Influence of magnesium concentrations on the biomass and biochemical variations in the freshwater algae, Chlorella vulgaris

Effects of dissolved cations, dissolved organic carbon, and exposure concentrations on per- and polyfluoroalkyl substances bioaccumulation in freshwater algae

Per- and polyfluoroalkyl substances (PFAS) have attracted global attention because of their persistence, toxicity, bioaccumulation potential, and associated adverse effects. As important primary producers, freshwater algae constitute the base of the food web in freshwater aquatic ecosystems. However, the effects of key environmental factors on PFAS uptake and bioaccumulation in freshwater algae have not been thoroughly studied. In this study, three bioaccumulation experiments were conducted to evaluate the influence of dissolved cations, dissolved organic carbon, and exposure concentrations on PFAS bioaccumulation in algae. Among the 14 studied PFAS, seven long-chain PFAS tended to bioaccumulate in algae. Elevated divalent cations (Ca2+ and Mg2+) and dissolved organic carbon did not significantly change the algal bioconcentration factors (BCFs) of PFAS, suggesting complexity of the interactions among PFAS, environmental factors, and biotic activities. Additionally, increasing exposure concentrations (0.5, 1, 5, and 10 μg/L of each PFAS) increased PFAS concentrations in algae but decreased the BCF values. This indicated that attention should be paid to the application of BCFs in future studies, including ecological risk assessment. Moreover, fluorotelomer sulfonic acids (FTSs) were incompletely recovered, suggesting that biotransformation occurred. Further studies should be conducted to evaluate whether algae play a role in FTSs biotransformation and to determine the mechanisms. Studying the impacts of key environmental factors on PFAS bioaccumulation in algae is crucial for understanding the bioaccumulation processes that occur at the lowest trophic level and that eventually affect the dynamics of entire aquatic ecosystems.

Production and Characterization of Silk Fibroin-Aloe vera Hydrogel: A Study on Extraction, Hydrogel Properties, and Release Mechanism

This work investigated the production and characterization of a silk fibroin (SF) hydrogel incorporated with an Aloe vera (AV) extract. Four extraction methods, ultrasound-assisted extraction with bath and probe, stirring, and Soxhlet, were tested, while the hydrogel was produced by a one-step freeze-thaw method. Besides the extraction yield, the antioxidant capacity of the extracts was accessed, which allowed to select the extract obtained by ultrasound-assisted extraction to be incorporated into the hydrogels. Hydrogels were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Rheological assay, swelling behavior, and water uptake capacity were measured. The SF-AV hydrogel was submitted to release test, and the data were mathematically modeled. The hydrogels exhibited malleability, insolubility in water, interconnected pores, and thermal and physical stability. The SF-AV hydrogel released 37% extract over 330 min, with diffusion controlled by the Fickian mechanism. These promising results make the SF-AV hydrogel an attractive choice for wound dressing and other biomaterial-related applications.

Optimization of Cultivation Conditions of Native Microalga Scenedesmus quadricauda and Evaluation of Lipids for Enhanced Biodiesel Production

Biofuels are considered to be among the primary alternatives to the use of fossil fuels. These fuels, made from feedstock or waste raw materials, have the advantage of being renewable and contributing much less to global warming. Microalgae are a promising biodiesel source. Microalgae, unlike traditional crops that are now used to make commercialized biodiesel, may be grown on non-agricultural land and has a greater capacity for growth and yield. Cultivation has been considered as a critical stage in the generation of biofuels. The goal of the present study is to learn that Scenedesmus quadricauda has a potential for biodiesel production in the near future. Optimization studies revealed that BG-11 medium, temperature of 25 °C, pH 7.0, glucose and sucrose (as carbon sources), static condition (for lipid accumulation) & shaking condition (for biomass yield), cultivation days of 18, 21, and 24 day, NaNO3 dosing of 1.0 mM followed by 0.8 mM (on 5th day of cultivation), 3% yeast extract dosing, 3000 lx light intensity, photoperiod cycles of 24L/0D (for biomass yield) and 18L/6D (for lipid production) and 10 mM concentration of NaCl (salinity stress) can be regarded as best suited physio-biochemical parameters for efficient biomass and lipid yield from S. quadricauda. FTIR indicated presence of various stretching of carbohydrates and lipids that again is supporting biodiesel production capability of S. quadricauda. SEM showed that cells of S. quadricauda under stress conditions became fragmented separated from coenobium and were not so compactly arranged. Present optimization studies along with Nile red fluorescence, FTIR and SEM revealed that S. quadricauda could be a suitable candidate to produce good quality biofuel and that also in stress conditions.

