Microalgae cultivation in photobioreactors:sustainable solutions for a greener future

Microalgae cultivation in photobioreactors(PBRs)has emerged as a promising and sustainable approach to address various environmental and energy challenges,offering a multitude of benefits across diverse applications.Recent developments in microalgae cultivation in photobioreactors have contributed substantially to the development and optimization of sustainable bioprocesses.This review presents a comprehensive analysis of recent innovations and breakthroughs in the field of microalgae cultivation,with a specific focus on their application in photobioreactors,aimed at paving the way for a greener future.This study in-depth examines the advantages of microalgae cultivation in photobioreactors,concentrating on its effectiveness in wastewater treatment,CO_(2)bioremediation,and the production of biofuels and high-value products.The review evaluates the effects of light,solar irradiation,temperature,nitrogen and phosphorus concentrations in culture media,CO_(2)concentrations,and pH on microalgae growth performance,including specific growth and biomass productivity.The study also examines open systems like unstirred ponds,raceway ponds,and circular ponds and closed systems like horizontal tubular,vertical bubble-column,airlift,flat panel,and plastic-bag photobioreactors,comparing their pros and cons.To optimize microalgae cultivation,key factors in photobioreactor design,including photosynthetic efficiencies,light/dark(L/D)cycles,CO_(2)concentrations,mass transfer,hydrodynamics behavior,and p H,are extensively investigated.In addition,the review outlines recent developments in large-scale photobioreactors and highlights the challenges and opportunities associated with photobioreactor scale-up and design parameter optimization,including genetic engineering and economic feasibility.This article is a vital resource for researchers,engineers,and industry professionals seeking sustainable bioprocesses and the application of microalgae-based technologies.

Design of Photobioreactors for Mass Cultivation of Photosynthetic Organisms

Photosynthetic microorganisms are important bioresources for producing desirable and environmentally benign products, and photobioreactors （PBRs） play important roles in these processes. Designing PBRs for photocatalysis is still challenging at present, and most reactors are designed and scaled up using semi- empirical approaches. No appropriate types of PBRs are available for mass cultivation due to the reactors＇ high capital and operating costs and short lifespan, which are mainly due to a current lack of deep understanding of the coupling of light, hydrodynamics, mass transfer, and cell growth in efficient reactor design. This review provides a critical overview of the key parameters that influence the performance of the PBRs, including light, mixing, mass transfer, temperature, pH, and capital and operating costs. The lifespan and the costs of cleaning and temperature control are also emphasized for commercial exploitation. Four types of PBRs-tubular, plastic bag, column airlift, and flat-panel airlift reactors are recommended for large- scale operations. In addition, this paper elaborates the modeling of PBRs using the tools of computational fluid dynamics for rational design. It also analyzes the difficulties in the numerical simulation, and presents the prospect for mechanism-based models.

Application of photobioreactors to cultivation of microalgae

An overview of photobioreactors now in use for production of microalgae world wide is presented, and the application of photobioreactors to the cultivation of microalgae is discussed in detail. It is pointed out that high cell density and industrial production of microalgae can be achieved using many kinds of closed photobioreactors including fermentor, tubular and flat plate photobioreactors, and the cultivation of Spirulina, Chlorella, Dunaliella tertiolecta and Porphyridium cruentrim by photobioreactors can achieve higher and steadier productivity than the cultivation of microalgae by an open air system. More and more researches indicate that tubular and flat plate photobioreactors are the development trend for photobioreactors with bubbles and air lift stirrers, and high bright light emitting diodes are the most economic light source with great potential for future development of photobioreactors. Photobioreactors can also be used for the production of high value metabolite (EPA or DHA) using some microalgae species for energy development and environment protection.

