Microalgal Cells Research Articles

Enhanced extracellular polymeric substances production defending microalgal cells against the stress of tetrabromobisphenol A

Enhanced extracellular polymeric substances production defending microalgal cells against the stress of tetrabromobisphenol A

Surface properties of membrane materials and their role in cell adhesion and biofilm formation of microalgae

In this study, the effects of surface properties of membrane materials on microalgae cell adhesion and biofilm formation were investigated using Chlorella vulgaris and five different types of membrane materials under hydrodynamic conditions. The results suggest that the contact angle (hydrophobicity), surface free energy, and free energy of cohesion of membrane materials alone could not sufficiently elucidate the selectivity of microalgae cell adhesion and biofilm formation on membrane materials surfaces, and membrane surface roughness played a dominant role in controlling biofilm formation rate, under tested hydrodynamic conditions. A lower level of biofilm EPS production was generally associated with a larger amount of biofilm formation. The zeta potential of membrane materials could enhance initial microalgae cell adhesion and biofilm formation through salt bridging or charge neutralization mechanisms.

A novel biomineralization-inspired flocculation approach for harvesting high quality microalgal biomass: Dual action of cationic polyelectrolytes and nanosilica

This study posed a novel biomimetic flocculation approach, aiming to efficiently harvest high-quality biomass of Scenedesmus quadricauda cultured with anaerobic digestate. Here, that poly(diallyldimethylammonium chloride) (PDADMAC) could serve as mimetic silicified proteins to spontaneously incorporate nanosilica onto microalgal cells, imparting diatom-like characteristics to S. quadricauda. Compared to the exponential growth phase (day 3), the highest harvesting efficiency (93.49%) was obtained at a lower dosage of PDADMAC (5 mg/g) in the stationary phase (day 6), which was attributed to changes in properties and composition of microalgal LB-EPS. On day 6, the hydrophobic functional groups in LB-EPS provided more binding sites during the flocculation process and formed a network structure of microalgal cells-flocculants-nanosilica. The resulting larger and more stable biomimetic silica shell promoted microalgal flocculation and sedimentation. Compared to conventional harvesting methods (centrifugation, polyacrylamide, alkaline flocculation), this method had the minimal negative impact on harvested biomass, with 9.95% of cell membranes damaged.

Flexibility and Function of Distal Substrate-Binding Tryptophans in the Blue Mussel β-Mannanase MeMan5A and Their Role in Hydrolysis and Transglycosylation

β-Mannanases hydrolyze β-mannans, important components of plant and microalgae cell walls. Retaining β-mannanases can also catalyze transglycosylation, forming new β-mannosidic bonds that are applicable for synthesis. This study focused on the blue mussel (Mytilus edulis) GH5_10 β-mannanase MeMan5A, which contains two semi-conserved tryptophans (W240 and W281) in the distal subsite +2 of its active site cleft. Variants of MeMan5A were generated by replacing one or both tryptophans with alanines. The substitutions reduced the enzyme’s catalytic efficiency (kcat/Km using galactomannan) by three-fold (W281A), five-fold (W240A), or 20-fold (W240A/W281A). Productive binding modes were analyzed by 18O labeling of hydrolysis products and mass spectrometry. Results show that the substitution of both tryptophans was required to shift away from the dominant binding mode of mannopentaose (spanning subsites −3 to +2), suggesting that both tryptophans contribute to glycan binding. NMR spectroscopy and molecular dynamics simulations were conducted to analyze protein flexibility and glycan binding. We suggest that W240 is rigid and contributes to +2 subsite mannosyl specificity, while W281 is flexible, which enables stacking interactions in the +2 subsite by loop movement to facilitate binding. The substitutions significantly reduced or eliminated transglycosylation with saccharides as glycosyl acceptors but had no significant effect on reactions with alcohols.

