Microstructure and antioxidative capacity of the microalgae mutant Chlorella PY-ZU1 during tilmicosin removal from wastewater under 15% CO2

Release kinetic study of microplastics from N95 face masks and consequent effects on freshwater alga Scenedesmus obliquus

The uncontrolled disposal of N95 face masks, widely used during the recent COVID-19 pandemic can release significant amounts of microplastics and other additives into aquatic bodies. This study aimed to: (i) to quantify and analyze the released microplastics and heavy metals from N95 face masks weathered for various time periods (24, 48, 72, 96, 120, and 144 h) and (ii) to assess the cytotoxicity potential of the leachates on a model organism, freshwater alga Scenedesmus obliquus. The mask leachates contained microplastics, polypropylene in different shapes and sizes, and heavy metals like Cu, Cd, and Zn. The leachates significantly reduced cell viability and increased reactive oxygen species (ROS) generation, antioxidant enzyme activity, and membrane damage. The effects were also accompanied by a significant drop in the photosynthetic yield. All of the examined parameters indicated a dose-response relationship, with longer leaching periods resulting in higher microplastic concentrations. Mask leachates severely damaged the structural integrity of the algal cells, as seen in scanning electron microscopy images. The findings of our study confirm that the releases from disposable N95 face masks pose a severe threat to freshwater microalgae, and the cascading effects would harm the aquatic ecosystems.

Recovery mechanism of a microalgal species, Chlorella sp. from toxicity of doxylamine: Physiological and biochemical changes, and transcriptomics

Ubiquitous distribution of pharmaceutical contaminants in environment has caused unexpected adverse effects on ecological organisms; however, how microorganisms recover from their toxicities remains largely unknown. In this study, we comprehensively investigated the effect of a representative pollutant, doxylamine (DOX) on a freshwater microalgal species, Chlorella sp. by analyzing the growth patterns, biochemical changes (total chlorophyll, carotenoid, carbohydrate, protein, and antioxidant enzymes), and transcriptomics. We found toxicity of DOX on Chlorella sp. was mainly caused by disrupting synthesis of ribosomes in nucleolus, and r/t RNA binding and processing. Intriguingly, additional bicarbonate enhanced the toxicity of DOX with decreasing the half-maximum effective concentrations from 15.34 mg L-1 to 4.63 mg L-1, which can be caused by inhibiting fatty acid oxidation and amino acid metabolism. Microalgal cells can recover from this stress via upregulating antioxidant enzymatic activities to neutralize oxidative stresses, and photosynthetic pathways and nitrogen metabolism to supply more energies and cellular signaling molecules. This study extended our understanding on how microalgae can recover from chemical toxicity, and also emphasized the effect of environmental factors on the toxicity of these contaminants on aquatic microorganisms.

Glutamicibacter nicotianae AT6: A new strain for the efficient biodegradation of tilmicosin

The degradation of tilmicosin (TLM), a semi-synthetic 16-membered macrolide antibiotic, has been receiving increasing attention. Conventionally, there are three tilmicosin degradation methods, and among them microbial degradation is considered the best due to its high efficiency, eco-friendliness, and low cost. Coincidently, we found a new strain, Glutamicibacter nicotianae sp. AT6, capable of degrading high-concentration TLM at 100 mg/L with a 97% removal efficiency. The role of tryptone was as well investigated, and the results revealed that the loading of tryptone had a significant influence on TLM removals. The toxicity assessment indicated that strain AT6 could efficiently convert TLM into less-toxic substances. Based on the identified intermediates, the degradation of TLM by AT6 processing through two distinct pathways was then proposed.

Assessing the role of the graphene family nanomaterials (GFNs: Graphene, GO, rGO) in modifying the toxicity potential and environmental risk of flame retardant, tetrabromobisphenol-A (TBBPA) in the marine microalgae Chlorella sp

In recent years, a growing concern has emerged regarding the environmental implications of flame retardants (FRs) like tetrabromobisphenol-A (TBBPA) and graphene family nanomaterials (GFNs), such as graphene, graphene oxide (GO), and reduced graphene oxide (rGO), on marine biota. Despite these substances' well-established individual toxicity profiles, there is a notable gap in understanding the physicochemical interactions within the binary mixtures and consequent changes in the toxicity potential. Therefore, our research focuses on elucidating the individual and combined toxicological impacts of TBBPA and GFNs on the marine alga Chlorella sp. Employing a suite of experimental methodologies, including Raman spectroscopy, contact angle measurements, electron microscopy, and chromatography, we examined the physicochemical interplay between the GFNs and TBBPA. The toxicity potentials of individual constituents and their binary combinations were assessed through growth inhibition assays, quantifying reactive oxygen species (ROS) generation and malondialdehyde (MDA) production, photosynthetic activity analyses, and various biochemical assays. The toxicity of TBBPA and graphene-based nanomaterials (GFNs) was examined individually and in combinations. Both pristine TBBPA and GFNs showed dose-dependent toxicity. While lower TBBPA concentrations exacerbated toxicity in binary mixtures, higher TBBPA levels reduced the toxic effects compared to pristine TBBPA treatments. The principal mechanism underlying toxicity was ROS generation, resulting in membrane damage and perturbation of photosynthetic parameters. Cluster heatmap and Pearson correlation were employed to assess correlations between the biological parameters. Finally, ecological risk assessment was undertaken to evaluate environmental impacts of the individual components and the mixture in the algae.

The aging of microplastics exacerbates the damage to photosynthetic performance and bioenergy production in microalgae (Chlorella pyrenoidosa)

The toxicity of microplastics (MPs) on freshwater plants has been widely studied, yet the influence of aged MPs remains largely unexplored. Herein, we investigated the influence of polyvinyl chloride (PVC) MPs, both before and after aging, at different environmentally relevant concentrations on Chlorella pyrenoidosa, a freshwater microalgae species widely recognized as a valuable biomass resource. During a 96-h period, both virgin and aged MPs hindered the growth of C. pyrenoidosa. The maximum growth inhibition rates were 32.40 % for virgin PVC at 250 mg/L and 44.72 % for aged PVC at 100 mg/L, respectively. Microalgae intracellular materials, i.e., protein and carbohydrate contents, consistently decreased after MP exposure, with more pronounced inhibition observed with aged PVC. Meanwhile, the MP aging significantly promoted the nitrogen uptake of C. pyrenoidosa, i.e., 1693.45 ± 42.29 mg/L (p < 0.01), contributing to the production of humic acid-like substances. Additionally, aged PVC induced lower chlorophyll a and Fv/Fm when compared to virgin PVC, suggesting a more serious inhibition of the photosynthesis process of microalgae. The toxicity of MPs to C. pyrenoidosa was strongly associated with intercellular oxidative stress levels. The results indicate that MP aging exacerbates the damage to photosynthetic performance and bioenergy production in microalgae, providing critical insights into the toxicity analysis of micro(nano)plastics on freshwater plants.

