Innovations in algal biorefineries for production of sustainable value chain biochemicals from the photosynthetic cell factories

The concept of biorefinery can explore and expand new dimensions of bio-based commodity production, which will be crucial for sustainable economic growth. A biorefinery is likely to transform biomass into renewable energy and bioenergies for human wellbeing, such as pigments, proteins and biopolymers. Photosynthetic biomass (plant and algae-based), utilized atmospheric CO2 fixation and cheaper substrates (industrial byprod-ucts) with simultaneous production of high value renewables (HVRs). However, due to their high potential of CO2 sequestration, utilization of wastewaters, algae could be considered a potential candidate as compared to terrestrial plants. In addition, pretreatment of algal biomass, its conversion and utilization are cheaper as compared to lignocellulosic waste. Techniques such as gasification, torrefaction, hydrothermal liquefaction can be utilized for the generation of bio-oil/biocrude, syngas, ash, and others, which can effectively be used for fuels and HVRs, respectively. Further, algal cultivation can also pose a potential advantage in terms of a zero-waste biorefinery as algal biomass consists of various proteins, lipids, carbohydrates, pigments and other bioactive components that can be utilized is different industrial sectors including cosmetics, nutraceuticals, and phar-maceuticals. However, alternative technology is required to reduce their production and extraction cost, where resources need to be utilized in a sustainable manner. In this context, the usage of some recyclable solvents such as green-solvents/ionic liquids to extract bioactive components without the cell disruption can acts as an effective technology for improving the algal biorefinery. Such "milking" technologies need further optimization of downstream processes to make it cost-effective. Similarly, for the upstream microalgal cultivation, biorefinery approach can combined with wastewater treatment/ bioremediation and GHG sequestration/ flue gas supple-mentation can be a promising approach to reduce the production cost. Therefore, with these advancements, an algal biorefinery can efficiently generate higher revenues. In this review, we discuss various upstream and downstream processing strategies and the potential possibilities, challenges and future perspectives of an algal biorefinery system has been discussed.