Biofilm and suspension-based cultivation of microalgae to treat anaerobic digestate food effluent (ADFE).

Anaerobic digestion of organic waste produces effluent (ADE) that requires further treatment. Biofilm-based microalgal cultivation is a favoured approach to ADE treatment. This study compared Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 in biofilm and suspension cultures to treat anaerobic digestate food effluent (ADFE). Chlorella sp. MUR 268 biofilm had significantly higher biomass (50.38 g m-2) than Scenedesmus sp. biofilm (9.39 g m-2). Conversely, Scenedesmus sp. yielded 1.5 times more biomass (1.2 g L-1) than Chlorella sp. in suspension. Chlorella sp. biofilm had 49.3 % higher areal productivity than suspension, while Scenedesmus sp. showed 87.3 % higher areal growth in suspension. Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 significantly removed nutrients in ADFE. In suspension, COD, ammoniacal nitrogen, and phosphate were reduced to 94.9, 5.2, and 5.98 mg L-1 for Chlorella sp. MUR 268, and 245, 2.89, and 3.22 mg L-1 for Scenedesmus sp. MUR 269, respectively. In biofilm, Chlorella sp. MUR 268 achieved reductions to 149.9, 1.16, and 3.57 mg L-1, while Scenedesmus sp. MUR 269 achieved 100.2, 6.9 and 2.07 mg L-1. Most of these values are below the recommended effluent discharge standard, highlighting the efficacy of this system in ADFE treatment. Biofilm cultures fixed 68-81 % of removed nitrogen in biomass, while in suspension, only 55-71 % ended in the biomass. Chlorella sp. MUR 268 biofilm fixed 88 % of removed phosphorus, while Scenedesmus sp. MUR 269 suspension fixed more phosphorus (55 %) than the biofilm counterpart (34 %). This biofilm design offers advantages like simplified, cost-effective operation, easy biomass recovery, and reduced water usage.

Potential use of sludge from El Ferrol Bay (Chimbote, Peru) for the production of lipids in the culture of Scenedesmus acutus (Meyen, 1829).

Despite the extensive development of microalgae biotechnology, it still requires new methodologies to lower production costs, especially in the field of biofuel production. Therefore, innovative methods that facilitate operations and enable cost-effective production are important in driving this industry. In this study, we propose a new low-cost and easy-to-use procedure, addressed to the generation of a culture medium for Scenedesmus acutus. The medium was obtained by thermal reduction of a sludge sample from El Ferrol Bay (Chimbote, Peru), whereby we obtained an aqueous medium. Our results indicated that the aqueous medium incorporates all necessary nutrients for microalgae production; allowing a maximum biomass of 0.75 ± 0.07 g/L with 60% of the medium; while high lipids production (59.42 ± 6.16%) was achieved with 20%. Besides, we quantified, in the experimental medium and at the end of the cultures, the levels of inorganic nutrients such as ammonium, nitrites, nitrates, and phosphates; in addition to COD and TOC, which were significantly reduced ( p < 0.05) after 7 days of culture, mainly in the treatment with 20%. These results suggest tremendous potential for sludge reuse, which also entails a cost reduction in microalgae biomass production, with additional positive impacts on large-scale application over highly polluted environments.

Improved microalgae growth and lipid production in anaerobic digestate with ultraviolet radiation pretreatment.

