Valorisation of starch production in microalgae biorefinery

The present research project was aimed at the valorisation of microalgal starch production within a biorefinery approach. The activity was carried out at the Dipartimento di Ingegneria Chimica, dei Materiale e della Produzione Industriale and at the Dipartimento di Biologia of the Università degli Studi di Napoli ‘Federico II’. Some tasks were carried out at the Laboratoire de Génie des Procédés environnement agro-alimentaire of the University of Nantes (France). The activity has been organized in four main paths: T1) Selection of a robust microalgal strain for starch production. This task was aimed to select a robust microalgal strain for industrial production of the biomass for biorefinery applications. The selection was based on the biomass and starch productivity. Two fresh water microalgae, Chlorella sorokiniana and Scenedesmus vacuolatus, and two seawater microalgae, Dunaliella tertiolecta and Tetraselmis chuii were investigated. C. sorokiniana was selected as the best starch producer. The effect of nitrogen and CO2 concentration on the biomass and starch productivity was investigated. At light irradiance of 300 μmol m-2s-1, the optimal concentration of nitrogen and CO2 were 32 mg L-1 and 2%, respevtively. A complete biochemical characterization of the microalgal biomass was carried out as a function of the growth time. The onset of nitrogen depletion was identified as the suitable condition for the simultaneous recovery of multiple products: starch, proteins, lipids (34, 37, 21 %DW, respectively). T2) Characterization of the microalgal starch granules. The goal of this task was to prove that the microalgal starch granules have interesting physic and chemical properties required for industrial applications. Limited information was available in literature about microalgal starch, then additional analysis were necessary to validate the potential applications of this starch type. C. sorokiniana starch extraction was optimized and a preliminary physic-chemical characterization was carried out. The results pointed out many similarities with cereals starch. However, the reduced size of the starch granules from microalgae addressed specific and high-value applications as emulsifier, molecules carrier, functionalization, bioplastics. T3) Intensification of microalgal biomass production. The increase in the microalgal biomass concentration and productivity are crucial issues for the process optimization. A new ultra-thin flat photobioreactor was designed and built. The performances were assessed for C. sorokiniana. The effect of the light intensity on the growth and the biochemical composition of C. sorokiniana was also investigated. Biomass concentration of 10 g L-1 was established in less than 100 hours at medium light irradiance of 300 μmol m-2 s-1. T4) Mild downstream processes for the recovery of starch and other components. The goal was the exploitation of several microalgal components. The simultaneous recovery of starch and antioxidants was carried out in cooperation with Dr. Ganna Petruk, Biotechnology PhD student. The recovery of starch and proteins from microalgae was carried out at Laboratoire de Génie des Procédés environnement agro-alimentaire, Nantes University. The effect of bead milling cell disruption on products recovery was investigated. A model to describe the disruption process was successfully applied to the product recovery. Integration of microalagal mechanical disruption, centrifugation and membrane separation for the simultaneous recovery of starch and proteins from microalgal biomass was investigated

New ultra-flat photobioreactor for intensive microalgal production: The effect of light irradiance

One of the main bottlenecks for the exploitation of microalgae is the low biomass concentration of the cultures: high harvesting costs and large cultivation area are always required. This bottleneck is partly due to a low light availability along the optical path of photobioreactors. An ultra-thin flat photobioreactor (UFP) (3 mm thickness) was proposed to increase both biomass concentration and productivity. The performance of the UFP was investigated: the effects of incident light intensity - from 50 and 1000 μmolPhotons m-1 s-1 - on cell growth, photosynthesis rate, and biochemical composition of Chlorella sorokiniana were characterized. The maximum microalgal concentration and the maximum areal productivity were 24 kg m−3 and 1.34 g m−2 h−1, respectively. The cell specific growth rate reached 0.1 h−1 at 1000 μmol m−2 s−1. The biochemical composition of the microalgal biomass changed with the light irradiance. Protein content increased from 35 up to 53% of DW with increasing the light intensity. The concentration of storage compounds, such as starch and lipids, decreased from 30 to 16% and from 30 to 10%, respectively, with increasing the light intensity. A limit in the maximum biomass concentration achievable was identified. Several hypotheses have been discussed. A light transfer model was applied to assess the presence of light limitation. Other hypotheses were analyzed in depth and the most feasible explanations were found to be a) the damage to the photosystem when exposed for long period to continuous and high light irradiances, b) nutrient limitation due to salt precipitation or c) gas-liquid transfer of the CO2. Finally, benefits and drawbacks of the ultra-thin culture system were discussed

