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Microalgae can produce biofuels, nutriceuticals, pigments and many other products, but commercialization has been limited by the cost of growing, harvesting and processing algal biomass. Nutrients, chiefly nitrogen and phosphorus, are a key cost for growing microalgae, but these nutrients are present in abundance in municipal wastewater where they pose environmental problems if not removed. This is not a traditional review article; rather, it is a fact-based set of suggestions that will have to be investigated by scientists and engineers. It is suggested that if microalgae were grown as biofilms rather than as planktonic cells, and if internal illumination rather than external illumination were employed, then the use of microalgae may provide useful improvements to the wastewater treatment process. The use of microalgae to remove nutrients from wastewater has been demonstrated, but has not yet been widely implemented due to cost, and because microalgae derived from wastewater treatment has not yet been demonstrated as a commercial source for value-added products. Future facilities are likely to be called Municipal Resource Recovery Facilities as wastewater will increasingly be viewed as a resource for water, biofuels, fertilizer, monitoring public health and value-added products. Advances in photonics will accelerate this transition.

Conventional sewage treatment applying activated sludge processes is energy-intensive and requires great financial input, hampering widespread implementation. The introduction of anaerobic membrane bioreactors (AnMBR) followed by an algal reactor growing species of commercial interest, may present an alternative, contributing to the envisaged resource recovery at sewage treatment plants. AnMBRs can be applied for organic matter removal with energy self-sufficiency, provided that effective membrane fouling management is applied. Haematococcus pluvialis, an algal species with commercial value, can be selected for ammonium and phosphate removal. Theoretical analysis showed that good pollutant removal, positive financial output, as well as a significant reduction in the amount of hazardous activated sludge can be achieved by applying the proposed process, showing interesting advantages over current sewage treatment processes. Microbial contamination to H. pluvialis is a challenge, and technologies for preventing the contamination during continuous sewage treatment need to be applied.

Conventional sewage treatment applying activated sludge processes is energy-intensive and requires great financial input, hampering widespread implementation. The introduction of anaerobic membrane bioreactors (AnMBR) followed by an algal reactor growing species of commercial interest, may present an alternative, contributing to the envisaged resource recovery at sewage treatment plants. AnMBRs can be applied for organic matter removal with energy self-sufficiency, provided that effective membrane fouling management is applied. Haematococcus pluvialis, an algal species with commercial value, can be selected for ammonium and phosphate removal. Theoretical analysis showed that good pollutant removal, positive financial output, as well as a significant reduction in the amount of hazardous activated sludge can be achieved by applying the proposed process, showing interesting advantages over current sewage treatment processes. Microbial contamination to H. pluvialis is a challenge, and technologies for preventing the contamination during continuous sewage treatment need to be applied.

Syftet var att finna en biologisk behandlingsmetodik för avloppsvatten som skullekunna reducera utsläpp av näringsämnen till recipienten Humlebäcken frånavloppsreningsverket (ARV) i Nyvång. Nyvångs reningsverk planeras uppgraderas och utökas och därtill har ärendet nekats då utsläpp till Humlebäcken förfaras bli för höga. Mikroalger som behandlingsmetod för avloppsvatten undersöktes via litteraturanalys ibåde svenska klimat och vid uppskalning. Det kunde inte hittas metodik eller teknik för att på industriell skala använda mikroalger till behandling av avloppsvatten idag. Dock presenteras flera olika tekniker som kan kopplas samman för ökad effektivitet. Vidare finns det stor potential om att mikroalgssystem kan kopplas samman med andra industriers spillvärme och rökgaser för ökad produktion av biomassa och rening av rökgas. Andra former av kemisk försedimentering och anaerob behandling från Energipositiv Rening presenteras, möjligheten finns att dessa kan kopplas samman med mikroalgssystem för komplett behandling till lägre kostnader av konventionell behandlingsteknik. Till slut presenteras påverkande faktorer vid nordiska klimat och utmaningar i form av striktare reningskrav och återföring av slam. Det presenteras kort om andra biologiska tekniker som svampodling och multitrofiskt vattenbruk vilka kan kopplas samman medmikroalgssystem för ökad resurseffektivitet och högre reningsgrad. Se figur 18 förgrafisk summering., The purpose was to find a biological treatment method for wastewater which could reduce emissions of nutrients to the recipient Humlebäcken from the wastewater treatment plant (WWTP) in Nyvång. Since Nyvång WWTP plans to upgrade and expand have been denied for fears of further contamination of Humlebäcken. Microalgae as a treatment method was examined in this literature analysis for Swedish climates and upscaling. For industrial purposes no technique or method could befound which could be applied to wastewater currently. Several techniques are presented however in the hopes that in combining them a higher efficiency might beachieved. If microalgae systems could be integrated with waste heat and flue gas from industry, then higher productivity could be achieved whilst reducing emissions from the flue gas. Other forms of pre-sedimentation and anaerobic treatment methods from EnergyPositive Purification systems are presented as there's a possibility these can be connected to microalgae systems for complete treatment and less costs. Factors which affect microalgae cultivation in Nordic climates and challenges in terms of stricter emission requirements and reuse of sludge are presented lastly. Other biological treatment methods like mushroom and multi-trophic aquaculture which can be integrated to microalgae systems are shown in hopes of achieving higher resource efficiency and pollution reduction. See figure 18 for graphical abstract.

