| The emissions of various organic pollutants has been increasing due to the growing process of industry and urbanization as well as people’s living standard, which is bringing the heaviest effects on the terrestrial ecosystems, especially on environmental soil quality in China. Polycyclic aromatic hydrocarbons(PAHs) are a class of typical persistent organic pollutants with high toxicity, persistence and bioaccumulation, which can be bioaccumulated along the food chains and enter the human body through several exposure routes including inhalation, dermal contact, and ingestion and result in a health risk. In recent years, the environmental pollution levels and the multi-media transfer and fate of PAHs in terrestrial ecosystem has been extensively concerned by the researchers and public. Therefore the development of control technologies and remediation methods for PAHs pollution are becoming increasingly highlights for its important role and status. The first objective of this thesis is to comparatively investigate the absorption and accumulation abilities of PAHs for some common plants in Lanzhou area, so as to screen potential plants with high absorbing and accumulating capacities to environmental PAHs in order to provide an insight on the scientific measures and programs of PAHs remediation based on the phytoremediation for the contaminated environment of terrestrial ecosystems in Lanzhou area. The second aim of this thesis is to study the remediation effects of biochars prepared by agriculture and livestock wastes for the soil PAHs pollution. As it is well known, the physicochemical properties and structures of these prepared biochars also have been analyzed and identified in order to infer the remediation mechanism by biochars. At last, the prepared biochars with high remediation effects were confirmed and were further investigated for their sorption capability on biochar-amended soil. The study results of this thesis can provide the scientific data and theoretical supporting for the PAHs phytoremediation in terrestrial ecosystems and soil PAHs remediation based on the biochars prepared by agriculture and livestock wastes as well as benefit to the waste resources and utilization of agriculture and livestock. Furthermore, this study can also strengthen the efficiency of PAHs polluted soil and give the guide for improving the ecological and living environment of Lanzhou. The main achievements of this thesis are as follows:(1) The study of cumulative characteristics for common plants in Lanzhou region: In this study, the highest PAHs concentrations were appeared in chenopodium glaucum herb and jujube tree among all collected plant samples. The contents of PAHs with low-ring were significantly higher than those of the high-ring PAHs. The special cumulative characteristics showed that the contents of PAHs in aboveground plants exhibited the positive correlation with the leaf surface area, namely the plants with larger surface area of leaves and stronger root could filter and absorb more PAHs from air and soil in terrestrial ecosystem.(2) The identification and characterization of physicochemical properties and structure for the biochars prepared by several agriculture and livestock wastes: As temperature increases, ash percent of biochars become higher, while yield become lower. The element composition of prepared biochars appeared a significant difference, and the specific surface area and pore structure of various biochars were affected by the different feedstocks and preparing temperatures. The variation trend of specific surface area was similar with that of micro pore volume. Moreover, the specific surface area had a significant increasing in term of micro pore producing with increasing temperature, in which the main reason was that, the missing of volatile organic matter from the biochar surface and heavier biomass carbonization during higher temperature. In addition, the results of identification showed that biochars were rich in several chemical functional groups including hydroxyl, carboxyl, carbonyl, and some inorganic mineral constituents such as carbonate, silicate, phosphate and so on. Furthermore, this study also found that the numbers of oxygen-containing functional groups on biochar surface decreased with the temperature rising, meanwhile, the degrees of alkalinity and aromaticity increased, which means that the PAHs adsorption capacities of biochars become stronger. The contents of aromatic carbon, hydroxyl and inorganic salts were higher for the biochars made from cow dung at 500℃(C500) and sheep manure at 600℃(S600) than those of biochars derived from wheat stalk and peanut shell at 300℃(P300 and W300). Overall, the special structure and the type of functional group were the dominant factors for the remediation efficiency of biochars.(3) The effects of various biochars on remediation for PAHs contaminated soil: The degradation efficiency of PAHs for indoor soil by added biochars varied with the number of rings of PAHs due to their higher volatility and lower lipophilic hydrophobicity, it is showed that low ring PAHs degraded faster in the early stage for the simulation experiment in indoor soil, while high ring PAHs mainly been removed in the later stage(second and third week).In addition, for similar pyrolysis temperature, removal efficiencies of biochars prepared from cattle and sheep manure were higher than those of prepared from wheat straw and peanut shell. Moreover, the results of this study also indicated that the degradation of PAHs in indoor soil was significantly enhanced by added biochars, in which adsorption capacity of biochars increased with heavier aromaticity. But the bioavailability of PAHs decreased in term of stronger fixation which limited its microbial degradation efficiency.(4) Remediation strategies and suggestions for PAHs contamination in terrestrial ecosystem: Based on the plant characteristics and phytoremediation goals in interrestrial ecosystem, variety plants can be planted together in order to well perform the phytoremediation in terrestrial ecosystems, such as to plant jujube tree and grow chenopodium glaucum herb on similar ground of place which not only for afforestation but also for a higher remediation efficiency for soil pollution. For PAHs contaminated soil, in this thesis the highest efficiency biochar was derived from cow dung at 500℃(C500) which played the most significant role in improving the removal effects for soil PAHs. In addition, the background PAHs content and the toxicity equivalent concentration of C500 biochar(prepared by cow dung) also showed it was at a lower ecologic risk and less harmful to human health. Finally a good remediation way was given for combining plant and preparing biochar for PAHs contaminated soil. |
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