Understanding microplastic aging driven by photosensitization of algal extracellular polymeric substances

The aging of microplastics (MPs) is extremely influenced by photochemically-produced reactive intermediates (PPRIs), which are mediated by natural photosensitive substances. Algal extracellular polymeric substances (EPS) can produce PPRIs when exposed to sunlight. Nonetheless, the specific role of EPS in the aging process of MPs remains unclear. This work systematically explored the aging process of polystyrene (PS) MPs in the EPS secreted by Chlorella vulgaris under simulated sunlight irradiation. The results revealed that the existence of EPS accelerated the degradation of PS MPs into particles with sizes less than 1 µm, while also facilitating the formation of hydroxy groups on the surface. The release rate of dissolved organic matter (DOM) from PS MPs was elevated from 0.120 mg·L-1·day-1 to 0.577 mg·L-1·day-1. The primary factor contributing to the elevated levels of DOM was humic acid-like compounds generated through the breakdown of PS. EPS accelerated the aging process of PS MPs by primarily mediating the formation of triplet excited states (3EPS*), singlet oxygen (1O2), and superoxide radicals (O2∙-), resulting in indirect degradation. 3EPS* was found to have the most substantial impact. This study makes a significant contribution to advance understanding of the environmental fate of MPs in aquatic environments impacted by algal blooms.

Construction of algal-bacterial consortia using green microalgae Chlorella vulgaris and As(III)-oxidizing bacteria: As tolerance and metabolomic profiling

Bioremediation became a promising technology to resolve arsenic (As) contamination in aquatic environment. Since monoculture such as microalgae or bacteria was sensitive to environmental disturbance and vulnerable to contamination, green microalgae Chlorella vulgaris and arsenite (As(III)) - oxidizing bacteria Pseudomonas sp. SMS11 were co-cultured to construct algal-bacterial consortia in the current study. The effects of algae-bacteria (A:B) ratio and exposure As(III) concentration on algal growth, As speciation and metabolomic profile were investigated. Algal growth arrested when treated with 100 mg/L As(III) without the co-cultured bacteria. By contrast, co-cultured with strain SMS11 significantly enhanced As tolerance in C. vulgaris especially with A:B ratio of 1:10. All the As(III) in culture media of the consortia were oxidized into As(V) on day 7. Methylation of As was observed on day 14. Over 1% and 0.5% of total As were converted into dimethylarsinic acid (DMA) after 21 days cultivation when the initial concentrations of As(III) were 1 and 10 mg/L, respectively. Metabolomic analysis was further performed to reveal the response of consortia metabolites to external As(III). The enriched metabolomic pathways were associated with carbohydrate, amino acid and energy metabolisms. Tricarboxylic acid cycle and glyoxylate and dicarboxylate metabolism were upregulated under As stress due to their biological functions on alleviating oxidative stress and protecting cells. Both carbohydrate and amino acid metabolisms provided precursors and potential substrates for energy production and cell protection under abiotic stress. Alterations of the pathways relevant to carbohydrate or amino acid metabolism were triggered by energy requirement.

New insights into Chlorella vulgaris applications

Environmental pollution is a big challenge that has been faced by humans in contemporary life. In this context, fossil fuel, cement production, and plastic waste pose a direct threat to the environment and biodiversity. One of the prominent solutions is the use of renewable sources, and different organisms to valorize wastes into green energy and bioplastics such as polylactic acid. Chlorella vulgaris, a microalgae, is a promising candidate to resolve these issues due to its ease of cultivation, fast growth, carbon dioxide uptake, and oxygen production during its growth on wastewater along with biofuels, and other productions. Thus, in this article, we focused on the potential of Chlorella vulgaris to be used in wastewater treatment, biohydrogen, biocement, biopolymer, food additives, and preservation, biodiesel which is seen to be the most promising for industrial scale, and related biorefineries with the most recent applications with a brief review of Chlorella and polylactic acid market size to realize the technical/nontechnical reasons behind the cost and obstacles that hinder the industrial production for the mentioned applications. We believe that our findings are important for those who are interested in scientific/financial research about microalgae.

Nanoplastics increase algal absorption and toxicity of Cd through alterations in cell wall structure and composition

Nanoplastics (NPs) may act as carriers of heavy metals and cause complex toxicity to aquatic organisms, while the exact role of NPs in the joint toxicity remains unclear. Here, we investigated the joint toxicity of polystyrene NPs (PS-NPs) and Cd to freshwater algae (Chlorella vulgaris). It was found that PS-NPs (1 mg L-1) could hardly enter algal cells and slightly inhibit algal growth (p < 0.01). The effect of PS-NPs as carriers on the joint toxicity of PS-NPs and heavy metals could be neglected because of the limited adsorption of Cd by PS-NPs, while the PS-NPs altered the cell wall structure and composition, which resulted in the increased algal absorption and toxicity of Cd. Compared to the low dose Cd (0.4 mg L-1) treatment alone, the extracellular and intracellular Cd contents in the cotreatment were significantly increased by 27.3 % and 18.0 %, respectively, due to the increased contents of cell wall polysaccharides (pectin and hemicellulose in particular) by the PS-NPs. Furthermore, after the high dose Cd (2 mg L-1) exposure, the inhibited polysaccharide biosynthesis and the loosen cell wall structure weakened the tolerance of cell wall to abiotic stress, facilitating the entry of PS-NPs into the algal cells and inducing the higher toxicity. These results elucidate the mechanism by which NPs enhance heavy metal toxicity to algae, providing a novel insight into environmental risks of NPs.

Ecotoxicity studies reveal that organic cations in dicamba-derived ionic liquids can pose a greater environmental risk than the herbicide itself

The following research provides novel and relevant insights into potential environmental consequences of combination of various organic cations with commercial systemic herbicide (dicamba), in accordance with a 'herbicidal ionic liquids' (HILs) strategy. Toxicity assays of five dicamba-based HILs comprising different hydrophobic and hydrophilic cations, namely choline [CHOL][DIC], ethyl betainate [BETC2][DIC], decyl betainate [BETC10][DIC], hexadecyl betainate [BETC16][DIC] and didecyldimethylammonium [DDA][DIC]), have been tested towards bacteria (Pseudomonas putida, Escherichia coli, Bacillus subtilis), algae (Chlorella vulgaris), fresh and marine water crustaceans (Daphnia magna, Artemia franciscana). The structure of respective substituents in the cation emerged as a decisive determinant of toxicity in the case of tested species. In consequence, small ions of natural origin ([CHOL] and [BETC2]) demonstrated toxicity numerous orders of magnitude lower compared to fully synthetic [DDA]. These results emphasize the role of cations' hydrophobicity, as well as origin, in the observed acute toxic effect. Time-dependent toxicity assays also indicated that betaine-type cations comprising an ester bond can rapidly transform into less harmful substances, which can generally result in a reduction in toxicity by even several orders of magnitude. Nonetheless, these findings challenge the concept of ionic liquids with herbicidal activity and give apparent parallels to adjuvant-dependent toxicity issues recently noted in typical herbicidal formulations.

Nutrients recovery from dairy wastewater by Chlorella vulgaris and comparison of the lipid's composition with various chlorella strains for biodiesel production

Microalgae biomass is regarded as a promising feedstock for biodiesel production. The biomass lipid content and fatty acids composition are among the main selective criteria when screening microalgae strains for biodiesel production. In this study, three strains of Chlorella microalgae (C. kessleri, C. sorokiniana, C. vulgaris) were cultivated nutrient media with different nitrogen contents, and on a medium with the addition of dairy wastewater. Moreover, microalgae grown on dairy wastewater allowed the removal of azote and phosphorous. The removal efficiency of 90%, 53% and 95% of ammonium nitrogen, total nitrogen and phosphate ions, respectively, were reached. The efficiency of wastewater treatment from inorganic carbon was 55%, while the maximum growth of biomass was achieved. All four samples of microalgae had a similar fatty acid profile. Palmitic acid (C16:0) was the most abundant saturated fatty acid (SFA), and is suitable for the production of biodiesel. The main unsaturated fatty acids (UFA) present in the samples were oleic acid (C18:1 n9); linoleic acid (C18:2 n6) and alpha-linolenic acid (C18:3 n3), which belong to omega-9, omega-6, omega-3, respectively.

Innovative vs classical methods for drying heterotrophic Chlorella vulgaris: Impact on protein quality and sensory properties

Drying is a necessary step in the microalgae production chain to reduce microbial load and oxidative degradation of the end product. Depending on the differences in applied temperature and treatment time, the process of drying can have a substantial impact on protein quality and aroma, important characteristics determining the incorporation potential in food products. In this study, we compared the drying of heterotrophic Chorella vulgaris with both innovative (agitated thin film drying (ATFD), pulse combustion drying (PCD) and solar drying (SolD)) and commonly used drying techniques (spray drying (SprD) and freeze drying (FD)). To evaluate the impact on protein quality, we evaluated techno-functional properties, in vitro digestibility (INFOGEST) as well as protein denaturation using differential scanning calorimetry (DSC). A sensory analysis was performed by a trained expert panel, combined with headspace solid-phase microextraction (HS-SPME) - gas chromatography-mass spectrometry (GC-MS) to determine volatile organic compounds (VOCs). ATFD was found to increase techno-functional properties such as gelling, water holding and solubility as well as in vitro protein digestibility. These observations could be related to induced cell disruption and protein denaturation by ATFD. Sensory analysis indicated an increased earthy off-flavor after ATFD. Interestingly, the high-temperature PCD led to an increase in cacao odor while low-temperature FD resulted in lower flavor, odors and VOCs. These results demonstrate that protein quality and sensorial properties of C. vulgaris can be steered through the type of drying, which could help in the selection of application-specific drying methods. Overall, this work could promote the incorporation of microalgal single cell proteins in different innovative food products.

