Influence of chitosan properties and operating parameters on the flocculation efficiency and harvesting of microalgae (Scenedesmus sp.).

Physicochemical and structural characteristics of chitosan prepared from Deep-sea shrimp (DCs), including degree of deacetylation (DD), molecular weight (Mw), viscosity, crystallinity index (CrI) and surface morphology were compared with a commercial chitosan (CCs). The DCs had a higher DD of 81.33 ± 0.40 %, whereas the CCs had a lower DD of 74.62 ± 0.64 %. Additionally, the DCs exhibited a lower Mw of 192.47 ± 2.5 kDa and viscosity of 646.00 ± 4.00 cP compared to the CCs, which had a Mw of 202.44 ± 0.28 kDa and viscosity of 689.67 ± 5.91 cP. This study investigated the influence of chitosan properties, particularly DD and Mw on the harvesting of Scenedesmus sp. along with the chitosan dosage, pH of the culture medium, mixing speed and time. Under optimal operating conditions, the microalgae removal efficiency of the DCs reached a significantly higher level (94.71 ± 0.20 %) compared to that of CCs (88.25 ± 0.41 %). Chitosan with a higher DD and low Mw demonstrated superior flocculation efficiency. The results highlight the significance of DD and Mw of chitosan and its influence on the flocculation of microalgae, providing valuable insights for optimizing the harvesting process with the non-toxic and natural flocculent, chitosan.

Comparative proteomics reveals energy and carbon metabolism changes in Scenedesmus quadricauda mutants induced by heavy-ion beam irradiation.

Microalgae's superior ability to fix carbon dioxide into biomass and high-value bioproducts remains underutilized in biotechnological applications due to a lack of comprehensive understanding of their carbon metabolism and energy conversion. In this work, the strain improvement technique heavy-ion beams (HIB) mutagenesis was employed on the environmentally adaptable microalgae Scenedesmus quadricauda. After several rounds of screening, two contrasting mutants were identified. S-#4 showed low photosynthetic activity and biomass productivity, while S-#26 exhibited adaptability to prolonged high light stress, achieving a 28.34 % increase in biomass yield compared to the wild-type strain. Integrating their photosynthetic characteristics and comparative proteomic analysis revealed that the contrasting protein regulations from central carbon metabolism mainly affects the two mutants' opposite biomass accumulation. Therefore, the divergent regulation of the tricarboxylic acid cycle following HIB mutagenesis could be potential targets for engineering microalgae with superior biomass and high-value products.

Effect of hydrothermal pretreatment on leachate fed Scenedesmus sp. biomass solubilization and biogas production.

The aim of the present study was to assess the effect of hydrothermal pretreatment on the solubilization and anaerobic digestion (AD) of Scenedesmus sp. biomass. At first, the microalgae was cultivated in 5% fresh leachate (FL) to recover nutrients such as nitrogen and phosphorus. Scenedesmus sp. grown in 5% FL obtained 100%, 77% and 97% removal efficiency of ammonium nitrogen (NH4+ - N), total Kjeldahl nitrogen (TKN) and phosphate phosphorous (PO43- -P), respectively. In the following step, the hydrothermal pretreatment of Scenedesmus sp. biomass was carried out at 120, 150 and 170 °C and retention time of 0, 30 and 60 min to evaluate its solubilization and biogas production through AD in batch test. Soluble chemical oxygen demand (sCOD) increased by 260% compared to untreated microalgae at 170 °C for 60 min. In comparison to untreated microalgae, the highest increase in biogas (70%) and methane yield (100%) was observed for 150 °C and 60 min pretreated microalgae as a consequence of hydrothermal pretreatment. Hydrothermal pretreatment has shown effectiveness in enhancing biomass solubilization and increasing biogas yield. Nevertheless, further research at the pilot scale is necessary to thoroughly evaluate the potential and feasibility of hydrothermal pretreatment for full-scale implementation.

Alternative green solvents associated with ultrasound-assisted extraction: A green chemistry approach for the extraction of carotenoids and chlorophylls from microalgae.