Graphical Abstract

The Microalgae Chlamydomonas for Bioremediation and Bioproduct Production

The extensive metabolic diversity of microalgae, coupled with their rapid growth rates and cost-effective production, position these organisms as highly promising resources for a wide range of biotechnological applications. These characteristics allow microalgae to address crucial needs in the agricultural, medical, and industrial sectors. Microalgae are proving to be valuable in various fields, including the remediation of diverse wastewater types, the production of biofuels and biofertilizers, and the extraction of various products from their biomass. For decades, the microalga Chlamydomonas has been widely used as a fundamental research model organism in various areas such as photosynthesis, respiration, sulfur and phosphorus metabolism, nitrogen metabolism, and flagella synthesis, among others. However, in recent years, the potential of Chlamydomonas as a biotechnological tool for bioremediation, biofertilization, biomass, and bioproducts production has been increasingly recognized. Bioremediation of wastewater using Chlamydomonas presents significant potential for sustainable reduction in contaminants and facilitates resource recovery and valorization of microalgal biomass, offering important economic benefits. Chlamydomonas has also established itself as a platform for the production of a wide variety of biotechnologically interesting products, such as different types of biofuels, and high-value-added products. The aim of this review is to achieve a comprehensive understanding of the potential of Chlamydomonas in these aspects, and to explore their interrelationship, which would offer significant environmental and biotechnological advantages.

Ecological patterns of phytoplankton across lake cross-section: insights into co-evolution of physicochemical conditions in Chashma Lake on Indus River

Physicochemical properties of water influence planktonic diversity and distribution, which is essential in obtaining basic knowledge of aquatic biodiversity. Thus current study aims to investigate the spatiotemporal diversity, abundance ratio, and distribution of phytoplankton species and their association with water quality parameters of Chashma Lake, Pakistan. During the study period from 2018 to 2019, we measured 13 physicochemical parameters across three selected sampling sites (S1, S2, and S3) in Chashma Lake, revealing both spatial and temporal variability. Dissolved oxygen (DO) was higher in S3, while S1 exhibited higher alkalinity levels, carbon dioxide, phosphorus, and chloride levels. The study identified 77 phytoplankton species grouped into five taxonomic categories, with Cyanobacteria dominating (39.90%), followed by Chlorophyta (33.4%) and Bacillariophyta (24.88%). Euglenozoa and Ochrophyta were less abundant (1.3% and 0.41%, respectively). Spatial variations in phytoplankton distribution were noted, with Chlorophyta being more abundant at S2, Bacillariophyta and Cyanobacteria at S1, and Euglenozoa dominating at S3. Canonical Correspondence Analysis (CCA) revealed the influence of various physicochemical parameters on phytoplankton distribution. This comprehensive study provides valuable insights for the ecological assessment and monitoring of water bodies. It is recommended that continuous monitoring is required to capture long-term trends, further explore the specific environmental drivers impacting phytoplankton dynamics, and consider management strategies for maintaining water quality and biodiversity in Chashma Lake.

Comparison of Different Pretreatment Processes Envisaging the Potential Use of Food Waste as Microalgae Substrate

A significant fraction of the food produced worldwide is currently lost or wasted throughout the supply chain, squandering natural and economic resources. Food waste valorization will be an important necessity in the coming years. This work investigates the ability of food waste to serve as a viable nutritional substrate for the heterotrophic growth of Chlorella vulgaris. The impact of different pretreatments on the elemental composition and microbial contamination of seven retail food waste mixtures was evaluated. Among the pretreatment methods applied to the food waste formulations, autoclaving was able to eliminate all microbial contamination and increase the availability of reducing sugars by 30%. Ohmic heating was also able to eliminate most of the contaminations in the food wastes in shorter time periods than autoclave. However, it has reduced the availability of reducing sugars, making it less preferable for microalgae heterotrophic cultivation. The direct utilization of food waste containing essential nutrients from fruits, vegetables, dairy and bakery products, and meat on the heterotrophic growth of microalgae allowed a biomass concentration of 2.2 × 108 cells·mL-1, being the culture able to consume more than 42% of the reducing sugars present in the substrate, thus demonstrating the economic and environmental potential of these wastes.