Pulsed electric field treatment for preservation of Chlorella suspensions and retention of gelling capacity

Pulsed electric field (PEF) processing has emerged as an alternative to thermal pasteurization for the shelf-life extension of heat-sensitive liquids at industrial scale. It offers the advantage of minimal alteration in physicochemical characteristics and functional properties. In this study, a pilot-scale continuous PEF processing (Toutlet < 55 °C) was applied to microalgae Chlorella vulgaris (Cv) suspensions (pH = 6.5), which was proposed as a functional ingredient for plant-based foods. Cv suspensions were inoculated with three distinct food spoilage microorganisms (Pseudomonas guariconensis, Enterobacter soli and Lactococcus lactis), isolated from the Cv biomass. PEF treatments were applied with varying electric field strength Eel of 16 to 28 kV/cm, pulse repetition rate f of 100 to 140 Hz, with a pulse width τ of 20 μs and an inlet product temperature Tin of 30 °C. The aim was to evaluate the PEF-induced microbial reduction and monitor the microbial outgrowth during a 10-day cold storage period (10 °C). Maximum inactivation of 4.1, 3.7 and 3.6 logs was achieved (28 kV/cm and 120 Hz) for the investigated isolates, respectively. Under these conditions, the critical electric field strengths Ecrit, above which inactivation was observed, ranged from 22.6 to 24.6 kV/cm. Moreover, repeated PEF treatment resulted in similar inactivation efficiency, indicating its potential to enhance shelf-life further.

Microalgal-bacterial immobilized co-culture as living biofilters for nutrient recovery from synthetic wastewater and their potential as biofertilizers

This study investigates nutrient recovery from synthetic municipal wastewater using co-immobilized cultures of Chlorella vulgaris TISTR 8580 (CV) and plant growth-promoting bacteria, Bacillus subtilis TISTR 1415 (BS) as living biofilters for a subsequent biofertilizer activity. The optimal condition for nutrient recovery was at the 1:1 ratio of CV/BS using mixed guar gum/carrageenan (GG/CG) binders. After 7-day wastewater treatment, the living biofilters removed 86.7 ± 0.5% of ammonium and 99.3 ± 0.3% of phosphates and were tested subsequently as biofertilizers for 20 days to grow selected plants. The highest optimal biomass and chlorophyll a content was 2 ± 0.3 g (CV/BS 3:1) and 12.4 ± 0.7 µg/g (CV/BS 1:1) from cucumber respectively, however, the close-to-neutral pH (8.0 ± 0.3) was observed from sunflower using CV/BS 1:1 living biofilters. Conclusively, the designed living biofilters exhibit the potential to recover nutrients from wastewater and be used as biofertilizers for circular agriculture.

while bioremediating ammonium and organic pollutants in municipal wastewater

Municipal wastewater is ubiquitously laden with myriad pollutants discharged primarily from a combination of domestic and industrial activities. These heterogeneous pollutants are threating the natural environments when the traditional activated sludge system fails sporadically to reduce the pollutants' toxicities. Besides, the activated sludge system is very energy intensive, bringing conundrums for decarbonization. This research endeavoured to employ Chlorella vulgaris sp. In converting pollutants from municipal wastewater into hydrogen via alternate light and dark fermentative process. The microalgae in attached form onto 1 cm3 of polyurethane foam cubes were adopted in optimizing light intensity and photoperiod during the light exposure duration. The highest hydrogen production was recorded at 52 mL amidst the synergistic light intensity and photoperiod of 200 μmolm-2s-1 and 12:12 h (light:dark h), respectively. At this lighting condition, the removals of chemical oxygen demand (COD) and ammoniacal nitrogen were both achieved at about 80%. The sustainability of microalgal fermentative performances was verified in recyclability study using similar immobilization support material. There were negligible diminishments of hydrogen production as well as both COD and ammoniacal nitrogen removals after five cycles, heralding inconsequential microalgal cells' washout from the polyurethane support when replacing the municipal wastewater medium at each cycle. The collected dataset was finally modelled into enhanced Monod equation aided by Python software tool of machine learning. The derived model was capable to predict the performances of microalgae to execute the fermentative process in producing hydrogen while subsisting municipal wastewater at arbitrary photoperiod. The enhanced model had a best fitting of R2 of 0.9857 as validated using an independent dataset. Concisely, the outcomes had contributed towards the advancement of municipal wastewater treatment via microalgal fermentative process in producing green hydrogen as a clean energy source to decarbonize the wastewater treatment facilities.

Hydrothermal co-liquefaction of microalgae, sugarcane bagasse, brewer's spent grain, and sludge from a paper recycling mill: Modeling and evaluation of biocrude and biochar yield

Biomass can be used as an energy source to thermochemical conversion processes to biocrude production. However, the supply and dependence on only one biomass for biocrude production can be an obstacle due to its seasonality, availability, and logistics costs. In this way, biomass waste and agroindustrial residues can be mixture and used as feedstock to the hydrothermal co-liquefaction (co-HTL) process as an alternative to obtaining biocrude. In this sense, the present paper analyzed the biocrude yield influence of the co-HTL from a quaternary unprecedented blend of different biomasses, such as sugarcane bagasse, brewer's spent grain (BSG), sludge from a paper recycling mill (PRM), and microalgae (Chlorella vulgaris). In this way, a simplex lattice design was employed and co-HTL experiments were carried out in a 2000 mL high-pressure stirred autoclave reactor under 275 °C for 60 min, considering 15% of feedstock/water ratio. Significant effects in each feedstock and their blends were analyzed aiming to increase biocrude and biochar yield. It was found that the addition of microalgae is only significant when considered more than 50% into the blend with BSG and PRM sludge to increase biocrude yield.

Effects of polystyrene nanoplastics and PCB-44 exposure on growth and physiological biochemistry of Chlorella vulgaris

Both NPs and PCBs are emerging contaminants widely distributed in the environment, and it is worth exploring whether the combination of the two contaminants causes serious pollution and harm. Therefore, we studied the effects of PS-NPs and PCB-44 alone and together after 96 h and 21 d of exposure to C. pyrenoidosa. The results showed that PS-NPs and PCB-44 affected the cell cycle of C. pyrenoidosa and inhibited its normal growth. Under PS-NPs and PCB-44 stress, the relative conductivity of the algal solution increased, the hydrophobicity of the algal cell surface decreased, and the synthesis of chlorophyll a and chlorophyll b was reduced. In addition to physiological, there are biochemical effects on C. pyrenoidosa. PS-NPs and PCB-44 exposure induced oxidative stress with significant changes in the enzymatic activities of SOD and CAT together with MDA content. Moreover, the relative expression of photosynthesis-related genes (psbA, rbcL, rbcS) all responded, negatively affecting photosynthesis. In particular, significant toxic effects were observed with single exposure to PCB-44 and co-exposure to PS-NPs and PCB-44, with similar trends of effects in acute and chronic experiments. Taken together, exposure to PS-NPs and PCB-44 caused negative effects on the growth and physiological biochemistry of C. pyrenoidosa. These results provide scientific information to further explore the effects of NPs and PCBs on aquatic organisms and ecosystems.

Predicting the Structure of Enzymes with Metal Cofactors: The Example of [FeFe] Hydrogenases

The advent of deep learning algorithms for protein folding opened a new era in the ability of predicting and optimizing the function of proteins once the sequence is known. The task is more intricate when cofactors like metal ions or small ligands are essential to functioning. In this case, the combined use of traditional simulation methods based on interatomic force fields and deep learning predictions is mandatory. We use the example of [FeFe] hydrogenases, enzymes of unicellular algae promising for biotechnology applications to illustrate this situation. [FeFe] hydrogenase is an iron-sulfur protein that catalyzes the chemical reduction of protons dissolved in liquid water into molecular hydrogen as a gas. Hydrogen production efficiency and cell sensitivity to dioxygen are important parameters to optimize the industrial applications of biological hydrogen production. Both parameters are related to the organization of iron-sulfur clusters within protein domains. In this work, we propose possible three-dimensional structures of Chlorella vulgaris 211/11P [FeFe] hydrogenase, the sequence of which was extracted from the recently published genome of the given strain. Initial structural models are built using: (i) the deep learning algorithm AlphaFold; (ii) the homology modeling server SwissModel; (iii) a manual construction based on the best known bacterial crystal structure. Missing iron-sulfur clusters are included and microsecond-long molecular dynamics of initial structures embedded into the water solution environment were performed. Multiple-walkers metadynamics was also used to enhance the sampling of structures encompassing both functional and non-functional organizations of iron-sulfur clusters. The resulting structural model provided by deep learning is consistent with functional [FeFe] hydrogenase characterized by peculiar interactions between cofactors and the protein matrix.