This study proposes a method for the ultrasonic extraction of carotenoids and chlorophyll from Scenedesmus obliquus and Arthrospira platensis microalgae with green solvents. Ethanol and ethanolic solutions of ionic liquids were tested with a variety of extraction parameters, including number of extractions, time of extraction, and solid-liquid ratio R(S/L), to determine the optimal conditions. After selecting the most effective green solvent (ethanol), the process conditions were established: R(S/L) of 1:10, three extraction cycles at 3 min each), giving an extraction yield of 2602.36 and 764.21 µgcarotenoids.gdried biomass-1; and 22.01 and 5.81 mgchlorophyll.gdried biomass-1 in S. obliquus and A. platensis, respectively. The carotenoid and chlorophyll extracts obtained using ethanol were shown to be potent scavengers of peroxyl radical, being 5.94 to 26.08 times more potent α-tocopherol. These findings pave the way for a green strategy for valorizing microalgal biocompounds through efficient and environmentally friendly technological processes.

Integrating electro-Fenton and microalgae for the sustainable management of real food processing wastewater.

The present study demonstrates, for the first time, the feasibility of a two-step process consisting of Electro-Fenton (EF) followed by microalgae to treat highly loaded real food processing wastewater along with resource recovery. In the first step, EF with a carbon felt cathode and Ti/RuO2-IrO2 anode was applied at different current densities (3.16 mA cm-2, 4.74 mA cm-2 and 6.32 mA cm-2) to decrease the amount of organic matter and turbidity and enhance biodegradability. In the second step, the EF effluents were submitted to microalgal treatment for 15 days using a mixed culture dominated by Scenedesmus sp., Chlorosarcinopsis sp., and Coelastrum sp. Results showed that current density impacted the amount of COD removed by EF, achieving the highest COD removal of 77.5% at 6.32 mA cm-2 with >95% and 74.3% of TSS and PO43- removal, respectively. With respect to microalgae, the highest COD removal of 85% was obtained by the culture in the EF effluent treated at 6.32 mA cm-2. Remarkably, not only 85% of the remaining organic matter was removed by microalgae, but also the totality of inorganic N and P compounds, as well as 65% of the Fe catalyst that was left after EF. The removal of inorganic species also demonstrates the high complementarity of both processes, since EF does not have the capacity to remove such compounds, while microalgae do not grow in the raw wastewater. Furthermore, a maximum of 0.8 g L-1 of biomass was produced after cultivation, with an accumulation of 32.2% of carbohydrates and 25.9% of lipids. The implementation of the two processes represents a promising sustainable approach for the management of industrial effluents, incorporating EF in a water and nutrient recycling system to produce biomass that could be valorized into clean fuels.

A whole process study of dual microalgae cultivation coupled to domestic wastewater treatment and wheat growth.

The multiple microalgal collaborative treatment of domestic wastewater has been extensively investigated, but its whole life cycle tracking and consequent potential have not been fully explored. Herein, a dual microalgal system was employed for domestic wastewater treatment, tracking the variation in microalgal growth and pollutants removal from shake flask scale to 18 L photobioreactors scales. The results showed that Chlorella sp. HL and Scenedesmus sp. LX1 combination had superior growth and water purification performance, and the interspecies soluble algal products promoted their growth. Through microalgae mixing ratio and inoculum size optimized, the highest biomass yield (0.42 ± 0.03 g/L) and over 91 % N, P removal rates were achieved in 18 L photobioreactor. Harvested microalgae treated in different forms all promoted wheat growth and suppressed yellow leaf rate. This study provided data support for the whole process tracking of dual microalgal system in treating domestic wastewater and improving wheat growth.

Biosynthesized BiFe2O4@Ag nanoparticles mediated Scenedesmus obliquus induce apoptosis in AGS gastric cancer cell line.

The use of magnetic metal nanoparticles has been considered in cancer treatment studies. In this study, BiFe2O4@Ag nanoparticles were synthesized biologically by Scenedesmus obliquus for the first time and their anticancer mechanism in a gastric cancer cell line was characterized. The physicochemical properties of the nanoparticles were evaluated by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic Light Scattering (DLS), and zeta potential analyses. Cell viability and nuclear damage were investigated by the MTT and Hoechst staining assays, respectively. Flow cytometry analysis was performed to determine the frequency of the necrotic and apoptotic cells as well as cell cycle analysis of the nanoparticles-treated cells. Physicochemical characterization showed that the synthesized particles were spherical, without impurities, in a size range of 38-83 nm, with DLS size and zeta potential of 295.7 nm and -27.7 mV, respectively. BiFe2O4@Ag nanoparticles were considerably more toxic for the gastric cancer cells (AGS cell line) than HEK293 normal cells with IC50 of 67 and 117 µg/ml, respectively. Treatment of AGS cells with the nanoparticles led to a remarkable increase in the percentage of late apoptosis (38.5 folds) and cell necrosis (13.4 folds) and caused cell cycle arrest, mainly at the S phase. Also, nuclear fragmentation and apoptotic bodies were observed in the gastric cancer cells treated with the nanoparticles. This study represents BiFe2O4@Ag as a novel anticancer candidate against gastric cancer that can induce cell apoptosis through DNA damage and inhibition of cell cycle progression.

