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Imidacloprid (IMI) is used extensively as an insecticide and poses a significant risk to both the ecological environment and human health. Biological methods are currently gaining recognition among the different strategies tested for wastewater treatment. This study focused on evaluating a recently discovered green alga, Scenedesmus sp. TXH202001, isolated from a municipal wastewater treatment plant (WWTP), exhibited notable capacity for IMI removal. After an 18-day evaluation, medium IMI concentrations (50 and 100 mg/L) facilitated the growth of microalgae whereas low (5 and 20 mg/L) and high (150 mg/L) concentrations had no discernible impact. No statistically significant disparities were detected in Fv/Fm, Malonaldehyde or Superoxide dismutase across all concentrations, suggesting Scenedesmus sp. TXH202001 exhibited notable resilience and adaptability to IMI conditions. Most notably, Scenedesmus sp. TXH202001 successfully eliminated > 99 % of IMI within 18 days subjected to IMI concentrations as high as 150 mg/L, which was contingent on the environmental factor of illumination. Molecular docking was used to identify the chemical reaction sites between IMI and typical degrading enzyme CYP450. Furthermore, the study revealed that the primary path for IMI removal was biodegradation and verified that the toxicity of the degraded product was lower than parent IMI in Caenorhabditis elegans. The efficacy of Scenedesmus sp. TXH202001 in wastewater was exceptional, thereby validating its practical utility., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The green microalgae Scenedesmus spp. can grow rapidly and produce significant amounts of protein or lipid. However, frequent microzooplankton contamination leading to reduced biomass productivity has hindered the microalgae commercialization. Here, a comprehensive investigation into harmful microzooplankton species in mass cultures of a commercially promising species Scenedesmus acuminatus were conducted throughout the year. Twenty-five microzooplankton species were identified, with the amoeba Vannella sp. and the ciliate Vorticella convallaria being the most harmful to algal cells. The results indicated that it was the harmful grazers, rather than the overall microzooplankton diversity, led to culture deterioration and reduced biomass yield. Increasing the concentration of algal inoculants or reducing culture temperature during hot summer days were found to be effective in mitigating the impact of these harmful grazers. The findings will contribute to the best management protocol for monitoring and controlling the harmful microzooplankton in mass cultures of S. acuminatus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Carbon supplementation strategies still have certain practical application constraints. Zn/Fe-based metal-organic frameworks (MOFs) nanoparticles that which are not toxic to Scenedesmus obliquus were successfully introduced into microalgal solutions to overcome low CO 2 solubility. The maximum specific surface area of MOFs reached 342.94 m 2 ·g -1 at a Zn/Fe molar ratio of 10/1. Under the optimal MOFs concentrations of 2.5 mg·L -1 , the conversion of inorganic carbon increased by 2.6-fold. When S. obliquuswas cultured in a MOFs-modified medium with 1.50 % CO 2 at 25 °C, the CO 2 mass transfer coefficient and mixing time reached 9.01 × 10 -3 min -1 and 55 s, respectively. The maximum chlorophyll-a content, biomass productivity, and CO 2 fixation efficiency reached 32.57 mg·L -1 , 0.240 g·L -1 ·d -1 and 21.6 %, respectively. Enriching CO 2 for ribulose-1,5-bisphosphate carboxylase/oxygenase carboxylation by MOFs may be the key to improving the photosynthetic efficiency of microalgae. This strategy could serve as a reference for improving the microalgal CO 2 fixation efficiency., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Selecting the optimal microalgal strain for carbon capture and biomass production is crucial for ensuring the commercial viability of microalgae-based biorefinery processes. This study aimed to evaluate the impact of varying bicarbonate concentrations on the growth rates, inorganic carbon (IC) utilization, and biochemical composition of three freshwater and two marine microalgal species. Parachlorella kessleri, Vischeria cf. stellata, and Porphyridium purpureum achieved the highest carbon removal efficiency (>85%) and biomass production at 6 g L -1 sodium bicarbonate (NaHCO 3 ), while Phaeodactylum tricornutum showed optimal performance at 1 g L -1 NaHCO 3 . The growth and carbon removal rate of Scenedesmus quadricauda increased with increasing NaHCO 3 concentrations, although its highest carbon removal efficiency (∼70%) was lower than the other species. Varying NaHCO 3 levels significantly impacted the biochemical composition of P. kessleri, S. quadricauda, and P. purpureum but did not affect the composition of the remaining species. The fatty acid profiles of the microalgae were dominated by C16 and C18 fatty acids, with P. purpureum and P. tricornutum yielding relatively high polyunsaturated fatty acid content ranging between 14% and 30%. Furthermore, bicarbonate concentration had a species-specific effect on the fatty acid and chlorophyll-a content. This study demonstrates the potential of bicarbonate as an effective IC source for microalgal cultivation, highlighting its ability to select microalgal species for various applications based on their carbon capture efficiency and biochemical composition., (© 2024 The Author(s). Biotechnology Journal published by Wiley‐VCH GmbH.)