Alleviating binary toxicity of polystyrene nanoplastics and atrazine to Chlorella vulgaris through humic acid interaction: Long-term toxicity using environmentally relevant concentrations

In this study, microalgae Chlorella vulgaris (C. vulgaris) were simultaneously exposed to environmental concentrations of amino-functionalized polystyrene nanoplastics (PS-NH2; 0.05, 0.1, 0.2, 0.3 and 0.4 mg/L) and the world's second most used pesticide, the herbicide atrazine (ATZ; 10 μg/L), in the absence and presence of humic acid (HA; 1 mg/L) for 21 days. Due to the low concentrations of PS-NH2, the majority of them could not cause a significant difference in the end-points of biomass, chlorophylls a and b, total antioxidant, total protein, and superoxide dismutase and malondialdehyde compared to the control group (p > 0.05). On the other hand, by adding ATZ to the PS-NH2, all the mentioned end-point values showed a considerable difference from the control (p < 0.05). The exposure of PS-NH2+ATZ treatments to the HA could remarkably reduce their toxicity, additionally, HA was able to decrease the changes in the expression of genes related to oxidative stress (e.g., superoxide dismutase, glutathione reductase, and catalase) in the C. vulgaris in the most toxic treatment group (e.g., PS-NH2+ATZ). The synergistic toxicity of the PS-NH2+ATZ group could be due to their enhanced bioavailability for algal cells. Nevertheless, the toxicity alleviation in the PS-NH2+ATZ treatment group after the addition of HA could be due to the eco-corona formation, and changes in their zeta potential from positive to negative value, which would increase their electrostatic repulsion with the C. vulgaris cells, in such a way that HA also caused a decrease in the formation of C. vulgaris-NPs hetero-aggregates. This research underscores the complex interplay between PS-NH2, ATZ, and HA in aquatic environments and their collective impact on microalgal communities.

Presence of humic acid in the environment holds promise as a potential mitigating factor for the joint toxicity of polystyrene nanoplastics and herbicide atrazine to Chlorella vulgaris: 96-H acute toxicity

Increasing amounts of amino-functionalized polystyrene nanoplastics (PS-NH2) are entering aquatic ecosystems, raising concerns. Hence, this study investigated 96-h acute toxicity of PS-NH2 and its combination with the pesticide atrazine (ATZ) in the absence/presence of humic acid (HA) on the microalgae Chlorella vulgaris (C. vulgaris). Results showed that both PS-NH2 and PS-NH2+ATZ reduced algal growth, photosynthetic pigments, protein content, and antioxidant capacity, while increasing enzymatic activities. Gene expression related to oxidative stress was altered in C. vulgaris exposed to these treatments. Morphological and intracellular changes were also observed. The combined toxicity of PS-NH2+ATZ demonstrated a synergistic effect, but the addition of environmentally relevant concentration of HA significantly alleviated its toxicity to C. vulgaris, indicating an antagonistic effect due to the emergence of an eco-corona, and entrapment and sedimentation of PS-NH2+ATZ particles by HA. This study firstly highlights the role of HA in mitigating the toxicity of PS-NH2 when combined with other harmful compounds, enhancing our understanding of HA's presence in the environment.

Bioadsorption, bioaccumulation and biodegradation of antibiotics by algae and their association with algal physiological state and antibiotic physicochemical properties

Bioadsorption, bioaccumulation and biodegradation processes in algae, play an important role in the biomagnification of antibiotics, or other organic pollutants, in aquatic food chains. In this study, the bioadsorption, bioaccumulation and biodegradation of norfloxacin [NFX], sulfamethazine [SMZ] and roxithromycin [RTM]) is investigated using a series of culture experiments. Chlorella vulgaris was exposed to these antibiotics with incubation periods of 24, 72, 120 and 168 h. Results show the bioadsorption concentration of antibiotics in extracellular matter increases with increasing alkaline phosphatase activity (AKP/ALP). The bioaccumulation concentrations of NFX, SMZ and RTM within cells significantly increase after early exposure, and subsequently decrease. There is a significant positive antibiotics correlation to superoxide dismutase (SOD), the photosynthetic electron transport rate (ETR) and maximum fluorescence after dark adaptation (Fv/Fm), while showing a negative correlation to malondialdehyde (MDA). The biodegradation percentages (Pb) of NFX, SMZ and RTM range from 39.3 - 97.2, 41.3 - 90.5, and 9.3 - 99.9, respectively, and significantly increase with increasing Fv/Fm, density and chlorophyll-a. The accumulation of antibiotics in extracellular and intracellular substances of C. vulgaris is affected by antibiotic biodegradation processes associated with cell physiological state. The results succinctly explain relationships between algal growth during antibiotics exposure and the bioadsorption and bioaccumulation of these antibiotics in cell walls and cell matter. The findings draw an insightful understanding of the accumulation of antibiotics in algae and provide a scientific basis for the better utilization of algae treatment technology in antibiotic contaminated wastewaters. Under low dose exposures, the biomagnification of antibiotics in algae is affected by bioadsorption, bioaccumulation and biodegradation.

Effects of micro-sized biodegradable plastics on Microcystis aeruginosa

Plethora of plastics are being used in current society, generating huge amounts of plastic waste. Non-biodegradability of conventional plastics is one of the main challenges to treat plastic waste. In an effort to increase the efficiency of plastic waste treatment, biodegradable plastics have gained attention. Although the use of biodegradable plastics has been increased, their potential effects on the environments are not fully elucidated yet. In this study, the impacts of micro-sized non-biodegradable plastic (i.e., polystyrene (PS)) and micro-sized biodegradable plastics (i.e., polycaprolactone (PCL) and polylactic acid (PLA)) on Microcystis aeruginosa were investigated. Regardless of microplastic (MP) types, MP treatments inhibited the growth of M. aeruginosa at the beginning (4 days) while significant dose-dependent effect was not observed in the range of 0.1 to 10 mg/L. However, after long-term exposure (12 days), micro-sized biodegradable plastics stimulated the growth of M. aeruginosa (up to 73 % increase compared to the control). The photosynthetic activity showed a similar trend to the cell growth. The MP treatments induced the production of extracellular polymeric substances (EPS). Indeed, micro-sized PCL and PLA stimulated the production of protein compounds in EPS. These might have affected the releases of chemicals from PCL and PLA, suggesting that the chemicals in biodegradable plastic leachates would promote the growth of M. aeruginosa in long-term exposure. The MP treatments also induced cyanotoxin (microcystin-LR) productions. Our results give a new insight into the cyanobacterial blooming and suggest a novel relationship between harmful algal blooms (HABs) and biodegradable plastics.

