass-water separation. However, such advantages may vary widely among different types of microalgal-bacterial biofilms, as the biofilms could be formed on different shapes and structures of attachment substratum, generating "false hope" for certain systems in large-scale wastewater treatment if the operating conditions and pollutants removal properties are evaluated based on the general term "microalgal-bacterial biofilm". This study, therefore, classified microalgal-bacterial biofilms into biofilms formed on 2D substratum, biofilms formed on 3D substratum, and biofilms formed without substratum (i.e. microalgal-bacterial granular sludge, MBGS). Biofilms formed on 2D substratum display higher microalgae fractions and nutrients removal efficiencies, while the adopted long hydraulic retention times were unacceptable for large-scale wastewater treatment. MBGS are featured with much lower microalgae fractions, most efficient pollutants removal, and acceptable retention times for realistic application, yet the feasibility of using natural sunlight should be further explored. 3D substratum systems display wide variations in operating conditions and pollutants removal properties because of diversified substratum shapes and structures. 2D and 3D substratum biofilms share more common in eukaryotic and prokaryotic microbial community structures, while MGBS biofilms are more enriched with microorganisms favoring EPS production, biofilm formation, and denitrification. The specific roles of stratified extracellular polymeric substances (EPS) in nutrients adsorption and condensation still require in-depth exploration. Nutrients removal uncertainties caused by microalgal-bacterial synergy decoupling under insufficient illumination, limited microbial community control, and possible greenhouse gas emission exacerbation arising from microalgal N2O generation were also indicated. This review is helpful for revealing the true potential of applying various microalgal-bacterial biofilms in large-scale wastewater treatment, and will provoke some insights on the challenges to the ideal state of synergistic pollutants reclamation and carbon neutrality via microalgal-bacterial interactions.

Toxic effects of thallium (Tl+) on prokaryotic alga Microcystis aeruginosa: Short and long-term influences by potassium and humic acid

Thallium (Tl) is a priority pollutant regulated by the US EPA. It is also a critical element commonly used in high technology industries; with an increasing demand for semiconductors nowadays, wastewater discharges from manufacturing plants or metal mining activities may result in elevated levels of thallium in receiving water harming aquatic organisms. Regarding the impact of thallium on freshwater algae, little attention has been paid to prokaryotic physiology through various exposure periods. In this bench-scale study, prokaryotic alga Microcystis aeruginosa PCC 7806 was cultured in modified BG11 medium and exposed to Tl+ (TlNO3) ranging from 250 to 1250 μg/L for 4 and 14 days. Throughout the experiment using flow cytometry assays, algal population, cell membrane integrity, oxidation stress level, and chlorophyll fluorescence were exacerbated following the exposure to 750 μg Tl/L (approximately 4-day effective concentration of Tl+ for reducing 50% of algal population). Potassium and humic acid (HA) (1-5 mg/L) were added to study their influences on the thallium toxicity. With the additions of potassium, thallium toxicities to algal population and physiology were not significantly changed within 4 days, while they were alleviated within 14 days. With the addition of HA at 1 mg/L, cell membrane integrity was significantly attenuated within 4 days; ameliorating effects on algal population and oxidative stress were not observed until day 14. Thallium toxicities on oxidative stress level and photosynthesis activity were exacerbated in the presence of HA at 3-5 mg/L. The study provides useful information for further studies on the mode of toxic action of Tl+ in prokaryotic algae; it also demonstrates the necessity of considering short and long-term exposure durations while incorporating water chemistry into assessment of thallium toxicity to algae.

