Preparation of N-doped cellulose-based hydrothermal carbon using a two-step hydrothermal induction assembly method for the efficient removal of Cr(VI) from wastewater.

Cr(VI) pollution is a growing problem that causes the deterioration of the environment and human health. We report the development of an effective adsorbent for the removal of Cr(VI) from wastewater. N-doped cellulose-based hydrothermal carbon (N-CHC) was prepared via a two-step hydrothermal method. The morphology and structural properties of N-CHC were investigated by various techniques. N-CHC has many O and N groups, which are suitable for Cr(VI) adsorption and reduction. Intermittent adsorption experiments showed that N-CHC had an adsorption capacity of 151.05 mg/g for Cr(VI) at pH 2, indicating excellent adsorption performance. Kinetic and thermodynamic analyses indicates that the adsorption of Cr(VI) on N-CHC follows a monolayer uniform adsorption process, which is a spontaneous endothermic process dominated by chemical interaction and limited by diffusion within particles. In a multi-ion system (Pb2+, Cd2+, Mn7+, Cl-, and SO42-), the selectivity of N-CHC toward Cr(VI) was 82.62%. In addition, N-CHC demonstrated excellent reuse performance over seven adsorption-desorption cycles; the Cr(VI) removal rate of N-CHC in 5-20 mg/L wastewater was >99.87%, confirming the potential of N-CHC for large-scale applications. CN/C-OR, pyridinic-N, and pyrrolic-N were found to play a critical role in the adsorption process. This study provides a new technology for Cr(VI) pollution control that could be utilized in large-scale production and other environmental applications.

Coupling of soil methane emissions at different depths under typical coastal wetland vegetation types.

As an important source of atmospheric methane, methane emissions from coastal wetlands are affected by many factors. However, the methane emission process and interrelated coupling mechanisms in coastal wetland soils of a variety of environments remain unclear owing to complex interactions between intensified anthropogenic activities and climate change in recent years. In this study, we investigated methane cycling processes and the response mechanisms of environmental and microbial factors in soils at different depths under four typical coastal wetland vegetation types of the Yellow River Delta, China, using laboratory culture and molecular biology techniques. Our results show that methane generation pathways differed among the different soil layers, and that the methane emission process has a special response to soil N compounds (NO3-, NH4+). We found that nitrogen can indirectly affect methane emission by impacting key physicochemical properties (pH, oxidation reduction potential, etc.) and some functional communities (mcrA, ANME-2d, sulfate-reducing bacteria (SRB), narG, nosZII). Methane production processes in shallow soils compete closely with sulfate reduction processes, while methane emissions facilitated in deeper soils due to denitrification processes. We believe that our results provide a reference for future research and wetland management practices that seek to mitigate the global greenhouse effect and climate change.

Soil nitrogen content and key functional microorganisms influence the response of wetland anaerobic oxidation of methane to trivalent iron input.

Trivalent iron (Fe3+)-dependent anaerobic oxidation of methane (Fe-AOM), which is mediated by metal-reducing bacteria, is widely recognized as a major sink for the greenhouse gas methane (CH4), and is a key driver of the carbon (C) biogeochemical cycle. However, the effect of Fe3+ addition on AOM in the present investigation is still ambiguous, and the mechanism is vague. In this study, we investigated the mechanism of changes in AOM response to Fe3+ input at different wetlands by using laboratory incubation methods combined with molecular biology techniques. Results indicated that Fe3+ input did not always lead to promoted AOM rates, which may be mediated by complex environmental factors, while lower soil total nitrogen (TN) had a positive effect on the response of AOM subjected to Fe3+ input. Notably, the promoted response of AOM was regulated by higher soil microbial diversity, of which the Shannon index was a key indicator leading to variation in the AOM response. Additionally, several biomarkers, including Planctomycetota and Burkholderiaceae, were key microorganisms responsible for alterations in AOM response. Our results suggest that the capacity of Fe3+ cycling-mediated AOM may gradually decrease in light of increasing anthropogenic N and Fe inputs to global estuarine wetlands, while its reaction processes will become more complex and more strongly coupled with multiple environmental factors. This finding contributes to the enhanced understanding and prediction of the wetland CH4-related C with Fe cycles, as well as provides theoretical support for the underlying mechanisms.

Soil nitrogen substances and denitrifying communities regulate the anaerobic oxidation of methane in wetlands of Yellow River Delta, China.

Anaerobic oxidation of methane (AOM) in wetland soils is widely recognized as a key sink for the greenhouse gas methane (CH4). The occurrence of this reaction is influenced by several factors, but the exact process and related mechanism of this reaction remain unclear, due to the complex interactions between multiple influencing factors in nature. Therefore, we investigated how environmental and microbial factors affect AOM in wetlands using laboratory incubation methods combined with molecular biology techniques. The results showed that wetland AOM was associated with a variety of environmental factors and microbial factors. The environmental factors include such as vegetation, depth, hydrogen ion concentration (pH), oxidation-reduction potential (ORP), electrical conductivity (EC), total nitrogen (TN), nitrate (NO3-), sulfate (SO42-), and nitrous oxide (N2O) flux, among them, soil N substances (TN, NO3-, N2O) have essential regulatory roles in the AOM process, while NO3- and N2O may be the key electron acceptors driving the AOM process under the coexistence of multiple electron acceptors. Moreover, denitrification communities (narG, nirS, nirK, nosZI, nosZII) and anaerobic methanotrophic (ANME-2d) were identified as important functional microorganisms affecting the AOM process, which is largely regulated by the former. In the environmental context of growing global anthropogenic N inputs to wetlands, these findings imply that N cycle-mediated AOM processes are a more important CH4 sink for controlling global climate change. This studying contributes to the knowledge and prediction of wetland CH4 biogeochemical cycling and provides a microbial ecology viewpoint on the AOM response to global environmental change.