An overview of microalgae biomass as a sustainable aquaculture feed ingredient: food security and circular economy

Mechanisms of the novel pesticide sodium dodecyl benzene sulfonate in the mitigation of protozoan ciliated pathogens during microalgal cultivation

Protozoan ciliates represent a common biological contaminant during microalgae cultivation, which will lead to a decline in microalgae productivity. This study investigated the effectiveness of sodium dodecyl benzene sulfonate (SDBS) in controlling ciliate populations within microalgae cultures. SDBS concentrations of 160 mg/L and 100 mg/L were found to effectively manage the representative species of ciliates contamination by Euplotes vannus and Uronema marinum during the cultivation of Synechococcus and Chlorella, and the growth vitality of microalgae has been restored. Additionally, SDBS at these concentrations reduced oxidative stress resistance and induced membrane damage to remove biological pollutants by modulating enzyme activity, affecting lipid, energy, amino acid metabolism pathways, and processes such as translation and protein folding. This research provides insights into the mechanisms through which SDBS effectively combats protozoan ciliates during the microalgal cultivation. This contributes to reduce biological pollution, ensure the overall productivity and healthy and sustainable management of microalgae ecosystems.

Microalgae as fishmeal alternatives in aquaculture: current status, existing problems, and possible solutions

Fishmeal is an indispensable ingredient for most aquatic animals. However, the finite supply and escalating price of fishmeal seriously limit its use in aquaculture. Thus the development of new, sustainable protein ingredients has been a research focus. Microalgae are potential fishmeal alternatives owing to their high protein content and balanced amino acid profile. Studies suggest that suitable replacement of fishmeal with microalgae is beneficial for fish growth performance, but excessive replacement would induce poor growth and feed utilization. Therefore, this paper aims to review research on the maximum substitutional level of fishmeal by microalgae and propose the main issues and possible solutions for fishmeal replacement by microalgae. The maximum replacement level is affected by microalgal species, fish feeding habits, quality of fishmeal and microalgal meals, and supplemental levels of fishmeal in the control group. Microalgae could generally replace 100%, 95%, 95%, 64.1%, 25.6%, and 18.6% fishmeal protein in diets of carp, shrimp, catfish, tilapia, marine fish, and salmon and trout, respectively. The main issues with fishmeal replacement using microalgae include low production and high production cost, poor digestibility, and anti-nutritional factors. Possible solutions to these problems are recommended in this paper. Overall, microalgae are promising fishmeal alternatives in aquaculture.

Photobioreactor configurations in cultivating microalgae biomass for biorefinery

Microalgae, highly prized for their protein, lipid, carbohydrate, phycocyanin, and carotenoid-rich biomass, have garnered significant industrial attention in the context of third-generation (3G) biorefineries, seeking sustainable alternatives to non-renewable resources. Two primarily cultivation methods, open ponds and closed photobioreactors systems, have emerged. Open ponds, favored for their cost-effectiveness in large-scale industrial production, although lacking precise environmental control, contrast with closed photobioreactors, offering controlled conditions and enhanced biomass production at the laboratory scale. However, their high operational costs challenge large-scale deployment. This review comprehensively examines the strength, weakness, and typical designs of both outdoor and indoor microalgae cultivation systems, with an emphasis on their application in terms of biorefinery concept. Additionally, it incorporates techno-economic analyses, providing insights into the financial aspects of microalgae biomass production. These multifaceted insights, encompassing both technological and economic dimensions, are important as the global interest in harnessing microalgae's valuable resources continue to grow.

New dienelactone hydrolase from microalgae bacterial community-Antibiofilm activity against fish pathogens and potential applications for aquaculture

Biofilms are resistant to many traditional antibiotics, which has led to search for new antimicrobials from different and unique sources. To harness the potential of aquatic microbial resources, we analyzed the meta-omics datasets of microalgae-bacteria communities and mined them for potential antimicrobial and quorum quenching enzymes. One of the most interesting candidates (Dlh3), a dienelactone hydrolase, is a α/β-protein with predicted eight α-helices and eight β-sheets. When it was applied to one of the major fish pathogens, Edwardsiella anguillarum, the biofilm development was reproducibly inhibited by up to 54.5%. The transcriptome dataset in presence of Dlh3 showed an upregulation in functions related to self-defense like active genes for export mechanisms and transport systems. The most interesting point regarding the biotechnological potential for aquaculture applications of Dlh3 are clear evidence of biofilm inhibition and that health and division of a relevant fish cell model (CHSE-214) was not impaired by the enzyme.

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.

