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To address issues related to climate crises, microalgae-based biofuels are considered a promising option for reducing carbon dioxide emissions in the transportation sector. However, despite extensive research conducted over the past 20 years, there are major limitations in the application of conventional algal biodiesel, such as the instability of oxygen-containing fuel, blending wall limitations (less than 20%), and poor cost competitiveness. Recently, biomass-based renewable hydrocarbon fuels (drop-in biofuels) have been considered technologically competitive alternatives to petrofuels owing to the advantages of carbon dioxide reduction, high energy density, and compatibility with existing infrastructure. This review discusses the integrative utilization of whole algal biomass for the development of an advanced algal biorefinery process that could strategically help produce drop-in biofuels and multiple by-products to meet the growing fuel demand and secure economic feasibility. This review provides an updated overview of recent technical advancements in the (1) mass cultivation of oleaginous algal biomass obtained from industrial wastes, (2) production of renewable biodiesel and bio-jet fuel using algal lipids via catalytic upgrading, and (3) diversification of bio-products generated from residual lipid-extracted biomass, such as hydrogen, methane, alcohols, bio-oils, organic acids, biosorbents, biomaterials, and nutrients. The challenges and prospects for practical application are discussed along with the major constraints on the commercialization of integrative algal biorefining. [Display omitted] • Integrative utilization of whole biomass is required for economic algal biorefining. • Mass cultivation of lipid-rich algal biomass using CO 2 -rich flue gas and wastewater. • Catalytic upgrading of renewable diesel and bio-jet fuel from algal neutral lipids. • Diversification of products from lipid-extracted biomass via subsequent conversions. [ABSTRACT FROM AUTHOR]

• Social changes on a global scale have challenged the nascent algal industry. • Drop-in fuel would be a new major target of algal lipid-based products. • Enhancing CO 2 fixing efficiency would be a major goal in outdoor cultivation. • An integrated refinery process is required for feasible whole cell utilization. Microalgae have been studied and tested for over 70 years. However, biodiesel, the prime target of the algal industry, has suffered from low competitiveness and current steps toward banning the internal combustion engine all over the world. Meanwhile, interest in reducing CO 2 emissions has grown as the world has witnessed disasters caused by global warming. In this situation, in order to maximize the benefits of the microalgal industry and surmount current limitations, new breakthroughs are being sought. First, drop-in fuel, mandatory for the aviation and maritime industries, has been discussed as a new product. Second, methods to secure stable and feasible outdoor cultivation focusing on CO 2 sequestration were investigated. Lastly, the need for an integrated refinery process to simultaneously produce multiple products has been discussed. While the merits of microalgae industry remain valid, further investigations into these new frontiers would put algal industry at the core of future bio-based economy. [ABSTRACT FROM AUTHOR]

