Marine Microalga Phaeodactylum Tricornutum Research Articles

Nutritional Value and Productivity Potential of the Marine Microalgae Nitzschia laevis, Phaeodactylum tricornutum and Isochrysis galbana.

Microalgae are considered promising sustainable feedstocks for the production of food, food additives, feeds, chemicals and various high-value products. Marine microalgae Phaeodactylum tricornutum, Isochrysis galbana and Nitzschia laevis are rich in fucoxanthin, which is effective for weight loss and metabolic diseases. The selection of microalgae species with outstanding nutritional profiles is fundamental for novel foods development, and the nutritional value of P. tricornutum, I. galbana and N. laevis are not yet fully understood. Hence, this study investigates and analyzes the nutritional components of the microalgae by chromatography and mass spectrometry, to explore their nutritional and industrial application potential. The results indicate that the three microalgae possess high nutritional value. Among them, P. tricornutum shows significantly higher levels of proteins (43.29%) and amino acids, while I. galbana has the highest content of carbohydrates (25.40%) and lipids (10.95%). Notwithstanding that P. tricornutum and I. galbana have higher fucoxanthin contents, N. laevis achieves the highest fucoxanthin productivity (6.21 mg/L/day) and polyunsaturated fatty acids (PUFAs) productivity (26.13 mg/L/day) because of the competitive cell density (2.89 g/L) and the advantageous specific growth rate (0.42/day). Thus, compared with P. tricornutum and I. galbana, N. laevis is a more promising candidate for co-production of fucoxanthin and PUFAs.

The Biosorption Capacity of the Marine Microalga Phaeodactylum tricornutum for the Removal of Toluidine Blue from Seawater.

A wide variety of dyes, such as toluidine blue (TB), are used daily for a multitude of purposes. After use, many of these compounds end up in aqueous effluents, reaching natural environments, including marine environments. The removal of these pollutants from marine environments must be considered a priority problem. The search for natural techniques, such as biosorption, is a preferred option to eliminate pollution from natural environments. However, biosorption studies in seawater are scarce. For this reason, the living biomass of the marine microalga Phaeodactylum tricornutum was studied to determine its ability to remove TB from seawater. The kinetics of the biosorption process, the isotherms, and the effect of light and pH were determined. This biomass showed a maximum TB removal capacity of 45 ± 2 mg g-1 in the presence of light. Light had a positive effect on the TB removal capacity of this living biomass. The best fitting kinetics was the pseudo-second order kinetics. The efficiency of the removal process increased with increasing pH. This removal was more effective at alkaline pH values. The results demonstrated the efficacy of P. tricornutum living biomass for the efficient removal of toluidine blue dye from seawater both in the presence and absence of light.

Discoloration and biosorption of Brilliant green dye in seawater using living biomass of the microalga Phaeodactylum tricornutum

Pollution by dyes is a serious environmental problem. Marine waters receive pollutants from many sources, however, there are few studies that deal with the elimination of pollutants from these environments. The search for effective, cheap, and ecological procedures to remove dyes from seawater is a current challenge. Biosorption meets these requirements, but it is necessary to find the best biosorbent for the operating conditions. Since microalgal biomass is considered a good biosorbent, the efficiency of living biomass from the marine microalga Phaeodactylum tricornutum to remove the Brilliant green dye from seawater was evaluated in this work. This dye showed spontaneous discoloration in seawater, showing a decrease in the amount of dye measured spectrophotometrically but not when measured by HPLC. Consequently, the difference between discoloration and true removal should be considered. It is shown that the determination of the biomass efficiency as biosorbent through spectrophotometric measurements could be wrong in some cases. Batch experiments were performed varying operational parameters, such as initial concentration of dye, contact time, and pH of the solution. At the lowest concentration of the dye (5 mg L-1), the algal biomass (0.4 g L-1) achieved total decolorization and removal (through biosorption) within 7 h, while at the highest concentration (200 mg L-1), discoloration was 96.3%, but removal was 32.6%. The spontaneous discoloration followed a pseudo-second-order kinetics. Pseudo-first-order kinetics and Langmuir isotherm best described the removal process, predicting a maximum biosorption capacity of 161.52±5.95 mg g-1. This natural biomass had a higher efficiency than other more complex biosorbents.