Inappropriate sterilization strategies inhibit microalgal growth when culturing microalgae with anaerobic digestate. This study aimed to scientifically select a low-cost disinfection pretreatment of anaerobic digestate for large-scale microalgae cultivations. In this work, three different methods, including autoclaving, ultraviolet or NaClO treatments, were employed to sterilize the municipal anaerobic digestate. Scenedesmus quadricauda was then cultured in diluted liquid digestate for the simultaneous lipid production and nutrient removal. The results indicated that the growth of S. quadricauda was inhibited after NaClO treatment due to the residual free chlorine. The 15-min ultraviolet effectively mitigated microbial contamination and increasing nutrient availability, enhancing the electron transport of microalgal photosynthesis. After 6-days cultivation, the microalgal biomass concentration of the ultraviolet group was 1.09 g/L, comparable to that of the autoclaving group (1.15 g/L). High nutrient removal efficiency was observed: COD (93.30 %), NH4+-N (92.56 %), TN (85.82 %) and TP (95.12 %). Moreover, S. quadricauda outcompeted the indigenous microorganisms, contributing to its dominance in the culture system of ultraviolet group. The facultative anaerobe Comamonadaceae and aerobes Moraxellaceae, rather than strict anaerobe Paludibacteraceae and Bacteroidetes_vadinHA17, played vital roles in synergistic removal of contaminants by bacteria and algae. The potential competition for nitrogen and phosphorus by bacteria contributed to the ultraviolet group having the greatest lipid content (48.19 %). Therefore, this work suggested using 15-min ultraviolet treatment for anaerobic digestate in large-scale microalgae cultivation.

Allelochemicals-mediated interaction between algae and bacteria: Direct and indirect contact.

Secondary metabolites with bioactivity are allelochemicals. This study adopted direct contact (R0) and indirect contact (separated by 0.45 µm membrane, R1-A for algae, R1-S for sludge) to reveal the role of metabolites especially allelochemicals on interaction of bacteria and algae. Direct contact exhibited better nutrients removal than indirect contact, due to less antibacterial allelochemicals and oxidative stress. Bacterial signaling molecules were not detected. The major algae-derived allelochemicals were 13-Docosenamide, 9-Octadecenamide, n-Hexadecanoic acid, erucic acid, octadecanoic acid, ß-sitosterol, and E,E,Z-1,3,12-Nonadecatriene-5,14-diol. Furthermore, presence of 13-Docosenamide and 9-Octadecenamide was associated with succession of Flavobacterium and suppression of nitrifying bacteria (Nitrosomonas, Ellin6067, and Nitrospira). Direct contact stimulated denitrifying bacteria Saccharimonadales and algae Scenedesmus, whereas indirect contact is friendly to Dechloromonas, Competibacter, nitrifying bacteria, algae Desmodesmus and Dictyosphaerium. This study highlights the essentiality of cell contact of bacteria-algae in establishing synergy, as cell contact mitigates antagonistic effect induced by metabolites.

Comprehensive Analysis of Lutein and Loroxanthin in Scenedesmus obliquus: From Quantification to Isolation.

Carotenoids are hydrophobic pigments produced exclusively by plants, fungi, and specific microbes. Microalgae are well suited for the production of valuable carotenoids due to their rapid growth, efficient isoprenoid production pathway, and ability to store these compounds within their cells. The possible markets for bio-products range from feed additives in aquaculture and agriculture to pharmaceutical uses. The production of carotenoids in microalgae is affected by several environmental conditions, which can be utilized to enhance productivity. The current study focused on optimizing the extraction parameters (time, temperature, and extraction number) to maximize the yield of carotenoids. Additionally, the impact of various nitrogen sources (ammonia, nitrate, nitrite, and urea) on the production of lutein and loroxanthin in Scenedesmus obliquus was examined. To isolate the carotenoids, 0.20 g of biomass was added to 0.20 g of CaCO3 and 10.0 mL of ethanol solution containing 0.01% (w/v) pyrogallol. Subsequently, the extraction was performed using an ultrasonic bath for a duration of 10 min at a temperature of 30 °C. This was followed by a four-hour saponification process using a 10% methanolic KOH solution. The concentration of lutein and loroxanthin was measured using HPLC-DAD at 446 nm, with a flow rate of 1.0 mL/min using a Waters YMC C30 Carotenoid column (4.6 × 250 mm, 5 µm). The confirmation of carotenoids after their isolation using preparative chromatography was achieved using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with an atmospheric pressure chemical ionization (APCI) probe and UV-vis spectroscopy. In summary, S. obliquus shows significant promise for the large-scale extraction of lutein and loroxanthin. The findings of this study provide strong support for the application of this technology to other species.

