Low Biomass Concentration Research Articles

Improving astaxanthin production of Haematococcus pluvialis by an efficient fed-batch strategy in a photobioreactor

Astaxanthin has attracted extensive attention due to its multiple physiological functions, but its production from Haematococcus pluvialis remains challenging due to low biomass concentration. In this study, an efficient fed-batch strategy was designed to improve the astaxanthin productivity at a stable pH level during mixotrophic growth of H. pluvialis. The acid feeding position was equipped with feeding medium to provide sufficient nutrients based on pH changes. Results suggested that pH level was increasing during acetate cultivation, and was a limiting factor for H. pluvialis growth. The biomass concentration was enhanced by 25.7% through stabilizing pH levels in batch culture. Based on linear relationship between nutrient consumption and pH change, a fed-batch strategy was designed and tested, increasing the biomass concentration by 90.6% to 1.62 g L−1 in the photobioreactor. At the molecular level, the photosynthetic efficiency was limited by reducing Rubisco activity and increasing NADPH oxidase activity, while carbon metabolism was enhanced by elevating pyruvate and ace-CoA contents. Furthermore, astaxanthin productivity was increased to 4.5 mg L−1 d−1 within pH range from 5 to 6, which was accompanied by the elevated pyruvate, ace-CoA, and lipid contents. The fed-batch strategy was promising for microalgal production due to its easy operation and high astaxanthin productivity.

Secretomics: a biochemical footprinting tool for developing microalgal cultivation strategies.

Microalgae offer a promising source of biofuel and a wide array of high-value biomolecules. Large-scale cultivation of microalgae at low density poses a significant challenge in terms of water management. High-density microalgae cultivation, however, can be challenging due to biochemical changes associated with growth dynamics. Therefore, there is a need for a biomarker that can predict the optimum density for high biomass cultivation. A locally isolated microalga Cyanobacterium aponinum CCC734 was grown with optimized nitrogen and phosphorus in the ratio of 12:1 for sustained high biomass productivity. To understand density-associated bottlenecks secretome dynamics were monitored at biomass densities from 0.6 ± 0.1 to 7 ± 0.1g/L (2 to 22 OD) in batch mode. Liquid chromatography coupled with mass spectrometry identified 880 exometabolites in the supernatant of C. aponinum CCC734. The PCA analysis showed similarity between exometabolite profiles at low (4 and 8 OD) and mid (12 and 16 OD), whereas distinctly separate at high biomass concentrations (20 and 22 OD). Ten exometabolites were selected based on their role in influencing growth and are specifically present at low, mid, and high biomass concentrations. Taking cues from secretome dynamics, 5.0 ± 0.5g/L biomass concentration (16 OD) was optimal for C. aponinum CCC734 cultivation. Further validation was performed with a semi-turbidostat mode of cultivation for 29days with a volumetric productivity of 1.0 ± 0.2g/L/day. The secretomes-based footprinting tool is the first comprehensive growth study of exometabolite at the molecular level at variable biomass densities. This tool may be utilized in analyzing and directing microalgal cultivation strategies and reduction in overall operating costs.

Developing single‐substrate steady‐state model for biohydrogen production in continuous anaerobic activated sludge–rotating biological contactor system: Novel insights on the process

Kinetic-modeling studies are a key step to attain economically practical technology in terms of efficient scheme and bioreactor scale-up to describe the substrate utilization, biomass growth, and product formation in the biohydrogen production process. Kinetic-modeling study of biohydrogen production from molasses using mixed culture was investigated in an anaerobic activated sludge-rotating biological contactor. Single-substrate with endogenous metabolism and Luedeking–Piret model was used to describe the kinetic parameters at different dilution rate (0.032-0.167 h−1) with influent concentration of 6, 15, and 24 g COD/L. The maximum experimentally estimated value of μmax, kS, and Yx/s was found to be 0.053 h−1, 9.98 g/L, and 0.11 g/g in dilution 0.167 h−1, respectively. It can be concluded that increase in dilution rate is a suitable for microbial activities in the biological hydrogen production process. Accordingly, maximum specific growth rate and hydrogen production rate will be increased. Contrariwise, decrease in dilution rate is associated with lower biomass concentration and higher endogenous metabolism. Therefore, dilution rate is an important parameter in production of biohydrogen in this bioreactor and should be kept in an appropriate range.

