Formation characteristics of disinfection byproducts from four different algal organic matter during chlorination and chloramination

Algal organic matter (AOM) has become an important precursor of disinfection byproducts (DBPs) in multiple drinking water sources. In this study, the formation of DBPs during chlorination and chloramination of AOMs from four algal species (Microcystis aeruginosa, Chlorella vulgaris, Scenedesmus obliquus, and Cyclotella sp.) under different conditions (disinfectant doses 4.0-8.0 mg/L as Cl₂, pH 6.0-8.0, and bromide 0-1.0 mg/L) were simultaneously investigated. Some common and specific characteristics of DBP formation have also been identified. The yields of total DBPs from the four AOMs were 3.28 × 10²-6.00 × 10² and 1.97 × 10²-3.70 × 10² nmol/mg C during chlorination and chloramination, respectively. The proportions of haloacetic acids (HAAs) in total DBPs were approximately ≥50%. Increasing disinfectant doses or pH only enhanced the yields of trihalomethanes (THMs) during chlorination but enhanced the yields of THMs, HAAs and dihaloacetonitriles (DHANs) during chloramination. Increasing bromide concentrations enhanced THM yields but decreased HAA yields during chlorination and chloramination, in addition to the shift from chlorinated DBPs to brominated DBPs. The DHAN yields of the four AOMs slightly decreased with bromide levels during chlorination, whereas different AOMs showed different trends with bromide levels during chloramination. During chlorination, C. vulgaris and S. obliquus AOMs generated higher THM and DHAN yields (at 4.0-5.0 mg/L as Cl₂) than the other AOMs. During chloramination, M. aeruginosa AOM generated higher THM and HAA yields than the other AOMs (at 0.1 mg/L bromide). Cyclotella sp. AOM had the highest THM-bromine substitution factors during chlorination and the highest DHAN-bromine substitution factors during both chlorination and chloramination (at 0.1 mg/L bromide).

Improving green hydrogen production from Chlorella vulgaris via formic acid-mediated hydrothermal carbonisation and neural network modelling

This study investigates the formic acid-mediated hydrothermal carbonisation (HTC) of microalgae biomass to enhance green hydrogen production. The effects of combined severity factor (CSF) and feedstock-to-suspension ratio (FSR) are examined on HTC gas formation, hydrochar yield and quality, and composition of the liquid phase. The hydrothermal conversion of Chlorella vulgaris was investigated in a CSF and FSR range of -2.529 and 2.943; and 5.0 wt.% - 25.0 wt.%. Artificial neural networks (ANNs) were developed based on experimental data to model and analyse the HTC process. The results show that green hydrogen formation can be increased up to 3.04 mol kg^-1 by applying CSF 2.433 and 12.5 wt.% FSR reaction conditions. The developed ANN model (BR-2-11-9-11) describes the hydrothermal process with high testing and training performance (MSE_z = 1.71E-06 & 1.40E-06) and accuracy (R² = 0.9974 & R² = 0.9781). The enhanced H₂ yield indicates an effective alternative green hydrogen production scenario at low temperatures using high-moisture-containing biomass feedstocks.

Carbon dissipation from surgical cotton production wastewater using macroalgae, microalgae, and activated sludge microbes

Surgical cotton production has drastically been increased in the past few years due to excessive use by medical health professionals especially in countries like India, which is among the top three exporters of cotton worldwide. The effluent generated from surgical cotton industries differ from textile effluents by the conspicuous absence of dyeing chemicals. This wastewater has a high concentration of suspended particles, COD, dissolved ions, organic carbon, and alkaline pH. Several studies have been published on the treatment of textile effluents and the degradation of dyeing chemicals, while the treatment studies on surgical cotton wastewater have been rarely reported in spite of their potential to cause pollution in receiving land/water bodies. Activated sludge microbes have been extensively studied and well documented in the treatment of several industrial effluent but does not match to the production of valuable biomass from algae. The global energy demand has prompted the scientific community to investigate and explore the possibility of using algae for energy production with simultaneous wastewater treatment. To the best of the authors' knowledge, no research articles have been published which compare the effectiveness of activated sludge microorganisms, microalgae, and macroalgae in removing contaminants from real wastewater. To date, there is a knowledge gap in understanding and selecting the right choice of biological system for effective and economical effluent treatment. In an attempt to minimize this gap, carbon removal by microalgae, macroalgae, and activated sludge microbes were investigated on real effluent from surgical cotton industries. It was observed that the strain of Chlorella vulgaris could dissipate 83% of COD from real wastewater, while consortia of macroalgae (consisting predominantly of Ulvaceae and Chaetomorpha) and activated sludge microbes could remove 81% and 69% of the carbon, respectively. The microalgal growth (in terms of wet weight) increased from 0.15 to 0.3 g, whereas the macroalgal wet weight increased from 1.5 to 3 g in over 7 days of batch experiments conducted in triplicates. This indicated the superlative performance of microalgae over activated sludge microbes in carbon dissipation.

Integrated toxicity assessment of DEHP and DBP toward aquatic ecosystem based on multiple trophic model assays

To comprehensively understand the toxic risks of phthalates to aquatic ecosystems, we examined the acute toxicity of di-(2-ethylhexyl) phthalate (DEHP) and di-butyl phthalate (DBP) on multiple trophic models, including algae (Chlorella vulgaris), Daphnia magna and fish (Danio rerio, Pseudorasbora parva). Thus, a 15-day zebrafish exposure was conducted to trace the dynamic changes of phthalate-induced toxic effects. Among the four species, D. magna exhibited the strongest sensitivity to both DEHP and DBP, followed by D. rerio and P. parva. C. vulgaris exhibited the lowest sensitivity to phthalates. The sub-chronic zebrafish assay demonstrated that 1000 μg/L DBP induced significant mortality at 15 days post-exposure (dpe), and DEHP exhibited no lethality at the tested concentrations (10-5000 μg/L). Zebrafish hepatic SOD activity and sod transcription levels were inhibited by DBP from 3 dpe, which was accompanied by increased malondialdehyde level, while zebrafish exposed to DEHP exhibited less oxidative damage. Both DEHP and DBP induced time-dependent alterations on Ache activity in zebrafish brains, thus indicating the potential neurotoxicity toward aquatic organisms. Additionally, 1000 μg/L and higher concentration of DBP caused hepatic DNA damage in zebrafish from 7 dpe. These results provide a better understanding of the health risks of phthalate to water environment.

Time-Resolved Kinetic Measurement of Microalgae Agglomeration for Screening of Polysaccharides-Based Coagulants/Flocculants

Time-resolved monitoring of microalgae agglomeration facilitates screening of coagulants/flocculants (CFs) from numerous biopolymer candidates. Herein, a filtering-flowing analysis (FFA) apparatus was developed in which dispersed microalgal cells were separated from coagulates and flocs formed by CFs and pumped into spectrophotometer for real-time quantification. Polysaccharides-based CFs for Microcystis aeruginosa and several other microalgae were tested. Cationic hydroxyethyl cellulose (CHEC), chitosan quaternary ammonium (CQA) and cationic guar gum (CGG) all triggered coagulation obeying a pseudo-second-order model. Maximal coagulation efficiencies were achieved at their respective critical dosages, i.e., 0.086 g/g_M.a. CHEC, 0.022 g/g_M.a. CQA, and 0.216 g/g_M.a. CGG. Although not active independently, bacterial exopolysaccharides (BEPS) aided coagulation of M. aeruginosa and allowed near 100% flocculation efficiency when 0.115 g/g_M.a. CQA and 1.44 g/g_M.a. xanthan were applied simultaneously. The apparatus is applicable to other microalgae species including Spirulina platensis, S. maxima, Chlorella vulgaris and Isochrysis galbana. Bio-based CFs sorted out using this apparatus could help develop cleaner processes for both remediation of harmful cyanobacterial blooms and microalgae-based biorefineries.

An In Silico Framework to Mine Bioactive Peptides from Annotated Proteomes: A Case Study on Pancreatic Alpha Amylase Inhibitory Peptides from Algae and Cyanobacteria

Bioactive peptides may exert beneficial activities in living organisms such as the regulation of glucose metabolism through the inhibition of alpha amylases. Algae and cyanobacteria are gaining a growing interest for their health-promoting properties, and possible effects on glucose metabolism have been described, although the underlying mechanisms need clarification. This study proposes a computer-driven workflow for a proteome-wide mining of alpha amylase inhibitory peptides from the proteome of Chlorella vulgaris, Auxenochlorella protothecoides and Aphanizomenon flos-aquae. Overall, this work presents an innovative and versatile approach to support the identification of bioactive peptides in annotated proteomes. The study: (i) highlighted the presence of alpha amylase inhibitory peptides within the proteomes under investigation (including ELS, which is among the most potent inhibitory tripeptides identified so far); (ii) mechanistically investigated the possible mechanisms of action; and (iii) prioritized further dedicated investigation on the proteome of C. vulgaris and A. flos-aquae, and on CSSL and PGG sequences.