Chemotactic Interactions of Scenedesmus sp. and Azospirillum brasilense Investigated by Microfluidic Methods.

The use of algae for industrial, biotechnological, and agricultural purposes is spreading globally. Scenedesmus species can play an essential role in the food industry and agriculture due to their favorable nutrient content and plant-stimulating properties. Previous research and the development of Scenedesmus-based foliar fertilizers raised several questions about the effectiveness of large-scale algal cultivation and the potential effects of algae on associative rhizobacteria. In the microbiological practice applied in agriculture, bacteria from the genus Azospirillum are one of the most studied plant growth-promoting, associative, nitrogen-fixing bacteria. Co-cultivation with Azospirillum species may be a new way of optimizing Scenedesmus culturing, but the functioning of the co-culture system still needs to be fully understood. It is known that Azospirillum brasilense can produce indole-3-acetic acid, which could stimulate algae growth as a plant hormone. However, the effect of microalgae on Azospirillum bacteria is unclear. In this study, we investigated the behavior of Azospirillum brasilense bacteria in the vicinity of Scenedesmus sp. or its supernatant using a microfluidic device consisting of physically separated but chemically coupled microchambers. Following the spatial distribution of bacteria within the device, we detected a positive chemotactic response toward the microalgae culture. To identify the metabolites responsible for this behavior, we tested the chemoeffector potential of citric acid and oxaloacetic acid, which, according to our HPLC analysis, were present in the algae supernatant in 0.074 mg/ml and 0.116 mg/ml concentrations, respectively. We found that oxaloacetic acid acts as a chemoattractant for Azospirillum brasilense.

Catalytic flash pyrolysis of Scenedesmus sp. post-extraction residue using low-cost HZSM-5 catalyst with the perspective to produce renewable aromatic hydrocarbons.

Recovering renewable chemicals from de-fatted microalgal residue derived from lipid extraction within the algal-derived biofuel sector is crucial, given the rising significance of microalgal-derived biodiesel as a potential substitute for petroleum-based liquid fuels. As a circular economy strategy, effective valorization of de-fatted biomass significantly improves the energetic and economic facets of establishing a sustainable algal-derived biofuel industry. In this scenario, this study investigates flash catalytic pyrolysis as a sustainable pathway for valorizing Scenedesmus sp. post-extraction residue (SPR), potentially yielding a bio-oil enriched with upgraded characteristics, especially renewable aromatic hydrocarbons. In the scope of this study, volatile products from catalytic and non-catalytic flash pyrolysis were characterized using a micro-furnace type temperature programmable pyrolyzer coupled with gas chromatographic separation and mass spectrometry detection (Py-GC/MS). Flash pyrolysis of SPR resulted in volatile products with elevated oxygen and nitrogen compounds with concentrations of 46.4% and 26.4%, respectively. In contrast, flash pyrolysis of lyophilized microalgal biomass resulted in lower concentrations of these compounds, with 40.9% oxygen and 17.3% nitrogen. Upgrading volatile pyrolysis products from SPR led to volatile products comprised of only hydrocarbons, while completely removing oxygen and nitrogen-containing compounds. This was achieved by utilizing a low-cost HZSM-5 catalyst within a catalytic bed at 500 °C. Catalytic experiments also indicate the potential conversion of SPR into a bio-oil rich in monocyclic aromatic hydrocarbons, primarily BETX, with toluene comprising over one-third of its composition, thus presenting a sustainable pathway for producing an aromatic hydrocarbon-rich bio-oil derived from SPR. Another significant finding was that 97.8% of the hydrocarbon fraction fell within the gasoline range (C5-C12), and 35.5% fell within the jet fuel range (C8-C16). Thus, flash catalytic pyrolysis of SPR exhibits significant promise for application in drop-in biofuel production, including green gasoline and bio-jet fuel, aligning with the principles of the circular economy, green chemistry, and bio-refinery.