Different responses of marine microalgae Phaeodactylum tricornutum upon exposures to WAF and CEWAF of crude oil: A case study coupled with stable isotopic signatures

Increasing use of chemical dispersants for oil spills highlights the need to understand their adverse effects on marine microalgae and nutrient assimilation because the toxic components of crude oil can be more bioavailable. We employed the crude oil water-accommodated fraction (WAF) and chemically enhanced WAF (CEWAF) to compare different responses in marine microalgae (Phaeodactylum tricornutum) coupled with stable isotopic signatures. The concentration and proportion of high-molecular-weight polycyclic aromatic hydrocarbons (HMW PAHs), which are key toxic components in crude oil, increased after dispersant addition. CEWAF exposure caused higher percent growth inhibition and a lower chlorophyll-a level of microalgae than those after WAF exposure. Compared with WAF exposure, CEWAF led to an enhancement in the self-defense mechanism of P. tricornutum, accompanied by an increased content of extracellular polymeric substances. 13C-depletion and carbon assimilation were altered in P. tricornutum, suggesting more HMW PAHs could be utilized as carbon sources by microalgae under CEWAF. CEWAF had no significant effects on the isotopic fractionation or assimilation of nitrogen in P. tricornutum. Our study unveiled the impact on the growth, physiological response, and nutrient assimilation of microalgae upon WAF and CEWAF exposures. Our data provide new insights into the ecological effects of dispersant applications for coastal oil spills.

Antagonistic Toxic Effects of Surfactants Mixtures to Bacteria Pseudomonas putida and Marine Microalgae Phaeodactylum tricornutum.

Surfactants can be found in an ever-widening variety of products and applications, in which the combination of several types of surfactants is used to reinforce their properties, looking for synergistic effects between them. After use, they tend to be discarded into wastewater, ending up in aquatic bodies with concerning harmful and toxic effects. The aim of this study is the toxicological assessment of three anionic surfactants (ether carboxylic derivative, EC) and three amphoteric surfactants (amine-oxide-based, AO), individually and in binary mixtures of them (1:1 w/w), to bacteria Pseudomonas putida and marine microalgae Phaeodactylum tricornutum. Critical Micelle Concentration (CMC) was determined to demonstrate the capacity to reduce surface tension and the toxicity of the surfactants and mixtures. Zeta potential (ζ-potential) and micelle diameter (MD) were also determined to confirm the formation of mixed surfactant micelles. The Model of Toxic Units (MTUs) was used to quantify the interactions of surfactants in binary mixtures and to predict if the concentration addition or response addition principle can be assumed for each mixture. The results showed a higher sensitivity of microalgae P. tricornutum to the surfactants tested and their mixtures than bacteria P. putida. Antagonism toxic effects have been detected in the mixture of EC + AO and in one binary mixture of different AOs; this is to say, the mixtures showed lower toxicity than expected.

Biochemical and Phylogenetic Characterization of a Novel NADP+-Specific Isocitrate Dehydrogenase From the Marine Microalga Phaeodactylum tricornutum.

Isocitrate dehydrogenase (IDH) family of proteins is classified into three subfamilies, namely, types I, II, and III. Although IDHs are widely distributed in bacteria, archaea, and eukaryotes, all type III IDHs reported to date are found only in prokaryotes. Herein, a novel type III IDH subfamily member from the marine microalga Phaeodactylum tricornutum (PtIDH2) was overexpressed, purified, and characterized in detail for the first time. Relatively few eukaryotic genomes encode this type of IDH and PtIDH2 shares the highest homology with marine bacterial monomeric IDHs, suggesting that PtIDH2 originated through a horizontal gene transfer event between a marine alga and a bacterium. Size-exclusion chromatography revealed that the native PtIDH2 is a homotetramer (∼320 kDa) in solution, comprising four monomeric IDH-like subunits (80 kDa each). Enzymatic characterization showed that PtIDH2 is a bivalent metal ion-dependent enzyme and Mn2+ is the optimal activator. The recombinant PtIDH2 protein exhibited maximal activity at 35°C and pH 8.0 in the presence of Mn2+. Heat-inactivation analysis revealed that PtIDH2 is a cold-adapted enzyme. Kinetic analysis demonstrated that PtIDH2 is a completely NADP+-specific IDH with no detectable NAD+-associated catalytic activity. The three putative key NADP+-binding residues (His604, Arg615, and Arg664) in PtIDH2 were also evaluated by site-directed mutagenesis. The H604L/R615D/R664S triple mutant showed a 3.25-fold preference for NAD+ over NADP+, implying that the coenzyme specificity of PtIDH2 can be converted from NADP+ to NAD+ through rational engineering approaches. Additionally, the roles of the conserved residues Ala718 and Leu742 in the thermostability of PtIDH2 were also explored by site-directed mutagenesis. We found that the L742F mutant displayed higher thermostability than wild-type PtIDH2. This study expands the phylogeny of the IDH family and provides new insights into the evolution of IDHs.

