【作者】 彭桂群；

【导师】 田光明；

【作者基本信息】 浙江大学 ， 环境工程， 2011， 博士

【摘要】 随着当今世界人口快速增长和经济的迅速发展,环境污染问题日益严重。各城市污水处理厂的大量兴建,缓解了城市生活污水和工业废水对环境的污染。但是污水处理过程中产生的大量污泥很容易对环境造成二次污染,由于污泥中含有丰富的氮、磷、钾等营养元素,其资源化土地利用已经成为当今研究的热点,但城市污泥中重金属元素却成为制约污泥资源化农业利用的关键因素。同时电镀工业由于使用了大量强酸、强碱、重金属溶液,甚至包括镉、氰化物、铬酐等有毒有害化学品,产生大量有害环境和人类健康的电镀废水,电镀废水处理基本上采用过量碱中和、絮凝沉淀法等工艺,由此产生的电镀污泥含有大量Cu、Pb、Zn、Cr、Ni等有毒重金属,如处理不当在雨水淋溶作用下,可能引起地表水、土壤、地下水的次生污染,甚至危及生物链,造成严重的重金属危害。近年来许多学者针对如何减少和去除污泥中重金属毒害作用开展了广泛的研究。目前去除污泥中重金属常用的有化学方法和生物沥滤处理。电动技术处理污泥能够同时去除不同的重金属,去除率高,反应周期较短；且到达电极室的重金属能集中去除或通过吸附、泵出、沉淀、离子交换膜等回收利用。本文以杭州污水处理厂污泥和杭州临平某电镀厂电镀污泥为研究对象,分别采用生物沥滤和电动修复法进行处理,通过不同的重金属活化措施来提高重金属的去除率,以期寻求经济高效去除或降低污泥中有毒有害重金属元素的途径。1.采用氧化亚铁硫细菌进行污泥生物沥滤,综合考虑同时减少污泥的实际处理量以及实现污泥重金属的高效去除等因素,选用10%接种量和10g.L-1底物FeSO4.7H2O为最佳反应参数。2.初始pH对污泥重金属生物沥滤效果有较大影响,其中Zn所受的影响程度大于Cu；污泥固体浓度越高,重金属去除率就越低且其溶解启动时间就越长,其中Zn快于Cu,但随着沥滤时间的延长,污泥浓度对沥滤效果的影响不大,在实际运行中可以提高处理污泥的固体浓度以降低处理成本；添加不同的有机物对重金属的沥出有较大的差异,其影响程度Cu大于Zn,醇类化合物和二羧基酸影响不大,而对于结构相似的单羧基有机酸来说,碳链越长,影响越小,分子量较高的芳香族有机酸对于重金属的去除也有明显抑制作用,其影响程度随着羧基数目的增加而加剧,但不及小分子有机酸显著；厌氧水解预酸化处理由于抑制了pH的降低和Eh的升高,降低了Cu的沥出,而对Zn几乎影响不大。3.生物沥滤后,污泥中重金属含量大大减少,且残留在污泥中的重金属大多以稳定形态存在,生物有效性低；污泥经生物沥滤后,流失的氮、磷和钾分别为27.3%、70%、5.4%,损失的有机质为41.3%,虽然有一定的流失,但仍能满足土地利用的需要；生物沥滤后污泥中高含量的Fe3+是植物生长的必需元素,很少造成毒性,且淋滤后的脱水污泥能制成生物有机铁肥等；因此生物沥滤后的污泥土地利用是非常安全的。4.生物沥滤-电动修复技术可以很好去除污泥中的铜和锌含量,反应结束后,在先生物沥滤后电动修复后,污泥泥相中的Cu、Zn的浓度为63.4mg.kg-1、33.3mg.kg-1,而同时生物沥滤和电动修复后,污泥泥相中的Cu、Zn的浓度为135.21mg.kg-1、82.34mg.kg-1,均达到我国污泥土地利用的重金属控制标准；且污泥泥相中的铜由以有机硫化物结合态为主转化为残渣态和碳酸盐结合态为主,而锌则由以碳酸盐结合态和有机硫化物结合态为主转化为以残渣态为主；同步生物沥滤和电动修复反应过程中,前期加入的FeSO4.7H2O中的Fe2+离子也随之电迁移至电极室,导致后期能源不足而影响有机硫化物结合态的转化,本研究认为先生物沥滤后电动修复较为经济。5.污泥硝酸酸化同时加阴极pH值控制处理能使电镀污泥中Zn、Ni、Cu和Pb交换态、碳酸盐结合态和有机硫化物态转化为可溶离子态,从而提高了去除率；而其虽能使污泥中的Cr有机硫化物态和碳酸盐结合态转化为可溶离子态,却不利于Cr的迁移,降低了Cr的去除率；反应后污泥中Zn、Ni、Cu、Pb和Cr的去除率分别为：74.02%、68.38%、39.22%、21.37%和12.80%。6.阴阳室采用TW(自来水),SDS和CA(柠檬酸)处理液处理后,三处理重金属去除率分别为20%-51%,26%-65%,34%-69%,其中EK-CA处理的污泥重金属去除率最高；电动修复后污泥重金属去除率为Cr>Zn>Ni>Cu>Pb;连续提取方法表明电动修复后重金属的结合形态与电极处理液密切相关,由最难提取的形态残渣态向易于提取形态可溶态,交换态,吸附态,有机结合态和碳酸盐结合态转化；且三个处理的总成本估算分别为0.14,0.19,0.57元每mol重金属,EK-TW处理成本最低,但其最低重金属去除率限制了其应用,综合考虑,EK-SDS处理最合算。7.不同pH的阴极缓冲液控制处理,电镀污泥重金属初始形态不同,重金属电动修复的效果也不同；阴极缓冲液pH控制为3时,Ni、Cu、Zn和Cr的去除效果较好,去除率分别达到70%、59%、30%和29%,而Pb的去除率以pH控制5的条件下最好,达46%；另外,各处理截面重金属浓度较实验前都有不同程度的降低,其中Cu、Pb和Ni在不同污泥截面分布较均匀,而Cr和Zn在各截面分布波动较大；重金属形态中可交换态和铁锰氧化物态的去除效果较差,而碳酸盐结合态和残渣态有显著去除,有机硫化物态去除效果一般。更多还原

【Abstract】 As the world population increasing quickly and economy growing fast, the problem of environmental pollution has become increasingly worse. In recent years, many municipal sewage treatment plants have been built, which effectively alleviate the pollution of water environment caused by the discharge of municipal sewage and industrial wastewater. At the same time, a large amount of sewage sludge produced during the process of sewage treatment may result in second pollution to the environment. Since there are high quality of nutrition elements such as nitrogen, phosphorus and kalium, the agricultural utilization of sewage sludge is become an important topics in nowadays research. However, the heavy metals in sewage sludge are the key factor which will restrict the utilization of sewage sludge in agriculture. At the same time, in the last decades, large amounts of polluted wastes associated with industrial, mining, agricultural, and chemical activities have been produced. Electroplating sludge is a heavy metals-bearing byproduct that comes from the electroplating industry’s activities. Some of it consists of multiple metals such as Cu, Ni, Zn, Cr, and Pb, etc. It is a discharged residue after chemical precipitation of heavy metals from acidic or alkaline solutions as well as rinse waters generated by the electroplating processes. The sludge is categorized as hazardous waste. If disposed improperly, these metals may:1) cause serious environmental damages polluting surface and ground water, and soil; 2) be transferred into human body via the food chain. In China alone, every year more than 100,000 tons of valuable heavy metals in the form of electroplating sludge is wasted. In order to have both sound environment