Research advances on impacts micro/nanoplastics and their carried pollutants on algae in aquatic ecosystems: A review

The widespread presence of micro/nanoplastics in aquatic ecosystems has certainly affected ecosystem functions and food chains/webs. The impact is worsened by the accumulation of different pollutants and microorganisms on the surface of microplastics. At the tissue, cellular, and molecular levels, micro/nanoplastics and the contaminants they carry can cause damage to aquatic organisms. Problematically, the toxic mechanism of micro/nanoplastics and contaminants on aquatic organisms is still not fully understood. Algae are key organisms in the aquatic ecosystem, serving as primary producers. The investigation of the toxic effects and mechanisms of micro/nanoparticles and pollutants on algae can contribute to understanding the impact on the aquatic ecosystem. Micro/nanoplastics inhibit algal growth, reduce chlorophyll and photosynthesis, induce ultrastructural changes, and affect gene expression in algae. The effects of energy flow can alter the productivity of aquatic organisms. The type, particle size, and concentration of micro/nanoparticles can influence their toxic effects on algae. Although there has been some research on the toxic effects of algae, the limited information has led to a significant lack of understanding of the underlying mechanisms. This paper provides a comprehensive review of the interactions between micro/nanoplastics, pollutants, and algae. The effects of various factors on algal toxicity are also analyzed. In addition, this article discusses the combined effects of microplastics, global warming, and oil pollution on algae and aquatic ecosystems in the context of global change. This research is of great importance for predicting future environmental changes. This review offers a more comprehensive understanding of the interactions between microplastics/nanoplastics and algae, as well as their impact on the carbon cycle.

An integrated approach for the phycoremediation of Pb(II) and the production of biofertilizer using nitrogen-fixing cyanobacteria

In recent years, growing attention has been directed toward the phycoremediation of heavy metals from bodies of water; however, many challenges remain. The nitrogen requirements for algal growth in nutrient-poor waters can lead to substantial costs. Moreover, proper management of the metal-loaded biomass is a concern. This study assessed the performance of two nitrogen-fixing cyanobacteria, Anabaena sp. and Nostoc muscorum, in treating Pb(II)-contaminated water without nitrogen under batch and fed-batch modes, as well as the subsequent utilization of the produced biomass as a biofertilizer. After 12 days of the batch mode with initial Pb(II) concentrations of 10, 20, 35, and 60 mg/L, Pb(II) removal efficiencies were 98.90%, 98.95%, 97.20%, and 84.98% by Anabaena sp. and 88.00%, 73.10%, 54.54%, and 26.83% by N. muscorum, respectively. Anabaena sp. sustained growth and Pb(II) removal under the fed-batch mode by adjusting hydraulic retention time based on the influent Pb(II) concentration. Decontamination of the metal-loaded Anabaena sp. biomass was performed and resulted in a Pb(II) desorption of 93%. The desorbed Anabaena sp. extract provided the nutrient requirements for Chlorella vulgaris. The proposed strategy provides simultaneous Pb(II) bioremediation and biofertilizer production in a system driven by light energy, atmospheric N₂, and CO₂.

How do freshwater microalgae and cyanobacteria respond to antibiotics?

Antibiotic pollution is an emerging environmental challenge. Residual antibiotics from various sources, including municipal and industrial wastewater, sewage discharges, and agricultural runoff, are continuously released into freshwater environments, turning them into reservoirs that contribute to the development and spread of antibiotic resistance. Thus, it is essential to understand the impacts of antibiotic residues on aquatic organisms, especially microalgae and cyanobacteria, due to their crucial roles as primary producers in the ecosystem. This review summarizes the effects of antibiotics on major biological processes in freshwater microalgae and cyanobacteria, including photosynthesis, oxidative stress, and the metabolism of macromolecules. Their adaptive mechanisms to antibiotics exposure, such as biodegradation, bioadsorption, and bioaccumulation, are also discussed. Moreover, this review highlights the important factors affecting the antibiotic removal pathways by these organisms, which will promote the use of microalgae-based technology for the removal of antibiotics. Finally, we offer some perspectives on the opportunities for further studies and applications.

Production and use of Scenedesmus acuminatus biomass in synthetic municipal wastewater for integrated biorefineries

Bioethanol production from algal biomass is a promising alternative for sustainable biofuel production. Algae possess a high photosynthetic capacity and an adaptive ability to thrive under harsh environmental conditions. The potential properties of Scenedesmus acuminatus CCALA 436 were assessed in this research for its bioethanol efficiency, and the effects of growing the algae in wastewater and at different concentrations of mepiquat chloride were studied. Also, pre-treatment efficiencies of different concentrations of calcium oxide were carried out on microalgae biomass. Superoxide dismutase, catalase activity, glutathione, and malondialdehyde contents of microalgae were examined, and the changes in chlorophyll, photoprotective carotenoid contents, and protein concentrations were determined. The results revealed that the maximum sugar and ethanol contents of Scenedesmus acuminatus CCALA 436 were 44.7 ± 1.5% and 20.32 g/L, respectively, for 50% wastewater and mepiquat chloride (2.5 mg/L) after pre-treatment with calcium oxide (0.08%). Additionally, the levels of oxidative enzymes varied depending on the wastewater concentrations. These findings indicate Scenedesmus acuminatus CCALA 436 grown in wastewater and mepiquat chloride can be used for the treatment of wastewater and the production of ethanol and high-value products such as carotenoid.

Toxic responses of freshwater microalgae Chlorella sorokiniana due to exposure of flame retardants

Flame retardants, such as Tetrabromobisphenol A (TBBPA), Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and tributyl phosphate (TBP), are frequently detected in surface water. However, the effects of FRs exposure on aquatic organisms especially freshwater microalgae are still unclear. In this study, the toxicities of TBBPA, TDCPP and TBP to microalgae Chlorella sorokiniana, in terms of growth inhibition, photosynthetic activity inhibition and oxidative damage, were investigated, and according ecological risks were assessed. The results showed that TBBPA, TDCPP and TBP had inhibitory effects on C. sorokiniana, with 96 h EC₅₀ (concentration for 50% of maximal effect) values of 7.606, 41.794 and 49.996 mg/L, respectively. Fv/Fm decreased as the increase of exposure time under 15 mg/L TBBPA. Under 50 mg/L TDCPP and 80 mg/L TBP exposure, Fv/Fm decreased significantly after 24 h. However, Fv/Fm rose after 96 h, indicating that the damaged photosynthetic activity was reversible. The content of chlorophyll a decreased, as the increase of TBBPA concentration from 3 to 15 mg/L. However, chlorophyll a increased first and then decreased, as the increase of TDCPP and TBP concentrations from 0 to 50 mg/L and 0-80 mg/L, respectively. Results indicated that C. sorokiniana could use the phosphorus of TDCPP and TBP to ensure the production of chlorophyll a. The risen content of reactive oxygen species, malondialdehyde as well as superoxide dismutase activity indicated that exposure to FRs induced oxidative stress. Additionally, the risk quotients showed that tested FRs had ecological risks in natural waters or wastewaters. This study provides insights into the toxicological mechanisms of different FRs toward freshwater microalgae for better understanding of according environmental risks.