The multiple microalgal collaborative treatment of domestic wastewater has been extensively investigated, but its whole life cycle tracking and consequent potential have not been fully explored. Herein, a dual microalgal system was employed for domestic wastewater treatment, tracking the variation in microalgal growth and pollutants removal from shake flask scale to 18 L photobioreactors scales. The results showed that Chlorella sp. HL and Scenedesmus sp. LX1 combination had superior growth and water purification performance, and the interspecies soluble algal products promoted their growth. Through microalgae mixing ratio and inoculum size optimized, the highest biomass yield (0.42 ± 0.03 g/L) and over 91 % N, P removal rates were achieved in 18 L photobioreactor. Harvested microalgae treated in different forms all promoted wheat growth and suppressed yellow leaf rate. This study provided data support for the whole process tracking of dual microalgal system in treating domestic wastewater and improving wheat growth., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Microalgae are increasingly recognized as promising organisms for bioremediation of organic pollutants. This study investigates the potential of enhancing the bioremediation efficiency of pyrene (PYR), a polycyclic aromatic hydrocarbon (PAH), through NaCl induced physiological and biochemical alterations in two microalgae species, Chlorella vulgaris and Scenedesmus acutus. Our findings reveal significant improvement in PYR removal when these microalgae were cultivated in the presence of 0.1% NaCl where PYR removal increased from 54 to 74% for C. vulgaris and from 26 to 75% for S. acutus. However, it was observed that NaCl induced stress had varying effects on the two species. While C. vulgaris exhibited increased PYR removal, it experienced reduced growth and biomass production, as well as lower photosynthetic efficiency when exposed to PYR and PYR + NaCl. In contrast, S. acutus displayed better growth and biomass accumulation under PYR + NaCl conditions, making it a more efficient candidate for enhancing PYR bioremediation in the presence of NaCl. In addition to assessing growth and biochemical content, we also investigated stress biomarkers, such as lipid peroxidation, polyphenol and proline contents. These findings suggest that S. acutus holds promise as an alternative microalgae species for PYR removal in the presence of NaCl, offering potential advantages in terms of bioremediation efficiency and ecological sustainability. This study highlights the importance of understanding the physiological and biochemical responses of microalgae to environmental stressors, which can be harnessed to optimize bioremediation strategies for the removal of organic pollutants like PYR., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The present study demonstrates, for the first time, the feasibility of a two-step process consisting of Electro-Fenton (EF) followed by microalgae to treat highly loaded real food processing wastewater along with resource recovery. In the first step, EF with a carbon felt cathode and Ti/RuO 2 -IrO 2 anode was applied at different current densities (3.16 mA cm -2 , 4.74 mA cm -2 and 6.32 mA cm -2 ) to decrease the amount of organic matter and turbidity and enhance biodegradability. In the second step, the EF effluents were submitted to microalgal treatment for 15 days using a mixed culture dominated by Scenedesmus sp., Chlorosarcinopsis sp., and Coelastrum sp. Results showed that current density impacted the amount of COD removed by EF, achieving the highest COD removal of 77.5% at 6.32 mA cm -2 with >95% and 74.3% of TSS and PO 4 3- removal, respectively. With respect to microalgae, the highest COD removal of 85% was obtained by the culture in the EF effluent treated at 6.32 mA cm -2 . Remarkably, not only 85% of the remaining organic matter was removed by microalgae, but also the totality of inorganic N and P compounds, as well as 65% of the Fe catalyst that was left after EF. The removal of inorganic species also demonstrates the high complementarity of both processes, since EF does not have the capacity to remove such compounds, while microalgae do not grow in the raw wastewater. Furthermore, a maximum of 0.8 g L -1 of biomass was produced after cultivation, with an accumulation of 32.2% of carbohydrates and 25.9% of lipids. The implementation of the two processes represents a promising sustainable approach for the management of industrial effluents, incorporating EF in a water and nutrient recycling system to produce biomass that could be valorized into clean fuels., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:, (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The possibility of obtaining energy or nutritive streams and bioremediation as an add-on opens new perspectives for the massive culturing of microalgal biomass on waste waters generated by the agro-food sector. Ordinary revenue streams are fully preserved, or even boosted, if they are used in microalgal cultivation; however, the suitability of wastewaters depends on multiple nutritional and toxic factors. Here, the effect of modulating the Olive Mill Wastewater (OMW) and cattle digestate (CD) fraction in the formulation of a growth medium on biomass accumulation and productivity of selected biomass fractions and their relevance for biofuel and/or feed production were tested for the microalga Scenedesmus dimorphus and for the cyanobacterium Arthrospira platensis (Spirulina). Tests highlighted the strong S. dimorphus adaptability to digestate, as on OMW, compared to A. platensis, with the maximum lipid storage (48 %) when culture medium was composed by 50 % of cattle digestate., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study proposes a method for the ultrasonic extraction of carotenoids and chlorophyll from Scenedesmus obliquus and Arthrospira platensis microalgae with green solvents. Ethanol and ethanolic solutions of ionic liquids were tested with a variety of extraction parameters, including number of extractions, time of extraction, and solid-liquid ratio R( S/L ), to determine the optimal conditions. After selecting the most effective green solvent (ethanol), the process conditions were established: R (S/L) of 1:10, three extraction cycles at 3 min each), giving an extraction yield of 2602.36 and 764.21 μg carotenoids .g dried biomass -1 ; and 22.01 and 5.81 mg chlorophyll .g dried biomass -1 in S. obliquus and A. platensis, respectively. The carotenoid and chlorophyll extracts obtained using ethanol were shown to be potent scavengers of peroxyl radical, being 5.94 to 26.08 times more potent α-tocopherol. These findings pave the way for a green strategy for valorizing microalgal biocompounds through efficient and environmentally friendly technological processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The global energy crisis has spurred a shift from conventional to clean and sustainable energy sources. Biomass derived from microalgae is emerging as an alternative energy source with diverse applications. Despite the numerous advantages of microalgae, large-scale biomass harvesting is not economical and convenient. Self-flocculation is considered an effective phenomenon facilitated by extracting the flocculating substances from microalgae that assist aggregation of algal cells into flocs. A novel cellulose-based bioflocculant has been synthesized from sewage water grown Chlorella sorokiniana and Scenedesmus abundans for harvesting application. The produced bioflocculant amounted to 38.5% and 19.38% of the dry weight of S. abundans and C. sorokiniana, respectively. Analysis via FTIR, XRD, and FESEM-EDX revealed the presence of cellulose hydroxyapatite (HA) in algae-derived cellulose. Harvesting efficiencies of 95.3% and 89.16% were attained for S. abundans and C. sorokiniana, respectively, at a dosage of 0.5 g/L. Furthermore, the bioflocculant was recovered, enabling its reuse with recovery efficiencies of 52% and 10% for S. abundans and C. sorokiniana, respectively. This simple and efficient approach has the potential to replace other harvesting methods, thereby contributing to the economic algal biofuel production., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

To understand the potential roles of terrestrial bamboo on controlling cyanobacterial blooms in aquatic systems, growth rates of the cyanobacterium Microcystis aeruginosa and its competitor algae were examined under different concentrations of bamboo extract. In mono-species cultures with unicellular algal strains, 5.0 g L -1 extract treatment suppressed M. aeruginosa growth, while it had little effect on the growth of green alga Scenedesmus obliquus or promoted the growth of diatom Nitzschia palea. In co-species cultures, the extract treatment increased the effect of S. obliquus and N. palea on the growth of M. aeruginosa. Under the extract treatment with a field-collected M. aeruginosa population, its cell density declined and its colony was etiolated and sank, while co-cultured N. palea increased explosively by invading the colony. These results suggest that bamboo forest stands along banks and artificially installed bamboo poles can affect the aquatic environment for phytoplankton community. Enhancing the growth of competitors, especially diatoms that can invade cyanobacterial colonies, by using extracts or by providing substrates for growth, was suggested to be the major way of the bloom control by bamboo., (© 2022. The Author(s).)

Small-scale photobioreactors (PBRs) in the inoculum stage were designed with internal (red or green) and external white LED light as an initial step of a larger-scale installation aimed at fulfilling the integral biorefinery concept for maximum utilization of microalgal biomass in a multifunctional laboratory. The specific growth rate of Scenedesmus obliquus (Turpin) Kützing biomass for given cultural conditions was analyzed by using MAPLE software. For the determination of total polyphenols, flavonoids, chlorophyll "a" and "b", carotenoids and lipids, UHPLC-HRMS, ISO-20776/1, ISO-10993-5 and CUPRAC tests were carried out. Under red light growing, a higher content of polyphenols was found, while the green light favoured the flavonoid accumulation in the biomass. Chlorophylls, carotenoids and lipids were in the same order of magnitude in both samples. The dichloromethane extracts obtained from the biomass of each PBR synergistically potentiated at low concentrations (0.01-0.05 mg/mL) the antibacterial activity of penicillin, fluoroquinolones or oregano essential oil against the selected food-borne pathogens ( Staphylococcus aureus , Escherichia coli and Salmonella typhimurium ) without showing any in vitro cytotoxicity. Both extracts exhibited good cupric ion-reducing antioxidant capacity at concentrations above 0.042-0.08 mg/mL. The UHPLC-HRMS analysis revealed that both extracts contained long chain fatty acids and carotenoids thus explaining their antibacterial and antioxidant potential. The applied engineering approach showed a great potential to modify microalgae metabolism for the synthesis of target compounds by S. obliquus with capacity for the development of health-promoting nutraceuticals for poultry farming.

Cerium is the most abundant rare earth metal in the earth's crust, and it has deleterious effects on aquatic ecosystems from fertilizer runoff. Scenedesmus obliquus is an oil-rich microalga that grows rapidly and is sensitive to many kinds of toxins. Given that microalgae are useful indicators of eutrophication and toxic stress, it was found that lower concentrations of cerium (0.50-5.00 mg·L -1 ) stimulated algal growth and increased chlorophyll a content, whereas higher concentrations (above 50.00 mg·L -1 ) had an inhibitory effect on algal growth and chlorophyll a content. The algal growth rate and chlorophyll a content peaked at a cerium concentration of 5.00 mg·L -1 . Both the donor and acceptor sides of photosystem II (PSII) reaction centers were sensitive to cerium-induced stress. Specifically, high concentrations of cerium damaged the oxygen evolving complex and PSII reaction center and suppressed electron transport at the donor and receptor side of the reaction center, influencing the absorption, transfer, and application of light energy in S. obliquus XJ002. In addition, we established a simple method to quantify the intracellular lipid content of S. obliquus XJ002, and the optimum staining conditions for Nile red were as follows: volume percentage of dimethyl sulfoxide was 2%, the concentration of Nile red was 2.0 µg·mL -1 , and the staining time of Nile red was 5 min. The addition of cerium resulted in a significant increase in the total lipid content of XJ002. When the concentration of cerium was 50 mg·L -1 , the total lipid content was 16.26% higher than the control group. This information will enhance our ability to utilize microelement fertilizer in biomass accumulation programs and will help to further reveal the key regulatory factors in the lipid metabolism, and would lay the foundation for promoting the research of microalgae bioenergy., (© 2020 International Union of Biochemistry and Molecular Biology, Inc.)

