Nitrogen uptake by the macro-algae Cladophora coelothrix and Cladophora parriaudii: Influence on growth, nitrogen preference and biochemical composition

The role of species thermal plasticity for alien species invasibility in a changing climate: A case study of Lophocladia trichoclados

The Mediterranean Sea provides fertile ground for understanding the complex interplay between invasive species and native habitats, particularly within the context of climate change. This thermal tolerance study reveals the remarkable ability of Lophocladia trichoclados, a red algae species that has proven highly invasive, to adapt to varying temperatures, particularly thriving in colder Mediterranean waters, where it can withstand temperatures as low as 14 °C, a trait not observed in its native habitat. This rapid acclimation, occurring in less than a century, might entail a trade-off with high temperature resistance. Additionally, all sampled populations in the Mediterranean share the same haplotype, suggesting a common origin and the possibility that we might be facing an exceptionally acclimatable and invasive strain. This high degree of acclimatability could determine the future spread capacity in a changing scenario, highlighting the importance of considering both acclimation and adaptation in understanding the expansion of invasive species' ranges.

New insights into chicken processing wastewater treatment: the role of the microalgae Parachlorella kessleri on nitrogen removal

Microalgal Technologies have recently been employed as an alternative treatment for high nitrogen content wastewater. Nitrogen is an essential nutrient for microalgae growth, and its presence in wastewater may be an alternative source to synthetic medium, contributing to a circular economy. This study aimed to investigate the effect of using Parachlorella kessleri cultivated in wastewater from the thermal processing of chicken meat. Experiments were performed to obtain the ideal sampling site, inoculum dosage, and contact time. P. kessleri had better growth in the sample from the settling basin. Nitrogen removal was 95% (0,15 mg TNK/107 cells) in 9 days, and the final nitrogen concentration was lower than 20 mg/L, and the nitrate concentration was lower than 1 mg/L. However, during the third cycle in the kinetic assay, there was a decline in the microalgae growth, occasioned by the accumulation of nitrite (38,4 mg/L) in the inside of the cell. The study demonstrated that nitrogen concentration is directly related to the cell growth of the algae. Parachlorella kessleri efficiently removed nitrogen from chicken meat thermal processing wastewater and is a potential option for tertiary treatment and valorisation of such effluent as a nitrogen source.

Effect of benthic and planktonic diatoms on the growth and biochemical composition of the commercial macroalga Pyropia haitanensis

This study delves into how two ecotypes of diatom affect the Pyropia haitanensis, a valuable and commercial red macroalga. We co-cultivated P. haitanensis with a planktonic diatom Skeletonema costatum and benthic diatom Navicula climacospheniae. The results showed that benthic diatom significantly hindered P. haitanensis growth, while planktonic ones had no major impact. The macroalga restrained planktonic diatom growth but did not affect benthic diatom. Photosynthetic pigments of macroalga, except chlorophyll, were higher, indicating stress when exposed to diatoms. Microscopic images revealed dense benthic diatom attachment, potentially stressing thalli due to limited light and EPS secretion. Total carbohydrate slightly decreased in both diatom treatments, while total protein significantly decreased with increasing benthic diatom densities. In summary, benthic diatom notably influenced P. haitanensis growth, pigments, and total protein levels. This study sheds light on the interaction between microalgal ecotypes and commercial macroalga P. haitanensis, which is crucial for its economic significance.

Kelps may compensate for low nitrate availability by using regenerated forms of nitrogen, including urea and ammonium

Nitrate, the form of nitrogen often associated with kelp growth, is typically low in summer during periods of high macroalgal growth. More ephemeral, regenerated forms of nitrogen, such as ammonium and urea, are much less studied as sources of nitrogen for kelps, despite the relatively high concentrations of regenerated nitrogen found in the Southern California Bight, where kelps are common. To assess how nitrogen uptake by kelps varies by species and nitrogen form in southern California, USA, we measured uptake rates of nitrate, ammonium, and urea by Macrocystis pyrifera and Eisenia arborea individuals from four regions characterized by differences in nitrogen availability-Orange County, San Pedro, eastern Santa Catalina Island, and western Santa Catalina Island-during the summers of 2021 and 2022. Seawater samples collected at each location showed that overall nitrogen availability was low, but ammonium and urea were often more abundant than nitrate. We also quantified the internal %nitrogen of each kelp blade collected, which was positively associated with ambient environmental nitrogen concentrations at the time of collection. We observed that both kelp species readily took up nitrate, ammonium, and urea, with M. pyrifera taking up nitrate and ammonium more efficiently than E. arborea. Urea uptake efficiency for both species increased as internal percent nitrogen decreased. Our results indicate that lesser-studied, more ephemeral forms of nitrogen can readily be taken up by these kelps, with possible upregulation of urea uptake as nitrogen availability declines.

Nitrogen and phosphorus limitations promoted bacterial nitrate metabolism and propagation of antibiotic resistome in the phycosphere of Auxenochlorella pyrenoidosa

Despite that nitrogen (N) and phosphorus (P) play critical roles in the lifecycle of microalgae, how N and P further affect the distribution of bacteria and antibiotic resistance genes (ARGs) in the phycosphere is still poorly understood. In this study, the effects of N and P on the distribution of ARGs in the phycosphere of Auxenochlorella pyrenoidosa were investigated. Results showed that the growth and chlorophyll synthesis of microalgae were inhibited when N or P was limited, regardless of the N/P ratios, but the extracellular polymeric substances content and nitrate assimilation efficiency were enhanced in contrast. Metagenomic sequencing revealed that N or P limitation resulted in the recruitment of specific bacteria that highly contribute to the nitrate metabolism in the phycosphere. Besides, N or P limitation promoted the propagation of phycosphere ARGs, primarily through horizontal gene transfer mediated by mobile genetic elements. The enrichment of specific bacteria induced by changes in the algal physiology also contributed to the ARGs proliferation under nutrient limitation. Our results demonstrated that the reduction of algal cells caused by nutrient limitation could promote the propagation of ARGs, which provides new insights into the occurrence and spread of ARGs in the phycosphere.