Flocculation of Chlorella vulgaris-induced algal blooms: critical conditions and mechanisms

Algal blooms have posed great threats to livestocks and human health. Although flocculation is effective, its efficiency may hinder the direct application for algal blooms. In this study, critical (optimal) conditions and mechanisms for AlCl₃, FeCl₃, poly-aluminum chloride (PAC), chitosan, and polydimethyldiallylammonium chloride (PDADMAC)-induced flocculation of Chlorella vulgaris (C. vulgaris) were studied. Results identified the critical conditions which can cause flocculation efficiencies over 90% in 45 min for the five flocculants. Specifically, 4~10-mg/L doses of PDADMAC were proved to be appropriate for the treatment of C. vulgaris-induced algal blooms at pH 6.0~12.0. To probe the underlying mechanisms, functional groups involved in flocculation, zeta potential, and species distribution were analyzed during flocculation. FT-IR results indicated that N-H stretching in amine and C-H deformation in aliphatics were involved in algal flocculation with FeCl₃, and C-H deformation played an important role with PDADMAC, PAC, and chitosan. For AlCl₃, zeta potential and species distribution results suggested that charge neutralization and adsorption bridging were responsible for algal flocculation at pH 6~8. However, adsorption bridging and sweeping effects were the main mechanisms at pH >3 for FeCl₃. The flocculation mechanisms for the rest of the three polymers were charge neutralization, adsorption bridging, and sweeping. Meanwhile, all the flocculation processes followed second-order kinetics. Strong linkages were found between the rate constant, fractal dimension, and flocculation efficiency (P < 0.05). The results of critical flocculation conditions and mechanisms indicated that PDADMAC was an excellent flocculant for C. vulgaris removing and recycling, especially in water bloom treatment.

Harvesting Chlorella vulgaris by electro-flotation with stainless steel cathode and non-sacrificial anode

As a promising method for efficiently harvesting microalgae, electro-flotation's performance is related to various factors including electrode design and process operating parameters. In this paper, bubble generation behavior on stainless-steel cathodes, with wire diameters of 0.8 mm, 0.2 mm and 0.05 mm, was studied. The results show that the bubble size increased with the increasing diameter of the electrode wire. Over 90 % harvesting efficiency was achieved using non-sacrificial anode. Extracellular polymeric substance is the main reason keeping bubbles from bursting.

Direct toxicity of the herbicide florasulam against Chlorella vulgaris: An integrated physiological and metabolomic analysis

Herbicides are the agents of choice for use in weed control; however, they can enter the aquatic environment, with potentially serious consequences for non-target organisms. Despite the possible deleterious effects, little information is available regarding the ecotoxicity of the herbicide florasulam toward aquatic organisms. Accordingly, in this study, we investigated the toxic effect of florasulam on the freshwater microalga Chlorella vulgaris and sought to identify the underlying mechanisms. For this, we employed a growth inhibition toxicity test, and then assessed the changes in physiological and metabolomic parameters, including photosynthetic pigment content, antioxidant system, intracellular structure and complexity, and metabolite levels. The results showed that treatment with florasulam for 96 h at the concentration of 2 mg/L, 2.84 mg/L, and 6 mg/L in medium significantly inhibited algal growth and photosynthetic pigment content. Moreover, the levels of reactive oxygen species were also increased, resulting in oxidative damage and the upregulation of the activities of several antioxidant enzymes. Transmission electron microscopic and flow cytometric analysis further demonstrated that exposure to florasulam (6 mg/L) for 96 h disrupted the cell structure of C. vulgaris, characterized by the loss of cell membrane integrity and alterations in cell morphology. Changes in amino acid metabolism, carbohydrate metabolism, and the antioxidant system were also observed and contributed to the suppressive effect of florasulam on the growth of this microalga. Our findings regarding the potential risks of florasulam in aquatic ecosystems provide a reference for the safe application of this herbicide in the environment.

Response and tolerance ability of Chlorella vulgaris to cadmium pollution stress

Cadmium, which is widely used in electroplating industry, chemical industry, electronic industry and nuclear industry, is harmful to human health and ecological environment. The effects of Cd at different initial concentrations on biomass, antioxidant enzyme activity and ultrastructure of Chlorella vulgaris were analysed in the present study. The results showed that C. vulgaris maintained a slow-growth trend at 3.0 mg/L Cd, and the peroxidase (POD) enzyme activity reached the highest at this concentration, which indicated that C. vulgaris could resist the oxidative damage of cells by increasing the enzyme activity, so as to improve the tolerance of C. vulgaris to Cd. When the concentration of Cd was 5.0 mg/L, although the activity of the superoxide dismutase enzyme was still very high, POD enzyme could not remove the hydrogen peroxide produced in cells in time, leading to cell damage and even death. Therefore, when the concentration reached 5.0 mg/L, the growth of C. vulgaris began to decline after four days of stress, and the cell structure was significantly damaged after six days of stress. And the higher concentration of Cd caused more Cd accumulation in cells and a serious damage to C. vulgaris. C. vulgaris can be used as an early warning indicator of Cd pollution, and it can be used for bioremediation of Cd contaminated water through tolerant subculture.

Adsorption mechanism of trace heavy metals on microplastics and simulating their effect on microalgae in river

Microplastics (MPs) and heavy-metal contamination in freshwater is an increasing concern. Fe, Mn, Pb, Zn, Cr, and Cd are common heavy metals that can easily flow into rivers causing water pollution. Microplastics act as carriers for heavy metals and increase the transport of contaminants in freshwater systems. We investigated the adsorption mechanisms of three kinds of MPs having similar particle sizes, namely polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), with respect to trace heavy metals of Pb, Cu, Cr, and Cd under different temperature and salinity conditions. The reaction kinetics of the adsorption of different trace heavy metals on different MPs were consistent with both the quasi primary and quasi secondary kinetic models, indicating the complexity of heavy metal adsorption by MPs. The adsorption rate of heavy metal on MPs was mainly controlled by intra-particle diffusion, and the isotherm model indicated that the adsorption of Pb, Cu, Cr, and Cd by MPs occurred in the form of monolayer physical adsorption. Additionally, an increase in temperature and decrease in salinity were favourable to improve the affinity of MPs toward heavy metals (through adsorption). Zeta potential measurements and Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that electrostatic force interaction was the main mechanism of the adsorption process; oxygen-containing functional groups, π-π interaction, and halogen bonds played important roles in the process of adsorption. Furthermore, the growth inhibition and oxidative stress of microalgae Chlorella vulgaris (GY-D27) due to PP, PS, and PVC were analysed; notably, MPs or Pb inhibited the growth of Chlorella vulgaris. However, the reduced toxicity to Chlorella vulgaris, with respect to a mixture of Pb and MPs, was confirmed using superoxide dismutase and catalase enzyme activities. Our results can be applied for the risk assessment of heavy metals and MPs in aquatic environments.

Influence of glyphosate and its metabolite aminomethylphosphonic acid on aquatic plants in different ecological niches

Glyphosate and its metabolite aminomethylphosphonic acid (AMPA) draw great concern due to their potential threat to aquatic ecosystems. The individual and combined effects of glyphosate and AMPA on aquatic plants in different ecological niches need to be explored. This study aimed to investigate the ecotoxicity of glyphosate and AMPA on the emergent macrophyte Acorus calamus, phytoplankton Chlorella vulgaris, and submerged macrophyte Vallisneria natans after their exposure to glyphosate and AMPA alone and to their mixture. Medium and low concentrations of glyphosate (≤ 0.5 mg L^-1) significantly inhibited the growth of V. natans and promoted the growth of C. vulgaris (P < 0.05) but had no significant effect on the growth of A. calamus (P > 0.05). AMPA (≤ 5.0 mg L^-1) did not significantly influence the relative growth rate (except C. vulgaris) or malonaldehyde levels but significantly altered the expression levels of chlorophyll-related genes and superoxide dismutase [Cu-Zn] genes in the aquatic plants examined. AMPA mainly affected the oxidative phosphorylation pathway in V. natans and not those in other two plants, indicating that V. natans was more sensitive to AMPA-induced oxidative damage. Moreover, antagonistic effects on plant growth were observed when plants were exposed to low concentrations of glyphosate + AMPA (≤ 0.1 + 0.1 mg L^-1). When the concentration of glyphosate + AMPA reached 0.5 + 0.5 and 5.0 + 5.0 mg L^-1, the growth of the submerged macrophyte was additively or synergistically inhibited, but the growth of the emergent macrophyte and phytoplankton was antagonistically inhibited. Our results indicated that both the individual and combined effects of glyphosate and AMPA might alter the vertical structure of shallow lakes and accelerate the conversion of shallow lakes from grass-based to algal-based lakes.

