Algal Suspension Research Articles

3D analysis of microplastic settling in algal suspensions

The influence of algae presence in surface water on the settling velocities of microplastics is unknown, and determining it is challenging due to the turbidity of algal suspensions. Measuring the settling velocity of microplastics has traditionally relied on either manual measurement techniques or 2D Particle Tracking Velocimetry (PTV). This study introduces a 3D-PTV method tailored to determine the effects of algae (Synechoccocussp.) on microplastic settling speeds in semi-large columns. We demonstrated that 3D PTV produces much more accurate results than 2D particle tracking. Testing the method in six experiments with varying algae concentrations revealed consistent results across the experiments and alignment with some theoretical approximations. The results were concurrent with calculated 2D speeds. No influence of algal density on settling velocities was found, which is highly relevant for microplastic fate modeling in eutrophic systems. We highlight the applicability and accuracy of 3D particle tracking velocimetry in further understanding microplastic settling behavior.

Light footprint of microalgae cultivation system addressed by modified Cornet model

The cultivation of microalgae is significantly influenced by light intensity and utilization efficiency. This study developed a modified Cornet (M−Cornet) model to assess the distribution of light intensity and flux in microalgae cultivation systems. Algal biofilm cultivation represents a more concentrated approach of algal suspension cultivation. Both follow the M−Cornet model and exhibit the same growth rates when cultured under identical conditions. Algal pigments and morphologies greatly impact the light absorption and scattering, resulting in light attenuation in intensity, penetration distance and light flux distribution. Algae varieties exhibit diverse light flux characteristics. 37% − 90% of the incident light is absorbed, of which, 80% to 90% is dissipated as heat. 10% to 63% of the incident light is scattered off the photobioreactor. The overall light utilization efficiency ranges 6% to 13%. The light footprint using the M−Cornet model offers valuable insights for photobioreactors designing and cultivation operating.

Thermal-bioconvection instability in a suspension of phototactic microorganisms heated from below

In this study, we investigate the linear stability of a suspension of motile algae under the combined influence of phototaxis and temperature gradients. The suspension, heated from below and illuminated from above with vertical collimated irradiation, sheds light on the intricate interplay between biological responses and thermal dynamics. The Navier–Stokes equation, thermal energy equation, and cell conservation equation are considered for the mathematical model. In suspension, the upper surface is taken as stress-free, while the lower surface is taken as rigid. The resulting eigenvalue problem, including the bioconvection Rayleigh and thermal Rayleigh numbers, is resolved numerically. Changes in the critical total intensity and Lewis number do not impact the critical threshold of the thermal Rayleigh number; however, they notably influence the critical bioconvection Rayleigh number. The critical total intensity and Lewis number destabilize the suspension. It is observed that heating from below enhances the instability of the layer. At higher temperatures, Rayleigh–Bénard convection dominates bioconvection, resulting in a single convection cell. Neutral curves of linear stability reveal transitions between stationary and oscillatory solutions. The results, validated against established methods, highlight the system’s response to parameters and phenomena such as Hopf bifurcations and limit cycles.

Enhancing pollutant removal and desalination in microbial desalination cells using a rotating algal biofilm cathode

Currently, most photosynthetic microbial desalination cells (PMDCs) employ suspended algae as cathode organisms to produce oxygen. However, this method requires expensive platinum as a catalyst to catalyze the binding of oxygen to cathode electrons. In this study, a PMDC using a rotating algal biofilm (RAB) as a biocathode was demonstrated. RAB not only generates enough oxygen as an electron acceptor but also enhances the combination of oxygen and electrons on the cathode. Furthermore, the RAB-MDC system exhibited excellent performance in pollutant removal and desalination. When using simulated wastewater as anolyte and catholyte, the RAB-MDC achieved impressive removal efficiencies for COD, TOC, and NH4+-N, reaching 91.0 ± 0.1 %, 74.7 ± 0.03 %, and 95.0 ± 0.05 %, respectively. The power density reached 89.5 mW/m3 at an external resistance of 1000 Ω, while the desalination efficiency was 36.0 %, with a desalination rate of 190.9 mg/d. Additionally, high-throughput 16S rDNA sequencing was employed to assess the relative abundance of microorganisms in the RAB-MDC device, facilitating guided culture in subsequent studies. In conclusion, this research demonstrates the potential of RAB as a biocathode in MDCs for comprehensive wastewater treatment, desalination, power generation, and nutrient recovery.