Photoheterotroph improved the growth and nutrient levels of Chlorella vulgaris and the related molecular mechanism

Microalgae are rich in fatty acids, proteins, and other nutrients, which have gained the general attention of researchers all over the world. For the development of Chlorella vulgaris in food and feed industry, this study was conducted to investigate the differences in C. vulgaris' growth and nutritional components under different culture conditions (autotrophic, heterotrophic, photoheterotrophic) and the internal factors through cell counting in combination with transcriptome and nutrient analyses. The results showed that, under the photoheterotrophic condition, Chlorella's growth and the contents of lipid and protein were significantly higher than that under the heterotrophic condition, and the moisture content was lower than that under the heterotrophic condition. The saturated fatty acid content under the photoheterotrophic condition was the lowest, while the polyunsaturated fatty acid content was significantly higher than those under the other two conditions. There were 46,583 differentially expressed genes (DEGs), including 33,039 up-regulated DEGs (70.93%) and 13,544 down-regulated DEGs (29.07%), under the photoheterotrophic condition in comparison with the autotrophic condition. The fold change between the two conditions of samples of up-regulated genes was higher than that of the down-regulated genes. The KEGG enrichment showed that the up-regulated DEGs in the photoheterotrophic condition were significantly enriched in 5 pathways, including protein processing in endoplasmic reticulum pathway, photosynthesis pathway, photosynthesis-antenna protein pathway, endocytosis pathway, and phosphonate and phosphinate metabolism pathway. DEGs related to fatty acid metabolic pathways were significantly enriched in the fatty acid biosynthesis pathway and the biosynthesis of unsaturated fatty acid pathway. The qPCR analysis showed that the expression pattern of the selected genes was consistent with that of transcriptome analysis. The results of this study lay a theoretical foundation for the large-scale production of Chlorella and its application in food, feed, and biodiesel. KEY POINTS: • Nutrient levels under photoheterotrophic condition were higher than other conditions. • Six important pathways were discovered that affect changes in nutritional composition. • Explored genes encode important enzymes in the differential metabolic pathways.

Biodegradability and bioavailability of dissolved substances in aquaculture effluent: Performance of indigenous bacteria, cyanobacteria, and green microalgae

Aquaculture is a controlled aquatic farming sector and one of the most important human food sources. Fish farming is one of the predominant, fast-growing sectors that supply seafood products worldwide. Along with its benefits, aquaculture practices can discharge large quantities of nutrients into the environment through non-treated or poorly treated wastewater. This study aims to understand the nutrient composition of fish wastewater and the use of indigenous bacteria, cyanobacteria, and microalgae as an alternative biological treatment method. Wastewater samples from a local fish farming facility were collected and treated using six different species of cyanobacteria and microalgae include Chroococcus minutus, Porphyridium cruentum, Chlorella vulgaris, Microcystis aeruginosa, Chlamydomonas reinhardtii, and Fischerella muscicola. All the samples were incubated for 21 days, and the following parameters were measured weekly: Chemical oxygen demand (COD), phosphate, total dissolved nitrogen, and dissolved inorganic nitrogen. In addition, dissolved organic nitrogen (DON), bioavailable DON (ABDON), and biodegradable DON (BDON) were calculated from the mass-balance equations. Colorimetric and digestive methods were used for the parameter measurements. The results showed that C. reinhardtii reduced the soluble COD concentration by 74.6 %, DON by 94.3 %, and phosphorous by more than 99 %. Moreover, M. aeruginosa, and C. minutus significantly reduced inorganic nitrogen species (>99 %). This alternative fish wastewater treatment method was explored to gain insight into fish wastewater nutrient composition and to create a sustainable alternative to conventional fish wastewater treatment methods.

Synthesis and utilization of biomass-derived sulfonated heterogeneous catalyst-BT-SO3H for microalgal biodiesel production

The study investigates the potential of utilizing banana trunk-derived porous activated biochar enriched with SO3H- as a catalyst for eco-friendly biodiesel production from the microalga Chlorella vulgaris. An extensive analysis, employing advanced techniques such as XRD, FTIR, TGA, XPS, NH3-TPD, BET, SEM-EDX, and TEM, was conducted to elucidate the physicochemical properties of BT-SO3H catalysts. The synthesized catalyst demonstrated its efficiency in converting the total lipids of Chlorella vulgaris into biodiesel, with varying concentrations of 3%, 5%, and 7%. Notably, using a 5% BT-SO3H concentration resulted in remarkably higher biodiesel production about 58.29%. Additionally, the fatty acid profile of C. vulgaris biodiesel indicated that C16:0 was the predominant fatty acid at 24.31%, followed by C18:1 (19.68%), C18:3 (11.45%), and C16:1 (7.56%). Furthermore, the biodiesel produced via 5% BT-SO3H was estimated to have higher levels of saturated fatty acids (SFAs) at 34.28%, monounsaturated fatty acids (MUFAs) at 30.70%, and polyunsaturated fatty acids (PUFAs) at 24.24%. These findings highlight the promising potential of BT-SO3H catalysts for efficient and environmentally friendly biodiesel production from microalgal species.

Physicochemical surface properties of Chlorella vulgaris: a multiscale assessment, from electrokinetic and proton uptake descriptors to intermolecular adhesion forces

Given the growing scientific and industrial interests in green microalgae, a comprehensive understanding of the forces controlling the colloidal stability of these bioparticles and their interactions with surrounding aqueous microenvironment is required. Accordingly, we addressed here the electrostatic and hydrophobic surface properties of Chlorella vulgaris from the population down to the individual cell levels. We first investigated the organisation of the electrical double layer at microalgae surfaces on the basis of electrophoresis measurements. Interpretation of the results beyond zeta-potential framework underlined the need to account for both the hydrodynamic softness of the algae cells and the heterogeneity of their interface formed with the outer electrolyte solution. We further explored the nature of the structural charge carriers at microalgae interfaces through potentiometric proton titrations. Extraction of the electrostatic descriptors of interest from such data was obscured by cell physiology processes and dependence thereof on prevailing measurement conditions, which includes light, temperature and medium salinity. As an alternative, cell electrostatics was successfully evaluated at the cellular level upon mapping the molecular interactions at stake between (positively and negatively) charged atomic force microscopy tips and algal surface via chemical force microscopy. A thorough comparison between charge-dependent tip-to-algae surface adhesion and hydrophobicity level of microalgae surface evidenced that the contribution of electrostatics to the overall interaction pattern is largest, and that the electrostatic/hydrophobic balance can be largely modulated by pH. Overall, the combination of multiscale physicochemical approaches allowed a drawing of some of the key biosurface properties that govern microalgae cell-cell and cell-surface interactions.

Toxicity of hexagonal boron nitride nanosheets to freshwater algae: Phospholipid membrane damage and carbon assimilation inhibition

Hexagonal boron nitride (h-BN) nanomaterials have attracted numerous attentions for application in various fields, including environmental governance. Understanding the environmental implications of h-BN is a prerequisite for its safe and sustainable use; nevertheless, information on the negative effect of h-BN on aquatic organisms and the underlying toxicity mechanisms is scarce. The present study found that low exposure doses (0.1-1 μg/mL) of micron-sized h-BN lamella apparently suppressed (maximally 45.3%) the growth of Chlorella vulgaris (a freshwater alga) via membrane damages and metabolic reprogramming. Experimental and simulation results verified that h-BN can penetrate into and then extract phospholipids from the cell membrane of algae due to the strong hydrophobic interactions between h-BN nanosheets and lipids, resulting in membrane permeabilization and integrity reduction. Oxidative stress-triggered lipid peroxidation also contributes to membrane destruction of algae. Metabolomics assay demonstrated that h-BN down-regulated the CO2-fixation associated Calvin cycle and glycolysis/gluconeogenesis pathways in algae, thereby inhibiting energy synthesis and antioxidation process. Despite releasing soluble B inside cells, the B species exhibited negligible toxicity. These findings highlight the phenomena and mechanisms of h-BN toxicity in photosynthetic algae, which have great implications for guiding their safe use under the scenarios of global carbon neutrality.

Response of Chlorella vulgaris to exposure to CuO NPs: Contributions of particulate and dissolved metal forms as modulated by tannic acid and pH

A suspension of copper oxide nanoparticles (CuO NPs) is a mixture of dissolved and particulate Cu, the relative proportions of which highly depend on the water chemistry. However, the relationship between different proportions of particulate and dissolved Cu and the overall toxicity of CuO NPs is still unknown. This study investigated the response of Chlorella vulgaris to CuO NPs at varying solution pH and at different tannic acid (TA) additions, with a focus on exploring whether and how dissolved and particulate Cu contribute to the overall toxicity of CuO NPs. The results of the exposure experiments demonstrated the involvement of both dissolved and particulate Cu in inducing toxicity of CuO NPs, and the inhibition of CuO NPs on cell density of Chlorella vulgaris was found to be significantly (p < 0.05) alleviated with increased levels of TA and pH (< 8). Using the independent action model, the contribution to toxicity of particulate Cu was found to be enhanced with increasing pH values and TA concentrations. The toxic unit indicator better (R2 = 0.86, p < 0.001) explained impacts of CuO NPs on micro-algae cells than commonly used mass concentrations (R2 = 0.27-0.77, p < 0.05) across different levels of pH and TA. Overall, our study provides an additivity-based method to improve the accuracy of toxicity prediction through including contributions to toxicity of both dissolved and particulate Cu and through eliminating the uneven distribution of data due to large variations in total Cu, particulate Cu, dissolved Cu, Cu2+ activities, Cu-TA complexes and other Cu-complexes concentrations with varying water chemistry conditions.