Immobilized Microalgae-Based Photobioreactor for CO2 Capture (IMC-CO2PBR): Efficiency Estimation, Technological Parameters, and Prototype Concept

Microalgae-mediated CO2 sequestration has been a subject of numerous research works and has become one of the most promising strategies to mitigate carbon dioxide emissions. However, feeding flue and exhaust gas into algae-based systems has been shown to destroy chloroplasts, as well as disrupt photosynthesis and other metabolic processes in microalgae, which directly limits CO2 uptake. CO2 biosequestration in existing photobioreactors (PBRs) is also limited by the low biomass concentration in the growth medium. Therefore, there is a real need to seek alternative solutions that would be competitive in terms of performance and cost-effectiveness. The present paper reports the results of experiments aimed to develop an innovative trickle bed reactor that uses immobilized algae to capture CO2 from flue and exhaust gas (IMC-CO2PBR). In the experiment, ambient air enriched with technical-grade CO2 to a CO2 concentration of 25% v/v was used. The microalgae immobilization technology employed in the experiment produced biomass yields approximating 100 g DM/dm3. A relationship was found between CO2 removal rates and gas volume flux: almost 40% of CO2 was removed at a feed of 25 dm3 of gas per hour, whereas in the 200 dm3/h group, the removal efficiency amounted to 5.9%. The work includes a determination of basic process parameters, presentation of a developed functional model and optimized lighting system, proposals for components to be used in the system, and recommendations for an automation and control system for a full-scale implementation.

Hydrothermal gasification of Scenedesmus obliquus and its derivatives: a thermodynamic study using Aspen Plus

AbstractThis study presents the simulation of hydrothermal gasification (HTG) of Scenedesmus obliquus microalgae and their derivatives using Aspen Plus V11. The effect of operating parameters such as temperature, pressure, and biomass concentration on the yield and composition of gaseous products using whole algae, lipid, and lipid extracted algae (LEA) as feedstocks was examined. The results showed that reaction pressure exhibited minimal impact whereas temperature, biomass concentration, and feedstock composition had significant effects on the composition of gaseous products. It was also found that a low temperature (400 °C) and biomass concentration of 40 wt% favored the production of methane‐rich gas. In contrast, high temperature (700 °C) and low biomass concentration (10 wt%) favored hydrogen‐rich gas production in all the three feedstocks considered. The highest mole fraction achieved for CH4 was 53.45, 61.70, and 52.20 mol%, which corresponded to a CH4 yield of 31.14, 56.90, and 30.15 mmol g−1 for whole algae, lipid, and LEA respectively. For H2 rich gas production, the highest mole fractions achieved were 55.77, 52.29, and 55.34 mol%, which correspond to H2 yields of 75.44, 105.51, and 73.49 mmol g−1 for whole algae, lipids, and LEA, respectively. The ranking order for the yield and lower heating value of the product gas from the HTG process is lipid > whole algae > LEA. This study has shown that hydrogen‐rich and methane‐rich gas can be produced from the hydrothermal gasification of microalgae as a function of the reaction conditions and feedstock composition. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Beyond the farm: Making edible protein from CO2 via hybrid bioinorganic electrosynthesis

Beyond the farm: Making edible protein from CO2 via hybrid bioinorganic electrosynthesis

Diversity and functional structure of soil animal communities suggest soil animal food webs to be buffered against changes in forest land use

