Sustainable remediation of Cr(VI)-contaminated soil by soil washing and subsequent recovery of washing agents using biochar supported nanoscale zero-valent iron.

Soil contamination by Cr(VI) has attracted widespread attention globally in recent years, but it remains a significant challenge in developing an environmentally friendly and eco-sustainable technique for the disposal of Cr(VI)-contaminated soil. Herein, a sustainable cyclic soil washing system for Cr(VI)-polluted soil remediation and the recovery of washing agents using biochar supported nanoscale zero-valent iron (nZVI-BC) was established. Citric acid (CA) was initially screened to desorb Cr(VI) from contaminated soil, mobilizing Cr from the highly bioaccessible fractions. The nZVI-BC exhibited superior properties for Cr(VI) and Cr(total) removal from spent effluent, allowing effective recovery of the washing agents. The elimination mechanism of Cr(total) by nZVI-BC involved the coordinated actions of electrostatic adsorption, reduction, and co-precipitation. The contributions to Cr(VI) reduction by Fe0, surface-bound Fe(II), and soluble Fe(II) were 0.6 %, 39.8 %, and 59.6 %, respectively. Meanwhile, CA favored the activity of surface-bound Fe(II) and Fe0 in nZVI-BC, enhancing the production of soluble Fe(II) to strengthen Cr(VI) removal. Finally, the recovered washing agent was proven to be reused three times. This study showcases that the combined soil washing using biodegradable chelant CA and effluent treatment by nZVI-BC could be a sustainable and promising strategy for Cr(VI)-contaminated soil remediation.

An interregional environmental assessment framework: revisiting environmental Kuznets curve in China.

Achieving the national emission reduction targets requires joint efforts of all jurisdictions, whose sustainable development is affected by complex economic and environmental interactions among regions. An interregional environmental assessment (IREA) framework is constructed for China using multiregional input-output techniques to unravel the carbon emission connections behind interregional economic activities. Then, consumption-based emission accounting is applied in sustainability assessment, in comparison with production-based environmental Kuznets curve (EKC) tests to examine the role of regional connections in shaping EKC. Empirical results expose significant asymmetric CO2 transfer among regions in China, where the Central and Western regions have become CO2 haven for the Eastern region. EKC is valid at the national level and manifests marked regional differences between production- and consumption-based curves. The pollution haven effect alters the EKC curve by expediting the emission peak in the developed Eastern region while delaying it in the developing Western region. Thus, revisiting EKCs in the IREA framework reveals that ignoring interregional connections would lead to misleading results. Only when both production- and consumption-based EKCs transcend their turning points can we claim that environmental governance has ushered in a new era of sustainable development.

Impact of low-carbon city pilot policies on urban green innovation from the perspective of spatial and temporal heterogeneity.

The low-carbon city pilot policy (LCPP) in China is an active response to climate change, with cities serving as the main agents of action. Enhancing green innovation at a city-wide level can effectively support the promotion of pilot cities' efforts towards sustainable growth. Using panel data from 204 prefectures collected from 2005 to 2019, we adopted the time-varying difference-in-differences (DID) model and the spatial Durbin model combined with time-varying DID (SDM-DID) to determine the impact of the LCPP on urban green innovation and its temporal and spatial heterogeneity. Empirical findings showed that (1) LCPP had a significant positive impact on urban green innovation, and green invention patents had a greater green innovation effect than green utility model patents. (2) Heterogeneity analysis revealed that in terms of geographical location, the pilot policy was more effective in promoting urban green innovation in the eastern and central regions in comparison to the western region. At the city level, the pilot policy had a greater impact on green innovation in first- and second-tier cities. With regard to city scale, large-scale cities showed a greater impact on green innovation than small- and medium-sized cities. (3) Mechanistic testing revealed that LCPPs stimulated urban green innovation by talent aggregation, increasing government support for innovation, and public participation; but the mechanism for alleviating financing constraints has yet to be effectively validated. (4) The LCPP showed a spatial spillover effect, whereby one city's low-carbon governance yielded institutional dividends for neighboring cities both geographically and economically, and the impact was more pronounced in those cities that were not resource-based. This study presents empirical evidence at the urban and spatial levels, supporting the comprehensive promotion of low-carbon city construction and development in China.