A direct contact bioassay using immobilized microalgal balls to evaluate the toxicity of contaminated field soils

The present study used a bioassay of immobilized microalgae (Chlorella vulgaris) via direct contact to assess the toxicity of eleven uncontaminated (reference) and five field contaminated soils with various physicochemical properties and contamination. Photosynthetic oxygen concentration in the headspace of the test kit by Chlorella vulgaris in the reference soils ranged between 12.93% and 14.80% and only 2.54%-7.14% in the contaminated soils, respectively. Inherent test variability (CV_i) values ranged between 2.90% and 9.04%; variation due to soil natural properties (CV_rs) ranged between 0.33% and 13.0%; and minimal detectable difference (MDD) values ranged from 4.69% to 11.6%. A computed toxicity threshold of 15% was established for microalgae soil toxicity tests based on calculations of the maximal tolerable inhibition (MTI). All contaminated soils were considered toxic to microalgae because their levels of inhibition ranged between 39.5% and 82.9%, exceeding the 15% toxicity threshold. It can be concluded that the elevated concentrations of heavy metals and organic contaminants in the contaminated soils induced the higher inhibitory levels. Overall, direct contact soil toxicity tests using immobilized microalgae provided coherent and repeatable data and can be utilized as a simple and suitable tool for the toxicity testing of contaminated field soils.

Effective removal of the rotifer Brachionus calyciflorus from a Chlorella vulgaris microalgal culture by homogeneous solar photo-Fenton at neutral pH

In this study, a citrate-modified photo-Fenton process was successfully applied to decontaminate a Chlorella vulgaris microalgae culture spiked with the rotifer Brachionus calyciflorus (5 individuals mL^-1). The applied treatment (1 mg L^-1 Fe²⁺, 20 mg L^-1 H₂O₂, 17.5 mg L^-1 citric acid) had only moderate effects on viability and regrowth of the microalgae since, after a short post-treatment delay of a few days, they reached final cell densities similar to that obtained for microalgae cultures that were not spiked. The decontamination was effective as no regrowth of rotifers was observed in the microalgae cultures after treatment. The efficacy of the citrate-modified photo-Fenton treatment was also studied with a higher starting concentration of 20 rotifers mL^-1 and was compared with a solar light/H₂O₂ treatment. Results show that both treatments had similar efficacies on the rotifer elimination, but that the citrate-modified photo-Fenton treatment had a lower negative impact on the regrowth of microalgae than the solar light/H₂O₂ treatment. However, when microalgae cultures were spiked with 20 rotifers mL^-1, rotifers were only partially inactivated and post-treatment regrowth occurred, which highlights the importance to apply the photo-Fenton process at an early stage of a contamination to achieve full rotifer elimination. In any case, a contamination with 5 rotifers mL^-1 is already a significant threat as numbers above 1000 rotifers mL^-1 were reached after 14 days and caused the microalgae culture to fail. Overall, our treatment suggests that the citrate-modified solar photo-Fenton process is an environmentally friendly solution to support the maintenance of contaminant-free microalgal cultures.

Enhanced photoautotrophic growth of Chlorella vulgaris in starch wastewater through photo-regulation strategy

Microalgae biomass production with starch wastewater (SW) is a promising approach to realize waste recovery and cost reduction due to the inherent copious nutrients and nontoxic compounds in SW. However, the application of this technique is significantly hindered by low biomass production on account of the poor photosynthetic efficiency of microalgae. In this regard, we proposed a photo-regulation strategy characterized by the adjusting of numbers of light/dark (L/D) cycles, and compositions of light wavelength, which was proved to be an effective method for stimulating intracellular photo electron transfer and enhancing photosynthetic efficiency, to boost microalgae biomass accumulation. Additionally, responses of the microalgae photo-biochemical conversion, and the wastewater treatment performance at various number of L/D cycles and light wavelengths were discussed. The experimental results indicated that the biomass production increased when the L/D period was increased from 2 h:2 h-12 h:12 h. When the L/D period was 2 h:2 h, the biomass production reached a maximum value of 1.28 g L^-1, which was 19.6% higher than that of the control group when the L/D period was 12 h:12 h. Furthermore, with respect to microalgae growth under monochromatic light, the maximum biomass concentration (1.25 g L^-1) and lipid content (32.2%) of Chlorella were achieved under blue light; whereas, the minimum values were attained under red light (1.05 g L^-1 and 19.3%, respectively). When the red light and blue light were mixed and supplied, the microalgae biomass productivity was higher than that under white light, and the highest lipid productivity was 109.0 mg^-1 L^-1 d under a blue: red ratio of 2:1. Moreover, gas chromatography analysis demonstrated that the methyl in the range of C16-C18 in the system was higher than 70%. Fatty acid methyl esters (FAMEs) containing palmitic acid (C16:0) and oleic acid (C18:1) are beneficial for production of biodiesel, and the quality of fatty acid methyl ester used in biodiesel production can be improved using microalgae cultured under the mixed wavelengths of blue and red. Finally, Chlorella was cultured in PBR and reached the peak concentration of 2.45 g L^-1 by semi-continuous process with the HRT regulation.

Enhancement of the immobilization on microalgae protective effects and carbamazepine removal by Chlorella vulgaris

Carbamazepine (CBZ) has drawn extensive attention due to their environmental threats. In this study, polyvinyl alcohol-sodium alginate polymers to immobilize Chlorella vulgaris (FACHB-8) were used to investigate whether immobilization can facilitate microalgae to alleviate the CBZ stress and enhance CBZ removal. The results showed that after immobilized treatment, the biomass of microalgae increased by approximately 20%, the maximum level of malondialdehyde content decreased from 28 to 13 μmol/g, and the photosynthetic capacity of F_V/F_M recovered to 90% of the control group. The CBZ removal rate increased from 67 to 84% by immobilization at a CBZ concentration of 80 mg·L^-1. The results indicated that immobilization technology can effectively protect microalgae from CBZ toxicity and improve the removal of CBZ, especially at high concentrations (> 50 mg/L). Biodegradation was the dominant pathway for microalgae to remove carbamazepine. This study added the understanding of the microalgae responses under immobilization and the interactions between immobilized microalgae and CBZ removal, thereby providing a novel insight into microalgae technology in high concentration wastewater treatments.

Microwave catalytic co-pyrolysis of Chlorella vulgaris and high density polyethylene over activated carbon supported monometallic: Characteristics and bio-oil analysis

Activated carbon (AC) has attracted much attention owing to its low cost and abundant sources. In this paper, three monometallic supported catalysts were prepared using AC as support (Ce/AC, Fe/AC, Ni/AC), and the effects of three catalysts on the microwave co-pyrolysis of Chlorella vulgaris (C. vulgaris) with high density polyethylene (HDPE) were studied. The results showed that the co-pyrolysis characteristics of C. vulgaris/HDPE = 1:1 (C1HP1) were significantly improved by three catalysts at high additions (>20 %). Among them, the C1HP1 group with 50 % Fe/AC addition had the shortest co-pyrolysis reaction time (2901 s). Besides, Ce/AC and Fe/AC have a promoting effect on bio-oil yields, while Ni/AC has an inhibiting effect. The maximum bio-oil yield (25.6 %) was obtained under 40 % addition of Fe/AC. Moreover, Ce/AC obtained the highest hydrocarbons content (66.68 %), while Fe/AC obtained the highest aromatic hydrocarbons content (36.64 %). Additionally, Ce/AC had the highest deoxygenation efficiency (47.33 %) and denitrification efficiency (42.28 %).

Bioethanol production from microalgae biomass at high-solids loadings

Industrial adoption of microalgae biofuel technology has always been hindered by its economic viability. To increase the feasibility of bioethanol production from microalgae, fermentation was applied to Chlorella vulgaris FSP-E biomass at high-solids loading conditions. First, Chlorella vulgaris FSP-E was cultivated to produce microalgae biomass with high carbohydrate content. Next, different ethanol-producing microorganisms were screened. Saccharomyces cerevisiae FAY-1 showed no inhibition when fermenting high initial glucose concentrations and was selected for the fermentation experiments at high-solids loadings. Optimization of acid hydrolysis at high biomass loading was also performed. The fermentation of microalgal biomass hydrolysate produced a final ethanol concentration and yield higher than most reported literature using microalgae feedstock. In addition, the kinetics of bioethanol fermentation of microalgae hydrolysate under high-solids loading were evaluated. These results showed the potential of fermenting microalgae biomass at high-solids loading in improving the viability of microalgae bioethanol production.

Flocculation kinetics and mechanisms of microalgae- and clay-containing suspensions in different microalgal growth phases

Interplays between microalgae and clay minerals enhance biologically mediated flocculation, thereby affecting the sedimentation and transportation of suspended particulate matter (SPM) in water and benthic environments. This interaction forms larger flocs with a higher settling velocity and enhances SPM sinking. The aim of this study was to investigate the flocculation kinetics of microalgae and clay in suspension and to elucidate the mechanisms associated with such interactions. Standard jar test experiments were conducted using various mixtures of kaolinite and microalgal samples from batch cultures (Chlorella vulgaris) to estimate biologically mediated flocculation kinetics. The organic matter (OM) composition secreted by the microalgae was characterized using a liquid chromatography - organic carbon detection system, and quantitative analysis of transparent exopolymer particles was conducted separately. A two-class flocculation kinetic model, based on the interaction between flocculi and flocs, was also adopted to quantitatively analyze the experimental data from flocculation. Results from the flocculation kinetic tests and OM analyses, in association with other data analyses (i.e., floc size distribution and flocculation kinetic model), showed that flocculation increased with OM concentration during the growth phase (10-20 d). However, on day 23 during the early stationary phase, flocculation kinetics started decreasing and substantially declined on day 30, even though the amount of OM (mainly biopolymers) continued to increase. Our results indicate that an adequate quantity of biopolymers produced by the microalgal cells in the growth phase enhanced floc-to-floc attachment and hence flocculation kinetics. In contrast, an excessive quantity of biopolymers and humic substances in the stationary phase enhanced the formation of polymeric backbone structures and flocculation via scavenging particles but simultaneously increased steric stabilization with the production of a large number of fragmented particles.

