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• 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]