Comparison of red microalgae (Porphyridium cruentum) culture conditions for bioethanol production

Role of microalgae in achieving sustainable development goals and circular economy

In 2015, the United Nations General Assembly (UNGA) set out 17 Sustainable Development Goals (SDGs) to be achieved by 2030. These goals highlight key objectives that must be addressed. Each target focuses on a unique perspective crucial to meeting these goals. Social, political, and economic issues are addressed to comprehensively review the main issues combating climate change and creating sustainable and environmentally friendly industries, jobs, and communities. Several mechanisms that involve judicious use of biological entities are among instruments that are being explored to achieve the targets of SDGs. Microalgae have an increasing interest in various sectors, including; renewable energy, food, environmental management, water purification, and the production of chemicals such as biofertilizers, cosmetics, and healthcare products. The significance of microalgae also arises from their tendency to consume CO2, which is the main greenhouse gas and the major contributor to the climate change. This work discusses the roles of microalgae in achieving the various SDGs. Moreover, this work elaborates on the contribution of microalgae to the circular economy. It was found that the microalgae contribute to all the 17th SDGs, where they directly contribute to 9th of the SDGs and indirectly contribute to the rest. The major contribution of the Microalgae is clear in SDG-6 "Clean water and sanitation", SDG-7 "Affordable and clean energy", and SDG-13 "Climate action". Furthermore, it was found that Microalgae have a significant contribution to the circular economy.

Algae in wastewater treatment, mechanism, and application of biomass for production of value-added product

The pollutants can enter water bodies at various point and non-point sources, and wastewater discharge remains a major pathway. Wastewater treatment effectively reduces contaminants, it is expensive and requires an eco-friendly and sustainable alternative approach to reduce treatment costs. Algae have recently emerged as a potentially cost-effective method to remediate toxic pollutants through the mechanism of biosorption, bioaccumulation, and intracellular degradation. Hence, before discharging the wastewater into the natural environment better solutions for environmental resource recovery and sustainable developments can be applied. More importantly, algae are a potential feedstock material for various industrial applications such as biofuel production. Currently, researchers are developing algae as a source for pharmaceuticals, biofuels, food additives, and bio-fertilizers. This review mainly focused on the potential of algae and their specific mechanisms involved in wastewater treatment and energy recovery systems leading to important industrial precursors. The review is highly beneficial for scientists, wastewater treatment plant operators, freshwater managers, and industrial communities to support the sustainable development of natural resources.

Microalgal Biorefinery Concepts’ Developments for Biofuel and Bioproducts: Current Perspective and Bottlenecks

Microalgae have received much interest as a biofuel feedstock. However, the economic feasibility of biofuel production from microalgae does not satisfy capital investors. Apart from the biofuels, it is necessary to produce high-value co-products from microalgae fraction to satisfy the economic aspects of microalgae biorefinery. In addition, microalgae-based wastewater treatment is considered as an alternative for the conventional wastewater treatment in terms of energy consumption, which is suitable for microalgae biorefinery approaches. The energy consumption of a microalgae wastewater treatment system (0.2 kW/h/m³) was reduced 10 times when compared to the conventional wastewater treatment system (to 2 kW/h/m³). Microalgae are rich in various biomolecules such as carbohydrates, proteins, lipids, pigments, vitamins, and antioxidants; all these valuable products can be utilized by nutritional, pharmaceutical, and cosmetic industries. There are several bottlenecks associated with microalgae biorefinery. Hence, it is essential to promote the sustainability of microalgal biorefinery with innovative ideas to produce biofuel with high-value products. This review attempted to bring out the trends and promising solutions to realize microalgal production of multiple products at an industrial scale. New perspectives and current challenges are discussed for the development of algal biorefinery concepts.

Algae biotechnology for industrial wastewater treatment, bioenergy production, and high-value bioproducts

A growing world population is causing hazardous compounds to form at an increasingly rapid rate, calling for ecological action. Wastewater management and treatment is an expensive process that requires appropriate integration technology to make it more feasible and cost-effective. Algae are of great interest as potential feedstocks for various applications, including environmental sustainability, biofuel production, and the manufacture of high-value bioproducts. Bioremediation with microalgae is a potential approach to reduce wastewater pollution. The need for effective nutrient recovery, greenhouse gas reduction, wastewater treatment, and biomass reuse has led to a wide interest in the use of microalgae for wastewater treatment. Furthermore, algae biomass can be used to produce bioenergy and high-value bioproducts. The use of microalgae as medicine (production of bioactive and medicinal compounds), biofuels, biofertilizers, and food additives has been explored by researchers around the world. Technological and economic barriers currently prevent the commercial use of algae, and optimal downstream processes are needed to reduce production costs. Therefore, the simultaneous use of microalgae for wastewater treatment and biofuel production could be an economical approach to address these issues. This article provides an overview of algae and their application in bioremediation, bioenergy production, and bioactive compound production. It also highlights the current problems and opportunities in the algae-based sector, which has recently become quite promising.