Background: The three-phase extraction process of olive oil produces highly contaminated wastewater (OMW). The elimination of this toxic by-product is an important environmental issue that requires the development of an appropriate management solution. The cultivation of microalgae using OMW as growth medium was therefore studied using single (the culture medium was formed by 0% to 80% ultrafiltered olive mill wastewater (OMUF) or OMW added to BG11) and two-stage strategies (microalgae were firstly cultivated in the BG11 medium. In the second stage, 40% and 80% of OMUF and OMW were added to the culture). In this work, biodegradation of OMW and subsequent extraction of lipid and antioxidant molecules was investigated as an ecofriendly method for the bioremediation and valorization of OMW., Results: For two-stage cultivation, OMUF and OMW stress enhanced the intracellular amount of polyphenol accumulated in Scenedesmus sp. and exhibited the highest 2, 2-diphenyl-1- picrylhydrazyl radical (DPPH) and 2,2'-azino-bis (3-ethylbenzoline-6-sulfonate) radical (ABTS) scavenging ability compared with single-stage cultivation. Moreover, the lipid profile is dominated by polyunsaturated acids. In the single-stage cultivation, the Ch a, Ch b, carotenoid, carbohydrate and lipid content of 2.57, 7.4, 1.69, 368, and 644 g kg -1 were observed in 40% OMUF added culture, respectively, along with high biomass productivity and 58% of polyphenol removal. Moreover, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that the biomass of Scenedesmus sp. cultured on 40% OMUF did not show any toxic effect, making it an efficient strategy., Conclusion: The results indicate that Scenedesmus sp. is a promising microalga for the biotreatment of OMW and the extraction of bioactive metabolites. © 2021 Society of Chemical Industry., (© 2021 Society of Chemical Industry.)

Carbon dioxide supplementation is significant for cell growth in autotrophic cultures of microalgae. However, the CO 2 utilization efficiency is quite low in most processes. Aimed at this problem, six kinds of physical absorption enhancers were investigated to enhance the biological carbon sequestration of microalgae. By the addition of a small amount of CO 2 absorption enhancer, the total inorganic carbon concentration of the medium was significantly increased. In addition, the biomass productivity of Scenedesmus dimorphus was maximally increased by 63% by the addition of propylene carbonate in flask cultures. In cultures using an air-lift photobioreactor equipped with a pH-feedback control system to supply CO 2 , the CO 2 consumption was maximally reduced by 71% with added polyethylene glycol dimethyl ether. This study indicates that the incorporation of physical absorption enhancers could be a promising approach to overcome the problems of low CO 2 utilization efficiency and high carbon source cost in algal biomass production., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Linear aggregation is present in some animals, such as the coordinated movement of ants and the migration of caterpillars and spinylobsters, but none has been reported on rotifers. The rotifers were collected and clone cultured in the laboratory at 25 ± 1°C, under natural light (light intensity ~130 lx, L:D = 14:10). The culture medium(pH = 7.3) was formulated as described by Suga et al., and rotifers were fed on the micro algae Scenedesmus obliquus grown in HB-4 medium to the exponential growth stage. When density was high (150 individuals ml-1), the behavior of rotifers was observed using a stereo microscope (Motic ES-18TZLED). In this paper, linear aggregation in Brachionus calyciflorus was found for the first time, and experiments were carried out to verify the correlation between linear aggregation and culture density of B. calyciflorus. With the increase of density, the number of aggregations increase, the number of individuals in the aggregation increased, and the maintenance time of the aggregation was also increased. Therefore, we speculate that the formation of aggregates is related to density and may be a behavioral signal of density increase, which may transmit information between density increase and formation of dormant eggs., Competing Interests: The authors have declared that no competing interests exist.

Microalgae have shown great potential as a source of biofuels, food, and other bioproducts. More recently, microfluidic devices have been employed in microalgae-related studies. However, at small fluid volumes, the options for controlling flow conditions are more limited and mixing becomes largely reliant on diffusion. In this study, we fabricated magnetic artificial cilia (MAC) and implemented them in millimeter scale culture wells and conducted growth experiments with Scenedesmus subspicatus while actuating the MAC in a rotating magnetic field to create flow and mixing. In addition, surface of MAC was made hydrophilic using plasma treatment and its effect on growth was compared with untreated, hydrophobic MAC. The experiments showed that the growth was enhanced by ten and two times with hydrophobic and hydrophilic MAC, respectively, compared with control groups which contain no MAC. This technique can be used to investigate mixing and flow in small sample volumes, and the enhancement in growth can be beneficial for the throughput of screening studies. Moreover, the methods used for creating and controlling MAC can be easily adopted in labs without microfabrication infrastructures, and they can be mastered by people with little prior experience in microfluidics., (© 2021 The Authors. Biotechnology and Bioengineering published by Wiley Periodicals LLC.)

The selection of a suitable growth regime can increase the physiological performance of microalgae and improve bioprocess based on these microorganisms from agro-industrial residues. Thus, this study assessed the biotechnology capacity-biomass production, biochemical composition, and nutrient uptake-from tequila vinasses (TVs) as the nutrient source of three indigenous microalgae-Chlorella sp., Scenedesmus sp., and Chlamydomonas sp.-cultured under heterotrophic and mixotrophic conditions. The results demonstrated that under the mixotrophic regime, the three microalgae evaluated reached the highest nitrogen uptake, biomass production, and cell compound accumulation. Under this condition, Chlorella sp. and Scenedesmus sp. showed the highest nutrient uptake and biomass production, 1.7 ± 0.3 and 1.9 ± 0.3 g L -1 , respectively; however, the biochemical composition, mainly carbohydrates and proteins, varied depending on the microalgal strain and its growth regime. Overall, our results demonstrated the biotechnological capacity of native microalgae from TVs, which may vary not only depending on the microalgal strain but also the culture strategy implemented and the characteristics of the residue used, highlighting-from a perspective of circular bio-economy-the feasibility of implementing microalgal bioprocess to reuse and valorize the nutrimental composition of TVs through biomass and high-valuable metabolite production, depicting a sustainable strategy for tequila agro-industry in Mexico.

Microalgae efficiently convert sunlight into lipids and carbohydrates, offering bio-based alternatives for energy and chemical production. Improving algal productivity and robustness against abiotic stress requires a systems level characterization enabled by functional genomics. Here, we characterize a halotolerant microalga Scenedesmus sp. NREL 46B-D3 demonstrating peak growth near 25 °C that reaches 30 g/m 2 /day and the highest biomass accumulation capacity post cell division reported to date for a halotolerant strain. Functional genomics analysis revealed that genes involved in lipid production, ion channels and antiporters are expanded and expressed. Exposure to temperature stress shifts fatty acid metabolism and increases amino acids synthesis. Co-expression analysis shows that many fatty acid biosynthesis genes are overexpressed with specific transcription factors under cold stress. These and other genes involved in the metabolic and regulatory response to temperature stress can be further explored for strain improvement.

