Toxicity of urban stormwater on Chlorella pyrenoidosa: Implications for reuse safety

Urban stormwater is an alternative water source used to mitigate water resource shortages, and ensuring the safety of stormwater reuse is essential. An in-depth understanding of both individual pollutant concentrations/loads in stormwater and holistic stormwater quality can be used to comprehensively evaluate how safely stormwater can be reused. The toxicity test takes all pollutants present in water samples into account, and the results reflect the integrated effect of these pollutants. In this study, the influence of urban stormwater sourced from different land uses on microalgae (Chlorella pyrenoidosa) and the possible toxicity mechanisms were investigated. The results showed that urban stormwater, particularly residential road stormwater, significantly inhibited microalgal growth. The chlorophyll contents of microalgae exposed to residential road stormwater were relatively lower, while the corresponding values were relatively higher for microalgae exposed to grassland road stormwater. Additionally, the antioxidant-related metabolism of microalgae could be dysregulated due to exposure to urban stormwater. A possible toxicity mechanism is that urban stormwater influences metabolic pathways related to chlorophyll synthesis and further hinders photosynthesis and hence microalgal growth. To resist oxidative stress and maintain regular microalgal cell activities, the ribosome metabolism pathway was upregulated. The research results contribute to elucidating the toxicity effects of urban stormwater and hence provide useful insight for ensuring the safety of stormwater reuse. It is also worth noting that the study outcomes can only represent the influence of land use on stormwater toxicity, while the impacts of other factors (particularly rainfall-runoff characteristics) have not been considered. Therefore, the consideration of all influential factors of stormwater is strongly recommended to generate more robust results in the future and provide more effective guidance for real practices related to stormwater reuse safety.

Impacts of microplastic and seawater acidification on unicellular red algae: Growth response, photosynthesis, antioxidant enzymes, and extracellular polymer substances

Microplastics (MPs) pollution and seawater acidification have increasingly become huge threats to the ocean ecosystem. Their impacts on microalgae are of great importance, since microalgae are the main primary producers and play a critical role in marine ecosystems. However, the impact of microplastics and acidification on unicellular red algae, which have a unique phycobiliprotein antenna system, remains unclear. Therefore, the impacts of polystyrene-MPs alone and the combined effects of MPs and seawater acidification on the typical unicellular marine red algae Porphyridium purpureum were investigated in the current study. The result showed that, under normal seawater condition, microalgae densities were increased by 17.75-41.67 % compared to the control when microalgae were exposed to small-sized MPs (0.1 μm) at concentrations of 5-100 mg L-1. In addition, the photosystem II and antioxidant enzyme system were not subjected to negative effects. The large-sized MPs (1 μm) boosted microalgae growth at a low concentration of MPs (5 mg L-1). However, it was observed that microalgae growth was significantly inhibited when MPs concentration increased up to 50 and 100 mg L-1, accompanied by the remarkably reduced Fv/Fm value and the elevated levels of SOD, CAT enzymes, phycoerythrin (PE), and extracellular polysaccharide (EPS). Compared to the normal seawater condition, microalgae densities were enhanced by 52.11-332.56 % under seawater acidification, depending on MPs sizes and concentrations, due to the formed CO2-enrichment condition and appropriate pH range. PE content in microalgal cells was significantly enhanced, but SOD and CAT activities as well as EPS content markedly decreased under acidification conditions. Overall, the impacts of seawater acidification were more pronounced than MPs impacts on microalgae growth and physiological responses. These findings will contribute to a substantial understanding of the effects of MPs on marine unicellular red microalgae, especially in future seawater acidification scenarios.