Forest soil and litter is inhabited by a diverse community of animals, which directly and indirectly rely on dead organic matter as habitat and food resource. However, community composition may be driven by biotic or abiotic forces, and these vary with changes in habitat structure and resource supply associated with forest land use. To evaluate these changes, we compiled comprehensive data on the species composition of soil animal communities and environmental factors in forest types varying in land-use intensity in each of three regions in Germany, i.e., coniferous, young managed, old managed, and unmanaged beech forests. Coniferous forests featured high amounts of leaf litter and low microbial biomass concentrations contrasting in particular unmanaged beech forests. However, soil animal diversity and functional community composition differed little between forest types, indicating resilience against disturbance and forest land use. Structural equation modelling suggested that despite a significant influence of forest management on resource abundance and quality, the biomass of most soil fauna functional groups was not directly affected by forest management or resource abundance/quality, potentially because microorganisms hamper the propagation of nutrients to higher trophic levels. Instead, detritivore biomass depended heavily on soil pH. Macrofauna decomposers thrived at high pH, whereas mesofauna decomposers benefitted from low soil pH, but also from low biomass of macrofauna decomposers, potentially due to habitat modification by macrofauna decomposers. The strong influence of soil pH shows that decomposer communities are structured predominantly by regional abiotic factors exceeding the role of local biotic factors such as forest type.

Production and monitoring of biomass and fucoxanthin with brown microalgae under outdoor conditions.

The effect of light on biomass and fucoxanthin (Fx) productivities was studied in two microalgae, Tisochrysis lutea and Phaeodactylum tricornutum. High and low biomass concentrations (1.1 and 0.4 g L−1) were tested in outdoor pilot‐scale flat‐panel photobioreactors at semi‐continuous cultivation mode. Fluorescence spectroscopy coupled with chemometric modeling was used to develop prediction models for Fx content and for biomass concentration to be applied for both microalgae species. Prediction models showed high R 2 for cell concentration (.93) and Fx content (.77). Biomass productivity was lower for high biomass concentration than low biomass concentration, for both microalgae (1.1 g L−1: 75.66 and 98.14 mg L−1 d−1, for T. lutea and P. tricornutum, respectively; 0.4 g L−1: 129.9 and 158.47 mg L−1 d−1, T. lutea and P. tricornutum). The same trend was observed in Fx productivity (1.1 g L−1: 1.14 and 1.41 mg L−1 d−1, T. lutea and P. tricornutum; 0.4 g L−1: 2.09 and 1.73 mg L−1 d−1, T. lutea and P. tricornutum). These results show that biomass and Fx productivities can be set by controlling biomass concentration under outdoor conditions and can be predicted using fluorescence spectroscopy. This monitoring tool opens new possibilities for online process control and optimization.

Achieving rapid thiosulfate-driven denitrification (TDD) in a granular sludge system

Sulfur-oxidizing bacteria (SOB) can drive a high level of autotrophic denitrification (AD) activity with thiosulfate (S2O32−) as the electron donor. However, the slow growth of SOB results in a low biomass concentration in the AD reactor and unsatisfactory biological nitrogen removal (BNR). In this study, our goal was to establish a high-rate thiosulfate-driven denitrification (TDD) system via sludge granulation. Granular sludge was successfully cultivated by increasing the nitrogen loading rate stepwise in thiosulfate-oxidizing/nitrate-reducing conditions in an upflow anaerobic blanket reactor. In the mature-granular-sludge reactor, a nitrate removal rate of 280 mg N/L/h was achieved with a nitrate removal efficiency of 97.7%±1.0% at a hydraulic retention time of only 15 minutes, with no nitrite detected in the effluent. Extracellular polymeric substance (EPS) analysis indicated that the proteins in loosely bound and tightly bound EPS were responsible for maintaining the compact structure of the TDD granular sludge. The dynamics of the microbial-community shift were identified by 16S rRNA high-throughput pyrosequencing analysis. The Sulfurimonas genus was found to be enriched at 74.1% of total community and may play the most critical role in the high-rate BNR. The batch assay results reveal that no nitrite accumulation occurred during nitrate reduction because the nitrate reduction rate (75.90±0.67 mg N/g MLVSS/h) was almost equal to the nitrite reduction rate (66.06±1.28 mg N/g MLVSS/h) in the thiosulfate-driven granular sludge reactor. The results of this study provide support for the establishment of a high-rate BNR system that maintains its stability with a low sludge yield.