Quantitative modelling reservoir microalgae proliferation in response to water-soluble anions and cations influx.

Atmospheric precipitation deposits acid-forming substances into surface water. However, the effects of water-soluble components on microalgae proliferation are poorly understood. This study analysed the growth characteristics of three microalgae bioindicators of water quality: Scenedesmus quadricauda, Chlorella vulgaris, and Scenedesmus obliquus, adopting on-site monitoring, culture experiments simulating 96 types of water by supplementing anions and cations, and predictive modelling. The result quantified pH > 3.0 rain with dominant Ca2+, Mg2+, and K+ cations, together with anions of NO3- and SO42-. The presence of Ca2+ of up to 0.1 mM and Mg2+ concentrations (>0.5 mM) suppressed Scenedesmus quadricauda growth. Soluble ions, luminosity, and pH had significant impacts (p ≤ 0.01) on increased microalgae proliferation. A newly proposed microalgae growth model predicted a 10.7-fold increase in cell density six days post-incubation in the case of rainfall. The modelling supports algal outbreaks and delays prediction during regional water cycles.

Bioremediation potential of the Chlorella and Scenedesmus microalgae in explosives production effluents.

This study explores microalgae-based bioremediation for treating black gunpowder production effluents, an understudied yet environmentally significant stream. Two native microalgae, Chlorella sp. MC18 (CH) and Scenedesmus sp. MJ23-R (SC), were assessed for growth kinetics and nutrient removal capabilities in culture media containing different proportions of untreated raw wastewater. Results show both species thrived in 100 % raw wastewater, displaying robust growth and substantial biomass production in parallelepiped-shaped photobioreactors. SC showed superior performance, with higher maximum specific growth rate (0.549 d-1), biomass yield (454.57 mg L-1) and biomass productivity (64.94 mg L-1 d-1) compared to CH (0.524 d-1, 380.60 mg L-1, 54.37 mg L-1 d-1, respectively). The use of 100 % raw wastewater as a culture medium eliminated the need for additional freshwater input, thus reducing the water footprint. The bioremediation process also resulted in a high removal efficiency in turbidity (>95 % CH, >76 % SC), total suspended solids (>93 % CH, >74 % SC), biochemical oxygen demand (BOD5) (>62 % CH, >93 % SC) and chemical oxygen demand (COD) (>63 % CH, >87 % SC), bringing the effluent into compliance with environmental regulations. Although nitrogen (>45 % CH, >57 % SC) and sulphate (>43 % CH, >35 % SC) removal efficiencies was high, potassium bioremediation was limited (<6 %). The proximate chemical composition of the microalgal biomass revealed different allocations to carbohydrates, lipids and proteins. The results suggest promising applications for biofuel production and aquaculture. This research highlights the potential of microalgae-based bioremediation for sustainable wastewater management in the explosives industry, contributing to the UN Sustainable Development Goals and promoting green industrial practices.

Removal of contaminants of emerging concern from pig manure in different operation stages of a thin-layer cascade photobioreactor. Relationship with concentrations in microalgae and manure.

The performance of a pilot-scale thin-layer cascade photobioreactor, operated in semicontinuous mode, for the removal of veterinary drug residues and other contaminants of emerging concern (CECs) from pig manure has been assessed in six operation stages. Chlorella sp. (70-90%), Scenedesmus sp. (10-25%) and Diatomea (<5%) comprise the microalgae species present during the stages. The global performance to remove the total CEC content in the photobioreactor effluent varied from 62 to 86% on each stage, while an CEC mean amount close to 8% was accumulated in the photobioreactor biomass. A relation with weather conditions was not observed. Elimination ratio was not related to the concentration in the influent which reached up to 8000 ng L-1 for some CECs. As expected, the concentrations of veterinary drugs were higher than those of non-veterinary CECs. The concentrations accumulated in the grown biomass were relative low, lower than 10 ng per fresh g excepting for a few cases. However, statistical data suggested that the linkage of CECs to microalgae biomass boosted their removal from the influent. Furthermore, it was observed that the manure liquid phase contained higher amounts of CECs than the solid phase.

