Microalgal Biomass Production Research Articles

Boosting the yields of microalgal biomass and high-value added products by phytohormones: A mechanistic insight using transcriptomics

Addition of phytohormones (diethyl aminoethyl hexanoate and indole acetic acid) at 10−5 M significantly increased the growth of a green microalga, Chlorella pyrenoidosa up to 62.25% achieving cell concentrations of 5.13╳107 cells ml−1. Yielding of high-value added byproducts (pigments, carbohydrate, proteins, and fatty acids) was more in presence of phytohormones comparing to the control. Further transcriptomics analysis demonstrated phytohormones upregulated numerous genes involved in DNA replication and repair pathways, and energy metabolisms (glycolysis, citrate cycle, and oxidative phosphorylation). Moreover, genes in purine metabolism, and porphyrin and chlorophyll metabolism were also more expressed by up to 6.49 times with phytohormones. These pathways can supply more cellular signaling molecules and antioxidant contents. This study carried new insights on the key driving factors in phytohormone enhanced microalgal biomass production processes, which can help to find more feasible application solutions of phytohormones in microalgal biofactories.

A newly isolated alkaliphilic cyanobacterium for biomass production with direct air CO2 capture

Large-scale microalgal biomass production usually relies on concentrated CO2 as the carbon source which is a major logistical and economic challenge because of the required infrastructure and geospatial constraints of siting large algal production facilities close to concentrated CO2 sources. By taking advantage of enhanced CO2 mass transfer within alkaline media due to the reaction between CO2 and OH-, carbon can be directly captured from the ambient air and used by the algae. Achieving such goal requires algal strains that can grow fast under alkaline conditions. In this study, a newly isolated alkaliphilic cyanobacterial strain Cyanobacterium sp. PNNL-SSL1 was characterized for its temperature, pH, and salinity tolerance. The result shows that PNNL-SSL1 could sustain grow at pH above 11.2 but exhibited the highest growth rates at pH below 10.5. The strain is a warm season strain and grows the best at 10 PSU (practical salinity unit). The strain was then evaluated in indoor climate simulation ponds under outdoor-relevant pond cultivation conditions with carbon supplied only through direct air CO2 capture at the culture surface. Two batch culture runs, at slightly different initial pH, exhibited average biomass productivity of 15.2 g m-2 day-1 on ash-free dry weight basis. CO2 was directly captured from the air at an average rate of 21.6 g CO2 m-2 day-1 (78.8 tons ha-1 yr-1), contributing 74% of the carbon fixed in the biomass. The results demonstrated that PNNL-SSL1 is a promising strain for biomass production using air CO2 as the carbon source.

Advances in Genetic Engineering in Improving Photosynthesis and Microalgal Productivity.

Even though sunlight energy far outweighs the energy required by human activities, its utilization is a key goal in the field of renewable energies. Microalgae have emerged as a promising new and sustainable feedstock for meeting rising food and feed demand. Because traditional methods of microalgal improvement are likely to have reached their limits, genetic engineering is expected to allow for further increases in the photosynthesis and productivity of microalgae. Understanding the mechanisms that control photosynthesis will enable researchers to identify targets for genetic engineering and, in the end, increase biomass yield, offsetting the costs of cultivation systems and downstream biomass processing. This review describes the molecular events that happen during photosynthesis and microalgal productivity through genetic engineering and discusses future strategies and the limitations of genetic engineering in microalgal productivity. We highlight the major achievements in manipulating the fundamental mechanisms of microalgal photosynthesis and biomass production, as well as promising approaches for making significant contributions to upcoming microalgal-based biotechnology.

Analysis of photosynthetic pigments pathway produced by CO2-toxicity-induced Scenedesmus obliquus

The coal-to-gas process produces carbon dioxide, which increases global warming, and its wastewater treatment generates sludge with high organic toxicity. Scenedesmus obliquus is a potential solution to such environmental problems, and photosynthetic pigments are the focus of this study. The optimal concentration of CO2 for the growth of Scenedesmus obliquus was found to be 30 % after increasing the concentration of CO2 (0.05 %–100 %). The accumulation of photosynthetic pigments during cultivation could reach 31.74 ± 1.33 mg/L, 11.21 ± 0.42 mg/L, and 5.59 ± 0.19 mg/L respectively, and the organic toxicity of sludge extract could be reduced by 44.97 %. Upregulation of A0A383VSL5, A0A383WMQ3, and A0A2Z4THB7 as photo systemic oxygen release proteins and propylene phosphate isomerase resulted in oxygen-evolving proteins in photosystem II, electron transport in photosystem I, and intermediates in carbon fixation. This is achieved by increasing the intracellular antennae protein and carbon fixation pathway, allowing Scenedesmus obliquus to both tolerate and fix CO2 and reduce the organic toxicity of sludge. These findings provide insights into the innovative strategy underlining the fixation of CO2, treatment and disposal of industrial residual sludge, and the enhancement of microalgal biomass production.

