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复合硫杆菌与MT基因工程菌对污泥重金属的联合生物淋滤

The Joint-bioleaching by Compound Thiobacilli and MT Genetic Bacteria of Heavy Metals in Sludge

【作者】 张弛

【导师】 王增长;

【作者基本信息】 太原理工大学 , 环境工程, 2012, 博士

【摘要】 污泥是由污水处理过程或水体运动过程所产生的固体沉淀物质。本课题的污泥主要是指污水处理厂的浓缩污泥。此类污泥是重要的环境污染物,其性质复杂、体积大、毒害性持久,污泥中的重金属处理更是环境污染控制领域的重要课题。尤其对于我国环境安全问题日益严重的今天,污泥重金属处理技术的研究是有生命力的课题。污泥农用是污泥资源化利用的重要方向,但污泥重金属的环境风险是制约污泥农用的瓶颈。传统的污泥消化、浓缩、脱水工艺不能有效去除其中的重金属。近年来新开发的针对重金属去除的技术存在着成本较高、操作困难、去除率有限、伴生二次毒性物、存在安全隐患等问题。生物法一直是备受环境工程领域关注的优选方法。用于污泥重金属处理的生物法包括生物淋滤以及植物提取等技术方法。其中的生物淋滤法具有适用面广、去除率较高、操作条件简单、添加基质廉价易得、反应温和、耗酸量少等优点。更主要的是,生物淋滤工艺可与污水厂原有的污泥消化工艺同步实施,并可以替代一部分污泥消化的功能,可利用污水厂原有构筑物,基建费小,因此是很有发展潜力的方法。近年来,对污泥生物淋滤技术的研究虽然较多,但对有些重金属元素的去除率并不理想,而且淋滤耗时过长,启动速率受反应体系的初始pH值以及水溶性有机物(DOM)等因素制约,这导致淋滤效率较低,运行成本过大。从机理研究角度而言,对污泥生物淋滤机理的研究成果较少尤其是对Cd、Ni、Cr、Pb淋滤机理的研究很少。从微生物种类而言,研究者对淋滤的研究大多集中于单独接种某一种硫杆菌上,而对多种化能自养菌复合淋滤的研究不多,对异养菌与化能自养菌联合淋滤的研究很少。本文在研究复合硫杆菌对污泥生物淋滤的基础上,采取异养菌与化能自养菌联合淋滤的思路,借助耐酸型金属硫蛋白基因工程菌(简称为MT基因工程菌),对氧化硫硫杆菌(T.t)与氧化亚铁硫杆菌(T.f)的生物淋滤发挥促进作用,提高污泥生物淋滤的效率。另一方面,对重金属负荷率对淋滤的影响、MT基因工程菌联合淋滤中重金属形态转化的机理进行了深入研究,对深化污泥生物淋滤机理作出了有益的探索。主要的研究内容和结论包括:(1)分别采用氧化硫硫杆菌(T.t)、氧化亚铁硫杆菌(T.f)、MT基因工程菌为主体菌种对污泥进行了单独菌种接种生物淋滤试验。结果显示,氧化硫硫杆菌(T.t)与氧化亚铁硫杆菌(T.f)均对污泥重金属表现出了较好的淋滤效果,但两种菌液在污泥重金属生物淋滤中具有较明显的差异。T.f比T.t淋滤效果好的元素是:Ni、Cd、Cr、Pb。其余元素采用T.t比T.f的淋滤效果好。这与不同重金属元素在原始污泥中的化学形态有关,也与各种重金属的淋滤机理不同有关;菌种的接种量主要是影响到污泥淋滤体系的酸化速率、酸化程度以及ORP的变化趋势。MT基因工程菌单独接种淋滤试验结果表明,MT基因工程菌对重金属具有少量去除能力。MT基因工程菌对6种重金属的亲和力顺序为Cd>Zn>Cr>Cu>Pb>Ni。(2)通过对复合硫杆菌对污泥重金属的去除效果进行研究,发现在底物充足的前提下,T.t与T.f菌实现了相互促进,表现出了比分别单独接种时相对较好的淋滤效果。