Carbon-negative and high-rate nutrient recovery from municipal wastewater using mixotrophic Scenedesmus acuminatus.

The efficiency of mixotrophic microalgae in enhancing the recovery of waste nutrients has been well established; however, the recovery rate is crucial in meeting the needs of field applications. This study evaluated the impact of media characteristics on nutrient recovery under mixotrophic conditions. The mixotrophic N recovery rate with S. acuminatus in modified BG-11 reached 2.59 mg L-1h-1. A mixotrophic growth optimization strategy was applied to achieve a high-rate nutrient recovery from municipal wastewater treatment plant effluents. The contribution of waste chemical oxygen demand (COD) to nutrient recovery was assessed using secondary effluent (SE) under heterotrophy. The results highlighted a significant increase in total nitrogen (TN) and total phosphorus (TP) recovery rates when glucose was supplied, indicating the additional carbon requirements for efficient nutrient recovery. The TN and TP recovery rates under mixotrophic conditions with the addition of trace metals and high cell density were enhanced by 91.94% and 92.53%, respectively, resulting in recovery rates of 3.43 mg L-1h-1 and 0.30 mg L-1h-1. The same conditions were used for nutrient recovery from primary effluent (PE), and the results were more satisfactory as the TN and TP recovery rates reached 4.79 and 0.55 mg L-1h-1, respectively. Additionally, the study estimated the carbon footprints (C-footprints) and areal footprints of mixotrophy-based nitrogen recovery. The findings revealed carbon footprints and areal footprints of -15.93 ± 4.57 tCO2e t-1 N recovery and 0.53 ± 0.19 m3 m-2d-1 wastewater, respectively. This high-rate nutrient recovery, achieved under a carbon-negative (C-negative) budget through mixotrophy, presents a novel strategy for efficiently recovering resources from municipal wastewater, thus facilitating resource recycling and ensuring environmental sustainability.

Growth of Scenedesmus obliquus in anaerobically digested swine wastewater from different cleaning processes for pollutants removal and biomass production.

Anaerobically digested swine wastewater (ASW) purification by microalgae provides a promising strategy for nutrients recovery, biomass production and CO2 capture. However, the characteristics of ASW from different cleaning processes vary greatly. At present, the cultivation of microalgae in ASW from different manure cleaning processes is rarely investigated and compared. That may bring uncertainty for microalgae growth using different ASW in large-scale application. Thus, the ASW from three cleaning processes were tested for cultivating microalgae, including manure dry collection (I), water flushing (II) and water submerging processes (III). The characteristics of ASW from three manure cleaning processes varied greatly such as nutrient and heavy metals levels. High concentration of ammonia and copper in ASW significantly inhibited microalgae growth. Fortunately, the supply of high CO2 (10%) effectively alleviated negative influences, ensuring microalgal growth at low dilution ratio. The characteristics of three ASW resulted in significant differences in microalgae growth and biomass components. The maximal biomass production in optimal diluted ASW-I, II and III reached 1.46 g L-1, 2.19 g L-1 and 2.47 g L-1, respectively. The removal of organic compounds, ammonia and phosphorus by optimal microalgae growth in diluted ASW-I, II and III was 50.6%/94.2%/64.7%, 63.7%/82.3%/57.6% and 83.2%/91.7%/59.7%, respectively. The culture in diluted ASW-I, II and III obtained the highest lipids production of 12.1 mg L-1·d-1, 16.5 mg L-1·d-1 and 19.4 mg L-1·d-1, respectively. The analysis of lipids compositions revealed that the proportion of saturated fatty acids accounted for 36.4%, 32.4% and 27.9 % in optimal diluted ASW-I, II and III, as ideal raw materials for biodiesel production.