protection and sustainable development that highly emphasizes resources reuse, it is of great importance to maximize the recovery and recycling of heavy metals economically from electroplating sludge. Many studies have been made to decrease and reduce the poisonous effect of the heavy metals in sewage sludge. At the present time, to remove heavy metals from sewage sludge, chemical extraction and bioleaching treatment were proposed. Electrokinetic (EK) technology is considered as one of the most promising methods to remove heavy metals from the matter with low hydraulic permeability including contaminated soils and sludges. The advantages of electrokinetic technology used for treatment of sewage sludge are the simultaneous removal of different heavy metals, high efficiency of removal and short time of the process. Heavy metals approaching electrodes could be removed or reclaimed by different methods, e.g., by adsorption, pumping out, precipitation or ion-selective membrane. In this research, the sewage sludge from the sewage treatment plant, Hangzhou and the electroplating sludge from an electroplate factory in Hangzhou city were taken and studied. The research’s aim is to find an economical and effective method to reduce or remove the poisonous heavy metals from sewage sludge and electroplating sludge by bioleaching and electrokinetic removal technology respectively, adding several activated reagents as processing fluids in the electrode chambers.1. In view of reducing the total treatment volume of sludge and achieving high removal efficency of heavy metals, when we bioleaching heavy metals from sludge by thiobacillus ferrooxidans,10% inoculums and 10g.L-1(w/v) ferrous sulfate as energy substrate is tested as the best reaction parameter.2. The initial sludge pH affected bioleaching efficency largely, and the effects on removal of heavy metals followed as Zn>Cu; The bioleaching efficency showed decreasing trend with the increase of sludge solid concentration, and the startup time of heavy metals dissolved from sludge increased with the solid concentration of sludge, and the startup time followed as Cu>Zn, However, the effects of solid concentration on removal of heavy metals is very small when the bioleaching time was prolonged, so in the practical run, we can enhance the solid concentration of sludge to reduce the cost; There was much discrepancy in effect of different organic compound addition on bioleaching, where the effect extent followed as Cu>Zn. The effect of the alcohol compound and the two carboxyl acid on bioleaching was low. The negative influence on bioleaching was decreased with the increase of carbon chain length of single carboxyl organic acid. The negative influence on bioleaching was increased with the increase of carboxyl number of aroma organic acid, and the negative effect was lower than that of organic acid with low molecular weight; The sludge treated with anaerobic hydrolyzed acidification declined the removal efficency of Cu, but the effect was small to that of Zn, due to neutralize the decrease of pH and the increase of Eh.3. After bioleaching, the content of heavy metals in sludge decrease sharply, the fractions of the residue metals in sludge mostly exist as stable fractions, so the bioavailability of heavy metals is very low; The losses of nitrogen,phosphorus, kalium and organic matter are 27.3%、70%、5.4% and 41.3% respectively,despite there have some losses, it can also meet the requirement of land utilization; The high content o ferric ions in the sludge after bioleaching is the essential element of plant growing, so it does not lead to the toxicity of land, and the dehydration sludge after bioleaching can produce organic ferric fertilizer; Consequently, the land utilization of this treated sludge is very secure.4. The combination of bioleaching and electrokinetic remediation has been proved to be an effective method to remove heavy metals from municipal sewage sludge. The results showed that using electrokinetic remediation for six