Microalgal Systems for Wastewater Treatment: Technological Trends and Challenges towards Waste Recovery

Wastewater (WW) treatment using microalgae has become a growing trend due the economic and environmental benefits of the process. As microalgae need CO2, nitrogen, and phosphorus to grow, they remove these potential pollutants from wastewaters, making them able to replace energetically expensive treatment steps in conventional WW treatment. Unlike traditional sludge, biomass can be used to produce biofuels, biofertilizers, high value chemicals, and even next-generation growth media for “organically” grown microalgal biomass targeting zero-waste policies and contributing to a more sustainable circular bioeconomy. The main challenge in this technology is the techno-economic feasibility of the system. Alternatives such as the isolation of novel strains, the use of native consortia, and the design of new bioreactors have been studied to overcome this and aid the scale-up of microalgal systems. This review focuses on the treatment of urban, industrial, and agricultural wastewaters by microalgae and their ability to not only remove, but also promote the reuse, of those pollutants. Opportunities and future prospects are discussed, including the upgrading of the produced biomass into valuable compounds, mainly biofuels.

Multi-product biorefinery from Arthrospira platensis biomass as feedstock for bioethanol and lactic acid production

With the aim to reach the maximum recovery of bulk and specialty bioproducts while minimizing waste generation, a multi-product biorefinery for ethanol and lactic acid production from the biomass of cyanobacterium Arthrospira platensis was investigated. Therefore, the residual biomass resulting from different pretreatments consisting of supercritical fluid extraction (SF) and microwave assisted extraction with non-polar (MN) and polar solvents (MP), previously applied on A. platensis to extract bioactive metabolites, was further valorized. In particular, it was used as a substrate for fermentation with Saccharomyces cerevisiae LPB-287 and Lactobacillus acidophilus ATCC 43121 to produce bioethanol (BE) and lactic acid (LA), respectively. The maximum concentrations achieved were 3.02 ± 0.07 g/L of BE by the MN process at 120 rpm 30 °C, and 9.67 ± 0.05 g/L of LA by the SF process at 120 rpm 37 °C. An economic analysis of BE and LA production was carried out to elucidate the impact of fermentation scale, fermenter costs, production titer, fermentation time and cyanobacterial biomass production cost. The results indicated that the critical variables are fermenter scale, equipment cost, and product titer; time process was analyzed but was not critical. As scale increased, costs tended to stabilize, but also more product was generated, which causes production costs per unit of product to sharply decrease. The median value of production cost was US$ 1.27 and US$ 0.39, for BE and LA, respectively, supporting the concept of cyanobacterium biomass being used for fermentation and subsequent extraction to obtain ethanol and lactic acid as end products from A. platensis.

Influence of Nutrient Manipulation on Growth and Biochemical Constituent in Anabaena variabilis and Nostoc muscorum to Enhance Biodiesel Production

The present study aims to improve biomass and biochemical constituents, especially lipid production of Anabaena variabilis and Nostoc muscorum by formulating an optimal growth condition using various concentrations of nutrients (NO3−, PO43− and CO32−) for biodiesel production. The supplementation of the three nutrients by +50% showed the maximum dry weight and biomass productivity, while the macromolecule contents were varied. The depletion of N-NO3− by 50% N-NO3− showed the maximum lipid yield (146.67 mg L−1) in A. variabilis and the maximum carbohydrate contents (285.33 mg L−1) in N. muscorum with an increase of 35% and 30% over control of the synthetic medium, respectively. However, variation in P-PO43− and C-CO32− showed insignificant improving results for all biochemical compositions in both cyanobacteria. A. variabilis was the superior species for lipid and protein accumulation; however, N. muscorum showed the maximum carbohydrate content. Accordingly, A. variabilis was selected for biodiesel production. In A. variabilis, −50% N-NO3− resulted in 35% higher lipid productivity compared to the control. Furthermore, the fatty acid profile and biodiesel quality-related parameters have improved under this condition. This study has revealed the strategies to improve A. variabilis lipid productivity for biodiesel production for small-scale in vitro application in terms of fuel quality under low nitrate levels.