A liquid digestate rich in ammonium nitrogen (8.3 g L−1) was collected from an agricultural biogas plant and supplied to microalgae cultures as their only nitrogen source. Chlorella vulgaris was cultivated for up to 21 days, both under controlled conditions in laboratory-scale glass-column photobioreactors as well as outdoors in an open pilot-scale thin-layer photobioreactor. By systematically addressing issues associated with the use of liquid digestate (i.e., turbidity, nutrient imbalance, ammonium toxicity, and acidification), microalgae were robustly cultivated at a high density and cultures achieved a net biomass dry weight of between 10 and 14 g L−1, and a productivity of up to 0.93 g L−1 d−1 (93% of maximum expectation). Cultivation in the thin-layer photobioreactor achieved areal productivities between 7 and 10 g m−2 d−1. Water acidification due to the uptake of ammonium by microalgae was prevented by a controlled addition of NaOH. A detailed mass balance showed that, despite high removal efficiencies (approximately 3% of the supplied nitrogen remained in the medium), microalgae assimilated only 40–60% of the supplied nitrogen and, consequently, a large amount of nitrogen was lost to the atmosphere.

Most of the world’s inhabitants still do not have access to sanitation facilities, particularly in remote or poor regions. Consequently, efficient solutions for decentralized wastewater treatment are urgently needed. This study investigates the technical feasibility of the coupling of an anaerobic membrane bioreactor (AnMBR) process with microalgae cultivation for decentralized domestic wastewater treatment. The results presented in this work are based on the 327-days operation of an 850-L AnMBR pilot-plant installed in a residential building in Hamburg, Germany, as well as on lab-scale and full-scale experiments conducted with the effluent of the AnMBR process (permeate) and with three microalgae species (Acutodesmus obliquus, Chlorella vulgaris and Chlorella sorokiniana). Over the eight main experimental phases of the AnMBR operation, chemical oxygen demand (COD) concentration in wastewater amounted to between 0.97 and 2.49 g∙L-1. Since between 86 % and 94 % of the COD was removed during the process, this showed a higher performance than other small decentralized wastewater treatment plants (WWTPs) and even competed with conventional German WWTPs. However, the organic loading rate, methane production and the hydraulic retention time were in the lower range of reported AnMBR-related values. This was due to a lower microorganism concentration in the reactor. Overall, 95 - 99 % of total nitrogen (TN) and 79 - 87 % of total phosphorus (TP) present in the wastewater were recovered in the permeate. During the lab-scale and full-scale experiments, the three microalgae species were able to assimilate the nutrients contained in the permeate and grow in this culture medium. Altogether, a similar performance to synthetic fertilizers was achieved. During the lab-scale experiments with Acutodesmus obliquus and Chlorella vulgaris, initial TN and TP concentrations were 64 - 115 mg∙L-1 and 7.1 - 14 mg∙L-1 respectively. During these experiments, a decrease of TN removal and biomass growth was punctually observed. This was due to a lack of iron in the permeate and could be easily counterbalanced by the supply of an iron salt and a chelating agent into the culture. Initial TN and TP concentrations were comparatively higher during the experiments conducted with Chlorella sorokiniana and ranged from 98 to 160 mg∙L-1 and 16 to 37 mg∙L-1 respectively. The reduced TN/TP ratio in the permeate led to an incomplete TP removal. For unfavorable TN/TP ratios, a solution leading to a complete TP removal must be implemented, such as the use of another microalgae species capable of adapting to low TN/TP ratios, pH increase or the use of iron or aluminum salts leading to TP precipitation. During the two full-scale experiments conducted with two flat panel photobioreactors in the fall and summer, ammonium and TP were completely removed. However, TN was totally assimilated only during the summer. The incomplete TN removal during the fall season was caused by the supply of flue gas containing NOx combined