Development of a new sterilization method for microalgae media using calcium hypochlorite as the sterilant

Calcium hypochlorite (Ca(ClO)2), which can be stably stored in powder form for a long period, is widely used as a disinfectant in various fields. A new sterilization process was developed in the present study, where a microalgal medium was sterilized using 0.02% Ca(ClO)2, followed by complete neutralization of the Ca(ClO)2 within 8 h through catalytic reaction of an MnCl2-Na2EDTA complex and a synergistic effect of glucose. When comparing the growth of Chlorella vulgaris in the autoclaved medium, a 2.65 times greater maximum cell growth was observed in cells grown in the medium prepared by treatment of Ca(ClO)2. This result indicates that denaturation of the medium by heat can hinder the growth of some microorganisms. In the case of cultivation of Euglena gracilis, successful culture growth was achieved without growth inhibition or contamination on a medium prepared in the same manner.

Acrylamide exposure induces growth retardation, neurotoxicity, stress, and immune/antioxidant disruption in Nile tilapia (Oreochromis niloticus): The alleviative effects of Chlorella vulgaris diets

This study looked at the toxic impacts of water-born acrylamide (ACR) on Nile tilapia (Oreochromis niloticus) in terms of behaviors, growth, immune/antioxidant parameters and their regulating genes, biochemical indices, tissue architecture, and resistance to Aeromonas hydrophila. As well as the probable ameliorative effect of Chlorella vulgaris (CV) microalgae as a feed additive against ACR exposure was studied. The 96-h lethal concentration 50 of ACR was investigated and found to be 34.67 mg/L for O. niloticus. For the chronic exposure study, a total of 180 healthy O. niloticus (24.33 ± 0.03 g) were allocated into four groups in tri-replicates (15 fish/replicate), C (control) and ACR groups were fed a basal diet and exposed to 0 and 1/10 of 96-h LC50 of ACR (3.46 mg/L), respectively. ACR+ CV5 and ACR+ CV10 groups were fed basal diets with 5 % and 10 % CV supplements, respectively and exposed to 1/10 of 96-h LC50 of ACR for 60 days. After the exposure trial (60 days) the experimental groups were challenged with A. hydrophila. The findings demonstrated that ACR exposure induced growth retardation (P˂0.01) (lower final body weight, body weight gain, specific growth rate, feed intake, protein efficiency ratio, final body length, and condition factor as well as higher feed conversion ratio). A substantial decrease in the immune/antioxidant parameters (P˂0.05) (lysozyme, serum bactericidal activity %, superoxide dismutase, and reduced glutathione) and neurotransmitter (acetylcholine esterase) (P˂0.01) was noticed with ACR exposure. A substantial increase (P˂0.01) in the serum levels of hepato-renal indicators, lipid peroxidation biomarker, and cortisol was noticed as a result of ACR exposure. ACR exposure resulted in up-regulation (P˂0.05) of the pro-inflammatory cytokines and down-regulation (P˂0.05) of the antioxidant-related gene expression. Furthermore, the hepatic, renal, brain, and splenic tissues were badly affected by ACR exposure. ACR-exposed fish were more sensitive to A. hydrophila infection and recorded the lowest survival rate (P˂0.01). Feeding the ACR-exposed fish with CV diets significantly improved the growth and immune/antioxidant status, as well as modulating the hepatorenal functions, stress, and neurotransmitter level compared to the exposed-non fed fish. In addition, modulation of the pro-inflammatory and antioxidant-related gene expression was noticed by CV supplementation. Dietary CV improved the tissue architecture and increased the resistance to A. hydrophila challenge in the ACR-exposed fish. Noteworthy, the inclusion of 10 % CV produced better results than 5 %. Overall, CV diets could be added as a feed supplement in the O. niloticus diet to boost the fish's health, productivity, and resistance to A. hydrophila challenge during ACR exposure.

Enhanced mono-aromatics production by the CH4-assisted pyrolysis of microalgae using Zn-based HZSM-5 catalysts

This study presents the catalytic pyrolysis of microalgae, Chlorella vulgaris (C. vulgaris), using pure CH4 and H2-rich gas evolved from CH4 decomposition on three different HZSM-5 catalysts loaded with Zn, Ga, and Pt, aimed specifically at producing high-value mono-aromatics such as benzene, toluene, ethylbenzene, and xylene (BTEX). In comparison with that for the typical inert N2 environment, a pure CH4 environment increased the bio-oil yield from 32.4 wt% to 37.4 wt% probably due to hydrogen and methyl radical insertion in the bio-oil components. Furthermore, the addition of bimetals further increased bio-oil yield. For example, ZnPtHZ led to a bio-oil yield of 47.7 wt% in pure CH4. ZnGaHZ resulted in the maximum BTEX yield (6.68 wt%), which could be explained by CH4 activation, co-aromatization, and hydrodeoxygenation. The BTEX yield could be further increased to 7.62 wt% when pyrolysis was conducted in H2-rich gas evolved from CH4 decomposition over ZnGaHZ, as rates of aromatization and hydrodeoxygenation were relatively high under this condition. This study experimentally validated that the combination of ZnGaHZ and CH4 decomposition synergistically increases BTEX production using C. vulgaris.

An integrated approach for wastewater treatment and algae cultivation: Nutrient removal analysis, biodiesel extraction, and energy and environmental metrics enhancement

Human urine is rich in nitrogen and phosphorus, and the presence of these elements in wastewater significantly disrupts the biogeochemical cycle. Meanwhile, green algal biomass cultivation is unfeasible without these nutrients. Hence, the present study integrates wastewater treatment and algae cultivation to extract biodiesel and improve its performance through fuel modification. Chlorella vulgaris algae was cultivated in different dilution ratios of water and urine, and the nutrient removal rate was analyzed. Chlorella vulgaris algae biodiesel (CAB) was derived through Bligh and Dyer's method followed by transesterification, and its functional and elemental groups were analyzed. The various volume concentrations of CAB were blended with regular diesel fuel (RDF), and 10% water was added to a 30% CAB blended RDF to evaluate the combustion performance and environmental impacts. The results of the experiments demonstrated that the algae cultivation effectively removed the wastewater nutrients. The functional and elemental groups of CAB are identical to those of RDF. The engine characteristics of test fuels report that the CAB-blend RDF fuel mixtures generate low carbon footprints, whereas negative impacts have been drawn for performance metrics and oxides of nitrogen emissions. The water-emulsified fuel outweighed the unfavorable effects and promoted more efficient and cleaner combustion.

Effect of different concentrations of gibberellins on attenuation of nutrient and antibiotics from aquaculture wastewater using microalgae-bacteria-fungi consortia system

This study assessed the effect of gibberellins (GAs) concentrations on antibiotic and nutrient removal using diverse microalgal-bacterial-fungal consortia. Five systems (Chlorella vulgaris, T1; C. vulgaris + S395-2 + Clonostachys rosea, T2; C. vulgaris + S395-2 + Ganoderma lucidum, T3; C. vulgaris + S395-2 + Pleurotus pulmonarius, T4; and C. vulgaris + S395-2, T5) were established, and optimal conditions and effective symbiosis were applied to improve antibiotic and nutrient removal. Consortium growth was T2 > T3 > T5 > T4 > T1, while GA impact ranked 50 mg L-1 > 20 mg L-1 > 80 mg L-1 > 0 mg L-1. After 7 days at 50 mg L-1 GAs, total nitrogen (TN), NH4-N, NO3-N, and total phosphorous (TP) removal reached 85.97 %, 78.08 %, 86.59 %, and 94.39 %, respectively. Florfenicol, oxytetracycline hydrochloride, ofloxacin, and sulfamethoxazole removal efficiencies were 67.77 %, 98.29 %, 90.47 %, and 94.92 %, respectively. These findings highlight GAs' significant role in enhancing antibiotic and nutrient removal.

Enhancing microalgae biomass production: Exploring improved scraping frequency in a hybrid cultivation system

Recently, hybrid systems, such as those incorporating high-rate algal ponds (HRAPs) and biofilm reactors (BRs), have shown promise in treating domestic wastewater while cultivating microalgae. In this context, the objective of the present study was to determine an improved scraping frequency to maximize microalgae biomass productivity in a mix of industrial (fruit-based juice production) and domestic wastewater. The mix was set to balance the carbon/nitrogen ratio. The scraping strategy involved maintaining 1 cm wide stripes to retain an inoculum in the reactor. Three scraping frequencies (2, 4, and 6 days) were evaluated. The findings indicate that a scraping frequency of each 2 days provided the highest biomass productivity (18.75 g total volatile solids m-2 d-1). The species' behavior varied with frequency: Chlorella vulgaris was abundant at 6-day intervals, whereas Tetradesmus obliquus favored shorter intervals. Biomass from more frequent scraping demonstrated a higher lipid content (15.45%). Extrapolymeric substance production was also highest at the 2-day frequency. Concerning wastewater treatment, the system removed 93% of dissolved organic carbon and ∼100% of ammoniacal nitrogen. Combining industrial and domestic wastewater sources to balance the carbon/nitrogen ratio enhanced treatment efficiency and biomass yield. This study highlights the potential of adjusting scraping frequencies in hybrid systems for improved wastewater treatment and microalgae production.