Tropical bloom-forming mesoalgae Cladophoropsis sp. and Laurencia sp.-responses to ammonium enrichment and a simulated heatwave

Algal blooms are increasing worldwide, driven by elevated nutrient inputs. However, it is still unknown how tropical benthic algae will respond to heatwaves, which are expected to be more frequent under global warming. In the present study, a multifactorial experiment was carried out to investigate the potential synergistic effects of increased ammonium inputs (25 μM, control at 2.5 μM) and a heatwave (31°C, control at 25°C) on the growth and physiology (e.g., ammonium uptake, nutrient assimilation, photosynthetic performance, and pigment concentrations) of two bloom-forming algal species, Cladophoropsis sp. and Laurencia sp. Both algae positively responded to elevated ammonium concentrations with higher growth and chlorophyll a and lutein concentrations. Increased temperature was generally a less important driver, interacting with elevated ammonium by decreasing the algaes' %N content and N:P ratios. Interestingly, this stress response was not captured by the photosynthetic yield (Fv/Fm) nor by the carbon assimilation (%C), which increased for both algae at higher temperatures. The negative effects of higher temperature were, however, buffered by nutrient inputs, showing an antagonistic response in the combined treatment for the concentration of VAZ (violaxanthin, antheraxanthin, zeaxanthin) and thalli growth. Ammonium uptake was initially higher for Cladophoropsis sp. and increased for Laurencia sp. over experimental time, showing an acclimation capacity even in a short time interval. This experiment shows that both algae benefited from increased ammonium pulses and were able to overcome the otherwise detrimental stress of increasingly emerging temperature anomalies, which provide them a strong competitive advantage and might support their further expansions in tropical marine systems.

Influence of nitrogen sources on wastewater treatment performance by filamentous algae in constructed wetland system

Although filamentous algae have the characteristics of high nutrient assimilation ability, and adaptation to different conditions, studies on their role in water purification of constructed wetlands (CWs) are limited. In this study, the wastewater treatment capacity under different nitrogen sources was explored by constructing a filamentous algal CW (FACW) system. Results confirmed the fast and stable operation efficiency of the FACW system. Ammonia nitrogen was preferred in Cladophora sp. absorption and assimilation. The nutrient consumption rate (NCR) for total nitrogen (TN) of AG was 2.65 mg g-1 d-1, much higher than that of nitrate nitrogen (NG) (0.89 mg g-1 d-1). The symbiosis of bacteria and Cladophora sp. Contributed to pollutant removal. A stable and diverse community of microorganisms was found on Cladophora sp. Surface, which revealed different phylogenetic relationships and functional bacterial proportions with those attached on sediment surface. In addition, temperature and light intensity have great influence on the purification ability of plants, and low hydraulic retention time is beneficial to the cost-effective operation of the system. This study provides a method to expand the utilization of wetland plants and apply large filamentous algae to the purification of wetland water quality.

WITHDRAWN: Unlimited possibilities to use Сladophora (Chlorophyta, Ulvophyceae, Cladophorales) biomass in agriculture and aquaculture with profit for the environment and humanity

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/policies/article-withdrawal). This article has been withdrawn at the request of the Publisher for legal reasons related to Elsevier's policy on Geographic Sanctions (https://www.elsevier.com/about/policies/trade-sanctions).

Heavy metal tolerance in microalgae: Detoxification mechanisms and applications

The proficiency of microalgae to resist heavy metals has potential to be beneficial in resolving various environmental challenges. Global situations such as the need for cost-effective and ecological ways of remediation of contaminated water and for the development of bioenergy sources could employ microalgae. In a medium with the presence of heavy metals, microalgae utilize different mechanisms to uptake the metal and further detoxify it. Biosorption and the next process of bioaccumulation are two such major steps and they also include the assistance of different transporters at different stages of heavy metal tolerance. This capability has also proved to be efficient in eradicating many heavy metals like Chromium, Copper, Lead, Arsenic, Mercury, Nickel and Cadmium from the environment they are present in. This indicates the possibility of the application of microalgae as a biological way of remediating contaminated water. Heavy metal resistance quality also allows various microalgal species to contribute in the generation of biofuels like biodiesel and biohydrogen. Many research works have also explored the capacity of microalgae in nanotechnology for the formation of nanoparticles due to its relevant characteristics. Various studies have also revealed that biochar deduced from microalgae or a combination of biochar and microalgae can have wide applications specially in deprivation of heavy metals from an environment. This review focuses on the strategies adopted by microalgae, various transporters involved in the process of tolerating heavy metals and the applications where microalgae can participate owing to its ability to resist metals.