with a low irradiance making the assimilation of NOx by the microalgae impossible. Nutrient uptake was usually higher than and biomass production similar to the values for similar light conditions reported in the literature. Overall, the results related to nutrient removal during microalgae cultivation indicate that this new process can compete with conventional WWTPs. In this study, the technical feasibility of the combination of an AnMBR process and microalgae cultivation was proved. If the different processes, especially the cultivation and harvesting of microalgal biomass, are energetically optimized, this new technology will be an adequate solution to the need for efficient decentralized wastewater treatment technologies., Ein Großteil der Weltbevölkerung hat keinen Zugang zu sanitären Einrichtungen, insbesondere in abgelegenen oder armen Regionen. Daher sind effiziente Lösungen für dezentrale Abwasserbehandlung dringend erforderlich. Diese Studie untersucht die Machbarkeit der Kopplung eines anaeroben Membranbioreaktors (AnMBR) mit Mikroalgenkultivierung zur dezentralen häuslichen Abwasserbehandlung. Die vorgestellten Ergebnisse basieren auf einem 327-Tage langen Betrieb einer 850-L AnMBR Pilotanlage in einem Hamburger Wohnhaus, sowie auf Labor- und Full-Scale-Versuchen mit dem Ablauf des AnMBR Prozesses (Permeat) und drei Mikroalgenarten (Acutodesmus obliquus, Chlorella vulgaris und Chlorella sorokiniana). Während der acht Hauptversuchsphasen des AnMBR-Betriebs betrug der chemische Sauerstoffbedarf (COD) im Abwasser zwischen 0,97 und 2,49 g∙L-1. Mit einer Entfernung des COD zwischen 86 % und 94 % zeigte der Prozess eine höhere Leistung als dezentrale Kleinkläranlagen und kann diesbezüglich auch mit konventionellen deutschen Kläranlagen konkurrieren. Die Leistung bezüglich Raumbelastung, Methanproduktion und hydraulischer Verweilzeit war jedoch im unteren Bereich der Literaturwerte. Dies ist auf eine geringere Konzentration von Mikroorganismen im Reaktor zurückzuführen. Insgesamt wurden 95 - 99 % des gesamten Stickstoffs (TN) und 79 - 87 % des gesamten Phosphors (TP) im Permeat zurückgewonnen. Während der Labor- und Full-Scale-Versuche konnten die drei Mikroalgenarten die Nährstoffe erfolgreich aufnehmen und wachsen. Insgesamt wurde eine ähnliche Leistung wie bei synthetischen Düngemitteln erzielt. Während der Laborversuche mit Acutodesmus obliquus und Chlorella vulgaris lagen die TN- und TP-Konzentrationen zunächst bei 64 - 115 mg∙L-1 bzw. 7.1 - 14 mg∙L-1. Während dieser Experimente wurde zum Teil eine Senkung der TN-Entfernung und des Biomassewachstums durch Eisenmangel im Permeat beobachtet, was durch die Zufuhr eines Eisensalzes und eines Chelatbildners problemlos ausgeglichen werden konnte. Die anfänglichen TN- und TP-Konzentrationen während der Laborversuche mit Chlorella sorokiniana waren im Vergleich höher und betrugen 98 - 160 bzw. 16 - 37 mg∙L-1. Das reduzierte TN/TP-Verhältnis führte zu einer unvollständigen TP-Entfernung. Für ungünstige TN/TP-Verhältnisse sind daher entsprechende Konzepte nötig, wie z.B. die Verwendung einer anderen Mikroalgenart, die sich an niedrige TN/TP Verhältnisse anpassen kann, eine pH-Erhöhung oder die Verwendung von Eisen- oder Aluminiumsalzen um TP-Ausfällungen herbeizuführen. Bei zwei Full-Scale-Versuchen im Herbst und im Sommer mit zwei Flach-Photobioreaktoren wurden Ammonium und TP vollständig entfernt. Allerdings wurde TN nur während des Sommers vollständig aufgenommen. Eine unvollständige TN-Entfernung im Herbst wurde durch die Zufuhr von NOx-haltigem Rauchgas in Verbindung mit schlechten Lichtverhältnissen verursacht. Im Vergleich zu Literaturwerten für ähnliche Lichtverhältnisse war die Nährstoffaufnahme höher und die Biomasseproduktion ähnlich. Bezüglich der Nährstoffentfernung konnte der Prozess mit konventionellen Kläranlagen konkurrieren. In dieser Studie wurde die technische Machbarkeit der Kombination eines AnMBR-Verfahrens mit Mikroalgenkultivierung nachgewiesen. Wenn die verschiedenen Prozesse, insbesondere die Kultivierung und Ernte von Mikroalgenbiomasse, energetisch optimiert werden, wird diese neue Technologie eine adäquate Lösung für den Bedarf an effizienten dezentralen Abwasserbehandlungstechnologien werden.

