Oxidative torrefaction of microalgae Chlorella sorokiniana: Process optimization by central composite design.

Microalgae are currently not viable as solid biofuels owing to their poor raw fuel properties. Torrefaction under oxidative media offers a cost-effective and energy-efficient process to address these drawbacks. A design of experiment was conducted using central composite design with three factors: temperature (200, 250, and 300 °C), time (10, 35, and 60 min), and O2 concentration (3, 12, and 21 vol%). The responses were solid yield, energy yield, higher heating value, and onset temperatures at 50% and 90% carbon conversion determined from thermogravimetric analysis. Temperature and time significantly affected all responses, while O2 concentration only affected higher heating value, energy yield and thermodegradation temperature at 90% conversion. Oxidative torrefaction of microalgae is recommended to be conducted at 200 °C, 10.6 min, 12% O2 where the energy yield and enhancement factor are 98.73% and 1.08, respectively. It is also more reactive under an air environment compared to inert torrefaction conditions.

COVID-19 and industrial waste mitigation via thermochemical technologies towards a circular economy: A state-of-the-art review.

The increasing awareness of waste circular economy has motivated valorization strategies for minimizing resource consumption and waste production in the private sector. With the rise of various industrial wastes and with the emergence of COVID-19 wastes, a sustainable approach is needed to mitigate the growing concern about wastes. Thermochemical treatment technologies in the form of direct combustion, torrefaction, pyrolysis, and gasification have been identified to have vital roles in the value-creation of various waste streams. Moreover, the alignment of thermochemical processes for waste mitigation concerning the circular economy framework needs to be established. Accordingly, a comprehensive review of the different thermochemical treatment options for industrial and the novel COVID-19 medical wastes streams is conducted in this study. This review focuses on highlighting the instrumental role of thermochemical conversion platforms in achieving a circular economy in the industrial sector. Various strategies in waste mitigation through various thermochemical processes such as management, recovery, reduction, and treatment are discussed. The results show that thermochemical technologies are beneficial in addressing the sustainability concerns on mitigating wastes from the industrial sector and wastes brought by the COVID-19 pandemic. This also includes the current issues faced as well as future perspectives of the thermochemical conversion technologies.

Biorefineries in circular bioeconomy: A comprehensive review.

Biorefinery is a sustainable means of generating multiple bioenergy products from various biomass feedstocks through the incorporation of relevant conversion technologies. With the increased attention of circular economy in the past half-decade with the emphasis of holistically addressing economic, environmental, and social aspects of the industrial-sector, biorefinery acts as a strategic mechanism for the realization of a circular bioeconomy. This study presents a comprehensive review of different biorefinery models used for various biomass feedstocks such as lignocelluloses, algae, and numerous waste-types. The review focuses on how biorefinery is instrumental in the transition of various biomass-based industries in a circular bioeconomy. The results reveal that the social-economic aspect of the industrial sector has a major influence on the full adoption of biorefineries in circular bioeconomy. Biomass wastes have played a major role in the implementation of biorefinery in circular bioeconomy. The current challenges are also presented along with future perspectives.