Combined effect of nitrogen and phosphorus on growth and biochemical composition of Tetradesmus obliquus (Turpin) M.J. Wynne

Microalgae have many biotechnological applications in various industries including food and feed, fertilizer, biofuel, cosmetics, pharmaceutics, and wastewater treatment. Since hey produce secondary metabolites under stress conditions such as pigments, carotenoids, hydrocarbons, and vitamins, investigating the effects of stress factors on growth parameters and biochemical composition of microalgal biomass is needed in producing bioproducts. In this paper, the combined effects of nitrogen and phosphorus on growth and the protein/amino acid and Lipid-FAMEs profiles of microalgae Tetradesmus obliquus (MAKUMACC-037) were investigated. Nitrogen and phosphorus deficiency reduced the algal growth. Biochemical composition was changed in a nitrogen and phosphorus dependent manner. High concentration of protein and lipid were associated with increased nitrogen and phosphorus concentration However, the FAMEs profiles were changed depending on only the nitrogen concentration.

Algal-bacterial consortium mediated system offers effective removal of nitrogen nutrients and antibiotic resistance genes

The sulfonamide antibiotic resistance genes (ARGs) especially sul1 was identified as the dominant in eutrophic water. The performance of Chlorella vulgaris-B. licheniformis consortium toward sul1 removal, total nitrogen (TN) removal, and the mechanism of sul1 removal was investigated. The removal efficiency of exogenous ARGs plasmids carrying sul1 reached (97.2 ± 2.3)%. The TN removal rate reached (98.5 ± 1.2)%. The enhancements of carbon metabolism, nitrogen metabolism, aminoacyl-tRNA biosynthesis, and glycoproteins had significant influences on sul1 and TN removals, under the premise of normal growth of algae and bacteria. The quantitative polymerase chain reaction (qPCR) results suggested that the absolute abundances of sul1 were low in algal-bacterial systems (0 gene copies/mL) compared with individual systems ((1 × 10⁶ ± 15) gene copies/mL). The duplication of sul1 was inhibited in algal cells and bacterial cells. The algal-bacterial consortium seems to be a promising technology for wastewater treatment with a potential to overcome the eutrophication and ARGs challenges.

Impact of immobilized algae and its consortium in biodegradation of the textile dyes

In biological engineering, cell immobilization is a modern technique for immobilizing free cells in a small space. Disintegration and elimination of azo dyes [Reactive Orange 122 (orange 2RL) and Reactive Red 194 (Reactive Red M-2BF)] were investigated by using Chlorococcum sp. and Chlorococcum sp. mixed with Scenedesmus obliquus, respectively. After 7 days of incubation, the maximum decolorization was spotted at 40 ppm for Reactive Orange 122 and 20 ppm for Reactive Red 194 by Chlorococcum sp. and Chlorococcum sp. mixed with S. obliquus, respectively. The findings revealed that the best decolorization activity was found at pH 11 and 25 °C under aeration conditions. BG11 was considered the best medium for azo dye decolorization with a high decolorization percentage. Additionally, different concentrations of nitrogen and phosphorus show the high activity of decolorization of both dyes. Referring to vitamins (thiamin and Ascorbic acid), all studied concentrations showed high decolorization activity with immobilized Chlorococcum sp. mixed with S. obliquus; however, different concentrations (20, 40, and 60 mg/l) of thiamin showed completely decolorization of Reactive Red 194 after 3 days, and 60 mg/l of ascorbic acid showed completely decolorization of Reactive Orange 122 after 5 days of inoculation. FT-IR and GC-Ms analysis for azo dyes after and before treatment with Immobilization of Chlorococcum sp. and Chlorococcum sp. mixed with Scenedesmus obliquus were detected. Novelty statement: The natural carrier algae and its consortium combined with a suitable immobilization technique were considered in this study, which is non-toxic, enhanced their bioremediation potential for dyes, and allowed multiple uses of biocatalysts. The novel use of the immobilization and its consortium of algae on the degradation efficiency of azo dyes and studying the effect of physicochemical conditions on decolorization and degradation of azo dyes. Application of immobilization techniques using microalgae could be excellent bioremediation of wastewaters.

Rapid start-up of photo-granule process in a photo-sequencing batch reactor under low aeration conditions: Effect of inoculum AGS size

The photo-granule process is an effective and economically feasible alternative for wastewater treatment, but little information is available regarding how to speed up the photo-granulation process. In this study, the effect of inoculum aerobic granular sludge (AGS) size on the start-up of the photo-granule process was investigated under low aeration conditions (superficial gas velocity of 0.5 cm/s). For this purpose, the inoculum AGS was sorted into various size-categories (0.4-0.8 mm, 0.8-1.4 mm, 1.4-2.2 mm, and > 2.2 mm) to serve as individual inoculum sludge. The excellent settling properties (SVI₅ of 39.3 mL/g), strong mechanical strength, efficient nutrient removal (COD: 94.2-97.1%; TN: 80.1-84.8%; TP: 60.4-91.5%), and high biodiesel yields (12.11 mg/g MLSS) were rapidly achieved in the system inoculated with 0.8-1.4 mm AGS. The granulation process was facilitated by filamentous algae as the nucleus, extracellular polymeric substances as the backbone, and the enrichment of functional bacteria (such as Thauera and Sphingorhabdus). Furthermore, the inherent influencing mechanisms of inoculum AGS size on the photo-granulation were revealed from cellular hydrophobicity, surface thermodynamics, and sludge aggregation behavior. This study provides a novel start-up approach of the photo-granule process by inoculating with the optimal AGS size, which is convenient, practically feasible and significantly reduced the aeration consumption.