Ecological impact of surfactant Tween-80 on plankton: High-scale analyses reveal deeper hazards

The ecological risks of surfactants have been largely neglected because of their low toxicity. Multiscale studies have indicated that even if a pollutant causes no acute toxicity in a test species, it may alter interspecific interactions and community characteristics through sublethal impacts on test organisms. Therefore, we investigated the lethal and sublethal responses of the plankton species Scenedesmus quadricauda, Chlorella vulgaris, and Daphnia magna, to surfactant Tween-80. Then, high-scale responses in grazer life-history traits and stability of the D. magna-larval damselfly system were further explored. The results showed that discernible adverse effects on the growth or survival of the three plankton species were evident only at exceptionally high concentrations (≥100 mg L-1). However, 10 mg L-1 of Tween-80 notably affected the MDA concentration in grazer species, simultaneously displaying a tendency to diminish grazer's heartbeat and swimming frequency. Furthermore, Tween-80 reduced the grazer reproductive capacity and increased its predation risk by larval damselflies, which ultimately jeopardized the stability of the D. magna-larval damselfly system at much lower concentrations (10-100 fold lower) than the individual-scale responses. This study provides evidence that high-scale traits are far more sensitive to Tween-80, compared with individual-scale traits for plankton organisms, suggesting that the ecological risks of Tween-80 demand careful reassessment. SYNOPSIS: The concentration of Tween-80 needed to induce changes in community characteristics is markedly lower than that needed to produce individual-scale consequences. Thus, high-scale analyses have broad implications for understanding the hazardous effects of surfactants compared with an individual-scale analysis.

Coupling anaerobic co-digestion of winery waste and waste activated sludge with a microalgae process: Optimization of a semi-continuous system

Wine production represents one of the most important agro-industrial sectors in Italy. Wine lees are the most significant waste in the winery industry and have high disposal and storage costs and few applications within the circular economy. In this study, anaerobic digestion and a microalgae coupled process was studied in order to treat wine lees and waste activated sludge produced within the same facility, with the aim of producing energy and valuable microalgae biomass that could be processed to recover biofuel or biostimulant. Chlorella vulgaris was cultivated on liquid digestate in a semi-continuous system without biomass recirculation. The best growth and phytoremediation performance were achieved applying a hydraulic retention time (HRT) of 20 days with a stable dry weight, lipid and protein storage of 1.85 ± 0.02 g l-1, 33.48 ± 7.54 % and 57.85 ± 10.14 % respectively. Lipid characterization highlighted the potential use in high quality biodiesel production, according to EN14214 (<12 % v/v linolenic acid). The microalgae reactor's liquid output showed high removal of ammonia (95.72 ± 2.10 %), but low organic soluble matter reduction. Further semi-continuous process optimization was carried out by increasing the time between digestate feeding and biomass recovery at HRT 10. These operative changes avoided biomass wash-out and provided a stable phytoremediation of the digestate with 84.58 ± 4.02 % ammonia removal, 33.01 ± 1.44 % sCOD removal, 38.06 ± 2.65 % of polyphenols removal.

Mechanism of heavy metal ion biosorption by microalgal cells: A mathematic approach

Microalgal biomasses have been established as promising biosorbents for biosorption to remove heavy metal ions (HMIs) from wastewaters and contaminated natural waterbodies. Understanding the mechanism is important for the development of cost-effective processes for large scale applications. In this paper, a simple mathematical model was proposed for the predication of biosorption capacity of HMI by microalgal cells based on single cell mass, cell size, and HMI radius. One fundamental assumption based on which this model was developed, i.e., the biosorption of HMI by microalgal cells is predominantly monolayer bio-adsorption, was established based on kinetic, isothermal, FTIR, and Pb(II) distribution data generated in this study and in literature. The model was validated using a combination of experimental and literature data as well, demonstrating its capability to provide reasonable estimations although with discrepancies. The biosorption capacities of HMIs (mmol/g) by Chlorella vulgaris were experimentally determined to be in the following order: Pb(II)(0.360)> Zn(II)(0.325)> Cu(II)(0.254)> Ni(II)(0.249)> Cd(II)(0.235)> Co(II)(0.182). We systematically investigated the deviations of the predicted biosorption capacities in term of the effects of a few important parameters that were unaccounted for in the model, including the nanostructures on cell surface, HMI electronegativity, and biosorption buffer pH. Results suggest that the nanostructures on cell wall, likely the hairlike fibers, might be the primary locations where the binding sites for HMI were housed. Furthermore, isothermal data, which is suported by the predictions of this model, indicate the each effective binding site on C. vulgaris cell surface could bind to more than one Co(II) in biosorption while each of the other five HMIs tested in this study required more than one binding sites.

Updated Chronic Copper Bioavailability Models for Invertebrates and Algae

Chronic copper (Cu) bioavailability models have been successfully implemented in European risk assessment frameworks and compliance evaluations. However, they were developed almost two decades ago, which calls for an update. In the study, we present updated chronic Cu bioavailability models for invertebrates and algae. They consider recent ecotoxicity data sets and use the more recent speciation model Windermere Humic Aqueous Model (WHAM) VII and an optimized model structure (i.e., a generalized bioavailability model [gBAM]). Contrary to the classic biotic ligand model, a gBAM models the effect of pH on Cu2+ toxicity via a log-linear relationship parametrized through the pH slope SpH . The recalibrated SpH parameters are -0.208 for invertebrates (Daphnia magna, two clones) and -0.975 for algae (Raphidocelis subcapitata and Chlorella vulgaris). The updated models predict 80% to 100% of the observed effect levels for eight different species within a factor of 2. The only exception was one of the two data sets considering subchronic 7-day mortality to Hyalella azteca: the prediction performance of the updated invertebrate model at pH ≥ 8.3 was poor because the effect of pH on Cu2+ toxicity appeared to be dependent on the pH itself (with a steeper pH slope compared with the updated invertebrate model at pH ≥ 8.1). The prediction performance of the updated Cu bioavailability models was similar to or better than that of the models used for regulatory application in Europe until now, with one exception (i.e., H. azteca). Together with the recently published fish bioavailability model, the models developed in the present study constitute a complete, updated, and consistent bioavailability model set. Overall, the updated chronic Cu bioavailability model set is robust and can be used in regulatory applications. The updated bioavailability model set is currently used under the European Union Registration, Evaluation, Authorisation, and Restriction of Chemicals framework regulation to guide the safe use of Cu. Environ Toxicol Chem 2024;43:450-467. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Evaluation on microalgae for the production of bio-chemicals and electricity

Recent advancement in biophotovoltaic systems using microalgae, coupled with biorefinery approach, would improve economy-feasibility in production. The major concern is its commercial strength in terms of scalability, strain selection and extraction procedure cost. It must compete with conventional feedstocks such as fossil fuels. This project proposes to enhance the economic feasibility of microalgae-based biorefinery by evaluating their performance for bio-electricity, bio-diesel and carotenoids production in a single cycle. The first part of the study was to construct and select a Bio-bottle Voltaic (BBV) device that would allow microalgae to grow and produce bioproducts, as well as generate the maximum current output reading derived from the microalgae's photosynthesis process. The second phase consisted of a 25-day investigation into the biorefinery performance of six different microalgal species in producing bio-electricity, bio-diesel and carotenoid in a prototype BBV device. The prototype BBV device with aluminium foil and pencil lead as its anode and cathode produced the highest carotenoid and biodiesel component production from the two microalgae tested, according to the results of the first phase of the experiment. In the second portion of the study, Scenedesmus dimorphus and Chlorella vulgaris were identified as the two microalgae most capable of maintaining their growth throughout the experiment. The maximum current reading observed for C. vulgaris was 653 mV. High Performance Liquid Chromatography analysis showed four major carotenoid compounds found which were Neoxanthin, Cantaxanthin, Astaxanthin and 9-cis antheraxanthin, and the highest carotenoid producer was C. vulgaris which recorded at 1.73 μg/mL. C. vulgaris recorded as the most alkanes producer with 22 compounds detected and Heptacosane and Heneicosane as the two major biodiesel compounds found in the extracts. Evaluation of C. vulgaris data showed that it has enormous potential for microalgal biorefinery candidates. Further ongoing research and development efforts for C. vulgaris will improve the economic viability of microalgae-based industries and reduce reliance on depleted fossil fuels.

Comparative assessment of microalgal growth kinetic models based on light intensity and biomass concentration

The comprehensive evaluation and validation of mathematical models for microalgal growth dynamics are essential for improving cultivation efficiency and optimising photobioreactor design. A considerable gap in comprehending the relation between microalgal growth, light intensity and biomass concentration arises since many studies focus solely on associating one of these factors. This paper compares microalgal growth kinetic models, specifically focusing on the combined impact of light intensity and biomass concentration. Considering a dataset (experimental results and literature values) concerning Chlorella vulgaris, nine kinetic models were assessed. Bannister and Grima models presented the best fitting performance to experimental data (RMSE ≤ 0.050 d-1; R2≥0.804; d2≥0.943). Cultivation conditions conducting photoinhibition were identified in some kinetic models. After testing these models on independent datasets, Bannister and Grima models presented superior predictive performance (RMSE = 0.022-0.023 d-1; R2 = 0.878-0.884; d2: 0.976-0.975). The models provide valuable tools for predicting microalgal growth and optimising operational parameters, reducing the need for time-consuming and costly experiments.

