【作者】 涂剑成；

【导师】 赵庆良；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2011， 博士

【摘要】 针对污泥中重金属进入土壤后会在土壤植物生态系统中累积,固化的重金属会由于环境条件变化被重新释放出来而造成的环境风险问题,本文采用化学方法脱除污泥中重金属和超声/微波的辅助手段提高化学脱除过程中的脱除效率及经济性,实现污泥安全利用。采用四级连续提取法对不同污水处理阶段污泥和不同污水处理厂脱水污泥中重金属形态分布及可移动性进行研究。考察污泥中水溶态、酸溶态、可还原态、可氧化态和残留态重金属的在污水处理过程中的变化以及与污泥性质的相关性。对不同污泥中重金属的潜在环境风险进行了评估。污泥中各重金属总量远高于黑土中背景含量值,对环境存在潜在的风险,污泥中Cu、Zn、Cd、Mn呈严重污染水平。污泥中Cu、Pb、Cr的可迁移性差,Zn和Mn的可迁移性强,其中Pb的形态在各污泥中的分布不受污水处理过程影响。Cd主要以有机物形态存在,Ni的可迁移性受污水处理过程影响。污泥中水溶态、酸溶态、可还原态Pb与污泥的理化性质正相关,污泥中Cu、Cr、Mn、Cd、Ni的水溶态、酸溶态、可还原态含量和有机物含量正相关。化学法脱除污泥中重金属的研究表明,化学提取剂种类是影响在污泥中重金属脱除效率的主要因素,其次是浸提时间和固液比。固液比为1:50和浸提时间为8h时污泥中7种重金属脱除效率最佳。无机酸比有机酸、螯合剂、无机盐对重金属的脱除效率高,脱除效率随pH的降低而升高。草酸脱除重金属效果要好于柠檬酸、琥珀酸、天冬氨酸,HEDTA脱除重金属效果要好于EDTA和DTPA,均表现为达到一定浓度时脱除效率不再增加。无机盐的重金属脱除效果最差。较高pH值环境条件下,HEDTA和草酸联合脱除重金属的效果单一试剂好。微波/超声作用下污泥中重金属脱除特性的研究表明,重金属的脱除效率随辐射时间的延长和功率密度增强而升高,高功率密度区的提升效果要优于低功率密度区,在相同的能量密度下,长辐射时间和低功率密度的脱除效率要好于短辐射时间和高功率密度的脱除效率。微波功率密度为7.7W/mL时最佳脱除效果的辐射时间为180s ,污泥中各重金属的脱除效率顺序为Zn>Ni>Cu>Mn>Cd>Cr>Pb;在能量密度为1260J/mL附近,微波能量穿透,重金属的脱除效率不再增加。超声辐射定功率为2.5W/mL时最佳脱除效果的微波辐射时间为660s ,污泥中各重金属的脱除效率顺序为Zn>Cu>Ni>Mn>Cd>Cr>Pb;在能量密度为1350J/mL附近,超声能量穿透,重金属脱除效率不再增加;超声过程中增加搅拌的效果要好于无搅拌的效果。微波/超声处理前后污泥中重金属形态分布及红外和荧光特性的研究表明,处理后污泥中Cu、Zn、Cd、Mn、Cr、Ni的水溶态、可还原态和酸溶态的几乎全部溶出,Cd和Pb有重新吸附现象。微波/超声处理后会改变污泥中有机物的基团,污泥中水溶态重金属主要结合在水溶性醇酚类分子间-OH基团上,酸溶态重金属主要以碳酸盐无机物形式存在,在超声处理后污泥中,部分酸溶态重金属与不饱和烯烃类物质结合,可还原形态的重金属主要与有机物中C-O及C-N相结合,重金属可氧化态大部分结合在直链条烷烃上和一部分与难溶性醇酚类分子间O-H相结合。微波/超声处理后污泥中可溶性蛋白质、腐植酸、富里酸物质全部溶出,残留的变性蛋白质与污泥结合很强。水溶态重金属与污泥中富里酸和腐植酸的O-H相结合,酸溶态重金属包裹在变性蛋白质中,可还原态重金属与富里酸/类蛋白质物质中C-O及C-N相结合,氧化态重金属与腐植酸类/类蛋白物质O-H和-CH₂-相结合。微波/超声处理的能耗比和处理后污泥的特性研究表明,在0-900J/mL和1350-1800J/mL能量密度条件下,超声的效果较好;在900-975J/mL和1275-1350J/mL能量密度条件下,微波/超声效果相当;在975-1275J/mL能量密度条件下,微波的效果较好。超声处理后污泥的营养成分含量低于微波处理后污泥,但均具有很高的农用价值。微波和超声处理后污泥中Cu、Zn、Mn、Cr、Ni不具有可移动性,就7种重金属总体而言,可迁移性风险已处于安全水平。微波和超声处理后污泥中重金属潜在的环境风险从重度降到了中等水平。污泥中重金属对蔬菜生长存在很强的抑制作用,在低施肥量时,微波处理污泥中重金属的抑制作用要强于超声;在高施肥量时,超声处理污泥中重金属的抑制作用要强于微波。微波和超声脱除重金属后污泥均可以安全有效利用。更多还原