Evaluation of electroflocculation harvesting on the antioxidant activity and toxicity of extracts from the microalgae Isochrysis galbana and Phaeodactylum tricornutum

The harvesting method is a challenge in microalgae production since it may influence the bioactivity of the product. This study aimed to evaluate if electroflocculation biomass harvesting altered the antioxidant properties and toxicity of methanol extracts from the marine microalgae Isochrysis galbana and Phaeodactylum tricornutum, compared with the traditional centrifugation approach. Analyses were based on the elimination of the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radical by the active ingredients from the extracts, thin-layer chromatography (TLC), calculation of IC50, and extract toxicity. Phaeodactylum tricornutum had similar DPPH-reactive fractions (with antioxidant activity) different from the β-carotene control in the TLC for both biomass-separating methods, but its IC50 was 63% higher for electroflocculation (lower antioxidant activity). Bands with antioxidant activity were absent in the TCL of I. galbana (non-DPPH-reactive) for both harvesting methods. The extracts did not present mortality for the study with the Artemia salina model. Therefore, electroflocculation can produce up to 10 times more biomass without cytotoxicity output but may decrease the antioxidant potential of microalgae extracts.

Transcriptome aberration in marine microalgae Phaeodactylum tricornutum induced by commercial naphthenic acids.

Naphthenic acids (NAs) are cycloalkyl linear carboxylic acids primarily originating from oil sand tailings water (OSTW), and the exposure to NAs affects the photosynthesis of marine microalgaes. However, the transcriptional response upon the stress of NAs remains unclear. Herein, we investigate the transcriptome alterations of marine Phaeodactylum tricornutum induced by NAs using RNA-sequencing. In total 70 differentially expressed genes (DEGs) are enriched in seven biological process pathways, and 48 DEGs are enriched in four molecular functions. Differentially expressed genes of P.tricornutum are primarily concentrated in three photosynthesis-related pathways including the porphyrin and chlorophyll metabolism pathway, the photosynthesis pathway, and the carbon fixation pathway in photosynthetic organisms. Five DEGs such as hemE, chlM, TPI/GapC3, FbaC5, and CHLH are validated using quantitative real-time PCR assay. NAs at low concentrations affect the material energy conversion efficiency of P.tricornutum, such as chlorophyll synthesis, electron transfer efficiency, and carbon assimilation.

Preventive Effects of the Marine Microalga Phaeodactylum tricornutum, Used as a Food Supplement, on Risk Factors Associated with Metabolic Syndrome in Wistar Rats.

Long-chain polyunsaturated fatty acids, n-3 series (n-3 LC-PUFA), are known for their preventive effects against cardiovascular disease. In an unfavourable economic and environmental context of fish oil production, marine microalgae could be an alternative source of n-3 LC-PUFA and are of interest for human nutrition. The aim of this study was to evaluate the effects of P. tricornutum, a microalga rich in eicosapentaenoic acid and used as a food supplement, on the metabolic disorders associated with metabolic syndrome and obesity development. Three male Wistar rat groups (n = 6) were submitted for eight weeks to a standard diet or high-fat diet (HF) with 10% fructose in drinking water, supplemented or not with 12% of P. tricornutum (HF-Phaeo). Supplementation led to n-3 LC-PUFA enrichment of lipids in the liver, plasma and erythrocytes. Plasma transaminases showed no difference between the HF and HF-Phaeo groups. Body weight, fat mass, inflammatory markers and insulinemia decreased in HF-Phaeo rats versus the HF group. Plasma total cholesterol, triacylglycerols and leptine diminished in HF-Phaeo rats, while HDL-cholesterol increased. In conclusion, this study highlights the beneficial effects of P. tricornutum in reducing the metabolic disorders associated with metabolic syndrome.