Effects of biochar on the manganese enrichment and oxidation by a microalga Scenedesmus quadricauda in the aquatic environment.

Microalgae play a significant impact in the biogeochemical cycle of Mn(II) in the aquatic ecosystem. Meanwhile, the inflow of biochar into the water bodies is bound to impact the aquatic organisms. However, the influence of biochar on the manganese transformation in algae-rich water has not drawn much attention. Thus, we studied the effects of rice straw biochar on manganese enrichment and oxidation by a common type of algae in freshwater (Scenedesmus quadricauda). The results showed that Mn(II) was absorbed intracellularly and adsorbed extracellularly by active algal cells. A significant portion of enriched Mn(II) was oxidized to amorphous precipitates MnO2, MnOOH, and Mn2O3. Moreover, the extracellular bound Mn(II) content in the coexistent system of algae and biochar increased compared with the pure Scenedesmus quadricauda system. Nevertheless, the intracellular Mn content was continually lowered as the biochar dose rose from an initial 0.2 to 2.0 g·L-1, suggesting that Mn assimilation of the cell was suppressed. It was calculated that the total enrichment ability of Scenedesmus quadricauda in the algae-biochar coexistent system was 0.31- 15.32 mg Mn/g biomass, more than that in the pure algae system. More importantly, with biochar in the algae system, the amount of generated MnOx increased, and more Mn(II) was oxidized into highly-charged Mn(IV). This was probably because the biochar could relieve the stress of massive Mn(II) on algae and support the MnOx precipitates. In brief, moderate biochar promoted the Mn(II) accumulation by algal cells and its oxidation activity. This study offers deeper insight into the bioconversion of Mn(II) by algae and the potential impact of biochar application to the aquatic system.

Synthesizing cationic polymers and tuning their properties for microalgae harvesting.

This study reports a facile technique to synthesize and tune the cationic polymer, poly(3-acrylamidopropyl)trimethylammonium chloride (PAPTAC), in terms of molecular weight and surface change for harvesting three microalgae species (Scenedesmus sp., P.purpureum, and C. vulgaris). The PAPTAC polymer was synthesised by UV-induced free-radical polymerisation. Polymer tuning was demonstrated by regulating the monomer concentration (60 to 360 mg/mL) and UV power (36 and 60 W) for polymerisation. The obtained PAPTAC polymer was evaluated for harvesting three different microalgae species and compared to a commercially available polymer. The highest flocculation efficiency for Scenedesmus sp. and P. purpureum was observed at a dosage of 25 mg-polymer/g of dry biomass by using PAPTAC-90, resulting in higher flocculation efficiency than the commercial polymer. Results in this study show evidence of effective neutralisation of the negative charge surface of microalgae cells by the produced cationic PAPTAC polymer and polymer bridging for effective flocculation. The obtained PAPTAC polymer was less effective for harvesting C. vulgaris, possibly due to other factors such as cell morphology and composition of extracellular polymeric substances of at the cell membrane that may also influence harvesting performance.

Effect of ultra-violet light radiation on Scenedesmus vacuolatus growth kinetics, metabolic performance, and preliminary biodegradation study.

