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

Adverse effects of iron-based nanoparticles on freshwater phytoplankton Scenedesmus armatus and Microcystis aeruginosa strains

Zero-valent nano-iron particles (nZVI) are increasingly present in freshwater aquatic environments due to their numerous applications in environmental remediation. However, despite the broad benefits associated with the use and development of nZVI nanoparticles, the potential risks of introducing them into the aquatic environment need to be considered. Special attention should be focused on primary producer organisms, the basal trophic level, whose impact affects the rest of the food web. Although there are numerous acute studies on the acute effects of these nanoparticles on photosynthetic primary producers, few studies focus on long-term exposures. The present study aimed at assessing the effects of nZVI on growth rate, photosynthesis activity, and reactive oxygen activity (ROS) on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa. Moreover, microcystin production was also evaluated. These parameters were assessed on both organisms singly exposed to 72 h-effective nZVI concentration for 10% maximal response for 28 days. The results showed that the cell growth rate of S. armatus was initially significantly altered and progressively reached control-like values at 28 days post-exposure, while M. aeruginosa did not show any significant difference concerning control values at any time. In both strains dark respiration (R) increased, unlike net photosynthesis (Pn), while gross photosynthesis (Pg) only slightly increased at 7 days of exposure and then became equal to control values at 28 days of exposure. The nZVI nanoparticles generated ROS progressively during the 28 days of exposure in both strains, although their formation was significantly higher on green algae than on cyanobacteria. These data can provide additional information to further investigate the potential risks of nZVI and ultimately help decision-makers make better informed decisions regarding the use of nZVI for environmental remediation.

Combined Effect of NZVI and H2O2 on the Cyanobacterium Microcystis aeruginosa: Performance and Mechanism

In order to eliminate the harmful cyanobacterium Microcystis aeruginosa and the algal organic matters (AOMs) produced by M. aeruginosa, the combined process of nanoscale zero-valent iron (NZVI) and hydrogen peroxide (H₂O₂) has been carried out, and the removal mechanism has also been clarified. As the initial cyanobacterial cell concentration is 1.0 (±0.05) × 10⁵ cells·mL^-1, all the treatments of NZVI, H₂O₂, and NZVI/H₂O₂ have inhibition effects on both the Chl a contents and photosynthetic pigments, with the Chl a removal efficiency of 47.3%, 80.5%, and 90.7% on the 5th day, respectively; moreover, the variation of ζ potential is proportional to that of the Chl a removal efficiency. The malondialdehyde content and superoxide dismutase activity are firstly increased and ultimately decreased to mitigate the oxidative stress under all the treatments. Compared with NZVI treatment alone, the oxidation of the H₂O₂ and NZVI/H₂O₂ processes can effectively destroy the antioxidant enzyme system and then inactivate the cyanobacterial cells, which further leads to the release of photosynthetic pigments and intracellular organic matters (IOM); in addition, the IOM removal efficiency (in terms of TOC) is 61.3% and 54.1% for the H₂O₂ and NZVI/H₂O₂ processes, respectively. Although NZVI is much more effective for extracellular organic matters (EOM) removal, it is less effective for IOM removal. The results of the three-dimensional EEM fluorescence spectra analysis further confirm that both H₂O₂ and NZVI/H₂O₂ have the ability to remove fluorescent substances from EOM and IOM, due to the oxidation mechanism; while NZVI has no removal effect for the fluorescent substances from EOM, it can remove part of fluorescent substances from IOM due to the agglomeration. All the results demonstrate that the NZVI/H₂O₂ process is a highly effective and applicable technology for the removal of M. aeruginosa and AOMs.