Interchangeable modular design and operation of photo-bioreactors for Chlorella vulgaris cultivation towards a zero-waste biorefinery

This study explores diverse cultivation modes for Chlorella vulgaris within a biorefinery at pilot scale that produces both biodiesel by transesterification of waste frying oils and syngas by gasification of organic wood waste. Given microalgae's comparatively modest biofuel yield relative to principal biorefinery products, the microalgae cultivation process is designed on the biofuels production rates. Liquid and gaseous waste streams are recycled inside the biorefinery: crude glycerol is mixed with wood to enhance the quality of syngas, wastewater is fed to microalgae so as flue gas. Also, the oil extracted from microalgae contributes to produce biodiesel and the waste cells are gasified. Considering that the optimal fit for each cultivation mode varies with the shape of the reactor, we propose a modular approach to assemble them in batteries of tubular, bubble flow, and airlift reactors, and present an operating design criterion that can fulfill the mass balance of the plant by adding/transforming the number of units inside the different batteries. Methods to adjust the operating conditions and control the operating parameters are also discussed. The designed configurations were operated recycling nominal waste streams of about 30 L d-1 of wastewater and 90 Nm3 h-1 of flue gas. Results confirm that the most advantageous one, in terms of volume per recycled waste streams, is a battery of 16 airlift reactors, operating in mixotrophic mode, with growing rate of 0.427 d-1, yield of 3.06, glycerol conversion 39 %, CO2 removal 64 % of inlet 6-10 %(mol) concentration. The same nominal waste streams can also be managed by 40 tubular reactors in almost heterotrophic conditions coupled with 12 bubble columns in autotrophic conditions; working respectively at growing rates of 0.395 d-1 and 0.362 d-1 and yields of 2.94 and 2.84. The battery of tubular reactors reached a glycerol conversion of 45 % and the array of bubble columns removed about 51 % of inlet 12-20 %(mol) CO2 concentration. A complete comparison is reported also in terms of dimensionless numbers and pumping/mixing requirements.

Exploring the molecular mechanism of Chlorella vulgaris in response to androstenedione exposure based on genes continuously up-regulated in transcription analysis

Androstenedione (ADSD) is one of the widely detected androgens in diverse aquatic environments. However, there were few reports on the molecular mechanism of Chlorella vulgaris exposure to ADSD. In our previous research, we have investigated the genes associated with chlorophyll metabolism in Chlorella vulgaris response to ADSD. In this study, we focus on continuously up-regulated genes to explore the mechanism underlying Chlorella vulgaris resistance to ADSD toxicity. Chlorella vulgaris was exposed to ADSD with five concentration gradients. The continuously up-regulated genes were enriched by Series Test of Cluster (STC) analysis and verified by qRT-PCR. Microalgae Super Oxidase Dimutase (SOD) and Microalgae Malonic dialdehyde (MDA), two indicators of oxidative stress, were determined by ELISA after exposure to ADSD. The results showed that ADSD can stimulate the production of extracellular polymeric substances (EPS) and lead to enlargement in the cell body of Chlorella vulgaris. In addition, steroid biosynthesis and oxidoreductase activity processes were consistently up-regulated upon exposure to ADSD. In conclusion, our study highlighted the crucial role of phenotypic modification, hormone synthesis, and redox mechanisms in protecting Chlorella vulgaris cells from the harmful effects of ADSD contamination.

Chlorella vulgaris extract conjugated magnetic iron nanoparticles in nile tilapia (Oreochromis niloticus): Growth promoting, immunostimulant and antioxidant role and combating against the synergistic infection with Ichthyophthirius multifiliis and Aeromonashydrophila

Nile tilapia reared under intensive conditions was more susceptible for Ichthyophthirius multifilii (I. multifiliis) infection eliciting higher mortality, lower productive rate and further bacterial coinfection with Aeromonas hydrophila (A. hydrophila). The higher potency of magnetic field of iron oxide nanoparticles (NPs) can kill pathogens through inhibiting their viability. Herein, coating of Chlorella vulgaris extract (ChVE) with magnetic iron oxide NPs (Mag iron NPs) can create an external magnetic field that facilitates their release inside the targeted tissues. Thus, the current study is focused on application of new functionalized properties of Mag iron NPs in combination with ChVE and their efficacy to alleviate I. multifiliis and subsequent infection with A. hydrophila in Nile tilapia. Four hundred fingerlings were divided into: control group (with no additives), three groups fed control diet supplemented with ChVE, Mag iron NPs and ChVE@Mag iron NPs for 90 days. At the end of feeding trial fish were challenged with I. multifiliis and at 9 days post challenge was coinfected by A. hydrophila. A remarkable higher growth rate and an improved feed conversion ratio were detected in group fed ChVE@Mag iron-NPs. The maximum expression of antioxidant enzymes in skin and gills tissues (GSH-Px, CAT, and SOD) which came in parallel with higher serum activities of these enzymes was identified in groups received ChVE@Mag iron-NPs. Furthermore, group fed a combination of ChVE and Mag iron-NPs showed a boosted immune response (higher lysozyme, IgM, ACH50, and MPO) prior to challenge with I. multifiliis. In contrast, fish fed ChVE@Mag iron-NPs supplemented diet had lower infection (decreased by 62%) and mortality rates (decreased by 84%), as well as less visible white spots (decreased by 92 % at 12 dpi) on the body surfaces and mucous score. Interestingly, post I. multifiliis the excessive inflammatory response in gill and skin tissues was subsided by feeding on ChVE@Mag iron-NPs as proved by down regulation of IL-1β, TNFα, COX-2 and iNOS and upregulation of IL-10, and IgM, IgT and Muc-2 genes. Notably, group exposed to I. multifiliis-showed higher mortality when exposed to Aeromonas hydrophilia (increased by 43 %) while group fed ChVE@Mag iron-NPs exhibited lower morality (2%). Moreover, the bacterial loads of A. hydrophilia in fish infected by I. multifiliis and fed control diet were higher than those received dietary supplement of ChVE, Mag iron-NPs and the most reduced load was obtained in group fed ChVE@Mag iron-NPs at 7 dpi. In conclusion, ChVE@Mag iron-NPs fed fish had stronger immune barrier and antioxidant functions of skin and gills, and better survival following I. multifiliis and A. hydrophilia infection.

Application of high shear-assisted liquid biphasic system for protein extraction from Chlorella sp

Microalgae is a sustainable alternative source to traditional proteins. Existing pretreatment methods for protein extraction from microalgae still lack scalability, are uneconomical and inefficient. Herein, high shear mixing (HSM) was applied to disrupt the rigid cell walls and was found to assist in protein release from microalgae. This study integrates HSM in liquid biphasic system with seven parameters being investigated on extraction efficiency (EE) and protein yield (Y). The highest EE and Y obtained are 96.83 ± 0.47 % and 40.98 ± 1.27 %, respectively, using 30% w/v K3PO4 salt, 60 % v/v alcohol, volume ratio of 1:1 and 0.5 % w/v biomass loading under shearing rate of 16,000 rpm for 1 min.

Induction of antioxidant activities of Arthrospira platensis and Chlorella vulgaris by modified culture conditions

Microalgae are considered a promising source for obtaining natural compounds with strong antioxidant activity. Despite the great progress made in this field, there is still need for further studies applying simple and cost-effective modifications to reveal their full potential and enhance antioxidant properties. Arthrospira platensis and Chlorella vulgaris are some of the most common cells studied for this purpose. In this study, it was aimed to develop a bioprocess for the enhancement of antioxidant properties of these two microalgae by evaluating the effect of different culture conditions. With this aim, the impacts of light intensity/reactive oxygen species and nitrogen sources/reactive oxygen species were evaluated for the A. platensis and C. vulgaris cells, respectively. Results showed that the antioxidant potential of A. platensis was found to be correlated with the phycocyanin and total phenolic content of cells, and 80 µmol photons m-2 s-1 light intensity induced antioxidant activity in a two-step cultivation mode. For C. vulgaris cells, maximum antioxidant activities of 68.10 ± 1.51% and 75.68 ± 0.66% were obtained in cultures with NH4Cl (0.016% (w/v)) for DPPH and ABTS assays, respectively. The applied oxidative stress factors exhibited different effects on the antioxidant activities of the cells because of their cellular morphologies and changing mechanisms of reactive oxygen species. These outcomes show the potential of applied modifications on cells and suggest a promising route to enhance antioxidant activities of microalgae for further research.

Phytohormone gibberellins treatment enhances multiple antibiotics removal efficiency of different bacteria-microalgae-fungi symbionts

To develop and characterize novel antibiotics removal biomaterial technology, we constructed three different bacteria-microalgae-fungi consortiums containing Chlorella vulgaris (C. vulgaris), endophytic bacterium, Clonostachys rosea (C. rosea), Ganoderma lucidum, and Pleurotus pulmonarius. The results showed that under treatment with 50 mg/L of gibberellins (GAs), the three bacteria-microalgae-fungi symbionts had maximal growth rates (0.317 ± 0.030 d-1) and the highest removal efficiency for seven different antibiotics. Among them, C. vulgaris-endophytic bacterium-C. rosea symbiont had the best performance, with antibiotics removal efficiencies of 96.0 ± 1.4 %, 91.1 ± 7.9 %, 48.7 ± 5.1 %, 34.6 ± 2.9 %, 61.0 ± 5.5 %, 63.7 ± 5.6 %, and 54.3 ± 4.9 % for tetracycline hydrochloride, oxytetracycline hydrochloride, ciprofloxacin, norfloxacin, sulfadiazine, sulfamethazine, and sulfamethoxazole, respectively. Overall, the present study demonstrates that 50 mg/L GAs enhances biomass production and antibiotics removal efficiency of bacteria-microalgae-fungi symbionts, providing a framework for future antibiotics-containing wastewater treatment using three-phase symbionts.