Membrane fouling during the harvesting of microalgae using static microfiltration

A challenge in the filtration of algal suspensions is the reduction in filtrate flow rate with time, associated with membrane fouling and filtercake formation. These two fouling mechanisms may occur simultaneously and have different effects on the scaling relationship of filtration rate with time, making quantitative predictions of the filtration behaviour complex. The foulants include suspended microalgal cells and their presumed Extracellular Polymeric Substances (EPS). To investigate this problem, we perform static microfiltration experiments to harvest oil-rich marine microalgae Nannochloropsis oculata. Batch filtration experiments of microalgal suspensions using glass-fibre membranes are conducted under filtration pressures varying between 0.5 and 200 kPa. Here we investigate the relative importance of potential fouling mechanisms, including pore plugging, entrance blocking, and filtercake formation. We examine variations in filtrate flux, using a novel approach involving numerical differentiation of the filtrate volume to identify how its scaling relationship with time and compare with the traditional root-time behaviour. These results are analysed with reference to the blocking filtration laws to determine the potential fouling mechanism. Rheology tests of both filtration feeds and filtrate are performed, and both optical and scanning electron microscopy are used to observe the filtercake. Our results show a significant drop in the filtrate flux after a spurt loss phase under pressure. The scaling analysis demonstrates a power law relationship between cumulative filtrate volume and time in the post-spurt phase. We show here, for the first time, that the scaling exponent varies with time, approaching a value close to 0.5 (i.e. the root-time behaviour) after a long period of time. Using the analysis, we conclude that the filtration process can be divided into various stages; a spurt loss phase when the pressure is initially applied, followed by a stage in which both internal and external filtercake formation occurs, and a final stage which is dominated by external filtercake formation (at which point root-time behaviour is observed). Furthermore, our findings suggest that fresh microalgal suspensions experienced a larger spurt loss compared to aged suspensions in microfiltration. This difference may be attributed to the limited production of EPS and microalgal debris during shorter cultivation periods. The microscopic observations reveal the invasion of microalgal cells into the membrane, which verifies the formation of an internal filtercake suggested by our scaling analysis. The contamination of the membrane increases with higher filtration pressures. Finally, we demonstrate that Fe3+ coagulant can be used to increase the microalgal particulate size before filtration, resulting in a much higher filtrate flux compared to uncoagulated suspensions. This result provides opportunities to reduce membrane contamination to a negligible level.

Introduction of Salicornia europaea L into in vitro culture

The goal of the research was to develop a technology for introducing Salicornia europaea L.into in vitro culture. Methods of cultivating meristems and callus cultures were studied. To cultivate meristems, the tip of the apical bud were used as an explant. Fragments of stems and leaves were used toobtain callus tissue. To study the influence of various factors on germination, seeds were soaked in sterile tap water and in solutions of gibberellin, cytokinin, auxin and NaCl, and were also subjected to cold stratification (independently and with subsequent placement in Knop’s agarized medium). Salicornia seeds were sterilized with various antiseptics: 70% alcohol, 10% aqueous solution of sodium hypochlorite («Belizna»), amoxicillinand 3% hydrogen peroxide. The ability of the culture to form callus was studied in MS medium. As a result, it was determined that the highest germination of seeds was observed in Knop medium after treating theseeds with a suspension of green algae of the Scenedesmus genus, as well as after preliminary cold stratification, and slightly less after treating the seeds with a solution of NaCl and gibberellic acid. The most effective method of seed sterilization turned out to be treatment with alcohol followed by treatment with sodium hypochlorite. A comparative analysis of seed germination in filter paper in Petri dishes, Knop agar medium, Murashige and Skoog (hormone-free) was carried out. The ability of S. europaea L. to form callusin MS medium with phytohormones was assessed. Conclusion. To improve germination, it is recommended to subject the seeds to cold stratification. To obtain aseptic explants quickly, it is recommended to germinate the seeds in the Knop nutrient medium, having previously sterilized them with alcohol, then with sodiumhypochlorite, followed by washing with distilled water. The most suitable type of microclonal propagationfor S. europaea L. is the production of callus tissue followed by induction of organogenesis or embryogenesis.

