Microalgae Production Systems Research Articles

Optimization of Recovery of Nutrients from Pig Manure Slurry through Combined Microbial Fuel Cell and Microalgae Treatment

Microbial fuel cells (MFCs) and microalgae–bacteria consortia represent two renewable and promising technologies of growing interest that enable wastewater treatment while obtaining high-value-added products. This study integrates MFCs and microalgae production systems to treat animal slurry, aiming to remove and recover organic and inorganic components while generating energy and producing biomass. The MFCs effectively eliminated Chemical Oxygen Demand (COD), organic nitrogen, and a portion of the suspended solids, achieving a maximum voltage of 195 mV and a power density of 87.03 mW·m−2. After pre-treatment with MFCs, the slurry was diluted to concentrations of 10%, 50%, and 100% and treated with microalgae–bacteria consortia. The results showed a biomass production of 0.51 g·L−1 and a productivity of 0.04 g·L−1·day−1 in the culture fed with 10% slurry, with significant removal efficiencies: 40.71% for COD, 97.76% for N-NH4+, 39.66% for N-NO2−, 47.37% for N-NO3−, and 94.37% for P-PO4−3. The combination of both technologies allowed for obtaining a properly purified slurry and the recovery of nutrients in the form of bioelectricity and high-value biomass. Increasing the concentration of animal slurry to be treated is essential to optimize and scale both technologies.

Recent Advancements in Photo-Bioreactors for Microalgae Cultivation: A Brief Overview

Inspired by the vast potential of microalgae in the bioeconomy and the numerous applications and benefits associated with their cultivation, a multitude of pilot- and industrial-scale microalgae production systems have been developed in recent years. Both open and closed cultivation systems have been successfully utilized, with closed photo-bioreactors (PBRs) emerging as the most versatile option for various applications and products, enabling the implementation of advanced optimization strategies. Therefore, this short review provides a comprehensive overview of the different PBR configurations and their recent applications, primarily in large-scale but also in pilot- and laboratory-scale microalgae cultivation. A detailed discussion of the advantages, limitations, specific applications and recent advancements of each type of PBR is presented to aid researchers, engineers and industry stakeholders in selecting the most suitable PBR design for their specific goals and constraints. Moreover, this review highlights the major challenges impeding the full commercialization of microalgal products and forecasts future trends in the microalgae-based industry. The diverse potential applications of microalgae in various sectors, including biofuels, nutraceuticals, pharmaceuticals, agriculture and environmental remediation, underscore the versatility and significance of the relevant cultivation technologies. By offering valuable insights into the future commercial scale and trends of microalgal biotechnology, this work sheds light on the challenges and opportunities facing this burgeoning industry.

Unraveling the Potential of Electrochemical pH-Swing Processes for Carbon Dioxide Capture and Utilization.

Global warming, driven by the accumulation of anthropogenic greenhouse gases, particularly CO2, in the atmosphere, has garnered significant attention due to its detrimental environmental impacts. To combat this critical issue, the deployment of CO2 capture and utilization (CCU) strategies has been considered as one of the technology-based solutions, leading to extensive scientific and engineering research. Electrochemical pH-swing (EPS) processes offer a promising approach to diverse CCU pathways, such as the delivery of pure CO2 gas, the delivery of bicarbonate (e.g., for microalgae cultivation), and the formation of carbonate minerals. In this study, we discuss several CCU pathways using EPS and provide an in-depth analysis of its mechanisms and potential applications, outlining its limitations from both thermodynamic and kinetic standpoints. The EPS process has demonstrated remarkable capabilities, achieving a CO2 capture efficiency of over 90% and unlocking valuable opportunities for CCU applications. We also develop an initial techno-economic assessment and provide the perspectives and challenges for future development and deployment of EPS. This study sheds light on the integration of EPS with CCU, closing the carbon cycle by effectively utilizing the products generated through the process, such as carbonate minerals and bicarbonate solution. For instance, the bicarbonate product can serve as a viable feedstock for bicarbonate-based microalgae production systems, with the added benefit of reducing costs by 40-80% compared to traditional gaseous CO2 delivery approaches. By integration of electrochemical technologies with CCU methods, this study underscores the immense potential for mitigating CO2 emissions and advancing sustainable practices to combat global warming. This study not only addresses the urgent need for effective solutions but also paves the way for a greener and more sustainable future.

