【作者】 牛秋雅；

【导师】 曾光明； 黄国和；

【作者基本信息】 湖南大学 ， 环境工程， 2013， 博士

【摘要】 多环芳烃(PAHs)能对生物体引起急慢性伤害,甚至致癌、致畸、致突变。近年来,越来越多的PAHs类物质通过尾气的释放、污泥的农业应用、废水的排放等途径进入环境。我国红壤丘陵区面积大、是重要的农业生产区、同时工业发达、污染严重。由于PAHs可通过食物链迁移和转化,其在土壤和水体中的积聚对人类健康和生态安全构成了巨大的威胁。同时,现代规模化农业导致大量的农业植物废物无法通过传统的利用途径被消耗,造成了生物资源的浪费和环境污染。针对多环芳烃污染土壤的修复,以强化生物降解和生物转化为基本特征的堆肥化技术相对于其它物理化学方法具有低成本和能够实现资源再生等优点。而由于PAHs具有高疏水性,其堆肥化微生物降解过程是个传质限制过程。含有PAHs的堆肥产品的使用将可能导致其在环境中重新集聚。利用高效降解菌降解PAHs相对于其它物理化学方法同样具有高效、低成本的优点。但其降解效率受到诸如温度、pH、共存污染物等环境条件的限制。污染环境中PAHs和重金属往往同时存在。二者在生物降解转化过程中发生交互作用,从而影响其降解转化的效率。基于以上原因,论文研究了一种利用堆肥化技术同时实现农业废物资源再生和PAHs污染丘陵红壤修复的方法；在此基础上,研究建立了两种能够强化堆肥化过程、提高堆肥化降解PAHs的效率、减少堆肥中残留PAHs的技术；并首次研究了PAHs和重金属在堆肥微生物降解转化过程中的交互作用及其机制；同时,论文驯化、筛选、鉴定了一种PAHs高效降解菌,并系统研究了高效降解菌的降解能力及其影响因素,且对其胞外酶和胞内酶的降解能力进行了初步研究。研究得到以下一些主要结果：(1)添加农业植物废物好氧堆肥化可以有效降解丘陵红壤中的PAHs。堆肥产品不仅对植物没有毒性而且还能促进种子的生长,从而同时实现了农业植物废物的资源化和PAHs污染土壤的修复。堆肥化32d,堆肥体中菲和芘的残留率可分别降至4.6%和9.2%。采用土壤：农业植物废物：树叶、干草：木屑为8：3：1：1时,堆料的有机物含量和C/N分别在适宜堆肥进行的有机物含量范围内和C/N比范围内。农业植物废物的添加使堆体微生物代谢活跃。细菌是降解有机物和PAHs的主要微生物类群。整个堆肥化过程pH在6.6至7.6之间波动。这个pH变化范围有利于菲的降解,也在最适宜堆肥化的pH范围之内。(2)臭氧预氧化能够降低堆料中PAHs的含量,减小其对后续堆肥化微生物的抑制作用,从而加快堆肥化的启动过程,因此,可以进一步提高堆肥化修复PAHs污染土壤的效率,并进一步降低堆肥产品中的PAHs含量。堆肥化31d时,经臭氧氧化-堆肥化处理的表层土壤中的菲和芘的残留率可分别降至1.1%和5.0%；堆料对植物已没有毒性。臭氧氧化处理中,土壤中的有机质会显著降低其去除PAHs的效率。(3)添加经驯化的活性污泥是另外一种能够进一步降低堆肥产品中PAHs含量的有效方法。活性污泥的添加显著加快了堆肥化进程和PAHs的降解过程。添加经驯化的活性污泥的堆样,堆肥化31d后菲和芘的残留率可分别降至1.5%和7.4%。(4)添加农业植物废物好氧堆肥化可以同时实现污染土壤中PAHs的降解和铅向难以生物利用的形态转化。堆肥化完成后,堆料对植物生长已没有抑制作用,可以二次利用。堆肥化32d,铅-菲复合污染的堆体中,菲的残留率降至9.6%,残渣态Pb的百分比超过50%。整个堆肥化过程不需要调节pH值。堆肥化中后期的堆体以偏碱性存在,有利于游离的铅离子形成沉淀,减轻其对堆肥微生物的抑制,从而促进菲的微生物降解。菲和铅在堆肥降解转化过程中存在交互作用。堆体中的Pb在一定程度上抑制了堆肥微生物的活性,并使液相中水溶性有机碳固定于固相、同时抑制堆体中胡敏酸和富里酸的生成,从而抑制了菲的降解。菲也抑制了Pb向难以生物利用形态转化的过程,但这种影响比较弱。(5)通过驯化培养和反复划线分离获得了一株PAHs高效降解菌。通过形态学观察、培养特性观察,综合生理生化实验结果和16S rDNA序列分析结果,将该菌归为Bacillus属,命名为Bacillus sp. PAHD3。该菌对萘、荧蒽、芴、菲和芘均能够利用。其降解PAHs的酶基因可能位于质粒DNA上。(6)Bacillus sp. PAHD3在pH5至pHH12的范围内均能够以菲为唯一碳源生长,且当降解体系的pH值为7.0时,其对菲的降解能力最强；该菌有较宽的底物浓度适应范围,培养7d,200mg·L-1的菲可全部被降解；500mg·L-1的菲可被降解90%以上；2000mg·L-1的菲可被降解70%以上。葡萄糖的添加对该菌降解菲的过程有抑制作用；而20mg·L-1的水杨酸对该菌降解菲的过程有促进作用；浓度为50mg·L-1的Tween-80和浓度为200mg·L-1的SDBS均促进该菌对菲的降解,且前者的促进作用比后者强。(7)在铅离子浓度0mg.L-1至500mg.L-1的范围内,Bacillus sp. PAHD3均能够降解菲。但铅离子对该菌降解菲的能力有一定的抑制作用,且该抑制作用随着铅离子浓度的增大而增大。偏酸性的环境能够减弱铅离子对该菌降解菲的抑制作用。铅离子能够影响该菌的细胞官能团、细胞形态、胞外酶、细胞分泌表面活性物质的能力,这可能是铅离子影响Bacillus sp. PAHD3菲降解能力的内在机制。(8) Bacillus sp. PAHD3胞内酶和胞外酶对菲和芘均有很高的降解活性。二者酶促反应的最适pH值分别为6.0和7.0,最适温度均为30℃。在最适条件下二者对菲的酶促去除率可分别达到98%和88%,对芘的去除率可分别达到90%和73%；其胞内酶的酶促降解作用强于其胞外酶的；pb2+与Cd2+对Bacillus sp. PAHD3胞外酶酶促去除菲均有抑制作用；低浓度的Pb2+和Cd2+对Bacillus sp. PAHD3胞内酶酶促去除菲有促进作用,高浓度的有抑制作用。(9)与接入经驯化的活性污泥堆肥化相比,接入Bacillus sp. PAHD3堆肥化对降解土壤中的PAHs而言没有显著的优势。更多还原

【Abstract】 Polycyclic aromatic hydrocarbons (PAHs) can cause acute or chronic toxic effect and have carcinogenic, teratogenic, mutagenic effect on living beings. In recent years, more and more PAHs have entered environment through the release of tail gas, the agricultural application of sewage sludge, and the discharge of waste water. Red soil hilly area is large in China, and is the important area for agricultural production. But it is polluted due to the developed industry. The enrichment of PAHs in soil and water environment poses a great threat to public health and ecological security because it can migrate and transform through food chain. At the same time, modern large-scale agriculture produces a large number of agricultural plant wastes, which can not consume through traditional way, resulting