Life cycle analysis of seawater biodesalination using algae

This study assesses environmental impacts of reverse osmosis and algae-based biodesalination in four scenarios using a life cycle assessment (LCA) approach. These scenarios encompass (1) a multistage conventional pre-treatment desalination system, (2) immobilized algae-based hybrid desalination system, (3) suspended algae pre-treatment hybrid system, and (4) an attached growth algae-based hybrid system with a low-pressure reverse osmosis (LPRO) system. The assessment integrates the ReCiPe and USEtox 2.0 methods, examining diverse phases such as construction, operation, waste treatment, and chemicals. The impact analysis unveils waste treatment as a significant contributor in Scenario 1. In Scenarios 2 and 3, the operational phase, driven by chemical consumption, emerges as a major factor by 60–70 %, causing environmental damage. Scenario 4 showcases superior environmental performance, notably in global warming potential, freshwater eutrophication, marine eutrophication, ozone layer depletion, and fossil resource scarcity. Results highlight that Scenario 2 and Scenario 3, utilizing immobilized and suspended growth biodesalination, do not align with favorable LCA outcomes. Overall, Scenario 4 displays the least environmental impact and a favorable carbon footprint. The study advocates pipeline brine disposal due to its greater convenience and lesser environmental damage. A sensitivity analysis emphasizes the advantages of shorter transportation distances for optimal brine disposal from the desalination plant to the sea.

Biophotonic Combined Energy System (BCES)

A comprehensive outline of a new approach in closed loop processing for energy utilisation and biomass genera tion using micro algae for electricity, heat and chemicals is presented - the Biophotonic Combined Energy System (BCES). The basic idea proposes that life-cycle management is an es sential strategy in research and business. In terms of the BCES a carbon cycle driven by solar radiation via the photosystems of the Chlorophyceae species Scenedesmus rubescens serves as the core process from which valuable materials are extracted. The resi dues serve as the substrate for biogas generation which is used to run a Combined Heat and Power Plant (CHP) equipped with a gas motor and an exhaust gas carbon dioxide and heat recovery system. The electricity generated is fed into the public grid and the thermal energy is used to make the right temperature for the micro algae suspension. The carbon dioxide from biogas combus tion is injected into the algae suspension thereby closing the elementary loop within the system.

Effect of scattered/diffuse flux on the phototactic bioconvection in the absence of collimated flux

The main objective of this paper is to investigate the impact of diffuse/scattered flux in the absence of collimated flux on the stability of an isotropic scattering algal suspension. The linear stability analysis predicts an unstable mode of disturbance shifts from a non-oscillatory (an overstable) to an overstable (a non-oscillatory) state at the variation of diffuse flux for fixed parameters at the bioconvective instability. However, overstable solutions are observed only at the higher cell swimming speed and a higher extinction coefficient. The critical Rayleigh number increases as the magnitude of diffuse flux intensifies. This indicates that a suspension illuminated by higher levels of diffuse flux is more stable. Furthermore, the lower (higher) swimming speed enhances (diminishes) the suspension's stability, especially in low (high) light conditions. Also, the horizontal component of swimming orientation becomes more influential with a higher level of diffuse flux, particularly at smaller pattern wavelengths, resulting in behavior akin to gyrotaxis in certain instances.