Cocultivation of White-Rot Fungi and Microalgae in the Presence of Nanocellulose

Cocultivation of fungi and algae can result in a mutualistic or antagonistic interaction depending on the species involved and the cultivation conditions. In this study, we investigated the growth behavior and enzymatic activity of two filamentous white-rot fungi (Trametes versicolor and Trametes pubescens) and two freshwater algae (Chlorella vulgaris and Scenedesmus vacuolatus) cocultured in the presence of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidized cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC). The growth of fungi and algae was studied in liquid, agar medium, and 3D-printed nanocellulose hydrogels. The results showed that cocultures grew faster under nutrient-rich conditions than in nutrient-depleted conditions. Key cellulose-degrading enzymes, including endoglucanase and laccase activities, were higher in liquid cocultures of T. versicolor and S. vacuolatus in the presence of cellulose compared to single cultures of fungi or algae. Although similar results were observed for cocultures of T. pubescens and C. vulgaris, laccase production diminished over time in these cultures. Fungi and algae were capable of growth in 3D-printed cellulose hydrogels. These results showed that cellulase enzyme production could be enhanced by cocultivating white-rot fungi with freshwater algae under nutrient-rich conditions with TEMPO-CNF and CNC. Additionally, the growth of white-rot fungi and freshwater algae in printed cellulose hydrogels demonstrates the potential use of fungi and algae in hydrogel systems for biotechnological applications, including biofuel production and bio-based fuel cell components. IMPORTANCE Depending on the conditions used to grow fungi and algae in the lab, they can interact in a mutually beneficial or negative way. These interactions could stimulate the organisms to produce enzymes in response to the interaction. We studied how wood decay fungi and freshwater algae grew in the presence and absence of cellulose, one of the basic building blocks of wood. How fungi and algae grew in 3D-printed cellulose hydrogels was also tested. Our results showed that fungi and algae partners produced significantly larger amounts of enzymes that degraded cellulose when grown with cellulose than when grown alone. In addition, fungi and algae were shown to grow in dense nanocellulose hydrogels and could survive the shear conditions during gel structuring while 3D-printing. These cultures could potentially be applied in the biotech industry for applications like energy production from cellulose, biofuel production, and bioremediation of cellulose material.

Elucidating the negatively influential and potentially toxic mechanism of single and combined micro-sized polyethylene and petroleum to Chlorella vulgaris at the cellular and molecular levels

Although microplastics (MPs; <5 mm) may interact with co-contaminants (e.g., petroleum) in marine aquatic systems, little is known about their combined toxicity. Therefore, this study explored the toxicities and their mechanisms of micro-sized polyethylene (mPE) and their combination with petroleum to Chlorella vulgaris. The single MPs at various particle sizes, concentrations, and aging degree, single petroleum, and their combinations, were found to pose toxicities to C. vulgaris. This study also found the microcosm's microbial diversity changed. The microbial communities in the C. vulgaris biotopes were altered under exposure to mPE and petroleum, and were disturbed by external factors such as MPs particle size, concentration, aging time, and the combination with petroleum. Furthermore, as compared with the toxicity of petroleum on microalgal transcriptional function, mPE caused less toxic to C. vulgaris, and only impact the posttranslational modification, protein turnover, and signal transduction processes. Most importantly, mPE reduced petroleum toxicity in C. vulgaris via regulating the ABC transporter, eukaryotic ribosome synthesis, and the citrate cycle metabolic pathways. Overall, our findings could fundamentally provide insights into the joint ecotoxicological effects of MPs and petroleum, and highlight the potential risks of co-exsiting pollutants.

Catalytic Deoxygenation of Hydrolyzed Oil of Chlorella Vulgaris Microalgae over Lanthanum-Embedded HZSM-5 Zeolite Catalyst to Produce Bio-Fuels

Microalgae is one of the most important sources of green hydrocarbons because it contains a high percentage of lipids and is likely to reduce reliance on fossil fuels. Several zeolite-based catalysts have a short lifetime due to coke-formation deactivation. In this study, a lanthanum-modified HZSM-5 zeolite catalyst for the conversion of crude oil into non-oxygenated compounds (hydrocarbons) and oxygenated compounds has been investigated. The crude oil of Chlorella Vulgaris microalgae was extracted using Soxhlet and converted into hydrolyzed oil (HO) through a transesterification reaction. The experiments were conducted in a batch reactor (300 °C, 1000 rpm, 7 bar of N₂, the catalyst to the algal HO ratio of 15% (wt.%) and 6 h). The results were organized into three groups: product yield, chemical composition, and carbon number distribution. The liquid products were investigated, including their elemental composition, higher heating value (HHV), atomic ratios of O/C and H/C, and degree of deoxygenation (DOD%). The loading of lanthanum into HZSM-5 zeolite with different loading percentages enhanced the acid sites needed for the algal HO conversion. Among all the synthesized catalysts, 10%La/HZSM-5 produced the highest conversion of the algal HO, the highest yield of hydrocarbons, the highest HHV, and the highest DOD%; those were 100%, 36.88%, 34.16 MJ/kg, and 56.11%, respectively. The enhanced catalytic conversion was due to the presence of lanthanum, which alters the active sites for the desired reactions of catalytic deoxygenation. The main effect of the modification of the parent HZSM-5 zeolite with lanthanum led to adjusting the acidic sites needed to increase the conversion (%) of the algal HO in the catalytic deoxygenation process and thus increase the hydrocarbon yield (%), which in turn led to an increase in the HHV and DOD%. The proposed La-based zeolite composite is promising for different energy applications due to its unique benefits compared to other expensive and less-stable catalysts.

Experimental and optimization studies on phycoremediation of dairy wastewater and biomass production efficiency of Chlorella vulgaris isolated from Ganga River, Haridwar, India

Dairy wastewaters (DWW) are rich in several pollutants, including high biochemical oxygen demand (BOD) and chemical oxygen demand (COD), and their unsafe disposal may cause damage to the environment. In this study, Chlorella vulgaris (identified as NIES:227 strain based on 28s rRNA sequencing) was isolated from the freshwater habitat of the Ganga River at Haridwar, India, and further tested for its efficacy in treating DWW. The phycoremediation experiments were conducted using three different DWW concentrations (0, 50, and 100%), operating temperatures (20, 25, and 30 °C), and light intensities (2000, 3000, and 4000 lx) using response surface methodology. Results showed that after 16 days of experiments, a significant (P < 0.05) reduction in BOD (96.65%) and COD (87.50%) along with a maximum biomass production of 1.757 g/L was achieved using 57.72% of dairy industry wastewater, 24.16 °C of reactor temperature, and 3874.51 lx of light intensity. The RSM models had coefficient of determination (R²) values above 0.9459 with a minimum difference between measured and predicted responses. Therefore, the findings of this study suggest that the isolated C. vulgaris can be effectively used to treat dairy wastewater along with significant production of algal biomass which can be further used for the generation of low-cost biofuel and other materials.

Quantifying the bioaccumulation of Pb to Chlorella vulgaris in the presence of dissolved organic matters with different molecular weights

Dissolved organic matter (DOM) is ubiquitous in natural waters which exhibits obvious effects on the toxicity of heavy metals. However, information on the toxicity of heavy metals in the presence of DOMs with different molecular weights (MWs) was still unclear. In this study, Suwannee river humic acid (SRHA) and algae-derived organic matter (ADOM) were selected as typical terrestrial and microbial DOMs, with the bulk DOMs fractionating into high MW (HMW-, 1 kDa ~ 0.45 μm) and low MW (LMW-, < 1 kDa) fractions to explore the MW-dependent heterogeneities in the bioaccumulation of Pb to Chlorella vulgaris. Results showed that, regardless of DOM types, the LMW fraction exhibited more acidic groups and humic-like substances than the HMW counterparts. Presence of bulk DOM can decrease the bioaccumulation of Pb, while the specific effects were MW- and type-dependent. The LMW-SRHA enhanced the bioaccumulation of Pb while the HMW counterpart alleviated the effects. However, both the HMW- and LMW-ADOM can reduce the bioaccumulation of Pb to C. vulgaris. Moreover, the correlation analysis showed a significant positive correlation between the content of phenolic-OH and the adsorbed/internalized amounts of Pb, demonstrating that the phenolic-OH played a critical role in altering the bioaccumulation of Pb. The results obtained in this study suggest that distribution of MWs, number of acidic functional groups, and metal complexation capacity within DOM pool should be considered for the eco-environmental risk assessment of heavy metals in aquatic environments.

