Integrated valorization system for simultaneous high strength organic wastewater treatment and astaxanthin production from Haematococcus pluvialis

Cultivation of microalgae in food processing effluent for pollution attenuation and astaxanthin production: a review of technological innovation and downstream application

Valorization of food processing effluent (FPE) by microalgae cultivation for astaxanthin production is regarded as a potential strategy to solve the environmental pollution of food processing industry and promote the development of eco-friendly agriculture. In this review paper, microalgal species which have the potential to be employed for astaxanthin in FPE were identified. Additionally, in terms of CO2 emission, the performances of microalgae cultivation and traditional methods for FPE remediation were compared. Thirdly, an in-depth discussion of some innovative technologies, which may be employed to lower the total cost, improve the nutrient profile of FPE, and enhance the astaxanthin synthesis, was provided. Finally, specific effects of dietary supplementation of algal astaxanthin on the growth rate, immune response, and pigmentation of animals were discussed. Based on the discussion of this work, the cultivation of microalgae in FPE for astaxanthin production is a value-adding process which can bring environmental benefits and ecological benefits to the food processing industry and agriculture. Particularly, technological innovations in recent years are promoting the shift of this new idea from academic research to practical application. In the coming future, with the reduction of the total cost of algal astaxanthin, policy support from the governments, and further improvement of the innovative technologies, the concept of growing microalgae in FPE for astaxanthin will be more applicable in the industry.

Advancement of Carotenogenesis of Astaxanthin from Haematococcus pluvialis: Recent Insight and Way Forward

The demand for astaxanthin has been increasing for many health applications ranging from pharmaceuticals, food, cosmetics, and aquaculture due to its bioactive properties. Haematococcus pluvialis is widely recognized as the microalgae species with the highest natural accumulation of astaxanthin, which has made it a valuable source for industrial production. Astaxanthin produced by other sources such as chemical synthesis or fermentation are often produced in the cis configuration, which has been shown to have lower bioactivity. Additionally, some sources of astaxanthin, such as shrimp, may denature or degrade when exposed to high temperatures, which can result in a loss of bioactivity. Producing natural astaxanthin through the cultivation of H. pluvialis is presently a demanding and time-consuming task, which incurs high expenses and restricts the cost-effective industrial production of this valuable substance. The production of astaxanthin occurs through two distinct pathways, namely the cytosolic mevalonate pathway and the chloroplast methylerythritol phosphate (MEP) pathway. The latest advancements in enhancing product quality and extracting techniques at a reasonable cost are emphasized in this review. The comparative of specific extraction processes of H. pluvialis biological astaxanthin production that may be applied to large-scale industries were assessed. The article covers a contemporary approach to optimizing microalgae culture for increased astaxanthin content, as well as obtaining preliminary data on the sustainability of astaxanthin production and astaxanthin marketing information.

Astaxanthin from microalgae: A review on structure, biosynthesis, production strategies and application

Astaxanthin is a red-colored secondary metabolite with excellent antioxidant properties, typically finds application as foods, feed, cosmetics, nutraceuticals, and medications. Astaxanthin is usually produced synthetically using chemicals and costs less as compared to the natural astaxanthin obtained from fish, shrimps, and microorganisms. Over the decades, astaxanthin has been naturally synthesized from Haematococcus pluvialis in commercial scales and remains exceptional, attributed to its higher bioactive properties as compared to synthetic astaxanthin. However, the production cost of algal astaxanthin is still high due to several bottlenecks prevailing in the upstream and downstream processes. To that end, the present study intends to review the recent trends and advancements in astaxanthin production from microalgae. The structure of astaxanthin, sources, production strategies of microalgal astaxanthin, and factors influencing the synthesis of microalgal astaxanthin were discussed while detailing the pathway involved in astaxanthin biosynthesis. The study also discusses the relevant downstream process used in commercial scales and details the applications of astaxanthin in various health related issues.