Enhanced microalgal biomass and lipid production with simultaneous effective removal of Cd using algae-bacteria-activated carbon consortium added with organic carbon source

Recently, using microalgae to remediate heavy metal polluted water has been attained a huge attention. However, heavy metals are generally toxic to microalgae and consequently decrease biomass accumulation. To address this issue, the feasibility of adding exogenous glucose, employing algae-bacteria system and algae-bacteria-activated carbon consortium to enhance microalgae growth were evaluated. The result showed that Cd2+ removal efficiency was negatively correlated with microalgal specific growth rate. The exogenous glucose alleviated the heavy metal toxicity to algal cells and thus increased the microalgae growth rate. Among the different treatments, the algae-bacteria-activated carbon combination had the highest biomass concentration (1.15 g L-1) and lipid yield (334.97 mg L-1), which were respectively 3.03 times of biomass (0.38 g L-1) and 4.92 times of lipid yield (68.08 mg L-1) in the single microalgae treatment system. Additionally, this algae-bacteria-activated carbon consortium remained a high Cd2+ removal efficiency (91.61%). In all, the present study developed an approach that had a great potential in simultaneous heavy metal wastewater treatment and microalgal lipid production.

Effects of light source and inter-species mixed culture on the growth of microalgae and bacteria for nutrient recycling and microalgae harvesting using black odorous water as the medium

To achieve the sustainable and effective removal efficiency of nutrients in black odorous water, light source, inter-species microalgae mixed culture, and the harvesting effect were all explored. The results showed that under a LED light source, the addition of interspecific soluble algal products (SAP) promoted the growth of Haematococcus pluvialis (H. pluvialis) M1, and its maximum specific growth rate was 1.76 times that of H. pluvialis cultivated alone. That was due to the hormesis effect between the two kinds of microalgae, the SAP produced by Scenedesmus could stimulate the growth of H. pluvialis. The algae and bacteria symbiotic system with black odorous water as the medium showed excellent performance to treat nutrients, where the concentration of ammonia nitrogen (NH₃-N) and total phosphorus (TP) (0.84, 0.23 mg/L) met the requirements of landscape water. The microbial diversity analysis revealed that the introduction of microalgae changed the dominant species of the bacterial community from Bacteroidota to Proteobacteria. Furthermore, timely microalgae harvesting could prevent water quality from deteriorating and was conducive to microalgae growth and resource recycling. The higher harvest efficiency (98.1%) of H. pluvialis was obtained when an inoculation size of 20% and 0.16 g/L FeCl₃ were provided.

Extensive investigation and beyond the removal of micro-polyvinyl chloride by microalgae to promote environmental health

Microplastics (MPs) remediation via algae could be a prospective strategy to address MPs pollution concerns. In this study, Chlorella sp. GEEL-08 was exposed to different gradient concentrations ranging from 0 to 200 mg L^-1 of polyvinyl chloride (PVC_0.2μm). Microalgal growth, total nitrogen (TN), total phosphorus (TP), and cations (Cu, Zn, Na, and K) removal were investigated. The oxidative stress enzymes such as superoxide dismutase (SOD) and malonaldehyde (MDA) were also assessed. The addition of 50 mg L^-1 mPVC resulted in the highest growth along with >99% removal of nutrients (TN and TP) and >80% removal of cations. However, the addition of 100-200 mg L^-1 mPVC inhibited microalgal growth by 8.8-12.3%. The stress-induced by mPVC was highly observed at 200 mg L^-1 mPVC on the 4th d with 70.8 U mg_prot^-1 and 62.3 nmol mg_prot^-1 of SOD and MDA, respectively. Fourier-transform infrared spectroscopy (FTIR) spectra confirmed that microalgal biomass retained mPVC. Thermogravimetric analysis/derivative thermogravimetric analysis (TGA/DTG) spectra showed that the organic matter of microalgal biomass attached with mPVC was decomposed faster than control, indicating the possibilities of using this biomass for pyrolysis and the formation of bio-products.