Eco-friendly rapid removal of triclosan from seawater using biomass of a microalgal species: Kinetic and equilibrium studies.

Triclosan is an important emerging pollutant. It has become ubiquitous due to its incomplete elimination in municipal wastewater treatment plants causing serious environmental problems. Biomass from microorganisms as sorbent of pollutants can be an eco-friendly alternative for triclosan removal. In this work, the elimination of triclosan using biomass (dead and living) of the marine microalga Phaeodactylum tricornutum was characterized in cultures exposed to light and in a complex solution (seawater). Maximum removal capacity, isotherms, kinetics, FTIR characterization, pH effect and reuse were evaluated and discussed. Photodegradation of triclosan was also evaluated. Both biomasses showed similar effectiveness; around 100% of pollutant was eliminated when its concentration was 1 mg L-1 in only 3 h using a biomass concentration of 0.4 g L-1. A pseudo-second order model guided the biosorption process. Considering the photodegradation as a first-order process, the whole process (photodegradation + biosorption) was suitably modelled with pseudo-third order and Elovich kinetics. Biosorption increased with the decrease in pH. Temkin isotherm showed the best fit for the experimental data. Both biomasses showed good reuse after five cycles, losing only 7% in efficiency. P. tricornutum biomass is an attractive eco-material for triclosan elimination with low-cost and easy handling than other sorbents.

Biosynthesis of Nutraceutical Fatty Acids by the Oleaginous Marine Microalgae Phaeodactylum tricornutum Utilizing Hydrolysates from Organosolv-Pretreated Birch and Spruce Biomass

Polyunsaturated fatty acids (PUFAs) are essential for human function, however they have to be provided through the diet. As their production from fish oil is environmentally unsustainable, there is demand for new sources of PUFAs. The aim of the present work was to establish the microalgal platform to produce nutraceutical-value PUFAs from forest biomass. To this end, the growth of Phaeodactylum tricornutum on birch and spruce hydrolysates was compared to autotrophic cultivation and glucose synthetic media. Total lipid generated by P. tricornutum grown mixotrophically on glucose, birch, and spruce hydrolysates was 1.21, 1.26, and 1.29 g/L, respectively. The highest eicosapentaenoic acid (EPA) production (256 mg/L) and productivity (19.69 mg/L/d) were observed on spruce hydrolysates. These values were considerably higher than those obtained from the cultivation without glucose (79.80 mg/L and 6.14 mg/L/d, respectively) and also from the photoautotrophic cultivation (26.86 mg/L and 2.44 mg/L/d, respectively). To the best of our knowledge, this is the first report describing the use of forest biomass as raw material for EPA and docosapentaenoic acid (DHA) production.

Towards a better understanding of the flocculation/flotation mechanism of the marine microalgae Phaeodactylum tricornutum under increased pH using atomic force microscopy

In the context of climate change, the interest for sustainable sources to produce energy is growing. One promising resource for biofuel production is microalgae, but their industrial use is limited by the lack of efficient harvesting techniques. In this study, we use a multi-scale approach to understand the magnesium hydroxide-mediated flocculation/flotation mechanism of Phaeodactylum tricornutum, an effective oil-producer diatom, under high pH. While flotation experiments give a population-scale quantification of the efficiency of flocculation/flotation using magnesium or calcium hydroxide, or at increased pH, AFM allows probing the mechanical properties of the cells at different pH values. Finally we develop an original strategy to functionalize AFM tips with hydroxide particles that we use in multiparametric imaging experiments to understand at the molecular scale the forces driving the adhesion of hydroxide particles to cells. Altogether, our results give a better understanding of the molecular mechanism underlying alkaline flocculation/flotation, paving the way towards the development of low-cost flocculant-free flotation harvesting processes.