Manipulation of co-pelletization for Chlorela vulgaris harvest by treatment of Aspergillus niger spore

The co-pelletization of microalgae with filamentous fungi was a promising approach for microalgae harvest. However, the real conditions of microalgae growth limited the arbitrary optimization of co-pellets formation with filamentous fungi. Therefore, it is urgent to develop an approach to manipulate the co-pelletization through treatment of A. niger spores. In this study, Aspergillus niger and Chlorella vulgaris were used as the model species of filamentous fungi and microalgae to investigate co-pellets formation using A. niger spores after by different pH solutions treatment, swelling, snailase treatment. The importance of spore treatments on C. vulgaris harvest in sequence was claimed based on response surface methodology analysis. The pH solutions treatment, swelling, snailase treatment of A. niger spore contributed 21.0%, 10.5%, 40.7% of harvest ratio of C. vulgaris respectively, which guided the application of spore treatment into co-pelletization. Treatment of spore was showed as an efficient approach to manipulate co-pelletization for microalgae harvest in diverse microalgae condition. This results promoted the application of co-pelletization technology in microalgae harvest of various conditions.

Microalgae biomass as a conditioner and regulator of soil quality and fertility

Characteristics of an acid soil cultivated with Urochloa brizantha cv. Marandu were evaluated in relation to two types of fertilization: a conventional one, chemical based on nitrogen and potassium, and a biofertilizer, based on microalgae biomass. The results were compared among three treatments, control, conventional, and biological fertilization, with seven replications each. The study evaluated microalgae community, total carbon and nitrogen contents, mineral nitrogen, and enzymatic activity. Chlorella vulgaris showed the highest organism density, which can be explained by its rapid growth and high resistance. The highest species diversity was detected in the control 1,380,938 org cm-3 and biological 1,841,250 org cm-3 treatments, with the latter showing a higher density of cyanobacteria, especially Pseudanabaena limnetica with 394,554 org cm-3. The soil treated with chemical fertilization showed higher nitrate (9.14 mg NKg-1 NO3--N) and potassium (52.32 mg dm-3) contents. The highest levels of sulfur (21.73 mg dm-3) and iron (96.46 mgdm-3) were detected in the biological treatment. The chemical treatment showed higher activity of the enzymes acid phosphatase, acetylglucosaminidase, and sulfatase, while α-glucosidase and leucine aminopeptidase stood out in the biological treatment. Soil properties were not significantly affected by the treatments. The use of microalgae biomass derived from wastewater treatment from milking parlors was evaluated and presented as a promising biofertilizer for agriculture, following the line of recovering nutrient-rich wastes. In this sense, although many challenges need to be overcome, the results suggest that microalgal-based fertilizers could lead to low-impact agriculture.

The effect of light intensity on microalgae biofilm structures and physiology under continuous illumination

The interest by biofilm-based microalgae technologies has increased lately due to productivity improvement, energy consumption reduction and easy harvesting. However, the effect of light, one key factor for system's operation, received less attention than for planktonic cultures. This work assessed the impact of Photon Flux Density (PFD) on Chlorella vulgaris biofilm dynamics (structure, physiology, activity). Microalgae biofilms were cultivated in a flow-cell system with PFD from 100 to 500 [Formula: see text]. In the first stage of biofilm development, uniform cell distribution was observed on the substratum exposed to 100 [Formula: see text] while cell clusters were formed under 500 [Formula: see text]. Though similar specific growth rate in exponential phase (ca. 0.3 [Formula: see text]) was obtained under all light intensities, biofilm cells at 500 [Formula: see text] seem to be ultimately photoinhibited (lower final cell density). Data confirm that Chlorella vulgaris showed a remarkable capability to cope with high light. This was marked for sessile cells at 300 [Formula: see text], which reduce very rapidly (in 2 days) their chlorophyll-a content, most probably to reduce photodamage, while maintaining a high final cell density. Besides cellular physiological adjustments, our data demonstrate that cellular spatial organization is light-dependent.

The apoptosis of Chlorella vulgaris and the release of intracellular organic matter under metalimnetic oxygen minimum conditions

Metalimnetic oxygen minimum (MOM) is a frequent occurrence in lakes and reservoirs, and its formation is related to the blooming and apoptosis of algae. In this study, the apoptosis mechanism of Chlorella vulgaris (C. vulgaris) and the release of intracellular organic matter (IOM) under different MOM conditions were analyzed by changing the dissolved oxygen (DO) (7.0 mg/L, 3.0 mg/L, and 0.3 mg/L) and water pressure (0.3 MPa and normal pressure). The integrity and auto-fluorescence of algae cells decreased rapidly in the first 8 days, and then stabilized gradually during the development of MOM. Compared with that of water pressures, DO had a significant effect on the activity of algal cells, and higher initial DO levels (3.0 mg/L and 7.0 mg/L) accelerated the lysis of algal cells. The integrity of algae cells decreased to 28.8 %, 31.8 % and 56.6 % at the initial DO of 7 mg/L, 3 mg/L and 0.3 mg/L under 0.3 MPa, respectively. Meanwhile, the concentration of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) continued to increase and reached their maximum at 8 or 12 days, respectively, due to the IOM release caused by algal cell rupture, and then gradually decreased due to microbial degradation. Consistent with the results of membrane integrity, the highest DOC and DON concentrations were found at higher initial DO conditions. By parallel factor analysis, the change in total organic matter fluorescence intensity was consistent with DOC, once again increasing in the first 8 days and then gradually decreasing. The increased humic-like component, which is related to higher aromaticity, led to the monotonic increase of HAAFPs and THMFPs. However, the released IOM of C. vulgaris had lower N-DBPFPs, with TCNMFP predominating primarily. In summary, these results shed new lights on exploring the apoptosis of algae and the release of IOM during the development of MOM.

Evaluation of Chlorella vulgaris biosorption capacity for phosphate and nitrate removal from wastewater

High wastewater production rates during the past few decades are mostly attributable to anthropogenic activities. The main components leading to the nutrient enrichment of natural water bodies are such as nitrogen, phosphorus, and other minerals. The main focus of this research was to assess the ability of using Chlorella vulgaris algae, a potent and environmentally benign material, to eliminate phosphate and nitrate ions from wastewater. FTIR results showed that the biologically active molecules that facilitate the binding of phosphate and nitrate ions unto the C. vulgaris are C=C and N-H amid. The ideal equilibrium time for adsorption was 24 h with an optimum pH of 7 and the mass ratio of algae and different anions concentration was 80%. Freundlich isotherm model was the best-fitted isotherm. Moreover, the results of the experiment fit more closely with the pseudo-second-order kinetic model than other models. Elovich kinetic model data for both ions showed that the adsorption rate was much higher than the desorption rate. The growing popularity of biosorbents in treating wastewater has led to an improvement in their affordability and availability, and C. vulgaris may now represent an environmentally friendly choice from an environmental, and economic standpoint.

Comparison of microalgal hydrochar and pyrochar: production, physicochemical properties, and environmental application

Microalgal biomass has been considered the third-generation biofuel production feedstock, but microalgae-derived biochar still needs to be thoroughly understood. This study aims to evaluate the production and physicochemical properties of microalgae-derived hydrochar produced by hydrothermal carbonization (HTC) process by comparison with pyrochar produced by dry thermal carbonization (DTC) process for environmental applications. Microalgal biochar was produced with commercially available Chlorella vulgaris microalgae using HTC and DTC processes under various temperature conditions. Pyrochar presented higher pH, ash contents, porosity, and surface area than hydrochar. Hydrochar gave more oxygen-containing functional groups on the surface and higher lead adsorption than pyrochar, making the microalgal hydrochar applicable in soil amendment and various environmental remediations. HTC could be an economically feasible thermochemical process for microalgal biochar production. It can produce hydrochar with high production yield from wet microalgae at low temperatures without a drying process.

Nutrient sequestration and lipid production potential of Chlorella vulgaris under pharmaceutical wastewater treatment: experimental, optimization, and prediction modeling studies

The efficient management and treatment of pharmaceutical industry wastewater (PIWW) have become a serious environmental issue due to its high toxicity. To overcome this problem, the present study deals with the phycoremediation of PIWW using Chlorella vulgaris microalga isolated from the Ganga River at Haridwar, India. For this, response surface methodology (RSM) and artificial neural network (ANN) tools were used to identify the best reduction of total phosphorus (TP) and total Kjeldahl's nitrogen (TKN) based pollutants along with the lipid production efficiency of C. vulgaris. Three different concentrations of pharmaceutical wastewater (0, 50, and 100%), operating temperatures (20, 25, and 30 °C), and light intensity (2000, 3000, and 4000 lx) were used to design the phycoremediation experiments having 6:18 h of dark/light period and reactor functional volume of 15L. Findings revealed that C. vulgaris was good enough to remove maximum TP (90.35%), TKN (83.55%) along 20.88% of lipid yield at 25.62 °C temperature, 60.73% PIWW concentration, and 4000 lx of light intensity, respectively. Based on the model performance and validation results, ANN showed more accuracy as compared to the RSM tool. Therefore, the findings of this study showed that C. vulgaris is capable of treating PIWW efficiently along with significant production of lipid content which can further be used in various applications including biofuel production.