Unraveling the Role of Microalgae in Mitigating Antibiotics and Antibiotic Resistance Genes in Photogranules Treating Antibiotic Wastewater

Harnessing the potential of specific antibiotic-degrading microalgal strains to optimize microalgal-bacterial granular sludge (MBGS) technology for sustainable antibiotic wastewater treatment and antibiotic resistance genes (ARGs) mitigation is currently limited. This article examined the performance of bacterial granular sludge (BGS) and MBGS (of Haematococcus pluvialis, an antibiotic-degrading microalga) systems in terms of stability, nutrient and antibiotic removal, and fate of ARGs and mobile genetic elements (MGEs) under multiclass antibiotic loads. The systems exhibited excellent performance under none and 50 μg/L mixed antibiotics and a decrease in performance at a higher concentration. The MBGS showed superior potential, higher nutrient removal, 53.9 mg/L/day higher chemical oxygen demand (COD) removal, and 5.2-8.2% improved antibiotic removal, notably for refractory antibiotics, and the system removal capacity was predicted. Metagenomic analysis revealed lower levels of ARGs and MGEs in effluent and biomass of MBGS compared to the BGS bioreactor. Particle association niche and projection pursuit regression models indicated that microalgae in MBGS may limit gene transfers among biomass and effluent, impeding ARG dissemination. Moreover, a discrepancy was found in the bacterial antibiotic-degrading biomarkers of BGS and MBGS systems due to the microalgal effect on the microcommunity. Altogether, these findings deepened our understanding of the microalgae's value in the MBGS system for antibiotic remediation and ARG propagation control.

Strategies and challenges to enhance commercial viability of algal biorefineries for biofuel production

The rise in energy consumption would quadruple in the coming century and the, existing energy resources might be insufficient to meet the demand of the growing population. An alternative and sustainable energy resource is therefore needed to address the fossil fuel deficiency. The utility of microalgae strains in the aspect of biorefinery has been in research for quite some time. Algal biorefinery is an alternate way of renewable energy however even after decades of research it still suffers from commercialization bottlenecks. The current manuscript reviews the scenarios where the innovation needs an ignition for its commercialization. This review discusses the prospects of up-scale cultivation, and harvesting algal biomass for biorefineries. It narrates algal biorefinery hurdles that can be solved using integrated technology approach, life cycle assessment and applications of nanotechnology. The review also sheds light upon the ties of algal biorefineries with its economic viability.

A Coculture of Photoautotrophs and Hydrolytic Heterotrophs Enables Efficient Upcycling of Starch from Wastewater toward Biomass-Derived Products: Synergistic Interactions Impacting Metabolism of the Consortium

Even with particular interest in sustainable development, due to the limited types of bioavailable carbon sources that could support heterotrophic/mixotrophic growth, microalgae-derived products still suffer from inconsistent yield and high costs. This study demonstrates a successful cocultivation of the photoautotroph Chlorella vulgaris with a hydrolytic-enzyme-abundant heterotroph, Saccharomycopsis fibuligera, enabling efficient starch upcycling from water/wastewater toward enhancing microalgae-dominant biomass and lipid production. The enzymatic activities of S. fibuligera contributed to the hydrolysis of starch into glucose, generating a 7-fold higher biomass through mixotrophic/heterotrophic growth of C. vulgaris. Further, scanning transmission electron microscopy (STEM) and quantitative analysis suggested a significantly induced accumulation of lipids in C. vulgaris. Results of meta-transcriptomics revealed the critical regulatory role of illumination in interaction shifting. Gene expression for glycolysis and lipid biosynthesis of C. vulgaris were highly activated during dark periods. Meanwhile, during illumination periods, genes coding for glucoamylase and the sulfur-related activities in S. fibuligera were significantly upregulated, leading to induced starch hydrolysis and potential increased competition for sulfur utilization, respectively. This study indicates that hydrolytic organisms could collaborate to make starch bioavailable for nonhydrolytic microalgae, thus broadening the substrate spectrum and making starch a novel biotechnological feedstock for microalgae-derived products, e.g., biofuels or single-cell protein.