Extraction of lutein by aqueous two-phase system including both cholinium and imidazolium-based ionic liquids from wet microalgae

Lutein is the main component of macular and retinal pigment so that it is essential for eye health. In addition, lutein is also related to various metabolic processes in the human body with strong antioxidant properties. The green extraction of lutein in wet microalgae is critical for the further applications as nutraceuticals and pharmaceuticals. Ionic liquid-based aqueous two-phase system (ATPS) is a green approach for multiple product extraction from microalgae. In this study, the extraction performances of ATPS composed of four different cholinium-based compounds (choline geranate, choline chloride, choline dihydrogen citrate and choline bitartrate) and polyethylene glycol 400 (PPG400) were compared. The choline dihydrogen citrate (Ch DHcit) showed a better extraction ability of lutein than other cholinium-based ILs. After optimizing the addition of cholinium-based ILs and PPG400, the ATPS with the best composition (PPG400: Ch Dhcit: water: algal suspension = 42:26:22:10 wt%) was applied to the extraction of lutein from wet Chlorella sp. Six imidazolium-based ionic liquids (1-ethyl-3-methylimidazole chloride, 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazole chloride, 1-hexyl-3-methylimidazole chloride and 1-hexyl-3-methylimidazolium bromide) were compared as an adjuvant for the lutein extraction from wet Chlorella sp. The introduction of a small amount of 1-ethyl-3-methylimidazole chloride ([C2mim]Cl) improved the extraction efficiency of lutein increased by 9.98 %. In the multiple-times extraction process, the total extraction efficiency of three times distribution reached 102.61 %. This paper provides a new approach to the extraction of lutein from algal biomass.

Effects of antidepressant exposure on aquatic communities assessed by a combination of morphological identification, functional measurements, environmental DNA metabarcoding and bioassays

The antidepressant fluoxetine is frequently detected in aquatic ecosystems, yet the effects on aquatic communities and ecosystems are still largely unknown. Therefore the aim of this study is to assess the effects of the long-term application of fluoxetine on key components of aquatic ecosystems including macroinvertebrate-, zooplankton-, phytoplankton- and microbial communities and organic matter decomposition by using traditional and non-traditional assessment methods. For this, we exposed 18 outdoor mesocosms (water volume of 1530 L and 10 cm of sediment) to five different concentrations of fluoxetine (0.2, 2, 20 and 200 μg/L) for eight weeks, followed by an eight-week recovery period. We quantified population and community effects by morphological identification, environmental DNA metabarcoding, in vitro and in vivo bioassays and measured organic matter decomposition as a measure of ecosystem functioning. We found effects of fluoxetine on bacterial, algal, zooplankton and macroinvertebrate communities and decomposition rates, mainly for the highest (200 μg/L) treatment. Treatment-related decreases in abundances were found for damselfly larvae (NOEC of 0.2 μg/L) and Sphaeriidae bivalves (NOEC of 20 μg/L), whereas Asellus aquaticus increased in abundance (NOEC <0.2 μg/L). Fluoxetine decreased photosynthetic activity and primary production of the suspended algae community. eDNA assessment provided additional insights by revealing that the algae belonging to the class Cryptophyceae and certain cyanobacteria taxa were the most negatively responding taxa to fluoxetine. Our results, together with results of others, suggest that fluoxetine can alter community structure and ecosystem functioning and that some impacts of fluoxetine on certain taxa can already be observed at environmentally realistic concentrations.

Interplay between Brownian and hydrodynamic tracer diffusion in suspensions of swimming microorganisms

The general problem of tracer diffusion in non-equilibrium baths is important in a wide range of systems, from the cellular level to geographical length scales. In this paper, we revisit the archetypical example of such a system: a collection of small passive particles immersed in a dilute suspension of non-interacting dipolar microswimmers, representing bacteria or algae. In particular, we consider the interplay between thermal (Brownian) diffusion and hydrodynamic (active) diffusion due to the persistent advection of tracers by microswimmer flow fields. Previously, it has been argued that even a moderate amount of Brownian diffusion is sufficient to significantly reduce the persistence time of tracer advection, leading to a significantly reduced value of the effective active diffusion coefficient $D_A$ compared to the non-Brownian case. Here, we show by large-scale simulations and kinetic theory that this effect is in fact practically relevant only for microswimmers that effectively remain stationary while still stirring up the surrounding fluid – so-called shakers. In contrast, for moderate and high values of the swimming speed, relevant for biological microswimmer suspensions, the effect of Brownian motion on $D_A$ is negligible, leading to the effects of advection by microswimmers and Brownian motion being additive. This conclusion contrasts with previous results from the literature, and encourages a reinterpretation of recent experimental measurements of $D_A$ for tracer particles of varying size in bacterial suspensions.