The impact of light/dark regimes on structure and physiology of Chlorella vulgaris biofilms.

Biofilm-based microalgae production technologies offer enormous potential for improving sustainability and productivity. However, the light pattern induced by these technologies is a key concern for optimization. In this work, the effects of light/dark cycles on architecture, growth, and physiology of Chlorella vulgaris biofilms were assessed in a millifluidic flow-cell with different time cycles (15 s to 3 min) keeping the average light constant at 100 μmol·m-2·s-1. Results showed that photoinhibition can be mitigated by applying a light fraction of 1/3 and a cycle time of 15 s. By contrast, when the cycle time is extended to 90 s and 3 min, photoinhibition is high and photoefficiency dramatically decreases. To cope with light stress, cells acclimate and organize themselves differently in space. A high peak light (500 μmol·m-2·s-1) triggers a stress, reducing cell division and inducing clusters in the biofilm. This work provides guidelines for optimizing rotating microalgae production systems in biofilms and assesses the minimum rotating frequency required to maintain the net growth rate close to that of continuous light of the same average intensity, mitigating photo-inhibition. The overall gain in productivity is then provided by the total surface of the biofilm turning in the illuminated surface area.

Influence of pH and dissolved oxygen control strategies on the performance of pilot-scale microalgae raceways using fertilizer or wastewater as the nutrient source

Dissolved oxygen concentration and pH are controllable and cost-effective variables that determine the success of microalgae-related processes. The present study compares different control strategies for pH and dissolved oxygen in pilot-scale microalgae production systems. Two 80 m2 raceway reactors were used, one operated with freshwater plus fertilizer and the other with wastewater as the nutrient source. Both were in semi-continuous mode at a fixed dilution rate of 0.2 day−1. A comparison between the classical On-Off and more advanced pH control strategies, such as PI and Event-based control, was performed, focusing on biomass productivity and the influence of all the process parameters on microalgae growth; "No control" of pH was also assayed. The results show that Event-based control was the best algorithm when using freshwater plus fertilizer. In contrast, no significant differences were observed using the different control strategies when wastewater was the nutrient source. These experiments were performed through selective control strategy, prioritizing pH over dissolved oxygen; however, it was demonstrated that they did not allow to achieve satisfactory dissolved oxygen removal results, especially for the fertilizer system. After modifying the gas diffuser configuration and improving the mass transfer, independent on-off strategies have been developed, permitting effective control of both variables and increasing productivity by up to 20% in both systems. Concluding, a detailed analysis of the energy demand for each strategy implemented in terms of gas consumption and gas flow to biomass ratio is provided.

Life cycle assessment of microalgae-derived biodiesel

PurposeMicroalgae-derived biofuels are considered a low-carbon alternative to fossil fuels. Nevertheless, as with all biofuels, there is still uncertainty around their sustainability. Most life cycle assessments (LCA) of microalgae biofuels so far used lab-based, scaled-up lab experimental data or data from the scientific literature. This article, provides evidence and analysis, undertaking an LCA using real-world data from an industrial facility that uses a combination of photobioreactor and fermenter systems.MethodsThe current well-to-wheel LCA study aimed to compare the environmental impacts of microalgae biodiesel production—under different energy regimes—and with petroleum-derived diesel. The functional unit was considered as “combustion of 1 MJ (Lower Heating Value) of algal biodiesel in an internal combustion engine (as B100)”. This LCA study considers the environmental and energy impacts from the construction of the facility, as well as those impacts from the operation of the facility. The foreground LCI data was collected from a real-world one-hectare microalgae production pilot facility. ReCiPe, IPCC AR5 (GWP100 and GWP20) and Global Temperature Potential (GTP) were implemented to assess the life cycle environmental impacts.Results and discussionThe assessment shows that when infrastructure is included, microalgae-derived biofuels are not yet favourable over petroleum-derived fuels on GWP100, and this becomes worse over shorter timescales. In terms of climate change (GWP100), whilst 1 MJ (LHV) of fossil-derived diesel would emit 8.84 × 10−2 kg CO2eq, 1 MJ of microalgae-derived biodiesel from a solar photovoltaic powered facility would emit 1.48 × 10−1 kg CO2eq. To be equal to petroleum-derived diesel in terms of GWP100, or perform better, productivity of the microalgae production system needs to be improved as the most effective solution. The results also showed that electricity and infrastructure were major sources of environmental impacts, as well as the yeast used within the fermenter. Moreover, it takes 0.99 MJ of direct energy per 1 MJ of microalgae biofuel produced, similar to the fossil fuel industry for 1 MJ of diesel.ConclusionsUsing infrastructure and operational models, the study shows that the facility does not compare well with petroleum-derived diesel unless productivity can be increased. Productivity improvements, be it through improvements to microalgae strains or improved photobioreactor designs, should be a priority to ensure microalgae become a sustainable fuel feedstock. Electricity use should be reduced as well, again, through improved cultivation system designs. In terms of the current system, the high impacts of yeast should be addressed, either through co-locating yeast production or through ensuring specific sources with lower impacts. Extracting lipids will effectively waste some high-value products, whilst the waste can be expected to be a mixture of unextracted lipids, polysaccharides or fibre, some proteins and minerals. It is also shown that harmonisations of the assessments are needed for future studies and real-world operation facilities to conclusively decide if microalgae should be used as fuel or if they would be better used for other products, such as feed or high-value products.

