Trends in microalgal-based systems as a promising concept for emerging contaminants and mineral salt recovery from municipal wastewater.

In the context of climate change leading to water scarcity for many people in the world, the treatment of municipal wastewater becomes a necessity. However, the reuse of this water requires secondary and tertiary treatment processes to reduce or eliminate a load of dissolved organic matter and various emerging contaminants. Microalgae have shown hitherto high potential applications of wastewater bioremediation thanks to their ecological plasticity and ability to remediate several pollutants and exhaust gases from industrial processes. However, this requires appropriate cultivation systems allowing their integration into wastewater treatment plants at appropriate insertion costs. This review aims to present different open and closed systems currently used in the treatment of municipal wastewater by microalgae. It provides an exhaustive approach to wastewater treatment systems using microalgae, integrating the most suitable used microalgae species and the main pollutants present in the treatment plants, with an emphasis on emerging contaminants. The remediation mechanisms as well as the capacity to sequester exhaust gases were also described. The review examines constraints and future perspectives of microalgae cultivation systems in this line of research.

Elaboration and Characterization of a New Heavy Metal Sensor Functionalized by Extracellular Polymeric Substances Isolated from a Tunisian Thermophilic Microalga Strain Graesiella sp.

The present study aimed to develop and characterize new heavy metal sensors functionalized by extracellular polymeric substances (EPSs) isolated from a Tunisian thermophilic microalga strain Graesiella sp. The elaborated sensor showed a highly homogeneous character and revealed a microstructural lamellar arrangement, high crystalline nature, and several functional groups. Electrochemical impedance spectroscopy (EIS) and acoustic wave sensing were used as sensing techniques to explore the ability of microalgae-EPS-functionalized sensors to detect cadmium and mercury as heavy metals. For impedimetric measurements, a two-dipole circuit was adopted and showed good-fitted results with a low total error. The acoustic sensor platforms showed good compatibility with EPS in adjacent water. For both EPS-functionalized sensors, metal ions (Cd2+, Hg2+) were successfully detected in the concentration range from 10-10 M to 10-4 M. Impedimetric sensor was more sensitive to Cd2+ at low concentrations before saturation at 10-7 M, while the acoustic sensor exhibited more sensitivity to Hg2+ over the full range. The results highlight a new potential alternative to use microalgae EPSs as a sensitive coating material for the detection of heavy metals. However, its use in a real liquid medium requires further investigation of its selectivity in the presence of other compounds.

A Novel Impedimetric Sensor Based on Cyanobacterial Extracellular Polymeric Substances for Microplastics Detection.

Cyanobacterial extracellular polymeric substances "EPS" have attracted intensive concern in biomedicine and food. Nevertheless, the use of those polymers as a sensor coating material has not yet been investigated mainly for microplastic detection. This study focuses on the application of EPS as a sensitive membrane deposited on a gold electrode and investigated with electrochemical impedance spectroscopy to detect four types of microplastics with a size range of 0.1 µm to 1 mm. The surface properties of this impedimetric sensor were investigated by Scanning electron microscopy, Fourier transforms infrared spectroscopy, and X-ray spectroscopy and, showed a high homogenous structure with the presence of several functional groups. The measurements showed a high homogenous structure with the presence of several functional groups. The EPS-based sensor could detect the four tested microplastics with a low limit of detection of 10-11 M. It is the first report focusing on EPS extracted from cyanobacteria that could be a new quantification method for low concentrations of microplastics. Supplementary Information: The online version contains supplementary material available at 10.1007/s10924-022-02555-6.

Bisphenol A removal by the Chlorophyta Picocystis sp.: optimization and kinetic study.