Temperature and irradiance are the two most relevant factors determining the performance of microalgae cultures in open raceway reactors. Moreover, inadequate temperature strongly reduces the biomass productivity in these systems even if enough sunlight is available. Controlling the temperature in large open raceway reactors is considered unaffordable because of the large amount of energy required. This study presents an indirect method for temperature regulation in microalgae raceway reactors by optimizing the culture depth. First, the effect of the culture depth on the raceway temperature is analyzed for different seasons of the year. Afterward, a simulation study is presented where the proposed control approach is compared to the normal operation mode with constant volume in the reactor. This study is also extended to industrial scale. Relevant improvements on the temperature factor and biomass production are presented. The developed knowledge allows the improvement of the performance in open raceway reactors up to 12% without involving additional energy and costs, being a suitable solution for large industrial reactors that until now have no options for controlling the temperature., (© 2020 Wiley Periodicals LLC.)

Flat panels are the most spread type of photobioreactors for studying light effects on a microalgae culture. Their low thickness, usually between 1 and 3 cm, aims at ensuring light homogeneity across the culture. Yet because optical density has to remain very low, studies are still limited to low cell density cultures. To alleviate this problem, even thinner photobioreactors can be designed. Nevertheless, thin flat panel reactors are very prone to induce high shear stress. This work aimed at designing a new millimeter thin panel photobioreactor to study light effects on Chlorella and Scenedesmus genera. We proposed a numerical workflow that is capable of assessing the shear stress intensity in such a reactor. The numerical predictions were validated at three different levels: 2D preliminary simulations were able to reproduce bubble commonly known behaviors; close to the nozzle, the predictions were successfully confronted to shadowgraphy experimental reference; at the mini bioreactor scale, experimental and numerical mixing were found to be close. After these throughout validations, shear stress intensity in the photobioreactor was calculated over 1000 Lagrangian tracers. The experienced shear stress was agglomerated at the population level. From the computed shear stress, it was possible to choose the minimal reactor thickness that would not hinder cell growth., (© 2020 International Union of Biochemistry and Molecular Biology, Inc.)

As typical endocrine disrupters, nonylphenol (NP) and octylphenol (OP) are emerging pollutants that have attracted wide attention. This study investigated the toxicity effects of NP and OP on microalgae Chlorella pyrenoidosa and Scenedesmus obliquus, particularly on their growth inhibition, photosynthetic pigment, chlorophyll fluorescence, and superoxide dismutase and malondialdehyde levels. Results showed that the 96 h EC 50 of NP and OP was 2.89 and 5.21 mg/L on C. pyrenoidosa, respectively, and 1.54 and 8.48 mg/L on S. obliquus, respectively. NP exerted a stronger inhibitory effect on cell growth, photosynthesis, and PSII activity, and it contributed more oxidative stress on C. pyrenoidosa than on S. obliquus. By contrast, OP exerted a stronger inhibitory effect on S. obliquus than on C. pyrenoidosa. Furthermore, the toxicity of OP to the tested microalgae was lower than that of NP. Principal component analysis (PCA) and Pearson's correlation indicate that the accumulation of reactive oxygen species is the dominant mechanism of NP and OP cellular toxicity. The principal components of NP and OP affecting microalgae are distinct in the PCA plot, and different endocrine disrupters have varying chemical-specific influences on algal cells. This study confirmed that the toxicity of NP and OP to microalgae C. pyrenoidosa and S. obliquus is chemical- and species-specific. These findings should be considered when assessing the health risk of environmental pollution., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The phytogenic algicide sanguinarine shows strong inhibitory effects on some bloom-forming cyanobacteria and exhibits great potential in cyanobacterial bloom mitigation. To evaluate the possible ecological effects of sanguinarine on microalgae, the effects and possible mechanisms of sanguinarine on the competition between bloom-forming cyanobacterium Raphidiopsis raciborskii (formerly named Cylindrospermopsis raciborskii) and green alga Scenedesmus obliquus were investigated through co-culture competition test and comparative toxicological study including growth characteristics, chlorophyll fluorescence transients, activities of antioxidant enzymes, and lipid peroxidation. The results of Raphidiopsis-Scenedesmus co-culture competition test showed that sanguinarine decreased the competition ability of R. raciborskii, which benefitted S. obliquus in winning the competition. Toxicological studies have shown that sanguinarine exhibited high inhibitory effects on the growth and photosynthesis of R. raciborskii but no obvious toxicity on S. obliquus at concentrations of no more than 80 μg L -1 . Oxidative damage partially contributed but was not the primary mechanism for the toxicity of sanguinarine on R. raciborskii. The results presented in this study indicate that sanguinarine may be a good algicidal candidate in mitigation of Raphidiopsis-based water bloom., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The potential of Scenedesmus dimorphus microalgae for CO 2 biofixation and lipid biosynthesis for bioenergy applications was evaluated in this study. Batch experiments were conducted using synthetic tertiary municipal wastewater samples at several nitrogen to phosphorus (NP) ratios (1 : 1 to 8 : 1) and CO 2 concentrations (∼0%, 2%, 4%, and 6% CO 2 in supplied air). Scenedesmus dimorphus was cultivated for 25 days and the growth is highly dependent on the CO 2 concentration and the NP ratio. An NP ratio of 2 : 1 produces a biomass yield of 733 mg/L when the microalga culture was supplied with air enriched with 2% CO 2 . The maximum CO 2 biofixation rate of 49.6 mg L -1  d -1 is at an NP ratio of 8 : 1 with 4% CO 2 . A colorimetric technique depending on sulpho-phospho-vanillin (SPV) was utilized for the determination of the intracellular lipid content. The highest lipid content of 31.6% as the dry weight of the biomass is at an NP ratio of 1 : 1 and 6% CO 2 . These results indicate that supplementation of suitable CO 2 with favorable NP ratio has a considerable effect on lipid accumulation in the microalgae Scenedesmus dimorphus biomass., (© 2020 Wiley-VCH GmbH.)

In a previous study, the sequential optimization and regulation of environmental parameters using the PhotoBiobox were demonstrated with high-throughput screening tests. In this study, we estimated changes in the biovolume-based composition of a polyculture built in vitro and composed of three algal strains: Chlorella sp., Scenedesmus sp., and Parachlorella sp. We performed this work using the PhotoBiobox under different temperatures (10-36°C) and light intensities (50-700 μmol/m -2 /s -1 ) in air and in 5% CO 2 . In 5% CO 2 , Chlorella sp. exhibited better adaptation to high temperatures than in air conditions. Pearson's correlation analysis showed that the composition of Parachlorella sp. was highly related to temperature whereas Chlorella sp. and Scenedesmus sp. showed negative correlations in both air and 5% CO 2 . Furthermore, light intensity slightly affected the composition of Scenedesmus sp., whereas no significant effect was observed in other species. Based on these results, it is speculated that temperature is an important factor in influencing changes in algal polyculture community structure (PCS). These results further confirm that the PhotoBiobox is a convenient and available tool for performance of lab-scale experiments on PCS changes. The application of the PhotoBiobox in PCS studies will provide new insight into polyculture-based ecology.