Production of chemicals and utilities in-house improves the environmental sustainability of phytoplankton-based biorefinery

Life cycle assessment was used to evaluate the environmental impacts of phytoplanktonic biofuels as possible sustainable alternatives to fossil fuels. Three scenarios were examined for converting planktonic biomass into higher-value commodities and energy streams using the alga Scenedesmus sp. and the cyanobacterium Arthrospira sp. as the species of interest. The first scenario (Sc-1) involved the production of biodiesel and glycerol from the planktonic biomass. In the second scenario (Sc-2), biodiesel and glycerol were generated from the planktonic biomass, and biogas was produced from the residual biomass. The process also involved using a catalyst derived from snail shells for biodiesel production. The third scenario (Sc-3) was similar to Sc-2 but converted CO2 from the biogas upgrading to methanol, which was then used in synthesizing biodiesel. The results indicated that Sc-2 and Sc-3 had a reduced potential (up to 60 % less) for damaging human health compared to Sc-1. Sc-2 and Sc-3 had up to 61 % less environmental impact than Sc-1. Sc-2 and Sc-3 reduced the total cumulative exergy demand by up to 44 % compared to Sc-1. In conclusion, producing chemicals and utilities within the biorefinery could significantly improve environmental sustainability, reduce waste, and diversify revenue streams.

Wastewater reuse in agriculture: Prospects and challenges

Sustainable water recycling and wastewater reuse are urgent nowadays considering water scarcity and increased water consumption through human activities. In 2015, United Nations Sustainable Development Goal 6 (UN SDG6) highlighted the necessity of recycling wastewater to guarantee water availability for individuals. Currently, wastewater irrigation (WWI) of crops and agricultural land appears essential. The present work overviews the quality of treated wastewater in terms of soil microbial activities, and discusses challenges and benefits of WWI in line with wastewater reuse in agriculture and aquaculture irrigation. Combined conventional-advanced wastewater treatment processes are specifically deliberated, considering the harmful impacts on human health arising from WWI originating from reuse of contaminated water (salts, organic pollutants, toxic metals, and microbial pathogens i.e., viruses and bacteria). The comprehensive literature survey revealed that, in addition to the increased levels of pathogen and microbial threats to human wellbeing, poorly-treated wastewater results in plant and soil contamination with toxic organic/inorganic chemicals, and microbial pathogens. The impact of long-term emerging pollutants like plastic nanoparticles should also be established in further studies, with the development of standardized analytical techniques for such hazardous chemicals. Likewise, the reliable, long-term and extensive judgment on heavy metals threat to human beings's health should be explored in future investigations.

Solar bioreactors used for the industrial production of microalgae

Microalgae are excellent sources of biomass containing several important compounds for human and animal nutrition-proteins, lipids, polysaccharides, pigments and antioxidants as well as bioactive secondary metabolites. In addition, they have a great biotechnological potential for nutraceuticals, and pharmaceuticals as well as for CO2 sequestration, wastewater treatment, and potentially also biofuel and biopolymer production. In this review, the industrial production of the most frequently used microalgae genera-Arthrospira, Chlorella, Dunaliella, Haematococcus, Nannochloropsis, Phaeodactylum, Porphyridium and several other species is discussed as concerns the applicability of the most widely used large-scale systems, solar bioreactors (SBRs)-open ponds, raceways, cascades, sleeves, columns, flat panels, tubular systems and others. Microalgae culturing is a complex process in which bioreactor operating parameters and physiological variables closely interact. The requirements of the biological system-microalgae culture are crucial to select the suitable type of SBR. When designing a cultivation process, the phototrophic production of microalgae biomass, it is necessary to employ SBRs that are adequately designed, built and operated to satisfy the physiological requirements of the selected microalgae species, considering also local climate. Moreover, scaling up microalgae cultures for commercial production requires qualified staff working out a suitable cultivation regime. KEY POINTS: • Large-scale solar bioreactors designed for microalgae culturing. • Most frequently used microalgae genera for commercial production. • Scale-up requires suitable cultivation conditions and well-elaborated protocols.

Experimental and theoretical investigations of rotating algae biofilm reactors (RABRs): Areal productivity, nutrient recovery, and energy efficiency

Microalgae biofilms have been demonstrated to recover nutrients from wastewater and serve as biomass feedstock for bioproducts. However, there is a need to develop a platform to quantitatively describe microalgae biofilm production, which can provide guidance and insights for improving biomass areal productivity and nutrient uptake efficiency. This paper proposes a unified experimental and theoretical framework to investigate algae biofilm growth on a rotating algae biofilm reactor (RABR). Experimental laboratory setups are used to conduct controlled experiments on testing environmental and operational factors for RABRs. We propose a differential-integral equation-based mathematical model for microalgae biofilm cultivation guided by laboratory experimental findings. The predictive mathematical model development is coordinated with laboratory experiments of biofilm areal productivity associated with ammonia and inorganic phosphorus uptake by RABRs. The unified experimental and theoretical tool is used to investigate the effects of RABR rotating velocity, duty cycle (DC), and light intensity on algae biofilm growth, areal productivity, nutrient uptake efficiency, and energy efficiency in wastewater treatment. Our framework indicates that maintaining a reasonable light intensity range improves biomass areal productivity and nutrient uptake efficiency. Our framework also indicates that faster RABR rotation benefits biomass areal productivity. However, maximizing the nutrient uptake efficiency requires a reasonably low RABR rotating speed. Energy efficiency is strongly correlated with RABR rotating speed and DC.