Microalgae production in olive mill wastewater fractions and cattle digestate slurry: Bioremediation effects and suitability for energy and feed uses.

The possibility of obtaining energy or nutritive streams and bioremediation as an add-on opens new perspectives for the massive culturing of microalgal biomass on waste waters generated by the agro-food sector. Ordinary revenue streams are fully preserved, or even boosted, if they are used in microalgal cultivation; however, the suitability of wastewaters depends on multiple nutritional and toxic factors. Here, the effect of modulating the Olive Mill Wastewater (OMW) and cattle digestate (CD) fraction in the formulation of a growth medium on biomass accumulation and productivity of selected biomass fractions and their relevance for biofuel and/or feed production were tested for the microalga Scenedesmus dimorphus and for the cyanobacterium Arthrospira platensis (Spirulina). Tests highlighted the strong S. dimorphus adaptability to digestate, as on OMW, compared to A. platensis, with the maximum lipid storage (48 %) when culture medium was composed by 50 % of cattle digestate.

Competence of algal consortia under municipal wastewater: remediation efficiency, photosynthetic performance, antioxidant defense mechanisms and biofuel production.

Utilizing monoalgal species for wastewater treatment is facing tremendous challenges owing to changing wastewater complexity in terms of physico-chemical characteristic, nutrient and metal concentration. The environmental conditions are also fluctuating therefore, the formation of robust system is of utmost importance for concomitant sustainable wastewater treatment and bioenergy production. In the present study, the tolerance and adaptability potential of algal consortia-1 (Chlorococcum humicola and Tetradesmus sp.) and consortia-2 (Chlorococcum humicola, Scenedesmus vacuolatus and Tetradesmus sp.) treated with municipal wastewater were examined under natural environmental conditions. The results exhibited that consortia-2 was more competent in recovering nitrate-nitrogen (82.92%), phosphorus (70.47%), and heavy metals (31-73.70%) from municipal wastewater (100%) than consortia-1. The results further depicted that total chlorophyll, carbohydrate, and protein content decreased significantly in wastewater-treated consortia-1 as compared to consortia-2. However, lipid content was increased by 4.01 and 1.17 folds in algal consortia-1 and consortia-2 compared to their respective controls. Moreover, absorption peak at 1740.6 cm-1 reflected higher biofuel-producing potential of consortia-1 as compared to consortia-2 as confirmed through FTIR spectroscopy. The results also revealed that consortia-2 showed the highest photosynthetic performance which was evident from the increment in the active photosystem-II reaction center (1.724 ± 0.068), quantum efficiency (0.633 ± 0.038), and performance index (3.752 ± 0.356). Further, a significant increase in photosynthetic parameters was observed in selected consortia at lag phase, while a noteworthy decline was observed at exponential and stationary phases in consortia-1 than consortia-2. The results also showed the maximum enhancement in ascorbic acid (2.43 folds), proline (3.34 folds), and cysteine (1.29 folds) in consortia-2, while SOD (1.75 folds), catalase (2.64 folds), and GR (1.19 folds) activity in consortia-1. Therefore, it can be concluded that due to remarkable flexibility and photosynthetic performance, consortia-2 could serve as a potential candidate for sustainable nutrient resource recovery and wastewater treatment, while consortia-1 for bio-fuel production in a natural environment. Thus, formation of algal consortia as the robust biosystem tolerates diverse environmental fluctuations together with wastewater complexity and ultimately can serve appropriate approach for environmental-friendly wastewater treatment and bioenergy production.

Using single-species and algal communities to determine long-term adverse effects of silver nanoparticles on freshwater phytoplankton.