The effect of light wavelengths on the physiological, biochemical and lutein content of the microalgal consortia Chlorella variabilis and Scenedesmus obliquus was evaluated using different light sources. Among different light treatments, cool-white fluorescent light produced the highest biomass of 673 mg L -1 with a specific growth rate of 0.75 day -1 followed by blue (500 mg L -1 ; 0.73 day -1 ). The chlorophyll content was enhanced under blue light (10.7 mg L -1 ) followed by cool fluorescent light (9.3 mg L -1 ), whereas the lutein productivity was enhanced under cool fluorescent light (7.22 mg g -1 ). Protein content of the microalgal consortia was enhanced under all light treatments with the highest protein accumulation under cool-white fluorescent light (~56% of dry mass) closely followed by amber light (52% of dry mass), whereas the carbohydrate content was higher under amber light (~35% of dry mass). The results revealed that the consortia could grow well on diluted dairy wastewater thereby reducing the cost of algal production when compared with the use of inorganic media and a two-phase culture process utilizing cool fluorescent and amber light could be employed for maximizing algal biomass and nutrient composition with enhanced lutein production. The study also emphasizes on the economic efficiency of LED lights in terms of biomass produced based on the modest electricity consumed and the importance of using amber light for cultivating microalgae for its nutrient content which has seldom been studied.

Two injectable reactive and sorption-active particle types were evaluated for their applicability in permeable reaction zones for in-situ removal of herbicides ("nanoremediation"). As model substances, atrazine and bromacil were used, two herbicides frequently occurring in groundwater. In order to provide recommendations for best use, particle performance was assessed regarding herbicide degradation and detoxification. For chemical reduction, Carbo-Iron® was studied, a composite material consisting of zerovalent iron and colloidal activated carbon. Carbo-Iron reduced bromacil with increased activity compared to nanoscale zerovalent iron (nZVI). The sole reaction product, 3-sec-butyl-6-methyluracil, showed 500-fold increase in half-maximal-effect concentration (EC 50 ) towards the chlorophyte Scendesmus vacuolatus compared to the parent compound. The detoxification based on dehalogenation confirmed the dependency of the specific mode-of-action on the carbon-halide bond. For atrazine, neither nZVI nor Carbo-Iron showed significant degradation under the conditions applied. As novel subsurface treatment option, Trap-Ox® zeolite FeBEA35 was studied for generation of in-situ permeable oxidation barriers. Both adsorbed atrazine and bromacil underwent fast unselective oxidation. The transformation products of the Fenton-like reaction were identified, and oxidation pathways derived. For atrazine, a 300-fold increase in EC 50 for S. vacuolatus was found over the duration of the reaction, and a loss of phytotoxicity to non-detectable levels for bromacil., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Nitrogen (N) sources have been target in microalgae cultivation studies, considering their nutritional impact on growth and high costs. Here, we have evaluated the growth of Scenedesmus obliquus BR003, applying alternative low-cost culture media containing ammonium and urea, or combinations of both N sources. The culture media were applied for indoor and outdoor cultivation, followed by growth analyses and metabolic characterization. The alternative culture media B4 and L4 supported higher biomass production (1.4 g L -1 ) compared to BG11 (nitrate-based medium). In addition, the lipid percentage was higher for B4 (ammonium-based culture medium), reaching up to 25% DW. High contents of carbohydrates (60%) and proteins (40%) were also obtained in media with ammonium and urea, respectively. Considering the lower costs of alternative fertilizer-based media, using ammonium and/or urea as N sources, and the high lipid content observed, we suggest these media as viable for large-scale production of S. obliquus.

Partial nitrification-Anammox process is an efficient and energy-saving method for nitrogen removal from low C/N wastewaters. In this study, partial nitrification was achieved in an algal-bacterial granular sludge system when treating low COD/NH 4 -N (309.4 mg L -1 /213.6 mg L -1 ) wastewater under sunlight irradiation (R S ). Sunlight irradiation, algae growth and free nitrous acid (FNA) decreased the activity of ammonia oxidizing bacteria (AOB) by 25.7% and completely inhibited the activity of nitrite oxidizing bacteria (NOB), resulting in a NH 4 -N removal efficiency of ≥99% and a nitrite accumulation efficiency of 96.5% in Rs. Compared with the control without sunlight irradiation (R C ), the algal-bacterial granules in R S produced 34.7% and 13.1% more proteins and polysaccharides, respectively, and exhibited a higher structure stability. The lipid content in the algal-bacterial granules was 68.7 mg g-SS -1 , which was about 2.1 times higher than that in the granules from R C , making the algal-bacterial granule a value-added biomass. Meanwhile, the content of unsaturated fatty acid methyl esters increased remarkably due to the growth of algae (Stigeoclonium, Scenedesmus and Navicula). The combined stress of sunlight irradiation, algae growth and high FNA in R S only slightly lowered the relative abundance of Nitrosomonadaceae (AOB family) from 7.5% to 5.8%, while Nitrospiraceae (NOB family) was severely inhibited and became undetectable., Competing Interests: Declaration of competing interests The authors declare no financial/commercial conflicts of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study aims to investigate the efficacy of lipid induction in Scenedesmus abundans by adding the effluent from dark fermentation of biohydrogen production. Four sets of experiments were conducted: control (sufficient nitrogen), nitrogen depletion, low concentration (0.3×) effluent addition, and high concentration (0.5×) effluent addition. The addition of low concentration effluent produced the highest biomass and lipid yields of 2.831 g/L and 1.238 g/L, corresponding to a lipid abundance of 43.72 wt%. Furthermore, S. abundans had high removal efficiencies for volatile fatty acids in the effluent (formic acid 100%, acetic acid 100%, propionic acid 98%, lactic acid 84%, and butyric acid 68%), and this is the first study demonstrating the ability of S. abundans in using formic acid and lactic acid to produce biomass and lipids. These results show that S. abundans have great abilities in simultaneous reducing organic acids in the effluent and producing valuable metabolites.

The enhanced lipid accumulation in microalgae is envisioned under special stress conditions with the cost of algal growth, which in turn affects the overall lipid productivity. The selection of suitable stress conditions facilitates better lipid productivity without any harmful effect on microalgae growth and algal biomass production. In the present study, we have attempted to select the best salinity conditions towards better growth, biomass accumulation, and lipid productivity of microalgae. The study also envisaged testing the feasibility of the stepwise salinity stress-induced cultivation approach to minimize the growth penalty effect of microalgae. The highest specific growth rate (0.129, 0.133, 0.113 µday -1 ) and doubling per day (0.185, 0.193, 0.163 per day) were obtained at salinity concentration of 40 mM NaCl in BG-11 medium for Scenedesmus quadricauda (Sq19), Scenedesmus dimorphus (Sd12), and Chlorella sp. (Chl16), respectively. Maximal lipid content of 18.28, 30.70, and 32.19%, and lipid productivity of 8.59, 13.81, and 10.27 mg l -1  day -1 were achieved at 160 mM of NaCl in BG-11 media with the Sq19, Sd12, and Chl16 algal isolates, respectively. The utilization of stepwise salinity stress (160 mM) induced cultivation of Sd12 algal isolate results in higher lipid content (39.42%) and slightly improved lipid productivity than the control (without any stress, 20.4% lipid content). The results indicate the feasibility of enhancing the lipid content and productivity through the salinity-induced stepwise cultivation strategy.

Methylisothiazolinone (MIT) is a widely used non-oxidizing biocide for membrane biofouling control in reverse osmosis (RO) systems usually with high dosages. However, few investigations have focused on MIT removal through bio-processes, since it is highly bio-toxic. This study proposed a novel biotreatment approach for efficient MIT degradation by Scenedesmus sp. LX1, a microalga with strong resistance capability against extreme MIT toxicity. Results showed that MIT (3 mg/L) could be completely removed within 4 days' cultivation with a half-life of only 0.79 d. Biodegradation was the primary removal mechanism and this metabolic process did not rely on bacterial consortia, soluble algal products secretion or algal growth. The main pathway was proposed as ring cleavage followed by methylation and carboxylation through the identification of MIT transformation products. MIT biodegradation followed the pseudo-first-order kinetics under growth control. A new kinetic model was presented to depict the MIT removal considering algal growth, and this model could be used for generally describing non-nutritive contaminants biodegradation. The algal biodegradation capability was independent of the initial biocide concentration, and MIT removal could be enhanced by increasing the initial algal density. Our results highlight the potential application of algal cultivation for MIT-containing wastewater biotreatment, such as RO concentrate., Competing Interests: Declaration of Competing Interest We declare that we have no known competing financial interests or personal relationships that could have appeared to influence the submitted work titled “Mechanism and kinetics of methylisothiazolinone removal by cultivation of Scenedesmus sp. LX1″.Signed by all authors as follows: Xiao-Xiong Wang, Wen-Long Wang, Guo-Hua Dao, Zi-Bin Xu, Tian-Yuan Zhang, Yin-Hu Wu, Hong-Ying Hu, (Copyright © 2019 Elsevier B.V. All rights reserved.)