具体而言,复合硫杆菌比单独接种T.t或T.f菌时的淋滤初期迟滞段缩短了,淋滤高效段提前到来,达到最高去除率所需的时间缩短了,总去除率提高有所提高。在不同的底物配比情况下,硫浓度越高,达到最低pH值时所消耗的时间也越短,但硫浓度超过4g/L后,对pH值下降速率的贡献并未显著提高。实验证明Fe2+可以作为S的促进型底物,或者说Fe2+的增加可以弥补S底物的不足。硫与Fe2+这两种底物对氧化硫硫杆菌(T.t)与氧化亚铁硫杆菌(T.f)的意义是有差异的,但这两种底物的配合使用能起到相互促进作用,发挥出单独使用任何底物难于实现的意义。不同底物配比条件对污泥淋滤体系的ORP值影响较大。(3)在复合硫杆菌采用固定体积比的前提下,对MT基因工程菌采用不同的添加比例进行淋滤试验。试验显示可选取“复合硫杆菌+6mL MT菌”作为本试验条件下的最佳接种量。在最佳底物、最佳接种量的前提下,MT菌—复合硫杆菌联合淋滤对不同的重金属元素生物淋滤的提高是有差异的。总体而言,大多数元素的淋滤去除率有提高,淋滤后期更加平稳,波动现象减弱,表明在MT菌的参与下,T.t菌与T.f菌更加稳定地发挥出了其淋滤功能。另一方面,T.t菌与T.f菌的酸化效应又反过来促进了MT菌的活性及其对重金属的络合效果。(4)在MT基因工程菌参与淋滤的前提下,通过对不同底物单质硫与FeSO4·7H2O的配比条件下各种重金属的去除效果进行研究,发现硫与Fe2+配比适当时,能够有效提高淋滤效果。有效促进了难淋滤重金属的浸出,实现了硫底物的节约。通过底物配比对S042-的影响规律研究,发现当底物配比中S0占优势时,可促进8042-的生成,但MS转化成S042-的速率受限制。在T.t和T.f混合菌液采用固定体积比的前提下,对每种重金属受MT菌接种量的影响情况进行了研究。发现MT菌对重金属淋滤的促进作用主要体现在淋滤的初期与中期,尤其是Cu、Ni、Cr、Pb在初期提高效果明显。对于Zn、Cd,5%接种组较好。(5)本文提出以“重金属负荷率”作为衡量单位质量硫杆菌以及复合菌、联合菌所承受的重金属离子负荷情况的新指标。试验表明,适宜的负荷率条件下生物淋滤不会受影响,试验所获得的去除率比未接种MT菌时同等负荷率时的去除率有显著提高。若以实现达标,而且淋滤时间不超过4d为衡量依据,Cu、Ni、Zn、Cd、Cr、Pb满足要求的重金属负荷率最大为:0.221、0.051、0.407、0.010、0.128、0.127mmg/mg。负荷率过高,淋滤会受抑制,主要表现为迟滞期变长。(6)通过对MT基因工程菌形成的大分子EPS(MT)与Fe3+结合成的EPS-Fe3+络合体对生物淋滤的促进作用进行研究。结果表明,大分子EPS(MT)与Fe3+结合能力较强。添加EPS(MT)-Fe+络合体后,Fe3+发挥出了促进氧化的能力,Cr、Pb的去除率分别提高了1.48、1.25倍。而且这种促进作用是持久的,可以长时间促进Fe3+维持可溶状态。(7)通过对Cu、Ni、Zn、Cd在EPS及细胞内外的分布特征进行研究,提出了针对重金属离子在细胞内外分布特征的简易判定标准。通过对MT基因工程菌代谢水溶性有机碳(DOC)的研究,表明MT菌可以利用污泥中原有的营养进行增殖,降解DOC,消除了部分硫杆菌生长的抑制因素。(8)通过对MT基因工程菌联合淋滤中重金属形态转化的机理进行研究。提出了依据污泥化学形态对原始污泥的分类方法。对Cu、Cd、Ni、 Zn、Cr、Pb六种重金属元素的生物淋滤机制进行了区别归类。研究表明Cu、Ni、Cd的生物淋滤过程是以直接机制为主的,Zn的生物淋滤过程是以间接机制为主的,Cr、Pb的生物淋滤过程属于混合机制。在机理分析中,初步明确了淋滤机制与原始污泥类型、淋滤中的主导菌群的对应关系,扩展了混合淋滤机制的内涵。