Exploring uranium bioaccumulation in the brown alga Ascophyllum nodosum: insights from multi-scale spectroscopy and imaging

Legacy radioactive waste can be defined as the radioactive waste produced during the infancy of the civil nuclear industry's development in the mid-20th Century, a time when, unfortunately, waste storage and treatment were not well planned. The marine environment is one of the environmental compartments worth studying in this regard because of legacy waste in specific locations of the seabed. Comprising nearly 70% of the earth's service, the oceans are the largest and indeed the final destination for contaminated fresh waters. For this reason, long-term studies of the accumulation biochemical mechanisms of metallic radionuclides in the marine ecosystem are required. In this context the brown algal compartment may be ecologically relevant because of forming large and dense algal beds in coastal areas and potential important biomass for contamination. This report presents the first step in the investigation of uranium (U, an element used in the nuclear cycle) bioaccumulation in the brown alga Ascophyllum nodosum using a multi-scale spectroscopic and imaging approach. Contamination of A. nodosum specimens in closed aquaria at 13 °C was performed with a defined quantity of U(VI) (10-5 M). The living algal uptake was quantified by ICP-MS and a localization study in the various algal compartments was carried out by combining electronic microscopy imaging (SEM), X-ray Absorption spectroscopy (XAS) and micro X-ray Florescence (μ-XRF). Data indicate that the brown alga is able to concentrate U(VI) by an active bioaccumulation mechanism, reaching an equilibrium state after 200 h of daily contamination. A comparison between living organisms and dry biomass confirms a stress-response process in the former, with an average bioaccumulation factor (BAF) of 10 ± 2 for living specimens (90% lower compared to dry biomass, 142 ± 5). Also, these results open new perspectives for a potential use of A. nodosum dry biomass as uranium biosorbent. The different partial BAFs (bioaccumulation factors) range from 3 (for thallus) to 49 (for receptacles) leading to a compartmentalization of uranium within the seaweed. This reveals a higher accumulation capacity in the receptacles, the algal reproductive parts. SEM images highlight the different tissue distributions among the compartments with a superficial absorption in the thallus and lateral branches and several hotspots in the oospheres of the female individuals. A preliminary speciation XAS analysis identified a distinct U speciation in the gametes-containing receptacles as a pseudo-autunite phosphate phase. Similarly, XAS measurements on the lateral branches (XANES) were not conclusive with regards to the occurrence of an alginate-U complex in these tissues. Nonetheless, the hypothesis that alginate may play a role in the speciation of U in the algal thallus tissues is still under consideration.

Recycling of nutrient medium to improve productivity in large-scale microalgal culture using a hybrid electrochemical water treatment system

Recycling and reusing of nutrient media in microalgal cultivation are important strategies to reduce water consumption and nutrient costs. However, these approaches have limitations, e.g., a decrease in biomass production, (because as reused media can inhibit biomass growth). To address these limitations, we applied a novel membrane filtration‒electrolysis‒ultraviolet hybrid water treatment method capable of laboratory-to-large-scale operation to increase biomass productivity and enable nutrient medium disinfection and recycling. In laboratory-scale experiments, electrolysis effectively remove the biological contaminants from the spent nutrient medium, resulting in a high on-site removal efficiency of dissolved organic carbon (DOC; 80.3 ± 5 %) and disinfection (99.5 ± 0.2 %). Compared to the results for the recycling of nutrient medium without water treatment, electrolysis resulted in a 1.5-fold increase in biomass production, which was attributable to the removal of biological inhibitors from electrochemically produced oxidants (mainly OCl-). In scaled-up applications, the hybrid system improved the quality of the recycled nutrient medium, with 85 ± 2 % turbidity removal, 75 ± 3 % DOC removal, and 99.5 ± 2 % disinfection efficiency, which was beneficial for biomass growth by removing biological inhibitors. After applying the hybrid water treatment method, we achieved a Spirulina biomass production of 0.47 ± 0.03 g L-1, similar to that obtained using a fresh medium (0.53 ± 0.02 g L-1). The on-site disinfection process described herein is practical and offers a cost-saving and environmental friendly alternative for nutrient medium recycling and reusing water in mass and sustainable cultivation of microalgae.