Cold stress treatment enhances production of metabolites and biodiesel feedstock in Porphyridium cruentum via adjustment of cell membrane fluidity

Porphyridium cruentum, a cell-wall-free marine Rhodophyta microalga was cultured under a 5-day cold stress at 0 °C and 15 °C, after reaching the late logarithmic growth phase. Compared with the control at 25 °C, the cold stress treatment significantly (p < 0.05) increased the microalgal biomass (1.21-fold); the amounts of total polyunsaturated fatty acids (1.22-fold); individual fatty acids including linoleic acid (1.50-fold) and eicosatrienoic acid (1.85-fold), and a major carotenoid zeaxanthin (1.53-fold). Furthermore, production of biodiesel feedstock including total C₁₆ + C₁₈ fatty acids was significantly enhanced (p < 0.05) by 1.18-fold after the cold stress treatment. Principal component analysis further indicated that the biosynthetic pathways of fatty acids and carotenoids in this microalga were correlated with the cold stress treatment. These results suggested that P. cruentum had adjusted its cellular membrane fluidity via an 'arm-raising and screw-bolt fastening' mechanism mediated by the synergistic roles of cis-unsaturated fatty acids and carotenoids. The insight obtained from the responses to cold stress in P. cruentum could be a novel technological approach to enhance the production of microalgal metabolites and biodiesel feedstock.

Isolation of Industrial Important Bioactive Compounds from Microalgae

Microalgae are known as a rich source of bioactive compounds which exhibit different biological activities. Increased demand for sustainable biomass for production of important bioactive components with various potential especially therapeutic applications has resulted in noticeable interest in algae. Utilisation of microalgae in multiple scopes has been growing in various industries ranging from harnessing renewable energy to exploitation of high-value products. The focuses of this review are on production and the use of value-added components obtained from microalgae with current and potential application in the pharmaceutical, nutraceutical, cosmeceutical, energy and agri-food industries, as well as for bioremediation. Moreover, this work discusses the advantage, potential new beneficial strains, applications, limitations, research gaps and future prospect of microalgae in industry.

Microalgae Cultivation Technologies as an Opportunity for Bioenergetic System Development—Advantages and Limitations

Microalgal biomass is currently considered as a sustainable and renewable feedstock for biofuel production (biohydrogen, biomethane, biodiesel) characterized by lower emissions of hazardous air pollutants than fossil fuels. Photobioreactors for microalgae growth can be exploited using many industrial and domestic wastes. It allows locating the commercial microalgal systems in areas that cannot be employed for agricultural purposes, i.e., near heating or wastewater treatment plants and other industrial facilities producing carbon dioxide and organic and nutrient compounds. Despite their high potential, the large-scale algal biomass production technologies are not popular because the systems for biomass production, separation, drainage, and conversion into energy carriers are difficult to explicitly assess and balance, considering the ecological and economical concerns. Most of the studies presented in the literature have been carried out on a small, laboratory scale. This significantly limits the possibility of obtaining reliable data for a comprehensive assessment of the efficiency of such solutions. Therefore, there is a need to verify the results in pilot-scale and the full technical-scale studies. This study summarizes the strengths and weaknesses of microalgal biomass production technologies for bioenergetic applications.

Porphyridium cruentum Grown in Ultra-Filtered Swine Wastewater and Its Effects on Microalgae Growth Productivity and Fatty Acid Composition

Microalgae have been extensively tested for their ability to create bio-based fuels. Microalgae have also been explored as an alternative wastewater treatment solution due to their significant uptake of nitrogen and phosphorus, as well as their ability to grow in different water types. Recently, there has been significant interest in combining these two characteristics to create economic and environmentally friendly biofuel using wastewater. This study examined the growth and lipid production of the microalgae Porphyridium (P.) cruentum grown in swine wastewater (ultra-filtered and raw) as compared with control media (L−1, modified f/2) at two different salt concentrations (seawater and saltwater). The cultivation of P. cruentum in the treated swine wastewater media (seawater = 5.18 ± 2.3 mgL−1day−1, saltwater = 3.32 ± 1.93 mgL−1day−1) resulted in a statistically similar biomass productivity compared to the control medium (seawater = 2.61 ± 2.47 mgL−1day−1, saltwater = 6.53 ± 0.81 mgL−1day−1) at the corresponding salt concentration. Furthermore, no major differences between the fatty acid compositions of microalgae in the treated swine wastewater medium and the control medium were observed. For all conditions, saturated acids were present in the highest amounts (≥67%), followed by polyunsaturated (≤22%) and finally monounsaturated (≤12%). This is the first study to find that P. cruentum could be used to remediate wastewater and then be turned into fuel by using swine wastewater with a similar productivity to the microalgae grown in control media.