Calcium ions-effect on performance, growth and extracellular nature of microalgal-bacterial symbiosis system treating wastewater

Microalgal-bacterial symbiosis (MABS) system treating wastewater has attracted great concern because of its advantages of carbon dioxide reduction and biomass energy production. However, due to the low density and negative surface charge of microalgae cells, the sedimentation and harvesting performance of microalgae biomass has been one limitation for the application of MABS system on wastewater treatment. This study investigated the performance enhancement of microalgae harvesting and wastewater treatment contributed by calcium ions (i.e., Ca²⁺) in the MABS system. Results showed that a low Ca²⁺ loading (i.e., 0.1 mM) promoted both COD and nutrients removal, with growth rates of 11.95, 6.53 and 1.21% for COD, TN and TP compared to control, and chlorophyll a was increased by 64.15%. Differently, a high Ca²⁺ loading (i.e., 10 mM) caused removal reductions by improving the aggregation of microalgae, with reduction rates of 34.82, 3.50 and 10.30% for COD, NH₄⁺-N and TP. Mechanism analysis indicated that redundant Ca²⁺ adsorbed on MABS aggregates and dissolved in wastewater decreased the dispersibility of microalgae cells by electrical neutralization and compressed double electric layer. Moreover, the presence of Ca²⁺ could improve extracellular secretions and promoted flocculation performance, with particle size increasing by 336.22%. The findings of this study may provide some solutions for the enhanced microalgae biomass harvest and nutrients removal from wastewater.

Dynamic Optimization Approach to Estimate Kinetic Parameters of Monod-Based Microalgae Growth Models

The biomass concentration of microalgae growth in photobioreactor was predicted using the Monod-based growth models. Kinetic parameters such as maximum specific growth rate and saturation constant of light intensity were evaluated by nonlinear least squares methods that focused on minimizing the sum of squares error (SSE). The importance of good initial guess for the nonlinear least squares method was also discussed. The optimal control problem of the microalgae growth model was determined based on parameter sensitivity. Therefore, a dynamic optimization approach was used where an optimal input design method was formulated to obtain a control function of a problem. The dynamic state equations, additional state equations, cost function, and Hamiltonian function were used to establish a control function of microalgae growth in a photobioreactor. Hence, the biomass production of microalgae can be predicted using numerical methods such as the Taylor series method.

Growth and metabolic responses to methyl viologen (1,1'-dimethyl - 4,4'-bipyridinium dichloride) on Chlorella vulgaris

Aquatic environments are especially susceptible to being contaminated by pesticides used in agricultural fields. Methyl viologen (MV) is an herbicide with high effectiveness for the control of unwanted land plants; however, it also has a high toxicity towards the algae in the aquatic environment. The objective of this work was to describe the effect of MV on photosynthetic metabolism and its relationship with respiration, growth and the content of photosynthetic pigments of Chlorella vulgaris. The cultures of C. vulgaris were exposed for 72 h at different concentrations of methyl viologen. The results show that growth, pigment content and metabolic activity decrease as the concentration of MV increases. Analysis of the photochemical activity indicates that MV produces an inhibition of electron transport between quinone A and quinone B of photosystem II. The inhibition of photosynthetic electron transport is directly related to the reduction of metabolic activity and cell growth. The results found in this research show that methyl viologen can be a toxic pollutant for primary producers in aquatic environments.

Effect of iron and phosphorus on the microalgae growth in co-culture

Iron and phosphorus (P) are the important micro- and macro-nutrient for microalgae growth, respectively. However, the effect of iron and P on microalgae growth in co-culture associating with the formation of dominate algae has not been investigated before. In the current study, Anabaene flos-aquae, Chlorella vulgaris and Melosira sp. were co-cultivated under the addition of different initial iron and P to reveal the effect of iron and phosphorus on the growth of microalgae. The results showed that the mean growth rate of A. flos-aquae, C. vulgaris and Melosira was 0.270, 0.261 and 0.062, respectively, indicating that the A. flos-aquae and C. vulgaris algae are liable to be the dominant algae while the growth of Melosira was restrained when co-cultured. The ratio of Fe to P has a significant impact on the growth of microalgae and could be regarded as an indicator of algae growth. Microalgae showed a much more obvious uptake of iron compared to that of P. The information obtained in the current study was useful for the forecast of water quality and the control of microalgae bloom.