ANALISIS POTENSI Chlorella Sp. DI PANTAI BASE-G SEBAGAI BAHAN BIODIESEL DENGAN UJI PROKSIMAT

Background: Phytoplankton is one of the microalgae that has great potential as an energy source, one of which is Chlorella sp.. Chlorella sp. is the largest producer of protein compared to other types of phytoplankton. The lipid and fatty acid content in microalgae is a source of energy that plays a role in the process of making biodiesel. Phytoplankton type Chlorella sp. easy to cultivate and breed. Supporting breeding in the process is supported by the use of fertilizers that are rich in nutrients so that it will optimize the growth of these phytoplankton. Generally fertilizer is divided into two, namely inorganic fertilizer and organic fertilizer. The aim of this research was to determine the fat content of Chlorella sp. which was obtained from the results of culture with the treatment of giving skipjack tuna fertilizer through a proximate test. Methods: This research was conducted by taking samples of Chlorella sp. At Base-G Beach. Samples were cultured and added liquid fertilizer from skipjack fish waste at a concentration of 4;8;12 ml/L. Chlorella sp. The culture results were calculated for cell density and tested for fat content through proximate fat analysis. Results: The study showed that the density of microalgae cells produced ranges from 0.21 x106 cells/ml to 0.51x106 cells/ml. The average proximate analysis of fat in microalgae was 0.022%-0.039% (w/w). The application of skipjack tuna waste fertilizer affected the proximate fat value of Chlorella sp. (p<0.05). Conclusion: The proximate fat content in Chlorella sp samples from Base-G beach which were cultured with the addition of liquid skipjack tuna waste fertilizer was 0.022-0.039% (w/w).

Occurrence of potentially toxic microalgae and diarrhetic shellfish toxins in the digestive tracts of green sea turtles (Chelonia mydas) from southern Brazil

Algal toxins are involved in the mortality and/or illness of marine organisms via consumption of contaminated prey, or upon direct exposure to toxic cells. In this study, the presence of potentially toxic microalgal cells was investigated within the digestive tract contents of a threatened species of green turtle (Chelonia mydas). Additionally, lipophilic toxins were determined by LC-MS/MS in tissue samples (liver, stomach and/or intestine) of selected animals (n = 39 individuals) found dead-stranded in southern Brazil, from winter/2015 to autumn/2016. Thirteen potentially toxic species of microalgae (both benthic and planktonic), including seven dinoflagellates, six cyanobacteria and one diatom, were found in the digestive tract contents of green turtles. Among them, dinoflagellates belonging to the Dinophysis acuminata species complex were the most frequent (36%) and abundant (maximum average abundance of 566 cells g−1 in spring/2015). Moreover, 23% of the examined sea turtles exhibited detectable levels of the diarrhetic shellfish toxin okadaic acid (OA) in washed digestive tissues. Seven individuals accumulated OA in their intestines (max. 24.1 ng g−1) and two in the stomachs (max. 7.4 ng g−1). Toxin levels in the tissues were directly and significantly (r = 0.70, p < 0.025) associated with the cell abundance of OA-producing D. acuminata and Prorocentrum lima species complexes within the digestive contents of green turtles. Although OA concentrations were relatively low, possible chronic exposure might deteriorate general health conditions of exposed sea turtles, increasing the risk for diseases. Okadaic acid has been regarded as a tumor-promoting compound and an environmental co-factor in the incidence of fibropapillomatosis, a frequent disease in juvenile green turtles inhabiting this geographic region. Even though, only one green turtle containing OA in the digestive tissues (out of six examined) also presented fibropapillomatosis in this study. Notwithstanding, sea turtles are sentinels of ocean health. Monitoring the accumulation of algal toxins and their negative effects on these organisms contributes to conserving biodiversity and marine habitats.

