Investigation on the role of ·OH for BPA removal in coastal sediments: The important mediation of low reactivity Fe(II).

Bisphenol A (BPA) in seawater tends to be deposited in coastal sediments. However, its degradation under tidal oscillations has not been explored comprehensively. Hydroxyl radicals (·OH) can be generated through Fe cycling under redox oscillations, which have a strong oxidizing capacity. This study focused on the contribution of Fe-mediated production of ·OH in BPA degradation under darkness. The removal of BPA was investigated by reoxygenating six natural coastal sediments, and three redox cycles were applied to prove the sustainability of the process. The importance of low reactivity Fe(II) in the production of ·OH was investigated, specifically, Fe(II) with carbonate and Fe(II) within goethite, hematite and magnetite. The degradation efficiency of BPA during reoxygenation of sediments was 76.78-94.82%, and the contribution of ·OH ranged from 36.74% to 74.51%. The path coefficient of ·OH on BPA degradation reached 0.6985 and the indirect effect of low reactivity Fe(II) on BPA degradation by mediating ·OH production reached 0.5240 obtained via partial least squares path modeling (PLS-PM). This study emphasizes the importance of low reactivity Fe(II) in ·OH production and provides a new perspective for the role of tidal-induced ·OH on the fate of refractory organic pollutants under darkness.

Plant development alters the nitrogen cycle in subsurface flow constructed wetlands: Implications to the strategies for intensified treatment performance.

Plant development greatly influences the composition structure and functions of microbial community in constructed wetlands (CWs) via plant root activities. However, our knowledge of the effect of plant development on microbial nitrogen (N) cycle is poorly understood. Here, we investigated the N removal performance and microbial structure in subsurface flow CWs at three time points corresponding to distinct stages of plant development: seedling, mature and wilting. Overall, the water parameters were profoundly affected by plant development with the increased root activities including radial oxygen loss (ROL) and root exudates (REs). The removal efficiency of NH4+-N was significantly highest at the mature stage (p < 0.01), while the removal performance of NO3--N at the seedling stage. The highest relative abundances of nitrification- and anammox-related microbes (Nitrospira, Nitrosomonas, and Candidatus Brocadia, etc.) and functional genes (Amo, Hdh, and Hzs) were observed in CWs at the mature stage, which can be attributed to the enhanced intensity of ROL, creating micro-habitat with high DO concentration. On the other hand, the highest relative abundances of denitrification- and DNRA-related microbes (Petrimonas, Geobacter, and Pseudomonas, etc.) and functional genes (Nxr, Nir, and Nar, etc.) were observed in CWs at the seedling and wilting stages, which can be explained by the absence of ROL and biological denitrification inhibitor derived from REs. Results give insights into microbial N cycle in CWs with different stages of plant development. More importantly, a potential solution for intensified N removal via the combination of practical operation and natural regulation is proposed.

Recent advances in soil remediation technology for heavy metal contaminated sites: A critical review.

With the increasing development of industry and urbanization, heavy metal contaminated sites have become progressively conspicuous, particularly by unreasonable emissions from electroplating, nonferrous metals smelting, mine tailing, etc. In recent years, soil remediation technologies for heavy metal contaminated sites have developed rapidly. New and effective remediation technologies have emerged successively, and more successful practical applications have appeared. Therefore, systematical summarization of the current progress is essential. As a result, in this paper, some mainstream soil remediation technologies for heavy metal contaminated sites, including physical remediation (soil thermal desorption and soil replacement), bioremediation (phytoremediation and microbial remediation), chemical remediation (chemical leaching, chemical stabilization, electrokinetic remediation-permeable reactive barrier, and chemical oxidation/reduction), as well as various combined remediation are comprehensively reviewed. The influencing factors, advantages, disadvantages, remediation mechanism, and practical applications are also deeply discussed. Besides, the corresponding remediation strategies are put forward for the remediation of heavily polluted sites such as the chemical industry, smelting, and tailing areas. Overall, this review will be beneficial for the in-depth understanding and provide references for the reasonable selection and development of soil remediation technology for heavy metal contaminated sites.