Effects of chemical oxygen demand (COD)/N ratios on pollutants removal in the subsurface wastewater infiltration systems with/without intermittent aeration.

The matrix oxidation reduction potential level, organic pollutants and nitrogen removal performances of eight subsurface wastewater infiltration systems (SWISs) (four with intermittent aeration, four without intermittent aeration) fed with influent chemical oxygen demand (COD)/N ratio of 3, 6, 12 and 18 were investigated. Nitrification of non-aerated SWISs was poor due to oxygen deficiency while higher COD/N ratios further led to lower COD and nitrogen removal rate. Intermittent aeration achieved almost complete nitrification, which successfully created aerobic conditions in the depth of 50 cm and did not change anoxic or anaerobic conditions in the depth of 80 and 110 cm. The sufficient carbon source in high COD/N ratio influent greatly promoted denitrification in SWISs with intermittent aeration. High average removal rates of COD (95.68%), ammonia nitrogen (NH4(+)-N) (99.32%) and total nitrogen (TN) (89.65%) were obtained with influent COD/N ratio of 12 in aerated SWISs. The results suggest that intermittent aeration was a reliable option to achieve high nitrogen removal in SWISs, especially with high COD/N ratio wastewater.

Terahertz spectra reconstructed using convolutional denoising autoencoder for identification of rice grains infested with Sitophilus oryzae at different growth stages.

Rice grains are often infected by Sitophilus oryzae due to improper storage, resulting in quality and quantity losses. The efficacy of terahertz time-domain spectroscopy (THz-TDS) technology in detecting Sitophilus oryzae at different stages of infestation in stored rice was employed in the current research. Terahertz (THz) spectra for rice grains infested by Sitophilus oryzae at different growth stages were acquired. Then, the convolutional denoising autoencoder (CDAE) was used to reconstruct THz spectra to reduce the noise-to-signal ratio. Finally, a random forest classification (RFC) model was developed to identify the infestation levels. Results showed that the RFC model based on the reconstructed second-order derivative spectrum with an accuracy of 84.78%, a specificity of 86.75%, a sensitivity of 86.36% and an F1-score of 85.87% performed better than the original first-order derivative THz spectrum with an accuracy of 89.13%, a specificity of 91.38%, a sensitivity of 88.18% and an F1-score of 89.16%. In addition, the convolutional layers inside the CDAE were visualized using feature maps to explain the improvement in results, illustrating that the CDAE can eliminate noise in the spectral data. Overall, THz spectra reconstructed with the CDAE provided a novel method for effective THz detection of infected grains.

Distinguishing pericarpium citri reticulatae of different origins using terahertz time-domain spectroscopy combined with convolutional neural networks.

The geographical indication of pericarpium citri reticulatae (PCR) is very important in grading the quality and price of PCRs. Therefore, terahertz time-domain spectroscopy (THz-TDS) technology combined with convolutional neural networks (CNN) was proposed to distinguish PCRs of different origins without damage in this study. The one-dimensional CNN (1D-CNN) model with an accuracy of 82.99% based on spectral data processed with SNV was established. The two-dimensional image features were transformed from unprocessed spectral data using the gramian angular field (GAF), the Markov transition field (MTF) and the recurrence plot (RP), which were used to build a two-dimensional CNN (2D-CNN) model with an accuracy of 78.33%. Further, the CNN models with different fusion methods were developed for fusing spectra data and image data. In addition, the adding spectra and images based on the CNN (Add-CNN) model with an accuracy of 86.17% performed better. Eventually, the Add-CNN model based on ten frequencies extracted using permutation importance (PI) achieved the identification of PCRs from different origins. Overall, the current study would provide a new method for identifying PCRs of different origins, which was expected to be used for the traceability of PCRs products.

Study on Reaction Sites of Active Structures in Coal Based on the ReaxFF Reactive Force Field.