Morphological and cellular organization of green microalgae to cope with cold stress in subarctic environment

Microalgae are one of the most widely dispersed living organisms on Earth and can be found even in extreme environments. Especially in such habitats, the microalgal cell wall plays an essential role as it is the first barrier in continuous contact with the surrounding and changing environment. In cold conditions microalgae can show changes in their morphology, also known as phenotypic plasticity which is the ability of an organism to show different phenotypes when exposed to different environmental conditions. In addition, presence or absence of algaenan is thought to be responsible for increase/decrease permeability and stiffness of the cell wall. The aim of this work was to evaluate and compare how microalgae cells can modify their cell wall components and cellular morphology under low-temperature conditions (5 °C) and differ during the exponential and stationary phases. Four microalgae species were studied: Coelastrella sp. 3–4, Chlorella vulgaris sp. 13–1, Haematococcus pluvialis, and Scenedesmus sp. B2–2, which were isolated from subarctic locations.Using a histochemical approach in conjunction with light microscopy, cell features such as size, organization and cell wall ornamentation were evaluated. Staining procedures showed changes in biochemical components such as pectins and presence or absence of exopolysaccharides and lipids. Results showed that Coelastrella cultures did not grow under low-temperature conditions. However, Chlorella vulgaris, Haematococcus pluvialis and Scenedesmus species demonstrated a slower growth rate, bigger and rounded cell-shape during cold condition. Furthermore, the latter microalgal strain also showed modification in algaenan presence as one of the main components in cell wall architecture, which can be related to the permeability of cell wall. Changes in other features such as cell organization and cell wall ornamentation were investigated.

A Review of the Harvesting Techniques of Microalgae

Algae are an important group of photosynthetic autotrophs and are commonly found in different types of water bodies, including paddy fields. The algal group possesses distinctive characteristics and ranges from prokaryotic cyanobacteria to eukaryotic algae. Within these, microalgae are unicellular microorganisms widely distributed in saltwater as well as freshwater environments. Microalgae species have been utilized in different fields, especially animal and human nutrition, medicine, bioremediation, and bio-fertilizers. Recently, numerous studies have reported the importance of microalgae in the production of biofuel. Further, microalgae have great carbon dioxide fixation efficiency during growth, so farmable land is not required for cultivating microalgae. Microalgae biomass production is a three-step process: cultivation, harvesting, and processing. Of these, the harvesting process is considered challenging due to its high cost, and it directly affects the processing step. In addition, several factors influence the harvesting process, including the size of microalgae cells (&lt;30 µm), cultural conditions of microalgae, electronegative property of cell membrane, growth rate, etc. The harvesting of microalgae is an elaborate process that involves different chemical or mechanical approaches. A number of harvesting techniques have been utilized to recover algal biomass, such as membrane filtration, chemical and bio-flocculation, flotation centrifugation, sedimentation, and coagulation. In this context, this review aims to discuss various types of techniques used for harvesting microalgae. This review could be useful for selecting appropriate harvesting technology for enhancing the yield of microalgae biomass.

Metabonomics analysis of microalga Scenedesmus obliquus under ciprofloxacin stress

The wide use of antibiotics in aquaculture has triggered global ecological security issue. Microalgal bioremediation is a promising strategy for antibiotics elimination due to carbon recovery, detoxification and various ecological advantages. However, a lack of understanding with respect to the corresponding regulation mechanism towards antibiotic stress may limit its practical applicability. The microalga Scenedesmus obliquus was shown to be capable of effectively eliminating ciprofloxacin (CIP), which is a common antibiotic used in aquaculture. However, the corresponding transcriptional alterations require further investigation and verification at the metabolomic level. Thus, this study uncovered the metabolomic profiles and detailed toxic and defense mechanisms towards CIP in S. obliquus using untargeted metabolomics. The enhanced oligosaccharide/polyol/lipid transport, up-regulation of carbohydrate and arachidonic acid metabolic pathways and increased energy production via EMP metabolism were observed as defense mechanisms of microalgal cells to xenobiotic CIP. The toxic metabolic responses included: (1) down-regulation of parts of mineral and organic transporters; (2) electrons competition between antibiotic and NAD during intracellular CIP degradation; and (3) suppressed expression of the hem gene in chlorophyll biosynthesis. This study describes the metabolic profile of microalgae during CIP elimination and reveals the key pathways from the perspective of metabolism, thereby providing information on the precise regulation of antibiotic bioremediation via microalgae.