Photofermentative hydrogen production by immobilized Rhodopseudomonas sp. S16-VOGS3 cells in photobioreactors

One of the most important solutions to overcome energy and environmental problems and to replace the fossil fuel-based economy could be the use of photosynthetic microorganisms.The use of photosynthetic microorganisms is a potential alternative to energy generation from fossil fuels because they efficiently produce hydrogen(H_(2)).Immobilization of photosynthetic microorganisms is used for many biotechnological applications such as H_(2) production.This method appears attractive because it restricts cell movement in an entrapped matrix.Immobilization of Rhodopseudomonas sp.S16-VOGS3 cells is a promising way to improve H_(2) production.In this work,the ability of immobilized Rhodopseudomonas sp.S16-VOGS3 cells to produce H_(2) was investigated in two types of PBRs.The PBRs used in this work were a cylindrical one with 0.2 L working volume(C-PBR)and a flat Roux type with 0.6 L working volume(FRT-PBR).The calcium alginate beads prepared were resistant to culture mixing and showed little leakage of cells,and the immobilized cells continued the photofermentation process in both PBRs.The immobilized cells in the C-PBR produced 936.8 mL of H_(2) with an average H_(2) production rate of 2.99 mL/h.The average productivity was 126.4μL(H_(2))/mg(cells)/h or 14.96 mL(H_(2))/L(culture)/h,and the light conversion efficiency was 2.37%.The immobilized cells in the FRT-PBR produced a total of 662.2 mL of H_(2) with an average H_(2) production rate of 1.55 mL/h.The average productivity was 31.1μL(H_(2))/mg(cells)/h or 2.58 mL(H_(2))/L(culture)/h,and the light conversion efficiency was 0.52%.The more uniform and therefore more efficient degree of bacterial cell mixing achieved in the C-PBR with cylindrical configuration played an important role compared to the FRT-PBR.In the FRT-PBR,the beads were aggregated at the bottom,which limited light penetration and resulted in low H_(2) production efficiency.

Progress in microalgae cultivation photobioreactors and applications in wastewater treatment:A review

Using microalgae to treat wastewater has received growing attention in the world because it is regarded as a novel means for wastewater treatment.It is commonly recognized that large-scale cultivation and commercial application of microalgae are limited by the development of photobioreactor(PBR).Although there are a lot of PBRs for microalgae pure cultivation which used culture medium,specialized PBRs designed for wastewater treatment are rare.The composition of wastewater is quite complicated;this might cause a very different photosynthetic effect of microalgae compared to those grown in a pure cultivation medium.Therefore,PBRs for wastewater treatment need to be redesigned and improved based on the existing PBRs that are used for microalgae pure cultivation.In this review,different PBRs for microalgae cultivation and wastewater treatment are summarized.PBR configurations,PBR design parameters and types of wastewater are presented.In addition,the wastewater treatment efficiency and biomass productivity were also compared among each type of PBRs.Moreover,some other promising PBRs are introduced in this review,and a two-stage cultivation mode which combines both closed and open system is discussed as well.Ultimately,this article focuses on current problems and gives an outlook for this field,aiming at providing a primary reference for microalgae cultivation by using wastewater.

Effect of Flating Photobioreactor Light-path on the Growth and Organic Matter Accumulation of Isochrysis galbana Parke

[Objective] The paper aims to provide references to cultivate I.galbana in a large scale and explore its medical value.[Method] I.galbana had been cultivated in different light-path flat plate bioreactors,and the growth condition and content of organic matter within cells of I.galbana had been analyzed.[Result] Growth rate and volumetric productivity of I.galbana cells increased as light-path of flat plate bioreactors decreased,however,daily areal output rate rose with the increasing of light path.The smaller the light path of flat plate bioreactors was,the more content of total lipids,protein and polysaccharide it had in I.galbana cells.[Conclusion] It is an effective way to improve production efficiently and reduce the cost by selecting the suitable bioreactors.