Conceptual Design of an Autotrophic Multi-Strain Microalgae-Based Biorefinery: Preliminary Techno-Economic and Life Cycle Assessments

Microalgae represent a promising solution in addressing the impacts associated with the current agricultural and manufacturing practices which are causing irreparable environmental damage. Microalgae have considerable biosynthetic potential, being a rich source of lipids, proteins, and high-value compounds. Under the scope of the H2020-BBI MULTI-STR3AM project, an innovative large-scale production system of valuable commodities for the food, feed, and fragrance sectors is being developed on the basis of microalgae, reducing costs, increasing the scale of production, and boosting value chain sustainability. In this work, we aimed to create a process model that can mimic an industrial plant to estimate mass and energy balances, optimize scheduling, and calculate production costs for a large-scale plant. Three autotrophic microalgae strains (Nannochloropsis sp., Dunaliella sp. and Spirulina sp.) were considered for this assessment, as well as the use of locally sourced CO2 (flue gas). The developed process model is a useful tool for obtaining the data required for techno-economic analysis (TEA) and life cycle assessment (LCA) of industrial biorefinery-based processes. Nannochloropsis sp. was the most economic option, whereas Dunaliella sp. was the most expensive strain to produce due to its lower productivity. Preliminary environmental assessments of the climate change impact category revealed that water recirculation and the use of flue gas could lead to values of 5.6, 10.6, and 9.2 kgCO2eq·kgAFDW−1 for Nannochloropsis sp., Dunaliella sp., and Spirulina sp., respectively, with electricity and NaCl as the main contributors. The obtained data allow for the quantification of the production costs and environmental impacts of the microalgal biomass fractions produced, which will be fundamental for future comparison studies and in determining if they are higher or lower than those of the replaced products. The process model developed in this work provides a useful tool for the evaluation and optimization of large-scale microalgae production systems.

Comparative life cycle assessment of conventional and novel microalgae production systems and environmental impact mitigation in urban-industrial symbiosis

The versatility of microalgae biomass as candidates for various products and bioremediation needs motivates interests towards design and implementation of novel microalgae bioreactors. Conventional open-reactors are reliant on large quantities of sunlight and space while yields are constrained by outdoor environment conditions. Conversely, closed-reactor systems like bubble columns reduces these constrains on microalgae growth while occupying far less space at the expense of high energy demands, notably from lighting systems. A novel patented closed reactor design has recently been proposed that improves the bubble column concept with an efficient and effective lighting system. The present study uses Life Cycle Assessment approach to compare the environmental performance of conventional reactors and the proposed internally luminated novel closed reactor design, expressing impacts per kg biostimulant for the Scenedesmus almeriensis harvest from such units. All performance data was collected from a pilot facility in Almeria, Spain. Urban-industrial symbiosis scenarios are also portrayed in the study using wastewater and incinerator flue gas. Results show that under synthetic nutrient and carbon inputs in Spanish pilot operations, the cumulative energy demand for the novel photobioreactors is similar to conventional vertically-stacked horizon bioreactors but are substantially more demanding than conventional open reactors. However, when leveraging renewable energy sources and the photosynthesis process to consume wastestreams in urban-industrial symbiosis scenarios, the novel photobioreactor was able to achieve up to 80 % improvements in several impact categories e.g. eutrophication and climate change. Impact mitigation credits per kg dwt biomass across all energy scenarios in symbiosis amount to ≈1.8 kg CO2eq and ≈0.09 kg PO4 eq. This highlights that such closed and internally illuminated photobioreactors can be competitive with conventional reactors, and have potential to harness photosynthesis to reduce environmental burdens in an urban-industrial symbiosis setting. Possible economies of scale and the associated potential gains in efficiencies are further discussed.

