碳氮循环与能源结构

The carbon and nitrogen cycles and energy supply structures

从描述碳、氮元素的生物地理化学循环入手,说明现有能源结构和其他人类活动,已经造成了地球大气层中(比较一百年以前),CO2的浓度增加了25%,甲烷、N2O、NOX的浓度都有明显增加。今天,全球固定氮的速度增加了一倍。碳、氮循环正在逐渐远离它们的动力学稳定状态,导致出现一系列严重生态环境问题。在碳、氮元素的生物地理化学循环的框架下,说明燃烧生物质(植物或植物提取物),阻断了有机碳进入非生物可得矿石燃料储存区的通道,额外增加了CO2的排放量,增加了氧气的消耗量,干扰了碳、氮元素的生物地理化学循环,使碳元素不能转变成养育土壤的有机肥料,破坏了自然界的自修复功能。还原碳的生物吸收,植物的光合作用不是唯一途径,至少有下列方式也可以实现:高分子物质降解物的相当数量代谢碳,在土壤中被植物直接吸收;溶解于水中,尤其是海洋中的HCO3―,可以被生物吸收;由亚硝酸菌属和硝化菌属作用的硝化过程是耗氧过程,氮的氧化伴随着碳元素的还原及生物吸收。另外,植物光合作用转化太阳能为化学燃料能,是一个效率(0.5%)相对低下的过程;生物质燃烧时,会生成NOX和N2O。然而,将生物质废料作为堆肥原料,获得的燃料,基本上没有额外增加CO2的排放量;获得的有机肥料,可减少化肥、农药造成的环境冲击,对建立农业可持续发展模式发挥作用。人类需要摆脱以碳元素为能量来源,以燃烧方式获得能量的思维定式,依靠自己的聪明才智,团结协作,共同构建清洁的、可持续发展的新型能源结构。

This article described the global carbon and nitrogen biogeochemical cycles as the point of departure, explicates that existing energy supply structures and other human activities have caused the increase of carbon dioxide concentration by 25%, in excess of double the methane concentration, increased the N20 emission rate by about 50%, and the concentration of NOx has substan- tially risen as well, compared to the composition of the atmosphere one hundred years before. Today, the global nitrogen fixation rate approximately has doubled that in 1950s. In a natural ecosystem, the carbon and nitrogen cycles are gradually digressing far from its steady state now. For these reasons, a series of serious ecological problems have arisen on our earth. The disturbance of the global carbon cycle leads to global wanning, to changes in sea level and patterns of rainfall. In addition, the disturbance of the global nitrogen leads to global fertilization, to increase in acidity and to a loss of biodiversity. Within the range of the global carbon and nitrogen biogeochanical cycles, it has been shown that biomass （plant matter or matter derived from plant） burned as fuel can lead to blocking organic carbon, some of which has been aggregated by geological process and transformed by heat and biological activity to form coal, petroleum, and natural gas （going underground into the bio-unavailable fossil fuels reservoirs ）, to increase extra oxygen consumption, to raise the amount of emission of carbon dioxide and to disturb biogeochemical cycle of carbon elements. As a result of biomass combustion, carbon elements cannot be converted into organic fertilizer of enriching soil, hence the self-repair function of nature being damaged. Photosynthesis of plants is not the sole means of bio-assimilation of reduced carbon. The bio-available carbon can be provided at least by the following ways： （1）Studies of the biodegradation of 14C-labelled Ecolyte polystyrene confirm that polymer fragments produced by the photo-degradation of certain plastic molecules are indeed attacked and metabolized by soil miero-organisms. In these tests, considerable amount of the carbon metabolized directly from soil is found in the bodies of the growing plants; （2）solution of HCO3- in water, especially HCO3- in the sea may be assimilated by living things; （3）nitrification is an aerobic process involving bacteria of the genera Nitrosomonas and Nitrobacter, and the oxidation of nitrogen is generally accompanied by the reduction and the bio-assimilation of carbon elements. In these processes, ordinarily neither CO2 is absorbed, nor O2 is let off. Moreover, the photosynthetic process is a relatively inefficient way of converting solar energy into chemical-fuel energy （an elaborative photosynthetic efficiency is about 0.5%）; combusting biomass is sure to cause pyrodenitrification and generate NOx and N2O. It is evident that competition between the use of agricultural land for food and for energy would become very important it has to give first priority to food production ifbiomass was to provide a substantial share of world energy in the decades ahead; biomass-derived transport fuels cannot meet the need of zero-emission vehicles, it is not ideal motive force of the future environmental protection vehicles. The following facts need to be recognized： biomass displacing fossil fuels can lead to reduction in carbon dioxide emissions at zero incremental cost, as well as greatly reduced local air pollution through the use of advanced energy conversion and end-use technologies; biomass energy systems offer much more flexibility to design plantations that are compatible with environmental goals than is possible with the growing of biomass for food and other economical crops. However, composting returns the waste of biomass to their natural biogeochemical cycles, and waste biomass is converted, with the addition of microorganisms, into chemicals, including alcohol fuels. The alcohols could be burned in place of gasoline, and they will not produce extra CO2 blow-off. Composting has much more important value in the future as it will reduce dependence of agriculture production on chemical fertilizers and pesticides, and support long-term sustainable agriculture. Humankind wants to abandon the mode of fixed thinking with regard to carbon elements as an energy source and energy taken by combusting techniques, as soon as possible. Planet Earth is a materially closed, but energetically open complex system. The only thing which enters or goes out of this terrestrial sphere is radiation. The radiation coming in is primarily solar energy. Humanity should and is researching clever ways to collect and transform the energy in sunlight cheaply, efficiently and in environmentally responsible ways, and other noncombustible renewable energy rely upon own wisdom and cooperation. This is a certain choice for sustainable development of a better society.