Cultivation of Microalgae <i>Monoraphidium</i>sp., in the Plant Pilot the Grand Valle Bio Energy, for Biodiesel Production

At present, Brazil imports approximately 11 billion liters/year of diesel. With the interruption of the works in the new Petrobras refineries, the projection is that by 2025 this volume will increase to 24.2 billion liters of diesel/year. In this sense, the biodiesel factory Grand Valle Bio Energy Ltda., located in the state of Rio de Janeiro, in conjunction with the FAPERJ makes some investments in technology development for the cultivation and use of microalgae as an alternative raw material in the production of biodiesel. Based on arguments previously said, this work presents the results of the microalgae cultivation Monoraphidium sp. in photobioreactors the pilot plant of the company. The installation with an area of 120 m2 is included with 2 open photobioreactors of type falling film (20 m × 1 m), with a cascade of 18mm and capacity of 4000 L. The lineage cultivated is selected from previous ecophysiological studies that are identified as promising for biodiesel production by having a high potential for the production of lipids. This lineage is maintained at collection of the stock of cultures Laboratory of Green Technologies of the School of Chemistry/ UFRJ. The cultivation was performed in means ASM-1 (Gorham et al., 1964), initial pH 8.0, with aeration and circulation average of 8 hours a day during 19 days. The culture was started with an inoculum of 1 × 107 cel/ml. The lipid production was determined in two phases of growth: on day 4 (exponential phase) and 15 day (stationary phase). For the determination and quantification of lipid content, two different methods were assessed for a sample of biomass, submitted to the same processes the separation and drying. The results showed the methodology of Bligh & Dyer with modifications as the most efficient in extracting lipids. The total lipid content of the biomass Monoraphidium sp. was 30.58%. The growth rate varied between 0.74 ± 0.01 and 0.68 ± 0.02.

A system combining microbial fuel cell with photobioreactor for continuous domestic wastewater treatment and bioelectricity generation

A coupled system consisting of an upflow membrane-less microbial fuel cell (upflow ML-MFC) and a photobioreactor was developed, and its effectiveness for continuous wastewater treatment and electricity production was evaluated. Wastewater was fed to the upflow ML-MFC to remove chemical oxygen demand (COD), phosphorus and nitrogen with simultaneous electricity generation. The effluent from the cathode compartment of the upflow ML-MFC was then continuously fed to an external photobioreactor for removing the remaining phosphorus and nitrogen using microalgae. Alone, the upflow ML-MFC produces a maximum power density of 481 mW/m 3 , and obtains 77.9% COD, 23.5% total phosphorus (TP) and 97.6% NH4+-N removals. When combined with the photobioreactor, the system achieves 99.3% TP and 99.0% NH4+-N total removal. These results show both the effectiveness and the potential application of the coupled system to continuously treat domestic wastewater and simultaneously generate electricity and biomass.

Enhanced removal of nitrate and phosphate from wastewater by Chlorella vulgaris: Multi-objective optimization and CFD simulation

To enhance the efficiency of wastewater biotreatment with microalgae, the effects of physical parameters need to be investigated and optimized. In this regard, the individual and interactive effects of temperature, p H and aeration rate on the performance of biological removal of nitrate and phosphate by Chlorella vulgaris were studied by response surface methodology(RSM). Furthermore, a multi-objective optimization technique was applied to the response equations to simultaneously find optimal combinations of input parameters capable of removing the highest possible amount of nitrate and phosphate. The optimal calculated values were temperature of 26.3 °C, pH of 8 and aeration rate of 4.7 L·min^(-1). Interestingly, under the optimum condition, approximately 85% of total nitrate and 77% of whole phosphate were removed after 48 h and 24 h, respectively, which were in excellent agreement with the predicted values. Finally, the effect of baffle on mixing performance and, as a result, on bioremoval efficiency was investigated in Stirred Tank Photobioreactor(STP) by means of Computational Fluid Dynamics(CFD). Flow behavior indicated substantial enhancement in mixing performance when the baffle was inserted into the tank. Obtained simulation results were validated experimentally. Under the optimum condition, due to proper mixing in baffled STP, nitrate and phosphate removal increased up to 93% and 86%,respectively, compared to unbaffled one.