Effect of external acetate added in aquaculture wastewater on mixotrophic cultivation of microalgae, nutrient removal, and membrane contamination in a membrane photobioreactor

The mixotrophic cultivation of microalgae in wastewater has attracted extensive attention due to its many advantages. In this study, acetate, which can be prepared by hydrolysis of aquaculture waste, was used as exogenous organic matter to promote the growth of Chlorella pyrenoidosa cultured in aquaculture wastewater. Microalgae cultivation was carried out in a membrane photobioreactor (MPBR) with continuous inflow and outflow mode. The results showed that exogenous acetate greatly promoted the mixotrophic growth of C. pyrenoidosa. When the dosage of acetate reached 1.0 g L-1, the relative growth rate of microalgae in the logarithmic stage reached 0.31 d-1, which was 4.4 times that of the control. As a result, exogenous acetate also promoted the removal of nutrients from aquaculture wastewater. During the stable operation stage of the MPBR with acetate added in the influent, an average of 87.41%-93.93% nitrogen and 76.34%-88.55% phosphorus was removed from the aquaculture wastewater containing 19.41 mg L-1 total inorganic nitrogen and 1.31 mg L-1 total inorganic phosphorus. However, it was worth noting that adding exogenous acetate also led to an increase in the membrane resistance of the membrane module in the MPBR. Membrane resistance was mainly composed of internal resistance (Ri) and cake resistance (Rc), and with the increase of acetate content in the influent, their proportion in the total resistance gradually increased. Ri contributed the major membrane resistance and was most affected by acetate dosage. Ri reached 32.04 × 1012 m-1 with 1 g L-1 acetate, which accounted for 69.49% of total resistance. Moreover, with the increase of influent acetate concentration of the MPBRs, both the number of insoluble contaminants and dissolved organic contaminants in the membrane modules increased. In addition, the composition of proteins, polysaccharides, and humus in dissolved organic contaminants was close to that in extracellular polymeric substances and soluble microbial products secreted by microalgae. These results suggested that the membrane fouling of membrane modules was closely related to the algal biomass content in the MPBRs. The above results provided a theoretical basis for reducing membrane fouling of MPBR.

Effects of polyethylene terephthalate microplastics on cell growth, intracellular products and oxidative stress of Scenedesmus sp

Polyethylene terephthalate (PET) has been widely utilized in the synthesis of textile materials and packaging of foods and beverages. In recent years, it has been commonly detected in the form of microplastics (MPs) in wastewater. However, the effects of PET MPs on microalgal intracellular products and their interrelationships have been poorly investigated. In this study, the microalgae Scenedesmus sp. Strain H-1 was exposed to PET MPs to explore their effects on the growth, intracellular products (such as lipids, carbohydrates, and proteins), and antioxidative defense systems of Scenedesmus sp. The results demonstrated that PET MPs significantly reduced Scenedesmus sp. cell growth, with a maximum inhibition rate of 38.25% in the 500 mg L-1 treatment group. PET MPs had negative effects on glucose and nitrate utilization rates and reduced intracellular carbohydrates, intracellular proteins, and photosynthetic pigments. Surprisingly, PET MPs reduced acetyl-CoA carboxylase activity but induced lipid accumulation in microalgae. In addition, PET MPs significantly decreased the essential linoleic acid concentration and increased the palmitic acid content, resulting in reduced biodiesel quality. PET MPs induced the production of reactive oxygen species and malondialdehyde as well as the activities of superoxide dismutase and catalase. The results of the PCA indicated that the response mechanism of Scenedesmus sp. to PET MPs exposure was synergistic. This study provides fundamental data on the impact of MPs on the intracellular products of microalgae.

Pilot study on ceramic flat membrane bioreactor in treatment of coal chemical wastewater

Some toxic and refractory pollutants in coal chemical wastewater can penetrate the biochemical treatment systems and cause high concentrations of suspended solids in the effluent, which may obstruct the subsequent advanced treatment. In this project, a submerged ceramic plate membrane system was integrated to the last oxic corridor of an existing multistage anoxic/oxic tank. In the ceramic flat membrane bioreactor, the influent chemical oxygen demand (COD) was 102.24-178.88 mg/L, with a removal ratio of approximately 30%. The NH3-N concentration in the effluent was relatively stable with an average value of 1.76 mg/L. The turbidity of the effluent was in the range of 0.235-0.852 NTU and was stable below 1 NTU. A flux of 30 L m-2·h-1 could meet the requirements of the pilot test. A gas-water ratio of 50:1 was found optimal. When the concentration of mixed liquor suspended solids (MLSS) was >3769 mg/L, the extracellular polymeric substance in the mixed solution was utilized by microorganisms as a substrate. High MLSS decreased membrane fouling rate. NaClO backwashing can effectively remove pollutants without adversely affecting the treatment efficiency of membrane bioreactors.