days after bioleaching for four days, the contents of Cu and Zn in sewage sludge were 63.4 mg.kg-1 and 33.3 mg.kg-1, respectively, while using electrokinetic remediation and bioleaching simultaneity, the contents were 135.21mg.kg-1 and 82.34mg.kg-1 respectively, which both could meet the Chinese standard for land application of the heavy metals in sewage sludge. During the reaction process, both the organic sulfide fraction of Cu and the carbonate-bound and organic sulfide fractions of Zn in sludge mainly transformed to dissociative metals which could easily migrated to the cathode zone with the process of electrokinetic remediation. During the reaction process by using electrokinetic remediation and bioleaching simultaneity, ferrous ions of the FeSO4.7H2O migrated to the electrode chamber which would lead to the shortage of energy sources at the back stage and then influence the transform of organic sulfide fractions. Therefore, this study proved that using electrokinetic remediation for six days after bioleaching for four days is the better economical and feasible treatment.5. After the experiment with acidified electroplating sludge and pH adjustment at cathode chamber, the exchangeable, carbonate and organic sulfate fractions of heavy metals in initial electroplating sludge were converted to soluble fraction which improved the efficiency of heavy metals, the removal efficiencies of heavy metals were attained:74.02% for Zn,68.38% for Ni,39.22% for Cu,21.37% for Pb. However, even the carbonate and sulfate fractions of Cr in initial electroplating sludge were converted to soluble fractionation, this treatment is not beneficial to improve the removal efficiency of Cr. The removal efficiency of Cr decreased from 77.83% of control treatment to 40.65% of electroplating sludge acidified treatment, and furthermore, decreased to 12.80% of pH adjusted in cathode chamber of acidified electroplating sludge treatment.6. The removal efficiency of metals were in the range of 20-51%,26-65%,34-69% for EK experiments with tap water, SDS,and citric acid as electrode processing fluid respectively. It was shown that a best performance was found in EK-CA experiment; Results were also showed that the metal removal efficiency by EK process was:Cr>Zn>Ni>Cu>Pb; The results of sequential extraction analysis revealed that the binding form of metals with sludge after EK experiment was changed from the residual form, the most difficult extraction type, to the soluble, exchangeable, sorbed and sulfate forms, the easier extraction types; The overall cost of these treatments can be estimated to 0.14,0.19 and 0.57 Yuan per mol of metals removed for EK experiments with tap water, SDS, and citric acid as processing fluid respectively; Although the lowest cost was found in EK-TW experiment, but the lowest removal efficiency was a limit for this experiment, it was found that the EK-SDS experiment was the most cost-effective.7. We investigated the effect of pH value of cathode buffer solution on electrokinetic remediation efficiency of heavy metals in the electroplating sludge. After EK remediation, all experiment systems had different remediation efficiency, and the best remediation effect of Ni、Cu、Zn and Cr was observed at pH 3.0 of cathode buffer solution, and the removal rates of Ni、Cu、Zn and Cr was 70%、59%、30% and 29% respectively, but the best remediation effect of Pb was observed at pH 5.0, and the removal rates of it was 46%. In addition, the concentrations of Zn, Cu, Cr, Pb and Ni in the five sections decreased in different degree, and the distribution of Cu、Pb and Ni was homogeneous in sections, but the distribution of Cr and Zn was fluctuated severely. We also found that all forms of heavy metals were removed partly, and among which the decrease of carbonate bound fraction and residual fraction heavy metal was most significant, but the decrease of exchangeable fraction and Fe-Mn oxide fraction heavy metal was not distinct, and the decrease of organic sulfate fraction was moderate.更多还原