【Abstract】 Sludge are the solid content which settled during the wastewater treatment process, or the water movement process.In this paper, the sludge mainly refers to the sludge with concentrating and dewatering in the sewage treatment plant.This kind of sludge is the important environmental pollutants, it has the complex properties, large volume, and its toxicity is prolonged.The treatment of heavy metals in sludge is the important subject of the environmental pollution contral fields. Especially for the increasingly serious environmental safety problems of China. The technologies of the treatment for heavy metals in sludge is a nice topic which has strong vitality.The agricultural disposal of sludge is an important route for the resource utilization of sludge in our agricultural country, but, the environmental risk of heavy metals in sludge is the bottleneck of the agricultural disposal. The heavy metals can not be efficiently eliminated from sludge by the traditional echnologies such as the digestion, concentration, dewatering for sewage sludge. In recent years, the new process exploited for heavy metals are beset by many serious problem such as high cost, severe conditions, low removal rates, associated secondary toxicant, potential safety hazard.The biological process has received considerable attention as one of the most potential advanced technologies for environmental engineering field. The application of biological process in heavy metal processing mainly include bioleaching, plant extract process etc. Among these biological process, bioleaching has many excellent features such as extensive adaptability, high removal rates, simple operation conditions, low cost bio-additive, and the reaction conditions are mild, low acid consumption. Above all, biological process can be synchronization actualize with the original digestion process in the sewage treatment plant. On the other hand, which can replace part of the functions of the digestion process. Further, it can use the primary buildings or structures of the sewage treatment plant, which result in smaller construction cost. So, its a potential advanced technologies.In recent years, there are many studies about bioleaching process of sludge, but, the removal rates for some heavy metal failed to produce the desired effects. Furthermore, the time-consuming is too long. The start-up rate of bioleaching is conditioned by various factors such as the initial pH of the reaction system and the dissolved organic matter (DOM). These factors lead to the lower removal rates, also the total operating cost will increase. In terms of the mechanism research, the previous literatures have few research results about the mechanism of the sludge bioleaching, especially in the bioleaching mechanism of Cd、Ni、Cr、Pb. In terms of the microorganism community sort, mainly concentrate on a single Thiobacilli, they had not done much work on compound-bioleaching of multi-chemoautotroph. Furthermore, the research about the joint-bioleaching by heterotrophic bacteria and chemoautotroph are very few.Based on the study about the sludge bioleaching by dint of compound Thiobacilli bacteria, this paper took a new idea of joint-bioleaching by heterotrophic bacteria and chemoautotroph, in virtue of Acid-Proof Metallothionein genetic engineering bacteria(MT genetic engineering bacteria), promote the process of bioleaching using Thiobacillus thiooxidans(T.t) and Thiobacillus ferrooxidant(T.f). The ultimate goal is improve the efficiency of the process. Furthermore, the effect of heavy metal load factor on bioleaching, and mechanism of heavy metal speciation transformation during the joint-bioleaching by MT genetic engineering bacteria were investigated detailedly. This paper does useful researches and trials to deepen the mechanism of bioleaching. The main study contents and findings are as follows:(1) Three independing bioleaching test which inoculated with isolated predominance strains were carried out, that respectively used Thiobacillus thiooxidans(T.t), Thiobacillus ferrooxidant(T.f), and MT genetic engineering bacteria as its predominance strain. The results indicated that, both Thiobacillus thiooxidans(T.t) and Thiobacillus ferrooxidant(T.f) showed preferable treating effect of bioleaching for heavy metal in sludge, but, there presented relatively significant differences between two kind of strains. The bioleaching of Ni、Cd、Cr、Pb with T.f showed better treating effect than T.t. The bioleaching of other element with T.t are better than T.f. These differences are relevant to the chemical speciation of variants heavy metal elements in aborignal sludge, its also relevant to the mechanism of the sludge bioleaching.The inoculation amount of Thiobacilli particularly affected the acidification rate, acidification degree, and the change trend of oxidation reduction potential (ORP). The bioleaching test that inoculated with isolated MT genetic engineering bacteria indicated that MT genetic engineering bacteria has small removal rates to heavy metals. The appetency sequence of MT genetic engineering bacteria on six heavy metals are:Cd>Zn>Cr>Cu> Pb>Ni.