Galaxolide (HHCB) is known to be persistent during wastewater treatment and has raised increasing concern due to its high detection frequency in the environment and potentially negative effects. However, little information is available on the degradation of HHCB by algae, the degradation mechanisms and the toxicity of HHCB on algae. In the present study, HHCB was found to be toxic to Navicula sp. and Scenedesmus quadricauda, with a 3 d EC 50 of 0.050 and 0.336 mg L -1 , respectively. Both microalgae showed high removal efficiency (72.9-100%) for HHCB. S. quadricauda showed a more satisfactory effect in the bioremediation of HHCB than Navicula sp. A total of four metabolites were found in the biotransformation processes of HHCB, and its possible metabolic pathways were proposed. Hydroxylation, methoxylation, methylation, ketonization, demethylation, and oxaloacetate conjunction contributed to the metabolism of HHCB in algal cells., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Life cycle assessment (LCA) of indigenous freshwater microalgae, Scenedesmus dimorphus, cultivation in open raceway pond and its conversion to biodiesel and biogas were carried out. The LCA inventory inputs for the biogas scenario was entirely based on primary data obtained from algal cultivation (in pilot scale raceway pond), harvesting, and biogas production; while only the downstream processing involved in biodiesel production namely drying, reaction and purification were based on secondary data. Overall, eight scenarios were modeled for the integrated process involving: algae-based CO 2 capture and downstream processing scenarios for biodiesel and biogas along with impact assessment of nutrient addition and extent of recycling in a life cycle perspective. The LCA results indicated a huge energy deficit and net CO 2 negative in terms of CO 2 capture for both the biodiesel and biogas scenarios, majorly due to lower algal biomass productivity and higher energy requirements for culture mixing. The sensitivity analysis indicated that variability in the biomass productivity has predominant effect on the primary energy demand and global warming potential (GWP, kg CO 2 eq.) followed by specific energy consumption for mixing algal culture. Furthermore, the LCA results indicated that biogas conversion route from microalgae was more energy efficient and sustainable than the biodiesel route. The overall findings of the study suggested that microalgae-mediated CO 2 capture and conversion to biodiesel and biogas production can be energy efficient at higher biomass productivity (> 10 g m -2  day -1 ) and via employing energy-efficient systems for culture mixing (< 2 W m -3 ).

Microalgae cultivation on tannery wastewater (TWW) has been examined in some studies as a possible biological application to reduce contamination load and discharge effluents safely. However, Growth aspects, different tolerate strains and enriching the medium were not well investigated. In our study we applied Scenedesmus sp., Chlorella variabilis and Chlorella sorokiniana with different TWW concentrations. C. sorokiniana and C. variabilis cell density, chlorophyll, and sugar content grew substantially as compared to control. C. sorokiniana biomass and total lipids folded three and two times in 25% and 40% TWW, respectively as compared to control. Scenedesmus sp. showed longer lag phase and lower performance compared to the other two strains. Kelp waste extract (KWE) was added to balance the nutrients supply for C. sorokiniana, of which growth and effluents indicators were then greatly promoted in all concentrations. As the lag phase was shortened from 8 to 4 days in 60% concentration, subsequently, chlorophyll, carbohydrates, biomass and total lipids appreciated by 184%, 400%, 162% and 135%, respectively. Furthermore, the COD and ammonium removals improved by 51% and 45%, respectively. These outcomes emphasize the suitability of using TWW for microalgae cultivation with the suitable concentration while adding kelp waste extract for further enhancement.

The current technologies of algal biofuels production and wastewater treatment (e.g., aerobic) process are still in question, due to the significant amount of fresh water and nutrients requirements for microalgae cultivation, and negative energy balance in both processes, especially when considered in the context of developing counties around the world. In this research, a simplistic sustainable approach of algal biofuels production from wastewater was proposed using a Hybrid Anaerobic Baffled Reactor (HABR) and Photobioreactor (PBR) system. The study suggests that the HABR was capable of removing most of the organic and solid (>90% COD and TSS removal) from wastewater, and produced a healthy feedstock (high N: P = 3:1) for microalgae cultivation in PBRs for biofuels production. A co-culture of Chlorella vulgaris, Chlorella sorokiniana, and Scenedesmus simris002 showed high lipid content up to 44.1%; and the dominant FAMEs composition (C16-C18) of 87.9% in produced biofuels. Perhaps, this proposed low-cost technological approach (e.g., HABR-PBR system) would connect the currently broken link of sustainable bioenergy generation and wastewater treatment pathway for developing countries., Competing Interests: The authors have declared that no competing interests exist.

In the present study, the effect of irradiance on growth performance of Scenedesmus obliquus was investigated, and various non-linear growth models were evaluated to predict its temporal evolution. This microalga was cultured in a LED-illuminated flat-panel gas-lift photobioreactor operated in batch mode at varying irradiance ranging from 50 to 200 µmol/m 2 /s keeping all the other physico-chemical parameters constant. When growth data in terms of optical density were fitted in sigmoidal growth models, three non-linear models, namely, Richards model, Gompertz model, and logistic model, were found to be the best fit. Comparing these models based on statistical information, the logistic model could more appropriately and precisely describe algal growth under varying light intensity. Finally, the parameters of the logistic model were determined using regression analysis and were incorporated in the logistic equation to investigate the kinetic characteristics of S. obliquus. The optimum light intensity (I opt ) for growth was found to be 150 µmol/m 2 /s, at which a maximum specific growth rate (µ opt ) of 0.35/day was obtained. The model developed was validated experimentally and could successfully explain the photo-inhibition phenomenon occurring at light intensity above 150 µmol/m 2 /s.

Microalgae have an excellent potential for producing valuable natural products, including biofuels. Therefore, it is imperative to explore and document the existing microalgal flora and utilize their potentials to cope the increasing human needs. The present work aims at exploring and characterizing newly isolated microalgae from desert Cholistan, a habitat with myriad algal diversity. Light microscopy, scanning electron microscopy, and molecular phylogenetic approaches were used for species-level identification. Characterization and growth optimization of Scendesmus sp. were analyzed under three different growth modes to determine the most favorable conditions for increasing biomass, growth rate, and lipid content. The results revealed that mixotrophic (MT) mode significantly increases photosynthetic activity, growth rate, and lipid content with glycerol as supplement carbon source. The investigated Scenedesmus dimorphous produced a maximum dry weight of 1.73 g L -1 , improved fatty acid methyl esters profile and yield lipid up to 40% of DCW (68 g L -1 ) under MT mode, which is almost double to that of photoautotrophic cultivation. The glycerol availability in medium has been identified as the critical element for boosting growth and lipid content. Thus, it can reduce the cost of biofuel production., (© 2019 Wiley Periodicals, Inc.)

