【作者】 冯丽娟；

【导师】 张立秋；

【作者基本信息】 北京林业大学 ， 生态环境工程， 2014， 博士

【摘要】 随着我国城镇污水处理量及处理率逐步提高,污泥作为污水处理过程中的副产物,其产量也在逐年递增。污泥的堆肥化处置能够将污泥中的植物营养元素转化为更易于被植物吸收利用的形式,同时又能去除污泥中的部分污染物,使污泥堆肥产品具有一定的资源化利用价值。污泥堆肥土地利用后,堆肥中残留的污染物,如多环芳烃(PAHs),可能会对土壤、植被、水系等各个环境介质造成潜在的影响,而对于PAHs在施用堆肥后的土壤系统中迁移转化的研究尚不完善。为了掌握施肥场地中PAHs的迁移转化规律,给污泥堆肥的土地利用提供参考和指导,开展了本课题的研究。本课题首先进行了三种草坪草(高羊茅、黑麦草、白三叶)的温室盆栽试验,风干堆肥施用比例分别为Okg/m2、1.5kg/m2、3.0kg/m2、4.5kg/m2、和6.0kg/m2,于施肥后不同的时间(三个月及九个月)对盆栽土壤及植物中的PAHs浓度进行分析测定,同时对部分植物进行修剪处理,研究施肥量和植物修剪处理对三种草本植物的生物量、植物富集PAHs浓度和土壤PAHs残留浓度的影响。试验结果表明,当施肥量(干肥)为0～4.5kg/m2时,三种草本植物的生物量随着施肥量的增大而增加,施肥土壤中植物生物量的增幅为8.17%～416.03%。植物对PAHs的吸收富集也与施肥量呈正相关。在最大施肥量(6.0kg/m2)下,高羊茅、黑麦草、白三叶中PAHs富集浓度为未施肥对照的172.8%、237.7%和179.5%。对植物(高羊茅、黑麦草)进行修剪有利于植物的生长和植物对PAHs的吸收富集。土壤中PAHs的残留浓度亦随施肥量的增加而增大。九个月后,种植高羊茅、黑麦草和白三叶的土壤中PAHs的残留率分别为20.4%～49.8%、27.2%～36.1%和22.5%～48.1%。综合植物生物量、植物对PAHs的富集和土壤中PAHs的残留三方面指标认为,本研究中,高羊茅是在施用污泥堆肥土壤中最适宜种植的植物,1.5kg/m2的污泥堆肥(干肥)施用量是有利于植物生长和PAHs降解的最佳施肥比例。利用初步筛选的高羊茅作为供试植物开展为期126天的温室盆栽试验,新鲜污泥施肥(含水率50%左右)施用比例为0%、10%、25%和50%的条件下,定期(每三周)对土壤和植物进行采样,分析PAHs的浓度变化,同时测定土壤中细菌总数、过氧化氢酶活性、脱氢酶活性等指标,研究PAHs在土壤中的降解规律及影响因素,同时分析PAHs在土壤-植物间及植物体内的迁移情况。试验结果表明,PAHs在土壤中的降解可以用一级动力学方程描述,方程的拟合系数大于0.88,其中无植物土壤中PAHs降解的一级动力学拟合系数更高(R2>0.93)。种植植物对降解土壤中的PAHs有促进作用。无植物土壤中PAHs降解率为34.78%～54.40%,而有植物土壤中PAHs降解率为40.84%～60.74%。其中2～3环低分子量PAHs的去除率均高于4～6环高分子量PAHs。施用堆肥的土壤中细菌总数、过氧化氢酶活性和脱氢酶活性均高于未施肥土壤。PAHs从有植物土壤中消失的过程中,有0.45%～1.78%的PAHs经植物吸收作用从土壤转移至植物根系,部分PAHs从植物根系进一步迁移至植物茎叶。植物中部分2～3环低分子量PAHs可经植物挥发作用从植物茎叶中消失,占植物吸收富集PAHs量的19.7%～40.0%。与2～3环低分子量PAHs不同的是,4～6环高分子量PAHs不会从植物中挥发。高分子量PAHs在植物中呈现持续累积的趋势。将盆栽试验扩大为场地试验,种植高羊茅、黑麦草、白三叶三种草本植物,进行施肥量(新鲜堆肥)Okg/m2、1.5kg/m2、3.0kg/m2、4.5kg/m2和6.0kg/m2的处理,考察PAHs在自然条件下的降解情况。同时,收集天然降雨及地下水,利用人工模拟降雨手段使地表产生径流,通过对雨水、地下水和径流中PAHs含量的测定分析,研究施用堆肥的土壤中PAHs的迁移情况。试验结果表明,自然条件下PAHs的降解率在16.04%～47.01%,明显低于温室模拟试验。雨水、地下水及地表径流中仅有低分子量PAHs检出,浓度为72.4～210ng/L,其中雨水PAHs浓度最高,地表径流次之,地下水中PAHs浓度最低。土壤中的PAHs会随地表径流和地下水迁移,从而减少土壤中的PAHs,但天然降雨会将部分PAHs带入土壤。综合以上研究结果,对施用堆肥的土壤系统中PAHs的迁移转化途径进行了归纳分析。在3.0kg/m2的施肥量下,堆肥引入的PAHs仅占土壤PAHs总量的19.34%～24.58%。堆肥中PAHs的解吸量受温度、pH值、腐殖酸添加量和堆肥添加量的影响,其中pH值为最主要的影响因素。土壤中PAHs的去除主要是通过微生物降解实现的,生物降解可去除土壤中31.72%～33.20%的PAHs。植物吸收和促进降解、挥发和光解、随地表径流及地下水迁移等途径对PAHs去除的贡献较小,以上几方面共同作用可去除土壤中8.41%～12.13%的PAHs。而超过50%的PAHs仍残留在土壤中,需要进一步采取措施予以去除。更多还原