(2) The leaching effect of heavy metals in sludge with compound Thiobacilli were investigated. The test results showed that the bioleaching realized the mutual promotion between T.t and T.f, on the premise of sufficient substrate. The compound bioleaching were better than the independing inoculated with isolated strains. Concretely speaking, the postponement stage in compound bioleaching were shortened than it with the isolated strains, the high efficiency stage in compound bioleaching were pushed up, the time to reach the highest leaching effect were shortened, the total removal rate were also improved. In the variants of substrate proportion, with the higher S(elemental sulfur) concentration, the time to reach the lowest pH were shortened. But when the S concentration were above4g/L, the contribution for the rate of decrease had not improved significantly. The test demonstrates, Fe2+can be used as the promotable substrate for S, or at least the increase of Fe2+can make up for the lack of S. For T.t and T.f, the value are different to the substrate S and Fe2+, but the coordinate application of two substrate can mutually promote each other. In these cases, they can produce the best possible results that the isolated substrate was difficult to achieve. The influences of the variants of substrate proportion to the sludge bioleaching are obvious.(3) The sludge bioleaching test based upon different additive proportion of MT genetic engineering bacteria were carried out, on the premise of fixation volume ratio (compound Thiobacilli). The test demonstrates that "compound Thiobacilli+6mL MT genetic bacteria" can use as the best inoculation amount for the test. The improvement for different heavy metal elements in the joint-bioleaching by compound Thiobacilli-MT genetic bacteria are discrepant, on the premise of the best substrate proportion and best inoculation amount. In general, the removal rates of bioleaching for most heavy metal elements were all improved, and the later stages of bioleaching showed a smoothly trend, the fluctuation phenomenon tended to weakened. This result indicated that, T.t and T.f produce more steady bioleaching function in presence of MT genetic bacteria. On the other hand, the acidification of T.t and T.f in return stimulates the activity of MT genetic bacteria and its complexing effect to heavy metals.(4) The leaching effect of every heavy metal under the different proportion of S(elemental sulfur) and FeSO4·7H2O were investigated, on the premise of the presence of MT genetic bacteria. The results indicated that the proper substrate proportion (S°and Fe2+) can improve the efficiency of the process effectively. It also promote the removal of obstinate heavy elements, and implement the save of substrate S(elemental sulfur).During the test about the change law of SO42-with variants of the substrate proportion, the results showed that the generation of SO42-was promoted when the S°dominates the substrate proportion, but the rate of transformation from MS to SO42-were circumscribed.The effect of inoculation amount (MT genetic bacteria) for the process effectively about six heavy elements were compared, on the premise of fixation volume ratio (compound bacteria liquid of T.t and T.f). The results showed that the promotability of MT genetic bacteria for bioleaching mainly shows in the initial stage and the middle stage, particularly for Cu、Ni、Cr、 Pb, there effect in the initial stage were improved obviously.5%inoculation amount is the best amount for Zn, Cd.(5) A new index was presented to measure the heavy metal load factor that undertaken by unit mass of Thiobacilli or compound Thiobacilli bacteria, or joint-bacteria in this paper. The results indicated that, the bioleaching treatment rates will not be affected with the fitting heavy metal load factors. The removal rates in these tests had been improved significantly than the removal rates without MT genetic bacteria. If we estimate the treating effect according to two targets:reach the standard, and the time-consuming does not more than4days, the best heavy metal load factors which meet the requirements are:0.221、0.051、0.407.0.010、0.128、0.127mg/mg. The treating effects would be inhibited if the load factors were too high, the main manifestation was the longer postponement stage.(6) The promotability effect with EPS-e3+complex which combined with macromolecule EPS(MT) and Fe3+that were formed by MT genetic bacteria were investigated. The results showed that the binding capacity of macromolecule EPS(MT) and Fe3+is strong enough. Fe3+improved the promoting capacity for oxidizing, when the EPS-Fe3+complex was added in, and the removal rates of C、Pb received rises of1.48and1.25times respectively. And this promoting capacity is lasting, it can promote to maintain Fe3+in solution state for long time.(7) The distribution characteristics of Cu、Ni、Zn、Cd in EPS(extracellular polymeric substance) and the intracellular or extracellular features were investigated. In this paper, a concise standard for determining the distribution characteristics in and out of cells about heavy metals was put forward. Also, the metabolic effect of dissolved organic carbon (DOC) with MT genetic bacteria was discussed. The results showed that MT genetic bacteria could proliferate using the original nutrition in sludge, and DOC would be degraded accompanied by the metabolizing. As a result, this metabolizing relieved some of the restraining factor for the growing of Thiobacilli.(8) The mechanism of heavy metal speciation transformation during the joint-bioleaching by MT genetic engineering bacteria were investigated. A new classification method on orignal sludge according to the chemical speciation of sludge was presented. The sludge bioleaching mechanism of six heavy metals C、Cd、Ni、Zn、Cr、Pb were categorized in the paper. The study demonstrates that the bioleaching process of Cu、Ni、Cd are mainly dominated by direct mechanism, the bioleaching process of Zn is mainly dominated by indirect mechanism, the bioleaching process of Cr、Pb are mainly dominated by combined mechanism. Within the analysis of above mechanism, the corresponding relation between the mechanism, the classification of the orignal sludge and the dominant microflora had been clarified tentatively, the study fruit expanded the connotation of combined mechanism bioleaching.

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