Sugar Beet Processing Wastewater Treatment by Microalgae through Biosorption

The aim of this study was to investigate the potential of environmental pollution reduction of sugar beet processing factory wastewater by the biorefinery approach and integration of microalgae biomass production. In the present study, Chlorella vulgaris was cultivated in wastewater collected from a sugar beet processing factory at the beginning and at the end of a sugar plant campaign in an aerobic bioreactor on a laboratory scale under controlled conditions, with an air flow of 0.4 L/min, a temperature of 26 °C, and pH = 8. Microalgae showed effective nutrient remediation from wastewater. During wastewater treatment, chemical oxygen demand (COD) and biological oxygen demand (BOD) removal efficiency was 93.7% and 98.1%, respectively; total organic carbon (TOC) content decreased by 95.7%. Nitrites and nitrates decreased by 96%, while the biggest decrease in metal ions was achieved for Ca and Mn (82.7% and 97.6%, respectively). The findings of this study suggest that coupling microalgae cultivation and wastewater treatment has a lot of potential for reducing contamination through biosorption, while also providing environmental advantages.

Aquaculture waste nutrients removal using microalgae with floating permeable nutrient uptake system (FPNUS)

Large area requirements and huge energy consumption restrict the applications of microalgae in wastewater treatment. In this study, in-situ nutrient removal was tested using a floating permeable nutrients uptake system with pore sizes of 1, 5, 10, and 40 µm, and Chlorella sorokiniana and Scenedesmus acuminatus. Results showed that N transfer rate across FPNUS varied with membrane pore size and N-type. Average transfer rate of NH₄⁺-N, NO₃^--N, and NO₂^--N across 1 µm membrane was 2.6, 14.6, and 2.3 mg m^-2h^-1, respectively, sufficient to support microalgal growth. The NH₄⁺-N and NO₃^--N removal rate in shrimp wastewater reached 1.32 and 1.88 mg L^-1d^-1, comparable to some BNR processes used in RAS. According to the developed area ratio prediction model, FPNUS to pond area ratio of 21% is sufficient to balance N loading of 0.05 mg L^-1d^-1. These results indicate extraordinary potential of in-situ nutrient removal from wastewaters using FPNUS.

Monitoring Microalgal Growth of Chlorella minutissima with a New All Solid-state Contact Nitrate Selective Sensor

As third generation feedstock, microalgae are microorganisms that can grow only in the optimum conditions. There are parameters including the concentration of macro and microelements in nutrient solution, pH, temperature, and light intensity that have significant impact on microalgal growth. In recent years, various sensing devices has been developed for sensitive measurement of these parameters during microalgal growth. In this study, a new potentiometric nitrate selective sensor was developed to indicate the nitrate uptake of microalgae and the effect of nitrate nutrient on microalgal growth, specifically, and this sensor was successfully applied to determine nitrate concentration in medium during microalgal growth. Moreover, the effects of nitrate, carbonate and phosphate concentration in the growth medium on biomass production of Chlorella minutissima were investigated by using Box-Behnken design method, and optimum conditions were determined for the highest biomass production of microalgae. As a result of the experiments, it was seen that the highest C. minutissima production was achieved using the medium consist of 2.63 g/L NaNO₃ , 0.35 g/L Na₂ CO₃ and 0.4 g/L KH₂ PO_4. Statistically, it was observed that there was a proportional relationship between the microalgae production and investigated parameters such as carbon, nitrogen and phosphate amounts of culture mediums. The electrode showed a wide linear range between 1.0×10^-1 and 5.0×10^-5 M with a detection limit of the 5×10^-6 M and the response time was found as 10 s. The results showed that developed nitrate selective sensor could be successfully applied for continuous measurement of nitrate in microalgal productions at reduced cost. This article is protected by copyright. All rights reserved.

Progress and challenges of contaminate removal from wastewater using microalgae biomass

The utilization of microalgae in treating wastewater has been an emerging topic focussed on finding an economically sustainable and environmentally friendly approach to treating wastewater. Over the last several years, different types of con microalgae and bacteria consortia have been experimented with to explore their potential in effectively treating wastewater from different sources. The basic features considered while determining efficiency is their capacity to remove nutrients including nitrogen (N) and phosphorus (P) and heavy metals like arsenic (As), lead (Pb), and copper (Cu). This paper reviews the efficiency of microalgae as an approach to treating wastewater from different sources and compares conventional and microalgae-based treatment systems. The paper also discusses the characteristics of wastewater, conventional methods of wastewater treatment that have been used so far, and the technological mechanisms for removing nutrients and heavy metals from contaminated water. Microalgae can successfully eliminate the suspended nutrients and have been reported to successfully remove N, P, and heavy metals by up to 99.6 %, 100 %, and 13%-100 % from different types of wastewater. However, although a microalgae-based wastewater treatment system offers some benefits, it also presents some challenges as outlined in the last section of this paper. Performance in eliminating nutrients from wastewater is affected by different parameters such as temperature, biomass productivity, osmotic ability, pH, O₂ concentration. Therefore, the conducting of pilot-scale studies and exploration of the complexities of contaminants under complex environmental conditions is recommended.

Enhancing growth and oil accumulation of a palmitoleic acid-rich Scenedesmus obliquus in mixotrophic cultivation with acetate and its potential for ammonium-containing wastewater purification and biodiesel production

