控制稻田甲烷排放的农业管理措施研究

１９９０～１９９２年连续３ａ,对北京和南京具有代表性稻田进行了甲烷排放通量测定。结果表明,甲烷排放日变化规律受土壤理化性质、农业管理措施、气候变化等影响而变化,在下午１５:００～１８:００出现高峰值￣(１－６),甲烷排放季节变化规律在分蘖期和孕穗期两次出现高峰。采取不同的农业管理措施对稻田甲烷排放的影响显著:间歇灌溉对烤田后的稻田能降低甲烷排放又可增加水稻产量;南方地区垅作栽培有利于减少冬水田甲烷排放,北方地区旱种可减少甲烷排放;有机肥能促进甲烷排放,稻田分蘖期和孕穗期施用硫酸铵和尿素能抑制甲烷排放。      

不同农业管理方式对北京地区稻田甲烷排放的影响研究

1990年7月4日到9月28日,对北京朝阳区洼里乡的麦茬稻田甲烷排放进行了测定研究,取得了不同农业管理条件下的一些初步结果。其中按农民常规管理方式的麦茬稻田甲烷平均排放通量为17.5mg/(m2·h)。该值可代表北京地区一般麦茬稻田甲烷排放水平。实验表明,水稻田甲烷排放受到灌溉方式、施肥类型及用量、气温等多种因子的影响,其中农业管理措施的影响是显著的。在农民传统施肥方式下,采用间歇灌溉的方式,比传统的淹灌能有效地提高水稻产量并减少稻田甲烷的排放。      

硫酸盐还原作用对废水厌氧处理的影响

采用半连续流运行方式研究了硫酸盐还原作用对废水厌氧处理的影响。试验结果表明:当温度为35℃,pH为7.2～7.4时,进水COD/SO42-≥10,硫酸盐还原作用不致于对产甲烷菌产生严重抑制;进水COD/SO42-≥5,反应器能承受的COD负荷小于2.05kg/ (m3·d),超过这一负荷,反应器会发生严重抑制;进水COD/SO42-≥2,反应器能承受的COD负荷小于1.0kg/(m3·d)。进水COD/SO42-比值越小,反应器能承受的COD负荷越低。反应器污泥浓度高有利于硫酸盐废水的处理。      

An estimate of the contribution of outdoor concrete yards used by livestock to the UK inventories of ammonia, nitrous oxide and methane

Many farms have unroofed concrete yards used by livestock. These concrete yards have received little attention as sources of gaseous emissions. From 1997 to 1999 measurements were made of emissions of ammonia (NH₃), nitrous oxide (N₂O) and methane (CH₄) from 11 concrete yards used by livestock. A postal survey was carried out to assess the areas of yards on farms in England and Wales to enable the measurements to be scaled up to estimate national emissions. Using the results of this study NH₃-N emissions from farm concrete yards were calculated to be ca. 35×10³ t annually. This is 13% of the current estimated total NH₃-N emission from UK livestock. Concrete yards were an insignificant source of N₂O and CH₄ which were both <0.01% of current estimates of agricultural emissions.     

Responses of CH(4), CO(2) and N(2)O fluxes to increasing nitrogen deposition in alpine grassland of the Tianshan Mountains

To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH₄, CO₂ and N₂O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH₄ uptake, CO₂ and N₂O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO₂ and N₂O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO₂ and N₂O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO₂ and N₂O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers.     

Effect of concentration and ignition position on vented methane–air explosions

Experiments were conducted in a 1 m³ vessel with a top vent to investigate the effect of methane concentration and ignition position on pressure buildup and flame behavior. Three pressure peaks (p₁, p₂, and P_ext) and two types of pressure oscillations (Helmholtz and acoustic oscillations) were observed. The rupture of vent cover results in p₁ that is insensitive to methane concentration and ignition position. Owing to the interaction between acoustic wave and the flame, p₂ forms in the central and top ignition explosions when the methane–air mixture is near–stoichiometric. When the methane–air mixture is centrally ignited, p₂ first increases and then decreases with an increase in the methane concentration. The external explosion-induced P_ext is observed only in the bottom ignition explosions with an amplitude of several kilopascals. Under the current experimental conditions, flame–acoustic interaction leads to the most serious explosions in central ignition tests. Methane concentration and ignition position have little effect on the frequency of Helmholtz and acoustic oscillations; however, the Helmholtz oscillation lasts longer and first decreases and then increases as the methane concentration increases for top ignition cases. The ignition position significantly affects the Taylor instability of the flame front resulting from the Helmholtz oscillation.     