Emerging algal organic matter from simulated on-line chemical cleaning of ultrafiltration membranes treating algae-containing water

Massive reproduction of algae due to the eutrophication of water body poses a new challenge to the water ecosystem. Despite ultrafiltration (UF) acting as an effective method to treat algae-containing waters, on-line chemical cleaning is frequently utilized to sustain the permeability of UF membranes. However, little attention is currently paid on the side-effects of practical on-line chemical cleaning on aqueous environments. Therefore, this work evaluated the generation of algae organic matter triggered by diverse membrane cleaning reagents (i.e., HCl, NaOH, NaClO, SDS and CA), and their subsequent fate in terms of biodegradation and membrane retention. The results indicated that NaOH, HCl and NaClO caused serious damage and lysis of algal cells, leading to the significant release of dissolved organic matter (DOM), while CA and SDS induced negligible DOM release. The occurrence of DOM release was able to cause extra biofouling, thus deteriorating the UF permeability. Furthermore, DOM was characterized in terms of three molecular weight ranges, i.e., high molecular weight (HMW, > 3400 Da), medium molecular weight (MMW, 150–3400 Da), and low molecular weight (LMW, <150 Da). Protein-related substances in the range of HMW and MMW were primarily produced under HCl and NaOH exposures. In contrast, NaClO led to an obvious release of humic-like materials with MMW. During the next round of UF operation, roughly 17 % to 31 % of these released DOM could be removed by via the joint actions of suspended algae biodegradation and fouling layer retention. Nevertheless, roughly 69 % to 83 % of these produced DOM eventually entered into the UF permeate, resulting in the deterioration of permeate quality. Consequently, the detailed mechanisms of DOM generation and subsequent removal by UF were proposed, which re-examined the origins of emerging contaminants in aqueous environment and shed new light on the strategies to ameliorate current practice of on-line membrane chemical cleaning.

Photochemical Release of Dissolved Organic Nitrogen from Algal Detritus and Sediment Particles in Lake Taihu, China

Solar irradiation in aquatic systems can induce the conversion of substances from the solid to the dissolved phase (photodissolution). Yet, the photochemical release of dissolved organic nitrogen (DON) from internal particles in lakes remains largely unknown. In this study, suspensions of algal detritus and sediment particles from a shallow eutrophic lake were exposed to simulated solar irradiation, and the release and compositional changes of dissolved organic matter were explored by measuring their UV–Visible absorption spectroscopy and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The photochemical release of inorganic nitrogen during the incubations was also investigated. Results showed that light irradiation induced stronger dissolved organic carbon and DON production in the algal detritus suspensions, with release rates of 1.17 mg C L−1 h−1 and 0.14 mg N L−1 h−1, respectively, at an algal detritus concentration of 0.1 dry g L−1. Light irradiation also induced compositional changes of DON in both algal and sediment suspensions. A larger number of DON molecules with lower molecular weight were continuously released in the algal suspensions, e.g., the total number of DON formulas increased from 1349 to 4135 during an 8 h irradiation. In contrast, upon irradiation of sediment suspensions, DON showed decreased molecular diversity and increased aromaticity. The photochemical release of ammonium (photoammonification) was also higher in the algal suspensions with a rate of 0.015 mg N L−1 h−1, which may contribute to the eutrophication of the lake. This study provides new molecular insights into the photochemical release of DON from typical internal particles in eutrophic lakes.