【Abstract】 Heavy metals in sewage sludge used for land application can be accumulated and be released in the soil environment, which caused serious environmental risks. So chemical extraction procedure was applied for removal of heavy metals from sewage sludge and ultrasound / microwave radiation was used to improve the chemical extraction rate of heavy metals for the safe land application of sewage sludge.A four-step sequential extraction procedure was used to investigate the heavy metal speciation in sludges from different stages of wastewater treatment process and from dewatered room of different wastewater treatment plants. The relationship between Water soluble, acid soluble, reducible, oxidisable, and residue fraction and sludge physiochemical properties was studied. The potential environmental risks heavy metals in sludges were evaluated.Total heavy metal in sludge is much higher than background value in the black soil, which is a potential risk to the environment. Cu, Zn, Cd, Mn in sludge has a serious pollution risk. Cu, Pb, Cr in sludge poorly migrate in soil environment, however Zn and Mn have strong mobility. Pb distribution in sludge has no changes during the wastewater treatment procedure, Ni has opposite change, Cd mainly exists in the organic form. Water soluble, acid soluble, reducible fraction of Pb and Al have positively related to physiochemical properties, water soluble, acid soluble, reducible fraction of Cu, Cr, Mn, Cd, Ni positively related with organic content in sludge.Chemical removal procedure indicated that the type of chemical agents used in extraction procedure is a key factor for removal of heavy metals from sludge, extraction time and solid-liquid ratio are also important factor for achieving high heavy metal extraction rate. 1:50 is an optimal solid-liquid ratio and 8h is an optimal extraction time for chemical extraction procedure. Extraction rate of heavy metals with organic acids are higher than extraction rate with organic acids, chelating agents, inorganic salts, increasing with decreasing pH. Oxalic acid is better than citric acid, succinic acid, aspartic acid on removal of heavy metals from sludge. HEDTA is better than EDTA and DTPA for extraction of heavy metals. Inorganic salts have low removal rate of heavy metals. The mixed agents of HEDTA and oxalic acid are better than a single reagent to remove heavy metals from sludge.Microwave / Ultrasound assisted chemical removal procedure presented that Heavy metal removal rates of them increase by increasing of radiation time and power density. Microwave / Ultrasound radiation on chemical extraction at high power density is more effective than it is at low-power-density. In the same energy density, long time and low power density radiation rate is better than a short time and high power density radiation rate on heavy metal extraction. The maximum removal rate of heavy metals at 7.7 W/mL can be achieved after 180s microwave radiation, the order of individual heavy metal removal rate is Zn > Ni > Cu > Mn > Cd > Cr > Pb. Microwave radiation have no further effects heavy metal removal when the energy density reached 1260 J/mL. The maximum removal rate of heavy metals at 2.5 W/mL ultrasound energy density can be achieved after 660sultrasound radiation, the order of individual heavy metal removal rate is Zn > Cu > Ni > Mn > Cd > Cr > Pb. ultrasound radiation have no further effects heavy metal removal when the energy density reached 1350 J/mL. Magnetic stirring on heavy metal removal procedure can enhance the rate of extraction with ultrasound radiation.Organic matter infrared and fluorescence characteristics and heavy metal speciation distribution in untreated sludge, microwave treated sludge and ultrasound treated sludge before and after four steps sequential extraction procedure showed that water soluble, acid soluble and reducible fraction of Cu, Zn, Cd, Mn, Cr, Ni were extracted from sludge, and Cd and Pb was resorbed by dissolved organic matter. Microwave / ultrasound treatment can change the group of original sludge; water soluble heavy metals are complexed with -OH groups of water-soluble alcohol and phenol; acid soluble heavy metals mainly exists in form bound with inorganic carbonate, partly existed in form bound with unsaturated olefins in ultrasound treated sludge; reducible heavy metals mainly were bound with C-O and C-N groups of organic matters; oxidisable heavy metals were complexed with direct paraffin and–OH groups between phenolic molecules. Dissolved protein, humic acid, fulvic acid substances were extracted by microwave / ultrasound assisted chemical extraction procedure. Water soluble heavy metals are bound with–OH groups of fulvic acid and humic acid matter in sludge; acid soluble heavy metals were wrapped in denatured protein matters; reducible heavy metals were bound with C-O and C-N groups of in fulvic acid / protein substances; oxidisable heavy metals were bound with -CH₂- and OH groups of humic acids / protein substances.Ultrasound radiation for improving the HEDTA-Oxalic extraction rate of heavy metals from sludge is more effective in 0-900 and 1350-1800 J/mL, microwave radiation is better than ultrasound radiation in 975-1275 J/mL, Ultrasound treatment has similar effects on heavy metal extraction with microwave treatment in 900-975 and 1275-1350 J/mL. Ultrasound and microwave treated sludge have high nutrient content and showed potential agricultural application value. Mobile fraction of Cu, Zn, Mn, Cr and Ni in sludge was extracted, which shows the low mobility in soil environment. The risk degree of potential accumulated environment from heavy metals in sludge is lowed to moderate level. Heavy metals can inhibit vegetables grown, inhibition of heavy metals in microwave treated sludge is strong at low sludge fertilization, and inhibition of heavy metals in ultrasound treated sludge is strong at high sludge fertilization. Sludges after microwave and ultrasound assisted HEDTA-Oxalic extraction of heavy metals can be safely utilized in sludge land application.更多还原