Effects of zinc and iron on the abundance of Microcystis in Lake Taihu under green light and turbulence conditions

Trace element is one of the important factors affecting the growth of Microcystis. The effects of zinc (0.4 mg/L) and iron (2 mg/L) on the abundance of Microcystis in Lake Taihu were investigated under continuous turbulence and green light conditions in a microcosm experiment. The study results showed that the abundance of Microcystis in the zinc treatment and the iron treatment group was 8.30% and 214% of that in the control group at the end of the experiment, respectively. The proportion of Cyanobacteria in the total phytoplankton biomass in the control, iron treatment, and zinc treatment group decreased from 99.99% at the beginning of the experiment to 13%, 18%, and 1% at the end of the experiment, respectively. At the end of the microcosm experiment, the phytoplankton community was dominated by Bacillariophyta in the control group, accounting for 63%, but it was dominated by Chlorophyta in the zinc treatment and the iron treatment group, accounting for 89% and 42%, respectively. The study results showed that under green light and turbulence, 0.4 mg/L zinc remarkably decreased the abundance of Microcystis, but 2 mg/L iron effectively increased the number of Microcystis and other algae. This research results provided a new idea for controlling Microcystis blooms.

Responses of benthic diatoms to waters affected by post-fire contamination

Wildfire effects go beyond direct impact in terrestrial ecosystems. Specifically, the periphytic communities of aquatic ecosystems standing within and downstream the burnt areas are relevant ecological receptors of post-fire runoff contamination. Nevertheless, the off-site impacts of wildfires in these communities are limitedly studied so far. The present study aimed to assess the effects of river water contaminated with ash-loaded runoff in the growth benthic diatom Navicula libonensis (Schoeman 1970). Four surface water samples were collected approximately one year after the wildfire for laboratory testing with the diatom: one was collected from a site upstream the burnt area, within the Unhais river (UU); three were collected from sites standing within the burnt area, one in the Unhais river (UB) and two in the Zêzere river (Z1 and Z2), reflecting different hydrological regimes. N. libonensis was proven able to discriminate among river sites affected and unaffected by wildfire runoff, reflecting, in general, the expected trends considering the physico-chemical characterization of the water samples. The water samples from the sites standing within the burnt area inhibited the biomass yield and growth rate of the tested diatom, ranking the samples regarding toxicity as follows: Z1 > UB > Z2 > UU. However, UB rather than Z1 presented the highest contaminant burden, namely metal elements, and some were found above widely accepted safety benchmarks (polycyclic aromatic hydrocarbons were not detected). This inconsistency can be linked to unknown interactions among metals within each water sample, to differential nutrient enrichment of samples, as well as hydrological factors. Overall, our results suggest that monospecific laboratory assays with sensitive diatoms can be valuable as cost-effective screening tools to prioritize sites affected by wildfires runoff requiring in-depth monitoring of negative effects in benthic producer communities.

Effect of complex iron on the phosphorus absorption by two freshwater algae

Iron plays an important role in physiological processes of microalgae and also affects the absorption of other nutrients by algae cells. Therefore, iron is one of the important controlling factors for algae bloom formation. This study investigated the effect of four kinds of complex iron (EDTA-Fe, ferric humate, ferric oxalate and ferric ammonium citrate) on the phosphorus absorption by two freshwater algae (Scenedesmus quadricauda and Anabaena flos-aquae). The results showed that the species and concentration of complex iron had a significant effect on the phosphorus uptake rate of S. quadricauda, but had only a slight effect on that of A. flos-aquae. The former exhibits positive influences on phosphorus absorption and was in the following order: ferric oxalate and EDTA-Fe > ferric humate and ammonium ferric citrate, and these effects depended on whether the presence of complex iron constitutes an environmental pressure for the growth of algal cells.

Bioavailability and effect of α-Fe2O3 nanoparticles on growth, fatty acid composition and morphological indices of Chlorella vulgaris