【Abstract】 Sewage sludge is a byproduct of wastewater treatment. The volume of sewage sludge gradually increases with the improvement of wastewater treatment capacity and ratio year by year. Nutrients in sludge could be converted to more available for plants, and parts of pollutants could be removed by sludge composting. Therefore, sludge compost can be utilized as organic fertilizer and has a certain value of resource utilization. However, residual contaminants, such as polycyclic aromatic hydrocarbons (PAHs), in compost could have effect on the environmental media, such as soil, vegetation and water system, after land application. And the research on migration and transformation of PAHs in soil systems fertilized with compost is not perfect. In order to know the rule of PAH migration and transformation in soil applied with compost and provide reference and guidance of land application of compost, this research has been conducted.First of all, a greenhouse experiment with three plants (tall fescue, ryegrass and white clover) has been investigated. In five different amendment ratios of dry compost to soil, PAH concentrations of soil and plants were analyzed after three and nine months of experiment. And some plants have been pruned. The effect of compost dosages and pruning plant on biomass of plants, PAH concentrations in plant and PAH residual concentrations in soil have been investigated. The results indicated that the biomass of plants and PAH concentrations in plants and soils increased with the more compost dosages in the range of0to4.5kg/m2. Biomasses of plants fertilized with compost were8.17%-416.03%higher than those without compost. When compost dosage was6.0kg/m2, PAH concentrations in tall fescue, ryegrass and white clover were1.73,2.38and1.79times of the unfertilized control. Pruning plants (tall fescue and ryegrass) are conducive to plant growth and uptake of PAHs. After nine months’experiment, PAH residual rates in soils planted with tall fescue, ryegrass and white clover were20.4%-49.8%,27.2%-36.1%and22.5%-48.1%, respectively. Considering the biomass and PAH concentrations in plants and soils, tall fescue were the best plant grown in compost-amended soil. And the optimum dosage of dry compost were1.5kg/m2, which is propitious to plant growth and PAH degradation.A greenhouse experiment with tall fescue was conducted with amendment ratios of fresh sludge compost to soil of0%,10%,25%and50%(w/w) to investigate the dissipation of PAHs in soils. The PAH concentrations in soil and plant, total number of bacteria in the soil, catalase activity and dehydrogenase activity were detected every three weeks. And migrations of PAHs from soil to plant and in plant were analyzed. The results demonstrated that PAH degradation in soil followed the first-order kinetics well in the study. And the determination coefficients in unplanted soils (R2>0.93) were higher than those in the corresponding planted soils (R2>0.88). Planting tall fescue has positive effect on PAH degradation in soil. The PAH dissipation rates were in the range of34.78%-54.40%in unplanted soils and40.84%-60.74%in planted soils. And the dissipation rates of2-3ring PAHs were higher than those of4-6ring PAHs. The total number of bacteria, catalase activity and dehydrogenase activity were higher in soils amended with compost than those without compost. During PAH dissipation in soil,0.45%-1.78%PAHs was transferred from soil to roots of tall fescue. And a part of these PAHs was migrated from roots to shoots of plant.2-3ring PAHs in plant may disappear from shoots of tall fescue by phytovolatilization, which accounts for19.7%-40.0%of total PAHs in plant. In the other hand,4-6ring PAHs could accumulate in roots and shoots of tall fescue.Field experiment with three plants were conducted with amendment ratios of fresh sludge compost to soil of0kg/m2,1.5kg/m2,3.0kg/m2,4.5kg/m2and6.0kg/m2to investigate PAH degradation under natural condition. At the same time, rainfall, groundwater and simulated runoff were collected and analyzed to investigate PAH migration in soils amended with compost. The results suggested that PAH degradation rates under natural condition were in range of16.04%-47.01%which was lower than those in greenhouse experiment.2-3ring PAHs were detected in rainfall, groundwater and runoff. And PAH concentrations in aqueous sample were in the range of72.4-210ng/L. The highest PAH concentration was found in rainfall, and the lowest shown in groundwater. PAHs migrated with runoff and groundwater would decrease the amount of PAHs in soil, but PAHs brought by rainfall would increase the amount of PAHs in soil.Based on the results of above experiments, the migration and transformation routes of PAHs in soil were concluded. PAHs in compost-amended soil derived from soil and compost. With amendment ratios of fresh sludge compost to soil of3.0kg/m2, PAHs introduced by compost accounted for19.34%-24.58%of total PAHs in soil. Desorption amount of PAHs in compost affected by temperature, pH value, humic acid concentration and compost dosage, which pH value was the most important factor. PAHs in soil were mainly removed through biodegradation by microorganism, which occupied31.72%-33.20%of total PAHs. Phytoaccumulation, degradation promoted by plant, volatilization, photodegradation and migration with runoff and groundwater contributed slightly to PAH dissipation, which accounted for8.41%-12.13%of total PAHs. More than50%of PAHs remained in soil, and advanced process should be performed to remove these PAHs from soil.更多还原