Effects of Tetracycline on Scenedesmus obliquus Microalgae Photosynthetic Processes

Tetracycline (TC) antibiotics can be detected worldwide in the aquatic environment due to their extensive use and low utilization efficiency, and they may affect the physiological processes of non-target organisms. In this study, the acute and sub-acute toxicities of TC on the freshwater microalga Scenedesmus obliquus were investigated with an emphasis on algal photosynthesis and transcription alterations during an 8 d TC exposure. The results showed that the IC₁₀, IC₃₀ and IC₅₀ values were 1.8, 4.1 and 6.9 mg/L, respectively. During sub-acute exposure, the microalgae of the IC₁₀ treatment was able to recover comparable growth to that of the control by day 7, while significantly lower cell densities were observed in the IC₃₀ and IC₅₀ treatments at the end of the exposure. The photosynthetic efficiency F_v/F_M of S. obliquus first decreased as the TC concentration increased and then returned to a level close to that of the control on day 8, accompanied by an increase in photosynthetic activities, including light harvesting, electron transport and energy dissipation. Transcriptomic analysis of the IC₁₀ treatment (1.8 mg/L TC) revealed that 2157 differentially expressed genes were up-regulated and 1629 were down-regulated compared with the control. KEGG and GO enrichments demonstrated that 28 photosynthesis-related genes involving light-harvesting chlorophyll protein complex, photosystem I, photosystem II, photosynthetic electron transport and enzymes were up-regulated, which may be the factor responsible for the enhanced photosynthesis and recovery of the microalgae. Our work may be helpful not only for gaining a better understanding of the environmental risk of TC at concentrations close to the real levels in natural waters, but also for explaining photosynthesis and related gene transcription induced by antibiotics.

Effects of Enrofloxacin on the Epiphytic Algal Communities Growing on the Leaf Surface of Vallisneria natans

Enrofloxacin (ENR) is a member of quinolones, which are extensively used in livestock farming and aquaculture to fight various bacterial diseases, but its residues are partially transferred to surface water and affect the local aquatic ecosystem. There are many studies on the effect of ENR on the growth of a single aquatic species, but few on the level of the aquatic community. Epiphytic algae, which are organisms attached to the surface of submerged plants, play an important role in the absorption of nitrogen and phosphorus in the ecological purification pond which are mainly constructed by submerged plants, and are commonly used in aquaculture effluent treatment. Enrofloxacin (ENR) is frequently detected in aquaculture ponds and possibly discharged into the purification pond, thus imposing stress on the pond ecosystem. Here, we performed a microcosm experiment to evaluate the short-term effects of pulsed ENR in different concentrations on the epiphytic algal communities growing on Vallisneria natans. Our results showed an overall pattern of “low-dose-promotion and high-dose-inhibition”, which means under low and median ENR concentrations, the epiphytic algal biomass was promoted, while under high ENR concentrations, the biomass was inhibited. This pattern was mainly attributed to the high tolerance of filamentous green algae and yellow-green algae to ENR. Very low concentrations of ENR also favored the growth of diatoms and cyanobacteria. These results demonstrate a significant alteration of epiphytic algal communities by ENR and also spark further research on the potential use of filamentous green algae for the removal of ENR in contaminated waters because of its high tolerance.

Physiological and transcriptomic responses of Chlorella sorokiniana to ciprofloxacin reveal molecular mechanisms for antibiotic removal

Microalgae-based technology is an effective and environmentally friendly method for antibiotics-contaminated wastewater treatment. To assess the tolerance and removal ability of Chlorella sorokiniana to ciprofloxacin (CIP), this study comprehensively revealed the responses of C. sorokiniana to CIP exposure and its degradation processes through physiological and transcriptomic analyses. Although the photosynthetic system was inhibited, the growth of C. sorokiniana was not negatively affected by CIP. Dissolved organic matter was analyzed and indicated that humic-like substances were released to alleviate the stress of CIP. In addition, the maximum removal of CIP was 83.3% under 20 mg L-1 CIP exposure. HPLC-MS/MS and RNA-Seq analyses suggested that CIP could be bioaccumulated and biodegraded by C. sorokiniana through the reactions of hydroxylation, demethylation, ring cleavage, oxidation, dehydrogenation, and decarboxylation with the help of intracellular oxidoreductases, especially cytochrome P450. Collectively, this research shows that C. sorokiniana have a great potential for removing CIP from wastewater.

Toxicity, biodegradation of moxifloxacin and gatifloxacin on Chlamydomonas reinhardtii and their metabolic fate

The novel fourth-generation fluoroquinolones (FQs) were developed to improve the antimicrobial activity and their utilization has rapidly increased in recent years. However, knowledge of the ecotoxicity and microalgae-mediated biodegradation of these novel FQs is limited. In this research, the toxic effects of moxifloxacin (MOX) and gatifloxacin (GAT) on Chlamydomonas reinhardtii as well as their biodegradation and metabolic fate were investigated. The results showed that the toxicity of MOX to C. reinhardtii was higher than that of GAT, and increased with culture time. Chlorophyll fluorescence and pigment content analyses suggested that the decrease in photosynthetic efficiency was primarily caused by the inhibition of electron transport after Q_A in PSII complex. These FQs induced oxidative damage in cells, and the antioxidation mechanisms of C. reinhardtii were analyzed. The maximum MOX removal of 77.67% by C. reinhardtii was achieved at 1 mg/L MOX, whereas the maximum GAT removal of 34.04% was attained at 20 mg/L GAT. The different hydrophilicity and lipophilicity of these FQs resulted in distinct findings in biodegradation experiments. Identification of the transformation products suggested that the likely biodegradation pathways of FQs by C. reinhardtii were hydroxylation, demethylation, and ring cleavage.

Trace phenolic acids simultaneously enhance degradation of chlorophenol and biofuel production by Chlorella regularis

Coupling the cultivation of microalgae with wastewater treatment is a promising technology to recover bioresources from wastewater. However, toxic pollutants in wastewater seriously inhibit the growth of microalgae and the removal of pollutants. Phenolic acids are similar to phytohormones, could potentially relieve the toxicity to microalgae and simultaneously promote pollutant degradation and lipid accumulation. Chlorella and 4-chlorophenol (4-CP) were utilized to simulate the toxic wastewater treatment, and the roles of two typical phenolic acids, such as p-hydroxybenzoic acid (p-HBA) and caffeic acid (CA), were explored. The 0.2 μM concentration of p-HBA or CA improved the specific growth rate by 7.6% by enhancing photosynthesis and DNA replication. The oxidative damage caused by 4-CP was reduced by 30.3-49.7% via the synthesis of more antioxidant enzymes and the direct scavenging of free radicals by phenolic acids. Furthermore, the 4-CP removal rate increased by 27.0%, and toxic 4-CP was degraded into non-toxic compounds. The phenolic acids did not change the 4-CP degradation pathway but accelerated its removal and detoxification by enhancing the expression of 4-CP degradation enzymes. Simultaneously, lipid production increased by 20.5-23.1% due to the upregulation of enzymes related to fatty acid and triacylglycerol synthesis. Trace phenolic acids stimulated the mitogen-activated protein kinase signaling cascade and the calcium signaling pathway to regulate the physiology of the microalgae and protect cells from toxic stress. This study provides a promising new strategy for toxic wastewater treatment and bioresource recovery.