[Inhibitory effects of Bellamya aeruginosa on common algae in freshwater blooms]

The increasingly frequent algal blooms in freshwater have become a major environmental problem in the world. In recent years, algae removal by the biological method is receiving more attention for its eco-friendly characteristics. In this study, we examined the effects of Bellamya aeruginosa, a common macrobenthic snail in eutrophic lakes in China, on the growth and photosynthesis activities of the common algae occurred in freshwater blooms, including cyanobacterium Microcystis aeruginosa, coupled with green algae Chlorella vulgaris and Scenedesmus obliquus. The main aims were to clarify the interactive relationships between B. aeruginosa and algae, and to verify feasibility of using B. aeruginosa as an algal-removing organism. The results showed that B. aeruginosa could feed a large amount of algae cells in a short period after inoculation, and reached the maximal removal rate of toxic and non-toxic M. aeruginosa as well as S. obliquus within 12 hours, which were 73.7%, 73.2%, and 51.1%, respectively. Furthermore, its feeding on C. vulgaris was stronger than on other algae, with the removal rate reaching 99.2% by the end of the experiment. The microcystins produced by the toxic M. aeruginosa accumulated in the body of B. aeruginosa induced the histopathological changes in the liver tissue, and thereby hindered the feeding of B. aeruginosa. In the late stage of the experiment, the photosynthetic activities of the algal cells under each treatment were significantly lower than that in the control, indicating that the feeding of B. aeruginosa damaged algal cells and inhibited their proliferation. In addition, in the mixture of non-toxic M. aeruginosa and S. obliquus, the selective feeding of B. aeruginosa caused the dominance of non-toxic M. aeruginosa to be replaced by S. obliquus. Therefore, B. aeruginosa could inhibit the photosynthesis and reduce the biomass of algae through feeding, and thus would eliminate or mitigate the formation of algal blooms.

Cerium oxide thin films: synthesis, characterization, photocatalytic activity and influence on microbial growth

The resistance of surfaces to biofouling remains a significant advantage for optical devices working in natural conditions, increasing their lifetime and reducing maintenance costs. This paper reports on the functionalities of transparent CeO₂ thin films with thicknesses between 25 and 600 nm deposited by reactive magnetron sputtering on the glass substrate. The CeO₂ photocatalytic performance exhibited an efficiency of 30% on imidacloprid degradation under 6 h of UV radiation and increased linearly with the irradiation time, suggesting a complete degradation within 48 h. The films did not alter the growth rate of the green algae Chlorella vulgaris after 72 h short-term exposure. The tested CeO₂ films proved to efficiently inhibit with high efficiency the Staphylococcus aureus biofilms and planktonic growth (reducing the counts of bacterial cells by 2 to 8 logs), demonstrating the promising potential of these materials for obtaining antimicrobial and antibiofilm surfaces, with broad applications for the biomedical, ecological and industrial fields.

Fluorescent Imaging and Sorting of High-Lipid-Content Strains of Green Algae by Using an Aggregation-Induced Emission Luminogen

Microalgae-based biofuels are receiving attention at the environmental, economic, and social levels because they are clean, renewable, and quickly produced. The green algae Chlorella vulgaris has been extensively studied in research laboratories and the biofuel industry as a model organism to increase lipid production to be cost-effective in commercial production. In this work, we utilized a lipid-droplet-specific luminogen with aggregation-induced emission (AIE) characteristics to increase the lipid production of C. vulgaris by fluorescent imaging and sorting of those algal cells with large and rich lipid droplets for subculturing. The AIE-active TPA-A enabled real-time monitoring of the size and number of lipid droplets in C. vulgaris during their growth period so that we can identify the best time for harvesting. Furthermore, the algae cells with high lipid content were identified and collected for subculturing by the technique of fluorescence-activated cell sorting (FACS). The lipid production in the generation of two successive selections was almost doubled compared to the generation with natural selection. This work demonstrated that the technologies of AIE and FACS could be applied together to improve the production of a third-generation biofuel.

Study of the Physicochemical and Biological Properties of the Lipid Complex of Marine Microalgae Isolated from the Coastal Areas of the Eastern Water Area of the Baltic Sea

The Baltic Sea algae species composition includes marine euryhaline, freshwater euryhaline, and true brackish water forms. This study aimed to isolate a lipid–pigment complex from microalgae of the Baltic Sea (Kaliningrad region) and investigate its antimicrobial activity against Gram-positive and Gram-negative bacteria. Microalgae were sampled using a box-shaped bottom sampler. Sequencing was used for identification. Spectroscopy and chromatography with mass spectroscopy were used to study the properties of microalgae. Antibiotic activity was determined by the disc diffusion test. Lipids were extracted using the Folch method. Analysis of the results demonstrated the presence of antimicrobial activity of the lipid–pigment complex of microalgae against E. coli (the zone diameter was 17.0 ± 0.47 mm and 17.0 ± 0.21 mm in Chlorella vulgaris and Arthrospira platensis, respectively) and Bacillus pumilus (maximum inhibition diameter 16.0 ± 0.27 mm in C. vulgaris and 16.0 ± 0.22 mm in A. platensis). The cytotoxic and antioxidant activities of the lipid complexes of microalgae C. vulgaris and A. platensis were established and their physicochemical properties and fatty acid composition were studied. The results demonstrated that the lipid–pigment complex under experimental conditions was the most effective against P. pentosaceus among Gram-positive bacteria. Antimicrobial activity is directly related to the concentration of the lipid–pigment complex. The presence of antibacterial activity in microalgae lipid–pigment complexes opens the door to the development of alternative natural preparations for the prevention of microbial contamination of feed. Because of their biological activity, Baltic Sea microalgae can be used as an alternative to banned antibiotics in a variety of fields, including agriculture, medicine, cosmetology, and food preservation.

[Characteristics of Phytoplankton Community Structure and Their Relationships with Environmental Factors in Autumn in Qinhe River Basin of Jincheng Region]

In October-November 2020, the phytoplankton and the aquatic environment from 62 sites in the mainstream of the Qinhe River and the largest tributary of the Qinhe River (Danhe River) in the Jincheng region were investigated to clarify the spatial pattern of phytoplankton communities and their driving factors. A total of 7 phyla and 47 species of phytoplankton were identified in the Qinhe River basin and were composed of Cryptophyta, Chlorophyta, Pyrrophyta, Chrysophyta, Bacillariophyta, Cyanophyta, and Crytophyta. Six dominant species in the Qinhe River included:Chlorella vulgaris, Cryptomonas erosa, Chroomonas acuta, Cyclotella stelligera, Chlorococcum, and Euglena viridis. Six dominant species in the Danhe River included:C. erosa, Frustulia vulgaris, E. viridis, C. vulgaris, Trachelomonas oblonga Lemm, and C. stelligera. The Shannon-Wiener diversity index (H') varied from 0.35 to 3.15, with a mean value 1.40. The Pielou evenness index (J) varied from 0.24 to 1.00, with a mean value of 0.68. H' values in the Qinhe River were higher than those in the Danhe River. J values were relatively low in the middle reaches of the Qinhe River and middle-low reaches of the Danhe River. The results in the Qinhe River through a canonical correspondence analysis (CCA) showed that the percent of forest land at a 300 m buffer was the driving factor of Chlorococcum in Chlorophyta, and nitrate, total phosphorus, and the percent of forest land at the 300 m buffer were the driving factors of E. viridis. Cyclotella stelligera was mainly influenced by the percent of urban land and water temperature, whereas C. vulgaris, C. erosa, and C. acuta were mainly influenced by the percent of farmland and residential land at the 300 m buffer. The results in the Danhe River via CCA showed that C. erosa and C. stelligera were mainly influenced by pH and sulfate, E. viridis was mainly influenced by the percent of urban land and grass land, T. oblonga Lemm was mainly influenced by chloride and the percent of forest land, F. vulgaris was mainly influenced by water temperature and the percent of farmland, and C. vulgaris was mainly influenced by ammonia and the percent of farmland.

Roles of illumination on distribution of phosphorus in Chlorella vulgaris under mixotrophic cultivation

Phosphorus (P) is a non-substitutable resource and global reserves of phosphate rock are limited. In this study, phosphorus recovery by Chlorella vulgaris, and the effects of different light intensities (2000 Lux, 5000 Lux, 8000 Lux, 12,000 Lux) on the phosphorus distribution in the soluble microbial product (SMP), extracellular polymeric substance (EPS) and intracellular polymeric substance (IPS) were analyzed. The results showed that the 5000 Lux was the optimum light intensity for P uptake and transformation by Chlorella vulgaris under mixotrophic cultivation. At the light intensity of 5000 Lux, the P uptake rate was 100% after 32 days of cultivation, and the concentration of intracellular organic phosphorus (OP) was 5.77 mg P/L. Moreover, EPS was the main P pool when inorganic phosphorus (IP) was depleted in bulk solution. Phosphorus recovery by microalgae is an important solution to treat P-containing wastewater.