The Chlorophyta Picocystis sp. isolated from a Tunisian household sewage pond appears promising for effective removal of Bisphenol A (BPA). Efficient and cost-effective technology for contaminants remediation relies on a tradeoff between several parameters such as removal efficiency, microorganism growth, and its tolerance to contaminant toxicity. This article demonstrates the optimum conditions achieving the highest removal rates and the minimal growth inhibition in batch cultures of Picocystis using response surface methodology. A central composite face-centered (CCF) design was used to determine the effects on removal and growth inhibition of four operating parameters: temperature, inoculum cell density, light intensity, and initial BPA concentration. Results showed that the maximal BPA removal was 91.36%, reached the optimal culture conditions of 30.7 °C, 25 × 105 cells ml-1 inoculum density, 80.6 µmol photons m-2 s-1 light intensity, and initial BPA concentration of 10 mg l-1. Various substrate inhibition models were used to fit the experimental data, and robustness analysis highlighted the Tessier model as more efficient to account for the interaction between Picocystis and BPA and predict removal efficiency. These results revealed how Picocystis respond to BPA contamination and suggest that optimization of experimental conditions can be effectively used to maximize BPA removal in the treatment process.HighlightsSurface response methodology was applied for optimization of BPA removal by the Chlorophyta Picocystis sp.Temperature, light intensity, inoculum cell density and initial BPA concentration were selected as factors that may affect BPA removal and microalgae growth.The optimal conditions for the maximum BPA removal and minimum growth inhibition were 30.7 °C; 80.6 µmol photons m-2 s-1; 25 × 105 cells ml-1 and 10 mg l-1 BPA.Teissier model was selected to fit the kinetic of BPA removal by Picocystis with R2 = 0.92.

Biodegradation of diclofenac by two green microalgae: Picocystis sp. and Graesiella sp.

The aim of the present study was to provide an integrated view of algal removal of diclofenac (DCF). Two isolated microalgal strains Picocystis sp. and Graesiella sp. were cultivated under different DCF concentrations and their growth, photosynthetic activity and diclofenac removal efficiency were monitored. Results showed that DCF had slight inhibitory effects on the microalgal growth which did not exceed 21% for Picocystis and 36% for Graesiella after 5 days. Both species showed different patterns in terms of removal efficiency. In presence of Picocystis sp., the amounts of removed DCF were up to 73%, 43% and 25% of 25, 50 and 100 mg L-1 respectively; whereas only 52%, 28% and 24% were removed in the presence of Graesiella at same DCF tested concentrations. DCF removal was insured mainly by biodegradation. To better reveal the mechanism involved, metabolites analyses were performed. Two DCF biodegradation/biotransformation products were detected in presence of Picocystis. This study indicated that Picocystis performed a satisfactory growth capacity and DCF removal efficiency and thus could be used for treatment of DCF contaminated aqueous systems.

Effect of Bisphenol A on the extremophilic microalgal strain Picocystis sp. (Chlorophyta) and its high BPA removal ability.

Bisphenol A (BPA) effects and removal by an alkaliphilic chlorophyta, Picocystis, were assessed. BPA at low concentrations (0-25 mg L-1) did not inhibit the Picocystis growth and photosynthesis during 5 days of exposure. At higher BPA concentrations (50 and 75 mg L-1), the growth inhibition did not exceed 43%. The net photosynthetic activity was dramatically reduced at high BPA concentrations while, the PSII activity was less affected. The exposure to increasing BPA concentrations induced an oxidative stress in Picocystis cells, as evidenced by increased malondialdehyde content and the over-expression of antioxidant activities (ascorbate peroxydase, gluthation-S-transferase and catalase). Picocystis exhibited high BPA removal efficiency, reaching 72% and 40% at 25 and 75 mg L-1 BPA. BPA removal was ensured mainly by biodegradation/biotransformation processes. Based on these results, the extended tolerance and the high removal ability of Picocystis make her a promising specie for use in BPA bioremediation.

Ultra-sensitive conductometric detection of pesticides based on inhibition of esterase activity in Arthrospira platensis.

Enzymatic conductometric biosensor, using immobilized Arthrospira platensis cells on gold interdigitated electrodes, for the detection of pesticides in water, was elaborated. Cholinesterase activity (AChE) was inhibited by pesticides and a variation of the local conductivity was measured after addition of the substrate acetylthiocholine chloride (AChCl). The Michaelis-Menten constant (Km) was evaluated to be 1.8 mM through a calibration curve of AChCl. Inhibition of AChE was observed with paraoxon-methyl, parathion-methyl, triazine and diuron with a detection limit of 10(-18) M, 10(-20) M, 10(-20) M and 10(-12) M, respectively and the half maximal inhibitory concentration (IC50) was determined at 10(-16) M, 10(-20) M, 10(-18) M and 10(-06) M, respectively. An important decrease of response time τ90% was recorded for AChE response towards AChCl after 30 min cell exposure to pesticides. Scanning electron microscopy images revealed a degradation of the cell surface in presence of pesticides at 10(-06) M.

