Xiangfeng Huang

Amid the escalating challenges of global climate change, promoting the sustainable and low-carbon transformation of wastewater treatment systems has become a critical pathway toward achieving carbon neutrality and sustainable urban infrastructure development. However, existing low-carbon technologies for wastewater treatment still lack systematic and sustainability-oriented evaluation approaches, which constrains the scientific selection of technologies and the optimization of low-carbon transition pathways. In this study, a comprehensive inventory of 30 low-carbon technologies was established across five categories, including equipment energy saving, process improvement, intelligent control, energy recovery, and resource recycling. Based on three dimensions, namely carbon reduction potential, economic performance, and technology readiness level, a Carbon Reduction–Economy–Technology Coupling Index (CRETCI) was developed to enable systematic quantitative evaluation and sustainability-oriented assessment of low-carbon technologies in wastewater treatment systems. The analysis of carbon reduction potential indicated that process improvement technologies exhibited the highest average carbon reduction potential, reaching approximately 0.136 kg CO₂e/m³, demonstrating significant advantages in deep emission reduction. Economic analysis revealed that energy recovery technologies showed the best economic performance, with all marginal abatement costs being negative, indicating strong synergistic benefits between economic returns and carbon mitigation. The technological maturity assessment demonstrated that both intelligent control and energy recovery technologies achieved a Technology Readiness Level (TRL) of 9, indicating a well-established foundation for engineering application. The TCECI evaluation results showed that energy recovery technologies achieved the highest comprehensive score (0.71), significantly outperforming process improvement technologies (0.57). This finding suggests that the current low-carbon technology system for wastewater treatment is characterized by a structural trade-off between high carbon reduction potential and high technological maturity. Overall, this study establishes a multidimensional sustainability evaluation framework integrating environmental benefits, economic feasibility, and technological applicability, thereby providing important theoretical support and practical decision-making guidance for sustainable wastewater management, low-carbon technology selection, and carbon-neutral transition pathway optimization in the wastewater treatment sector.

Enhancing soil carbon sequestration is a pivotal strategy for mitigating global climate change. Integrating the “microbial carbon pump (MCP)” and “mineral carbon pump (MnCP)” frameworks is essential for a holistic understanding of soil organic carbon (SOC) stabilization. While biochar (BC) is a recognized carbon sequestration tool, the mechanistic pathways by which it mediates the synergy between these distinct carbon pumps remain elusive. This review synthesizes current advances to position BC as a critical “bridge” driving the coupled MCP–MnCP system. Beyond serving as recalcitrant carbon, BC strengthens the MCP by providing microbial habitats, optimizing community structure, and enhancing carbon use efficiency to promote necromass accumulation. Simultaneously, BC fortifies the MnCP via mechanisms including the formation of stable organo-mineral complexes through surface functional groups, the facilitation of microaggregate genesis, and the mediation of redox reactions. This bridging efficacy offers a novel theoretical framework for developing predictable, controllable soil carbon technologies. Furthermore, we explore the theoretical basis for integrating BC into the coupled MCP–MnCP system. Future research must prioritize cross-scale mechanistic dissection, advance the precision design of BC functionality, and incorporate its “dual carbon pump” enhancement effects into life cycle assessment frameworks to fully realize its potential in climate mitigation and sustainable agriculture.