Growth Behavior, Biomass Composition and Fatty Acid Methyl Esters (FAMEs) Production Potential of Chlamydomonas reinhardtii, and Chlorella vulgaris Cultures

The production of biomolecules by microalgae has a wide range of applications in the development of various materials and products, such as biodiesel, food supplements, and cosmetics. Microalgae biomass can be produced using waste and in a smaller space than other types of crops (e.g., soja, corn), which shows microalgae's great potential as a source of biomass. Among the produced biomolecules of greatest interest are carbohydrates, proteins, lipids, and fatty acids. In this study, the production of these biomolecules was determined in two strains of microalgae (Chlamydomonas reinhardtii and Chlorella vulgaris) when exposed to different concentrations of nitrogen, phosphorus, and sulfur. Results show a significant microalgal growth (3.69 g L-1) and carbohydrates (163 mg g-1) increase in C. reinhardtii under low nitrogen concentration. Also, higher lipids content was produced under low sulfur concentration (246 mg g-1). It was observed that sulfur variation could affect in a negative way proteins production in C. reinhardtii culture. In the case of C. vulgaris, a higher biomass production was obtained in the standard culture medium (1.37 g L-1), and under a low-phosphorus condition, C. vulgaris produced a higher lipids concentration (248 mg g-1). It was observed that a low concentration of nitrogen had a better effect on the accumulation of fatty acid methyl esters (FAMEs) (C16-C18) in both microalgae. These results lead us to visualize the effects that the variation in macronutrients can have on the growth of microalgae and their possible utility for the production of microalgae-based subproducts.

Microalgae as a Nutraceutical Tool to Antagonize the Impairment of Redox Status Induced by SNPs: Implications on Insulin Resistance

Microalgae represent a growing innovative source of nutraceuticals such as carotenoids and phenolic compound which are naturally present within these single-celled organisms or can be induced in response to specific growth conditions. The presence of the unfavourable allelic variant in genes involved in the control of oxidative stress, due to one or more SNPs in gene encoding protein involved in the regulation of redox balance, can lead to pathological conditions such as insulin resistance, which, in turn, is directly involved in the pathogenesis of type 2 diabetes mellitus. In this review we provide an overview of the main SNPs in antioxidant genes involved in the promotion of insulin resistance with a focus on the potential role of microalgae-derived antioxidant molecules as novel nutritional tools to mitigate oxidative stress and improve insulin sensitivity.

Potential of Microalgae Extracts for Food and Feed Supplementation-A Promising Source of Antioxidant and Anti-Inflammatory Compounds

Microalgae are known producers of antioxidant and anti-inflammatory compounds, making them natural alternatives to be used as food and feed functional ingredients. This study aimed to valorise biomass and exploit new applications and commercial value for four commercially available microalgae: Isochrysis galbana, Nannochloropsis sp., Tetraselmis sp., and Phaeodactylum tricornutum. For that, five extracts were obtained: acetone (A), ethanol (E), water (W), ethanol:water (EW). The antioxidant capacity (ABTS^•+/DPPH^•/^•NO/O₂^•-/ORAC-FL) and anti-inflammatory capacity (HBRC/COX-2) of the extracts were screened. The general biochemical composition (carbohydrates, soluble proteins, and lipids) and the main groups of bioactive compounds (carotenoids, phenolic compounds, and peptides) of extracts were quantified. The results of antioxidant assays revealed the potential of some microalgae extracts: in ABTS^•+, Nannochloropsis sp. E and Tetraselmis sp. A, E, and P; in DPPH^•, Tetraselmis sp. A and E; in ^•NO, P. tricornutum E and EW; in O₂^•-, Tetraselmis sp. W; and in ORAC-FL, I. galbana EW and P. tricornutum EW. Concerning anti-inflammatory capacity, P. tricornutum EW and Tetraselmis sp. W showed a promising HBRC protective effect and COX-2 inhibition. Hence, Tetraselmis sp. and P. tricornutum extracts seem to have potential to be incorporated as feed and food functional ingredients and preservatives.