Realization process of microalgal biorefinery: The optional approach toward carbon net-zero emission

Increasing carbon dioxide (CO2) emission has already become a dire threat to the human race and Earth's ecology. Microalgae are recommended to be engineered as CO2 fixers in biorefinery, which play crucial roles in responding climate change and accelerating the transition to a sustainable future. This review sorted through each segment of microalgal biorefinery to explore the potential for its practical implementation and commercialization, offering valuable insights into research trends and identifies challenges that needed to be addressed in the development process. Firstly, the known mechanisms of microalgal photosynthetic CO2 fixation and the approaches for strain improvement were summarized. The significance of process regulation for strengthening fixation efficiency and augmenting competitiveness was emphasized, with a specific focus on CO2 and light optimization strategies. Thereafter, the massive potential of microalgal refineries for various bioresource production was discussed in detail, and the integration with contaminant reclamation was mentioned for economic and ecological benefits. Subsequently, economic and environmental impacts of microalgal biorefinery were evaluated via life cycle assessment (LCA) and techno-economic analysis (TEA) to lit up commercial feasibility. Finally, the current obstacles and future perspectives were discussed objectively to offer an impartial reference for future researchers and investors.

Valorization of CO2 to β-farnesene in Rhodobacter sphaeroides

The valorization of CO₂ into valuable products is a sustainable strategy to help overcome the climate crisis. In particular, biological conversion is attractive as it can produce long-chain hydrocarbons such as terpenoids. This study reports the high yield of β-farnesene production from CO₂ by expressing heterologous β-farnesene synthase (FS) into Rhodobacter sphaeroides. To increase the expression of FS, a strong active promoter and a ribosome binding site (RBS) were engineered. Moreover, β-farnesene production was improved further through the supply of exogenous antioxidants and additional nutrients. Finally, β-farnesene was produced from CO₂ at a titer of 44.53 mg/L and yield of 234.08 mg/g, values that were correspondingly 23 times and 46 times higher than those from the initial production of β-farnesene. Altogether, the results here suggest that the autotrophic production of β-farnesene can provide a starting point for achieving a circular carbon economy.

Perception of chemical recycling and its role in the transition towards a circular carbon economy: A case study in Germany

Chemical recycling (CR) is an emerging theme in waste management which has the potential to contribute to a low carbon, resource efficient and sustainable economy. In enabling the use of carbonaceous waste as secondary carbon feedstock to replace fossil resources for the production of organic chemicals, it could support efforts to transit carbon intensive industries from the linear to a circular carbon economy. This study investigated stakeholders' perception of CR as a multifaceted construct. Objective is to complement technological-economical-ecological evaluations of CR innovations, and inform socio-political discussions about its role in the transformation of carbon intensive and dependent industries. An exploratory case study approach consisting of a qualitative survey and a semi-structured workshop discussion is utilized to assess the perception of CR and its perceived role in the transformation of Germany's chemical and waste management industries. Findings enabled insights into how CR is understood, what are seen as desirable inputs and outputs, perceived advantages compared to conventional recycling and thermal treatment as well as obstacles to its implementation. Additionally, the outcomes revealed policy and regulatory needs which will have to be addressed in order to successfully implement CR as a complementary building block of sustainable waste management. Study findings thus provide valuable information and insights to support managerial decision-making as well as the development and prioritization of measures by policymakers to regulate the implementation of CR technologies.