Study on the factors of hydrogen sulfide production from lignite bacterial sulfate reduction based on response surface method.

Bacterial sulfate reduction (BSR) is one of the key factors leading to the anomalous accumulation of hydrogen sulphide in coal mines. Environmental factors such as temperature and pH play a crucial role in the metabolism and degradation of coal by sulfate-reducing bacteria (SRB). In this study, coal samples were selected from Shengli Coal Mine, and SRB strains were isolated and purified from mine water using a dilution spread-plate anaerobic cultivation method. Based on single-factor experiments and response surface methodology (RSM), the impact of temperature, pH, oxidation-reduction potential (ORP), chemical oxygen demand to sulfate ratio (COD/SO42-) on the generation of hydrogen sulphide during brown coal BSR was analyzed. The results showed that the anaerobic degradation of coal by SRB was inhibited by either too high or too low a temperature to produce hydrogen sulfide, and the greatest production of hydrogen sulfide occurred at a temperature of about 30 °C; The greatest production of hydrogen sulfide occurred at an initial ambient pH of 7.5; COD/SO42- ratio of around 2.0 is most conducive to hydrogen sulphide generation; the lower ORP value is more favorable for hydrogen sulfide generation. The optimal conditions obtained by RSM were: temperature of 30.37 °C, pH of 7.64 and COD/SO42- of 1.96. Under these conditions, the hydrogen sulfide concentration was 56.79 mg/L, the pH value was 8.40, the ORP value was -274 mV, and the SO42- utilization rate was 58.04%. The RSM results showed that temperature, ambient pH and COD/SO42- had a significant effect on hydrogen sulfide production, and the degree of effect was: ambient pH > temperature > COD/SO42-.

Study on emergency evacuation in underground urban complexes.

With progressive urbanization and the development and utilization of urban underground space, underground urban complexes (UUCs) have been increasingly used. UUCs have brought much convenience to people's lives. However, due to their enclosed nature and complexity, it has been an urgent issue to avoid (or reduce) casualties and allow rapid and safe evacuation of people during an emergency. In this study, the evacuation simulation software Pathfinder was used. Based on the steering model, the variation of the total evacuation time and pedestrian flow at main exits with different simulated evacuation measures, congestion at key nodes and people's path selection were compared and analyzed. Then, the critical locations in the spatial layout of UUCs that were prone to evacuation bottleneck effects were focused on and determined. The evacuation effectiveness of UUCs in an emergency was studied to investigate the problems of emergency evacuation in UUCs. It is found that in UUCs, the bottleneck effects were likely to occur at stairway entrances and exits as well as supermarket checkout counters and caused severe congestion. These locations should be focused on during emergency evacuation. For key locations prone to evacuation bottlenecks, increasing the width of exits or setting up auxiliary evacuation channels could be an effective measure to improve evacuation efficiency. In addition, formulating rational evacuation rules can be a favorable measure for emergency evacuation. However, during the evacuation, the herd mentality in people has an uncertain (positive or negative) impact on evacuation effectiveness. Setting up diversion walls may improve evacuation efficiency and reduce congestion to a certain extent, while evacuation confusion and chaos are prone to occur after diversion. These findings in this study have significant implications for improving the emergency management of UUCs.

Research Advances of Prevention and Control of Hydrogen Sulfide in Coal Mines.

Sudden emission and casualty accidents caused by abnormal enrichment of hydrogen sulfide (H2S) in coal mines are becoming frequent increasingly, causing major casualties and environmental pollution. Scholars in various countries have developed various measuring devices for hydrogen sulfide content in coal and rock formations and their calculation methods. The existing prevention and control technologies of H2S in coal mines were summarized in various countries. According to the distribution characteristics, occurrence modes, and emission forms of H2S in coal mines, the prevention and control technologies of H2S in coal-bearing strata, airflow in tunnel, and underground water body are mainly introduced. Analyzed the effects of different ventilation systems on prevention and control of H2S, which include conventional ventilation system, partial homotropal ventilation system, and full homotropal ventilation system. The methods used mainly include neutralization by injecting alkalizer through drilling in coal seams with high pressure, spraying alkalizer in tunnel, attenuation by increasing wind amount, changing the ventilation method, pumping, dredging, and blocking the water that contains H2S as well as comprehensive prevention and control method. The basic agents adopted mainly include sodium carbonate (the mass percentage concentration is about 0.5% ~ 3.0%) and sodium bicarbonate solution, and some basic solution is added by an additive, such as surfactant, Fenton reagent, sodium dodecyl benzene sulfonate, sodium hypochlorite, or chloramine-T. The treatment effect and the main problems of each prevention and control technology are analyzed, and a comprehensive method of prevention and control techniques of H2S in coal mines is proposed. According to current technological level as well as the cost, the effective prevention and control techniques of H2S should take the occurrence, distribution, and emission forms of H2S in coal mines as well as the content into consideration.