Cellular Automata Machine Modeling to obtain optimal conditions and productivity of microalgae biomass

Microalgae is a promising source of superior biomass for sustainable food sources, high value products, and 3rd generation biofuel. The main factors affecting growth, carbon fixation and biomass production of microalgae are species type, CO2 supply, nutrients, light, temperature, pH and mixing. This paper discusses the precision farming approach in microalgae biomass production using the Cellular Automata Machine modeling, i.e., Probabilistic Cellular Automata. Cellular Automata is a decentralized computing model that provides a useful platform to model the complex dynamic systems such as growth of cells. The application of this method on a large-scale microalgae production system can simulate and model the characteristics of microalgae growth and biomass. In conclusion, the Biological Lattice Gas Cellular Automaton (BIO-LGCA) has been proposed as modeling tools to obtain the optimal conditions and maximum productivity in microalgae biomass production.

Challenges and opportunities to increase economic feasibility and sustainability of mixotrophic cultivation of green microalgae of the genus Chlorella

Green microalgae belonging to the genus Chlorella have long been used as health foods and additives for human consumption, as well as animal feed. These photosynthetic microorganisms have also found application in the bioremediation of wastewater and bio-mitigation of CO2. In the last decades, Chlorella microalgae have attracted considerable attention due to their great potential as feedstock for production of biofuels and high-value products. This review explores key aspects related to the cultivation of different Chlorella species under mixotrophic conditions. Common organic compounds and cheap substrates used for mixotrophic microalgal growth are presented. Bottlenecks and strategies to increase economic feasibility and sustainability of mixotrophic cultivation of Chlorella for future commercial production are also discussed. In this sense, the use of wastewater as a nutrient source for microalgae cultivation seems to be a promising alternative to improve the sustainability and economic feasibility of microalgae production systems. However, since wastewater presents a complex composition, methods to minimize the risk of contamination should be developed. Additionally, the screening of novel mixotrophic species of Chlorella capable of both assimilating a wide range of organic compounds from wastewater and accumulating high content of molecules of interest (e.g., lipids) would be highly recommended.

Comparative Life Cycle Assessment of Conventional and Novel Microalgae Production Systems and Environmental Impact Mitigation in Urban-Industrial Symbiosis

Comparative Life Cycle Assessment of Conventional and Novel Microalgae Production Systems and Environmental Impact Mitigation in Urban-Industrial Symbiosis

Implementation of a microalgae and live prey production system (daphnia) to improve African catfish Clarias gariepinus fry growth

Fish farming in Senegal encounters many difficulties, especially during the first life stages, which are more demanding for food and more sensitive to variations in the physicochemical parameters. Most of the species of aquaculture interest have offspring whose size at birth is very small, thus requiring a particular rich food adapted to the size of the mouth (e.g. live preys which are very rich in nutritive reserves). The objective of this study was to set up a production system of live prey, daphnia for the feeding of fish fry. It consisted of culturing microalgae that were used to fed daphnia reared to fed the fry of the African catfish, Clarias gariepinus. The temperature and dissolved oxygen content in the culture and rearing media were monitored throughout the experiment. The results on species identification showed that the cultured microalgae and reared daphnia species are Microcystis sp and Daphnia magna, respectively. Analyses of algal biomass and daphnia abundance show an increase in these parameters with time. Temperature variations do not affect algal biomass, daphnia abundance and fry growth. On the other hand, a decrease in dissolved oxygen content below a certain threshold (6mg/l) leads to a decrease in algal biomass and daphnia abundance. Among the three feeding rates 1.5g, 3g, 4.5g (the equivalent of 0.5L, 1L, and 1.5L of microalgae, respectively) that were used to feed daphnia, the feeding rate of 3g of biomass corresponding to 1L is more adequate as it gave the best production. The comparison of the effects of the types of feed shows that live daphnia give better growths of C. gariepinus fry than the artificial feed, which may be due to their adequate size and nutrient richness. Thus, this study contributes to the establishment of live prey production systems to boost local aquaculture development and demonstrates the importance of daphnia for the feeding of early fish life stages.