Identification of an industrial microalgal strain for starch production in biorefinery context : The effect of nitrogen and carbon concentration on starch accumulation

The recent trends in microalgal cultures are focused on the biorefinery of the biomass components. Some of them are not completely valorised, for example starch. Since there is a wide market for starch products in food and non-food industries, the exploitation of microalgal starch fractions could improve the economic sustainability of microalgae production. In this perspective, the optimization of nitrogen and carbon source uptake for starch accumulation is a critical point for reducing the nitrogen requirement footprint and to increase CO2 capture. In this study, four robust microalgal strains, already known as starch-accumulating strain, were investigated: Chlorella sorokiniana, Scenedesmus vacuolatus, Dunaliella tertiolecta, and Tetraselmis chuii. C. sorokiniana was selected as the best starch producer in the biorefinery context, and the role nitrogen and CO2 concentration had on the starch production was investigated. For light irradiance of 300 μmol m−2 s−1 the optimal nitrogen concentration for growth and starch accumulation resulted 32 mg L−1. The CO2 concentration clearly does not influence the starch accumulation, but concentrations distant from 2% negatively influence microalgal growth, affecting the final starch productivity. The biomass composition during the batch growth of C. sorokiniana was also analysed in order to explicitly characterise the dynamic of starch accumulation during the different growth phases. Protein content decreased during N-depletion, carbohydrates were mainly produced during the early N-depletion, followed by the accumulation of lipids in the late depletion

Autotrophic starch production by Chlamydomonas species

Microalgal autotrophic cultures may be used as starch feedstocks for a wide spectrum of food and non-food applications, starch-based plastics production included. Chlamydomonas is known to accumulate carbohydrates, but only Chlamydomonas reinhardtii is widely studied. This is the first paper that analyzes the starch content and production rate of four non-conventional Chlamydomonas species and compares their performances to the benchmark C. reinhardtii. Two culture systems—shaken flasks and inclined bubble column (IBC) photobioreactors—and nitrogen depletion conditions were characterized. The irradiance was set at 95 μmol photons m−2 s−1 for flask system and at 220 μmol photons m−2 s−1 for photobioreactors. CO2 and light depletion in shaken flasks strongly affected growth rate and starch production. Under these limiting condition, Chlamydomonas applanata had the best starch productivity of 1.2 mg L−1 day−1. In IBC photobioreactors, the microalgal growth rate and starch production improved with respect to the flask system and nitrogen depletion promoted starch accumulation. The best results of starch productivity and maximum starch fraction were 53 mg L−1 day−1 and 45%DW for Chlamydomonas oblonga and Chlamydomonas moewusii, respectively. This was 49 % more than the studied benchmark. A fast and simple method for starch localization in the microalgal cells was also proposed. The starch granules surrounded the pyrenoid under the growth phase, while they fill the whole cell under nutrient depletion

Autotrophic starch production by Chlamydomonas species

Microalgal autotrophic cultures may be used as starch feedstocks for a wide spectrum of food and non-food applications, starch-based plastics production included. Chlamydomonas is known to accumulate carbohydrates, but only Chlamydomonas reinhardtii is widely studied. This is the first paper that analyzes the starch content and production rate of four non-conventional Chlamydomonas species and compares their performances to the benchmark C. reinhardtii. Two culture systems—shaken flasks and inclined bubble column (IBC) photobioreactors—and nitrogen depletion conditions were characterized. The irradiance was set at 95 μmol photons m−2 s−1 for flask system and at 220 μmol photons m−2 s−1 for photobioreactors. CO2 and light depletion in shaken flasks strongly affected growth rate and starch production. Under these limiting condition, Chlamydomonas applanata had the best starch productivity of 1.2 mg L−1 day−1. In IBC photobioreactors, the microalgal growth rate and starch production improved with respect to the flask system and nitrogen depletion promoted starch accumulation. The best results of starch productivity and maximum starch fraction were 53 mg L−1 day−1 and 45%DW for Chlamydomonas oblonga and Chlamydomonas moewusii, respectively. This was 49 % more than the studied benchmark. A fast and simple method for starch localization in the microalgal cells was also proposed. The starch granules surrounded the pyrenoid under the growth phase, while they fill the whole cell under nutrient depletion291105114sem informaçã