Pattern formation in photo-controlled bioconvection

The model eukaryotic microalgae Chlamydomonas reinhardtii is well known for its ability to generate bioconvection flows that are associated to intricate concentration patterns. Recently, it was demonstrated that the propensity of these algae to move toward a light source – a phenomenon termed phototaxis – can be exploited to locally concentrate micro-organisms and induce (photo)-bioconvection in algal suspensions by inducing a localised excess of density. In the present study we show experimentally that a cell population in a thin liquid layer self-organises in the presence of a heterogeneous light field and displays remarkable symmetry-breaking instabilities that are ruled by both the width of the light beam and the photo-bioconvection Rayleigh number. Beside circular stable states, fingers, dendrites and wave instabilities are reported, quantified and classified in a general phase diagram. Next, we use lubrication theory to develop an asymptotic model for bioconvection in a thin liquid layer, that includes the influences of both gyrotaxis and phototaxis. We obtain a single nonlinear anisotropic diffusion–drift equation describing the spatiotemporal evolution of the depth-averaged algal population. Analytical and numerical solutions are presented and show a very good agreement with the experimental results. In particular, we show that the dendrite instability arises as a result of a subtle coupling between the nonlinearity of the phototactic response, the gyrotactic effect and the self-induced bioconvective flows. Such complex flow fields might find applications in photo-bioreactors, through the efficient stirring of the harvested biomass.

Effect of Exposure Concentration and Growth Conditions on the Association of Cerium Oxide Nanoparticles with Green Algae.

The increasing release of engineered nanoparticles (NPs) into aquatic ecosystems makes it crucial to understand the interactions of NPs with aquatic organisms, such as algae. In this study, the association of CeO2 NPs with unicellular algae (Raphidocelis subcapitata) and changes to the cellular elemental profile were investigated using three exposure concentrations (1, 50, and 1000 µg CeO2/L) at two different algal growth conditions-exponential and inhibited growth (1% glutaraldehyde). After a 24 h-exposure, algal suspensions were settled by gravity and CeO2-NP/algae association was analyzed by single-cell inductively coupled plasma quadrupole mass spectrometry (sc-ICP-QMS) and ICP time-of-flight MS (sc-ICP-TOFMS). Concurrent detection of the cellular fingerprint with cerium indicated NP association with algae (adsorption/uptake) and changes in the cellular elemental profiles. Less than 5% of cells were associated with NPs when exposed to 1 µg/L. For 50 µg/L exposures in growing and inhibited cell treatments, 4% and 16% of cells were associated with CeO2 NPs, respectively. ICP-TOFMS analysis made it possible to exclude cellular exudates associated with CeO2 NPs due to the cellular fingerprint. Growing and inhibited cells had different elemental profile changes following exposure to CeO2 NPs-e.g., growing cells had higher Mg and lower P contents independent of CeO2 concentration compared to inhibited cells.

Dewatering of Scenedesmus obliquus Cultivation Substrate with Microfiltration: Potential and Challenges for Water Reuse and Effective Harvesting

In the microalgae harvesting process, which includes a step for dewatering the algal suspension, directly reusing extracted water in situ would decrease the freshwater footprint of cultivation systems. Among various algae harvesting techniques, membrane-based filtration has shown numerous advantages. This study evaluated the reuse of permeate streams derived from Scenedesmus obliquus (S. obliquus) biomass filtration under bench-scale and pilot-scale conditions. In particular, this study identified a series of challenges and mechanisms that influence the water reuse potential and the robustness of the membrane harvesting system. In a preliminary phase of this investigation, the health status of the initial biomass was found to have important implications for the harvesting performance and quality of the permeate stream to be reused; healthy biomass ensured better dewatering performance (i.e., higher water fluxes) and higher quality of the permeate water streams. A series of bench-scale filtration experiments with different combinations of cross-flow velocity and pressure values were performed to identify the operative conditions that would maximize water productivity. The selected conditions, 2.4 m·s−1 and 1.4 bar (1 bar = 105 Pa), respectively, were then applied to drive pilot-scale microfiltration tests to reuse the collected permeate as a new cultivation medium for S. obliquus growth in a pilot-scale photobioreactor. The investigation revealed key differences between the behavior of the membrane systems at the two scales (bench and pilot). It indicated the potential for beneficial reuse of the permeate stream as the pilot-scale experiments ensured high harvesting performance and growth rates of biomass in permeate water that were highly similar to those recorded in the ideal cultivation medium. Finally, different nutrient reintegration protocols were investigated, revealing that both macro- and micro-nutrient levels are critical for the success of the reuse approach.