Production optimisation of Tisochrysis lutea as a live feed for juvenile Sydney rock oysters, Saccostrea glomerata, using large-scale photobioreactors

The aquaculture industry uses microalgae as a live feed for juvenile oysters in hatcheries to meet their nutritional requirements, including their need for several essential Poly Unsaturated Fatty Acids (PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The mass culture of microalgae is not only a major bottleneck for the production of juvenile oysters, but also a significant cost, accounting for 20–50% of hatchery operating costs. Currently, low biomass concentrations, high production costs and poor cultivation systems limit the quantity and quality of microalgae feed. This study focused on Tisochrysis lutea, a microalgae species commonly used in aquaculture, and we assessed the potential of photobioreactors with an improved light source and CO2 input to increase biomass production and improve biochemical composition of algal feed. Two photobioreactor systems were compared: the current industry set up (DPI) comprising fluorescent lighting and minimal CO2 input versus an optimized system utilising LEDs and increased CO2. Cultures of T. lutea were monitored over a 12-day growth period and harvested on day 14 for biochemical analysis. Final cell density was significantly higher in the optimized system relative to the conventional culture systems (6.2 × 106 cells / mL versus 3.7 × 106 cells / mL, respectively). The biochemical profile of T. lutea was not significantly different between the two photobioreactors systems. The algal biomass produced during this comparative experiment was used in a feeding trial on oyster spat, Saccostrea glomerata. Spat fed with algae produced in optimized vs conventional photobioreactors showed no significant difference in growth, but oyster spat fed with T. lutea grown in optimized photobioreactors did show a significant increase in their EPA content. Overall, our results contribute to our understanding of how altered culture conditions affect microalgal production and biochemical composition, and subsequently of oyster spat. This study further supports the potential of LEDs to reduce operating costs for oyster hatcheries but also to significantly improve microalgae yield with no negative effect on the condition of oyster spats production.

Scaling-Up the Anaerobic Digestion of Pretreated Microalgal Biomass within a Water Resource Recovery Facility

Microalgae-based wastewater treatment plants are low-cost alternatives for recovering nutrients from contaminated effluents through microalgal biomass, which may be subsequently processed into valuable bioproducts and bioenergy. Anaerobic digestion for biogas and biomethane production is the most straightforward and applicable technology for bioenergy recovery. However, pretreatment techniques may be needed to enhance the anaerobic biodegradability of microalgae. To date, very few full-scale systems have been put through, due to acknowledged bottlenecks such as low biomass concentration after conventional harvesting and inefficient processing into valuable products. The aim of this study was to evaluate the anaerobic digestion of pretreated microalgal biomass in a demonstration-scale microalgae biorefinery, and to compare the results obtained with previous research conducted at lab-scale, in order to assess the scalability of this bioprocess. In the lab-scale experiments, real municipal wastewater was treated in high rate algal ponds (2 × 0.47 m3), and harvested microalgal biomass was thickened and digested to produce biogas. It was observed how the methane yield increased by 67% after implementing a thermal pretreatment step (at 75 °C for 10 h), and therefore the very same pretreatment was applied in the demonstration-scale study. In this case, agricultural runoff was treated in semi-closed tubular photobioreactors (3 × 11.7 m3), and harvested microalgal biomass was thickened and thermally pretreated before undergoing the anaerobic digestion to produce biogas. The results showed a VS removal of 70% in the reactor and a methane yield up to 0.24 L CH4/g VS, which were similar to the lab-scale results. Furthermore, photosynthetic biogas upgrading led to the production of biomethane, while the digestate was treated in a constructed wetland to obtain a biofertilizer. In this way, the demonstration-scale plant evidenced the feasibility of recovering resources (biomethane and biofertilizer) from agricultural runoff using microalgae-based systems coupled with anaerobic digestion of the microalgal biomass.

Preserving Microbial Community Integrity in Oilfield Produced Water.