A palmitoleic acid-rich Scenedesmus obliquus strain SXND-02 was isolated from ammonium-containing wastewater. Biomass and lipid production were examined for this microalgal strain in photoautotrophic, heterotrophic, and mixotrophic cultivations, respectively, in order to extend its application in wastewater purification coupled with production of valued bio-products. Among the tested conditions, the microalga had better growth and higher lipid accumulation in mixotrophy. NH₄Cl inhibited the microalgal growth in photoautotrophic cultivation. However, NaAc alleviated this inhibition in both heterotrophy and mixotrophy. Using 7 g L^-1 NaAc and 0.5 g L^-1 NH₄Cl as carbon and nitrogen sources significantly increased the algal biomass and lipid yields under mixotrophic cultivation, with the highest levels up to 1.0 g L^-1 and 59.88%, respectively. Fatty acid profiling indicated that palmitoleic acid was 23% in the S. obliquus SXND-02 under mixotrophic condition, which was about 21-fold higher than that in the control S. obliquus. Furthermore, this microalgal strain was tested in the chicken farm wastewater (CFW) containing high ammonium. Compared with other treatments, the S. obliquus SXND-02 cultivated in the 1/2 CFW + NaAc medium produced larger amounts of biomass (2.18 g L^-1) and lipids (50.22%), and simultaneously higher removal rates of total nitrogen (TN) (80%), total ammonium nitrogen (TAN) (68%), total phosphate (TP) (82%), biological oxygen demand (BOD) (86%) and chemical oxygen demand (COD) (89%) from wastewater. The present data indicate that this excellent microalga can be used in mixotrophic cultivation for wastewater purification coupled with commercial production of valued biomass and high-quality algal oils.

Soil Organic Carbon Enrichment Triggers In Situ Nitrogen Interception by Phototrophic Biofilms at the Soil-Water Interface: From Regional Scale to Microscale

Phototrophic biofilms are easy to grow at sediment/soil-water interfaces (SWIs) in shallow aquatic ecosystems and greatly impact nutrient biogeochemical cycles. However, the pathways by which they contribute to nitrogen interception and interact with sediment/soil remains largely unknown. Here, we conducted a field investigation in paddy fields in various regions of China and found that nitrogen immobilized in biofilm biomass significantly positively correlated with soil organic carbon (SOC) content. A microcosm experiment showed that this was due to increased bacterial and algal diversity, biomass accumulation, and inorganic nitrogen assimilation at high SOC, especially high dissolved organic carbon (DOC) levels. The metatranscriptomics results further verified that many KO groups of PSII, PSI, AP, and PC in antenna proteins and glutamate synthesis were distinctly expressed at elevated SOC and DOC levels. Our results elucidated the effects and possible pathways of how SOC enrichment triggers photosynthesis and nitrogen immobilization by phototrophic biofilms. The results will provide meaningful information for in situ nitrogen interception by using phototrophic biofilms at the SWI in human-made wetlands to change internal nitrogen cycling.

Removal of metals from aqueous solutions using dried Cladophora parriaudii of varying biochemical composition

Macroalgal biosorption has shown promise for the removal of metal ions from wastewaters, whose presence can pose a threat to the aquatic environment. There is a wealth of literature published on macroalgal biosorption, the common thread being that the biosorbent material was collected from the field, under undefined conditions. These studies offer little insight into the impact of prior cultivation or biomass production practices upon the biosorbent material, its adsorptive physico-chemical properties and its subsequent capacity for metal removal. The present study sought to investigate the influence of changes in macroalgal cultivation, specifically nutrient regime, upon biomass properties and the resultant adsorption performance. The macroalga Cladophora parriaudii was cultivated under six different nutrient regimes; 2:1 and 12:1 N:P molar ratios, with nitrogen supplied either as ammonium (NH₄⁺), nitrate (NO₃^-), or urea (CO(NH₂)₂). These nutrient regimes were designed to produce biomass of varying biochemical and cell surface profiles. After cultivation, the biomass was rinsed, dried, biochemically analysed and then used for the removal of four individual metals from solution. Metal removal varied considerably between treatments and across initial metal concentrations, with removal values of 46-85%, 9-80%, 8-71%, and 49-94% achieved for Al, Cu, Mn, and Pb, respectively, with initial metal concentrations varying between 0 and 150 mg L^-1. The observed variation in metal removal can only be attributed to differences in biochemistry and cell surface properties of the biosorbent induced by nutrient regime, as all other variables were constant. This study demonstrates that prior cultivation conditions influence the biochemistry of a biosorbent material, namely macroalgae Cladophora parriaudii, which has an impact upon metal removal. This aspect should be given due consideration for future biosorption research and when reviewing already published literature.

Nitrogen enrichment mediates the effects of high temperature on the growth, photosynthesis, and biochemical constituents of Gracilaria blodgettii and Gracilaria lemaneiformis

Gracilaria blodgettii and Gracilaria lemaneiformis are often adopted as tools to purify aquaculture tail water. However, there has been such phenomenon that high temperature in summer restricts the process of aquaculture. To explore the adaptive capacity of G. blodgettii and G. lemaneiformis, we experimented them and cultured for 12 days under three temperatures (20, 25, and 30 °C) and three levels of multiple nitrogen sources (0.12, 0.6 and 4.4 mg L-1). Their growth, photosynthetic characteristics, and biochemical compositions including the contents of pigments and soluble protein were determined to investigate the single and interactive effects of temperatures and nitrogen levels on these two species. The results showed that in terms of G. blodgettii, the higher growth rate and more pigment (chlorophyll a and carotenoids) contents were observed at 25 and 30 °C in comparison to 20 °C, and the pigments showed maximum contents at 25 °C. More nitrogen improved the growth rate, net photosynthetic rate (Pn) at 25 and 30 °C, Fv/Fm at 20 °C, maximal photosynthetic electron transfer rate (ETRm), as well as soluble protein content at 20 and 25 °C. Additionally, the growth rate, Pn, and ETRm of G. lemaneiformis all showed a decline as increasing temperature; analogously high nitrogen concentration increased the growth rate at 25 and 30 °C, Fv/Fm at each temperature, ETRm, and pigments contents at 20 °C, as well as soluble protein content at 20 and 25 °C. Conclusions indicated that high temperature restricted the growth rate, inhibited photosynthetic characteristics, and decreased the soluble protein content of G. lemaneiformis. The reduced photosynthetic performance, pigments, and soluble protein contents of G. blodgettii were noted under similar conditions. However, nitrogen enrichment induced the greater resistant level to high temperature, and G. blodgettii showed better response. These findings suggested that these two Gracilaria species possessed a certain adaptability to tail water from aquaculture at high temperature and G. blodgettii can resist more to. Therefore, it seems to be an alternative and workable scheme to adopt some suitable macroalgae to optimize the solution to present purification of aquaculture wastewater or eutrophic waters under high temperature.