Advantages and Limitations of Anaerobic Wastewater Treatment—Technological Basics, Development Directions, and Technological Innovations

Anaerobic wastewater treatment is still a dynamically developing technology ensuring the effective degradation of organic compounds and biogas production. As evidenced in the large scale-up, this technological solution surpasses aerobic methods in many aspects. Its advantages stem from the feasibility of operation at a high organic load rate, the smaller production of difficult-to-manage sewage sludge, the smaller space and cubature required, and the high-methane biogas ultimately produced. The exploitation of anaerobic reactors is in line with the assumption of a circular economy, material recycling by reduced CO2 emissions and energy consumption, and the production of renewable energy. Despite their unquestionable advantages, there is still a need to seek novel approaches and improve the currently exploited installations. The key avenues of research entail improvements in the stability of bioreactor operations and the enhancement of bioreactor adaptability to changing and unfavorable process parameters. The versatility of such systems would also be greatly improved by increasing nitrogen and phosphorus removal rates. Attempts have been made to achieve these goals by setting up separate zones within bioreactors for the individual steps of methane fermentation, incorporating active fillings to promote nutrient removal, and introducing chemical and physical treatments. An interesting solution is also the use of microwave radiation to stimulate temperature conditions and induce non-thermal phenomena, such as enhancing the enzymatic activity of methanogenic microflora. Another prospective approach is to integrate digesters into microalgal biomass production systems. The aim of this review paper is to present the thus-far technological knowledge about anaerobic wastewater treatment, including standard solutions and innovative ones, the effectiveness of which has been corroborated in pilot-scale installations.

Production of microalgal biomass and lipids with superior biodiesel-properties by manipulating various trophic modes and simultaneously optimizing key energy sources

Two promising oleaginous microalgae, Scenedesmus sp. SPP and marine Chlorella sp. were cultivated under various trophic modes. Both microalgae grew best under mixotrophic/nitrogen-rich mode, indicating good metabolisms of both inorganic (CO2) and organic (glucose) carbon sources. While mixotrophic/nitrogen-starvation conditions promoted the accumulation of lipids with superior biodiesel properties. The key energy sources, including light intensity, CO2 and glucose concentrations, for mixotrophic cultivation of the selected Scenedesmus sp. SPP was simultaneously optimized by Response Surface Methodology. High light intensity combined with high CO2 retarded growth but stimulated lipid/pigment synthesis. Two-stage mixotrophic cultivation using optimal conditions for biomass (light intensity 4.8 klux, CO2 13%, glucose 1% under nitrogen-rich mode) followed by those for lipid accumulation (light intensity 6.0 klux, CO2 15%, glucose 1% under nitrogen-starvation mode) successfully enhanced biomass by 1.46 folds and lipids by 1.39 folds and also improved the biodiesel properties. These strategies may significantly contribute to the development of microalgae-based biofuel and biochemical industries.

Microalgae production in human urine: Fundamentals, opportunities, and perspectives.

The biological treatment of source-separated human urine to produce biofuel, nutraceutical, and high-value chemicals is getting increasing attention. Especially, photoautotrophic microalgae can use human urine as media to achieve environmentally and economically viable large-scale cultivation. This review presents a comprehensive overview of the up-to-date advancements in microalgae cultivation employing urine in photobioreactors (PBRs). The standard matrices describing algal growth and nutrient removal/recovery have been summarized to provide a platform for fair comparison among different studies. Specific consideration has been given to the critical operating factors to understand how the PBRs should be maintained to achieve high efficiencies. Finally, we discuss the perspectives that emphasize the impacts of co-existing bacteria, contamination by human metabolites, and genetic engineering on the practical microalgal biomass production in urine.

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants’ load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Enhancing Bioenergy Production from the Raw and Defatted Microalgal Biomass Using Wastewater as the Cultivation Medium.