A viewpoint on the use of microalgae as an alternative feedstuff in the context of pig and poultry feeding-a special emphasis on tropical regions.

With the current increase in meat and animal products consumption, there is a need to make production systems more sustainable. The use of microalgae in monogastric feeds, replacing widely used conventional feedstuffs such corn and soybean, can be a solution to overcome this problem. Several studies have shown promising results in the use of microalgae in feeding of both pigs and poultry. However, there are several important constraints associated to the production of microalgae. Such constraints are particularly limiting in the context of tropical regions. Research and scientific development on microalgae production systems are thus essential so that may be widely used in monogastric feeding. Herein, we conduct an overview of the major findings in the use of microalgae in the context of monogastric feeding and analyse the major constraints associated to its production and use, particularly in the specific context of tropical regions.

Evaluation of preliminary plant design for Chlorella vulgaris microalgae production focused on cosmetics purposes

Although there are currently different large-scale microalgae production systems, its performance is subject to high production cost problems. That is why the main goal of this research is analyzing the feasibility of obtaining the Chlorella vulgaris microalgae from a proposed preliminary industrial plant design, considering its use in the cosmeceutical industry as skin care. Parameters used in the SuperPro Designer simulations were programmed based on experimental data reported from bibliography. For biomass and cell extract production, a Bold Basal enriched medium at 1% with soy flour was used. It is found that mass flow significantly affects production costs since a product value of 8.58 USD/ml was estimated operating the plant with 20 kg/h of mass flow. Interestingly 84 % unit reduction cost was improved by operating the proposed plant at 140 kg/h mass flow since 1.34 USD/ml of cosmetic product was determined. These findings show the potentiality of Chlorella vulgaris to be positioned in the world market. The latter, by considering its dependence on a successfully large scale plant. The above, in order to identify potential improvements focused on maximizing productivity and profits at the lowest operating cost.

Combining medium recirculation with alternating the microalga production strain: a laboratory and pilot scale cultivation test

Reuse of growth medium after biomass harvesting is a cost-saving approach to improve the economic feasibility of algae mass cultivation. Algal exudates, cell debris and varying amounts of residual nutrients, impose challenges to the recycling of spent medium. In this study, the potential of combining reused medium from different algae species for growing monocultures of other algal strains was evaluated by making use of three successive cultivation setups with increasing volume; 400 mL in turbidostat mode, 2.6 L and 220 L in semi-continuous mode. Cultivation on replenished medium derived from Nannochloropsis sp. and Tisochrysis lutea, had no adverse effect on the productivity of either of the strains, regardless of whether they were grown in their own recycled medium or that of the other alga. Microfiltration of the reused medium proved to be sufficient to avoid cross-contamination. Moreover, a substantial average reduction in water footprint (77%) and nutrient cost (68% or 9 €·kg−1 dry biomass) was achieved. Extension and validation of the medium recycling approach to other economically interesting algae species can contribute to improving the economic feasibility of large scale microalgae production systems.

Cultivation of aquaculture feed Isochrysis zhangjiangensis in low-cost wave driven floating photobioreactor without aeration device

This study aimed to use floating photobioreactor (PBR) to produce microalgae biomass for aquaculture applications, and this was tested with cultivation of Isochrysis zhangjiangensis. The highest cell density of 16.1 ± 0.61 × 106 cell L–1 was obtained in an outdoor culture with a depth of 5.0 cm in 1.0 m2 floating PBR, but deeper culture resulted in higher biomass productivity. Large-scale cultivation at size of 10 m2 (1000 L) produced the highest cell density of 17.8 × 106 cell L–1 and highest biomass productivity of 0.115 g L–1 d–1, which was at the same level as that for flat-panel PBR (100 L). This developed technique provides an innovative approach to produce microalgae on site for use as fresh aquaculture feed, as well as fresh cells for use as seed inoculums for large-area aquaculture water bodies. This approach provides not only a low-cost microalgae production system but also better integration between microalgae production and aquaculture.

