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土壤重金属污染是影响人类健康和生态环境质量的世界性问题[1-2]. 固定/稳定化和直接去除是重金属污染土壤修复的两种主要方法[1,3]. 修复技术主要有固定化、玻璃化、电动修复、植物修复和化学淋洗修复[1-3]. 土壤淋洗修复技术可以将重金属转移至液相以达到永久去除土壤中重金属的目的,是一种高效、低成本的方法,尤其适用于重度污染土壤[2,4-5]. 尽管淋洗剂(乙二胺四乙酸(EDTA)、谷氨酸N, N-二乙酸(GLDA)、乙二胺二琥珀酸(EDDS)和柠檬酸)对土壤中重金属去除效率高,但产生大量的淋洗废液中重金属主要以稳定的络合物形式存在,在较宽的pH范围内均有较高的稳定性,易造成二次污染问题[6]. 去除络合态重金属常用的方法有化学沉淀法、化学氧化法和离子交换法,但普遍存在产泥量大、处理条件复杂、费用较高等问题[6-8]. 与传统的化学处理方法相比,生物处理具有微生物来源广泛、适应性强、成本低、效率高、对环境友好等优点而有广阔应用前景[9].
近年来,学者们对硫酸盐还原菌(SRB)处理重金属污染废水进行了广泛的研究[9-11]. 研究表明,SRB可以去除传统废水中90%以上的Zn2+、Cu2+、Cd2+、Pb2+、Ni2+和Cr6+[9-11]. 一般来说,SRB去除废水中重金属离子主要通过硫化物沉淀和死菌体吸附[11-12]. 硫化物沉淀的形成过程分为两个阶段:(1)SRB利用硫酸盐作为电子受体氧化简单有机化合物生成碳酸氢根离子和硫化氢;(2)生物生成的硫化氢与游离重金属阳离子反应生成金属硫化物沉淀[9]. 此外,死菌体通过细胞壁上的官能团直接吸附重金属,有利于废水中重金属的去除[12].
虽然SRB对传统废水中的重金属离子具有很高的去除效率,但淋洗废液中的重金属主要以络合态形式存在[7],有研究报道SRB可以通过还原反应机理有效地去除Fe(Ⅲ)和Cr(Ⅵ)的络合形态[13-14],与高价态重金属相比,对于二价态重金属络合物去除的报道较少. Hakansson等[15]利用SRB产生的H2S处理络合态Pb和Cu的沉淀率达98%. 然而,据我们所知,二价重金属络合物的去除机理还不清楚. 不同络合剂如何影响SRB对络合态重金属的去除率,除形成金属硫化物沉淀外,细菌对络合态重金属的吸附效率几乎没有报道.
为了深入了解SRB对二价态重金属络合物的去除机理,利用不同络合剂形成Cu(Ⅱ)络合物,研究了分离SRB (Shewanella sp. JN01)对不同络合态Cu的去除效果及不同途径对菌株去除Cu(Ⅱ)络合物的贡献及其机理,以期达到淋洗废液的资源化再生和无害化处理提供科学依据.
Shewanella sp. JN01对水体系不同络合态Cu的去除效果及机理
Removal efficiency and mechanism of different kinds of copper complexes from aqueous system by Shewanella sp. JN01
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摘要: 土壤淋洗废液处理难点在于废水中含有高浓度的稳定重金属络合物. 本研究分离了一株硫酸盐还原菌(Shewanella sp. JN01),探讨了其对模拟淋洗废液中不同络合态Cu (Cu-乙二胺四乙酸(Cu-EDTA)、Cu-谷氨酸N,N-二乙酸(Cu-GLDA)、Cu-柠檬酸(Cu-CA)和Cu-混合淋洗剂(Cu-MC))的去除效果及机理. 结果表明,活菌体和死菌体对不同络合态Cu的去除率分别大于80%和小于8%. 显然,死菌体细胞表面吸附作用对络合态Cu去除效率的贡献十分有限. 因此,Shewanella sp. JN01去除络合态Cu的主要机制是先破络,再形成CuS沉淀. Shewanella sp. JN01对不同络合态Cu的去除率为Cu-CA >Cu-MC >Cu-GLDA >Cu-EDTA,这一变化趋势与它们的稳定性常数和毒性的变化趋势相反,结果进一步证实了破络是微生物去除络合态重金属的限制性步骤. Shewanella sp. JN01能够有效去除土壤淋洗废液中重金属络合物,在淋洗废液再生利用方面具有潜在应用前景.
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关键词:
- 土壤淋洗废液 /
- 络合态Cu /
- Shewanella sp. JN01 /
- 硫化物 /
- 沉淀.
Abstract: The difficulty in the treatment of soil washing effluent lies in its high concentrations of stable heavy metal complexes. This study isolated a strain of sulfate-reducing bacteria (Shewanella sp. JN01) to explore the removal efficiency and mechanism of different heavy metal complexes [Cu-ethylenediaminetetraacetic acid (Cu-EDTA), Cu-N, N-bis(carboxymethyl) glutamic acid (Cu-GLDA), Cu-citrate (Cu-CA) and Cu-mixed chelator (Cu-MC)] from the simulated soil washing effluent by Shewanella sp. JN01. The results showed that removal efficiencies of different Cu complexes by the alive and dead Shewanella sp. JN01 were above 80% and below 8%, respectively. Evidently, the contribution of sorption of Cu complexes by cell surface of the dead strain to its total removal efficiency was limited. Therefore, the dominant removal mechanism of Cu complexes by Shewanella sp. JN01 was related to dechelation first and then formation of CuS precipitation. The removal efficiencies of different Cu complexes by Shewanella sp. JN01 varied as the trend of Cu-CA > Cu-MC > Cu-GLDA > Cu-EDTA, which was opposite to the trend of their stability constants and toxicity. This finding further confirmed that the dechelation was a limiting step to remove heavy metal complexes by microorganisms. Collectively, the results of this study indicate that Shewanella sp. JN01 can effectively remove the heavy metal complexes from soil washing effluent, which has potential application prospects for recycling use of soil washing effluent.-
Key words:
- soil washing effluent /
- copper complexes /
- Shewanella sp. JN01 /
- sulfide /
- precipitation.
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表 1 SRB富集培养基的组成
Table 1. Composition of SRB enrichment medium
药品名称
Pharmaceutical ingredients质量浓度/(g·L−1)
Mass concentrationK2HPO4 0.5 (NH4)2SO4 2.5 NaHCO3 0.5 CaCl2 0.2 MgSO4 1 乳酸钠
sodium lactate20 mL·L−1 L-抗坏血酸
L-Ascorbic acid0.1 L-半胱氨酸盐酸盐
L-Cysteine hydrochloride monohydrate0.5 酵母膏
yeast extract1.5 (NH4)2Fe(SO4)2·6H2O 0.5 表 2 不同处理中沉淀物中的原子比(Cu与络合剂物质的量比为1:10)
Table 2. The atomic ratios of precipitates from different treatments (molar ratio of Cu and complexing agent =1:10).
元素
Element原子比/%
AtomShewanella sp. JN01 Cu2+ Cu-EDTA Cu-GLDA Cu-CA Cu-MC C 63.30 67.13 78.21 71.85 72.00 75.19 O 29.85 19.45 19.03 16.13 23.28 21.69 S 6.85 9.07 1.70 6.64 3.36 1.57 Cu ND 4.34 1.07 5.38 1.36 1.56 ND.,未检出. ND., not detected. -
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