Improving the efficiency of using energy and decreasing impacts on the environment will be an inevitable choice for future development. Based on this direction, three kinds of medium (modified anaerobic digestion wastewater, anaerobic digestion wastewater and a standard growth medium BG11) were used to culture microalgae towards achieving high-quality biodiesel products. The results showed that microalgae culturing with anaerobic digestate wastewater could increase lipid content (21.8%); however, the modified anaerobic digestion wastewater can boost the microalgal biomass production to 0.78 ± 0.01 g/L when compared with (0.35-0.54 g/L) the other two groups. Besides the first step lipid extraction, the elemental composition, thermogravimetric and pyrolysis products of the defatted microalgal residues were also analysed to delve into the utilisation potential of microalgae biomass. Defatted microalgae from modified wastewater by pyrolysis at 650 °C resulted in an increase in the total content of valuable products (39.47%) with no significant difference in the content of toxic compounds compared to other groups. Moreover, the results of the life cycle assessment showed that the environmental impact (388.9 mPET2000) was lower than that of raw wastewater (418.1 mPET2000) and standard medium (497.3 mPET2000)-cultivated groups. Consequently, the method of culturing microalgae in modified wastewater and pyrolyzing algal residues has a potential to increase renewable energy production and reduce environmental impact.

Oxygen stress mitigation for microalgal biomass productivity improvement in outdoor raceway ponds

Dissolved oxygen (DO) concentrations at supersaturated levels are commonly observed in microalgae cultures due to photosynthesis. Unlike cultivation in closed photobioreactors, the impact of excessive oxygen and the mitigation methods in open systems such as raceway ponds have hardly been studied. In this study, photosynthetic rates of Monoraphidium minutum 26B-AM and Scenedesmus obliquus UTEX393, two of the top DISCOVR strains for outdoor raceway cultivation, were compared at different DO levels. Increasing DO from 0 to 30 mg L−1 caused a 36.6 % and 26.1 % reduction in photosynthetic rate for M. minutum 26B-AM and S. obliquus UTEX393, respectively. To improve the outdoor pond biomass productivity of each strain, three oxygen stress mitigation methods were tested. The first method raised the dissolved bicarbonate concentration by an order of magnitude to favor bicarbonate transport into the cell, increasing the CO2:O2 ratio near RuBisCO, thus reducing photorespiration. Although this method increased the observed photosynthesis rate of M. minutum 26B-AM by 26 % and S. obliquus UTEX393 by 13 % in laboratory testing, it failed to improve biomass productivity under outdoor pond conditions for both strains. The second method added sodium sulfite as an oxygen scavenger to chemically lower the DO concentration in the culture. Chemical reduction of dissolved molecular oxygen did not significantly improve the biomass productivity of M. minutum 26B-AM; however, a 10 % improvement in biomass productivity for S. obliquus UTEX393 was observed. The final method sparged cultures with air to strip oxygen out of the liquid medium. This did not improve the biomass productivity of M. minutum 26B-AM, likely due to unfavorable weather conditions during cold season cultivation; however, an improvement of 36 % in biomass productivity was achieved for S. obliquus UTEX393 during the warm season cultivation. Of the three tested methods, air-sparging was the most effective and practical for improving outdoor biomass production.

High-cell-density heterotrophic cultivation of microalga Chlorella sorokiniana FZU60 for achieving ultra-high lutein production efficiency

Chlorella sorokiniana has received particular attention as a promising candidate for microalgal biomass and lutein production. In this work, heterotrophic cultivation was explored to improve the lutein production efficiency of a lutein-rich microalga C. sorokiniana FZU60. Flask cultivation results showed that the highest lutein productivity was achieved at 30°C with an initial cell concentration of 1.40 g/L. Furthermore, six types of fed-batch strategies based on nutrient composition and concentration were examined using a 5 L fermenter. Among them, ultra-high lutein production (415.93 mg/L) and productivity (82.50 mg/L/d) with lutein content of 2.57 mg/g were achieved with fed-batch 3F (i.e., pulse-feeding with concentrated urea-N medium to achieve a 3-fold nutrient concentration). The lutein production performance achieved is much higher than the reported values. This work demonstrates that heterotrophic cultivation of C. sorokiniana FZU60 with the proposed fed-batch strategy could significantly enhance the production performance and the commercial viability of microalgae-derived lutein.

A revolving algae biofilm based photosynthetic microbial fuel cell for simultaneous energy recovery, pollutants removal, and algae production.