Effects of marine phycotoxin dinophysistoxin-1 on the growth and cell cycle of Isochrysis galbana

The phycotoxin dinophysistoxins are widely distributed in the global marine environments and potentially threaten marine organisms and human health. The mechanism of the dinophysistoxin toxicity in inhibiting the growth of microalgae is less well understood. In this study, effects of the dissolved dinophysistoxin-1 (DTX1) on the growth, pigment contents, PSII photosynthetic efficiency, oxidative stress response and cell cycle of the marine microalga Isochrysis galbana were investigated. Growth of I. galbana was significantly inhibited by DTX1 with 0.6–1.5 μmol L−1 in a 96-h batch culture, corresponding the 96 h-EC50 of DTX1 at 0.835 μmol L−1. The maximum quantum yield of PSII (Fv/Fm), and light utilization efficiency (α) were obviously reduced by DTX1 at 1.5 μmol L−1 during 96-h exposure. Contents of most of pigments were generally reduced by DTX1 with a dose-depend pattern in microalgal cells except for diatoxanthin. The ROS levels were increased by DTX1 with 0.6–1.5 μmol L−1 after 72-h exposure, while the contents or activities of MDA, GSH, SOD and CAT were significantly increased by DTX1 at 1.5 μmol L−1 at 96 h. The inhibitory effect of DTX1 on the growth of I. galbana was mainly caused by the production of ROS in the cells. Cell cycle analysis showed that the I. galbana cell cycle was arrested by DTX1 at G2/M phase. This study enhances the understanding of the chemical ecology effects of DTX1 on marine microalgae and also provides fundamental data for deriving water quality criteria of DSTs for marine organisms.

Non-immersed zigzag microalgae biofilm overcoming high turbidity and ammonia of wastewater for muti-pollutants bio-purification

Biological treatment that utilizes microalgae technology has demonstrated outstanding efficacy in the wastewater purification and nutrients recovery. However, the high turbidity of the digested piggery wastewater (DPW) leads to serious light attenuation and the culture mode of suspended microalgae results in a huge landing area. Thus, to overcome light attenuation in DPW, a non-immersed titled zigzag microalgae biofilm was constructed by attaching it onto a porous cotton cloth. As a result, the light could directly irradiate microalgae biofilm that attached on both sides of the cotton cloth, and the microalgal biofilm area was up to 6 m2 per bioreactor landing area. When the non-immersed zigzag microalgae biofilm bioreactor (N-Z-MBP) was used to treat wastewater with an ammonia nitrogen (NH4+-N) concentration of 362 mg L−1, the NH4+-N was completely removed in just 5 days and the maximum growth rate of microalgae biofilm reached 7.02 g m−2 d−1. After 21 days of long-term sequencing batch operation for the N-Z-MBP, the biomass density of the biofilm reached 52 g m−2 and remained at this high value for the next 14 days. Most importantly, during the 35 days’ running, the NH4+ -N maximum removal rate of single batch reached up to 65 mg L−1 d−1 and its concentration in the effluent was always below the discharge standard value (80 mg L−1 form GB18596–2001 of China) and total phosphorus was completely removed in each batch. Furthermore, the biomass concentration of microalgae cells in the effluent of the N-Z-MBP was almost zero, indicating that the non-submerged biofilm achieved in situ separation of microalgae from the wastewater. This work suggests that the N-Z-MBP can effectively purify DPW over a long period, providing a possible strategy to treat wastewater with high ammonia nitrogen and high turbidity.

Size-Tunable Elasto-Inertial Sorting of Haematococcus pluvialis in the Ultrastretchable Microchannel.

Haematococcus pluvialis is a good source of astaxanthin, which reduces oxidation in the human body, treats inflammation, and slows the growth of breast and skin cancer cells. Since the size of H. pluvialis is often closely related to astaxanthin yield, size-based microalgal separation has far-reaching significance for high-value algae extraction and algal directed evolution. In this work, we report a novel size-tunable elasto-inertial sorting of H. pluvialis in the Ecoflex ultrastretchable microfluidic devices. Ecoflex microfluidic chips can deform and be flexible, bringing flexibility and stretchability to microchannels as well as new possibilities for large-scale modulation of channel geometry. Here, the effects of velocity, channel elongation, and particle size on the elasto-inertial migration of particles are systematically studied. We found that channel elongation has a strong regulating effect on particle focusing. In addition, we verified the continuous regulation of the sorting threshold of microalgal cells by stretching the channel, providing technical support for the extraction and directed evolution of high-yield microalgae.

