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伴随着人类工业、农业等活动的日益频繁,土壤中抗生素、重金属含量日益超标所引发的环境污染问题,备受社会关注[1]。抗生素对土壤微生物存在低剂量促进和高剂量抑制作用,与重金属共存时,抗生素的含电子供体基团可与重金属离子结合,使得自身的电荷被中和,从而变得更加稳定,导致其在环境中的持久性增强,最终通过生物富集作用,加大对人体和动植物的危害[2-4]。重金属铅(Pb)在血铅水平为10 mg·dL−1时[5],即可对儿童神经发育产生不良影响,伴随着畜禽粪肥施用、工业产出、大气沉积等,其在土壤环境介质中的检出质量分数范围为2.7~300 mg·kg−1[6-7],而其高溶解性和高迁移性,则进一步加剧了它的生态毒性。金霉素 (CTC) 作为四环素类 (TCs) 抗生素家族的一员,在土壤中的检出频率高 (81.3%~91.6%) ,检出质量分数大 (5.85~33.37 mg·kg−1) [6, 8-10],其还会与重金属通过交叉抗性和共选择性对土壤微生物产生长期选择性压力,诱发耐药菌和新污染物-抗性基因 (Antibiotic resistance genes,ARGs) 的产生,威胁生态安全。GUO等[11]研究发现Pb可降低土壤微生物群落的多样性,并且会和土霉素 (OTC) 共同作用,增加土壤ARGs的丰度。WANG等[12]指出Pb会促进土壤-植物系统中植物根生细菌和土壤ARGs的积累。目前,关于土壤抗生素和重金属复合污染环境归趋及相互作用的研究报道较多,对于二者复合污染诱导土壤微生物群落结构、酶活性以及ARGs变化的作用机理也多有研究[3-4, 13-15],但是如何采取绿色经济的技术手段对过量排入土壤中的重金属和抗生素进行固定或去除,对环境生态安全来讲意义重大,却研究较少。
高级氧化法[16]、植物修复法[17]和生物修复法[18]等常被用做重金属和抗生素复合污染土壤的修复,但高级氧化法降解抗生素产生的次生产物会对土壤带来二次危害,植物修复法周期较长,生物修复会带来物种入侵。基于生态安全、经济成本及操作可行性的考虑,向重金属和抗生素污染土壤中投加稳定剂进行原位修复是很好的途径[13]。生物质碳、黏土类矿物、含磷矿物等材料,廉价、易得,常被用于土壤原位修复的稳定剂。然而,生物质碳的加入大大提高了土壤的pH值[19-20],为土壤后续利用带来碱度过高的困扰,而单纯使用天然黏土类矿物,虽然有效但并不高效,含磷矿物的添加虽然可以达到很好的效果,却被视为对磷资源的一种浪费。鸟粪石结晶法同步回收污水氮磷并将回收产品用于重金属和抗生素复合污染土壤修复,由于兼具经济和环保效益,成为土壤修复领域的研究热点[13, 21-23]。有研究[7]将鸟粪石负载沸石用于Cu和TC复合污染土壤的原位修复,可将生物可利用性Cu和TC含量分别降低 73.0%和71.3%。
多项研究表明,氧化镁改性硅藻土可实现沼液中氮磷的同步回收[21-23],回收产品-鸟粪石负载硅藻土 (SD) 可实现污水中Pb (II) 和CTC的同步去除[23]。基于此,本研究以SD为土壤调理剂、以Pb和CTC复合污染土壤作为研究对象,考察SD加入前后土壤Pb和CTC的赋存状态、土壤理化性质和微生物群落的变化,探究SD对Pb和CTC复合污染土壤的修复效果和机制,以期为污水氮磷资源化以及重金属和抗生素复合污染土壤的原位修复提供技术支持。
鸟粪石负载硅藻土对土壤铅和金霉素的同步修复作用
Simultaneous remediation of lead and chlortetracycline in contaminated soil by addition of struvite-loaded diatomite
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摘要: 使用镁盐改性硅藻土回收沼液中氮磷制得鸟粪石负载硅藻土 (Struvite-loaded diatomite,SD) ,将其用于土壤中铅 (Pb) 和金霉素 (CTC) 复合污染的原位修复。采用吸附-解吸实验评估SD对Pb和CTC迁移特性的影响,同时,通过测定土壤pH和酸缓冲能力、土壤Pb和CTC的有效态和形态、土壤速效磷和微生物群落结构变化等考察SD对土壤Pb和CTC的钝化能力,借助SEM、XRD、FT-IR等表征手段揭示其修复机理。结果表明,SD能有效降低Pb和CTC在土壤中的迁移特性;SD投加质量分数为3%,稳定49 d后,土壤酸中和能力提升1倍以上,土壤有效态Pb和CTC含量分别降低26%和56%,酸溶态Pb占比降低10%,残渣态Pb占比升高18%, CTC的水溶态和松散结合态占比分别降低5%和13%,紧密结合态CTC升高11%,一定程度上降低了Pb和CTC在土壤中的生物有效性;SD的投加可提升土壤速效磷含量,提高土壤微生物的相对丰度和多样性,尤其增加酸杆菌门 (Acidobacteria) 、绿弯菌门 (Chloroflexi) 和芽单胞菌门 (Gemmatimonadetes) 的相对丰度,降低放线菌门 (Actinobacteria) 和厚壁菌门 (Firmicutes) 的相对丰度;SD对土壤Pb和CTC的钝化机制主要为吸附和沉淀的协同作用。该研究可为污水氮磷资源化利用和重金属抗生素复合污染土壤原位修复提供参考。Abstract: Struvite-loaded diatomite (SD), a product of nutrient recovery process from biogas slurry, has been applied as a soil amendment for soil multi-polluted with Pb and chlortetracycline (CTC). In this study, the effect of SD on the mobility characteristics of Pb and CTC in soil were evaluated by adsorption-desorption experiments. The passivation ability of SD on Pb and CTC were investigated through measuring