Photosynthetic microbial fuel cell (PMFC) based on algal cathode can integrate of wastewater treatment with microalgal biomass production. However, both the traditional suspended algae and the immobilized algae cathode systems have the problems of high cost caused by Pt catalyst and ion-exchange membrane. In this work, a new equipment for membrane-free PMFC is reported based on the optimization of the most expensive MFC components: the separator and the cathode. Using a revolving algae-bacteria biofilm cathode in a photosynthetic membrane-free microbial fuel cell (RAB-MFC) can obtain pollutants removal and algal biomass production as well as electrons generation. The highest chemical oxygen demand (COD) removal rates of the anode and cathode chambers reached 93.5 ± 2.6% and 95.8% ± 0.8%, respectively. The ammonia removal efficiency in anode and cathode chambers was 91.1 ± 1.3% and 98.0 ± 0.6%, respectively, corresponding to an ammonia removal rate of 0.92 ± 0.02 mg/L/h. The maximum current density and power density were 136.1 mA/m2 and 33.1 mW/m2. The average biomass production of algae biofilm was higher than 30 g/m2. The 18S rDNA sequencing analysis the eukaryotic community and revealed high operational taxonomic units (OTUs) of Chlorophyta (44.43%) was dominant phyla with low COD level, while Ciliophora (54.36%) replaced Chlorophyta as the dominant phyla when COD increased. 16S rDNA high-throughput sequencing revealed that biofilms on the cathode contained a variety of prokaryote taxa, including Proteobacteria, Bacteroidota, Firmicutes, while there was only 0.23–0.26% photosynthesizing prokaryote found in the cathode biofilm. Collectively, this work demonstrated that RAB can be used as a bio-cathode in PMFC for pollutants removal from wastewater as well as electricity generation.

Mass transfer characteristics and effect of flue gas used in microalgae culture.

Flue gas not only contains carbon dioxide (CO2) but also air pollutants (sulfur oxides (SOx) and nitrogen oxides (NOx)). The effective utilization of flue gas could help us to reduce the cost of microalgal biomass production. This study assessed and explored the utilization of flue gas for the absorption characteristics of different components and their biological effect in microalgal culture systems. In abiotic absorption experiments, the absorptivity of CO2 was reduced by a maximum of 3.1%, and the concentration of the available carbon source in the culture medium was decreased by 6.7% when sulfur dioxide (SO2, at 100mg/m3) was presented in the flue gas. Meanwhile, the presence of oxygen (O2, at 4%) in the flue gas improved the absorptivity of nitric oxide (NO). When Scenedesmus dimorphus was cultured using bisulfites and nitrites (at 10mmol/L and 8mmol/L, respectively) as the sulfur and nitrogen sources, SOx and NOx in the flue gas did not significantly affect growth of microalgal cells and the carbohydrate, lipid, and protein content. The consumption rates of nutrient elements were calculated, which could provide an adjustment strategy for the initial gas source when culturing microalgae with the flue gas. This study indicates that the flue gas used for microalgal culture should be partially desulfurized, so that the SOx and CO2 concentrations can optimize growth of microalgal cells, while the denitrification might not be needed since the flue gas can be oxidized to utilize the NO. KEY POINTS: • The concentration of the available carbon source in the culture medium was decreased when SO2 was presented in the flue gas, and the presence of O2 in the flue gas improved the absorptivity of NO. • An adjustment strategy for the initial gas source when culturing microalgae with the flue gas was firstly proposed. • For flue gas containing 10% CO2 and 60mg/m3 of SO2, growth of Scenedesmus dimorphus showed no difference in cell growth in normal culture conditions.

Developing food waste biorefinery: using optimized inclined thin layer pond to overcome constraints of microalgal biomass production on food waste digestate

Diversion of food waste from landfill through anaerobic digestion is a sustainable form of energy production (biogas) and the waste effluent (digestate) can be utilised as nutrient supply for microalgae cultivation. However, digestate has very high nutrient concentrations and is highly turbid, making it difficult to utilize as a nutrient source with conventional microalgae cultivation systems. Here we compared the efficiencies of a conventional open raceway pond (ORWP) and an improved inclined thin layer photobioreactor (ITLP) for the utilization and treatment of food waste derived digestate by Chlorella sp. The ITLP improved on volumetric and areal productivities by 17 and 3 times over the ORWP, with values of 0.563 and 31.916 g m −2 day −1 respectively. Areal nutrient removal via microalgae biomass were 2359.759 ± 64.75 and 260.815 ± 7.16 mg m −2 day −1 for nitrogen and phosphorous respectively in the ITLP, which are 2.8 times higher than obtained in the ORWP. The ITLP’s superiority stems from its ability to support a much higher average biomass yield of 6.807 g L −1, which was 7 times higher than in the ORWP. Mean irradiance in-situ was higher in the ITLP, irradiance distribution and utilization by the culture in the ITLP was 44% more efficient than in the ORWP. Our results indicate that the ITLP is a far more productive system than conventional raceway ponds. This demonstrates that integration of ITLP microalgae cultivation using digestate has the potential to make digestate management yield net benefit in food waste biorefinery settings.