Hydrothermal Liquefaction (HTL) could be a promising and better alternative to other techniques for energy recovery from municipal sewage sludge (MSS). However, the nutrients (i.e., N, and P) recovery potential from the byproducts, generated in the HTL of MSS, needs to be studied so that a comprehensive sludge management practice could be adopted. In this study, HTL process temperature (275–400 °C), and reaction time (30–120 min) were first investigated for biocrude yield and release of the nutrients to the aqueous phase liquid (APL) and biochar. The maximum energy recovery (i.e., 59%) and maximum energy return on investment (i.e., 3.5) were obtained at 350 °C and 60 min of holding time. With the increase in HTL reaction time, the concentration of nitrogen in the APL increased (5.1 to 6.8 mg/L) while the concentration of phosphorus decreased (0.89 to 0.22 mg/L); the opposite was observed for the biochar. The nutrient recycling efficiency from the APL using microalgae was found to be strain-specific; nitrogen recycling efficiency by Picochlorum sp. and Chlorella sp. were 95.4 and 58.6%, respectively. The APL, derived from 1 kg MSS, could potentially produce 0.49 kg microalgal biomass. Since the concentrations of various metals in the biochar samples were substantially lower compared to their concentrations in raw MSS, the application of biochar as a soil conditioner could be very promising. Overall, net positive energy could be recovered from MSS using the HTL process, while the nutrients in the APL could be used to cultivate specific microalgae, and biochar could be applied to enhance the soil quality. The authors would like to acknowledge the support of Qatar National Research Fund (QNRF, a member of Qatar Foundation) for providing the funding (under grants UREP21-101-2-045, and NPRP8-646-2-272) for this study. The authors thank Ms. Noora from Environmental Science Center (ESC), QU, for the GC–MS analysis of the biocrude samples. The authors would also like to acknowledge the support of Mr. Solaiman from Central laboratory Unit (CLU) of Qatar University for the ICP-OES analyses of the samples.