Determining a representative microbial signature from any given location is dependent on robust sample collection and handling. Different sampling locations and hence sample properties can vary widely; for example, soil would be collected and handled differently compared to liquid samples. In the event that sample material has a low concentration of biomass, large quantities need to be collected for microbial community analysis. This is certainly the case when investigating the microbiology of oilfield systems, wherein produced water (PW) is one of the most common sources for microbial sampling. As the detrimental effects of microbial metabolism within these industrial milieus are becoming increasingly well-established, the characterization of microbial community composition using molecular biological analyses is becoming more commonplace for accurate monitoring. As this field continues to develop, the importance for standardized operating protocols cannot be understated, so that industry can make the most informed operational decisions possible. Accurately identifying oilfield microbial communities is paramount, as improper preservation and storage following sample collection is known to lead to erroneous microbial identifications. Preserving oilfield PW can be challenging, as many locations are remote, requiring lengthy periods of time before samples can be processed and analyzed. While previous studies have characterized the effects of various preservatives on concentrated, filtered, or purified microbial samples, to the best of our knowledge, no such study has been undertaken on low biomass liquid samples. To this end, we investigated the effectiveness of nine different preservation conditions on PW collected from the same sampling location within a heavy-oil producing field, and monitored how the microbial community changed over the period of a month. Our results reveal that the choice of preservative drastically affects microbial community, and should be selected with careful consideration before sampling occurs.

Dissolved oxygen deficits in a shallow eutrophic aquatic ecosystem (fishpond) – Sediment oxygen demand and water column respiration alternately drive the oxygen regime

Biological processes tend to dominate the oxygen regime of productive waters. However, in shallow aquatic ecosystems, it is unclear whether the oxygen regime is driven by oxygen production and consumption in the water column or by sediment oxygen demand (SOD). In managed eutrophic ecosystems, this question is especially important in the context of extreme daily oscillations of dissolved oxygen (DO) that could breach physiological limits of heterotrophic aerobic organisms. High-frequency measurement of DO, temperature, global radiation (Gl.Rad.), and pH in a 0.6 m deep, 22 ha eutrophic fishpond Rod (Czech Republic) shows that the oxygen regime depended on the ecosystem state. Over the clearwater period in the early season, the DO level reflected ecosystem heterotrophy with relatively low daily DO oscillations. However, during the summer phytoplankton bloom, the fishpond was primarily autotrophic with extreme DO fluctuation. During late summer, a collapse of the phytoplankton bloom and an associated shift towards heterotrophy and DO deficit frequently occur. In-situ mesocosm experiments in Rod fishpond were conducted throughout 2018 and 2019 growing seasons, to address the importance of SOD to the oxygen regime. We enclosed the water column in transparent and opaque/dark plastic cylinders open or closed to the sediment. The results show that the proportional contribution of SOD to total respiration decreased from 70 to 90% at low phytoplankton biomass (expressed as Chlorophyll-a (Chl-a) concentration) to approximately 10% at phytoplankton bloom. At night, the difference between the oxygen consumption in the cylinders with or without sediment was statistically significant, when the concentration of Chl-a was <100 μg·L−1. On the contrary, the difference was not significant when the concentration of Chl-a was >100 μg·L−1. This revealed that the impact of SOD is negligible at high phytoplankton biomass.

Optimization of trace elements in purified glycerol for microbial lipid and citric acid production by Yarrowia lipolytica SKY7

Purified glycerol obtained after acid treatment of crude glycerol solution was used as the carbon source for lipid and citric acid production using Y. lipolytica SKY7. Although purified glycerol was high in phosphorus, it was important to investigate the impact of fortification of trace elements in the medium on cell growth, lipid and citric acid (CA) production. When all the trace elements (including phosphates and sulfates) required for growth and lipid production were added to the purified glycerol medium, high biomass (51.67 g/L) and lipid concentration (19.47 g/L) were observed at 96 h of fed-batch fermentation with low CA concentration of 5.42 g/L. The purified glycerol medium without additional trace elements gave low biomass (27.67 g/L), lipid concentration (9.35 g/L) at 80 h of fed-batch fermentation, but gave high CA concentration (24.51 g/L). When purified glycerol was provided with only sulfates or all elements except KH2PO4, low biomass (32.59 g/L and 38.52 g/L) and citric acid concentration (1 g/L and 2.42 g/L) were obtained at 96 h.