Potential of microalgae cultivation using nutrient-rich wastewater and harvesting performance by biocoagulants/bioflocculants: Mechanism, multi-conversion of biomass into valuable products, and future challenges

Microalgae have been identified as one of the new feedstocks for renewable energy production . The conversion of microalgae into various valuable products has also been increasing in the last decade. Microalgae harvesting, one of the most important stages in microalgae production, has been studied and reviewed by many researchers. However, most harvesting methods still utilize chemicals during the process, which make harvested biomass not directly ready for food/feed production and pharmaceutical-related processes. Biocoagulants/bioflocculants are emerging compounds that can be used during the harvesting of microalgae because their existence does not introduce toxicity in the harvested biomass. Considering its potential to produce ready-to-use biomass, biocoagulants/bioflocculants have a bright future in microalgal biomass production processes. This review article highlights simultaneous wastewater treatment and microalgal biomass production as an emerging method in accommodating a circular economy paradigm. This paper juxtaposes the utilization of chemical-based coagulants/flocculants and biocoagulants/bioflocculants in harvesting microalgae. Biodegradability , effectiveness, harvested biomass characteristics, and potential of medium reuse are emphasized in the discussion. The agglomeration mechanisms of microalgae during harvesting, recent advances in the microalgal biomass conversions, and future challenges related to the utilization of biocoagulants/bioflocculants are also described in detail. Microalgae harvesting by using biocoagulants/bioflocculants is a feasible and promising environmentally friendly technology for microalgal biomass production. • Performances of microalgae harvesting using biocoagulants/bioflocculants are discussed. • Cultivation of microalgae using wastewater is discussed. • Mechanisms of microalgae harvesting are elaborated. • Conversion of microalgae biomass into valuable products are highlighted. • Future challenges on algae harvesting using biocoagulants/bioflocculants are discussed.

Production of Antioxidants and High Value Biomass from Nannochloropsis oculata: Effects of pH, Temperature and Light Period in Batch Photobioreactors

Nannochloropsis oculata is a marine microalgal species with a great potential as food or feed due to its high pigment, protein and eicosapentaenoic acid contents. However, for such an application to be realized on a large scale, a biorefinery approach is necessary due to the high cost of microalgal biomass production. For example, techno economic analyses have suggested the co-production of food or feed with antioxidants, which can be extracted and supplied separately to the market. The aim of this study was to investigate the effect of cultivation conditions on the antioxidant capacity of Nannochlosopsis oculata extracts, derived with ultrasound-assisted extraction at room temperature, as well as the proximate composition and fatty acid profile of the biomass. A fractional factorial approach was applied to examine the effects of temperature (20–35 °C), pH (6.5–9.5) and light period (24:0, 12:12). At the end of each run, biomass was collected, washed with 0.5M ammonium bicarbonate and freeze-dried. Antioxidant capacity as gallic acid equivalents as well as pigment content were measured in the ethanolic extracts. Optimal conditions were different for productivity and biomass composition. Interesting results regarding the effect of light period (LP) and pH require further investigation, whereas the effect of moisture on the extraction process was confounded with biomass composition. Finally, further data is provided regarding the relation between chlorophyll content and apparent phenolic content using the Folin–Ciocalteu assay, in agreement with our previous work.

Suitability of pre-digested dairy effluent for mixotrophic cultivation of the hydrogen-producing microalgae Tetraselmis subcordiformis

ABSTRACT The costs associated with microalgal biomass production can be reduced by leveraging alternative and cheap growth media. Digestate from fermentation reactors is a particularly interesting candidate for use in cultivating mixotrophic species. The aim of the present study was to assess whether pre-digested milk-industry effluent can be harnessed to grow Tetraselmis subcordiformis and produce hydrogen. The experimental series with 25% and 50% effluent in the growth medium performed the best, producing more than 2000 mgVS biomass/dm3. The biogas produced in these variants contained over 60% hydrogen. Increasing the effluent in the medium to 75% led to significant deterioration of performance, both in terms of T. subcordiformis biomass growth and biohydrogen production. The highest efficiency of nitrogen and phosphorus removal, respectively 98.1 ± 1.9% and 97.1 ± 1.4%, was observed in the system to which 25% of sewage was introduced. Increasing the share of fermented wastewater directly reduced the efficiency of removing biogenic compounds. A very strong negative correlation was found between initial N-NH4 in the growth medium and T. subcordiformis biomass production rates (R2 = 0.9177).