Growth and Physiological Features of Cyanobacterium Anabaena sp. Strain PCC 7120 in a Glucose-Mixotrophic Culture

Mixotrophic growth is one potential mode for mass culture of microalgae and cyanobacteria particularly suitable for the production of high value bioactive compounds and fine chemicals.The typical heterocystous cyanobacterium Anabaena sp.PCC 7120 was grown in the presence of exogenous glucose in light.Glucose improved the cell growth evidently,the maximal specific growth rate under mixotrophic condition（0.38 d 1）being 1.6-fold of that of photoautotrophic growth.Mixotrophy caused a variation in cellular pigment composition,increasing the content of chlorophyll a and decreasing the contents of carotenoid and phycobiliprotein relative to chlorophyll a.Fluorescence emission from photosystem II（PSII）relative to photosystem I was enhanced in mixotrophic cells,implying an increased energy distribution in PSII.Glucokinase（EC 2.7.1.2）activity was further induced in the presence of glucose.The mixotrophic culture was scaled up in a 15 L airlift photobioreactor equipped with an inner and an outer light source.A modified Monod model incorporating the specific growth rate and the average light intensity in the reactor was developed to describe cell growth appropriately.The understanding of mixotrophic growth and relevant physiological features of Anabaena sp.PCC 7120 would be meaningful for cultivation and exploitation of this important cyanobacterial strain.

Design of a Novel Photobioreactor for Culture of Microalgae

This paper presents the design of a novel photobioreactor for cultivation of microalgae. The body of the reactor with volume of about 40 L is parallelipipedic and divided in five compartments that can be put in series. The optical guides, plunged perpendicularly into the compartments, are upright Plexiglas plates on which side faces there are able to diffuse light laterally and ensure an even distribution of light in the medium. External airlifts through the side columns are used for mixing of culture medium. The external light source is a SON-T lamp mounted inside a projector that provides a conical light dispersion, it is interchangeable and may take different positions. The design offers the photobioreactor characteristics including mainly interchangeable light source, homogenous distribution of light, perfect mixing of suspension of algae, high ratio of illuminating surface to volume of reactor, compactness and absence of contamination. Schemes, view of the photobioractor and data of continuous culture forSpirulina maxima are presented.

Microalgae Cultivation Using Offshore Membrane Enclosures for Growing Algae (OMEGA)

OMEGA is a system for cultivating microalgae using wastewater contained in floating photobioreactors (PBRs) deployed in marine environments and thereby eliminating competition with agriculture for water, fertilizer, and land. The offshore placement in protected bays near coastal cities co-locates OMEGA with wastewater outfalls and sources of CO2-rich flue gas on shore. To evaluate the feasibility of OMEGA, microalgae were grown on secondary-treated wastewater supplemented with simulated flue gas (8.5% CO2 V/V) in a 110-liter prototype system tested using a seawater tank. The flow-through system consisted of tubular PBRs made of transparent linear low-density polyethylene, a gas exchange and harvesting column (GEHC), two pumps, and an instrumentation and control (I&C) system. The PBRs contained regularly spaced swirl vanes to create helical flow and mixing for the circulating culture. About 5% of the culture volume was continuously diverted through the GEHC to manage dissolved oxygen concentrations, provide supplemental CO2, harvest microalgae from a settling chamber, and add fresh wastewater to replenish nutrients. The I&C system controlled CO2 injection and recorded dissolved oxygen levels, totalized CO2 flow, temperature, circulation rates, photosynthetic active radiation (PAR), and the photosynthetic efficiency as determined by fast repetition rate fluorometry. In two experimental trials, totaling 23 days in April and May 2012, microalgae productivity averaged 14.1 ± 1.3 grams of dry biomass per square meter of PBR surface area per day (n = 16), supplemental CO2 was converted to biomass with >50% efficiency, and >90% of the ammonia-nitrogen was recovered from secondary effluent. If OMEGA can be optimized for energy efficiency and scaled up economically, it has the potential to contribute significantly to biofuels production and wastewater treatment.

The Growth Factors Involved in Microalgae Cultivation for Biofuel Production: A Review

The growing demand for energy and the negative environmental impacts of fossil fuel use are triggering global searches for a renewable and eco-friendly alternative biofuel. Microalgae are considered as one of the most promising feedstocks for biofuel production, due to many advantages including cultivation in non-arable land and being able to grow in wastewater or seawater. That is why;microalgae-based biofuels are regarded as one of the best candidates to replace fossil fuels. There are two main types of microalgae cultivation systems: Open Raceway Ponds and Closed Photobioreactos (PBRs). Due to some limitations in Open Raceways, PBRs have become the most favorable choice for biofuel producers, even though it is costly. To make the process viable, the growth of microalgae for biofuel production should be cost-effective. One way to achieve this goal is to optimize the environmental factors that influence their growth during the cultivation stage to increase the accumulation of bio-compounds of fuel. Algal growth relies mostly on nutrients, CO2 concentration, pH and salinity, light intensity and quality, temperature and finally mixing, which directly affects all other factors. Thus, before designing PBR, a thorough study on these growth parameters is needed. In the present study, we reviewed and evaluated these growth influencing factors in an extensive way to optimize biofuel production.