Esta revisión analiza la asimilación de C, N y P por microalgas y la influencia de los factores dependientes del pH (solubilidad, estado de ionización y biodisponibilidad), así como la adición de CO2 y su interacción en el tratamiento terciario de aguas municipales durante la producción de biomasa de microalgas. Este estudio destaca la importancia de monitorizar condiciones críticas como: 1) la interacción entre el pH y las especies de carbono inorgánico; 2) la biodisponibilidad de P; 3) reducción de N por formación de NH3 y 4) toxicidad de NH3. Por otra parte, para el uso óptimo de aire enriquecido con CO2 se recomienda considerar: 1) el suministro intermitente y variable de CO2 para evitar pérdidas a la atmósfera; 2) optimizar el consumo de CO2 evitando la acidificación del pH por formación de H2CO3 e inhibición de las microalgas en etapas tempranas de cultivo; y 3) conservación de pH óptimo (≈ 8,5) a través del sistema de amortiguamiento CO2 / HCO3_. Finalmente, se sugiere que las tecnologías biológicas basadas en el cultivo de microalgas para la eliminación de nutrientes y cumplimiento de normativas ambientales, representan una alternativa viable, que une el reciclaje y revalorización de recursos a través de la generación y usos potenciales de la biomasa (e.g., fertilizantes, pigmentos y antioxidantes). This review discusses microalgae assimilation of C, N and P as affected by pH-dependent factors (solubility, ionization state and bioavailability) and CO2 enrichment in tertiary water treatment during microalgae biomass production. This study indicates the importance of monitoring critical conditions such as: 1) pH and inorganic carbon species interaction; 2) P bioavailability; 3) nitrogen removal through NH3 volatilization and 4) NH3 toxicity. Also, optimal CO2 enriched air considerations, such as: 1) combining intermittent and variable CO2 enrichment to avoid losses into the atmosphere; 2) preventing microalgae growth inhibition due to H2CO3 formation and pH acidification at early stages of the culture and 3) maintenance of optimal pH (≈ 8.5) through the buffer system (CO2 / HCO3_). Finally, we suggest that biological technologies based on microalgae culture to remove excessive nutrient loads and compliance with environmental laws from water, represent a viable alternative attached to recycling and revaluation of resources through the generation and potential uses of biomass (e.g., fertilizer, pigments and antioxidants).

espanolEsta revision analiza la asimilacion de C, N y P por microalgas y la influencia de los factores dependientes del pH (solubilidad, estado de ionizacion y biodisponibilidad), asi como la adicion de CO2 y su interaccion en el tratamiento terciario de aguas municipales durante la produccion de biomasa de microalgas. Este estudio destaca la importancia de monitorizar condiciones criticas como: 1) la interaccion entre el pH y las especies de carbono inorganico; 2) la biodisponibilidad de P; 3) reduccion de N por formacion de NH3 y 4) toxicidad de NH3. Por otra parte, para el uso optimo de aire enriquecido con CO2 se recomienda considerar: 1) el suministro intermitente y variable de CO2 para evitar perdidas a la atmosfera; 2) optimizar el consumo de CO2 evitando la acidificacion del pH por formacion de H2CO3 e inhibicion de las microalgas en etapas tempranas de cultivo; y 3) conservacion de pH optimo (≈ 8,5) a traves del sistema de amortiguamiento CO2 / HCO3_. Finalmente, se sugiere que las tecnologias biologicas basadas en el cultivo de microalgas para la eliminacion de nutrientes y cumplimiento de normativas ambientales, representan una alternativa viable, que une el reciclaje y revalorizacion de recursos a traves de la generacion y usos potenciales de la biomasa (e.g., fertilizantes, pigmentos y antioxidantes). EnglishThis review discusses microalgae assimilation of C, N and P as affected by pH-dependent factors (solubility, ionization state and bioavailability) and CO2 enrichment in tertiary water treatment during microalgae biomass production. This study indicates the importance of monitoring critical conditions such as: 1) pH and inorganic carbon species interaction; 2) P bioavailability; 3) nitrogen removal through NH3 volatilization and 4) NH3 toxicity. Also, optimal CO2 enriched air considerations, such as: 1) combining intermittent and variable CO2 enrichment to avoid losses into the atmosphere; 2) preventing microalgae growth inhibition due to H2CO3 formation and pH acidification at early stages of the culture and 3) maintenance of optimal pH (≈ 8.5) through the buffer system (CO2 / HCO3_). Finally, we suggest that biological technologies based on microalgae culture to remove excessive nutrient loads and compliance with environmental laws from water, represent a viable alternative attached to recycling and revaluation of resources through the generation and potential uses of biomass (e.g., fertilizer, pigments and antioxidants).