Bead milling disruption kinetics of microalgae: Process modeling, optimization and application to biomolecules recovery from Chlorella sorokiniana

International audienceIndustrial development of microalgae biomass valorization relies on process optimization and controlled scale-up. Both need robust modeling: (i) for biomass production and (ii) for integrated processes in the downstream processing (DSP). Cell disruption and primary fractionation are key steps in DSP. In this study, a kinetic model, including microalgal cell size distribution, was developed for Chlorella sorokiniana disruption in continuous bead milling. Glass beads of 0.4 mm size at impeller tip velocity of 14 m.s(-1) were used as optimal conditions for efficient cell disruption. These conditions allowed faster disruption of big cells than small ones. A modified expression of the Stress Number, including cell size effect, was then proposed and validated. Separation of starch, proteins and chlorophyll by mild centrifugation was studied as function of the disruption parameters. Low energy consumption conditions led to extreme comminution. An intermediate zone drew attention for allowing moderate energy consumption and efficient metabolites separation by centrifugation

Current Bottlenecks and Challenges of the Microalgal Biorefinery

Microalgae are increasingly considered as sources of renewable feedstocks for industrial production, and microalgae production now focuses on the multiproduct microalgal biorefinery. However, such a biorefinery presents several bottlenecks that are mainly associated with downstream processes. This reduced downstream efficiency results from unsolved problems related to the culture strategy for the accumulation of different products – the protein versus lipid dilemma – and the dilute nature of the microalgal culture. We identify new trends and propose promising solutions for realizing microalgal biorefineries at industrial scale. New perspectives and challenges are identified in protein properties and in the integration and cooptimization of culture and downstream processes.</p

Microalgal biorefinery approach: integration and co-optimisation of the different unit operations

International audienc

Microalgae as new sources of starch: Isolation and characterization of microalgal starch granules

Starch is a very important biopolymer used in the modern society. It is a basic element of our diet (35% of daily calories in UE and USA). Moreover, it is widely used in the non-food industries. Indeed, the market of the non-food applications is nowadays growing and it includes chemical additives, bulking agents, and bioplastics productions (e.g. Mater-Bi by Novamont). The key starch features for industrial applications are: size and shape distributions of starch granules, crystallinity, amylose-amylopectin ratio, thermal properties. These features are critical to address the starch processing in the industrial production. Nowadays the main sources of small starch granules that fulfil the industrial requirements are maize, wheat, rice, oats, and amaranth. However, the reduced availability of arable lands and the increase of food demand ask for alternative sources for starch not in competition with food cultures. Microalgae are considered a novel highly efficient starch producers. Their starch content can reach the 40%W. They do not require arable land and fresh water for their cultivation. Nevertheless, limited information is available in literature about physico-chemical characterization of microalgal starch. Therefore, additional analysis about molecular weight, crystallinity, and amylose fraction are required to validate the potential industrial applications of this starch type. The present contribution reports a study on starch granules present in the microalga Chlorella sorokiniana. The granules were isolated and a preliminary physico-chemical characterization was carried out. The microalgal starch was characterized by small granules of about 1 μm with a narrow size distribution (key feature for some applications). The molecular weight of microalgal starch is comparable with that of plantstarch sources. The amylose content and crystallinity pattern were similar to cereal starch. Moreover, the high gelatinization temperature of 110 °C makes these granules suitable for system requiring high processing temperature such as for biodegradable materials