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在石油开采、加工、运输及使用过程中,原油以及各种石油制品的泄漏和排放事故时有发生,不可避免地会造成土壤的石油污染[1]。而土壤石油污染普遍是多种污染物复合污染,而不是单一污染。石油污染物中除了含有大量有机物外,还含有重金属等,他们会进入土壤并对生态环境造成复合污染[2-3]。近年来,我国部分油气田地区遭受了不同程度的石油-重金属复合污染。例如,长宁某页岩气井场土壤中含有原油和重金属镍2种污染物[4];黄河三角洲石油污染土壤中重金属元素多达10余种[5]。土壤中多种污染物之间的相互作用使得修复过程变得更加复杂。重金属与有机污染物之间的相互作用可能会改变污染物的形态、溶解度和生物可利用度,从而相互抑制或促进彼此的修复效率[6]。重金属及石油中多环芳烃等具有致癌性和诱变性[7-8],会对人体健康和自然生态系统造成极大威胁[9-10],因此,有机-重金属复合污染问题在全球范围内引起了极大的关注[11]。目前,针对石油-重金属复合污染土壤修复的研究已迫在眉睫。
微生物修复是去除或降解土壤污染物的最常见和最可靠的技术之一,该技术主要是利用微生物的新陈代谢及生物吸附等作用修复污染土壤。但是,将游离菌加入土壤中易受不良环境影响,导致修复效果不佳。固定化微生物技术(IMT)可为外源微生物提供保护屏障,避免微生物受环境的不利影响,包括与土著微生物竞争、污染物浓度过高、pH和温度不适宜等[12-13]。WANG等[14]发现,固定化微生物可以促进盐碱地中多环芳烃的降解,效果优于游离菌。张秀霞等[15-16]研究了固定化微生物修复石油污染土壤过程中对土壤生物学特性及理化性质的影响,结果表明,固定化微生物处理方式对石油烃降解效果最好,能增加土壤酶活性,对pH具有缓冲作用。IMT不仅可用于修复有机污染土壤,还可应用于重金属污染土壤。有研究表明,生物炭吸附固定化微生物对土壤中U、Cd钝化效果显著[17]。
目前,关于固定化微生物技术的研究多聚焦于单一污染土壤,针对有机-重金属复合污染土壤的研究鲜见报道[18]。外源微生物的加入可能会影响土壤微生物生态平衡[19],故在修复过程中不仅要考察固定化微生物对有机-重金属复合污染土壤修复效果,还要考察其对土壤环境的影响[20]。土壤酶活性和土壤细菌数量作为土壤生物学特性相关指标,可作为评价修复状况和污染对土壤性质影响的指标[15, 21]。
本研究从四川长宁-威远地区页岩气开发井场重度污染区的含油土壤中筛选出1株具有镉抗性和石油烃降解能力的菌株,以玉米芯生物炭作为固定化材料负载该菌株,研究固定化微生物对镉-石油烃污染土壤的修复效果,以期为复合污染土壤的生物修复提供参考。
利用生物炭负载微生物修复石油烃-镉复合污染土壤
Remediation of petroleum hydrocarbon-cadmium co-contaminated soil by biochar loaded microorganisms
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摘要: 自四川省长宁某石油烃-重金属镉复合污染土壤中,筛选出1株具有重金属镉(Cd)抗性和石油烃降解能力的菌株,采用吸附法将菌株固定于玉米芯生物炭上制备成固定化微生物,并探讨固定化微生物技术(IMT)对土壤石油烃的降解效率以及重金属固定化效果。鉴定结果表明,成功筛选出的具有Cd抗性的石油烃降解菌经鉴定属于柠檬酸杆菌属(Citrobacter sp
.)。实验结果表明:固定化微生物修复石油烃-重金属镉复合污染土壤60 d后,固定化微生物对石油烃降解率达51.25%,显著高于游离菌组(40.44%)、生物炭组(31.11%)和空白组(15.18%)(P<0.05);同时,固定化微生物能够高效固定土壤重金属Cd,使其从可交换态、有机结合态向残渣态转变,可使其残渣态与初始土壤相比增加6.68倍;固定化微生物组的土壤pH较初始出现轻微下降,但维持于8.42~8.75;此外,固定化微生物可显著增加土壤细菌数量(2.48×108 cfu·g−1)(P<0.05),土壤脱氢酶活性、过氧化氢酶活性以及多酚氧化酶活性(P<0.05)。因此,采用生物炭固定化微生物技术,可在高效降解石油烃的同时,提高重金属Cd固定化效果。该研究结果可为IMT技术修复石油烃-镉复合污染土壤提供参考。 Abstract: A bacterial strain with heavy metal cadmium (Cd) resistance and petroleum hydrocarbons degradation ability was isolated from petroleum hydrocarbons and heavy metal Cd co-contaminated soil sampled from Changning, Sichuan province. The strain was fixed on corncob biochar by adsorption method to obtain immobilized microorganisms. The degradation efficiency of soil petroleum hydrocarbons and the immobilization effect of heavy metals by immobilized microorganism technology (IMT) were investigated. The results showed that the selected strain had the ability of Cd resistance and petroleum hydrocarbons degradation, which was identified as Citrobacter sp. Remediation of petroleum hydrocarbon-heavy metal Cd contaminated soil by immobilized microorganisms after 60 d, the degradation rate of petroleum hydrocarbons by immobilized microorganisms was 51.25%, significantly higher than that of the free bacteria group (40.44%), biochar group (31.11%) and blank group (15.18%) (P<0.05). At the same time, immobilized microorganisms could effectively immobilize the heavy metal Cd in the soil by changing the exchangeable and organic matter-bound species to the residual species, which could increase the residual species by 6.68 times compared with the initial soil. The addition of immobilized microorganisms caused slight decrease of soil pH compared with that in the initial stage, but maintained 8.42~8.75. Moreover, immobilized microorganisms significantly increased the number of soil bacteria (2.48×108 cfu·g−1) (P<0.05), soil dehydrogenase activity, catalase activity and polyphenol oxidase activity (P<0.05). Biochar immobilized microorganisms could not only efficiently degrade petroleum hydrocarbons, but also improve the heavy metal immobilization. The research results could provide theoretical support for remediation of petroleum-Cd co-contaminated soil by IMT.-
Key words:
- immobilized microorganism /
- petroleum hydrocarbon /
- cadmium /
- co-contaminated soil
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表 1 污染土壤理化性质
Table 1. Major physicochemical characteristics of the soil
有机质/
(mg·kg−1)总氮/
(mg·kg−1)总磷/
(mg·kg−1)pH 含水率/
%石油烃/
(mg·kg−1)Cd/(mg·kg−1) 可交换态 碳酸盐
结合态铁锰氧化物
结合态有机
结合态残渣态 总量 5679.74 436.50 65.47 8.65 13.83 10000 3.15 0.88 0.54 1.21 0.30 6.08 表 2 菌株W8和柠檬酸杆菌的生理生化特性对照
Table 2. Physiological and biochemical characteristics of strain W8 and Citrobacter sp.
生理生化反应 实验结果 柠檬酸杆菌 生理生化反应 实验结果 柠檬酸杆菌 革兰氏染色 − − 甲基红实验 + + 酪蛋白水解实验 − D 硝酸盐还原实验 + + 动力实验 − + 糖发酵实验 + + 接触酶实验 − + V-P实验 − − 柠檬酸盐实验 + + 硫化氢产生实验 + D 吲哚实验 + d 明胶液化实验 − − 注:“+”表示呈阳性;“−”表示呈阴性;“d”表示大部分为阳性;“D”表示不同分类单位间反应不同。 -
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