Kinetics Growth and Recovery of Valuable Nutrients from Selangor Peat Swamp and Pristine Forest Soils Using Different Extraction Methods as Potential Microalgae Growth Enhancers

Soil extracts are useful nutrients to enhance the growth of microalgae. Therefore, the present study attempts for the use of virgin soils from Peninsular Malaysia as growth enhancer. Soils collected from Raja Musa Forest Reserve (RMFR) and Ayer Hitam Forest Reserve (AHFR) were treated using different extraction methods. The total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and dissolved organic carbon (DOC) concentrations in the autoclave methods were relatively higher than natural extraction with up to 132.0 mg N/L, 10.7 mg P/L, and 2629 mg C/L, respectively for RMFR. The results of TDN, TDP, and DOC suggested that the best extraction methods are autoclaved at 121 °C twice with increasing 87%, 84%, and 95%, respectively. Chlorella vulgaris TRG 4C dominated the growth at 121 °C twice extraction method in the RMRF and AHRF samples, with increasing 54.3% and 14%, respectively. The specific growth rate (µ) of both microalgae were relatively higher, 0.23 d^-1 in the Ayer Hitam Soil. This extract served well as a microalgal growth promoter, reducing the cost and the needs for synthetic medium. Mass production of microalgae as aquatic feed will be attempted eventually. The high recovery rate of nutrients has a huge potential to serve as a growth promoter for microalgae.

Insight into nitrogen and phosphorus coupling effects on mixotrophic Chlorella vulgaris growth under stably controlled nutrient conditions

In water environment, nitrogen (N) and phosphorus (P) are biochemically dependent nutrients following the co-limitation concept for algae growth under mixotrophic mode. From a practical viewpoint, algae growth may not bring about significant change of the background nutrient concentration of an actual waterbody in contrast to a conventional batch system. In order to better understand the growth pattern of microalgae in aquatic environments, a series of experiments were conducted under stably controlled N-P levels for studying the N-P coupling effect on mixotrophic Chlorella vulgaris growth process, with attention paid to the physiological and biochemical characteristics. It was found that within the concentration range of N = 1-8 mg·L^-1 and P = 0.1-1.0 mg·L^-1, the variation of the N-P level slightly affected the specific growth rate, but significantly influenced nutrients uptake, biomass dry weight, chlorophyll contents of the grown C. vulgaris. The biochemical and elemental composition of the microalgae tended to be more sensitive to the N-P concentrations and ratios in the lower nutrient range (1-2 mg N·L^-1, 0.1-0.4 mg P·L^-1) in which the highest N and P conversion rates were gained as 90.18 ± 1.23% and 60.47 ± 1.59%, respectively. The P assimilation and conversion efficiencies were much affected by both N and P supplies, while the P supply showed little influence on N assimilation and conversion efficiencies. It was also noticed that the N level greatly affected the metabolic pathway involving nutrient assimilation, carbohydrate fixation and monosaccharide profile, resulting in conversion of the dominant fraction of protein at N ≤ 2 mg·L^-1 into other biochemical compositions including lipids at N ≥ 3 mg·L^-1. The fatty acid methyl esters (FAMEs) composition tended to differ with varied nutrient levels. These findings may deepen our understanding of algal growth in aquatic environment and provide perspective for eutrophication control.

Integrating micro-algae into wastewater treatment: A review

Improving the ecological status of water sources is a growing focus for many developed and developing nations, in particular with reducing nitrogen and phosphorus in wastewater effluent. In recent years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment.

Isotopically labelled macroalgae: A new method for determining sources of excess nitrogen pollution

RATIONALE

Stable nitrogen isotope ratios (δ15 N) can be used to discern sources of excess nitrogen pollution in water. The δ15 N values of nitrate in water often do not reflect the true δ15 N source value owing to high temporal variation, and there are high analytical costs associated with obtaining δ15 N values from water nitrate. To find alternative solutions, we isotopically labelled macroalgae (i.e. seaweed) beyond natural variation as a new method for determining sources of excess nitrogen pollution in seawater.

METHODS

Fucus vesiculosus (bladder wrack) non-fertile tips were collected from Easington Colliery, County Durham, UK, and cultured in two isotopically enriched solutions containing ammonium sulphate with δ15 N values of 170 ± 5‰ and -60 ± 3‰ for a period of 19 days. The macroalgae were cultured in separate opened glass jars in an incubator with set temperature (11°C) and light (125 μmol photons m-2 s-2 on a light/dark rhythm of 16 h/8 h). The oven-dried tips were analysed for δ15 N over the 19-day experiment.

RESULTS

The macroalgal tips incorporated the isotopically enriched solutions rapidly, reaching 50% of the isotopically enriched seawater after ca 11 days for the 15 N-enriched solution and ca 15 days for the 14 N-enriched solution. δ15 N values were incorporated more into the torn base of the macroalgal tips than into the middle and apex regions.