Sustainable Cost-Effective Microalgae Harvesting Strategies for the Production of Biofuel and Oleochemicals

Microalgae have been explored for sustainable production of biofuel and chemicals. Microalgae is promising feed stock for the production of several oleochemicals. It has the ability to utilize a variety of low cost feed stocks, accumulated large quantities of lipids and variety of value added products in their biomass. One of the major obstacles associated with the conversion of algae into value-added products is harvesting. The harvesting of algae is the most problematic area due to its low sedimentation rate, low biomass concentration, and high capital costs. Harvesting of algae is carried out by different physical, chemical, mechanical, biological, and electrolytic methods such as sedimentation, centrifugation, microstraining, dissolved air flotation, electrolytic flotation, chemical flocculation, bioflocculation, autoflocculation, Filtration. This review highlights the various methods of microalgae harvesting with advantages and future perspective of sustainable and cost-effective harvesting of microalgae.

Experimental assessment and mathematical modelling of the growth of Chlorella vulgaris under photoautotrophic, heterotrophic and mixotrophic conditions

Microalgae show great potential for wastewater treatment and nutrient recovery. However, microalgae cultivation and harvesting are affected by the low biomass concentrations which are inherent to the photoautotrophic growth process. Mixotrophic growth can be a solution as it increases microalgae biomass concentration independently from the incident light intensity. In this work, a combined respirometric-titrimetric unit was used to assess the microalgae kinetics during such mixotrophic growth conditions for Chlorella vulgaris. Based on the experimental results, a microalgae model was extended in order to gain more insight in the delicate balance between photoautotrophic and heterotrophic growth. The results suggest that during heterotrophic growth with light in absence of external inorganic carbon sources (i.e. photoheterotrophic growth), all CO2 produced by the heterotrophic pathway is internally recycled for photoautotrophic growth. Moreover, it was shown that photoautotrophic growth is the preferential growth mechanism under mixotrophic cultivation conditions (i.e. light + inorganic carbon + organic carbon), but that high oxygen concentrations activate the heterotrophic growth pathway to avoid photorespiration. The extended microalgae model supports these findings, with good model performance for all conducted experiments.

The effect of two antifungal commercial formulations on the metabolism of a commercial Saccharomyces cerevisiae strain and their repercussion on fermentation evolution and phenylalanine catabolism

The effect of two commercial formulations (incorporating mepanipyrim and tetraconazole as active substances) on the metabolism of Saccharomyces cerevisiae Lalvin T73™, growing on a synthetic grape must, and their influence on the alcoholic fermentation course and the biosynthesis of volatiles derived from phenylalanine catabolism was studied. No relevant effects were observed for mepanipyrim except for glycerol production. On the contrary, in the presence of tetraconazole many genes and some proteins related to cell cycle progression and mitosis were repressed. This fact could explain the lower biomass concentration and the lower sugar consumption registered for tetraconazole at the end of the study. However, the biomass-to-ethanol yield was higher in connection with the overexpression of the ADH1 gene. The presence of tetraconazole residues seems to accelerate the Ehrlich pathway. These results agree with the overexpression of several genes (BAT1, PDC1, PDC5, ADH1, SFA1, ATF2, PFK1, PFK2 and ARO3) and a higher abundance of two proteins (Gap1p and Atf2p) involved in this metabolic pathway.

Harvesting microalgal-bacterial biomass from biogas upgrading process and evaluating the impact of flocculants on their growth during repeated recycling of the spent medium