Using molecular weight-based fluorescent detector to characterize dissolved effluent organic matter in oxidation ditch with algae

Implementation of microalgae has been considered for enhancing effluent wastewater quality. However, it can cause environmental issues due to the release of extracellular and algal organic matter in the biological process. This study aimed to investigate the characteristics of dissolved effluent as algae- and bacteria-derived organic matter during the oxidation ditch process. Furthermore, experiments were conducted under three combinations filled by Spirulina platensis, Chlorella vulgaris, and without microalgae. The results showed that dissolved effluent organic matter was more aromatic and hydrophobic than before treatment. Fluorescence spectroscopy identified two components-aromatic protein-like and soluble microbial product-like components-at excitation/emission of 230/345 nm and 320/345 nm after treatment, instead of fulvic acid-like at 230/420 nm and humic acid-like at 320/420 nm in raw wastewater. These components were fractionated based on the average of molecular weight cut-offs (MWCOs), and high (MWCOs > 50,000 Da), medium (MWCOs 50,000-1650 Da), and low molecular weights (MWCOs < 1650 Da) were reported. Biological oxidation ditch under symbiosis algal bacteria generated humic and fulvic acid with a higher MWCOs than the process without algal. The quality and quantity of dissolved effluent organic matter in an oxidation ditch reactor were significantly affected by algal-bacteria symbiotic.

Microwave catalytic co-pyrolysis of chlorella vulgaris and oily sludge: Characteristics and bio-oil analysis

Co-pyrolysis of Chlorella vulgaris (CV) and Oily sludge (OS) under different mixing ratios were investigated by microwave furnace. NiO, activated carbon (AC) and their 1:1 compound (N1A1) with different additions (5%, 10%, 15% and 20%) were selected as microwave additives to study the effects on optimum mixing ratio of co-pyrolysis. The results indicated that mixing ratio of CV/OS = 1:1 (C1O1) was optimum for co-pyrolysis. Besides, 10% AC was optimal on improving pyrolysis characteristics of the C1O1 group. The most significant synergistic interaction of NiO and AC occurred in the 10% N1A1 group. Moreover, hydrocarbons in bio-oil of the C1O1 group increased by 31.84% compared with theoretical values, while nitrogenous, oxygenated compounds decreased by 74.18% and 19.01%. Addition of 10% N1A1 in the C1O1 group increased aliphatic hydrocarbons by 22.44%, and decreased nitrogenous, oxygenated compounds by 41.79% and 36.58%. Overall, 10% N1A1 was conducive for the C1O1 group to obtain high-quality bio-oil.

Study on co-pyrolysis and products of Chlorella vulgaris and rice straw catalyzed by activated carbon/HZSM-5 additives

The weight loss characteristics, product distribution and bio-oil composition of co-pyrolysis of rice straw (RS) and Chlorella vulgaris (CV) were investigated by microwave oven. Then, the catalytic effect of activated carbon (AC) and HZSM-5 on these characteristics were studied. Results showed that AC strongly improved co-pyrolysis weight loss characteristics and obtained maximum average weight loss rate (R_a) at 30% addition with 0.01639 wt.%/s. While HZSM-5 promoted the characteristics as addition was lower than 10%. In the case of compound additives, 20% A7H3 obtained the maximum R_a (0.01413 wt.%/s). Furthermore, both single AC and HZSM-5 showed negative effect on bio-oil production, while 20% A7H3 (AC/HZSM-5 = 7:3) achieved the maximum production (24%). For bio-oil composition, 30% A10H0 showed strong selectivity for phenol and N-heterocycle and 10% A0H10 showed strong aromatization capacity, and the addition of 20% A7H3 increased the hydrocarbons content from 20.79% to 31.63% compared with the blank group.

Effects of harvesting on morphological and biochemical characteristics of microalgal biomass harvested by polyacrylamide addition, pH-induced flocculation, and centrifugation

The effects of microalgae harvesting methods on microalgal biomass quality were evaluated using three species namely the freshwater green alga Chlorella vulgaris, marine red alga Porphyridium purpureum and marine diatom Phaeodactylum tricornutum. Harvesting efficiencies of polyacrylamide addition, alkaline addition, and centrifugation ranged from 85 to 95, 59-92 and 100%, respectively, across these species. Morphology of the harvested cells (i.e. compromised cell walls) was significantly impacted by alkaline pH-induced flocculation for all three species. Over 50% of C. vulgaris cells were compromised with alkaline pH compared to < 10% with polyacrylamide and centrifugation. The metabolic profiles varied depending on harvesting methods. Species-specific decrease of certain metabolites was observed. These results suggest that the method of harvest can alter the metabolic profile of the biomass amongst the three harvesting methods, polyacrylamide addition showed higher harvesting efficiency with less compromised cells and higher retention of industry important biochemicals.

Potential use of Chlorella vulgaris KCBAL01 from a freshwater stream receiving treated textile effluent in hexavalent chromium [Cr(VI)] removal in extremely acidic conditions

Remediation of hexavalent chromium with conventional chemical and physical methods is a costly process, while replacing some critical steps in physiochemical remediation with self-sustaining bioremediation agents are expected to be cost-effective and environmentally friendly implementation. In this study, a microalga isolated from a freshwater stream receiving treated textile wastewater was identified up to its molecular level and investigated its ability to tolerate and remove hexavalent chromium from extremely acidic conditions under different temperatures. The ability of microalgae to tolerate and remove Cr(VI) was investigated by growing it in BG11 media with different pH (1, 2, 3 & 7), amended with several concentrations of Cr(VI) and incubated under different temperatures for 96 hrs. Microalga was identified as Chlorella vulgaris and found that the isolated strain has a higher hexavalent chromium removal potential in extremely acidic conditions than in neutral pH conditions at 25 °C. In contrast, its Cr(VI) removal potential is significantly influenced by the pH and temperature of the growth medium. Furthermore, it exhibited a permanent viability loss at extreme acidic conditions (pH 1 - 3) and prolonged exposure to the higher chromium content. The microalga investigated will be a highly useful bioagent in hexavalent chromium remediation in high acidic conditions.

Residual palm kernel expeller as the support material and alimentation provider in enhancing attached microalgal growth for quality biodiesel production

Albeit the biodiesel production from suspended microalgal system has gained immense interests in recent years, the domineering limitation of being economically infeasible has hindered this technology from partaking into a large-scale operation. To curtail this issue, attached growth system had been introduced by various studies; however, those were still unable to alleviate the socio-economic challenges faced in commercializing the microalgal biomass production. Thus, this study had developed a novel approach in cultivating-cum-harvesting attached Chlorella vulgaris sp. microalgae, whilst using solid organic waste of palm kernel expeller (PKE) as the supporting and alimentation material for microalgal biofilm formation. The effects of three variables, namely, PKE dosage, light intensity, and photoperiod, were initially modelled and later optimized using Response Surface Methodology tool. The derived statistical models could predict the growth performances of attached microalgal biomass and lipid productivity. The optimum growing condition was attained at PKE dosage of 5.67 g/L, light intensity of 197 μmol/m² s and photoperiod of 8 light and 16 dark hours/cycle, achieving the microalgal density and lipid content of 9.87 ± 0.05 g/g and 3.39 ± 0.28 g/g, respectively, with lipid productivity of 29.6 mg/L day. This optimum condition had led to the intensification of biodiesel quality with a high percentage of monounsaturated fatty acid, i.e., oleic acid (C18:1), encompassing 81.86% of total fatty acid methyl ester components. Given that the positive acquisition of PKE as an excellent supporting material in enhancing the microalgal density and lipid productivity that had resulted in the commercially viable biodiesel quality, this study served as a novel revolution in augmenting the microalgae and solid waste utilities for sustainable energy generation.

Metabolomics-Guided Comparison of Pollen and Microalgae-Based Artificial Diets in Honey Bees

Managed honey bee colonies used for crop pollination are fed artificial diets to offset nutritional deficiencies related to land-use intensification and climate change. In this study, we formulated novel microalgae diets using Chlorella vulgaris and Arthrospira platensis (spirulina) biomass and fed them to young adult honey bee workers. Diet-induced changes in bee metabolite profiles were studied relative to a natural pollen diet using liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) metabolomics. Untargeted analyses of pollen- and microalgae-fed bees revealed significant overlap, with 248 shared features determined by LC-MS and 87 shared features determined by GC-MS. Further metabolomic commonalities were evident upon subtraction of unique diet features. Twenty-five identified metabolites were influenced by diet, which included complex lipids, essential fatty acids, vitamins, and phytochemicals. The metabolomics results are useful to understand mechanisms underlying favorable growth performance as well as increased antioxidant and heat shock protein gene expression in bees fed the microalgae diets. We conclude that the tested microalgae have potential as sustainable feed additives and as a source of bee health-modulating natural products. Metabolomics-guided diet development could eventually help tailor feed interventions to achieve precision nutrition in honey bees and other livestock animals.