Astaxanthin production from the microalga Haematococcus lacustris with a dual substrate mixotrophy strategy

This study investigates the development of dual-substrate mixotrophy strategy to cultivate the microalga Haematococcus lacustris for astaxanthin production. The influence of different concentrations of acetate and pyruvate on biomass productivity was first assessed individually, and then both substrates were used together to improve biomass growth in the green phase and astaxanthin accumulation in red the phase. The results showed that dual-substrates mixotrophy significantly increased the biomass productivity during green growth phase up to 2-fold compared to phototrophic controls. Furthermore, supplementation of dual-substrate to the red phase increased astaxanthin accumulation by 10% in the dual-substrate group compared to single-substrate acetate and no substrate. This dual-substrate mixotrophy approach shows promise for cultivating Haematococcus for commercial production of biological astaxanthin in indoor closed systems.

Enhancing the biochemical growth of Haematococcus pluvialis by mitigation of broad-spectrum light stress in wastewater cultures

In this study, the microalgae Haematococcus pluvialis were cultivated in wastewater inoculated into low-density polypropylene plastic air pillows (LDPE-PAPs) under a light stress. The cells were irradiated to different light stresses using white LED lights (WLs) as the control, and broad-spectrum lights (BLs) as a test for the period of 32 days. It was observed that the inoculum (70 × 10² mL^-1 cells) of H. pluvialis algal cells increased almost 30 and 40 times in WL and BL, respectively, at day 32 coherent to its biomass productivity. Higher lipid concentration of up to 36.85 μg mL^-1 was observed in BL irradiated cells compared to 13.215 μg L^-1 dry weight of biomass in WL. The chlorophyll 'a' content was 2.6 times greater in BL (3.46 μg mL^-1) compared to that in WL (1.32 μg mL^-1) with total carotenoids being about 1.5 times greater in BL compared to WL on day 32. The yield of red pigment 'Astaxanthin' was about 27% greater in BL than in WL. The presence, of different carotenoids including astaxanthin was also confirmed by HPLC, whereas fatty acid methyl esters (FAMEs) were confirmed by GC-MS. This study further confirmed that wastewater alongwith with light stress is suitable for the biochemical growth of H. pluvialis with good biomass yield as well as carotenoid accumulation. Additionally there was 46% reduction in chemical oxygen demand (COD) in a far more efficient manner when cultured in recycled LDPE-PAP. Such type of cultivation of H. pluvialis made the overall process economical and suitable for upscaling to produce value-added products such as lipids, pigments, biomass, and biofuel for commercial applications.

Astaxanthin as a King of Ketocarotenoids: Structure, Synthesis, Accumulation, Bioavailability and Antioxidant Properties

Astaxanthin (3,3-dihydroxy-β, β-carotene-4,4-dione) is a ketocarotenoid synthesized by Haematococcus pluvialis/lacustris, Chromochloris zofingiensis, Chlorococcum, Bracteacoccus aggregatus, Coelastrella rubescence, Phaffia rhodozyma, some bacteria (Paracoccus carotinifaciens), yeasts, and lobsters, among others However, it is majorly synthesized by Haematococcus lacustris alone (about 4%). The richness of natural astaxanthin over synthetic astaxanthin has drawn the attention of industrialists to cultivate and extract it via two stage cultivation process. However, the cultivation in photobioreactors is expensive, and converting it in soluble form so that it can be easily assimilated by our digestive system requires downstream processing techniques which are not cost-effective. This has made the cost of astaxanthin expensive, prompting pharmaceutical and nutraceutical companies to switch over to synthetic astaxanthin. This review discusses the chemical character of astaxanthin, more inexpensive cultivating techniques, and its bioavailability. Additionally, the antioxidant character of this microalgal product against many diseases is discussed, which can make this natural compound an excellent drug to minimize inflammation and its consequences.