Stealth microplastics pollutants: Toxicological evaluation of polyethylene terephthalate-based glitters on the microalga Desmodesmus sp. and its color effect.

Polyethylene terephthalate-based glitters (PET glitters) are a potential source of primary microplastics in the environment. However, the bioeffects of PET glitters and the associated leachates remain largely unknown. In this study, we investigated the individual and combined toxicity of five colors (silver, black, red, green, and blue) of PET glitters and their corresponding leachates on the cellular responses of Desmodesmus sp. The results indicated that the photosynthesis of Desmodesmus sp. could be partly affected by PET glitters through the shading effect, but not that of growth. Conversely, the leachates of red and green PET glitters significantly inhibited the growth of the microalga, suggesting a higher risk associated with additives leached from these colors of PET glitters. Furthermore, the adverse effects of the co-occurrence of PET glitters and leachates were closely related to oxidative stress responses in the microalgal cells, along with a color effect, which could be mainly attributed to variations in the composition and abundance of toxic additives in different colors of PET glitters. Overall, our findings provide insights into the ecological risks posed by glitters in aquatic environments and emphasize the importance of considering color factors in assessing microplastics toxicity.

Recovery of Chlorella biomass using Fe3O4 and Fe3O4@SiO2 magnetic nanoparticles: isotherm and thermodynamic characteristics of adsorption

AbstractHarvesting microalgae by centrifugation and filtration is very costly, affecting technical and economical feasibility of downstream processing of algal biomas to bioproducts. Flocculation is a potential technique for recovery of algae biomass. Particularly, flocculation using magnetic nanoparticles offers high separation efficiency due to their high surface area and magnetic properties. In this work, the synthesized magnetic nanoparticles including Fe3O4 and Fe3O4@SiO2 were used to harvest C. sorokiniana TH01 from aqueous suspension. The effects of pH, adsorbent dosage, algal biomass concentration, temperature and reaction time on harvesting performance were investigated. It was revealed that the optimal C. sorokiniana TH01 harvesting conditions for Fe3O4 were pH of 5, adsorbent dosage of 0.5 g/L, biomass concentration of 2‐2.5 g/L, temperature 25oC and reaction time 20‐30 min. For Fe3O4@SiO2, the optimal conditions were pH of 7, adsorbent dosage of 0.6 g/L, with the same biomass concentration, temperature and reaction time as Fe3O4. Under the optimal conditions, Fe3O4 and Fe3O4@SiO2 can be regenerated up to three cycles with harvesting efficiency till remained over 55%. Adsorption of C. sorokiniana TH01 on Fe3O4 and Fe3O4@SiO2 exhibited the best fitness with Langmuir isortherm with R2 and maximal adsorption capacity estimated of 0.995 and 6.55 g/g and 0.9971 and 9.53 g/g, respectively. Thermodynamics study revealed that an adsorption of C. sorokiniana TH01 on Fe3O4 and Fe3O4@SiO2 was exothermic process. Furthermore, XRD, EDS, SEM, TGA and FT‐IR data confirmed the successful binding of microalgae cells on surfaces of Fe3O4 and Fe3O4@SiO2. The super‐magnetization intensities (&gt; 22 emu/g) of the synthesized materials demonstrated an excellent separation capability with external magnetic devices.