Phycoremediation of milk processing wastewater and lipid-rich biomass production using Chlorella vulgaris under continuous batch system

This study compiles the results of phycoremediation of milk processing wastewater (MPWW) and production of lipid-rich Chlorella vulgaris biomass using a continuous batch system operated for 12-wks. After a 4-wks interval, a new MPWW was loaded photobioreactor to provide appropriate nutrient supply to algae. Results indicated that MPWW supported the algal growth efficiently and the maximum algal growth was recorded in the ranges of 400.36 to 421.58 mg L^-1 during 4-wk's of the cultivation cycle. Average reduction in total nitrogen, TN (45.82-69.18%); nitrate, NO₃ (93.32-94.54%); total ammonium nitrogen, TAN (92.94-94.54%); sulphate, SO₄^-2 (85.13-87.34%); total phosphorus (75.09-78.78%); and biochemical oxygen demands, BOD (89.53-92.40%) was recorded during 12-wks phycoremediation of MPWW. Harvested algal biomass (dry weight basis, DW) exhibited a significant content of total sugar (45.5%) and total lipid (39.7%). The lipid profiling results indicated the presence of palmitic acid (39.9%), oleic acid (21.08%), linoleic acid (13.13%), and other C18 compounds in algal biomass, suggesting the suitability of MPWW for Chlorella vulgaris cultivations. Algal biomass exhibited a high heating value (MJ/Kg of DW) in the range of 17.3 to 25.1, comparable to other lignocellulose biomass to be used for bioenergy purposes. Results of this study indicate that MPWW could be utilized as a valuable medium for Chlorella vulgaris cultivation under a circular economy approach: wastewater treatment and bioenergy feedstock production. The effect of controlled environmental conditions on algal growth behavior and lipid composition in biomass, while using MPWW as a medium, could be investigated in future studies.

Detailed Characterization of the Cell Wall Structure and Composition of Nordic Green Microalgae

Green microalgae are attractive to food, pharmaceutical, and biofuel industries due to the promising and diverse properties of their intracellular components. In current biotechnological applications, however, clear bottlenecks are the cell disruption and cell harvesting steps. Challenges in both of these processes are directly linked to the properties of the microalgal cell wall. The aim of this study was to explore the cell wall compositions and morphologies of four Nordic microalgal strains (Chlorella vulgaris (13-1), Scenedesmus sp. (B2-2), Haematococcus pluvialis, and Coelastrella sp. (3-4)) and their changes in relation to logarithmic and stationary growth phases. Transmission electron microscopy imaging enabled us to visualize the cell walls and to observe structural elements such as spines, microfibrillar hairs, or layers. Using cryogenic X-ray photoelectron spectroscopy, we quantified lipid, protein, and polysaccharide content of the outer surface of the microalgal cell wall in cultures. Fourier transform infrared spectroscopy highlighted changes between growth phases within the polysaccharide and protein fractions of the cell wall. Very prominent differences were observed in sugar and protein composition of the Scenedesmus sp. (B2-2) cell wall compared to the cell walls of the other three Nordic strains using trimethylsilyl derivatization.

Microalgal flocculation and sedimentation: spatiotemporal evaluation of the effects of the pH and calcium concentration

The high cost of harvesting microalgae is a major hurdle for the microalgae industry, and an efficient pre-concentration method is required. In this study, the effects of using different pH values (between pH 3 and 11) and calcium (Ca²⁺) concentrations (between 0 and 5 mM) on Chlorella vulgaris sedimentation were investigated by evaluating the spacio-temporal distributions of microalgae cells. Fast and efficient sedimentation occurred (within 10 min) at a high Ca²⁺ concentration (5 mM) at pH 9 and 11. However, the sediment volume was lower at a Ca²⁺ concentration of 3 mM than at a Ca²⁺ concentration of 5 mM. This indicated that the Ca²⁺ concentration strongly affected the sediment volume. Fast sedimentation and a low sediment volume were found at pH 7 and a Ca²⁺ concentration of 5 mM, probably because of the neutral charge in the system (adhesion to calcium precipitates would have occurred at a high pH). The highest Ca²⁺ recovery (82%) was achieved when sediment produced at pH 11 and a Ca²⁺ concentration of 5 mM was acidified to pH 3.

Species sensitivity distributions for ethylparaben to derive protective concentrations for soil ecosystems

Ethylparaben is used as an antifungal preservative. Although some countries have implemented regulations for human exposure to parabens, environmental regulations for ethylparaben have not been established. This study provides new toxicological data for ethylparaben, for which data regarding soil organisms were previously lacking. Although ethylparaben toxicity has been reported in other species, we present herein the first comprehensive study of its toxicity in soil organisms. We used 12 test species (Lycopersicon esculentum, Vigna radiata, Hordeum vulgare, Oryza sativa, Eisenia andrei, Folsomia candida, Lobella sokamensis, Caenorhabiditis elegans, Chlamydomonas reinhardtii, Chlorococcum infusionum, Chlorella sorokiniana, Chlorella vulgaris) from eight taxonomic groups for acute bioassays and nine test species (L. esculentum, V. radiata, H. vulgare, O. sativa, C. reinhardtii, C. infusionum, C. sorokiniana, and C. vulgaris) from five taxonomic groups for chronic bioassays. A suite of acute and chronic toxicity tests, using 21 soil species, was conducted to estimate EC₅₀ values, which facilitated the construction of species sensitivity distributions (SSDs) and the calculation of protective concentrations (PCs). Acute and chronic PC₉₅ values (protective concentration for 95% of species) for ethylparaben were estimated to be 14 and 5 mg/kg dry soil, respectively. To the best of our knowledge, this is the first study to evaluate the toxicity of ethylparaben to soil species and derive PCs for soil ecosystems based on SSDs. Therefore, the data presented in this study can be used as a basis for further investigations of paraben toxicity to the soil environment.

Application of Microalgal Physiological Response as Biomarker for Evaluating the Toxicity of the Textile Dye Alizarin Red S

Textile dyes are becoming a growing threat to the environment. This report presents the findings of the study on the toxicity of the textile dye Alizarin Red S on two freshwater microalgae. The acute toxicity assay revealed that 96-h EC₅₀ values of Chlorella vulgaris and Spirulina platensis were 29.81 mg/L and 18.94 mg/L respectively. The pigments chlorophyll-a, b and carotenoids in C. vulgaris on 96-h exposure to the dye were 2.91, 3.29 and 3.01 times lower in analogy to control whereas Spirulina platensis showed 2.89and 2.56 fold decrease in chlorophyll-a and carotenoid content than control. After the test period of 96-h with dye, the protein content of C. vulgaris and S. platensis were 2.33 and 1.77 times lower compared to the control. The growth inhibition rate, pigment as well as the protein content declined in compliance with the rise in dye concentration, which anticipate paradigm about the toxic effects of the textile dye.

Dietary chlorella (Chlorella vulgaris) supplementation effectively improves body color, alleviates muscle inflammation and inhibits apoptosis in largemouth bass (Micropterus salmoides)

Muscle quality, antioxidant status, and inflammatory and apoptotic molecule expression were investigated in juvenile largemouth bass fed five levels of Chlorella for 60 days. The results showed that muscle quality can be improved by increasing the muscle crude protein content, muscle and skin brightness value (L*), redness value (a*) and yellowness value (b*) in Chlorella-supplemented diets without affecting the growth and muscle fiber development of fish. Chlorella supplementation did not cause oxidative stress in muscle, but optimal Chlorella administration alleviated the muscle inflammatory response by downregulating the nuclear factor κB (NF-κB)-mediated proinflammatory factors such as interleukin 1β (IL-1β) and interleukin 8 (IL-8). Moreover, anti-apoptotic effects were induced by upregulation of anti-apoptotic genes, such as b cell lymphoma-2 (bcl-2) and myeloid cell leukemia-1 (mcl-1), and downregulation of pro-apoptotic genes, including bcl2-associated x (bax) and caspase3. In conclusion, Chlorella improved muscle quality, alleviated muscle inflammation and resisted muscle apoptosis.

The role of microplastics in microalgae cells aggregation: A study at the molecular scale using atomic force microscopy

Plastic pollution has become a significant concern in aquatic ecosystems, where photosynthetic microorganisms such as microalgae represent a major point of entry in the food chain. For this reason an important challenge is to better understand the consequences of plastic pollution on microalgae and the mechanisms underlying the interaction between plastic particles and cell's interfaces. In this study, to answer such questions, we developed an interdisciplinary approach to investigate the role of plastic microparticles in the aggregation of a freshwater microalgae species, Chlorella vulgaris. First, the biophysical characterization, using atomic force microscopy, of the synthetic plastic microparticles used showed that they have in fact similar properties than the ones found in the environment, with a rough, irregular and hydrophobic surface, thereby making them a relevant model. Then a combination of optical imaging and separation experiments showed that the presence of plastic particles in microalgae cultures induced the production of exopolysaccharides (EPS) by the cells, responsible for their aggregation. However, cells that were not cultured with plastic particles could also form aggregates when exposed to the particles after culture. To understand this, advanced single-cell force spectroscopy experiments were performed to probe the interactions between cells and plastic microparticles; the results showed that cells could directly interact with plastic particles through hydrophobic interactions. In conclusion, our experimental approach allowed highlighting the two mechanisms by which plastic microparticles trigger cell aggregation; by direct contact or by inducing the production of EPS by the cells. Because these microalgae aggregates containing plastic are then consumed by bigger animals, these results are important to understand the consequences of plastic pollution on a large scale.

