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Supplementing cultivation media with exogenous carbon sources enhances biomass and lipid production in microalgae. Utilization of renewable organic carbon from agricultural residues can potentially reduce the cost of algae cultivation, while enhancing sustainability. In the present investigation a medium was developed from sweet sorghum bagasse for cultivation of Chlorella under mixotrophic conditions. Using response surface methodology, the optimal values of critical process parameters were determined, namely inoculum cell density (O.D. 750 ) of 0.786, SSB hydrolysate content of the medium 25% v/v, and zero medium salinity, to achieve maximum lipid productivity of 120 mg/L/d. Enhanced biomass (3.44 g/L) and lipid content (40% of dry cell weight) were observed when the alga was cultivated in SSB hydrolysate under mixotrophic conditions compared to heterotrophic and photoautotrophic conditions. A time course investigation revealed distinct physiological responses in terms of cellular growth and biochemical composition of C. vulgaris cultivated in the various trophic modes. The determined carbohydrate and lipid profiles indicate that sugar addition to the cultivation medium boosts neutral lipid synthesis compared to structural lipids, suggesting that carbon flux is channeled towards triacylglycerol synthesis in the cells. Furthermore, the fatty acid profile of lipids extracted from mixotrophically grown cultures contained more saturated and monosaturated fatty acids, which are suitable for biofuel manufacturing. Scale-up studies in a photobioreactor using SSB hydrolysate achieved a biomass concentration of 2.83 g/L consisting of 34% lipids and 26% carbohydrates. These results confirmed that SSB hydrolysate is a promising feedstock for mixotrophic cultivation of Chlorella and synthesis of algal bioproducts and biofuels.

Propionic acid is an important organic acid with wide industrial applications, especially in the food industry. It is currently produced from petrochemicals via chemical routes. Increasing concerns about greenhouse gas emissions from fossil fuels and a growing consumer preference for bio-based products have led to interest in fermentative production of propionic acid, but it is not yet competitive with chemical production. To improve the economic feasibility and sustainability of bio-propionic acid, fermentation performance in terms of concentration, yield, and productivity must be improved and the cost of raw materials must be reduced. These goals require robust microbial producers and inexpensive renewable feedstocks, so the present review focuses on bacterial producers of propionic acid and promising sources of substrates as carbon sources. Emphasis is placed on assessing the capacity of propionibacteria and the various approaches pursued in an effort to improve their performance through metabolic engineering. A wide range of substrates employed in propionic acid fermentation is analyzed with particular interest in the prospects of inexpensive renewable feedstocks, such as cellulosic biomass and industrial residues, to produce cost-competitive bio-propionic acid.Key points• Fermentative propionic acid production emerges as competitor to chemical synthesis.• Various bacteria synthesize propionic acid, but propionibacteria are the best producers.• Biomass substrates hold promise to reduce propionic acid fermentation cost.

Microalgae are increasingly viewed as renewable biological resources for a wide range of chemical compounds that can be used as or transformed into biomaterials through biorefining to foster the bioeconomy of the future. Besides the well-established biofuel potential of microalgae, key microalgal bioactive compounds, such as lipids, proteins, polysaccharides, pigments, vitamins, and polyphenols, possess a wide range of biomedical and nutritional attributes. Hence, microalgae can find value-added applications in the nutraceutical, pharmaceutical, cosmetics, personal care, animal food, and agricultural industries. Microalgal biomass can be processed into biomaterials for use in dyes, paints, bioplastics, biopolymers, and nanoparticles, or as hydrochar and biochar in solid fuel cells and soil amendments. Equally important is the use of microalgae in environmental applications, where they can serve in heavy metal bioremediation, wastewater treatment, and carbon sequestration thanks to their nutrient uptake and adsorptive properties. The present article provides a comprehensive review of microalgae specifically focused on biomaterial production and environmental applications in an effort to assess their current status and spur further deployment into the commercial arena.

Oleaginous microalgae and yeasts represent promising candidates for large-scale production of lipids, which can be utilized for production of drop-in biofuels, nutraceuticals, pigments, and cosmetics. However, low lipid productivity and costly downstream processing continue to hamper the commercial deployment of oleaginous microorganisms. Strain improvement can play an essential role in the development of such industrial microorganisms by increasing lipid production and hence reducing production costs. The main means of strain improvement are random mutagenesis, adaptive laboratory evolution (ALE), and rational genetic engineering. Among these, random mutagenesis and ALE are straight forward, low-cost, and do not require thorough knowledge of the microorganism’s genetic composition. This paper reviews available mutagenesis and ALE techniques and screening methods to effectively select for oleaginous microalgae and yeasts with enhanced lipid yield and understand the alterations caused to metabolic pathways, which could subsequently serve as the basis for further targeted genetic engineering.