Biocompatible liquid-type carbon nanodots (C-paints) as light delivery materials for cell growth and astaxanthin induction of Haematococcus pluvialis

In this study, we aimed to demonstrate the feasibility of the application of biocompatible liquid type fluorescent carbon nanodots (C-paints) to microalgae by improving microalgae productivity. C-paints were prepared by a simple process of ultrasound irradiation using polyethylene glycol (PEG) as a passivation agent. The resulting C-paints exhibited a carbonyl-rich surface with good uniformity of particle size, excellent water solubility, photo-stability, fluorescence efficiency, and good biocompatibility (<10.0 mg mL^-1 of C-paints concentration). In the practical application of C-paints to microalgae culture, the most effective and optimized condition leading to growth promoting effect was observed at a C-paints concentration of 1.0 mg mL^-1 (>20% higher than the control cell content). A C-paints concentration of 1-10.0 mg mL^-1 induced an approximately >1.8 times higher astaxanthin content than the control cells. The high light delivery effect of non-cytotoxic C-paints was applied as a stress condition for H. pluvialis growth and was found to play a major role in enhancing productivity. Notably, the results from this study are an essential approach to improve astaxanthin production, which can be used in various applications because of its therapeutic effects such as cancer prevention, anti-inflammation, immune stimulation, and treatment of muscle-soreness.

Effect of different kinds of complex iron on the growth of Anabaena flos-aquae

As a necessary micronutrient for algal growth, iron (Fe) has important effects on the physiological metabolism and enzymatic reactions of algae. In this study, a series of experiments were designed to compare the effects of different kinds of iron on the growth of Anabaena flos-aquae. Results showed that the promotion of iron species on algae growth was in order of ferric ammonium citrate > EDTA-Fe > iron ions > iron oxalate. When the concentration of iron is in the range of 0.1-0.8 mg/L, iron species have more significant influences on Anabaena bloom compared with iron concentration. Our experiments also revealed that A. flos-aquae has the strongest adsorption capacity for iron ion among the four iron sources and further induced. This leads to the toxicity of the iron ion group to algal cells at low concentration.

Efficient microalgae removal from aqueous medium through auto-flocculation: investigating growth-dependent role of organic matter

This study investigated the growth-dependent role of algal organic matters (AOMs) to achieve high removal efficiency (R.E) of microalgae. The results showed that the microalgae cells produced 96 ± 2% of total AOMs as loose bound AOMSS (LB-AOMs) and 4 ± 1% as cell-bound (CB-AOMs) in exponential phase. In stationary phase, LB-AOMs and CB-AOMs were 46 ± 0.7percentage and 54 ± 0.2 percentage, respectively. The R.Es in exponential and stationary phase were 83 ± 2.6% and 66 ± 1.2%, respectively. It is found that the difference of biomass concentration (between exponential and stationary phase) had no significant impact on the R.E (P > 0.01). Further investigations revealed that LB-AOMs inhibit flocculation in exponential and CB-AOMs in stationary phase; however, CB-AOMs showed stronger inhibition than the LB-AOMs (P < 0.01). The provision of calcium (17 ± 0.9 mg/L) to the culture reduced the AOMs inhibition and improved the R.E from 66 ± 1.2% (in control) to 90 ± 4.2%. An increase in R.E was attributed to the interaction of calcium with AOMs and subsequently acting as a flocculant. The findings of this study can be valuable to improve the performance of auto-flocculation technology, which is mainly limited by the presence of AOMs. Graphical Abstract.

Enhancement of microalgal growth and biocomponent-based transformations for improved biofuel recovery: A review

Microalgal biomass has received much attention as feedstock for biofuel production due to its capacity to accumulate a substantial amount of biocomponents (including lipid, carbohydrate, and protein), high growth rate, and environmental benefit. However, commercial realization of microalgal biofuel is a challenge due to its low biomass production and insufficient technology for complete utilization of biomass. Recently, advanced strategies have been explored to overcome the challenges of conventional approaches and to achieve maximum possible outcomes in terms of growth. These strategies include a combination of stress factors; co-culturing with other microorganisms; and addition of salts, flue gases, and phytohormones. This review summarizes the recent progress in the application of single and combined abiotic stress conditions to stimulate microalgal growth and its biocomponents. An innovative schematic model is presented of the biomass-energy conversion pathway that proposes the transformation of all potential biocomponents of microalgae into biofuels.