Effects of nutrient profiles and light regime on the production of exopolysaccharide by Porphyridium cruentum

In order to increase the yield of polysaccharides from Porphyridium cruentum and the cell biomass, we investigated several important cultural conditions such as nutrient-salts, light irradiance as well as growth conditions in the flat plate photobioreacturs （FPPBR） with different light-path. We have found that the optimal （OCM II ） was a superior medium for extracellular polysaccharide production than the f/2 and Koch medium, and the polysaccharide production with OCM II was increased by 1.79 times and 1.62 times compared with that of f/2 and Koch medium; the yields of polysaccharides were also improved by optimizing the light intensity and irradiation length Furthermore, we significantly enhanced the yields of both the biomass and extracellular polysaccharidc using a small light-path photobioreactor, and about 2.1 times increase of polysaccharide production was observed in FPPBR-30 than in FPPBR-100. Overall, the process for polysaccharides production was improved and this would facilitate further studies on such polysaccharidcs such as their antiviral and antitumor activities.

SPIRULINA CULTIVATION IN CHINA

This paper reviews and discusses the development and many problems of Spirulinacultivation in China, points out the advantages and disadvantages of open photobioreactor system, andpredicts that seawater Spirulina cultivation will be a new trend to be strengthened and emphasized due toits special physiological characteristics, easier managment, lower fertilizer cost, and higher resistance tocontaminants and rare pollution of chemicals.

H_2 PRODUCTION BY ANABAENA VARIABILIS MUTANT IN COMPUTER CONTROLLED TWO-STAGE AIR-LIFT TUBULAR PHOTOBIOREACTOR

A 4.34 liter two stage air lift photobioreactor incorporating Anabaena variabilis ATCC29413 mutant PK84 was used to study H 2 production. Results showed that H 2 production increased with increasing light intensity from 47 μE/(m 2·s) up to 190 μE/(m 2·s), but that further increase of light intensity decreased the H 2 production because of the inhibition due to the high pO 2. The data also indicated that longer argon gas charge resulted in more H 2 produced due to the increase of nitrogenase activities and heterocyst frequency, and that more than 1.3 L net H 2 was produced from this computer controlled photobioreactor.

Split internal-loop photobioreactor for Scenedesmus sp.microalgae:Culturing and hydrodynamics

In this study,the evaluation of the performance of the split internal loop photobioreactor for culturing a species of green microalgae,Scenedesmus sp.under different operating superficial gas velocity and during a different time of growth(i.e.,starting for the first day until end day of the culturing process)was addressed.The evaluation of the performance of the split internal loop photobioreactor was included assessing the density,pH,temperature,viscosity,surface tension,the optical density,cell population,dry biomass,and chlorophyll of the culture medium of the microalgae culturing.Additionally,the hydrodynamics of a Split Internal-Loop Photobioreactor with microalgae culturing was comprehensively quantified.Radioactive particle tracking(RPT)and gamma-ray computed tomography(CT)techniques were applied for the first time to quantify and address the influence of microalgae culture on the hydrodynamic parameters.The hydrodynamics parameters such as local liquid velocity field,shear stresses,turbulent kinetic energy,and local gas holdup profiles were measured at different superficial gas velocities as well as under different times of algae growth.The obtained results indicate that the flow distribution may significantly affect the performance of the photobioreactor,which may have substantial effects on the cultivation process.The obtained experimental data can serve as benchmark data for the evaluation and validation of computational fluid dynamics(CFD)codes and their closures.This,in turn,allows us to develop efficient reactors and consequently improving the productivity and selectivity of these photobioreactors.