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.

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.

Conversion of residual algal biomass to value-added products is essential for enhancing the economics of algae cultivation. Algal hydrochar produced via hydrothermal carbonization of lipid-extracted Picochlorum oculatum is a material rich in oxygen functional groups and carbon (up to 67.3%) and hence a promising candidate for remediation of wastewaters. The hydrothermal carbonization conditions were optimized and the adsorption capacity of the hydrochar was tested for metal removal. By the end of the remediation process, cumulative removal of Al3+, Cu2+, Fe2+, Mg2+, Mn2+, and Pb2+ reached 89, 98, 75, 88, 75, and 100%, respectively. The adsorption of all metals was found to follow pseudo second-order kinetics and the Langmuir isotherm. Overall, when hydrothermal carbonization is applied to lipid-extracted algae, it generates a promising biobased adsorbent with value-added potential in metal remediation.

Air-cushion (AC) packaging has become widely used worldwide. ACs are air-filled, dual plastic packaging solutions commonly found surrounding and protecting items of value within shipping enclosures during transit. Herein, we report on a laboratory assessment employing ACs as a microalgal photobioreactor (PBR). Such a PBR inherently addresses many of the operational issues typically encountered with open raceway ponds and closed photobioreactors, such as evaporative water loss, external contamination, and predation. Using half-filled ACs, the performance of microalgal species Chlorella vulgaris, Nannochloropsis oculata , and Cyclotella cryptica (diatom) was examined and the ash-free dry cell weight and overall biomass productivity determined to be 2.39 g/L and 298.55 mg/L/day for N. oculata , 0.85 g/L and 141.36 mg/L/day for C. vulgaris, and 0.67 g/L and 96.08 mg/L/day for C. cryptica. Furthermore, maximum lipid productivity of 25.54 mg/L/day AFDCW and carbohydrate productivity of 53.69 mg/L/day AFDCW were achieved by C. cryptica , while maximum protein productivity of 247.42 mg/L/day AFDCW was attained by N. oculata . Data from this work will be useful in determining the applicability and life-cycle profile of repurposed and reused ACs as potential microalgal photobioreactors depending upon the end product of interest, scale utilized, and production costs.

Landfilling of municipal waste, an environmental challenge worldwide, results in the continuous formation of significant amounts of leachate, which poses a severe contamination threat to ground and surface water resources. Landfill leachate (LL) is generated by rainwater percolating through disposed waste materials and must be treated effectively before safe discharge into the environment. LL contains numerous pollutants and toxic substances, such as dissolved organic matter, inorganic chemicals, heavy metals, and anthropogenic organic compounds. Currently, LL treatment is carried out by a combination of physical, chemical, and microbial technologies. Microalgae are now viewed as a promising sustainable addition to the repertoire of technologies for treating LL. Photosynthetic algae have been shown to grow in LL under laboratory conditions, while some species have also been employed in larger-scale LL treatments. Treating leachate with algae can contribute to sustainable waste management at existing landfills by remediating low-quality water for recycling and reuse and generating large amounts of algal biomass for cost-effective manufacturing of biofuels and bioproducts. In this review, we will examine LL composition, traditional leachate treatment technologies, LL toxicity to algae, and the potential of employing algae at LL treatment facilities. Emphasis is placed on how algae can be integrated with existing technologies for biological treatment of LL, turning leachate from an environmental liability to an asset that can produce value-added biofuels and bioproducts for the bioeconomy.

The Brazilian government’s decision to open the Amazon biome to sugarcane expansion reignited EU concerns regarding the sustainability of Brazil’s sugar sector, hindering the ratification of the EU-Mercosur trade agreement. Meanwhile, in the EU, certain conventional biofuels face stricter controls, whilst uncertainty surrounding the commercialisation of more sustainable advanced-biofuels renders bioethanol as a short- to medium-term fix. This paper examines Brazil’s land-use changes and associated greenhouse gas emissions arising from an EU driven ethanol import policy and projections for other 13 biocommodities. Results suggest that Brazil’s sugarcane could satisfy growing ethanol demand and comply with EU environmental criteria, since almost all sugarcane expansion is expected to occur on long-established pasturelands in the South and Midwest. However, expansion of sugarcane is also driven by competition for viable lands with other relevant commodities, mainly soy and beef. As a result, deforestation trends in the Amazon and Cerrado biomes linked to soy and beef production could jeopardize Brazil’s contribution to the Paris agreement with an additional 1 ± 0.3 billion CO 2 eq tonnes above its First NDC target by 2030. Trade talks with a narrow focus on a single commodity could thus risk unsustainable outcomes, calling for systemic sustainability benchmarks, should the deal be ratified.