To study the reaction paths and reaction mechanisms of the active structures in coal during the oxidation process, the oxygen-free pyrolysis and oxygen-containing combustion were simulated for nine active structures in coal based on the ReaxFF MD method. A separate simulation analysis of the active structure yielded that O2 inhibited the reaction of H1. As the branched chain grows, the reaction paths of C2 and Q2 follow the direction of the reaction of carboxyl and aldehyde groups to CO2 and CO. Considering the reaction rates and reaction process products of A1, B1, and B3 structures, it is obtained that O2 has the greatest contribution to the decomposition reaction of aliphatic hydrocarbon structures. This is due to the strong electron-absorbing property of O2 that attracts H radicals to generate HO2, which in turn affects the reaction path of the active structure. Tracing the reaction process reveals that OH and oxygen-containing radicals under oxygen-free conditions greatly influence the active structural reaction.

Division of coal spontaneous combustion stages and selection of indicator gases.

Investigating the division of coal spontaneous combustion stages and the selection of indicator gases is significant to the safe production of coal mines. In this study, the characteristic temperature of coal spontaneous combustion, the generation law of indicator gases, the combustion process, and the division of the combustion stages of coal samples taken from Hongqingliang (HQL) and Dayan (DY) mines were investigated using thermogravimetric analysis experiment, indicator gas detection experiment, and coal oxidation spontaneous combustion experiment. The results of the thermogravimetric analysis experiment showed that the pyrolysis temperatures of the HQL and DY coals were 115.76°C and 131.80°C, and the ignition temperatures were 337.74°C and 360.18°C, respectively. The indicator gas detection results showed that the first-appearance temperature of C2H4 was 85°C for the HQL and DY coals, whereas the first-appearance temperature of C2H6 varied: 115°C for the HQL coal and 130°C for the DY coal. The first-appearance temperatures of C2H2 were 180°C and 195°C for the HQL and DY coals, respectively. The experiments on coal oxidation spontaneous combustion showed that the spontaneous combustion period of the HQL and DY coals were 35.45 and 42.3 days, respectively. The heating process during combustion could be divided into four stages: a latent period of spontaneous combustion, a slow spontaneous heating period, an accelerated spontaneous heating period, and a period of combustion. The critical temperature of each stage showed a good correlation with the incipient temperature of the indicator gases, namely C2H2, C2H4, and C2H6, and the appearance of the above gases can be used to characterize the degree of spontaneous combustion of coal.

Regularity of Mine Gas Flow Disaster Induced by Gas Natural Ventilation Pressure after Coal and Gas Outbursts.

The gas pressure generated during a coal and gas outburst is an important factor affecting the stability of mine ventilation systems. The gas released from an outburst flows and diffuses in the mine, leading to an uneven distribution of the air in the mine ventilation system and the formation of natural wind pressure. Because of the effect of the gas pressure, the mine ventilation system becomes disordered, leading to a counter flow in the roadway. This increases the complexity of the gas movement, extends the influence range of the gas, enlarges the disaster area in the mine, and exacerbates the destructiveness. In this study, the TF1M simulation program was applied to simulate a coal and gas outburst accident that occurred in the 1747 heading roadway of the Sizhuang Coal Mine, in a bid to reproduce the entire process of the diffusion flow of the counter current and outburst gas in the mine roadway. Moreover, the dynamic influence of the gas pressure on the entire ventilation network was analyzed. An experimental device was set up to test the relationship between the natural wind pressure and the height difference of the roadway and density of the gas flow, and the formation and mechanism of the natural wind pressure were explored. By analyzing the experimental and numerical results, the variation law of the air flow and the law of gas movement under the influence of gas pressure were summarized. The movement law and influencing factors of the gas during the mine outburst period were studied, the influence range of the gas was determined, the distribution law of the gas concentration after the outburst was obtained, and further expansion of the gas was prevented. This study has theoretical and practical significance in enhancing our understanding of the development process of mine gas disasters, which can help establish effective emergency response strategies and reasonably implement postdisaster relief measures.