HYDROGEN PHOTOPRODUCTION OF A.VARIABILIS INCORPORATED IN A PHOTOBIOREACTOR

H2 photoproduction and nitrogenase activities in two strains of Anabaena variabilismarked wild type ATCC 29413 and mutant PK84 exposed to thermal stress (temperature higher than thenormal incubation temperature of 30℃) were studied. Cultures of both strains collected from any intervalof logarithmic growth phase exhibited high H2 photoproduction and nitrogenase activities when exposed tolimited time heat shock during the assay process. In contrast, the algal H2 photoproduction rate of bothstrains fluctuated with long term thermal stress caused hy increasing the growth temperature from 30℃ to36℃.The changes of nitrogenase (the key H2 photobiosynhetic enzyme) activities in the mutant PK84showed variation tendency similar to that of H2 photoproduction during exposure to thermal stress, indicat-ing that fluctuation of H2 photopnduction in the mutant was mainly due to the variation of nitrogenase ac-tivities. A temporary maximal H2 photoproduction in the mutant PK84 (wild type ATCC29413 ) was ob-served when cells po at 36℃ for 14 (6) days. However, the responses of nitrogenase activities in thewild type to thermal stress were not completely similar to those in the mutant in spite of similar variationsof H2 photoproduction in both strains. The data obtained in these studies suggested tha the activities ofother enzymes (in the wild strain) involved in H2 photoproduction were affected by thermal stress since H2photoporduction maximized or dropped to 0 without variation tendency similar to that of nitrogenase activi-ties.Furthermore, an enhancement of H2 photoproduction speed of the mutant strain cultured in a 4.4 Llaboratory photobioreactor was also observed when it was subjected to short time continuous charge of ar-gon, and temperature rise.All these results indicated that high temperature plays an important role in the photo-autotrophic H2photoproduction, and that long term thermal stress is unfavourable for net H2 phooproduction in bothstrains of A. variabilis though short-time heat shock is conducive to H2 photoproduction.

Mixotrophic Cultivation of Tetraselmis sp.-1 in Airlift Photobioreactor

Tetraselmis sp.-1 is a new microalgae strain constructed by cell fusion technique. In this paper, the mixotrophic cultivation of Tetraselmis sp.-1 in airlift photobioreactor is investigated. Firstly, the paper calculates the light attenuation in the mixotrophic medium, and sets the light attenuation model. Secondly, it uses the same dissolved oxygen coefficient (K d) of flask culture to select the aeration of bioreactor. Finally, it sets the growth kinetic model, production (chlorophyll-a and total lipid) kinetic models and substrate (glucose) consumption kinetic model of Tetraselmis sp.-1 in airlift photobioreactor.

Photobioreactor of Microalgas for CO_(2) Biofixation

Microalgae are unicellular organisms capable of photosynthesis, turning sunlight and carbon dioxide (CO2) into rich biomass. Precisely because of this definition, in recent years various sectors have been targeting their ability to reduce CO2 emissions and the capacity of simultaneously synthesize biomass which can be later used to produce bio-fuels. Besides being considered fast-growth microorganisms, microalgae have a diverse biochemical composition with similar characteristics to traditional biomass. In this context, the present work aimed to evaluate the biofixation of CO2 by the microalgae Monoraphidium sp., cultivated in a closed-window type photobioreactor, as well as characterization of microalgal biomass produced in relation to the total lipid content (TL), lipids converted into biodiesel (LCB), carbohydrates and proteins. The results achieved showed that the best result was obtained after 24 h of cultivation, where for each gram of biomass produced approximately 1.2 g of CO2 were consumed. In the growth phase the average biomass productivity in the Janela photobioreactor was 58 mg&middot;L-1&middot;day-1 concluding that microalgae culture systems could be coupled to the chimneys of large industries emitters CO2 using this gas, resulting from combustion processes, in the process of photosynthesis. The biomass Monoraphidium sp. produced had a content of lipids converted into biodiesel of approximately 8.36% ± 2.69%, carbohydrates 32% ± 3.37% and proteins 34.26% ± 0.41%.