CONCLUSIONS

F. vesiculosus rapidly incorporates the isotopic ratio of the artificial seawater solution to which it is translocated. The laboratory-developed isotopically labelled macroalgae can be manufactured to generate 'unnatural' δ15 N values for translocation into coastal environments. This approach can provide an efficient, low-cost alternative to current analytical methods for determining and monitoring nitrogen pollution.

Exposure to environmental concentrations of fipronil and 2,4-D mixtures causes physiological, morphological and biochemical changes in Raphidocelis subcapitata

The occurrence of pesticides and their mixtures in the environment can alter the ecological relationships between aquatic food chains. Since fipronil and 2,4-dichlorophenoxyacetic acid (2,4-D) are commonly found together in Brazilian water bodies, the present study aimed to investigate through an integrative approach the toxicity mechanisms of environmentally relevant concentrations of pesticides Regent® 800 WG (active ingredient - a.i. fipronil), DMA® 806 BR (a.i. 2,4-D) isolated and in mixtures on the green alga Raphidocelis subcapitata using multiple parameters: physiological (growth rate and chlorophyll a fluorescence), morphological (cell complexity and size), biochemical (composition of lipid classes) and related to the photosynthetic activity (variable fluorescence, the maximum quantum yield of the photosystem II - PSII - and the efficiency of the oxygen evolving complex - OEC - of PSII). The results indicated that fipronil significantly inhibited algal population growth, increased the chlorophyll a content (observed by fluorescence), cell size and lipid class content of triacylglycerol (TAG), free fatty acid (FFA) and acetone mobile polar lipid (AMPL) and, on the other hand, decreased variable fluorescence of algae. The tested concentrations of 2,4-D increased the chlorophyll a fluorescence, the cell size and the lipid classes TAG and FFA. The pesticide mixtures have had more effects on algae than isolated compounds, causing alterations in all parameters analyzed, including photosynthetic activity (maximum quantum yield and efficiency of the oxygen evolving complex of the PSII), in which no alterations were observed for the toxicity of the single pesticides. The results suggest that these analyses are important to evaluate pesticide toxicity mechanisms in ecological risk assessments of tropical regions. Thus, here we demonstrate the importance of using multiple parameters in ecotoxicological studies to obtain a better understanding of the toxicity of these compounds for phytoplankton.

Removal of nutrients from Organic Liquid Agricultural Waste using filamentous algae

A feasibility analysis of tertiary treatment for Organic Liquid Agricultural Waste is presented using filamentous algae belonging to the genus Cladophora sp. as an alternative to chemical tertiary treatment. The main advantages of tertiary treatments that use biological systems are the low cost investment and the minimal dependence on environmental variables. In this work we demonstrate that filamentous algae reduces the nutrient load of nitrate (circa 75%) and phosphate (circa 86%) from the organic waste effluents coming from dairy farms after nine days of culture, with the added advantage being that after the treatment period, algae removal can be achieved by simple procedures. Currently, the organic wastewater is discarded into fields and local streams. However, the algae can acquire value as a by-product since it has various uses as compost, cellulose, and biogas. A disadvantage of this system is that clean water must be used to achieve enough water transparency to allow algae growth. Even so, the nutrient reduction system of the organic effluents proposed is friendly to the ecosystem, compared to tertiary treatments that use chemicals to precipitate and collect nutrients such as nitrates and phosphates.

Wastewater treatment using filamentous algae - A review

Wastewater treatment using algae is a promising approach for efficient removal of contaminating nutrients and their conversion into useful products. Monocultures of filamentous algae provide easier harvesting compared to microalgae, and better control of biomass quality than polyculture systems such as algal turf scrubbers. In this review, recent research into wastewater treatment using freshwater filamentous algae is compiled and critically analysed. Focus is given to filamentous algae monocultures, with key relevant findings from microalgae and polyculture systems discussed and compared. The application of monocultures of filamentous algae is an emerging area of research. Gaps are identified in our understanding of key aspects important to large-scale system design, including criteria for species selection, influence of nutrient type and loading, inorganic carbon supply, algae-bacteria interactions, and parameters such as pond depth, mixing and harvesting regimes. This technology has much promise, however future research is needed to maximise productivity and wastewater treatment efficiency.

Toxic effects and metabolic fate of carbamazepine in diatom Navicula sp. as influenced by humic acid and nitrogen species

Carbamazepine (CAB) is a commonly detected pharmaceutical in the surface waters. In the present study, we evaluated the effect of humic acid (HA) and nitrogen species on the toxicity of CAB in a typical diatom Navicula sp., and its metabolic fate. The Navicula sp. showed a high sensitivity to CAB (72 h EC₅₀ = 0.179 mg L^-1). The addition of HA (< 30 mg L^-1) and ammonium could promote the growth of Navicula sp. during 6 d of exposure to CAB. CAB underwent rapid dissipation in the algal culture. The degradation of CAB in Navicula sp. cultures was significantly increased by the addition of HA and higher HA contents caused more degradation of CAB. Degradation and accumulation of CAB in Navicula sp. were significantly inhibited by ammonium. Five metabolites were found and possible degradation pathways of CAB in the algal cell were proposed. Methoxylation, demethylation, glucuronidation and hydroxylation contributed to CAB transformation in the algal cell.