Cultivation of blue green algae (Arthrospira platensis Gomont, 1892) in wastewater for biodiesel production

The production of biodiesel has become an important issue in the effort to reduce gas emissions due to the climate change crisis; therefore, algae have widely used to produce biodiesel for energy sustainability. The present study represented an effort to assess the ability of the alga Arthrospira platensis to produce fatty acids involved in biofuel (diesel) by cultivation in Zarrouk media enriched with different municipal wastewater concentrations. Wastewater was used in different concentrations (5, 15, 25, 35 and 100% [control]). Five fatty acids from the alga were determined and included in the present study. These were inoleic acid, palmitic acid, oleic acid, gamma-linolenic acid, and docosahexaenoic acid. Impact of different cultivation conditions were studied in terms of observed changes in growth rate, doubling time, total carbohydrate, total protein, chlorophyll a, carotenoids, phycocyanin, allophycocyanin, and phycobiliproteins. Results showed an increase in the values of growth rate, total protein content, chlorophyll a, and levels of carotenoids at all treatments except for carbohydrate content, which decreased with an increasing concentration of wastewater. The high value of doubling time (11.605 days) was recorded at treatment 5%. Fatty acids yields were increased at treatment 5% and 15%. The highest concentrations of fatty acids were 3.108 mg/g for oleic acid, gamma-linolenic acid (28.401 mg/g), docosahexaenoic acid (41.707 mg/g), palmitic acid (1.305 mg/g), and linoleic acid (0.296 mg/g). Moreover, the range of phycocyanin (0.017-0.084 mg/l), allophycocyanin (0.023-0.095 mg/l), and phycobiliproteins (0.041-0.180 mg/l) were obtained in treatment with 15-100%, respectively. Cultivation with municipal wastewater reduced the values of nitrate, phosphate, and electrical conductivity as well as increased dissolved oxygen. Maximum electrical conductivity was recorded in untreated wastewater with algae, while the highest level of dissolved oxygen was noted at 35% concentration. The use of the household wastewater is more environmentally friendly as an alternative of the traditional cultivation techniques used for long-term for biofuel production.

Growth Behavior, Biomass Composition and Fatty Acid Methyl Esters (FAMEs) Production Potential of Chlamydomonas reinhardtii, and Chlorella vulgaris Cultures

The production of biomolecules by microalgae has a wide range of applications in the development of various materials and products, such as biodiesel, food supplements, and cosmetics. Microalgae biomass can be produced using waste and in a smaller space than other types of crops (e.g., soja, corn), which shows microalgae's great potential as a source of biomass. Among the produced biomolecules of greatest interest are carbohydrates, proteins, lipids, and fatty acids. In this study, the production of these biomolecules was determined in two strains of microalgae (Chlamydomonas reinhardtii and Chlorella vulgaris) when exposed to different concentrations of nitrogen, phosphorus, and sulfur. Results show a significant microalgal growth (3.69 g L-1) and carbohydrates (163 mg g-1) increase in C. reinhardtii under low nitrogen concentration. Also, higher lipids content was produced under low sulfur concentration (246 mg g-1). It was observed that sulfur variation could affect in a negative way proteins production in C. reinhardtii culture. In the case of C. vulgaris, a higher biomass production was obtained in the standard culture medium (1.37 g L-1), and under a low-phosphorus condition, C. vulgaris produced a higher lipids concentration (248 mg g-1). It was observed that a low concentration of nitrogen had a better effect on the accumulation of fatty acid methyl esters (FAMEs) (C16-C18) in both microalgae. These results lead us to visualize the effects that the variation in macronutrients can have on the growth of microalgae and their possible utility for the production of microalgae-based subproducts.