Microalgae biomass deconstruction using green solvents: Challenges and future opportunities

Microalgae enablefixation of CO₂into carbohydrates, lipids, and proteins through inter and intracellularly biochemical pathways. These cellular components can be extracted and transformed into renewable energy, chemicals, and materials through biochemical and thermochemical transformation processes.However, recalcitrant cell wall andlack of environmentally benign efficient pretreatment processes are key obstacles in the commercialization of microalgal biorefineries.Thus,current article describes the microalgal chemical structure, type, and structural rigidity and summarizes the traditional pretreatment methods to extract cell wall constituents. Green solvents such as ionic liquid (ILs), deep eutectic solvents (DES), and natural deep eutectic solvents (NDESs) have shown interesting solvent characteristics to pretreat biomass with selective biocomponent extraction from microalgae. Further research is needed in task-specific IL/DES design, cation-anion organization, structural activity understanding of ILs-biocomponents, environmental toxicity, biodegradability, and recyclability for deployment of carbon-neutral technologies. Additionally, coupling the microalgal industry with biorefineries may facilitate waste management, sustainability, and gross revenue.

Anaerobic recalcitrance in wastewater treatment: A review

Anaerobic treatment is applied as an alternative to traditional aerobic treatment for recalcitrant compound degradation. This review highlighted the recalcitrant compounds in wastewaters and their pathways under aerobic and anaerobic conditions. Forty-one recalcitrant compounds commonly found in wastewater along with associated anaerobic removal performance were summarized from current research. Anaerobic degradability of wastewater could not be appropriately evaluated by BOD/COD ratio, which should only be suitable for determining aerobic degradability. Recalcitrant wastewaters with a low BOD/COD ratio may be handled by anaerobic treatments after the adaption and provision of sufficient electron donors. Novel indicator characterizing the anaerobic recalcitrance of wastewater is called for, essential for emergent needs to resource recovery from high-strength recalcitrant wastewater for fulfilling appeals of circular bioeconomy of modern societies.

Microalgae-Based Biorefineries: Challenges and Future Trends to Produce Carbohydrate Enriched Biomass, High-Added Value Products and Bioactive Compounds

Simple Summary

Microalgae-based biorefineries allow the simultaneous production of microalgae biomass enriched in a particular macromolecule and high-added and low-value products if a proper selection of the microalgae species and the cultivation conditions are adequate for the purpose. This review discusses the challenges and future trends related to microalgae-based biorefineries stressing the multi-product approach and the use of raw wastewater or pretreated wastewater to improve the cost-benefit ratio of biomass and products. Emphasis is given to the production of biomass enriched in carbohydrates. Microalgae-bioactive compounds as potential therapeutical and health promoters are also discussed. Future and novel trends following the circular economy strategy are also discussed.

Abstract

Microalgae have demonstrated a large potential in biotechnology as a source of various macromolecules (proteins, carbohydrates, and lipids) and high-added value products (pigments, poly-unsaturated fatty acids, peptides, exo-polysaccharides, etc.). The production of biomass at a large scale becomes more economically feasible when it is part of a biorefinery designed within the circular economy concept. Thus, the aim of this critical review is to highlight and discuss challenges and future trends related to the multi-product microalgae-based biorefineries, including both phototrophic and mixotrophic cultures treating wastewater and the recovery of biomass as a source of valuable macromolecules and high-added and low-value products (biofertilizers and biostimulants). The therapeutic properties of some microalgae-bioactive compounds are also discussed. Novel trends such as the screening of species for antimicrobial compounds, the production of bioplastics using wastewater, the circular economy strategy, and the need for more Life Cycle Assessment studies (LCA) are suggested as some of the future research lines.