The physical and chemical properties of silver nanoparticles (AgNPs) have led to their increasing use in various fields such as medicine, food, and industry. Evidence has proven that AgNPs cause adverse effects in aquatic ecosystems, especially when the release of Ag is prolonged in time. Several studies have shown short-term adverse effects of AgNPs on freshwater phytoplankton, but few studies have analysed the impact of long-term exposures on these populations. Our studies were carried out to assess the effects of AgNPs on growth rate, photosynthesis activity, and reactive oxygen species (ROS) generation on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa, and additionally on microcystin (MC-LR) generation from these cyanobacteria. The tests were conducted both in single-species cultures and in phytoplanktonic communities exposed to 1 ngL-1 AgNPs for 28 days. The results showed that cell growth rate of both single-species cultures decreased significantly at the beginning and progressively reached control-like values at 28 days post-exposure. This effect was similar for the community-cultured cyanobacteria, but not for the green algae, which maintained a sustained decrease in growth rate. While gross photosynthesis (Pg) increased in both strains exposed in single cultures, dark respiration (R) and net photosynthesis (Pn) decreased in S. armatus and M. aeruginosa, respectively. These effects were mitigated when both strains were exposed under community culture conditions. Similarly, the ROS generation shown by both strains exposed in single-species cultures was mitigated when exposure occurred in community cultures. MC-LR production and release were significantly decreased in both single-species and community exposures. These results can supply helpful information to further investigate the potential risks of AgNPs and ultimately help policymakers make better-informed decisions about their utilization for environmental restoration.

Enhanced biomethane production from Scenedesmus sp. using polymer harvesting and expired COVID-19 disinfectant for pretreatment.

This study evaluates the repurposing of expired isopropanol (IPA) COVID-19 disinfectant (64% w/w) to pretreat algal biomass for enhancing methane (CH4) yield. The impact of harvesting methods (centrifugation and polymer flocculation) and microwave pretreatment on CH4 production from Scenedesmus sp. microalgal biomass were also investigated. Results show minimal impact of harvesting methods on the CH4 yield, with wet centrifuged and polymer-harvested biomass exhibiting comparable and low CH4 production at 66 and 74 L/kgvolatile solid, respectively. However, microalgae drying significantly increased CH4 yield compared to wet biomass, attributed to cell shrinkage and enhanced digestibility. Consequently, microwave and IPA pretreatment significantly enhanced CH4 production when applied to dried microalgae, yielding a 135% and 212% increase, respectively, compared to non-pretreated wet biomass. These findings underscore the advantage of using dried Scenedesmus sp. over wet biomass and highlight the synergistic effect of combining oven drying with IPA treatment to boost CH4 production whilst reducing COVID-19 waste.

Self-flocculation behaviour of cellulose-based bioflocculant synthesized from sewage water grown Chlorella sorokiniana and Scenedesmus abundans.

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

Biodiesel production from the Scenedesmus sp. and utilization of pigment from de-oiled biomass as sensitizer in the dye-sensitized solar cell (DSSC) for performance enhancement.

Dye-sensitized solar cell (DSSC) using algal photosynthetic pigments has got rampant attention as it converts sunlight into electricity. Therefore, in this present research, the neutral lipid extracted from the green alga Scenedesmus sp. was used for biodiesel production, and concurrently, pigments extracted from the de-oiled biomass cake were used as a sensitizer in DSSC to evaluate its performance efficacy with and without PVDF (Polyvinylidene fluoride). Initially, neutral lipids extracted from the Scenedesmus sp. were converted to biodiesel with a yield of 72.9%, and the de-oiled biomass was subjected to pigment extraction (17.65 mg/g) to use as a sensitizer in DSSC. This study proposes two DSSC test models, i.e., PVDF (Polyvinylidene fluoride) - bound cell and cell without any PVDF binder. For the PVDF-coated DSSC, the average energy conversion efficiency reached about 14.3%, the open circuit voltage was 0.55 V, and the short circuit current was 144.5 mA. The unbound cells showed a reduction in efficiency, voltage, and current, and notably, efficiency of 10.44% on day 1 was decreased to 3.32%, and the open circuit voltage and short circuit current of 0.38V and 144 mA were decreased to 0.24V and 130 mA after 10 days, under 40 mW/cm2 input power. The PVDF-coated solar cell has maintained its efficiency range of 16.32%-11.22%, which is higher than the PVDF-unbound cell for a tested timeline of 30 days. The fill factor of 0.47 was observed in PVDF- unbound DSSC under 40 mW/cm2 as input power, while it was increased to 0.577 when PVDF was used as a binder. The PVDF-coated cell has low degradation compared with the PVDF-uncoated cell. These results offer dual benefits as the production of biodiesel from microalgal lipids and electricity generation from the DSSC using the pigments of biodiesel-extracted algal biomass.

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.

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.

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.

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.

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.

Enhancing bioremediation potential of microalgae Chlorella vulgaris and Scenedesmus acutus by NaCl for pyrene degradation.

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