Solid waste characteristics and their relationship to gas production in tropical landfill

Solid waste characteristics and landfill gas emission rate in tropical landfill was investigated in this study. The experiment was conducted at a pilot landfill cell in Thailand where fresh and two-year-old wastes in the cell were characterized at various depths of 1.5, 3, 4.5 and 6 m. Incoming solid wastes to the landfill were mainly composed of plastic and foam (24.05%). Other major components were food wastes (16.8%) and paper (13.3%). The determination of material components in disposed wastes has shown that the major identifiable components in the wastes were plastic and foam which are resistant to biodegradation. The density of solid waste increased along the depth of the landfill from 240 kg m⁻³ at the top to 1,260 kg m⁻³ at the bottom. Reduction of volatile solids content in waste samples along the depth of landfill suggests that biodegradation of solid waste has taken place to a greater extent at the bottom of the landfill. Gas production rates obtained from anaerobic batch experiment were in agreement with field measurements showing that the rates increased along the depth of the landfill cell. They were found in range between 0.05 and 0.89 l kg⁻¹ volatile solids day⁻¹. Average emission rate of methane through the final cover soil layer was estimated as 23.95 g⁻²day⁻¹ and 1.17 g⁻²day⁻¹ during the dry and rainy seasons, respectively.     

Experimental and simulation studies on the influence of carbon monoxide on explosion characteristics of methane

In underground coal mining, methane explosions often can cause tremendous disasters. In the meantime, carbon monoxide (CO), generated during the process of coal oxidation, may appear in the air. Therefore, the explosion characteristics of the mixture of CH₄ and CO must be investigated to prevent gas explosion accidents in coal mines. We conducted experiments by using a 20-L nearly spherical gas explosion testing device. The software FLACS was used to simulate the explosion of the mixture of CH₄ and CO at various mixing concentrations, and the simulation results corresponded to experimental results. With the increase of CO concentration, both upper and lower explosive limits of CH₄ decreased. On the whole, the explosion characteristic parameters of CH₄ and the mixture are similar. When CH₄ concentration was below the stoichiometric concentration, the addition of CO could promote the intensity of gas explosion; oppositely, excessive CO would inhibit the gas explosion reaction. The inhibitory effects become more significant as the concentration of CH₄ increases.     

Suppression of different functional group modified powders on 9.5% CH4-air explosion and molecular simulation mechanism

Thiol and urea functionalized montmorillonite powders were successfully prepared by silane coupling agent treatments in this work. The pyrolysis characteristics, surface functional groups, and distribution of particle size of untreated montmorillonite powders (Mt), the hydroxyl functionalized montmorillonite (O–Mt), the urea functionalized montmorillonite (N–Mt), and the thiol functionalized montmorillonite (S–Mt), which was derived from the previous research, were respectively characterized by utilizing the thermogravimetric differential scanning calorimetry, Fourier transform infrared spectroscopy, as well as the laser particle analyzer. The suppression effect of the S–Mt, O–Mt, Mt, and N–Mt on a 9.5% CH₄ explosion was tested in the duct system (5 L). The obtained results indicated that N–Mt and O–Mt exhibited a better explosion suppression effect than Mt and S–Mt at the same mass concentration. Additionally, the methane/air explosion suppression mechanism of these powders could be explained by molecular simulation results that indicated the negatively electrophilic potential regions exist on the surface of O–Mt and N–Mt. Moreover, NH₄∙、 NCO∙ and ∙OH radicals, which can interrupt explosive chain reactions, were easily generated by N–Mt and O–Mt.