This Ph. D. project is aimed to improve the efficiency and the sustainability of microalgal cultivation in view of large-scale biofuels production. Experiments as well as modeling and process simulation were used to investigate: i) the light utilization efficiency in algal photobioreactors and ii) different strategies for the recovery and recycling of nutrients. First of all, microalgal growth in continuous photobioreactors is modeled in order to identify optimum working conditions that allow maximum productivity, accounting for light intensity and regime, as well as for axial dispersion. Then, the integration of photovoltaic (PV) technologies with photobioreactors is studied as a possible technical solution to improve the photons utilization per surface area. In this regard, experiments applying either standard, low-cost silicon solar cells or a novel organic dye-sensitized semi-transparent photovoltaic module on the reactor surface are reported. An energetic and economic analysis of microalgal cultivation in a photovoltaic greenhouse, with the roof partially covered by PV panels is also presented. Two different strategies for nutrients recovery and recycling are investigated, namely flash hydrolysis (FH) of whole algal biomass and anaerobic digestion (AD) of lipid-extracted residues. The nutrients-rich aqueous phases produced by FH of two different algal species (Scenedesmus sp. and Nannochloropsis gaditana) are used to assess the growth performances of the respective algae in this medium. As an alternative to the direct recycling of the aqueous hydrolysate, the possibility of precipitating the nutrients in stable fertilizers is also reported. The biogas production from AD of lipid-extracted microalgae is evaluated, and the subsequent growth rate in the liquid digestate was compared to that obtained in standard synthetic medium. Finally, the experimental data gained from FH and AD are used to implement process simulations with the aim of evaluating the material and energy balances and to assess the feasibility on a large-scale.

The effluent from the biogas process was tested as a nutrient source during cultivation of the protein-rich and edible microalgae Spirulina (Arthrospira platensis) and compared with conventional Spirulina medium. Equal biomass production was observed until late exponential phase and no significant differences could be observed between the treatments in protein amount, amino acid composition, and total lipid concentration. The concentration of the pigment phycocyanin differed significantly between Spirulina medium and the effluent-based medium (63.3 ± 11.7 and 86.2 ± 1.9 mg g−1, respectively). Slightly higher concentrations of saturated fatty acids, mainly palmitic acid, were observed in the biomass produced in Spirulina medium than in that produced in the effluent-based medium. In the biomass produced in the effluent-based medium, the cadmium concentration was 0.07 ± 0.05 mg kg−1 of dry weight, whereas it was below the detection limit in the biomass produced in Spirulina medium. There is a need to identify new food and feed resources and a possible future scenario is to integrate Spirulina production into the biogas plant for protein production as it contains more than 60% of protein on dry weight basis. In that scenario, it is important to control heavy metal concentrations in the biogas slurry fed to Spirulina.

Hydrothermal Liquefaction (HTL) for algal biomass conversion is a promising technology capable of producing high yields of biocrude as well as partitioning even higher quantity of nutrients in the aqueous phase. To assess the feasibility of utilizing the aqueous phase, HTL of Nannochloropsis sp. was carried out in the temperature range of 275 to 350 °C and Residence Times (RT) ranging between 5 and 60 min The effect of reaction conditions on the NO 3 − , PO 4 3 − , SO 4 2 − , Cl − , Na + , and K + ions as well as Chemical Oxygen Demand (COD) and pH was investigated with view of recycling the aqueous phase for either cultivation or energy generation via Anaerobic Digestion (AD), quantified via Lifecycle Assessment (LCA). It addition to substantial nutrient partitioning at short RT, an increase in alkalinity to almost pH 10 and decrease in COD at longer RT was observed. The LCA investigation found reaction conditions of 275 °C/30 min and 350 °C/10 min to be most suitable for nutrient and energy recovery but both processing routes offer environmental benefit at all reaction conditions, however recycling for cultivation has marginally better environmental credentials compared to AD.

