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Additional file 4: Table S1.

Additional file 1: Table S1. Morphological database of the sporophyll units (dispersed) in this study. S2. The detailed calculation process about wing loading. S3. The detailed calculation process about wind dispersal.

On the basis of the four factors of spontaneous combustion of coal, the causes of such combustion in the tunnel fall of ground were comprehensively analyzed. The causes include the generation of float coal, influence of hot wind pressure on the laneway, and airflow dynamic pressure caused by sloping roadways. According to the characteristics of a fire that occurred in the intake airflow roadway of working face 12190 in the Geng Cun Coal Mine, a three-phase foam composed of mud, nitrogen, and water was used to extinguish the fire. The foam was injected into the fire zone through boreholes on the tunnel roof. Given the precise scheme and reliability of the technology, the fire was successfully extinguished. The specific technological process and parameters of the technology are discussed in detail. It is concluded that the three-phase foam is useful in preventing spontaneous combustion of coal in the tunnel fall of ground. It serves as a new method for preventing such phenomenon in extra-thick coal seam.

The gas explosions often occur under mine gas and spontaneous combustion coupling in coal mines. The coupling of mine gas and spontaneous combustion is a complex disaster, and the character of the disaster is not clear now. The paper primarily discussed the character of gas explosion under mine gas and spontaneous combustion coupling. The explosion concentration range of mixed gases including CH 4 and CO is studied. And the potential area and the course of explosion detonated by spontaneous combustion of coal is analyzed. When the spontaneous combustion of coal occurs, it can produce plenty of CO and fire-heating air pressure in the goaf. Experiments show that the upper limit of explosion concentration rises rapidly and the lower limit rises slowly with the increase of CO in the mixed gas of CH 4 and CO. The fire-heating air pressure results in continuous mix of the gases and heat convection under vortex action between the combustion zone and non-firing zone. Thus, gas explosion occurs. In order to prevent high-concentration gas in the goaf and spontaneous combustion which detonates gas explosion in the coal mine, three-phase foam with nitrogen is adopted to restrain gas explosion and reduce coal temperature.

In order to investigate the inhibition characteristics of green and environmentally friendly sand suspending thickener, we applied the self-designed Temperature Program Experiment System to test three different inhibiting substances, the calcium chloride, the soluble glass, and the sand suspending thicker, for comparison. Comparing the oxidation temperature curves of the primordial coal with the ones processed by inhibiting substances, we found that the temperatures of processed coals were all quite low and the temperature of the coal processed by sand suspending thickener the lowest. Therefore, the sand suspending thickener is the best material among the tested materials for fire-fighting in coal mine.

To enhance the efficiency and economy of mine fire control, the technology of threephase foam for preventing spontaneous combustion of coal in goaf is developed here. The producing flow of three-phase foam and main technical parameters are introduced briefly. Chemical dynamics equation was set up. According to controlling parameters in the equation: the reactant concentration of C and O2, the temperature (T) of coal and surroundings, the hole rate (e) of goaf, etc, the mechanism of three-phase foam for preventing spontaneous combustion of coal in goaf was studied. By the application of three-phase foam in workface N2703 of Daxing coal mine, which had been high temperature and fire point, the change on concentration of CO and O2 were contrasted in sampling gas and temperature in goaf. It had effectively prevented the fire. The result showed that the effect of three-phase foam for preventing spontaneous combustion of coal in goaf was excellent, and it is a new technology for mine fire prevention and with good prospect.

The feasibility of an inexpensive wastewater treatment system is evaluated in this study. An integrated biological pond system was operated for more than 3 years to purify the wastewater from a medium-sized city, Central China. The experiment was conducted in 3 phases with different treatment combinations for testing their purification efficiencies. The pond system was divided into 3 functional regions: influent purification, effluent upgrading and multi-utilization. These regions were further divided into several zones and subzones. Various kinds of aquatic organisms, including macrophytes, algae, microorganisms and zooplankton, were effectively cooperating in the wastewater treatment in this system. The system attained high reductions of BOD5, COD, TSS, TN, TP and other pollutants. The purification efficiencies of this system were higher than those of most traditional oxidation ponds or ordinary macrophyte ponds. The mutagenic effect and numbers of bacteria and viruses declined significantly during the process of purification. After the wastewater flowed through the upgrading zone, the concentrations of pollutants and algae evidently decreased. Plant harvesting did not yield dramatic effects on reductions of the main pollutants, though it did significantly affect the biomass productivity of the macrophytes. The effluent from this system could be utilized in irrigation and aquaculture. Some aquatic products were harvested from this system and some biomass was utilized for food, fertilizer, fodder and some other uses. The wastewater was reclaimed for various purposes.