Development of an alternative medium via completely replaces the medium components by mixed wastewater and crude glycerol for efficient production of docosahexaenoic acid by Schizochytrium sp

Exorbitant substrates for Schizochytrium culture result in the high cost of docosahexaenoic acid (DHA) production. In order to develop a feasible approach that is expected to reduce DHA production cost, Schizochytrium sp. S31 cultivation with a mixture of saline wastewater (SWW) and tofu whey wastewater (TWW) was investigated in this study. Using glucose as the carbon source, the maximum biomass and DHA yield in cultures using mixed wastewater containing 5% SWW reached 19.08 and 2.66 g/L, respectively, which were 2.29 and 2.66 times higher than those of cultures using control medium. Moreover, a good wastewater treatment performance was achieved as approximately 60% of the COD, TN, and TP were reduced in the cultures using mixed wastewater with a SWW ratio of 5%. The mixed wastewater presented better performance on DHA production than control medium using all tested carbon sources including glucose, fructose, and pure and crude glycerol. The components of control medium can be completely replaced by the mixed wastewater and crude glycerol. It is expected to effectively decrease the medium cost for DHA production and reduce the environmental risk of food processing wastewater.

Microalgae based wastewater treatment coupled to the production of high value agricultural products: Current needs and challenges

One of the main social and economic challenges of the 21st century will be to overcome the worlds' water deficit expected by the end of this decade. Microalgae based wastewater treatment has been suggested as a strategy to recover nutrients from wastewater while simultaneously producing clean water. Consortia of microalgae and bacteria are responsible for recovering nutrients from wastewater. A better understanding of how environmental and operational conditions affect the composition of the microalgae-bacteria consortia would allow to maximise nutrient recoveries and biomass productivities. Most of the studies reported to date showed promising results, although up-scaling of these processes to reactors larger than 100 m² is needed to better predict their industrial relevance. The main advantage of microalgae based wastewater treatment is that valuable biomass with unlimited applications is produced as a co-product. The aim of the current paper was to review microalgae based wastewater treatment processes focusing on strategies that allow increasing both biomass productivities and nutrient recoveries. Moreover, the benefits of microalgae based agricultural products were also discussed.

Use of Fungal Mycelium as Biosupport in the Formation of Lichen-Like Structure: Recovery of Algal Grown in Sugarcane Molasses for Lipid Accumulation and Balanced Fatty Acid Profile

In this study, a lichen-like structure was obtained through the production of a unique biomass, formed by algae cells of Scenedesmus obliquus adhering to the mycelium of filamentous fungal Mucor circinelloides. This structure was composed in two steps; in the first one, microalgal cells and spores were incubated separately, and in the second one, after 72 h of growth, isolated, mature mycelium was harvested and added to cell culture. For spores’ incubation, a culture medium containing only 2 g·L⁻¹ of glucose and minerals was used. This culture medium, with low sugar content, provided a fungal biomass to the anchorage of microalgae cells. WC medium was used without and with sugarcane molasses supplementation for microalgae cells’ incubation. The lichen-type structure that was formed resulted in 99.7% efficiency in the recovery of microalgae cells and in up to 80% efficiency in the recovery of algae biomass in the lichen biomass composition. In addition, the resulting consortium attained a satisfactory lipid accumulation value (38.2 wt%) with a balanced fatty acid composition of 52.7% saturated plus monounsaturated fatty acids and 47.4% polyunsaturated fatty acids. Since fungal species are easy to recover, unlike microalgae, the lichen-like structure produced indicates an efficient low-cost bioremediation and harvesting alternative; in addition, it provides an oleaginous biomass for various industrial applications.

Evaluating the effect of microalga Haematococcus pluvialis bioaugmentation on aerobic membrane bioreactor in terms of performance, membrane fouling and microbial community structure