Effects of Different Environmental Factors on the Growth and Bioactive Substance Accumulation of Porphyridium purpureum

Genus Porphyridium is a primitive single-celled red algae widely distributed in seawater, freshwater, and moist soil. It can synthesize bioactive substances such as phycoerythrin, extracellular polysaccharides and polyunsaturated fatty acids during the growth process. In this paper, the culture and bioactive substance yield of Porphyridium purpureum were studied by setting salinity, nitrogen-to-phosphorus ratio, and pH at different gradient levels. The results showed that the optimal conditions for the growth of P. purpureum were salinity 34 ppt, nitrogen-to-phosphorus ratio 169:1, and pH 8; the optimal conditions for obtaining the polysaccharides were salinity 17 ppt, nitrogen-to-phosphorus ratio 14:1, and pH 8; the optimal conditions for obtaining phycoerythrin were salinity 17 ppt, nitrogen-to-phosphorus ratio 68:1, and pH 8; the optimal conditions for obtaining the lipids were salinity 34 ppt, nitrogen-to-phosphorus ratio 1:1, and pH 8. In actual production applications, culture conditions should be set according to different product accumulation purposes in order to achieve the optimal production efficiency.

Advances in the production of bioactive substances from marine unicellular microalgae Porphyridium spp

Porphyridium spp. are a group of unicellular marine microalgae belonging to the Rhodophyta, which evolved over one billion years and are a source of a variety of natural active components. They can naturally and efficiently accumulate phycobilin, sulfated polysaccharides, polyunsaturated fatty acids and other bioactive substances. At present, numerous attempts have been made to explore the species Porphyridium spp., whereas mainly focused on cultivation methods, metabolism regulation and the function and application of bioactive products. There is a lack of systematic summary of the existing research conclusions. In this paper, we summarized the representative results related to culture and metabolism, analyzed and discussed the existing bottleneck restrictions for their large scale application, and proposed the potential industrial development and research direction in the future. This paper is expected to provide reference and thread for research and application of Porphyridium spp..

New horizons in culture and valorization of red microalgae

Research on marine microalgae has been abundantly published and patented these last years leading to the production and/or the characterization of some biomolecules such as pigments, proteins, enzymes, biofuels, polyunsaturated fatty acids, enzymes and hydrocolloids. This literature focusing on metabolic pathways, structural characterization of biomolecules, taxonomy, optimization of culture conditions, biorefinery and downstream process is often optimistic considering the valorization of these biocompounds. However, the accumulation of knowledge associated with the development of processes and technologies for biomass production and its treatment has sometimes led to success in the commercial arena. In the history of the microalgae market, red marine microalgae are well positioned particularly for applications in the field of high value pigment and hydrocolloid productions. This review aims to establish the state of the art of the diversity of red marine microalgae, the advances in characterization of their metabolites and the developments of bioprocesses to produce this biomass.

Recent developments in synthetic biology and metabolic engineering in microalgae towards biofuel production

In the wake of the uprising global energy crisis, microalgae have emerged as an alternate feedstock for biofuel production. In addition, microalgae bear immense potential as bio-cell factories in terms of producing key chemicals, recombinant proteins, enzymes, lipid, hydrogen and alcohol. Abstraction of such high-value products (algal biorefinery approach) facilitates to make microalgae-based renewable energy an economically viable option. Synthetic biology is an emerging field that harmoniously blends science and engineering to help design and construct novel biological systems, with an aim to achieve rationally formulated objectives. However, resources and tools used for such nuclear manipulation, construction of synthetic gene network and genome-scale reconstruction of microalgae are limited. Herein, we present recent developments in the upcoming field of microalgae employed as a model system for synthetic biology applications and highlight the importance of genome-scale reconstruction models and kinetic models, to maximize the metabolic output by understanding the intricacies of algal growth. This review also examines the role played by microalgae as biorefineries, microalgal culture conditions and various operating parameters that need to be optimized to yield biofuel that can be economically competitive with fossil fuels.

Enzymatic Processes in Marine Biotechnology

In previous review articles the attention of the biocatalytically oriented scientific community towards the marine environment as a source of biocatalysts focused on the habitat-related properties of marine enzymes. Updates have already appeared in the literature, including marine examples of oxidoreductases, hydrolases, transferases, isomerases, ligases, and lyases ready for food and pharmaceutical applications. Here a new approach for searching the literature and presenting a more refined analysis is adopted with respect to previous surveys, centering the attention on the enzymatic process rather than on a single novel activity. Fields of applications are easily individuated: (i) the biorefinery value-chain, where the provision of biomass is one of the most important aspects, with aquaculture as the prominent sector; (ii) the food industry, where the interest in the marine domain is similarly developed to deal with the enzymatic procedures adopted in food manipulation; (iii) the selective and easy extraction/modification of structurally complex marine molecules, where enzymatic treatments are a recognized tool to improve efficiency and selectivity; and (iv) marine biomarkers and derived applications (bioremediation) in pollution monitoring are also included in that these studies could be of high significance for the appreciation of marine bioprocesses.