Ultra-sensitive conductometric detection of heavy metals based on inhibition of alkaline phosphatase activity from Arthrospira platensis.

This study is based on the conductometric measurement of alkaline phosphatase activity (APA) from the cyanobacterium, Arthrospira platensis, called Spirulina. Cyanobacterium cells were directly immobilized, by physical adsorption, on the ceramic part of gold interdigitated transducers. This activity was inhibited in the presence of heavy metals and a variation of the local conductivity was measured after addition of the substrate. The Michaelis-Menten constant (Km) was evaluated to be 0.75 mM through a calibration curve of the substrate, disodium 4-nitrophenylphosphate p-nitrophenyl phosphate (pNPP). Inhibition of APA was observed with cadmium and mercury with a detection limit of 10(-20) M. The half maximal inhibitory concentration (IC50) was determined at 10(-19) M for Cd(2+) and 10(-17) M for Hg(2+), and the binding affinity of heavy metal (Ki) was equal to the IC50. On the sensor surface, scanning electron microscopy (SEM) images revealed a remarkable evolution of the cyanobacterium's external surface that was attributable to the first defense mechanism against toxic heavy metals in trace. This effect was also confirmed through the important increase of response time τ(90%) recorded for APA response towards the substrate pNPP after cell exposure to metallic cations. Lifetime of the Spirulina-based biosensor was estimated to be more than 25 days.

Evaluation of Arthrospira platensis extracellular polymeric substances production in photoautotrophic, heterotrophic and mixotrophic conditions.

The kinetic study of Arthrospira platensis extracellular polymeric substances (EPS) production under different trophic modes-photoautotrophy (100 µmol photons m(-2) s(-1)), heterotrophy (1.5 g/L glucose), and mixotrophy (100 µmol photons m(-2) s(-1) and 1.5 g/L glucose)-was investigated. Under photoautotrophic and heterotrophic conditions, the maximum EPS production 219.61 ± 4.73 and 30.30 ± 1.97 mg/L, respectively, occurred during the stationary phase. Under a mixotrophic condition, the maximum EPS production (290.50 ± 2.21 mg/L) was observed during the early stationary phase. The highest specific EPS productivity (433.62 mg/g per day) was obtained under a photoautotrophic culture. The lowest specific EPS productivity (38.33 mg/g per day) was observed for the heterotrophic culture. The effects of glucose concentration, light intensity, and their interaction in mixotrophic culture on A. platensis EPS production were evaluated by means of 32 factorial design and response surface methodology. This design was carried out with a glucose concentration of 0.5, 1.5, and 2.5 g/L and at light levels of 50, 100, and 150 µmol photons m(-2) s(-1). Statistical analysis of the model demonstrated that EPS concentration and EPS yield were mainly influenced by glucose concentration and that conditions optimizing EPS concentration were dissimilar from those optimizing EPS yield. The highest maximum predicted EPS concentration (369.3 mg/L) was found at 150 µmol photons m(-2) s(-1) light intensity and 2.4 g/L glucose concentration, while the highest maximum predicted EPS yield (364.3 mg/g) was recorded at 115 µmol photons m(-2) s(-1) light intensity and 1.8 g/L glucose concentration.

Evaluation of cytotoxicity and biological activities in extracellular polysaccharides released by cyanobacterium Arthrospira platensis

The aim of this work was to evaluate the cytotoxicity of Arthrospira platensis Extracellular Polymeric Substances (EPS) for colon cancer and kidney cell lines. Results showed that EPS were free from cytotoxic effects. A variety of solvents were assessed for their ability to extract the bioactive ingredients from EPS. Methanol gave the highest yield (75.75 percent) than other solvents. The extracts were tested for activities against a collection of Gram+/- bacteria. The methanol extract exhibited a more potent activity than the other organic extracts, whereas the aqueous extract was active against Staphylococcus epidermis (Gram+) and Salmonella typhimurium (Gram-). Finally, The extracts were also tested for the antioxidant activity, using the Trolox Equivalent Antioxidant Activity assay. The methanol extract displayed a moderate antioxidant activity (TEAC = 0.027 mg/ml). The HPLC analysis of this extract revealed two distinct peaks: 8.1 kDa (8.31 min) and 4.1 kDa (8.54 min).