Impacts of fulvic acid and Cr(VI) on metabolism and chromium removal pathways of green microalgae

Green microalgae are highly efficient and cost-effective in the removal of heavy metals from water. However, dissolved organic matter (DOM), such as fulvic acid (FA), can impact their growth and heavy metal accumulation. Nonetheless, the specific mechanisms underlying these effects remain poorly understood. This study investigated the effects of different FA concentrations on the development, metabolism, and chromium (Cr) enrichment of Chlorella vulgaris, a standard green microalga. The findings revealed that low FA concentrations alleviated Cr-induced stress, stimulated microalgal growth, and enhanced energy conservation by suppressing chlorophyll synthesis. The highest chromium enrichment and reduction rates of 38.73% and 57.95% were observed when FA concentration reached 20 mg/L of total organic carbon (TOC). Furthermore, FA facilitated chromium removal by C. vulgaris through extracellular adsorption. Examination of microalgal cell surface functional groups and ultrastructure indicated that FA increased adsorption site electrons by promoting extracellular polymeric substance (EPS) secretion and enhancing the oxygen content of acidic functional groups. As a result, FA contributed to elevated enrichment and reduction rates of Cr in microalgal cells. These findings provide a theoretical basis for the prevention and control of heavy metal pollution in water environments.

Heterogeneous aggregation between microplastics and microalgae: May provide new insights for microplastics removal

Existing studies have shown that microplastics (MPs) as artificial surfaces can be colonized by plankton microorganisms. However, systematic research on exploring the aggregation formation process of MPs and microalgae is still lacking and particularly the influencing factors of aggregation remain to be elucidated. Therefore, this study investigated the heterogeneous aggregation process between various microalgal species (i.e., Chlorella vulgaris, Scenedesmus obliquus, Tetraselmis subcordiformis, Chaetoceros müelleri and Streptococcus westermani) and MPs (i.e., mPS and mPLA) with different sizes (i.e., 74 μm and 613 μm), concentrations (i.e., 0.1 g/L, 1 g/L and 2 g/L) and shapes (i.e., the particle and sheet). The results showed that microalgae can first attach to the holes or protrusions of MPs and highly accumulate in the local region, and then multi-layer aggregation can be formed subsequently. The aggregation degree between MPs and microalgae was closely related to the MPs shape and size, and was less related to the MPs concentration. The aggregation speed of small-sized MPs (e.g., 74 μm) was faster than the large-sized ones (e.g., 613 μm). The MPs in a shape of sheet were more obvious than those in particle on their aggregation with microalgae. The density of aggregates was increased compared with pristine MPs, which is related to the cell density and cell number of attached microalgae. For the same type of MPs, the aggregation degree for the tested microalgae was as follows: Scenedesmus obliquus > C. vulgaris > T. subcordiformis > C. müelleri > S. westermani. Meanwhile, MPs inhibited cell growth of microalgae, particularly under the circumstance of their aggregation, by limiting the gas and mass transfer between microalgal cells and the extracellular environment. The heterogeneous aggregation of MPs and microalgae may provide new ideas for treatment and controlling of MPs in the environment.

Effects of Polystyrene Microparticles on Growth and Physiological Metabolism of Microalgae Scendesmus obliquus

Plastic products are widely used due to their lightness, durability, low cost, and malleability, and their threat to the environment is becoming increasingly apparent. However, the detailed mechanism of such an effect is unclear. Due to improper treatment, microplastic contamination is very much studied in the areas around sewage outfalls or some plastic manufacturers, and its content is high. To investigate the ecological impact of microplastics in this particular area, we evaluated the toxic effect of polystyrene microplastics (PS-MPs) on the microalgae Scenedesmus obliquus (S. obliquus). In particular, the cell growth, photosynthesis, antioxidant enzyme activity, membrane permeability, and morphology of the microalgae in the presence of different PS-MP concentrations were monitored. These new data revealed an increase in microalgae cell growth as an early response to low-dose PS-MP exposure with a maximum inhabitation rate of −3.33%. In contrast, a higher concentration of PS-MP solution leads to a significant inhibition within the test concentration, with a maximum inhabitation rate of 43.62%. Meanwhile, a decreased photosynthesis activity of S. obliquus was observed during the exposure. Moreover, PS-MPs induced oxidative damage to the algae cells, exhibiting decreased antioxidant activities and enhanced lipid peroxidation reactions, as evidenced by the reduction in the superoxide dismutase (SOD) level and increased malondialdehyde (MDA) content, as well as damaged cell membrane and soluble protein. Collectively, our study systematically investigates the toxicity of microplastics on microalgae, providing a deep insight into the possible influences of plastic pollution on the whole food web in the aquatic ecosystem.

