Solar technology‒closed loop synergy facilitates low-carbon circular bioeconomy in microalgal wastewater treatment

Abstract The circular bioeconomy framework addresses the global transition toward resource-efficient and low-carbon economies. The use of microalgae in sustainable circular bioeconomy largely suffers from energy consumption and underutilization of residual biomass, leading to greenhouse gas (GHG) emissions. This analysis-based perspective reveals that closed loop microalgal wastewater systems reduce GHG emissions by >50% and enhance valorization of residual biomass for value-added products compared to open loop approach. Integrating solar technologies in closed loop system further reduces GHG emissions by 99% and aligns with 11 UN sustainable development goals, making it a suitable model for a zero-waste and low-carbon circular bioeconomy

Sustainability Evaluation of Immobilized Acid-Adapted Microalgal Technology in Acid Mine Drainage Remediation following Emergy and Carbon Footprint Analysis

Sustainability evaluation of wastewater treatment helps to reduce greenhouse gas emissions, as it emphasizes the development of green technologies and optimum resource use rather than the end-of-pipe treatment. The conventional approaches for treating acid mine drainages (AMDs) are efficient; however, they need enormous amounts of energy, making them less sustainable and causing greater environmental concern. We recently demonstrated the potential of immobilized acid-adapted microalgal technology for AMD remediation. Here, this novel approach has been evaluated following emergy and carbon footprint analysis for its sustainability in AMD treatment. Our results showed that imported energy inputs contributed significantly (>90%) to the overall emergy and were much lower than in passive and active treatment systems. The microalgal treatment required 2–15 times more renewable inputs than the other two treatment systems. Additionally, the emergy indices indicated higher environmental loading ratio and lower per cent renewability, suggesting the need for adequate renewable inputs in the immobilized microalgal system. The emergy yield ratio for biodiesel production from the microalgal biomass after AMD treatment was >1.0, which indicates a better emergy return on total emergy spent. Based on greenhouse gas emissions, carbon footprint analysis (CFA), was performed using default emission factors, in accordance with the IPCC standards and the National Greenhouse Energy Reporting (NGER) program of Australia. Interestingly, CFA of acid-adapted microalgal technology revealed significant greenhouse gas emissions due to usage of various construction materials as per IPCC, while SCOPE 2 emissions from purchased electricity were evident as per NGER. Our findings indicate that the immobilized microalgal technology is highly sustainable in AMD treatment, and its potential could be realized further by including solar energy into the overall treatment system

Emergy Analysis and Life Cycle Assessment for Evaluating the Sustainability of Solar-Integrated Ecotechnologies in Winery Wastewater Treatment

Innovative approaches in sustainable wastewater management are vital in addressing climate change. This study introduces a novel assessment of solar-integrated ecotechnologies, focusing on the constructed wetland (CW) and microalgae-based systems, viz., high-rate algal pond (HRAP) and photobioreactor (PBR), for the treatment of winery wastewater. Utilizing Emergy analysis and life cycle assessment (LCA), we comprehensively compared these technologies in terms of environmental impact, resource recovery efficiency, and circular economy integration. Our Emergy analysis of the HRAP revealed a substantial reliance on renewable inputs (94%) and its lower nonrenewable resource consumption compared to the CW system. The Emergy sustainability index initially indicated a preference for the CW system (42.93 sej year–1; sej = solar emjoule), but deeper analysis showed greater sustainability in the HRAP (341 sej year–1) and PBR (118 sej year–1). LCA results further revealed that PBR systems had a significant land-use footprint, impacting other environmental indices such as photochemical ozone formation and freshwater eutrophication. Additionally, the HRAP and PBR demonstrated a marked reduction in greenhouse gas emissions (−24800 and −23700 kg of CO2-eq, respectively) compared to the CW system (320 kg of CO2-eq). Life cycle cost analysis underscored the economic viability of these systems, with Scenario 3 (PBR) emerging as the most economically sustainable, exhibiting the highest internal rate of return (IRR) at 21.11% and a positive net present value after 20 years. Conversely, Scenario 1 (CW system), with its significant initial investment of AU$741220, showed no IRR due to the absence of revenue generation. Importantly, our study introduces circularity index scores as a novel element, revealing that the HRAP and PBR effectively incorporate circularity measures across various impact categories. These measures had moderate impacts, as indicated by scores close to but not exceeding 0.10, whereas the CW system showed no significant improvement, highlighting the need for more robust circularity strategies. Overall, our integrated framework provides a holistic view of the environmental impact and economic aspects, emphasizing the potential of solar-integrated microalgal systems in promoting circular (bio)economy practices and sustainable environmental management in the viticulture sector

Kernel-Based Biodiesel Production from Non-Edible Oil Seeds: Techniques, Optimization, and Environmental Implications

Biodiesel represents a renewable alternative to conventional diesel, offering comparable potential. This paper delves into the production of biodiesel from non-edible oil seeds, emphasizing kernel-based feedstocks for their sustainable qualities. We discuss the critical stages of kernel separation and degumming, offering an in-depth examination of seed distribution, attributes, pretreatment, and oil extraction methodologies. Additionally, the paper considers the status of life cycle assessment (LCA) associated with biodiesel. Furthermore, it outlines the necessary steps toward sustainable biodiesel production and underscores the importance of integrating a sustainable circular bioeconomy in biodiesel synthesis

Statistical analysis on stress induced lipid accumulation along with the major cell components of Chlorella sp

Abstract: A sequential optimization based on statistical design was employed to optimize the different stress conditions of autotrophic, heterotrophic and mixotrophic levels for the enrichment of lipid in fresh water algae Chlorella sp. The selected individual parameters such as initial pH level, glucose concentration and KNO 3 concentration of the medium were optimized by the central composite design under response surface methodology. The maximum lipid content of 49.8% was achieved at the mixotrophic growth condition at 5 g/L of glucose concentration, 3 g/L of KNO 3 concentration and pH 7.6 amidst the considered different growth conditions such as autotrophic, heterotrophic and mixotrophic levels comprising along with that of the different individual stress parameters. Similarly maximum protein and chlorophyll yields were achieved at the mixotrophic level with high nitrogen content