Assessing changes in the toxicity of effluents from intensive marine fish farms over time by using a battery of bioassays

Although intensive marine fish farming is often assumed to be eco-friendly, the associated activity can lead to chronic exposure of marine organisms to potentially toxic discharges. Moreover, despite the increasing popularity of integrated multi-trophic aquaculture (IMTA), studies of the effects of fish farm effluents are almost non-existent. In the present study, the changes in the toxic potential of effluents from five land-based marine fish farms in NW Spain subjected for different lengths of time to a biodegradation procedure (for 0, 48, 120, and 240 h) were assessed in a battery of bioassays including organisms from different trophic levels (Vibrio fischeri, Isochrysis galbana, and Paracentrotus lividus). The results of the bioassays at the different times were then considered together with farm water flow in the Potential Ecotoxic Effects Probe (PEEP) index. Despite the high volumes of effluents discharged, the generally low toxicity of the effluents hinders assessment of potentially toxic effects. However, dose-response curves and statistical analysis demonstrated the existence of toxic effects during the first five days of the biodegradation procedure, especially immediately after sampling. The proposed modification of the PEEP index better reflects the changes in toxicity over time. Graphical abstract ᅟ.

Potential effects of TiO2 nanoparticles and TiCl4 in saltwater to Phaeodactylum tricornutum and Artemia franciscana

Nanosized titanium dioxide (nTiO₂) is widespread in many commercial products and several authors investigated its ecotoxicity effects focusing mainly on freshwater environments. Data on saltwater species are still lacking or present contradicting results. We compared for the first time the toxicity of TiCl₄ and nTiO₂ considering standard toxicity tests with microalgae Phaeodactylum tricornutum (growth inhibition test, 1.8-90mg/L) and crustacean Artemia franciscana (mortality test, 0.5-64mg/L). For A. franciscana, two alternative scenarios were considered beside standard protocol: i) darkness; and ii) starvation. About microalgae, results evidenced that effects of TiCl₄ (EC50=63mg/L) were greater than nTiO₂ (no EC50), but IC10 and IC20 were significantly lower suggesting that nTiO₂ is more harmful than TiCl₄ at lower concentrations. The effects of TiCl₄ to crustaceans larvae in all exposure scenarios were lower compared to nTiO₂ (EC50(96h)=15mg/L - standard protocol). During toxicity testing, the absence of light generally lowered nTiO₂ effects while starvation increased the toxicity of both TiCl₄ and nTiO₂.

Streptomycin affects the growth and photochemical activity of the alga Chlorella vulgaris

Antibiotics are increasingly being used in human and veterinary medicine, as well as pest control in agriculture. Recently, their emergence in the aquatic environment has become a global concern. The aim of this study was to evaluate the effect of streptomycin on growth and photosynthetic activity of Chlorella vulgaris after 72h exposure. We found that growth, photosynthetic activity and the content of the D1 protein of photosystem II decreased. Analysis of chlorophyll a fluorescence emission shows a reduction in the energy transfer between the antenna complex and reaction center. Also the activity of the oxygen evolution complex and electron flow between QA and QB were significantly reduced; in contrast, we found an increase in the reduction rate of the acceptor side of photosystem I. The foregoing can be attributed to the inhibition of the synthesis of the D1 protein and perhaps other coded chloroplast proteins that are part of the electron transport chain which are essential for the transformation of solar energy in the photosystems. We conclude that micromolar concentrations of streptomycin can affect growth and photosynthetic activity of Chlorella vulgaris. The accumulation of antibiotics in the environment can become an ecological problem for primary producers in the aquatic environment.