The wide application of α-Fe₂O₃ nanoparticles (NPs) in different fields has resulted in release and accumulation of these materials into the aquatic ecosystem. Therefore, it is important to understand the potential impact of these NPs on aquatic organisms especially primary producers i.e., microalgae. Present study aimed to investigate the bioavailability and the effect of α-Fe₂O₃ NPs on growth of iron deprived cells of Chlorella vulgaris. Results showed that α-Fe₂O₃ NPs are not available as iron source to support the growth of C. vulgaris. Moreover，α-Fe₂O₃ NPs induced stress condition to C. vulgaris, which were reflected in its growth rates, total lipid contents, fatty acid profile and cell morphology. Specifically, low concentrations of α-Fe₂O₃ NPs (0.1, 0.5, 2.5, 5, 10 mg/L) showed similar growth profile and total lipid contents at both exponential and stationary growth phases. At 50 and 100 mg/L α-Fe₂O₃ NPs concentrations biomass reduced by 41.2% and 83.7% whereas total lipid contents increased by 39.7% and 25.5% respectively at exponential growth phase along with reduction in fatty acids. The results illustrated novel insights into the microalgal interaction with nanoparticles, providing fundamental knowledge for the development of future microalgae ecology and cultivation technology.

Analysis of the Status and Improvement of Microalgal Phosphorus Removal from Municipal Wastewater

Phosphorus, as one of the main pollutants in municipal sewage, has received increasing attention recently. Phosphorus recovery also increases the sustainable development of municipal wastewater. Since algae have the ability to effectively redirect nutrients, including phosphorus, from municipal sewage to algae biomass, municipal sewage treatments involving microalgae have piqued the interest of many researchers. The phosphorus removal depends on the potential of the microalgae to absorb, preserve, or degrade phosphorus in municipal wastewater. It is, therefore, of great interest to study the mechanisms underlying the absorption, storage, and degradation of phosphorus by microalgae to ensure the viability of this phosphorus removal process in wastewater. The objectives of this review were to summarize phosphorus metabolism in microalgae, examine key external and internal factors impacting phosphorous removal by microalgae from wastewater, and examine the status of phosphorous-metabolism-related research to improve our understanding of microalgae-based municipal wastewater treatments. In addition, the methods of recovery of microalgae after phosphorous removal were summarized to ensure the sustainability of municipal wastewater treatment. Finally, a potential approach using nanomaterials was proposed to enhance the overall phosphorous removal performance in municipal wastewater through the addition of nanoparticles such as magnesium and iron.

Phycobiliproteins from Anabaena variabilis CCC421 and its production enhancement strategies using combinatory evolutionary algorithm approach

The production of phycobiliproteins (PBPs) from cyanobacteria represents both the industrial application and their commercial value. In this study, the capability of Anabaena variabilis CCC421 for the production of PBPs was evaluated which was further improved by optimization of selected BG-11 medium components viz. FAC, K₂HPO₄ and trace metals. A design matrix approach using evolutionary algorithm comprised of genetic-algorithm (GA) and fuzzy-logic-methodology (FLM), i.e., GA-Fuzzy, was used for the optimization. The maximum production of PBPs obtained with combinatory approach of GA-Fuzzy was 408.5 mg/L at an optimum combination of factors (FAC 0.153 g/L, K₂HPO₄ 0.2 g/L and Trace metals 0.5 ml/L) which was a 2.13 fold more than the control medium. This novel approach is very useful for modulating biological processes since various nutrients and metabolites have greater influence on these processes.

Effect of limitation of iron and manganese on microalgae growth in fresh water

Eutrophication is caused by the rapid growth of microalgae. Iron and manganese are important micronutrients for microalgae growth. However, the effect of the limitation of iron and manganese on microalgae growth in fresh water has not been well understood. In this study, natural mixed algae, Anabaena flosaquae and Scenedesmus quadricanda, were cultivated under different quotas of iron and manganese to reveal the effect of the limitation of iron and manganese on the growth of microalgae in fresh water. The results showed that the growth rate of algae is influenced more by iron than by manganese. However, the effect of manganese cannot be overlooked: when the initial manganese quota was replete, i.e. 0.6-0.8 mg l^-1, manganese was able to relieve the effect of iron limitation on microalgae growth in fresh water. We further found that the microalgae showed an uptake preference for iron over manganese. Iron had a competitive effect on manganese uptake, while manganese had less impact on iron uptake by microalgae. The information obtained in the current study is useful for the provision of water quality warnings and for the control of microalgae bloom in fresh water.