Microalgal-bacterial consortium can be used to upgrade biogas by removing CO2 and H2S. Photosynthetic biogas upgrading requires harvesting microalgal-bacterial biomass in order to use the biomass-free cultivation medium as scrubbing liquid in the absorption column. In this study, the efficiency of different flocculants (Zetag 8125, cationically modified cellulose nanocrystals, Tanfloc, chitosan, and FeCl3) to harvest microalgal-bacterial biomass used for biogas upgrading in alkaline medium (inorganic carbon concentration up to 1800 mg L−1 and a pH ~10) was evaluated. Zetag and cationic cellulose nanocrystals resulted in maximum flocculation efficiencies of 95% (optimal dose 30 mg g−1) and 93% (optimal dose 20 mg g−1), respectively. Low flocculation was observed with other flocculants at doses as high as 200 mg g−1, which can be ascribed to the high pH of the alkaline medium. Zetag and cationic cellulose nanocrystals were selected for harvesting the biomass during semi-continuous cultivation of the microalgal consortium. Both Zetag and cationic cellulose nanocrystals were effective in flocculating the biomass with efficiencies of over 90% during five successive harvesting cycles. Gravity settling of the flocs formed by Zetag and cationic cellulose nanocrystals resulted in low biomass concentration factors of 7.7 and 2.0, respectively. Screening of flocs using a nylon mesh screen (pore size of 180 μm) resulted in a biomass concentration factor as high as 19.8. Zetag and cationic cellulose nanocrystals could be useful in harvesting biomass under high alkaline conditions without detrimental effects on biomass growth.

Modeling biomass production during progressive nitrogen starvation by North Swedish green microalgae

Five newly isolated green algal species from Northern Sweden and one culture collection strain were tested for their ability to remove nitrogen and accumulate carbohydrates and neutral lipids (TAGs) under progressive nitrogen starvation. All six microalgal species increased biomass during N starvation, the amount of proteins decreased, and species dependent either TAGs and/or carbohydrates accumulated. Biomass of the algal strains Coelastrella sp. 3-4, Scenedesmus sp. B2-2 and S. obliquus RISE (UTEX 417) had very low final TAG content (≤3.4%) and high carbohydrate content (>41%) at the end of the starvation period. C. astroideum RW10 accumulated 9.2% TAGs and 53.9% carbohydrates during N-starvation; due to its modest growth rate (1.60 g/L and 1.06 1/day) resulting in low final biomass concentration, its cumulativeTAG and carbohydrate productivity were poor (175 mgTAG/system and 1.03 gCARBS/system). C. vulgaris 13-1 preferentially accumulated TAGs (10.3%) over carbohydrates (35%), with low minimal and maximal N quotas (2.27 and 11.6 mM/gDW) in its biomass and a very high growth rate (1.86 1/day) and cumulative TAGs productivity (278 mgTAG/system). Desmodesmus sp. RUC2 had the highest final biomass concentration (3.48 g/L) as well as cumulative TAG and carbohydrate productivity (269 mgTAG/system and 1.79 gCARBS/system). This species had the lowest minimal and maximal N quotas (1.58 and 8.50 mM/gDW) of all tested species, it can produce high amounts of biomass even when the available nitrogen concentration is low.A Droop's mathematical model with four basic parameters was applied to interpret the experimental data on N assimilation and biomass production under N starvation. The model corresponded well to the experimental data and therefore can successfully be applied to predict biomass production and N assimilation in Nordic algal species.

Assessing the performances of an aerobic membrane bioreactor for textile wastewater treatment: Influence of dye mass loading rate and biomass concentration

Textile industry is being a very demanding consumer of high-quality water with highest wastewater discharge. Membrane bioreactor (MBR) was employed widely to treat dying effluents due to its distinct advantages over conventional techniques. This study investigated the potential of biological treatment employing a microbial community ‘IHK22′ under MBR laboratory-scale conditions to decolourize reconstituted textile wastewater in order to be reused. First, the bioreactor was conducted at a low biomass concentration of 4 gMLVSS⋅L−1. Decolourization performances were maintained at very high rates (91–100 %) for dye mass loading rates in the range of 1.25–2.5 mg⋅gMLVSS-1⋅d-1. Then, the dye concentration was increased to 7.5 mg⋅gMLVSS-1⋅d-1, the decolourization performances of the MBR have been affected (80–87 %). When the biomass concentration has been increased to 8gMLVSS⋅L−1, thus, a total MBR decolourization was then observed (100 %). Under 320 mg⋅gMLVSS-1⋅d-1 and regardless of the operating period of the MBR, all the microorganisms and microfiltration membrane allow the elimination of most soluble organic matter of the treated effluent (80–90 %). Obtained results indicate that the dye mass loading rate can influence the efficiency of dye removal through an MBR. The use of an appropriate biomass concentration significantly improves the MBR performances for an effective textile wastewater treatment.