The comparative effects of visible light and UV-A radiation on the combined toxicity of P25 TiO2 nanoparticles and polystyrene microplastics on Chlorella sp

The ubiquitous presence of TiO2 nanoparticles (nTiO2) and microplastics (MPs) in marine ecosystems has raised serious concerns about their combined impact on marine biota. This study investigated the combined toxic effect of nTiO2 (1 mg/L) and NH2 and COOH surface functionalized polystyrene MPs (PSMPs) (2.5 and 10 mg/L) on Chlorella sp. All the experiments were carried out under both visible light and UV-A radiation conditions to elucidate the impact of light on the combined toxicity of these pollutants. Growth inhibition results indicated that pristine nTiO2 exhibited a more toxic effect (38%) under UV-A radiation when compared to visible light conditions (27%). However, no significant change in the growth inhibitory effects of pristine PSMPs was observed between visible light and UVA radiation conditions. The combined pollutants (nTiO2 + 10 mg/L PSMPs) under UV-A radiation exhibited more growth inhibition (nTiO2 + NH2 PSMPs 66%; nTiO2 + COOH PSMPs 50%) than under visible light conditions (nTiO2 + NH2 PSMPs 55%; TiO2 + COOH PSMPs 44%). Independent action modeling indicated that the mixture of nTiO2 with PSMPs (10 mg/L) exhibited an additive effect on the algal growth inhibition under both the light conditions. The photoactive nTiO2 promoted increased production of reactive oxygen species under UV-A exposure, resulting in cellular damage, lipid peroxidation, and impaired photosynthesis. The effects were more pronounced in case of the mixtures where PSMPs added to the oxidative stress. The toxic effects of the binary mixtures of nTiO2 and PSMPs were further confirmed through the field emission electron microscopy, revealing specific morphological abnormalities. This study provides valuable insights into the potential risks associated with the combination of nTiO2 and MPs in marine environments, considering the influence of environmentally relevant light conditions and the test medium.

High-efficiency harvesting of microalgae enabled by chitosan-coated magnetic biochar

Magnetic flocculation which uses magnetic particles is an emerging technology for harvesting microalgae. However, the potential modification and use of cost-effective and sustainable biochar-based composites is still in its infancy. As such, this study aimed to compare the harvesting efficiency of peanut shell biochar (BC), biochar modified with FeCl3 (FeBC), and biochar dual-modified with chitosan and FeCl3 (CTS@FeBC) on microalgae. The results showed CTS@FeBC exhibited significantly higher microalgae harvesting efficiency compared to BC and FeBC. Both acidic and alkaline conditions were favorable for harvesting microalgae by CTS@FeBC. At pH 2 and pH 12, the harvesting efficiency reached 96.9% and 98.8% within 2 min, respectively. The primary adsorption mechanism of CTS@FeBC on microalgae mainly involved electrostatic attraction and sweeping flocculation. Furthermore, CTS@FeBC also showed good biocompatibility and reusability. This study clearly demonstrated a promising technique for microalgae harvesting using biochar-based materials, offering valuable insights and potential applications in sustainable bioresource management.

Effects of light quality on microalgae cultivation: bibliometric analysis, mini-review, and regulation approaches

The ever-increasing concern for energy shortages and greenhouse effect has triggered the development of sustainable green technologies. Microalgae have received more attention due to the characteristics of biofuel production and CO2 fixation. From the perspective of autotrophic growth, the optimization of light quality has the potential to promote biomass production and bio-component accumulation in microalgae at low cost. In this study, bibliometric analysis was used to describe the basic features, identify the hotspots, and predict future trends of the research related to the light quality on microalgae cultivation. In addition, a mini-review referring to regulation methods of light quality was provided to optimize the framework of research. Results demonstrated that China has the greatest interest in this area. The destination of most research was to obtain biofuels and high-value-added products. Both blue and red lights were identified as the crucial spectrums for microalgae cultivation. However, sunlight is the most affordable light resource, which could not be fully utilized by microalgae through the photosynthetic process. Hence, some regulation approaches (e.g., dyes, plasmonic scattering, and carbon-based quantum dots) are proposed to increase the proportion of beneficial spectrum for enhancement of photosynthetic efficiency. In summary, this review introduces state-of-the-art research and provides theoretical guidance for light quality optimization in microalgae cultivation to obtain more benefits.