Study on the removal and degradation mechanism of microcystin-LR by the UV/Fenton system

Microcystin-LR (MC-LR) is highly hepatotoxic and potentially carcinogenic to humans. Therefore, removing MC-LR from water bodies is of paramount importance. This study aimed to investigate the removal efficacy of the UV/Fenton system on MC-LR from copper-green microcystin and to explore its degradation mechanism in simulated real algae-containing wastewater. The results showed that at an initial concentration of 5 μg·L−1, a combination of 300 μmol·L−1 H2O2, 125 μmol·L−1 FeSO4, and 5 min of UV irradiation under average radiation intensity of 48 μW·cm−2 resulted in a removal efficiency of 90.65 % for MC-LR. The reduction of extracellular soluble microbial metabolites of Microcystis aeruginosa confirmed the UV/Fenton method's degradation efficiency for MC-LR, while the observation of the functional group CH and OCO in the treatment group indicated effective binding sites in the coagulation process. However, the presence of humic substances in algal organic matter (AOM) and some proteins and polysaccharides in the algal cell suspension competed with MC-LR for HO·, resulting in a decreased removal effect (78.36 %) in simulated actual algae-containing wastewater. These quantitative results provide an experimental basis and theoretical foundation for controlling cyanobacterial water blooms and ensuring drinking water quality safety.

Phototactic bioconvection with the combined effect of diffuse and oblique collimated flux on an algal suspension

The objective of this paper is mainly to investigate the combined effect of diffuse and oblique collimated flux on the onset of phototactic bioconvection. The onset of phototactic bioconvection is examined numerically in a finite-depth algal suspension via linear stability theory. At bioconvective instability, an unstable mode of disturbance shifts from a non-oscillatory (an overstable) to an overstable (a non-oscillatory) state at the variation in oblique incidence angle/diffuse flux for fixed parameters. If n convection cells are piled up on another vertically, then the bioconvective solution of the linear stability problem is called mode n. For some parameters, mode 2 instability is switched to mode 1 instability as the angle of incidence/diffuse flux varies. In addition, diffuse flux (or oblique collimated flux) enhances algal suspension stability (or instability).

EFFECTS OF THE INTERACTION BETWEEN ALGAE AND MICROPLASTICS ON LIFE-HISTORY TRAITS OF DAPHNIA PULEX CLONES

Microplastic (MP) pollution is potentially a big threat to many aquatic organisms. However, we currently know very little about the effects of small MPs on phenotypes and the extent to which genetic and environmental factors modify the effects of MPs. I studied the direct and indirect effects of 9.5 - 11.5 μm polystyrene microspheres on the life history traits (time to maturation, total number of offspring, size of adults) of Daphnia pulex clone Bel 19 and Bel 87. The D. pulex clones were exposed to two different concentrations (low 0.001 mg/l and high 1 mg/l) of MP. Each clone had two groups of individuals. One group of individuals was fed with algae food (no MP aging) to observe direct effects, and another group with algae food (MP aging) to observe indirect effects on the life history traits. MPs were aged in algae suspension for 7 days. Individuals were fed with an amount of carbon concentration 1 mg/l. I used laboratory exposure to answer the research questions - 1) do D. pulex clones differ in the susceptibility to MP pollution in terms of life history traits? and 2) are there any signicant differences between direct and indirect effects of MPs on life history traits of D. pulex clones? The results from the study showed that the D. pulex clones differ signicantly in the susceptibility to MP pollution in terms of the observed life history traits, which demonstrate the importance of incorporating genetic variation into the assessments of the impacts of plastic particle exposure. Signicant differences were also observed between the direct and indirect effects of MP on life history traits of D. pulex clones. Among the observed traits, time to maturation is the most affected one by indirect effect with the largest effect size (almost 3 times higher than the direct effect size). The results indicate that indirect ecological effects might lead to effect thresholds at levels considered eld relevant to the direct effects