The effect of naphthenic acids on physiological characteristics of the microalgae Phaeodactylum tricornutum and Platymonas helgolandica var. tsingtaoensis

Naphthenic acids (NAs) account for 1–2% of crude oil and represent its main acidic component. However, the aquatoxic effects of NAs on marine phytoplankton and their ecological risks have remained largely unknown. Using the marine microalgae Phaeodactylum tricornutum and Platymonas helgolandica var. tsingtaoensis as the target, we studied the effects of NAs on their growth, cell morphology and physiological characteristics. The cell density decreased as the concentrations of NAs increased, indicating that they had an adverse effect on growth of the investigated algae in a concentration-dependent manner. Moreover, scanning electron microscopy revealed NAs exposure caused damage such as deformed cells, shrunken surface and ruptured cell structures. Exposure to NAs at higher concentrations for 48 h significantly increased the content of chlorophyll (Chl) a and b in P. tricornutum, but decreased their levels in P. helgolandica var. tsingtaoensis. NAs with concentrations no higher than 4 mg/L gradually enhanced the Chl fluorescence (ChlF) parameters and decreased the ChlF parameters at higher concentrations for the two marine microalgae. Additionally, NAs induced hormesis on photosynthetic efficiency of the two microalgae and also have the species difference in their aquatic toxicity. Overall, the results of this study provide a better understanding of the physiological responses of phytoplankton and will enable better risk assessments of NAs.

An investigation into the effect of culture conditions on fucoxanthin production using the marine microalgae Phaeodactylum tricornutum

Fucoxanthin is a carotenoid pigment produced by algae that has a range of potential health benefits. Despite the obvious interest in developing a process for the production of fucoxanthin, relatively few authors have systematically examined the impact of culture conditions (i.e. the light intensity, medium composition and CO2 addition) on fucoxanthin production. In this work, we have addressed this issue using the marine microalgae Phaeodactylum tricornutum. It was found that at low light intensities (100μmol photons m−2s−1) the specific fucoxanthin concentration was greater (42.8±19.5mgg−1) than at a higher intensity of 210μmol photons m−2s−1 (9.9±4.2mgg−1). Addition of nitrate to the medium led to a significant increase in the specific fucoxanthin concentration with the maximum specific concentration (59.2±22.8mgg−1), volumetric concentration (20.5mgL−1) and bioreactor productivity (2.3mgL−1 day−1) being observed with the nitrate enriched medium. These reproducible results from our systematic investigation into the effect of culture conditions on fucoxanthin production are highly encouraging and clearly demonstrate the potential for P.tricornutum to be employed as a natural source of fucoxanthin in nutraceutical applications.

Identification of a putative seipin ortholog involved in lipid accumulation in marine microalga Phaeodactylum tricornutum

There is a huge interest in exploiting microalgae as an alternative bioenergy resource. Genetic improvement of microalgal strains with significant commercial potential is urgently demanded. Seipin has been shown to be associated with adipocyte differentiation and lipid droplet (LD) formation in mammals. However, very little is known about seipin in microalgae. Here, we identified a putative seipin in the oleaginous marine diatom Phaeodactylum tricornutum and developed a transgenic strain with overexpressed seipin. The transgenic strain possessed higher neutral lipid content and larger LDs than the wild type, and neutral lipid content was increased by 57%. Moreover, in this transgenic strain, the relative content of saturated fatty acids in total fatty acids was increased significantly, which improved lipid quality for the oil refinery. Our findings elucidated the significant potential role of seipin in regulating lipid accumulation and LD formation in microalgae for the first time.