In this study, considering the enhancement potential of microalgae and MBRs for wastewater treatment, the microalgae Haematococcus pluvialis, which is a freshwater species of Chlorophyta with a high capacity to synthesize astaxanthin, was bioaugmented into an aerobic MBR to investigate its potential on treatment of antibiotics in wastewater, reducing membrane biofouling, and impact on the microbial community structure. For this purpose, two control MBRs, with and without antibiotics, alongside an MBR bioaugmented with H. pluvialis, were set under mesophilic conditions, using inoculum from a local wastewater treatment facility and synthetic wastewater. The common antibiotics sulfamethoxazole (SMX), tetracycline (TET) and erythromycin (ERY) were selected to investigate removal efficiencies by Haematococcus pluvialis in an MBR for this study. In the bioaugmented reactor, membrane biofouling was delayed by 33% and chemical oxygen demand removal increased by 6%. The highest removal of antibiotics was observed for TET with a 20% enhancement from 69.75% (C2) to 89.73% (HP). The results also suggested that H. pluvialis reconstructed indigenous and biofilm microbial communities in MBR. The biodegradation network was modified and the relative abundance of Proteobacteria increased, while Firmicutes and Bacteroidetes were significantly reduced.

A comprehensive review on carbon source effect of microalgae lipid accumulation for biofuel production

Energy is a major driving force for the economic development. Due to the scarcity of fossil fuels and negative impact on the environment, it is important to develop renewable and sustainable energy sources for humankind. Microalgae as the primary feedstock for biodiesel has shown great application potential. However, lipid yield from microalgae is limited by the upstream cost, which restrain the realization of large-scale biofuel production. The modification of lipid-rich microalgae cell has become the focus over the last few decades to improve the lipid content and productivity of microalgae. Carbon is a vital nutrient that regulates the growth and metabolism of microalgae. Different carbon sources are assimilated by microalgae cells via different pathways. Inorganic carbon sources are mainly used through the CO₂-concentrating mechanisms (CCMs), while organic carbon sources are absorbed by microalgae mainly through the Pentose Phosphate (PPP) Pathway and the Embden-Meyerhof-Pranas (EMP) pathway. Therefore, the addition of carbon source has a significant impact on the production of microalgae biomass and lipid accumulation. In this paper, mechanisms of lipid synthesis and carbon uptake of microalgae were introduced, and the effects of different carbon conditions (types, concentrations, and addition methods) on lipid accumulation in microalgal biomass production and biodiesel production were comprehensively discussed. This review also highlights the recent advances in microalgae lipid cultivation with large-scale commercialization and the development prospects of biodiesel production. Current challenges and constructive suggestions are proposed on cost-benefit concerns in large-scale production of microalgae biodiesel.

Bacterial-algal coupling system for high strength mariculture wastewater treatment: Effect of temperature on nutrient recovery and microalgae cultivation

In the present study, bacterial-algal coupling system, an integration process of acidogenic fermentation and microalgae cultivation was used for high strength mariculture wastewater (HSMW) treatment, resource recovery and low-cost biomass production. The effect of temperature on Chlorella vulgaris (C. vulgaris) cultivation was investigated with culture medium of acidogenic liquid. The results showed that acidogenic liquid could be used as culture medium for C. vulgaris and higher biomass was obtained compared to control. The acidogenic liquid obtained at initial pH of 8 was the most suitable culture medium for C. vulgaris growth due to befitting C/N and considerable volatile fatty acids. Moreover, the optimum temperature for C. vulgaris cultivation was 25 °C and the removal efficiency of chemical oxygen demand (COD) and NH₄⁺-N from acidogenic liquid could reach 94.4% and 68.8%, respectively. The outcome could create an innovative value chain with environmental sustainability and economic feasibility in aquaculture industry.

Carotenoids from fungi and microalgae: A review on their recent production, extraction, and developments

The demand for carotenoids from natural sources obtained by biological extraction methods is increasing with the development of biotechnology and the continued awareness of food safety. Natural plant-derived carotenoids have a relatively high production cost and are affected by the season, while microbial-derived carotenoids are favored due to their natural, high-efficiency, low production cost, and ease of industrialization. This article reviewed the following aspects of natural carotenoids derived from microorganisms: (1) the structures and properties of main carotenoids; (2) fungal and microalgal sources of the main carotenoids; (3) influencing factors and modes of improvement for carotenoids production; (4) efficient extraction methods for carotenoids; and (5) the commercial value of carotenoids. This review provided a reference and guidance for the development of natural carotenoids derived from microorganisms.