Co-culturing microalgae with endophytic bacteria from bamboo for efficient nutrient and heavy metal removal coupling with biogas upgrading

The construction of dominant algal species and bacterial strains in algal treatment technology was crucial for pollutant removal. In order to enhance the purification capability of microalgae toward heavy metals in water as well as biogas slurry and biogas, symbiotic systems were respectively constructed using Chlorella vulgaris and two different endogenous bacteria (microalgal endophytic bacteria S395-2 and plant endophytic bacteria BEB7). The results demonstrated that the endogenous bacteria (S395-2 and BEB7) effectively promote the growth, biomass yield, photosynthetic activity, and carbonic anhydrase activity of microalgae. Additionally, BEB7 exhibited superior promotion effects on microalgae compared to S395-2. Moreover, the BEB7-microalgae co-cultivation system not only efficiently removed heavy metals from water but also effectively purified the nutrients and CO2 in biogas slurry. The optimal effect was observed when the ratio of BEB7 to microalgae was 10:1. This study has established a solid theoretical foundation for the application of microalgae in pollutant purification. PRACTITIONER POINTS: Endogenous bacteria effectively promoted microalgal performance. The optimal ratio of BEB7 to microalgae was 10:1. Chlorella vulgaris-BEB7 showed the best removal performance.

Chlorella vulgaris extract and Imiquimod as new therapeutic targets for leishmaniasis: An immunological approach

The therapeutic regimen for the treatment of American Tegumentary Leishmaniasis (ATL) is targeted at the death of the parasite; therefore, it is essential to develop a treatment that can act on the parasite, combined with the modulation of the inflammatory profile. Thus, the aim of this study was to make an in vitro evaluation of the therapeutic potential of Chlorella vulgaris extract (CV) and Imiquimod for ATL. Selectivity indices (SI) were determined by inhibitory concentration assays (IC50) in L. braziliensis cells and cytotoxic concentrations (CC50) were measured in human cells using the MTT method, based on the CV microalgae extract (IC50 concentrations of 15.63 to 500 µg/mL; CC50 concentrations of 62.5-1000 µg/mL) in comparison with the reference drugs and Imiquimod. The immune response was evaluated in healthy human cells by gene expression (RT-qPCR) and cytokine production (Flow Cytometry). The CV extract (SI = 6.89) indicated promising results by showing higher SI than meglumine antimoniate (SI = 3.44) (reference drug). In all analyses, CV presented a protective profile by stimulating the production of Th1 profile cytokines to a larger extent than the reference drugs. Imiquimod showed a high expression for Tbx21, GATA3, RORc and Foxp3 genes, with increased production only of the TNF cytokine. Therefore, the data highlight the natural extract and Imiquimod as strong therapeutic or adjuvant candidates against ATL, owing to modulation of immune response profiles, low toxicity in human cells and toxic action on the parasite.

Energy balance survey for the design and auto-thermal thermophilic aerobic digestion of algal-based membrane bioreactor for Landfill Leachate Treatment(under organic loading rates): Experimental and simulation-based ANN and NSGA-II

Although algal-based membrane bioreactors (AMBRs) have been demonstrated to be effective in treating wastewater (landfill leachate), there needs to be more research into the effectiveness of these systems. This study aims to determine whether AMBR is effective in treating landfill leachate with hydraulic retention times (HRTs) of 8, 12, 14, 16, 21, and 24 h to maximize AMBR's energy efficiency, microalgal biomass production, and removal efficiency using artificial neural network (ANN) models. Experimental results and simulations indicate that biomass production in bioreactors depends heavily on HRT. A decrease in HRT increases algal (Chlorella vulgaris) biomass productivity. Results also showed that 80% of chemical oxygen demand (COD) was removed from algal biomass by bioreactors. To determine the most efficient way to process the features as mentioned above, nondominated sorting genetic algorithm II (NSGA-II) techniques were applied. A mesophilic, suspended-thermophilic, and attached-thermophilic organic loading rate (OLR) of 1.28, 1.06, and 2 kg/m3/day was obtained for each method. Compared to suspended-thermophilic growth (3.43 kg/m3.day) and mesophilic growth (1.28 kg/m3.day), attached-thermophilic growth has a critical loading rate of 10.5 kg/m3.day. An energy audit and an assessment of the system's auto-thermality were performed at the end of the calculation using the Monod equation for biomass production rate (Y) and bacteria death constant (Kd). According to the results, a high removal level of COD (at least 4000 mg COD/liter) leads to auto-thermality.

Eco-friendly microalgae harvesting using lipid-cored particles with a comparative life-cycle assessment

This study proposed an innovative approach using lipid-cored particles (LCPs) aimed at addressing the efficiency, cost, and environmental impact challenges in microalgae harvesting. Cetyltrimethylammonium bromide (CTAB) and chitosan (CS) were used to modify LCPs and to optimize efficiency and investigate the mechanisms of harvesting with Chlorella vulgaris. Results showed that a maximum harvesting efficiency of 97.14 % was achieved using CS-LCPs. Zeta potential and microscopic images revealed the presence of embedded CS-LCPs within microalgal flocs. Fractal dimension data suggested looser aggregates of CS-LCPs and Chlorella vulgaris, corroborated by Excitation-emission matrices (EEM) analysis further confirmation the presence of bridging networks. Moreover, life cycle assessment of five harvesting methods pointed freshwater ecotoxicity potential (FEP) and terrestrial ecotoxicity potential (TEP) as major environmental impacts, mainly from flocculant use, carrier production, and electricity consumption. Notably, LCPs showed the lowest global warming potential (GWP) at 1.54 kg CO2 eq, offering a viable, low-carbon, cost-effective harvesting alternative.

Synergies of pH-induced calcium phosphate precipitation and magnetic separation for energy-efficient harvesting of freshwater microalgae

Energy- and time-consuming concentration steps currently limit the industrial application of microalgae. Compared to state-of-the-art technologies, magnetic separation shows a high potential for efficient harvesting of microalgae. This study presents a novel approach to combine pH-induced calcium phosphate precipitation with cheap natural magnetite microparticles for magnetic separation of the freshwater microalgae Chlorella vulgaris. Harvesting efficiencies up to 98% were achieved at moderate pH and low particle and calcium phosphate concentrations in a model medium. However, cultivation-dependent high loads of algogenic organic matter can severely inhibit flocculation and particle/algae interactions, requiring higher salt concentrations or pH. Harvesting efficiencies above 90% were still attainable at moderate pH with increased calcium phosphate concentrations of 10mM. Acidification of the suspension to pH 5 allows for simple and reversible particle recycling. The presented process provides a promising path to universal and cost-effective harvesting, advancing the utilization of microalgae as a sustainable bioresource.

Differential impacts of interactions between Serendipita indica, Chlorella vulgaris, Ulva lactuca and Padina pavonica on Basil (Ocimum basilicumL.)

Plant biostimulants (PBs) are used globally to increase crop yield and productivity. PBs such as (Serendipita indica) or algal extracts stimulate and accelerate plant physiological processes. The physiological, ecological, and biochemical effects of (Serendipita indica) or algal extracts individually and in combination on basil plant (Ocimum basilicum L.) were investigated. Macroalgae samples were collected from Abu Qir, Alexandria, Egypt. The growth parameters, chlorophyll index, and biochemical composition of basil were analyzed at 90th day. The (Chlorella vulgaris) + (Serendipita indica) (MI + F) treatment increased chlorophyll index by 61.7% (SPAD) compared to control. (Chlorella vulgaris) had the highest growth hormones, including GA3 at 158.2 ppb, GA4 at 149.1 ppb, GA7 at 142.6 ppb, IAA at 136.6 ppb, and TC at 130.9 ppb, while (Ulva lactuca) had the lowest. The MI + F treatment yielded the highest essential oil and antioxidant values. Treatment with (Chlorella vulgaris) increased S. indica colonization by 66%. In contrast, Ulva lactuca and (Padina Pavonica) inhibited S. indica colonization by 80% and 40%, respectively. (Ulva lactuca) and (Padina Pavonica) inhibited S. indica colonization by 80% and 40%, respectively. Combined treatments had a greater influence on basil performance than the individual treatments. The evidence of synergistic/additive benefits to plants performance due to the interactive effects of (Chlorella vulgaris) and (Serendipita indica) had been studied. Complementary modes of action between (Chlorella vulgaris) and (Serendipita indica), through their components newly emerging properties on basil, may explain observed synergistic effects. This study explores the potential of microbial-algal interactions, particularly (Chlorella vulgaris) and (Serendipita indica), as innovative plant biostimulants. These interactions demonstrate positive effects on basil growth, offering promise for more effective microbial-based formulations to enhance crop productivity and sustainability in agriculture. These novelties will help create a second generation of PBs with integrated and complementary actions.