Pyrogenic Black Carbon Suppresses Microbial Methane Production by Serving as a Terminal Electron Acceptor.

Methane (CH4) is the second most important greenhouse gas, 27 times as potent as CO2 and responsible for >30% of the current anthropogenic warming. Globally, more than half of CH4 is produced microbially through methanogenesis. Pyrogenic black carbon possesses a considerable electron storage capacity (ESC) and can be an electron donor or acceptor for abiotic and microbial redox transformation. Using wood-derived biochar as a model black carbon, we demonstrated that air-oxidized black carbon served as an electron acceptor to support anaerobic oxidation of organic substrates, thereby suppressing CH4 production. Black carbon-respiring bacteria were immediately active and outcompeted methanogens. Significant CH4 did not form until the bioavailable electron-accepting capacity of the biochar was exhausted. An experiment with labeled acetate (13CH3COO-) yielded 1:1 13CH4 and 12CO2 without biochar and predominantly 13CO2 with biochar, indicating that biochar enabled anaerobic acetate oxidation at the expense of methanogenesis. Methanogens were enriched following acetate fermentation but only in the absence of biochar. The electron balance shows that approximately half (∼2.4 mmol/g) of biochar's ESC was utilized by the culture, corresponding to the portion of the ESC > +0.173 V (vs SHE). These results provide a mechanistic basis for quantifying the climate impact of black carbon and developing ESC-based applications to reduce CH4 emissions from biogenic sources.

GATR: A Road Network Traffic Violation Prediction Method Based on Graph Attention Network.

Prediction of traffic violations plays a key role in transportation safety. Combining with deep learning to predict traffic violations has become a new development trend. However, existing methods are based on regular spatial grids which leads to a fuzzy spatial expression and ignores the strong correlation between traffic violations and road network. A spatial topological graph can express the spatiotemporal correlation more accurately and then improve the accuracy of traffic violation prediction. Therefore, we propose a GATR (graph attention network based on road network) model to predict the spatiotemporal distribution of traffic violations, which adopts a graph attention network model combined with historical traffic violation features, external environmental features, and urban functional features. Experiments show that the GATR model can express the spatiotemporal distribution pattern of traffic violations more clearly and has higher prediction accuracy (RMSE = 1.7078) than Conv-LSTM (RMSE = 1.9180). The verification of the GATR model based on GNN Explainer shows the subgraph of the road network and the influence degree of features, which proves GATR is reasonable. GATR can provide an important reference for prevention and control of traffic violations and improve traffic safety.

Temporal-spatial analysis of crop residue burning in China and its impact on aerosol pollution.

China has performed crop residue burning (CRB) for a long time and has suffered from resultant environmental pollution. High temporal resolution has not been fully discussed in attempts to address the temporal and spatial impact of CRB in China on air quality. Our study used the MOD14A1 product of the MODerate resolution Imaging Spectrometer (MODIS) to extract the daily CRB for China during the period from 2014 to 2016, and the daily aerosol optical depth (AOD) provided by MODIS Collection 6 was obtained to simultaneously reflect the air pollution. First, the study area was classified into five subregions. A temporal analysis was conducted on the daily variation in the number of CRB events and the regional mean value of AOD, the spatial contribution ratio of CRB on aerosol pollution was then calculated, and finally, a temporal and spatial Pearson correlation was calculated to find the spatially varying relationship between CRB and aerosol. The results suggest the following: (1) CRB possesses seasonal characteristics that are associated with the harvest time or sowing time of major crops in the region. (2) The impact of CRB on aerosol was delayed by 1-6 days. (3) High contribution ratios (70%-90%) occurred in northeast China on a large scale; even when the impact of the CRB on aerosol pollution in the Huang-Huai-Hai river basin occurred on a large scale, the value was merely approximately 30%. Relatively low contributions of CRB have been found in other places, whereas the contribution of CRB was severe in some places with high-density populations. (4) Temporal-spatial correlation provided an accurate index to reflect the correlation of CRB and aerosol in a specific location, which suggests that, in places with large scale and dense CRB, CRB tends to have a high positive correlation with aerosol pollution for each day.

The adsorption characteristics of fluoride on commercial activated carbon treated with quaternary ammonium salts (Quats).

Commercial activated carbon was treated with six quaternary ammonium salts (Quats), namely, hexyltrimethylammonium (HTMA), octyltrimethylammonium (OTMA), decyltrimethylammonium (DCTMA), dodecyltrimethylammonium (DDTMA), Tetradecyltrimethylammonium (TDTMA), and hexadecyltrimethylammoium (HDTMA) as to enhance the fluoride adsorption capacity. In batch mode experiments, fluoride adsorption onto the Quats-treated activated carbon decreased dramatically with increase in solution pH. Fluoride removal by the Quats-treated activated carbons was closely related to the Quats chain length at less-than critical micelle concentration (CMC). Multi-site adsorption isotherm described fluoride adsorption characteristics well. Results showed that activated carbon treated with DDTMA exhibited the best fluoride adsorption density among all Quats investigated. DDTMA-treated activated carbons exhibited two-fold increase in the fluoride adsorption capacity compared to the untreated activated carbon. Results of regeneration, by alkaline desorption and/or Quats re-loading, showed fluoride-laden activated carbons have high reusability. DDTMA increased the positive surface charge of the activated carbon that enhanced fluoride adsorption. DDTMA-treated activated carbon was promising for fluoride removal from water with much enhanced removal capacity.

Highly efficient arsenic removal using a composite of ultrafine magnetite nanoparticles interlinked by silane coupling agents.

Arsenic (As) contamination in groundwater is a great environmental health concern and is often the result of contact between groundwater and arsenic-containing rocks or sediments and from variation of pH and redox potentials in the subsurface. In the past decade, magnetite nanoparticles (MNPs) have been shown to have high adsorption activity towards As. Alerted by the reported cytotoxicity of 5­12 nm MNP, we studied the adsorption behavior of 1.15 nm MNP and a MNP composite (MNPC), MNPs interlinked by silane coupling agents. With an initial concentration of As at 25 mg L(-1), MNPs exhibited high adsorption capacity for As(V) and As (III), 206.9 mg·g(-1) and 168.6 mg·g(-1) under anaerobic conditions, respectively, and 109.9 mg·g(-1) and 108.6 mg·g(-1) under aerobic conditions, respectively. Under aerobic conditions, MNPC achieved even higher adsorption capacity than MNP, 165.1 mg·g(-1) on As(V) and 157.9 mg·mg(-1) on As(III). For As(V) at 50 mg L(-1), MNPC achieved an adsorption capacity as high as 341.8 mg·g(-1), the highest in the literature. A kinetic study indicated that this adsorption reaction can reach equilibrium within 15 min and the rate constant of As(V) is about 1.9 times higher than that of As(III). These results suggested that MNPC can serve as a highly effective adsorbent for fast removal of As.