in the waste of biological resource and environmental pollution.For the remediation of the soil polluted by PAHs, composting technology with the basic characteristics of strengthening biodegradation and biotransformation is lower cost and easier to realize resource recycling than the other physical and chemical methods. The degradation of PAHs during composting is limited by mass transfer due to its high hydrophobicity. The utilization of composting product containing residual PAHs may result in the re-enrichment of PAHs in environment.The method utilizing high efficient PAHs-degrading bacteria to degrade PAHs is also more efficient, lower cost than the other physical and chemical methods. But the degradation efficiency is limited by environmental conditions such as temperature, pH, and the coexistence of pollutants.Heavy metals and PAHs tend to exist at the same time in the polluted environment. They may interact and thus affect the efficency of biotransformation or biodegradation.Based on the above reasons, a method, which utilize composting technology to realize both the recycling of agricultural waste and the remediation of the red hilly soil polluted by PAHs, was presented, and futhermore two strengthening methods, by which the degradation efficiency of PAHs was increased and the residual PAHs was decreased during composting, were studied. The interaction between PAHs and heavy metals during compositng was also studied. One high efficient PAHs-degrading bacterium was isolated based on acclimatizing, screening and identifying. And both its degradation ability and the degradation ability of its enzymes were studied. The important results were listed as following:(1) PAHs in polluted soil were efficiently degraded by composting adding agricultural plant waste, which product was unharmful to plant and furthermore promoted its growth. Accordingly, both the reuse of agricultural plant waste and the restoration of PAHs contaminated soil were realized at the same time. After composting for32d, the residual rate of phenanthrene (PHE) and pyrene(Pyr) were4.6%and9.2%, respectively. When the ratio of the soil, agricultural plant wastes, leaves and hay, and wood chips was8:3:1:1, the organic matter content and C/N were respectively suitable for composting. The addition of agricultural plant waste stimulated the microbial metabolism. Bacterium was the main microbial group to degrade organic matter and PAHs. The pH ranged from6.6to7.6during composting process, which was favorable for the biodegradation of PHE and the composting process.(2) Pre-ozonation further decreased PHE in soil and thus decreased its inhibition on the composting microbes and quickened the startup of the following composting. After composting for31d, the residual rates of PHE and Pyr in surface red soil were1.1and5.0%, respectively, and the phytotoxicity of the contaminated soil disappeared. The organic content in soil remarkably decreased the efficiency of removing PAHs by ozonation.(3) Composting with inoculation of acclimatized activated sludge was also an effective method for further decreasing PAHs in composting product. The addition of acclimatized activated sludge made both the composting and the degradation of PAHs more rapid and further decreased PAHs in composting materials. The residual rate of PHE and Pyr were decreased to1.5%and7.4%, respectively, by composting for31d.