Positive interactions such as facilitation play an important role during the biological colonization and species succession in harsh or changing environments. However, the direct evidence of such ecological interaction in microbial communities remains rare. Using common freshwater microalgae isolated from a High Rate Algal Pond HRAP treating wastewaters, we investigated with both experimental and modeling approaches the direct facilitation between two algal strains during the colonization phase. Our results demonstrate that the first colonization by microalgae under a severe chemical condition arose from the rapid growth of pioneer species such as Chlorella sorokiniana, which facilitated the subsequent colonization of low growth specialists such as Scenedesmus pectinatus. The pioneer species rapidly depleted the total available ammonia nitrogen favoring the specialist species initially inhibited by free ammonia toxicity. This latter species ultimately dominated the algal community through competitive exclusion under low nutrient conditions. We show that microbial successions are not only regulated by climatic conditions but also by interactions between species based on the ability to modify their growth conditions. We suggest that facilitation within the aquatic microbial communities is a widespread ecological interaction under a vast range of environmental stress.

Sulfur availability and the end products of its metabolism, cysteine, glutathione and phytochelatins, play an important role in heavy metal tolerance, chromium included. Sulfate and chromate not only compete for the transporters but also for assimilation enzymes and chromium tolerance in various organisms has been associated to differences in this pathway. We investigated the mechanisms of Cr(VI)-tolerance increase induced by S-starvation focusing on the role of ATP sulfurylase (ATS) in two strains of Scenedesmus acutus with different chromium sensitivity. S-starvation enhances the defence potential by increasing sulfate uptake/assimilation and decreasing chromium uptake, thus suggesting a change in the transport system. We isolated two isoforms of the enzyme, SaATS1 and SaATS2, with different sensitivity to sulfur availability, and analysed them in S-sufficient and S-replete condition both in standard and in chromium supplemented medium. SaATS2 expression is different in the two strains and presumably marks a different sulfur perception/exploitation in the Cr-tolerant. Its induction and silencing are compatible with a role in the transient tolerance increase induced by S-starvation. This enzyme can however hardly be responsible for the large cysteine production of the Cr-tolerant strain after starvation, suggesting that cytosolic rather than chloroplastic cysteine production is differently regulated in the two strains., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Biogas, a gaseous effluent from the anaerobic digestion of organic waste, is considered an important source of energy, since it has a composition mainly of methane (CH 4 ; 55-75%) and CO 2 (20-60%). Today, CO 2 from biogas is an excellent carbon source to induce high microalgal biomass production; however, each microalga strain can have different optimal CO 2 concentrations for maximizing their bio-refinery capacity as well as different ability to endure stressful conditions of industrial effluents. This study assessed the bio-refinery capacity of Chlorella sp. and Scenedesmus sp., native of Lago de Chapala, Mexico, from biogas, as well as the effect of high CO 2 and methane concentrations on the physiological performance to grow, capture CO 2 and biochemical composition of both microalgae cultured under different biogas compositions. The results show that both microalgae have the biotechnological potential to endure biogas compositions of 25% CO 2 -75% CH 4 . Under this condition, the biomass production attained by Chlorella sp. and Scenedesmus sp. was 1.77 ± 0.32 and 2.25 ± 0.20 g L -1 , respectively, with a biochemical composition mainly of carbohydrates and proteins. Overall, this study demonstrates that both microalgae have the ability to endure the stressful biogas composition without affecting their physiological capacity to capture CO 2 and biosynthesize high-value metabolites. Moreover, it is worth highlighting the importance of screening wild-type microalgae from local ecosystems to determine their physiological capacity for each biotechnological application.

Phthalate esters are highly present in aquatic plastic litter, which can interfere with the biological processes in the wildlife. In this work, the commonly found freshwater microalga Scenedesmus sp. was exposed to environmental concentrations (0.02, 1 and 100 μg L -1 ) and to a higher concentration (500 μg L -1 ) of dibutyl phthalate (DBP), which is an environmental pollutant. The growth, pH variation, production of photosynthetic pigments, proteins and carbohydrates were evaluated. The main inhibition effect of DBP on the microalgal growth was observed in the first 48 h of the exposure (EC 50 : 41.88 μg L -1 ). A reduction in the photosynthetic pigment concentration was observed for the 0.02, 1 and 100 μg L -1 conditions indicating that the DBP downregulated the growth rate and affected the photosynthetic process. A significant increase in protein production was only observed under 500 μg L -1 DBP exposure. The extracellular carbohydrates production slightly decreased with the presence of DBP, with a stronger decrease occurring in the 500 μg L -1 condition. These results highlight the environmental risk evaluation and ecotoxicological effects of DBP on the production of biovaluable compounds by microalgae. The results also emphasize the importance of assessing the consequences of the environmental concentrations exposure as a result of the DBP dose-dependent correlation effects., (Copyright © 2019 Elsevier B.V. All rights reserved.)

We have worked out a rapid 1-day test based on photosynthesis measurements to estimate suitable growth temperature of microalgae cultures. To verify the proposed procedure, several microalgae-Chlorella, Nostoc, Synechocystis, Scenedesmus, and Cylindrospermum-were cultured under controlled laboratory conditions (irradiance, temperature, mixing, CO 2 , and nutrient supply) to find the optima of photosynthetic activity using the range between 15 and 35 °C. These activities were recorded at each temperature step after 2 h of acclimation which should be sufficient as oxygen production and the PQ cycle are regulated by fast processes. Photosynthetic activity was measured using three techniques-oxygen production/respiration, saturating pulse analysis of fluorescence quenching, and fast fluorescence induction kinetics-to estimate the temperature optima which should correspond to high growth rate. We measured all variables that might have been directly related to growth-photosynthetic oxygen evolution, maximum photochemical yield of PSII, F v /F m , relative electron transport rate rETR max , and the transients V j and V i determined by fast fluorescence induction curves. When the temperature optima for photosynthetic activity were verified in growth tests, we found good correlation. For most of tested microalgae strains, temperature around 30 °C was found to be the most suitable at this setting. We concluded that the developed test can be used as a rapid 1-day pre-screening to estimate a suitable growth temperature of microalgae strains before they are cultured in a pilot scale.

This study compared the performance of microalga growth, nutrient removal, algal organic matter, and energy storage products in mixotrophic, photoautotrophic, and heterotrophic conditions. Scenedesmus obliquus was used as a model species. Mixotrophic condition showed the highest specific growth rate of 0.96 d -1 as well as the fastest nitrogen and phosphorus removal rate of 85.17 mg-N g-cell -1 day -1 and 11.49 mg-P g-cell -1 day -1 , respectively, compared with photoautotrophic and heterotrophic conditions. Mixotrophic microalgae had relatively higher carbohydrates and lipids contents (21.8 and 24.0%) than photoautotrophic and heterotrophic conditions. Meanwhile, algal organic matter (AOM) in the medium was produced at the highest level under photoautotrophic condition. Mixotrophic condition was more efficient in terms of microalga growth, nutrient removal, production of energy storage products, and suppression of AOM, and would be adaptable for wastewater treatment process.