This study presents the effect of ultra-violet (UV) light radiation on the process kinetics, metabolic performance, and biodegradation capability of Scenedesmus vacuolatus. The impact of the UV radiation on S. vacuolatus morphology, chlorophyll, carotenoid, carbohydrates, proteins, lipid accumulation, growth rate, substrate affinity and substrate versatility were evaluated. Thereafter, a preliminary biodegradative potential of UV-exposed S. vacuolatus on spent coolant waste (SCW) was carried out based on dehydrogenase activity (DHA) and total petroleum hydrocarbon degradation (TPH). Pronounced structural changes were observed in S. vacuolatus exposed to UV radiation for 24 h compared to the 2, 4, 6, 12 and 48 h UV exposure. Exposure of S. vacuolatus to UV radiation improved cellular chlorophyll (chla = 1.89-fold, chlb = 2.02-fold), carotenoid (1.24-fold), carbohydrates (4.62-fold), proteins (1.44-fold) and lipid accumulations (1.40-fold). In addition, the 24 h UV exposed S. vacuolatus showed a significant increase in substrate affinity (1/Ks) (0.959), specific growth rate (µ) (0.024 h-1) and biomass accumulation (0.513 g/L) by 1.50, 2 and 1.9-fold respectively. Moreover, enhanced DHA (55%) and TPH (100%) degradation efficiency were observed in UV-exposed S. vacuolatus. These findings provided major insights into the use of UV radiation to enhance S. vacuolatus biodegradative performance towards sustainable green environment negating the use of expensive chemicals and other unfriendly environmental practices.

Polystyrene nanoplastics alter the ecotoxicological effects of diclofenac on freshwater microalgae Scenedesmus obliquus.

Due to the escalating risk of plastic pollution, nanoplastics have attracted considerable attention in the recent past. They can co-exist and interact with other contaminants like pharmaceuticals in the aquatic environment. Therefore, it is pertinent to understand how these pollutants interact with one another in the ecosystem. The current study examined the individual and combined effects of fluorescent polystyrene nanoplastics (FNPs) and diclofenac (DCF) on Scenedesmus obliquus using a full factorial design. The toxicity of S. obliquus significantly increased in a dose-dependent manner upon exposure to pristine forms of DCF and FNPs. The major cause of individual toxicity of DCF and FNPs in S. obliquus was oxidative stress. In the combined toxicity tests when FNPs (0.01, 0.1, and 1 mg L-1) and DCF (1 mg L-1) were mixed, a synergistic effect was noted compared to the respective pristine FNPs. However, when the DCF concentration in the mixture was decreased to 0.25 mg L-1, the combined toxicity with FNPs (0.01, 0.1, and 1 mg L-1) reduced indicating an antagonistic effect. The independent action model also showed an antagonistic effect for low-dose combinations of DCF and a synergistic effect for high-dose combinations. The estimation of oxidative stress parameters, antioxidant enzyme activity, and photosynthetic pigment content in the algae further validated the cytotoxicity data. The mean hydrodynamic diameter and surface charge analyses further indicated that the colloidal stability of the FNPs in the medium was affected when they were combined with DCF. The key reason for differences in the cytotoxicity of combinations could be observed variations in the aggregation of FNPs and differential adsorption patterns of DCF on the FNPs. These factors efficiently altered cell-particle interactions in the mixture demonstrating a hormesis effect. Thus, this current study highlighted the hazardous nature of the nanoplastics and their co-exposure risks with pharmaceuticals on microalgae in freshwater environments.

Toxicity of tigecycline on the freshwater microalga Scenedesmus obliquus: Photosynthetic and transcriptional responses.

Tigecycline (TGC) is a new tetracycline antibiotic medication against multidrug-resistant bacteria. However, the toxicity of TGC to microalgae remains largely unknown. In this study, the toxicity of TGC on Scenedesmus obliquus was examined, focusing on changes in algal growth, photosynthetic activity, and transcriptome. According to an acute toxicity test, the IC10 and IC50 values were 0.72 mg/L and 4.15 mg/L, respectively. Analyses of photosynthetic efficiency and related parameters, such as light absorption, energy capture, and electron transport, identified a 35% perturbation in the IC50 group, while the IC10 group remained largely unaffected. Transcriptomic analysis showed that in the IC10 and IC50 treatment groups, there were 874 differentially expressed genes (DEGs) (220 upregulated and 654 downregulated) and 4289 DEGs (2660 upregulated and 1629 downregulated), respectively. Gene Ontology enrichment analysis showed that TGC treatment markedly affected photosynthesis, electron transport, and chloroplast functions. In the IC50 group, a clear upregulation of genes related to photosynthesis and chloroplast functions was observed, which could be an adaptive stress response. In the IC10 group, significant downregulation of DEGs involved in ribosomal pathways and peptide biosynthesis processes was observed. Kyoto Encyclopedia of Gene and Genomes enrichment analysis showed that treatment with TGC also disrupted energy production, protein synthesis, and metabolic processes in S. obliquus. Significant downregulation of key proteins related to Photosystem II was observed under the IC10 TGC treatment. Conversely, IC50 TGC treatment resulted in substantial upregulation across a broad array of photosystem-related proteins from both Photosystems II and I. IC10 and IC50 TGC treatments differentially influenced proteins involved in the photosynthetic electron transport process. This study emphasizes the potential risks of TGC pollution to microalgae, which contributes to a better understanding of the effects of antibiotic contamination in aquatic ecosystems.