(4) Composting with agricultural plant waste both decreased the residual PHE in composting product and promoted the morphological transformation of Pb. When composting was completed, the product could be reused because it was unharmful to plant, in which the percentage of PHE was decreased to9.6%and more than50%of Pb was bound to the residual fraction. During composting, pH could guarantee the composting without adjustment and the alkaline environment in the middle and the later periods of composting was helpful for the precipitation of lead ion, which reduced its inhibition on composting microbes and promoted the biodegradation of PHE. The coexistence of Pb inhibited the biodegradation of PHE to some extent by inhibiting the growth of composting microbes, decreasing the dissolved organic carbon, humic acid and fulvic acid. On the other hand, the coexistence of PHE inhibited the transformation of lead. But this effect was weak.(5) One high efficient PAHs-degrading bacterium was isolated by acclimatizing and screening. It was identified as Bacillus sp. and named Bacillus sp. PAHD3through the observation of morphology, cultural characteristics, physiological and biochemical experiments and the analysis of16S rDNA sequences. Naphthalene, fluo-ranthene, fluorene, phenanthrene and pyrene were all able to be utilized by this bacterium. And its gene for degrading PAHs existed in plasmid.(6) Bacillus sp. PAHD3was able to grow with the sole carbon source of PHE under the pH value of5to12. And the degradation was most efficient under the pH value of7.0. The concentration range of PHE which Bacillus sp. PAHD3could utiliaze was wide. After7d, PHE with the concentration of200mg·L-1,500mg·L-1and2000mg·L-1were degraded by100%, more than90%, and more than70%, respectively. Glucose showed inhibitory effect on the biodegradation of PHE while salicylic acid of20mg·L-1stimulated its degradation. Both Tween-80(50mg·L-1) and SDBS (200mg·L-1) promoted the biodegradation of PHE, and the former effect was bigger than the latter.(7) Under the concentration ranging from0mg·L-1to500mg·L-1, Bacillus sp. PAHD3was able to degrade PHE. But lead ion had certain inhibitory effect on the biodegradation of PHE, furthermore the inhibition increased with the increase of lead ion concentration. Acid environment could abate this inhibition. Lead ions affected the functional group, the extracellular enzymes, the cell morphology and the ability to produce surfacants of Bacillus sp. PAHD3. It was the internal mechanism of lead affecting the biodegradation of PHE.(8) Both intracellular and extracellular enzymes of Bacillus sp. PAHD3were efficient on degrading both PHE and pyrene. The removal rate of PHE (pyrene) reached98%(90%) by intracellular enzymes under the optimal pH value of6.0, and 88%(73%) by extracellular enzymes under the optimal pH value of7.0. The degradation of PHE by intracellular enzyme was stronger than by the extracellular enzymes. The optimum temperature for the above degradation was30℃. Both Pb2+and Cd2+inhibited the removal of PHE by extracellular enzymes. Pb2+and Cd2+of low concentration stimulated enzymatic removal of PHE, while which of high concentration had an opposite effect.(9) Compared with composting soil with the addition of activated sludge, composting soil with the addition of Bacillus sp. PAHD3was not more efficient for degrading PAHs.更多还原