Improved sequential production of hydrogen and caproate by addition of biochar prepared from cornstalk residues

This study proposes a new model in which ethanol and acetate produced by dark fermentation are processed by Clostridium kluyveri for chain elongation to produce caproate with an addition of biochar prepared from cornstalk residues after acid pretreatment and enzymatic hydrolysis (AERBC) in the dark fermentation and chain elongation processes. The results show a 6-25% increase in hydrogen production in dark fermentation with adding AERBC, and the maximum concentration of caproate in the new model reached 1740 mg/L, 61% higher than that in the control group. In addition, caproate was obtained by dark fermentation, using liquid metabolites as substrates with an initial pH range of 6.5-7.5. Finally, the electron balance and electron transfer efficiency in the new model were analyzed, and the role of AERBC in dark fermentation and chain elongation was investigated. This study provides a new reference for the use of dark-fermented liquid metabolites and cornstalk residue.

Comprehensive understanding of the regulatory mechanism by which selenium nanoparticles boost CO2 fixation and cadmium tolerance in lipid-producing green algae under recycled medium

Recycled medium plus cadmium is a promising technique for reducing the cultivation cost and enhancing the yield of microalgae lipids. However, oxidative stress and cadmium toxicity significantly hinder the resulting photosynthetic efficiency, cell growth and cell activity. Herein, selenium nanoparticles (SeNPs) were used to increase the total biomass, biolipid productivity, and tolerance to cadmium. Wide-ranging analyses of photosynthesis, energy yield, fatty acid profiles, cellular ultrastructure, and oxidative stress biomarkers were conducted to examine the function of SeNPs in CO2 fixation and cadmium resistance in Ankistrodesmus sp. EHY. The application of 15 μM cadmium and 2 mg L-1 SeNPs further enhanced the algal biomass productivity and lipid productivity to 500.64 mg L-1 d-1 and 301.14 mg L-1 d-1, respectively. Moreover, the rates of CO2 fixation, chlorophyll synthesis and total nitrogen removal were similarly increased by the application of SeNPs. Exogenous SeNPs strengthened cell growth and cadmium tolerance by upregulating photosynthesis, the TCA cycle and the antioxidant system, reducing the uptake and translocation of cadmium, and decreasing the levels of reactive oxidative stress (ROS), extracellular polymeric substances (EPSs) and cellular Cd2+ level in EHY under recycled medium and cadmium stress conditions. Additionally, a maximum energy yield of 127.40 KJ L-1 and a lipid content of 60.15% were achieved in the presence of both SeNPs and cadmium stress. This study may inspire the efficient disposal of recycled medium and biolipid production while also filling the knowledge gaps regarding the mechanisms of SeNP functions in carbon fixation and cadmium tolerance in microalgae.

Simultaneous enhancement of lipid biosynthesis and solvent extraction of Chlorella using aminoclay nanoparticles

Magnesium aminoclay nanoparticles (MgANs) exert opposing effects on photosynthetic microalgae by promoting carbon dioxide (CO₂) uptake and inducing oxidative stress. This study explored the potential application of MgAN in the production of algal lipids under high CO₂ concentrations. The impact of MgAN (0.05-1.0 g/L) on cell growth, lipid accumulation, and solvent extractability varied among three tested oleaginous Chlorella strains (N113, KR-1, and M082). Among them, only KR-1 exhibited significant improvement in both total lipid content (379.4 mg/g cell) and hexane lipid extraction efficiency (54.5%) in the presence of MgAN compared to those of controls (320.3 mg/g cell and 46.1%, respectively). This improvement was attributed to the increased biosynthesis of triacylglycerols and a thinner cell wall based on thin-layer chromatography and electronic microscopy, respectively. These findings suggest that using MgAN with robust algal strains can enhance the efficiency of cost-intensive extraction processes while simultaneously increasing the algal lipid content.