Toxicological Effects of Microplastics and Sulfadiazine on the Microalgae Chlamydomonas reinhardtii

Despite the fact that microplastics (MPs) facilitate the adsorption of environmental organic pollutants and influence their toxicity for organisms, more study is needed on the combination of MPs and antibiotics pollutant effects. In this study, polystyrene MPs (1 and 5 μm) and sulfadiazine (SDZ) were examined separately and in combination on freshwater microalga, Chlamydomonas reinhardtii. The results suggest that both the MPs and SDZ alone and in combination inhibited the growth of microalgae with an increasing concentration of MPs and SDZ (5–200 mg l^–1); however, the inhibition rate was reduced by combination. Upon exposure for 7 days, both the MPs and SDZ inhibited algal growth, reduced chlorophyll content, and enhanced superoxide dismutase (SOD) activities, whereas glutathione peroxidase (GSH-Px) activity was elevated only with the exposure of 1 μm MPs. Fluorescence microscopy and scanning electron microscopy also indicated that particle size contributed to the combined toxicity by aggregating MPs with periphery pollutants. Further, the amount of extracellular secretory protein increased in the presence of MPs and SDZ removal ratio decreased when MPs and SDZ coexisted, suggesting that MPs affected SDZ metabolism by microalgae. The particle size of microplastics affected the toxicity of MPs on microalgae and the combined effect of MPs and SDZ could be mitigated by MPs adsorption. These findings provide insight into microalgae responses to the combination of MPs and antibiotics in water ecosystems.

Occurrence of antibiotics in waters, removal by microalgae-based systems, and their toxicological effects: A review

Global antibiotics consumption has been on the rise, leading to increased antibiotics release into the environment, which threatens public health by selecting for antibiotic resistant bacteria and resistance genes, and may endanger the entire ecosystem by impairing primary production. Conventional bacteria-based treatment methods are only moderately effective in antibiotics removal, while abiotic approaches such as advanced oxidation and adsorption are costly and energy/chemical intensive, and may cause secondary pollution. Considered as a promising alternative, microalgae-based technology requires no extra chemical addition, and can realize tremendous CO₂ mitigation accompanying growth related pollutants removal. Previous studies on microalgae-based antibiotics removal, however, focused more on the removal performances than on the removal mechanisms, and few studies have concerned the toxicity of antibiotics to microalgae during the treatment process. Yet understanding the removal mechanisms can be of great help for targeted microalgae-based antibiotics removal performances improvement. Moreover, most of the removal and toxicity studies were carried out using environment-irrelevant high concentrations of antibiotics, leading to reduced guidance for real-world situations. Integrating the two research fields can be helpful for both improving antibiotics removal and avoiding toxicological effects to primary producers by the residual pollutants. This study, therefore, aims to build a link connecting the occurrence of antibiotics in the aquatic environment, the removal of antibiotics by microalgae-based processes, and the toxicity of antibiotics to microalgae. Distribution of various categories of antibiotics in different water environments were summarized, together with the antibiotics removal mechanisms and performances in microalgae-based systems, and the toxicological mechanisms and toxicity of antibiotics to microalgae after either short-term or long-term exposure. Current research gaps and future prospects were also analyzed. The review could provide much valuable information to the related fields, and provoke interesting thoughts on integrating microalgae-based antibiotics removal research and toxicity research on the basis of environmentally relevant concentrations.

Metabolic Mechanism of Sulfadimethoxine Biodegradation by Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025

Antibiotic resistance is one of the most important environmental challenges. Microalgae has been considered as a promising green media for environmental purification. In this work, sulfadimethoxine (SDM) biodegradation potential of Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025 is investigated. Experimental results indicated that the tested freshwater and marine microalgae strains presented stress response to SDM addition. For Chlorella sp. L38, it has a good adaptability to SDM condition via antioxidant enzyme secretion (SOD, MDA, and CAT up to 23.27 U/mg, 21.99 μmol/g, and 0.31 nmol/min/mg) with removal rate around 88%. P. tricornutum MASCC-0025 exhibited 100% removal of 0.5 mg/L SDM. With increasing salinity (adding a certain amount of NaCl) of cultivation media, the removal rate of SDM by microalgae increased. Although its adaptive process was slower than Chlorella sp. L38, the salinity advantage would facilitate enzyme accumulation. It indicated that microalgae could be used to remove SDM from freshwater and marine environment via suitable microalgae strain screening.

Defense pathways of Chlamydomonas reinhardtii under silver nanoparticle stress: Extracellular biosorption, internalization and antioxidant genes

Numerous studies have been investigated the toxic effects of silver nanoparticle (Ag-NPs) on algae; however, little attention has been paid to the defense pathways of algae cells to Ag-NPs. In the study, Chlamydomonas reinhardtii (C. reinhardtii) was selected as a model organism to investigate the defense mechanisms to Ag-NPs exposure. The results showed that exopolysaccharide and protein in bound-extracellular polymeric substances significantly increased under Ag-NPs stress. These metal-binding groups including C-O-C (exopolysaccharide), CH₃/CH₂ (proteins), O-H/N-H (hydroxyl group) and C-H (alkyl groups) played a key role in extracellular biosorption. The internalized or strongly bound Ag (1.90%-17.45% of total contents) was higher than the loosely surface biosorption (0.31%-1.79%). The accumulation of glutathione disulfide (GSSG), together with the decline of reduced glutathione/GSSG (GSH/GSSG) ratio in C. reinhardtii cells, indicated a significant oxidative stress caused by exposure of Ag-NPs. The increasing phytochelatin accompanied with the decreasing GSH level indicated a critical role to intracellular detoxification of Ag. Furthermore, upregulation of antioxidant genes (MSOD, QTOX2, CAT1, GPX2, APX and VTE3) can cope with oxidative stress of Ag-NPs or Ag⁺. The up-regulation of ascorbate peroxidase (APX) and glutathione peroxidase (GPX2) genes and the reduction in GSH contents showed that the toxicity of Ag-NPs could be mediated by an intracellular ascorbate-GSH defense pathway. These findings can provide valuable information on ecotoxicity of Ag-NPs, potential bioremediation and adaptation capabilities of algal cells to Ag-NPs.

Potassium supplement enhanced cadmium removal in a Microcystis aeruginosa photobioreactor: Evidence from actual and simulated wastewater

In this study, a Microcystis aeruginosa-based photobioreactor (M. aeruginosa-based PBR) was developed for the removal of cadmium (Cd²⁺) from diluted actual mine wastewater (DW) and Cd²⁺-contained simulated wastewater (SW), with a uniform Cd²⁺ concentration of 0.5 mg/L. For the DW and SW, both K⁺ -abundant (DWA & SWA) and K⁺-insufficient (DWB & SWB) treatments were conducted. It was found that continuous supplementation of K⁺ benefited Cd²⁺ removal. The Cd²⁺ removal efficiency in SWA reached 70% during the 41 days of operation, which was 20% higher than that in the SWB. The K⁺ addition triggered great higher Cd²⁺ removal efficiency (90%) in the DWA in comparison to the SWA. The Cd²⁺ assimilation by M. aeruginosa and Cd²⁺ retention on M. aeruginosa surface were the primary processes involved in the PBR system. The K⁺ starvation triggered a 45% and 43% loss of M. aeruginosa biomass in the DWA and the DWB, respectively. Hence, the Cd²⁺ removal efficiency in DWB increased significantly, and this was attributed to the increased abundance of non-living cells and enhanced bioretention of Cd²⁺. The results revealed that continuous K⁺ supplementation enhanced the Cd²⁺ removal efficiency in the M. aeruginosa-based PBR jointly by prompting algal cell growth, Cd²⁺ assimilation and biosorption, as well as Cd²⁺ retention on the algal cells.