Changes in growth and composition of the marine microalgae Phaeodactylum tricornutum and Nannochloropsis salina in response to changing sodium bicarbonate concentrations

Oils, carbohydrates, and fats generated by microalgae are being refined in an effort to produce biofuels. The research presented here examines two marine microalgae, Nannochloropsis salina (green alga) and Phaeodactylum tricornutum (diatom), when grown with 0 (no addition), 0.5, 1.0, 2.0, and 5.0 g L−1 NaHCO3 added to an f/2 medium during the growth phase (GP) and a nutrient induced (nitrate limitation) lipid formation phase (LP). We hypothesize that the addition of NaHCO3 is a sustainable and practical strategy to increase cellular density and concentrations of lipids in microalgae as well as the rate of lipid accumulation. In N. salina, final cell densities were significantly (p [NaHCO3] during the GP. During the LP, cell densities were generally higher in the NaHCO3-treated cells compared with controls. F V/F M (efficiency of photosystem II) patterns paralleled those for cell density with generally higher values with higher concentrations of NaHCO3 and significantly different values between controls and 5.0 g L−1 NaHCO3 at the end of the GP (p < 0.05). F V/F M was variable between treatments in P. tricornutum (0.3–0.65) but less so in N. salina for (0.5–0.7) regardless of [NaHCO3]. The lipid index (measured with Nile red), used as a proxy for triacylglycerides (TAGs), was 10.2 ± 6.5 and 4.4 ± 2.9 (fluorescence units/OD cells ×1000) for N. salina and P. tricornutum, respectively, at the end of the GP. At the end of the LP, the lipid index was eight and four times higher than during the GP in the corresponding 5.0 g L−1 NaHCO3 treatments, revealing that N. salina was accumulating more lipid than P. tricornutum. Dry weights essentially doubled during LP compared with GP for N. salina; this was not the case for P. tricornutum. In general, the percentage of ash in dry weights was significantly higher in the LP relative to the corresponding GP treatments for P. tricornutum; this was not the case for N. salina. During the LP, there was also less soluble protein in N. salina compared to GP; differences were not significant in cells growing with 2.0 or 5.0 g L−1 NaHCO3. In P. tricornutum, faster growing cells had more soluble protein during the GP and LP; differences between treatments were significant. P. tricornutum generally accumulated significantly more crude protein than N. salina at higher [NaHCO3]; there was three times more crude protein in the highest NaHCO3 (5.0 g L−1) treatment compared with the controls. C:N ratios (mol:mol) were similar across treatments during GP: 7.03 ± 0.12 and 10.16 ± 0.41 for N. salina and P. tricornutum, respectively. Further, C:N ratios increased with increasing [NaHCO3] during LP. Species-specific fatty acid methyl ester (FAMEs) profiles were observed. While C16:0 was lower in P. tricornutum compared to N. salina, the diatom produced more C16:1 and C14 but not C18:3. Monounsaturated fatty acids (MUFA) significantly increased in N. salina in the LP compared to GP and in response to increasing [NaHCO3] (t tests; p < 0.05). Saturated fatty acids (SFA) responded similarly but to a lesser degree. There were more polyunsaturated fatty acids (PUFA) in N. salina than MUFAs or SFAs. In P. tricornutum, there were generally more SFAs, MUFAs and PUFAs in P. tricornutum during LP than GP in the corresponding NaHCO3 treatments. These findings reveal the importance of considering NaHCO3 as a supplemental carbon source in the culturing marine phytoplankton in large-scale production for biofuels.

The stimulating effect of exometabolites of the marine microalgae Phaeodactylum tricornutum Bohlin on reproduction of Listeria monocytogenes

The biological activity of ethyl acetate extract of exometabolites from the marine microalgae Phaeodactylum tricornutum against a test culture of Listeria monocytogenes 4b has been investigated. It was shown that the stimulating effect of algal exometabolites on the growth of pathogenic bacteria increased maximally by 98.3% on day 6 of the cultivation, if the active substances comprising the culture liquid of P. tricornutum were separated by successive extractions with solvents in order of increasing polarity (hexane, benzene, ethyl acetate), and by 150% on day 3, if the substances from the ethyl acetate extract of exometabolites were separated by column chromatography. It is noted that the fraction of biologically active substances maximally stimulating the growth of L. monocytogenes can be used to prepare an accumulation medium for detecting these patho- genic bacteria in marine environments and hydrobionts.

