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Microalgae hold promise as a sustainable source of biofuels and bioproducts but their commercial development is impeded by high cultivation costs, primarily for growth nutrients, and concerns about the water-intensive nature of algae cultivation. As a result, minimizing water and nutrient input is imperative to reducing algal operating costs, while enhancing the sustainability of future algal biorefineries. However, spent media recycling often results in the accumulation of growth inhibitors, such as free fatty acids, polysaccharides, polyunsaturated aldehydes, and humic acid, which negatively affect algal growth and productivity. In this review, we critically assess media recycling research findings to assess the advantages and disadvantages of spent media reuse for a wide range of algae strains. Particular emphasis is placed on strategies to overcome growth inhibition through spent media treatment processes, such as ultraviolet oxidation, activated carbon, ultrasonication, microfiltration, crop rotation, and nutrient replenishment. [ABSTRACT FROM AUTHOR]

Aquatic algae are a rich source of a wide range of bioproducts intended to compete for a sizable global market share. Thanks to the gradual shift towards the use of natural products, microalgae-derived bioactive compounds offer an ecofriendly and vegan option to the cosmeceutical sector, whose products aim to improve skin health but currently consist of mostly synthetic chemicals. In particular, algae-derived vitamins and their precursors are being explored and widely used in the cosmeceuticals industry as compounds that contain biologically active ingredients with therapeutic benefits. The present review highlights the current strategies for industrial production of an array of vitamins from algae for cosmeceutical applications. When compared to traditional plant sources, algae have been found to accumulate vitamins, such as A, B1, B2, B6, B12, C and E, in high concentrations. The purpose of this review is to provide context for the development of a green and sustainable algae-derived bioeconomy by summarizing and comparing the current market for vitamins and precursors derived from algae, as well as presenting novel strategies and key findings from the most recent research in this area. Emphasis is placed on novel biotechnological interventions that encompass genetic modifications, genetic engineering, and media development to enhance vitamin biosynthesis. [ABSTRACT FROM AUTHOR]

To minimize the cost of algae-based biofuels and bioproducts, boosting biomass productivity and enhancing the stability of cultures in outdoor cultivation systems are imperative. Strain improvement strategies, mainly adaptive evolution, random mutagenesis, and genetic engineering, focus on perturbing the metabolism of algae to develop desired phenotypes. However, the aforementioned techniques are time- and labor-intensive with a possibility of reversion of the mutated/adapted phenotypes back to wild type. In this regard, the chemical genetics approach has emerged as a rapid and powerful approach to preferentially direct the metabolism of algae towards desired target products with the incorporation of small chemical modulators in a dose-dependent manner. In this review, we critically asses the use of chemical modulators to tweak the metabolism of several algal species and enhance biomass production, bioproduct yield, and resilience to abiotic stressors. The review highlights important categories of chemical modulators and the techniques employed to identify and screen such small effective molecules. Chemical modulators enable the re-design and fine-tuning of targeted algal metabolic pathways rendering chemical genetics a promising approach for enhancing algal productivity particularly in large-scale cultivation. • Use of chemical modulators helps generate desired algal phenotypes. • High throughput screening can identify potential chemical modulators. • Phytohormones, amino acids, inhibitors, and metabolites boost algal productivity. • Exogenous addition of chemical modulators alleviates oxidative stress in algae. • Chemical genetics can facilitate development of algal biofuels and bioproducts. [ABSTRACT FROM AUTHOR]