Recycling spent water from microalgae harvesting by fungal pellets to re-cultivate Chlorella vulgaris under different nutrient loads for biodiesel production

Fungal pellet is an emerging material to collect oleaginous microalgae, but rare studies have noticed that harvested water is available resource for the next round of cultivation. To systematically optimize regrowth performances of microalgae Chlorella vulgaris, separated water after harvesting by fungi Aspergillus oryzae was prepared under different N/P ratios. The results showed that chlorophylls and enzymes were significantly affected by the proportion of N and P. Although nutrient deficiency was functioned as a stress factor to restrict carbohydrate and protein synthesis, lipid content was obviously increased by 12.69%. The percentage of saturated fatty acids associated with oxidation stability increased, while this part in fresh wastewater accounted for only 36.96%. The favorable biomass concentration (1.37 g/L) with the highest lipid yield (0.42 g/L) appeared in N/P of 6:1. More strikingly, suitable conditions could save 52.4% of cultivation costs. These experiments confirmed that reusing bioflocculated water could be effectively utilized for biodiesel production.

New concept in swine wastewater treatment: development of a self-sustaining synergetic microalgae-bacteria symbiosis (ABS) system to achieve environmental sustainability

Much attention has been paid to developing methods capable of synchronous removal of pollutants from swine wastewater. Due to the natural symbiotic interactions between microalgae and bacteria, the microalgae-bacteria symbiosis (ABS) system has been found to have potential for treating wastewater. However, the corresponding biological mechanisms in the ABS system and the role of dynamic microbial community evolution in pollutant removal systems remain poorly understood. Therefore, we investigate the potential of an ABS system for pollutant removal applications and analyze the bacterial consortium symbiotically combined with Chlorella sp. MA1 and Coelastrella sp. KE4. The NH₄⁺-N and PO₄^3--P removal efficiencies were significantly increased from 12.79% to 99.52% and 35.66% to 96.06% due to biotic interactions between the microalgae and bacteria. The abundance of bacterial taxa and genes related to oxidative stress, cell growth and nitrogen transfer were found to increase in response to photosynthesis, respiration and NH₄⁺-N uptake. Furthermore, pathogen inactivation was induced via microalgae, co-driven by microbial succession under high dissolved oxygen conditions. In this microalgae-enhanced ABS system, the interactions between microalgae and bacteria are established for pathogens elimination and nitrogen cycling, verifying that the ABS system is an effective and environmentally sustainable swine wastewater treatment method.

Current advances in microalgae-based bioremediation and other technologies for emerging contaminants treatment

Emerging contaminants (EC) have been detected in effluents and drinking water in concentrations that can harm to a variety of organisms. Therefore, several technologies are developed to treat these compounds, either for their complete removal or degradation in less toxic by-products. Some technologies applied to the treatment of EC, such as adsorption, advanced oxidative processes, membrane separation processes, and bioremediation through microalgal metabolism, were identified by thematic maps. In this review, we used a bibliometric software from >1000 articles. These manuscripts, in general, present removals from 0% to 100% for different ECs. This efficiency varies between treatment technologies and the contaminants' physical-chemical properties and their concentration and operational parameters. This review explored the bioremediation of EC through microalgae with greater emphasis. The main mechanisms of action of microalgae in the bioremediation of ECs are biodegradation bioadsorption, and bioaccumulation. Also, physicochemical properties and removal efficiencies of >50 emerging contaminants are presented. Although there are challenges related to the generation of more toxic by-products and economic and environmental viability, these can be minimized with advances in the development of treatment technologies and even through the integration of different techniques to make the treatment of contaminants emerging from environmental media more sustainable.

Effects of moxifloxacin and gatifloxacin stress on growth, photosynthesis, antioxidant responses, and microcystin release in Microcystis aeruginosa

Moxifloxacin (MOX) and gatifloxacin (GAT) are fourth-generation fluoroquinolone antibiotics that are frequently detected in surface water environments and pose a threat to aquatic organisms. However, research into their toxicity to Microcystis aeruginosa, a cyanobacterium, has thus far been limited. In the present study, we investigated the effects of these antibiotics on M. aeruginosa growth, photosynthesis, oxidative stress, and microcystin (MC) release. The results of the 96 h EC₅₀ values of MOX and GAT were 60.34 and 25.30 μg/L, respectively, and the risk quotients calculated indicated that these antibiotics could pose considerable ecological risks at actual environmental concentrations. Photosynthetic fluorescence intensity was shown to decline markedly, and Fv/Fm significantly decreased without any evidence of recovery, suggesting that the organism's photosystems were irreversibly damaged. Chlorophyll a and carotenoid content decreased, whereas the ratio of carotenoids to chlorophyll a increased, indicating that carotenoids were less susceptible to damage than chlorophyll a. The reactive oxygen species and malondialdehyde content significantly increased, as well as the superoxide dismutase and catalase activities, indicating that exposure caused serious oxidative stress. Additionally, MC release increased. These results demonstrate that the environmental risks posed by MOX and GAT should be given serious consideration, particularly as their use is increasing.

Effects of three antibiotics on growth and antioxidant response of Chlorella pyrenoidosa and Anabaena cylindrica

Antibiotics are essential for treatments of bacterial infection and play important roles in the fields of aquaculture and animal husbandry. Antibiotics are accumulated in water and soil due to the excessive consumption and incomplete treatment of antibiotic wastewater. The accumulation of antibiotics in ecological systems leads to global environmental risks. The toxic effects of spiramycin (SPI), tigecycline (TGC), and amoxicillin (AMX) on Chlorella pyrenoidesa and Anabaena cylindrica were evaluated based on growth inhibition experiments, and determinations of ROS production and antioxidant enzyme activities (catalase, superoxide dismutase, and malondialdehyde). Half maximal effective concentrations (EC50) of TGC, SPI, and AMX for A. cylindrica were 62.52 μg/L, 38.40 μg/L, and 7.66 mg/L, respectively. Those were 6.20 mg/L, 4.58 mg/L, and > 2 g/L for C. pyrenoidesa, respectively. It was shown that A. cylindrica was much more sensitive to these antibiotics than C. pyrenoidesa. In addition, EC50 values of SPI and TGC were lower than that of AMX. It was indicated that SPI and TGC had higher toxic than AMX to C. pyrenoidesa and A. cylindrica. The current study is helpful to evaluating possible ecological risks of TGC, SPI, and AMX by green microalgae and cyanobacteria.