Role of Microalgal Biotechnology in Environmental Sustainability-A Mini Review

Sustainability is a main rule in environmental resource management, and it included operational productivity, minimization of natural effect and socio-economic contemplations; which are all related. Many research projects have been conducted on finding alternative of energy from renewable sources and utilization of waste materials. Based on the previous studies one of the most environmentally friendly and sustainable methods for biofuel sources is using microalgae for the production of lipids and wastewater as its nutrient source. Microalgae are maintainable sources of biomass for fuel, food, and feed likewise as contaminant elimination from wastewater. Light, CO2, and inorganic nutrients like nitrogen and phosphorous are vital for microalgae growth. The aim of this study is thus to introduce an optimum conditions of microalgae cultivation for nutrient removal from wastewater which may impact the bioenergy production like biodiesel production. Utilizing wastewater is a common method to reduce environmental impacts, recycle water and nutrients, and decrease the volume of wastewater being transported and treated. Therefore, developing microalgae production systems would help reduce greenhouse gas emissions by capturing CO2 and producing an alternative for fossil fuels would be valuable and sustainable.

Sustainability Analysis of Microalgae Production Systems: A Review on Resource with Unexploited High-Value Reserves.

Sustainability, at present, is a prominent component in the development of production systems that aim to provide the future energy and material resources. Microalgae are a promising feedstock; however, the sustainability of algae-based production systems is still under debate. Commercial market volumes of algae-derived products are still narrow. The extraction and conversion of primary metabolites to biofuels requires cultivation at large scales; cost-effective methods are therefore highly desirable. This work presents a complete and up to date review on sustainability analysis of various microalgae production scenarios, including techno-economic, environmental, and social impacts, both in large-scale plants for bioenergy production and in medium-scale cultivars intended for the production of high added-value chemicals. The results show that further efforts in algal-based research should be directed to improving the productivity, the development of multi product scenarios, a better valorization of coproducts, the integration with current industrial facilities to provide sustainable nutrient resources from waste streams, and the integration of renewable technologies such as wind energy in algae cultivars.

Critical review of strategies for CO2 delivery to large-scale microalgae cultures

Abstract Microalgae have great, yet relatively untapped potential as a highly productive crop for the production of animal and aquaculture feed, biofuels, and nutraceutical products. Compared to conventional terrestrial crops they have a very fast growth rate and can be produced on non-arable land. During microalgae cultivation, carbon dioxide (CO2) is supplied as the carbon source for photosynthesising microalgae. There are a number of potential CO2 supplies including air, flue gas and purified CO2. In addition, several strategies have been applied to the delivery of CO2 to microalgae production systems, including directly bubbling CO2-rich gas, microbubbles, porous membrane spargers and non-porous membrane contactors. This article provides a comparative analysis of the different CO2 supply and delivery strategies and how they relate to each other.

Environmental load assessment for an integrated design of microalgae system of palm oil mill in Indonesia

The environmental load of continuous bioenergy production from palm oil (Elaeis guineensis) included with a proposed 10 ha of microalgae production system were assessed to be implemented in Indonesia. Material and energy balances, greenhouse gas (GHG) emission, nutrient requirement and also water scarcity during bioenergy production cycle were evaluated. The integrated system was developed for 60 tons h−1 of fresh fruit bunch (FFB) processing capacity of a conventional mill. Aggregate of energy-profit ratio from the proposed system was 5.20, which indicates a positive balance. The total water footprint for each palm oil and microalgae cultivation was 3.18 and 2.85 m3 kg−1 of biodiesel production, respectively. Microalgae mix-culture has the potential to treat organic compounds from palm oil mill effluent (POME) and combined with flue gases from biomass and biogas power plant as the alternative nutrient sources contributed to net-reduction of GHG emission for 158.8 tons ha−1 of microalgae culture, annually. The integrated system produced 26,471 tons of biodiesel that included 223 tons from microalgae and contribute to 39.90% of total GHG emission reduction from diesel fuel substitute. Additional co-product of 520.33 tons year−1 of animal feed from defatted biomass also possible to be produced and have potential for environmental benefits.