In this study, zeolite was employed for the separation and recovery of P from synthetic wastewater and its use as phosphorus (P) source for the cultivation of the green microalga Chlorella vulgaris and the cyanobacterium Arthrospira (Spirulina) platensis. At P-loaded zeolite concentration of 0.15–1 g/L, in which P was limited, the two species displayed quite different behavior regarding their growth and biomass composition. C. vulgaris preferred to increase the intracellular P and did not synthesize biomass, while A. platensis synthesized biomass keeping the intracellular P as low as possible. In addition under P limitation, C. vulgaris did display some little alteration of the biomass composition, while A. platensis did it significantly, accumulating carbohydrates around 70% from about 15%–20% (control). Both species could desorb P from zeolite biologically. A. platensis could recover over 65% and C. vulgaris 25% of the P bounded onto zeolite. When P-loaded zeolite concentration increased to 5 g/L, P was adequate to support growth for both species. Especially in the case of C. vulgaris, growth was stimulated from the presence of P-loaded zeolite and produced more biomass compared to the control. ispartof: International Journal of Molecular Sciences vol:16 issue:2 pages:4250-4264 ispartof: location:Switzerland status: published

The present doctoral thesis aimed to achieve a robust cultivation of microalgae by recycling nitrogen from a liquid digestate. However, the use of non-sterile nutrient source increases the risks of contamination of undesired organisms such as bacteria, viruses, protozoa, and rotifers. Therefore, the thesis also aimed to develop a cheap and bio-compatible decontamination method, which can be applied to microalgae during their cultivation. To reach these objectives, three projects were carried out. In the first project, microalgae (Chlorella vulgaris) were successfully cultivated at high-density with liquid digestate from anaerobic digestion as a nitrogen source. The cultivation was carried out at laboratory and pilot scales in glass-column and thin-layer photobioreactors, respectively. Biomass dry weight and productivity reached values up to 18.6 grams per liter and 0.93 grams per liter per day, respectively. To obtain these results, a cultivation method was developed to overcome inherent issues associated to the use of liquid digestate such as the acidification of the water, ammonium toxicity, turbidity, and nutrient imbalance. The nitrogen mass balance was carried out during the cultivation and it shows that only 40 to 60 % of the nitrogen supplied to the cultures were assimilated in the biomass. Surprisingly, accumulation of nitrogen in the supernatant accounted only for approximatively 3 %. Therefore, a large fraction of the nitrogen was lost to the atmosphere. In the second project, a citrate-modified photo-Fenton (PF) process was used to treat microalgae cultures contaminated with the bacterium Escherichia coli. The aim was to set experimental conditions where physiological and morphological differences can be used to favor the inactivation of bacteria and to minimize the loss of microalgae. Results showed that the citrate-modified PF was more effective against bacteria than a solar light/hydrogen peroxide treatment, while being less effective against microalgae. If the treatment was applied at an early-stage contamination, bacteria were fully inactivated, while the microalgae loss of viable cells was about three orders of magnitude. In the third project, the citrate-modified PF process was used to treat microalgae cultures contaminated by the rotifer Brachionus calyciflorus, a predator of microalgae, which can lead cultures to failure due to its high consumption rate of algal cells. Then, treated cultures were cultivated up to 14 days to assess the efficacy of the treatment. Results show that the citrate-modified PF and solar light/hydrogen peroxide treatments had equivalent efficacy to inactivate rotifers. However, the PF process remained less harmful for microalgae. When the citrate-modified PF treatment was applied to an early-stage contamination (5 rotifers per mL), the decontamination was effective and no regrowth of rotifers was observed. However, the cultivation of contaminated cultures, which were not treated, failed due to an increasing rotifer population (>1000 individuals per mL after 14 days of cultivation). As a whole, the present doctoral thesis contributes to the development of more robust and sustainable cultures of microalgae. Methods were developed to cultivate microalgae at high-density with liquid digestate and to control biological contaminants. Finally, challenges and opportunities were discussed as a perspective for further works.