Investigation of basic properties of fly ash from urban waste incinerators in China

Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence （XRF）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）. The leaching toxicity procedure and some factors influencing heavy metals distribution in fly ash were further investigated. Experimental results indicate that the fly ash structures are complex and its properties are variable. The results of XRF and SEM revealed that the major elements （〉10000 mg/kg, listed in decreasing order of abundance） in fly ash are O, Ca, Cl, Si, S, K, Na, Al, Fe and Zn. These elements account for 93% to 97%, and the content of Cl ranges from 6.93% to 29.18 %, while that of SiO2 does from 4.48% to 24.84%. The minor elements （1000 to 10000 mg/kg） include Cr, Cu and Pb. Primary heavy metals in fly ash include Zn, Pb, Cr, Cu etc. According to standard leaching test, heavy metal leaching levels vary from 0 to 163.10 mg/L （Pb） and from 0.049 to 164.90 mg/L （Zn）, mostly exceeding the Chinese Identification Standard for hazardous wastes. Morphology of fly ash is irregular, with both amorphous structures and polycrystalline aggregates. Further research showed that heavy metals were volatilized at a high furnace temperature, condensed when cooling down during the post-furnace system and captured at air pollution control systems. Generally, heavy metals are mainly present in the forms of aerosol particulates or tiny particulates enriched on surfaces of fly ash particles. The properties of fly ash are greatly influenced by the treatment capacities of incinerators or the variation of waste retention time in chamber. Fly ash from combustors of larger capacities generally has higher contents of volatile component and higher leaching toxicity, while those of smaller capacities often produce fly ash containing higher levels of nonvolatile components and has lower toxicity. The content of heavy metals and leaching toxicity maybe have no convincing correlation, and high alkali content of CaO greatly contribute to leaching toxicity of heavy metal and acid neutralization capacity against acid rain.     

中国种养系统的氮流动及其环境影响

利用集成完全氮平衡模型和农业污染清单的中国种养系统氮流动模型(nitrogen flow model for farming-feeding system in China,NFM-FFS),研究了2003年中国种养系统中的氮流动及其环境影响.结果表明,2003年中国种养系统土壤虽然氮素表观盈余,但实际亏损623.9×104t,平均亏损13.7 kg/hm2,土壤整体面临含氮量减少和退化的风险.由于中国氮素投入(肥料和各类有机肥)主要集中于耕地系统,对牧草地的投入很少,耕地系统的氮素盈余了1 761.9×104t,平均盈余142.8 kg/hm2,中国牧草地系统氮素亏损2 385.7×104t,平均亏损90.7 kg/hm2.因此平衡耕地和牧草地的氮素投入既可减少农业生产对水环境的影响,又可有效控制牧草地退化.2003年,中国种养系统中总氮损失为2266×104t,其中随径流进入地表水的495.8×104t和淋洗进入地下水的102.4×104t最终沉积在河流、湖泊和海洋中,很少有机会再进入种养系统循环.耕地的肥料施用是中国种养系统向地表水和地下水最主要的氮输出源,应是农业污染控制和管理的重点.     

抗生素在地下环境中的淋溶迁移能力分析

文章在总结归类环境中抗生素的基础上,按物理化学以及药物性质对抗生素进行分类,筛选出含列于EPA中的优先控制污染物,计算各种抗生素的地下水污染指数GUS值并估算各类抗生素的淋溶迁移性。同时,结合水文地质条件,总结出地下环境中影响抗生素淋溶迁移及污染地下水的影响因素。结果显示,在总结出18类196种抗生素(除复合类药物之外)中,可计算地下水污染指数GUS值的抗生素133种,含列于EPA优先控制污染物的抗生素有97种;具有高淋溶迁移性的抗生素有123种,占所有抗生素的62.76%。土壤溶液中抗生素浓度和抗生素本身物理化学性质以及土壤类型、土壤pH值、有机质含量、植物覆盖情况等场地水文地质条件是影响抗生素淋溶迁移的重要影响因素。