Comparative evaluation of four Chlorella species treating mariculture wastewater under different photoperiods: Nitrogen removal performance, enzyme activity, and antioxidant response

The nitrogen removal performance, nitrogen metabolism enzyme activities, and antioxidant response of four Chlorella species (Chlorella sp., Chlorella vulgaris, Chlorella sorokiniana, and Chlorella protothecoides) were compared under different light: dark (L:D) photoperiods during treating mariculture wastewater. The increase of light duration in the range of 8L:16D to 16L:8D was beneficial to the chlorophyll synthesis of selected four Chlorella species. Chlorella vulgaris was the most effective to treat mariculture wastewater than Chlorella sp., Chlorella sorokiniana, and Chlorella protothecoides. and its microalgae density, photosynthetic activity, and nitrogen metabolism enzyme activity were higher than those of the other three Chlorella species. An obvious oxidative stress in microalgal cells was under 20L:4D photoperiod, which led to a decrease in photosynthetic activity and nitrogen metabolizing enzyme activity. Among the four Chlorella species, Chlorella protothecoides had the highest degree of light-induced stress and ROS accumulation. This study can provide suitable microalgae and optimal photoperiod for treating mariculture wastewater.

Performance of membrane photobioreactor for integrated Spirulina strain cultivation and nutrient removal of membrane bioreactor effluent

Water reuse by wastewater treatment techniques is implemented to promote a circular economy strategy and alleviate water shortage. The microalgae-based wastewater treatment is an environmentally friendly tool to treat secondary or tertiary wastewater by removing the remaining nutrients, primarily dissolved nitrogen (N) and phosphorus (P). This research aimed to study the membrane photobioreactor (MPBR) performance to treat nitrate nitrogen (NO3-N) and phosphate (PO4) that remained in the membrane bioreactor (MBR) effluent by varying hydraulic retention times (HRTs) and solids retention times (SRTs). Bench-scale of MPBR (63 L) was continuously operated by cultivating Spirulina sp. TISTR 8875. The LED light intensity of 3000–5000 lux was provided 24 h daily. The experimental studies evaluated HRTs in the range of 6.4–9.7 days and SRTs at 20, 40, 60, and 80 days, and the microalgae cells were not removed (infinite SRT). The results showed that the HRT range of 7.7–7.8 days and SRT range of 60–80 days exhibited NO3-N and PO4 removal efficiencies of 39.3–40.9% and 43.8–46.6%, respectively, with the NO3-N and PO4 removal rates of 2.47–2.55 and 0.22–0.23 mg/L-d, respectively. In addition, iron (Fe) in the form of FeEDTA, has been added to the microalgae cultivation at a concentration of 0.07 g/L. It was found that Fe plays an essential role in the growth of microalgae and increases nutrient removal efficiency. The experimental results indicate that the cultivation of Spirulina sp. TISTR 8875 is expected to treat nutrients by the MPBR system as a promising water reuse and nutrient recovery potential.

Quantitative Viability Assessment of Microalgae for Advanced Wastewater Treatment by Flow Cytometry

The nutrient uptake capacity of microalgae can be applied in advanced wastewater treatment processes. This study was set to develop a rapid and effective method for assessing the viability (i.e., live or dead) of microalgae applied for advanced wastewater treatment using a flow cytometry. Especially, a methodology to selectively evaluate the quantitative viability of only microalgae present in wastewaters having the co-culture of microalgae and bacteria was proposed. The live and dead cells of microalgae could be discriminated using chlorophyll autofluorescence and the SYTOX Green method developed in this study. Cell viability in live and dead conditions of microalgae showed about 90% accuracy, and about 40% viability ratio was derived in half-live and half-dead conditions. This result shows the potential to quantitatively evaluate the activity of microalgae in the wastewater environment.