Response of microalgae Chlorella vulgaris to Cr stress and continuous Cr removal in a membrane photobioreactor

This study evaluated the toxicity of Cr(VI) to microalgae Chlorella vulgaris, and its removal by continuous microalgae cultivation in membrane photobioreactor (MPBR). Batch cultivation in photobioreactors showed that low concentration of Cr(VI) (0.5 and 1.0 mg L^-1) stimulated the growth of C. vulgaris, while 2.0 and 5.0 mg L^-1 Cr(VI) in the wastewater significantly inhibited the growth of C. vulgaris. Superoxide dismutase and catalase activities that represented cellular antioxidant capacity significantly increased at 0.5 and 1.0 mg L^-1 Cr(VI), and then gradually decreased with the continuous increase of Cr(VI) concentration. The content of malondialdehyde, which represents the degree of cellular oxidative damage, increased with the increase of Cr(VI) concentration and reached the peak value at 2.0 mg L-1 Cr(VI). C. vulgaris was then cultured in MPBR equipped with hollow-fiber ultrafiltration membrane module to achieve continuous removal of Cr from wastewater. With the in-situ solid-liquid separation function of the membrane module, solid retention time (SRT) and hydraulic retention time (HRT) of the reactor could be controlled separately. Experimental results showed that both SRT and HRT had significant effects on the algal biomass production and pollutants removal. During the continuous operation, MPBR achieved a maximum total Cr reduction of 50.0% at HRT of 3-day and SRT of 40-day, and a maximum volumetric removal rate of total Cr of 0.21 mg L^-1 d^-1 at HRT of 2-day and SRT of 40-day.

Switchable solvent N, N, N', N'-tetraethyl-1, 3-propanediamine was dissociated into cationic surfactant to promote cell disruption and lipid extraction from wet microalgae for biodiesel production

Switchable solvent N, N, N', N'-tetraethyl-1,3-propanediamine (TEPDA) was proposed to extract lipids from wet Nannochloropsis oceanica with a 5% higher extraction efficiency than chloroform-methanol. It was found that TEPDA acted mainly as an organic solvent to soften and dissolve lipids, while a small amount of TEPDA was dissociated into tertiary amine ion, i.e.,(C₂H₅)₂N-(CH₂)₃-NH⁺(C₂H₅)₂. This cation acted as a surfactant to promote cell disruption and lipid separation. With moisture increasing from 0 to 84 wt%, more TEPDA was dissociated into cationic surfactant to induce local rearrangement of phospholipid bilayers in cell membranes through electrostatic interaction, resulting in the fractal dimension of disrupted cells increased from 1.49 to 1.66. Accordingly, the yield of fatty acid methyl ester (FAME) through transesterification of lipids extracted with TEPDA increased by 9%, while FAME yield from lipids extracted with chloroform and n-hexane decreased by 41% and 65%, respectively.

Degradation and metabolic pathways of sulfamethazine and enrofloxacin in Chlorella vulgaris and Scenedesmus obliquus treatment systems

The degradation and metabolic pathways of sulfamethazine (SMZ) and enrofloxacin (ENR) via microalgal treatment systems were investigated in this study. SMZ and ENR applied at 1-25 mg L^-1 did not significantly inhibit the growth of Chlorella vulgaris or Scenedesmus obliquus. SMZ and ENR exposure did not significantly alter the maximum quantum efficiencies of C. vulgaris and S. obliquus. When cultured at light intensities of 45-50 μmol photon m^-2 s^-1, the C. vulgaris and S. obliquus treatment systems achieved 24% and 11% degradation, respectively. The greatest removal of ENR was 52% and 43.3%, for C. vulgaris and S. obliquus treatment systems, respectively, after 15 days. The results indicated that the degradation of SMZ and ENR occurred by a combination of biodegradation and photolysis. Kinetic investigations revealed that the removal of SMZ and ENR (5 mg L^-1) followed a first-order model, with apparent rate constants (k) ranging from 0.0141 to 0.0048 day^-1 and 0.0132 to 0.0086 day^-1, respectively. Fifteen metabolites of SMZ and five intermediates of ENR were identified by UPLC-MS, and degradation pathways for SMZ and ENR were proposed. SMZ transformation reactions included ring cleavage, hydroxylation, methylation, and oxidation, whereas ENR was degraded by dealkylation, decarboxylation, and defluorination. Graphical abstract.

Different interaction performance between microplastics and microalgae: The bio-elimination potential of Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025

Microplastics have recently been identified as an important emerging global problem which affects marine organisms and even humans. As a green and cost-effective environmental purification alternative, microalgae have attracted more and more attention. In this work, the interaction between microplastics (PP, PE, PET and PVC) and microalgae (Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025) has been investigated. In addition, SEM and TEM characterization were also carried out to observe interactions between microplastics and microalgae. Experimental results indicated that there was an obvious inhibition effect of microplastics on Phaeodactylum tricornutum MASCC-0025 growth with inhibition ratio up to 21.1%. By contrast, Chlorella sp. L38 presented strong adaptive capacity to microplastics. The key active enzymes concentration variation and characterization (SEM and TEM) images also verified the toxic effect of tested microplastics on Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025. The toxic effect might be explained by the possible leaching of additives of four tested microplastics. It could also be observed that microalgae have a potential to be used as an alternative bio-solution for microplastics treatment.

Using polyethylene glycol to promote Nannochloropsis oceanica growth with 15 vol% CO2

CO₂ capture with microalgae has been put forward in response to global concern on greenhouse gas emission. However, the short residence time and slow diffusion of CO₂ in water limits the growth of microalgae. In order to improve CO₂ transfer from gas phase to liquid phase and utilization by algal cells, polyethylene glycol 200 (PEG 200) was used as CO₂ absorbent to promote growth of Nannochloropsis oceanica with the bubbling of 15 vol% CO₂. Total inorganic carbon (TIC) absorbed in culture medium remained constant at 5.6 mM when 15 vol% CO₂ was bubbled continuously. PEG 200 in the medium provided additional CO₂ absorption from 0.6 to 4.8 mM when PEG 200 concentration increased from 0.5 to 4 mM. The specific growth rate of N. oceanica reached the maximum (1.41 d^-1) with 1 mM PEG 200 in culture medium, which was 21.5% higher than the specific growth rate without PEG 200. About 79% of the increase in biomass was attributed to the increased TIC with more CO₂ dissolution in culture medium because of PEG 200, and about 21% was attributed to PEG 200 itself utilized as an organic carbon source. In conclusion, PEG 200 as a CO₂ absorbent can effectively capture flue-gas CO₂ for algal growth.

Toxicity, Biodegradation, and Metabolic Fate of Organophosphorus Pesticide Trichlorfon on the Freshwater Algae Chlamydomonas reinhardtii

This study investigated the toxicity of trichlorfon (TCF) to the freshwater algae Chlamydomonas reinhardtii, as well as its biodegradation and metabolic fate. The growth of C. reinhardtii decreased with increasing TCF concentration, and the maximum inhibition ratio was 51.3% at 200 mg L^-1 TCF compared to the control. Analyses of pigment content, chlorophyll fluorescence, and antioxidant enzymes indicated that C. reinhardtii can produce resistance and acclimatize to the presence of TCF. The variations in pH during cultivation suggested that photosynthetic microalgae have innate advantages over bacteria and fungi in remediating TCF. A 100% biodegradation rate was achieved at a maximum concentration of 100 mg L^-1 TCF. Ten metabolites were identified by GC-MS, and the degradation pathways of TCF by the algae were proposed. This research demonstrated that C. reinhardtii is highly tolerant to and can efficiently degrade TCF. Thus, C. reinhardtii can be used to remove traces of TCF from natural water environments and to treat TCF-contaminated wastewater.