Modeling and optimization of key design parameters of bioreactors are critical for development of economically and technically viable algae technologies. The objective of this study is to use computational fluid dynamics (CFD) modeling to design a novel enclosed Horizontal BioReactor (HBR) equipped with a paddle wheel that incurs low capital and operating costs like raceway ponds, but achieves high productivities like enclosed photobioreactors. For the HBR the aspect ratio (length-to-width), paddle wheel diameter and positioning, culture depth, and baffle spacing can be manipulated to achieve adequate flow of the culture that minimizes the formation of low-velocity areas, below 20 cm/s, termed “dead zones”. The CFD procedure focused on minimizing dead volume and power consumption. A small-scale HBR (3 m 2 of surface area) was used for development and validation of the hydrodynamic model, whose parameters were calculated using experimental data. The model was then applied to a pilot-scale HBR (40 m 2 ) that is operated outdoors. Placing the paddle wheel at either end of the reactor or incorporating baffles minimized the dead volume. The same effect was also achieved by increasing the size of the paddle wheel or the number of paddle wheels or the depth of the culture. On the other hand, increasing the reactor's aspect ratio resulted in more dead volume, although it decreased power consumption. These findings will be incorporated into the design of large-scale HBRs (200 m 2 ) for commercial deployment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low lignin content in algae makes thermochemical conversion to chars cost-effective. • Slow pyrolysis and HTC are preferred methods for algal char production. • Higher porosity and more diverse functional groups boost algal sorbent properties. • Enriched ash content in algal chars leads to higher cation exchange properties. • Modification of algal char enhances biosorbent properties. Biochar and hydrochar are carbon-rich solid products of algal and terrestrial biomass obtained through various thermochemical processes, mainly hydrothermal liquefaction, pyrolysis, and hydrothermal carbonization. Both are regarded as economical, potent, and environmentally friendly adsorbents for wastewater remediation. The versatile applicability of biochar and hydrochar, which is due to their enhanced surface physicochemical properties, includes efficient metal biosorption, soil fertility enhancement, and carbon sequestration. Consequently, there has been an increase in research for producing and exploiting biochar and hydrochar from algae. Both micro- and macro-algal biomass have strong potential due to their sustainability footprint and distinct properties. This review focuses on a comprehensive account of the synthesis of algal biochar and hydrochar and use in wastewater treatment to develop innovative solutions for efficient mitigation of several aqueous pollutants and heavy metal ions. The review discusses the various thermochemical production routes, biophysical characterization techniques, and modes of mechanism for wastewater bioremediation. Algal-based biochar and hydrochar are reported to have higher porosity and more diverse functional groups such as amines, hydroxyl, and carboxyl compared to their cellulosic and waste-derived counterparts, demonstrating an increased wastewater remediation efficiency. In addition, presence of inorganic metal including sodium, potassium, magnesium, and phosphorus in algal chars facilitates the formation of mesopores and graphite structures, improving their cation exchange capacity. Moreover, algal chars may exhibit pH buffering capacity, which could help stabilize the pH during wastewater treatment processes. Notably, the low O/C content of algal hydrochars enhances the binding and removal of organic pollutants including toxic dyes and antibiotics. The review highlights the development of modified algal chars to enhance the porosity, surface area, structural integrity, and adsorption capacity enabling a higher bioremediation potential. [ABSTRACT FROM AUTHOR]

[Display omitted] • Use of spent media reduces water footprint and nutrient demand in algae cultivation. • Spent media fostered enhanced algal PUFA and carbohydrate production. • Nitrogen uptake, TCA cycle, and phospholipid synthesis downregulated in spent media. • Extracellular matter accumulated inhibiting algal growth past the 2nd use cycle. • Humic acid and free fatty acids were the major extracellular inhibitors. The recycling of unfiltered spent media during cultivation of Chlorella vulgaris was studied using metabolomics in an effort to enhance water and nutrient sustainability and reduce operating costs in algal biorefineries. Cultivation in spent media resulted in reduced biomass and lipid productivity by 14% and 19%, respectively, compared to fresh media. The decrease was related to a detected lower nutrient uptake. Nevertheless, carbohydrate content (28% of dry cell weight) and α-linolenic acid content (27 % of fatty acids) were higher in spent media cultures than in fresh media. Metabolomics analysis of intracellular metabolites revealed downregulation of nitrogen assimilation, tricarboxylic acid cycle, structural lipids, and energy metabolism, but upregulation of stress mitigation and carbohydrate synthesis. No growth was supported by spent media during a second cultivation cycle and was likely due to the identified extracellular accumulation of humic acid and free fatty acids that acted as growth auto-inhibitors. [ABSTRACT FROM AUTHOR]