Coupling wastewater valorization with sustainable biofuel production: Comparison of lab- and pilot-scale biomass yields of Chlorella sorokiniana grown in wastewater under photoautotrophic and mixotrophic conditions.

Microalgae are the important biofuel precursors and their economic cultivation can be boosted under mixotrophic (MT) conditions while employing different industrial wastewaters containing organic carbon. In the current research, the quantitative analysis of microalgal biomass production under MT and photoautotrophic (PT) cultivation conditions both at lab and pilot scales was studied. For the purpose, a pre-identified microalgal species Chlorella sorokiniana was cultivated mixotrophically and photoautotrophically at lab and pilot scales. Artificially prepared wastewater containing 2% (w/v) sugarcane molasses was used for MT cultivation. However, for PT cultivation, atmospheric CO2 was the only carbon source. After 15 days of aerobic incubation, microalgal biomass was harvested and analyzed for biomass productivity. Cultivation conditions and cultivation scale posed significant and non-significant impact, respectively on biomass productivities. However, biomass productivity was comparatively higher for the biomass raised under MT conditions at lab scale. The recorded values of biomass productivity were 88.75±9.51 and 127.68±7.91mgL-1d-1 for the biomass raised at lab scale under PT and MT conditions, respectively. Pilot-scale cultivation depicted biomass productivities as 83.49±7.87 and 124.88±3.76mgL-1d-1 under PT and MT conditions, respectively. High biomass production under MT conditions may suggest the elevated production of biofuels from microalgae. Future studies on biomass production while utilizing different industrial wastewaters at pilot scale and in open raceway ponds are needed for viable production of microalgae-based fuels.

Control of bacterial contamination in microalgae cultures integrated with wastewater treatment by applying feast and famine conditions

The integration of microalgae production with wastewater treatment can significantly increase economic and environmental sustainability of the treatment process and of the microalgal biomass production. However, a major bottleneck of this strategy is the control of contamination by heterotrophic bacteria, which compete with microalgae for the organic substrate and can negatively affect the quality of the produced biomass. Here, a strategy to control bacterial contamination is proposed, whereby a first batch phase with the medium replete in the organic substrate (feast) is followed by a second batch phase without the organic substrate (famine). Permeates from microfiltration and ultrafiltration of cheese whey were used as sources of organic substrates, with different C/N. Biomass production and pollutant removal were analyzed, and the growth kinetics of microalgae and bacteria were characterized and modeled to determine the specific growth rate (µmax) during the feast phase and the decay rate (kD) during the famine phase. Bacteria had µmax (0.16 h−1) about two folds higher than microalgae (0.07 h−1), however, bacteria lysed in larger fraction during the famine phase, allowing to reduce contamination. A remarkable finding was that, for both microalgae and bacteria, only a cell subpopulation experienced lysis during the famine phase. The fraction of resistant cells was higher for microalgae and decreased with increasing the C/N ratio in the initial medium, indicating that cell-to-cell heterogeneity for carbon storage is crucial in determining cell resistance. Guidelines are derived to maximize microalgae biomass productivity and pollutant removal while maintaining a prescribed bacterial contamination.

Biomass and eicosapentaenoic acid production from Amphora sp. under different environmental and nutritional conditions.

Eicosapentaenoic acid (EPA) could be extracted from diatoms such as Amphora sp. present abundantly in the ecosystems. In view of the key environmental and nutritional factors governing the diatoms growth rate, culture conditions were optimized for the biomass yield, total lipid content, EPA yield, and fatty acid composition under two main cultivation regimes: photoautotrophic and heterotrophic. The fastest growth rate about 0.20±0.02g/L and the highest EPA yield about 9.19±3.56mgEPA/g biomass were obtained by adding 10g/L glucose and sucrose, respectively. Under photoautotrophic culture conditions, Amphora sp. rendered higher EPA yield at 100rpm and 16:8 light/dark cycle. Total fatty acids produced predominantly comprised of an approximate 40-70% of saturated fatty acids, followed by 10-27% of monounsaturated fatty acids and then 8-25% of polyunsaturated fatty acids. These findings were able to pave a way for huge-scale microalgal biomass production in commercial EPA production.