Use of microalgae based technology for the removal of antibiotics from wastewater: A review

The antibiotic resistance induced by the release of antibiotics to the environment has urged research towards developing effective technologies for antibiotic removal from wastewater. Traditional technologies such as activated sludge processes are not effective for antibiotic removal. Recently, microalgae-based technology has been explored as a potential alternative for the treatment of wastewater containing antibiotics by adsorption, accumulation, biodegradation, photodegradation, and hydrolysis. In this review, the toxicities of antibiotics on microalgae, the mechanisms of antibiotic removal by microalgae, and the integration of microalgae with other technologies such as ultraviolet irradiation (photocatalysis), advanced oxidation, and complementary microorganism degradation for antibiotic removal were discussed. The limitations of current microalgae-based technology and future research needs were also discussed.

Biodegradation and metabolic fate of thiamphenicol via Chlorella sp. UTEX1602 and L38

Thiamphenicol (TAP) is a typical medicament in animal husbandry and aquaculture for treating diverse infections. In this work, thiamphenicol biodegradation performance via microalgae was tested. The cultivation results showed that TAP could be biodegraded via the target algae. Chlorella sp. L38 presented strong adaptive ability to high concentration TAP. Biodegradation, biosorption and bioaccumulation were the dominant metabolic fates. Biodegradation contributed around 97% of the total removal efficiency at the TAP concentration of 46.2 mg·L^-1. The removal of TAP by Chlorella L38 and UTEX1602 agreed with the kinetic range of zero-order reaction, and the shortest half-lives were 3.2 d and 5.0 d. Based on the identification of metabolites, the metabolic pathway of TAP by microalgae was proposed, including chlorination, chlorine substitution, dehydration and hydroxylation. Therefore, biological treatment via microalgae has the potential for TAP purification.

Effect of PHRs and PCPs on Microalgal Growth, Metabolism and Microalgae-Based Bioremediation Processes: A Review

In this review, the effect of pharmaceuticals (PHRs) and personal care products (PCPs) on microalgal growth and metabolism is reported. Concentrations of various PHRs and PCPs that cause inhibition and toxicity to growths of different microalgal strains are summarized and compared. The effect of PHRs and PCPs on microalgal metabolism (oxidative stress, enzyme activity, pigments, proteins, lipids, carbohydrates, toxins), as well as on the cellular morphology, is discussed. Literature data concerning the removal of PHRs and PCPs from wastewaters by living microalgal cultures, with the emphasis on microalgal growth, are gathered and discussed. The potential of simultaneously bioremediating PHRs/PCPs-containing wastewaters and cultivating microalgae for biomass production in a single process is considered. In the light of reviewed data, the feasibility of post-bioremediation microalgal biomass is discussed in terms of its contamination, biosafety and further usage for production of value-added biomolecules (pigments, lipids, proteins) and biomass as a whole.

Biodegradability and mechanism of florfenicol via Chlorella sp. UTEX1602 and L38: Experimental study

In this work, florfenicol removal via two kinds Chlorella sp. (UTEX1602 and L38) was investigated. The experimental results indicated that FF could be removed by biodegradation associated with microalgae growth. Compared to Chlorella sp. UTEX1602, L38 had a good self-adjustment capacity at the condition of high initial FF concentration. The biodegradation of FF followed the first order kinetic model with half-lives ranged from 3.53 to 7.63 days at different initial concentration. The removal efficiency of FF could achieve 97% when the FF concentration was set at 46 mg·L^-1. While the FF concentration in the medium increased to 159 mg·L^-1, more than 74% FF could still be purified via Chlorella sp. L38. Therefore, Chlorella sp. L38 could be promising alternative algae to be used for FF removal from different water sources.

Serial lantern-shaped draft tube enhanced flashing light effect for improving CO2 fixation with microalgae in a gas-lift circumflux column photobioreactor

A novel serial lantern-shaped draft tube (LDT) that generates vortices is proposed to increase radial velocity between dark and light regions for improving CO₂ fixation with microalgae in a gas-lift circumflux column (GCC) photobioreactor. Clockwise vortices are generated in the downflow outerloop of the GCC photobioreactor with LDT. Radial velocity was improved from 1.50 to 4.35 × 10^-2 m/s, thereby decreased liquid cycle period between dark and light regions by 1.9 times. Mixing time decreased by 21%, and mass transfer coefficient increased by 26% with LDT. Liquid radial velocity in the downflow outerloop and mass transfer coefficient in the GCC photobioreactor both first increased and then decreased when single-lantern height was increased. Peak CO₂ fixation rate increased from 0.62 to 0.87 g/L/d, microalgal biomass yield increased by 50%. Removal efficiencies of pollutants (chemical oxygen demand, ammonium, tilmicosin, and ethinylestradiol) in wastewater were 62-90% with microalgae growth in GCC photobioreactor with LDT.

Removing ethinylestradiol from wastewater by microalgae mutant Chlorella PY-ZU1 with CO2 fixation

Removal of endocrine-disrupting chemical ethinylestradiol (EE2) from wastewater by microalgal mutant Chlorella PY-ZU1 under 15% CO₂ were investigated. Moreover, the effects of EE2 on microscopic structure and antioxidation ability of microalgal cells were determined. EE2 concentrations in range of 0.01-5 mg L^-1 stimulated microalgal growth. Increasing the original EE2 concentration from 0 to 5 mg L^-1 increased the cell fractal dimension from 1.38 to 1.59 and reduced the cell size from 5.18 to 3.41 μm. Meanwhile, superoxide dismutase and catalase activities, which represented cellular antioxidant capacity, first increased from 44.59 and 0.54 U mL^-1 to peak values of 65.57 and 1.49 U mL^-1, respectively, and then correspondingly decreased to 34.36 and 0.36 U mL^-1. Malondialdehyde content that indicated the cell oxidation damage degree first decreased from 2.57 to 2.03 nmol mL^-1, then increased to 2.59 nmol mL^-1. The highest EE2 removal efficiency of 94% by Chlorella PY-ZU1 was achieved at the original EE2 concentration of 5 mg L^-1.

Investigation of the removal mechanism of antibiotic ceftazidime by green algae and subsequent microbic impact assessment

The present study provides an integrated view of algal removal of the antibiotic ceftazidime and its basic parent structure 7-aminocephalosporanic acid (7-ACA), including contribution analysis, bacteriostatic and aquatic toxic assessment and metabolite verification. 92.70% and 96.07% of the two target compounds was removed after the algal treatment, respectively. The algal removal can be separated into three steps: a rapid adsorption, a slow cell wall-transmission and the final biodegradation. Additionally, while ceftazidime demonstrated an excellent inhibitory effect on Escherichia coli, there was no bacteriostasis introduced after the algal treatment, which could avoid favoring the harmful selective pressure. On the other hand, no significant aquatic impact of the two target compounds on rotifers was observed and it was not enhanced after the algal treatment. To better reveal the mechanism involved, metabolite analyses were performed. Δ-3 ceftazidime and trans-ceftazidime were regarded as the metabolites of ceftazidime and the metabolite of 7-ACA was regarded as a compound which shared the similar structure with 4-chlorocinnamic acid. Our study indicated that the green algae performed a satisfactory growth capacity and played a dominant role for the biodegradation of the target antibiotics, which achieved high removal efficiency and low environmental impact.