Assessing the toxicity of chemical compounds associated with marine land-based fish farms: The use of mini-scale microalgal toxicity tests

Many chemicals that are currently used in aquaculture have not been evaluated with regard to their specific effects on the aquatic environment. In the present study, the toxic effects of several chemicals associated with land-based marine fish farming activities were assessed using two species of marine microalgae (Phaeodactylum tricornutum and Isochrysis galbana). Mini-scale toxicity tests were performed with six antibiotics (amoxicillin, ampicillin, flumequine, oxytetracycline, streptomycin and sulfadiazine) and two disinfectants (formaldehyde and hypochlorite). Amoxicillin and streptomycin did not exert toxic effects. Sulfadiazine was the most toxic chemical; the EC50 values were 0.11 mg/L and 1.44 mg/L for P. tricornutum and I. galbana respectively. As expected, the disinfectants displayed high toxicity, and P. tricornutum was particularly sensitive to these compounds. Although the differences in microalgal sensitivity depended on the chemical considered, both species were highly sensitive to most of the compounds tested. We recommend the inclusion of mini-scale microalgal toxicity tests in environmental risk assessment (ERA) and environmental monitoring plans because they are cost-effective and rapid.

Anaerobic digestibility of Scenedesmus obliquus and Phaeodactylum tricornutum under mesophilic and thermophilic conditions

Two types of non-axenic algal cultures, one dominated by the freshwater microalgae Scenedesmus obliquus and the other by the marine microalgae Phaeodactylum tricornutum, were cultivated in two types of simple photobioreactor systems . The production rates, expressed on dry matter (DM) basis, were in the order of 0.12 and 0.18 g DM L −1 d −1 for S. obliquus and P. tricornutum respectively. The biogas potential of algal biomass was assessed by performing standardized batch digestion as well as digestion in a hybrid flow-through reactor (combining a sludge blanket and a carrier bed), the latter under mesophilic and thermophilic conditions. Biomethane potential assays revealed the ultimate methane yield ( B 0) of P. tricornutum biomass to be about a factor of 1.5 higher than that of S. obliquus biomass, i.e. 0.36 and 0.24 L CH 4 g −1 volatile solids (VS) added respectively. For S. obliquus biomass, the hybrid flow-through reactor tests operated at volumetric organic loading rate (Bv) of 2.8 gVS L −1 d −1 indicated low conversion efficiencies ranging between 26–31% at a hydraulic retention time (HRT) of 2.2 days for mesophilic and thermophilic conditions respectively. When digesting P. tricornutum at a Bv of 1.9 gVS L −1 d −1 at either mesophilic or thermophilic conditions and at an HRT of 2.2 days, an overall conversion efficiency of about 50% was obtained. This work indicated that the hydrolysis of the algae cells is limiting the anaerobic processing of intensively grown S. obliquus and P. tricornutum biomass.

Ozonation of synthetic versus natural textile tannins: recalcitrance and toxicity towards Phaeodactylum tricornutum

A sound in-plant pollution control strategy can only be defined by paying due attention to bio-recalcitrance and toxicity. In this context the levels of toxicity and inert COD introduced to textile dyebath discharges by two alternative auxiliary chemicals, namely natural tannin (NT) and synthetic tannin (ST), were investigated. The effect of 40 minutes ozonation at 1,000 mg h(-1) at pH 3.5 on the segregated effluent streams containing the above-mentioned tannin formulations was evaluated in terms of changes in toxicity and recalcitrance. The effect of ozonation on the COD distribution of raw and ozonated NT and ST samples according to their molecular weight cut-offs was also assessed. Both untreated tannin formulations exerted high acute toxicity towards marine microalgae Phaeodactylum tricornutum. Moderate decrease in the toxicity levels of both tannins was observed upon ozonation. The raw NT formulation with a COD content more than twice that of its alternative raw ST had an initially inert soluble COD content of only 25 mg/L, while the initially inert COD was 135 mg/L for ST. As the initially inert soluble COD content of NT was considerably lower, this textile auxiliary did not need chemical pretreatment to improve its biodegradability. On the other hand, the initially inert soluble COD content of ST was reduced by 70% by ozone pretreatment. In terms of residual COD contents achievable after passing through a biological treatment system, raw NT and pretreated ST formulations yielded 100 and 95 mg/L COD, respectively. The highest proportion of COD (46% for NT and 88% for ST) was found in the <1 kDa range. The same fraction increased to 93% for NT after ozonation, while for ST no significant change was observed in the COD distribution of the molecular weight cut-offs after ozonation.