• Algal-biomass-derived (R)-GVL production with perfect enantiomeric excess (>99.99) • LA was obtained from G. verrucosa through acidic hydrothermal conversion. • Chemoenzymatic reaction converted LA to (R)-GVL via 4-HV. • Residual algal biomass was used to prepare anode for LiB via simple heat treatment. • The results can construct to viable zero-waste biorefinery and circular bioeconomy. Mankind is facing a severe climate crisis caused by fossil fuel-derived CO 2 emissions. Although biorefineries utilizing biomass have been considered the best option for carbon-neutrality, most biorefinery-derived products have not yet been promising for economic feasibility; various strategies have been developed to increase economic competitiveness, and zero-waste biorefineries are challenging options. Herein, we aim to develop an algal biomass-based zero-waste biorefinery for producing enantioselective (R)-γ-valerolactone ((R)-GVL) and carbonaceous electrodes applicable for Li-ion batteries (LiBs). Various algal biomasses were hydrothermally oxidized to produce levulinic acid (LA) as an intermediate for producing (R)-GVL, resulting that Gracilaria verrucosa was selected as feedstock. For the hydroxylation of G. verrucosa -derived LA to 4-hydroxyvaleric acid (4-HV), 3-hydroxybutyrate dehydrogenase (HBDH) was explored through genome mining and further engineered. The engineered HBDH successfully converted G. verrucosa -derived LA to 4-HV, which was subsequently lactonized under acidic conditions, resulting in optically pure (R)-GVL. To our knowledge, this is the first report of the production of an algal biomass-derived enantioselective (R)-GVL with a perfect enantiomeric excess (>99.99 %) that can be used as a precursor for more valuable biopharmaceuticals and bioplastics than biofuels. Furthermore, residual G. verrucosa after hydrothermal oxidation was used as a carbonaceous anode material for LIBs for the first time; hard carbon anodes, which were prepared through simple heat treatment (800 ℃, 3 h, argon atmosphere), exhibit good capacities of 231, 191, 133, 108, 97 and 86 mAh/g at 0.05, 0.1, 0.5, 1, 1.5, and 2 A/g, respectively. The results discussed herein can provide insights into zero-waste biorefineries applicable for diverse industrial fields (e.g., biopolymer, biopharmaceutical and energy storage) and contribute to the construction of closed-carbon-loops for coping with climate change. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chlorella sp. ABC-001 showed the best growth and lipid yield with flue gas 10% CO 2. • Chlorella sp. ABC-001 was unaffected by NO but SO 2 severely inhibited cell growth. • Galdieria sulphuraria was adopted to remove SO 2 and enhance CO 2 and NO removal. • SO 2 removal is attributed to ionic interactions as well as assimilation by cells. • The dual-strain system showed stable growth under simulated flue gas supply. This study aims to propose a biological system that allows for direct utilization of flue gas for carbon dioxide capture and utilization by microalgae. The strain Chlorella sp. ABC-001 is employed for its high growth rate as well as lipid and carbohydrate content. Toxicity tests showed that cell growth was unaffected by NO, but the presence of SO 2 showed critical damage on cell growth. Hence, an extremophile alga, Galdieria sulphuraria 5587.1 was applied to build a dual-strain cultivation system to mitigate the effect of SO 2 toxicity and increase CO 2 capture efficiency. All SO 2 was removed by Galdieria culture and the system exhibited stable growth from a simulated flue gas stream containing CO 2 , NO and SO 2. Combined CO 2 biofixation rate of 793 mg/L/d and lipid productivity of 113 mg/L/d was achieved. The results showed that this new cultivation system is a promising alternative for reducing CO 2 emissions from power plants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Whole-cell biomass utilization was completed with newly integrated biorefinery. • Hydrolysis yielded 89 % of total carbohydrate within 4 min using optimized process. • Volume reduction decreased solvent usage by 75 % and recovered all oil within 20 min. • Bioethanol yield of sole hydrolysate was comparable with conventional YPD medium. • Newly developed process decreased OPEX and CAPEX by 82.7 % and 70.1 %, respectively. Microalgae are a promising source of biomass for the production of biofuels, but their use is currently infeasible because of changes in the biofuel market and the lack of an optimized refinery process. The biomass of oleaginous microalgae consists of up to 50% lipids and 50% carbohydrates and proteins, so the biorefinery process must be able to use whole cell biomass. In this work, an alternative process to the standard biorefinery approach of lipid extraction and treatment of lipid-extracted residue was developed and tested using oleaginous Chlorella sp. ABC-001. First, a hydrolysis process was optimized to achieve cell lysis. At 170 °C and 0.1 N H 2 SO 4 , 89.0% of total carbohydrates were hydrolyzed to monosaccharides within 4 min. Then, a volume reduction process (brief and mild centrifugation) was applied to reduce the extraction time and the use of organic solvent. By reducing the aqueous phase from the hydrolysate, all lipids were extracted by vortexing with just a quarter of the original volume (10 mL) within 20 min. Finally, after extraction the aqueous phase was utilized as the sole growth medium for ethanol production by Saccharomyces cerevisiae KL17. The resulting ethanol yield was 0.39 g ethanol/g sugar, comparable to that achieved using conventional yeast-peptone-dextrose (YPD) medium (0.41 g ethanol/g sugar). Furthermore, relative to the conventional process, techno-economic analysis confirmed that the newly developed process decreased operational expenditures by 82.7% and decreased capital expenditures by 70.1%. [ABSTRACT FROM AUTHOR]

This study informs harmful chemicals generation from polyurethane waste into the environment and suggests sustainable disposal platform with waste valorization. [Display omitted] • Automotive seat form (ASF) was upgraded into value-added products through pyrolysis. • Ni catalyst converted harmful aromatic chemicals into syngas. • CO 2 synergistically contributed to harmful chemical conversion into syngas. • CO 2 also contributed to extended catalyst stability in catalytic pyrolysis of ASF. In automotive industry, plastic consumption has substantially increased due to its affordability, durability, and lightness. However, the massive generation of plastic wastes from the automotive industry becomes a growing environmental concern. Current disposal methods of end-of-life vehicles (ELVs) are incineration and landfilling, but these methods generate toxic chemicals and leachate into the environment. To propose more sustainable disposal platform for ELVs, this study used a pyrolysis process using CO 2 as a reaction medium. As a case study, automotive seat form (ASF) in ELVs was disposed and valorized through the CO 2 -assisted pyrolysis. ASF, composed of polyurethane, generated harmful aromatic compounds during pyrolysis process such as benzene, aniline and their derivatives. To convert harmful chemicals into value-added syngas (H 2 and CO), catalytic pyrolysis of ASF was performed using a nickel catalyst. Effects of both CO 2 and nickel catalyst showed 89.9 wt% reduction of toxic chemical production by converting them into syngas, as comparing to pyrolysis without Ni catalyst. Gas-phase-reaction between CO 2 and pyrogenic products from ASF resulted in more than 200 times of CO production. Also, CO 2 suppressed catalyst deactivation. Therefore, this study suggested that CO 2 and plastic waste from ELVs can be converted to value-added products through CO 2 -assisted catalytic pyrolysis. [ABSTRACT FROM AUTHOR]