Concerns have been raised regarding the ecotoxicity of ionic liquids (ILs) owing to their wide usage in numerous fields. Three imidazolium chloride ILs with different numbers of methyl substituents, 1-decyl-imidazolium chloride ([C 10 IM]Cl), 1-decyl-3-methylimidazolium chloride ([C 10 MIM]Cl), and 1-decyl-2,3-dimethylimidazolium chloride ([C 10 DMIM]Cl), were examined to assess their effects on growth, photosynthesis pigments content, chlorophyll fluorescence, photosynthetic and respiration rate, and cellular ultrastructure of Scenedesmus obliquus. The results showed that algal growth was significantly inhibited by ILs treatments. The observed IC 50,48h doses were 0.10 mg/L [C 10 IM]Cl, 0.01 mg/L [C 10 MIM]Cl, and 0.02 mg/L [C 10 DMIM]Cl. The chlorophyll a, chlorophyll b, and total chlorophyll content declined, and the chlorophyll fluorescence parameters, minimal fluorescence yield (F 0 ), maximal fluorescence yield (F m ), maximum quantum yield of PSII photochemistry (F v /F m ), effective quantum yield of PSII [Y(II)], non-photochemical quenching (NPQ) and non-photosynthetic losses yield [Y(NO)] were notably affected by ILs in a dose-dependent manner. ILs affected the primary photosynthetic reaction, impaired heat dissipation capability, and diminished photosynthetic efficiency, indicating negative effects on photosystem II. The photosynthetic and respiration rates of algal cells were also reduced due to the ILs treatments. The adverse effects of ILs on plasmolysis and chloroplast deformation were examined using ultrastructural analyses; chloroplast swelling and lamellar structure almost disappeared after the [C 10 MIM]Cl treatment, and an increased number of starch grains and vacuoles was observed after all ILs treatments. The results indicated that one-methyl-substituted ILs were more toxic than non-methyl-substituted ILs, which were also more toxic than di-methyl-substituted ILs. The toxicity of the examined ILs showed the following order: [C 10 IM]Cl < [C 10 DMIM]Cl ≤ [C 10 MIM]Cl., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

This study compared the efficiency of nutrient removal and lipid accumulation by a monoculture of Scenedesmus obliquus and mixed cultures of microalgae. The highest removal efficiencies of ammonium (99.2%), phosphate (91.2%), and total organic carbon (83.6%) occurred in the monoculture. All the mixed cultures were dominated by S. quadricauda; in some mixed cultures, the proportions of Chlamydomonas reinhardtii and C. microsphaera reached > 20%. The lipid content and lipid production in the monoculture were 15.9% and 52.3 mg kg -1 , respectively, significantly higher than those in all the mixed cultures of microalgae. In all the mixed cultures, the proportion of palmitic acid was > 50%. The results suggest that the monoculture had advantages over the mixed culture of microalgae in terms of nutrient removal and lipid production.

Microalga Scenedesmus vacuolatus exhibited maximum growth, protein and carbohydrate contents at 10.0 mM concentration of nitrate, 1.0 mM of glutamate nitrogen and at C/N ratio (12 mM acetate+10 mM nitrate). However, these cell constituents showed the highest values in the C+N grown cells, but the lipid content was found to be the highest glutamate grown cells. FTIR analysis of Lipid/Carbohydrate and Lipid/Protein ratio and flow cytometric analysis of neutral lipids revealed higher lipid content in the glutamate grown cells than in the nitrogen starved, nitrate and C+N grown cells. The nitrate reductase activity was the highest in the C+ N grown cells and the lowest activity was found in the glutamate grown cells. A corollary of these results suggested that suppression of nitrogen assimilatory system, whether by glutamate or by nitrogen deprivation, was the most suitable physiological condition for enhanced lipid synthesis and biofuel production in microalgal cells., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Single and multispecies algal bioassays were assessed using copper toxicity with three green algae (Scenedesmus subspicatus, Scenedesmus quadricauda and Ankistrodesmus angustus) and one blue-green algae species (Oscillatoria prolifera). Single and multispecies toxicity tests were conducted based on cell density as per standard toxicity testing, and on equivalent surface area. A higher copper sulfate toxicity was registered for O. prolifera, followed by S. subspicatus, S. quadricauda, and A. angustus in single-species toxicity tests based on cell density. Single species toxicity tests based on surface area showed increased copper toxicity with increasing algal surface area except for A. angustus. In multispecies control bioassays, the growth of A. angustus was inhibited in the presence of other species in surface area-based tests. As compared to single species bioassays, O. prolifera, and S. quadricauda showed a decreased sensitivity to copper sulfate in both cell density and surface area based multispecies tests. However, for the algae species with the smallest surface area, S. subspicatus, 96h-EC 50 value decreased in multispecies bioassays based on surface area as compared to the single species test, while it increased in multispecies bioassays based on cell density. The difference in S. subspicatus sensitivity to copper between tests based on cell density and surface area supports the need to adopt multispecies toxicity testing based on surface area to avoid the confounding effect on copper toxicity of increased biomass for metal binding. 96h-EC 50 values for all species combined in the multispecies test based on cell density and on surface area were significantly different from 96h-EC 50 values obtained in single species bioassays. These results demonstrate that single-species bioassays may over- or underestimate metal toxicity in natural waters., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Scenedesmus rotundus was isolated from metal contaminated petroleum industry effluent and its tolerance to Cadmium and Zinc was tested using different concentrations of CdCl 2 and ZnCl 2 ranging from 0.001 mM to 1.0 mM of Cd and 0.03 mM to 1.21 mM of Zn amended in Bolds Basal medium. The changes in cell count recorded at regular intervals upto a period of 24 days revealed a concentration dependent inhibition in growth. Concentration of the metal, at which 50% of the cells are live and metabolically active referred to as EC 50 was calculated as 0.04 mM for Cd and 0.2 mM for Zn. Further, the effect of EC 50 of the metals on the protein content, uptake of metals at varying pH, oxidative stress markers including lipid peroxidation, protein oxidation andnd oxygen uptake, levels of enzymatic antioxidants such as catalase and superoxide dismutase and non-enzymatic antioxidants namely, GSH and PC 4 were determined. Though a direct correlation could not be drawn between pH and metal uptake, the compartmentalization of the metal during the lag phase and exponential phase was evident, most of the metal was present in extracellular fractions in the former, while in the later it was internalized. Our study shows a clear correlation between toxicity of Cd and the ability of the algae to synthesize PC 4 from GSH and chelate it leading to detoxification, while Zn treatment led to an increase in the activity of catalase and superoxide dismutase and replete GSH pools. Further the changes in the cell wall structure at EC 50 of Cd and Zn were studied. This is the first report on effect of heavy metals on the structural modifications of the cell wall of Scenedesmus in general and Scenedesmus rotundus in particular, indicating appearance of granules on the entire cell surface in both Cd and Zn treatments, with the degree of granulation increasing in the order of pH 12 > 10 > 8 in Cd treatment. Further structures of higher order resembling minute wheels are observed in Cd treated cells are also reported.

In their environments, aquatic organisms are simultaneously exposed to mixtures of several endocrine disrupting compounds, including hormones. However, most of the toxicity studies so far focused on effects of single contaminants. The available information on the potential toxicity of combined hormones on microalgae is extremely limited. For these reasons the aim of this study was to evaluate the individual and mixture effect of estrone (E1), ß-estradiol (E2), estriol (E3), 17-α-ethinylestradiol (EE2), progesterone (PRO), 5-pregnen-3β-ol-20-one (PRE), levonorgestrel (LG) and testosterone (TST) on Chlorella vulgaris and Scenedesmus armatus. Green algae cells were exposed to different concentrations (0.1-100 mg L -1 ) of hormones for 14 days. Biomass in the form of dry weight and chlorophyll a was examined. The decreasing order of toxicity (based on EC 50 , 14d) to Chlorella vulgaris and Scenedesmus armatus was: EE2>PRO > E2>PRE > TST > E3>LG > E1 and EE2>PRO > TST > E2>PRE > LG > E1>E3, respectively. Chlorella vulgaris was more sensitive to the effects of hormones than Scenedesmus armatus. Although mixed hormones were more toxic to green algae than single hormones, in the ecosystem mixtures can pose higher ecological risk than single pollutants. Therefore, data on the toxicology of both single and mixed hormones is very valuable for assessment of the possibility of adverse ecological effects caused by these pollutants. Furthermore, these results suggest that environmental exposure to hormone mixtures may cause toxicity levels different to the sum of those of the single hormones and provides a basic understanding of their toxic effect on algae., (Copyright © 2019 Elsevier Ltd. All rights reserved.)