Enhancing biomass, lipid production, and nutrient utilization of the microalga Monoraphidium sp. QLZ-3 in walnut shell extracts supplemented with carbon dioxide

Microalgae are a promising biofuel resource, but their high cost and low productivity hinder their commercial applications. In the present study, Monoraphidium sp. QLZ-3 was cultivated in walnut shell extracts (WSE) supplemented with carbon dioxide (CO₂). Biomass was enhanced from 0.40 g L^-1 to 1.18 g L^-1, and lipid content reached 49.54% in WSE-12% CO₂ media. Biomass and lipid productivity reached 196.88 and 97.52 mg L^-1 d^-1, which were 1.33- and 1.57-fold higher than those of the control, respectively. The amount of carbohydrates increased, but the protein contents decreased. Furthermore, the application of CO₂ promoted nutrient and polyphenol absorption and upregulated the expression levels of lipid biosynthetic genes of this WSE-cultivated alga. These results indicated that coupling WSE and CO₂ could be an efficient strategy to enhance biofuel production by microalgae.

Salinity mediates the effects of nitrogen enrichment on the growth, photosynthesis, and biochemical composition of Ulva prolifera

To study the combined effects of multiple nitrogen (N) sources and salinity on the growth and physiology on macroalgae, we cultured Ulva prolifera under three N levels (N₀, 0.1235 mg L^-1; N₁, 0.6 mg L^-1; and N₂, 4.4 mg L^-1; the ratios were 18:74:8 for NH₄-N, NO₃-N, and NO₂-N, respectively) and three salinity conditions (15, 25, and 35). Then, the growth, pigment content, photosynthetic performance, superoxide dismutase (SOD) activity, and contents of soluble protein and carbohydrates were measured. The results showed the following: (1) Compared to that grown at salinity 25, the growth of U. prolifera decreased under salinity 35, especially under the N₀ and N₂ levels, but there were no significant effects of salinity 15 under any of the N levels. (2) There were no significant effects of salinity on the chlorophyll a (Chla) content, but compared to the content at salinity 25, the chlorophyll b (Chlb) content was enhanced by salinity 15 and 35; lower ratio values between Chla and carotenoids (Car) occurred under the salinity 25 treatment. Under each salinity condition, the pigments were enhanced by a high N level. (3) A relatively higher salinity level decreased the photosynthetic oxygen evolution rate, while a higher N level increased this value. Compared to the rate at salinity 25, the dark respiration rate (R_d) significantly increased at salinity 15 under the N₀ condition. (4) SOD activity was enhanced by a high N level, but no significant effects of salinity were observed. (5) The carbohydrate content was enhanced at salinity 35 under the N₀ and N₁ levels, and under salinity 15, this value increased with increasing N levels. In conclusion, although the growth of U. prolifera decreased at high N levels under high salinity conditions, a high N level induced an increase in photosynthesis, while no significant decrease in growth occurred. These findings indicate that low salinity and high N levels may be nonnegligible reasons why this species thrives, and low salinity was the better choice when this species was used for wastewater treatment.

Nitrogen fertilizers promote plant growth and assist in manganese (Mn) accumulation by Polygonum pubescens Blume cultured in Mn tailings soil

This study examined how different nitrogen (N) forms and application levels promote plant growth and assist in manganese (Mn) remediation of Polygonum pubescens Blume (P. pubescens) cultured in soil with a high Mn level. The effects of ammonium chloride (a) and urea (u), at three application levels (10, 20, and 30 mg L^-1 N) and control (no N addition, CK) on the growth, Mn accumulation, and enzymatic anti-oxidative defenses of P. pubescens were examined. In general, both ammonium-N and urea-N promoted the plant mass and height of P. pubescens. The total Mn amount of roots, stems, and leaves in N treatments were higher (p < 0.05) than that of CK. The ammonium-N treatments showed greater plant biomass and Mn accumulation compared to the urea-N ones. In general, the accumulations of Mn, Cr, Zn, and Cu were significantly lower (p < 0.05) in the N fertilizer treatment than those in the control; while the accumulations of Pb were higher (p < 0.05) in P. pubescens across all N fertilizer treatments than those in the control. The N addition decreased the contents of O₂^- and H₂O₂ in the leaves of P. pubescens, while increasing the activities of enzymatic anti-oxidative defenses.

Responses of Raphidocelis subcapitata exposed to Cd and Pb: Mechanisms of toxicity assessed by multiple endpoints

Microalgae have been widely used in ecotoxicological studies in order to evaluate the impacts of heavy metals in aquatic ecosystems. However, there are few studies that analyze the effects of metals in an integrative way on photosynthetic apparatus of freshwater microalgae in the generation of reactive oxygen species (ROS) and biochemical composition. Therefore, this study aimed to assess cadmium (Cd) and lead (Pb) toxicity using synchronously physiological and biochemical endpoints, specially detecting lipidic classes for the very first time during Cd and Pb-exposure to Raphidocelis subcapitata. Here we show that analyzing the algae growth, the IC50-72 h for Cd was 0.04 µM and for Pb was 0.78 µM. In general, the Cd affected the biochemical parameters more, leading to an increase in total lipid content (7.2-fold), total carbohydrates (3.5-fold) and ROS production (3.7-fold). The higher production of lipids and carbohydrates during Cd-exposure probably acted as a defense mechanism, helping to reduce the extent of damage caused by the metal in the photosynthetic apparatus. For Pb, the physiological parameters were more sensitive, which resulted in changes of chlorophyll a synthesis and a reduction of both efficiency of oxygen-evolving complex and quantum yields. Besides that, we observed changes in the lipid class composition during Cd and Pb-exposure, suggesting these analyses as great biomarkers to assess metal toxicity mechanisms in ecological risk assessments. Thereby, here we demonstrate the importance of using multiple endpoints in ecotoxicological studies in order to obtain a better understanding of the mechanisms of metal toxicity to R. subcapitata.