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

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

Eco-friendly cultivation of microalgae using a horizontal twin layer system for treatment of real solid waste leachate.

Solid waste leachate (SWL) requires dilution with water to offset the negative effects of high nutrient concentration and organic compounds for its microalgae-based treatment. Among attached cultivation systems, twin layer is a technology in which limited information is available on treatment of high strength wastewater using microalgae. Moreover, widespread application of twin layer technology is limited due to cost of substrate and source layer used. In the present study, potential of Scenedesmus sp. for the treatment of SWL was assessed on horizontal twin layer system (HTLS). Novel and cost-effective substrate layers were tested as attachment material. Wetland treated municipal wastewater (WMW) was used to prepare SWL dilutions viz, 5%, 10%, 15%, 20% and 25% SWL. Recycled printing paper showed maximum biomass productivity of 5.19 g m-2 d-1. Among all the SWL dilutions, Scenedesmus sp. achieved maximum growth of 103.05 g m-2 in 5% SWL which was 16% higher than WMW alone. The maximum removal rate of NH4+ -N, TKN, and PO43- P was obtained in 20% SWL which was 1371, 1588 and 153 mg m-2 d-1 respectively. Varying concentrations of nutrients in different SWL dilutions significantly affected lipid biosynthesis, with enhanced productivity of 2.28 g m-2 d-1 achieved in 5% SWL compared to 0.97 g m-2 d-1 in 20% SWL. Hence, it can be concluded that 5% SWL dilution was good for biomass and lipid production, while the highest nutrient removal rates were obtained at 20% SWL mainly attributed to biotic and abiotic processes. Based on these results HTLS can be a promising technology for pilot scale to explore industrialized application of wastewater treatment and algal production.

Processing and characterization of antimicrobial bioplastic films based on green microalgae Scenedesmus obliquus extract-loaded polyurethane.

The green microalga Scenedesmus obliquus, isolated from the Egyptian environment, was used for the synthesis of bio-based plastic materials. Polyurethane (PU) was blended with different proportions (0%, 10%, 20%, and 40%) of chloroform extract to form bioplastic films. The bioplastic films were characterized using water vapor transmission rate measurements and scanning electron microscopy (SEM). The WVTR of pure PU was 193.37 g/m2. day, while the values of algae/PU films were 129.74, 122.56, and 99.75 g/m2.day. S. obliquus reported having Palmitic, which possesses antimicrobial activity and acts as an effective antimicrobial agent in the synthesized bioplastic films. Antimicrobial activity of the algal extract and the synthesized bioplastic films were tested against two Gram-positive bacteria; Staphylococcus aureus, Enterococcus faecalis, two Gram-negative bacteria; Escherichia coli, Pseudomonas aeruginosa, and Candida albicans as a model for fungi. The results indicated that S. obliquus extract exhibited a clear antimicrobial activity against all tested microbes. The antimicrobial rate of bioplastic films containing 40% of the extract reached 100% after 2 h of contact with E. coli and E. faecalis. In conclusion, this study offers a promising future for the use of biodegradable antimicrobial bioplastic films as an affordable and environmentally friendly alternative to plastics in many applications.