Toxicity Effects of Engineered Iron Nanoparticles (Fe3O4) on the Growth, Cell Density, and Pigment Content of Chlorella vulgaris

This study investigated the effects of Fe₃O₄ nanoparticles released from synthesized thiourea catalyst on the biological aspects of Chlorella vulgaris. Fe₃O₄ concentrations (0, 10, 100, 250, 500, 750, and 1000 mg L^-1) were used for the exposure tests. Biological parameters of C. vulgaris, including cell density, cell viability, and pigment content, were assessed. Bioconcentration and bioaccumulation factors were evaluated for contaminated microalgae. Non-carcinogenic risks were then assessed using target hazard quotient (THQ) for potential risks in human consumptions. Findings showed that C. vulgaris cell number increased from 0 to 500 mg L^-1 of Fe₃O₄ concentration. Chlorophyll a represented a time-dependent response, and greatest values were detected in 250 and 500 mg L^-1 Fe₃O₄ at 4.2 and 4 mg/g, respectively. Chlorophyll b content showed a time-related manner in exposure to Fe₃O₄ with the highest values recorded at 250 mg L^-1 after 96 h. Moreover, bioaccumulation displayed a dose-dependent response at 15,000 µg/g dw in 1000 mg L^-1, whereas the lowest concentration was in the control group at 1700 µg/g dw. The bioconcentration factor showed a concentration-relevant decrease in all iron treatments and 10 mg L^-1 of Fe₃O₄ represented the greatest BCF at 327.3611. Non-carcinogenic risks illustrated negligible hazard (THQ < 1) and the largest EDI and THQ were calculated in 1000 mg L^-1 at 7.4332E-07 (mg kg^-1 day^-1) and 1.06189E-09, respectively. Together, iron is an essential trace element for biological purposes in aquatic systems, but in exceeding concentrations could impose toxicity effects to C. vulgaris populations.

Enhancement of plant growth regulators production from microalgae cultivated in treated sewage wastewater (TSW)

The aim of this work is to develop an efficient method for detection and evaluation of the plant growth regulators produced from cyanobacteria species (Anabaena oryzae and Nostoc muscorum) cultivated on BG11₀, and Chlorophyta alga (Chlorella vulgaris) cultivated on BG11 in addition to the cultivation of these strains on treated sewage wastewater (TSW) combined with control media (BG11 and BG11₀) at different concentrations (100, 75 and 50%). Bioassays were performed on Wheat coleoptile length and Cucumber cotyledons fresh weight for indole acetic acid (IAA) and Benzyl adenine (BA) detection. In addition, application experiments of IAA and BA presence in algal extract were applied on tomato plantlets and soybean callus. The obtained results of A. oryzae and N. muscorum extracts (grown on BG11₀ and 100% sewage media) with optimum conc. of IAA and BA showed moderate shoot length and leaves number as well as high root initiation of tomato explant compared to control. While dimethyl sulfoxide (DMSO), IAA conc. as well as IAA + BA conc. showed no effect on branching and leaf expansion. The results of C. vulgaris (grown on BG11) also revealed that the shoot had high leaves number and greatest root initiation, without branching and leaf expansion. On the other hand, 100% TSW had a moderate shoot, leaves number and high root initiation. Extracts of A. oryzae and N. muscorum (grown on BG11₀) induced 1.5-fold increase in soybean callus fresh weight, while the growth on 100% TSW was shown to be less effective. Moreover, extract of C. vulgaris (grown on BG11) induced a moderate effect, while its growth on 100% TSW was shown to be less effective in soybean callus fresh weight increment.

Stochastic LCA Model of Upscaling the Production of Microalgal Compounds

Microalgae are currently being investigated for their promising metabolites but assessing the environmental impact of producing these compounds remains a challenge. Microalgae cultivation performance results from the complex interaction of biological, technological, geographical, and physical factors, which bioengineers try to optimize during the upscaling process. The path from the discovery of a microalgal compound to its industrial production is therefore highly uncertain. Nonetheless, it is key to anticipate the potential environmental impacts associated with the future production of a microalgal target compound. This is achieved in this study by developing an ex-ante, parameterized, and consequential LCA model that performs dynamic simulations of microalgae cultivation. The model is applied to calculate the environmental impacts of 9000 stochastically generated combinations of photobioreactor geometries and operational setups. The demonstration of the model is done for a fictive microalgal strain, parameterized to resemble Chlorella vulgaris, and a fictive target compound assumed to be a carbohydrate. The simulations are performed in Aalborg, Denmark, and Granada, Spain to appreciate geographical variability, which highly affects the requirements for thermoregulation. Open-source documentation allows full reproducibility and further use of the model for the ex-ante assessment of microalgal products.

Response of fungi-microalgae pellets to copper regulation in the removal of sulfonamides and release of dissolved organic matters

Both sulfonamides (SAs) and copper (Cu(II)) were frequently detected together in swine wastewater. In this study, the regulation of Cu(II) on SAs adsorption and release of dissolved organic matters (DOMs) by fungi-microalgae pellets (FM-pellets) were investigated. Aspergillus oryzae pellets were prepared for combination with Chlorella vulgaris and the optimal conditions were at agitation speed of 130 rpm, fungi to microalgae ratio of 10:1 and the combined time of 3 h with the highest combination efficiency of 98.65%. The results showed that adsorption was the main mechanism for SAs removal. FM-pellets exhibited a high SAs adsorption potential within 6 h, and the adsorption capacity of sulfamethazine (SMZ), sulfamonomethoxine (SMM) and sulfamethoxazole (SMX) was 1.07, 0.94 and 1.67 mg/g, respectively. Furthermore, the removal of SMX, SMZ and SMM was greatly promoted from 62.31% to 85.21%, 58.71-67.91% and 64.17-80.31%, respectively, under the presence of 2 mg/L Cu(II) through ion exchange and adsorption bridging. DOMs were analyzed by the parallel factor (PARAFAC) to demonstrate the response mechanism of FM-pellets to Cu(II). Protein-like substances and NADH in DOMs released by FM-pellets formed complexes with Cu(II) to alleviate the damage on the organism. These findings provide new insights into the mechanism and response of Cu(II) in the removal of SAs by FM-pellets.

Removal of carbon and nitrogen in wastewater from a poultry processing plant in a photobioreactor cultivated with the microalga Chlorella vulgaris

This study evaluates the removal of COD and nitrogen from poultry wastewater in photobioreactors. Cell growth, the effect of light intensity (3200, 9800, and 12000 lux) and air flow (1.6, 3.2, and 4.8 L min^-1) as a source of CO₂ in bold basal medium and wastewater with different concentrations of COD were evaluated. The growth kinetics were modeled by using the Gompertz model and logistic model for both culture media. COD removals of up to 95% were achieved, and poultry wastewater was found to be a viable growing medium for Chlorella vulgaris. Finally, the wastewater met Mexican standards, and biomass was obtained with products valued as lipids (3.2 g lipid/100 g biomass) and proteins (342.94 mg L^-1). The culture was found to have a dilatory behavior, and the rheological models of Ostwald de Waele, Ostwald de Waele linealized and Herschel Bulkley were utilized, showing a laminar behavior.

Integrating eco-technological approach for textile dye effluent treatment and carbon dioxide capturing from unicellular microalga Chlorella vulgaris RDS03: a synergistic method

A pilot-scale treatment method was used in the present study to test the biosorption of textile dye from textile effluent and carbon dioxide using Chlorella vulgaris RDS03. The textile dye effluent treatment achieved that textile dye biosorption capacity (q_max) rate of 98.84% on 15 days of treatment using Chlorella vulgaris RDS03. The Langmuir and Freundlich isotherm kinetics model indicated that the higher R² value 0.98. The microalga Chlorella vulgaris RDS03 was captured-96.86% of CO₂ analyzed by CO₂ utilization and biofixation kinetics, 4.65 mgmL^-1 of biomass, 189.26 mgg^-1 of carbohydrate, 233.89 mgg^-1 of lipid, 4.3 mLg^-1 of bioethanol and 4.9 mLg^-1 of biodiesel produced. We performed fatty acid methyl ester (FAME) profiling using gas chromatography-mass spectrometry (GCMS). We found 40 types of biodiesel compounds, specifically myristic acid, pentadecanoic acid, octadecanoic acid, palmitic acid, and oleic acid. The high-performance liquid chromatography (HPLC) validated and analyzed the produced bioethanol.Novelty of the Research• Unicellular microalga Chlorella vulgaris RDS03 was isolated from the freshwater region and investigated their biosorption efficiency against hazardous synthetic azo textile dyes.• Chlorella vulgaris RDS03 ability to biosorption 96.86% of environmental polluted carbon dioxide• Treated biomass was used to produce ecofriendly, unpolluted and green energy such as biofuels (biodiesel and bioethanol).