soil pH, soil acid neutralization capacity, the bioavailable states and different binding states to soil of Pb and CTC, the bioavailable phosphorus and microbial community structure and so on. Also, the properties of the adsorbents were characterized by SEM, XRD, and FT-IR to reveal the the potential mechanisms during this process as well. The results showed that the immobilization ability of SD for Pb and CTC was much higher than that of soil, which can effectively reduce the migration properties of these two pollutants. Compared with the control group, the acid neutralization capacity of soil can be doubled by adding 3 wt% SD after stabilizing for 49 d. Meanwhile, the content of bioavailable Pb and CTC in soil was decreased by 26% and 56%, respectively. Specifically, the proportion of Pb in acid-soluble state has been cut down by 10%, and there was a 18% growth of Pb in residual state. The proportions of water-soluble state and loosely bound state of CTC reduced by 5% and 13%, and the proportion of its tightly bound state raised by 11%. Moreover, the usage of SD increased the content of bioavailable phosphorus and promoted the relative abundance and diversity of soil microorganisms, especially increasing the relative abundance of Acidobacteria, Chloroflexi and Gemmatimonadetes, accompanied by decreasing the relative abundance of Actinobacteria and Firmicutes. The passivation mechanisms of the SD to Pb and CTC were mainly adsorption and precipitation. The results of this study provide a useful guideline for the resource utilization of nitrogen and phosphorus in sewage and in-situ remediation of soil contaminated by heavy metals and antibiotics.
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Key words:
- struvite /
- lead /
- chlortetracycline /
- combined pollution /
- in-situ remediation of soil
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图 2 Pb(II) 和CTC在SD和土壤上的吸附等温线以及Pb(II)和CTC在H2O、CaCl2、乙酸/柠檬酸解吸下的滞后系数HI
Figure 2. Pb(II) and CTC adsorption by SD and soil in aqueous solution: Adsorption isotherms of Pb(II) adsorption on SD and soil with 50 mg L−1 CTC; adsorption isotherms of CTC adsorption on SD and soil with 200 mg L−1 Pb(II); the corresponding hysteresis index (HI) for Pb(II) and CTC desorption by using H2O, CaCl2, acetic acid/citric acid
表 1 供试土壤的基本理化性质
Table 1. Basic physiochemical properties of the tested soil
土壤类型 pH 黏土质量比/% 沙质土质量比/% 砂质土质量比/% 背景土壤 7.69 15.15 43.22 41.63 Pb(II) 和CTC污染土壤 6.59 15.15 43.22 41.63 土壤类型 土壤TOC含量/% 速效磷/ (mg·kg−1) 总Pb /(mg·kg−1) 总CTC/ (mg·kg−1) 背景土壤 0.049 43.27 1.15 1.02 Pb(II) 和CTC污染土壤 0.051 37.23 303.74 30.68 表 2 磷回收产物SD的EDS图谱元素原子占比和质量比
Table 2. Atomic proportion and mass ratio of EDS atlas for SD
元素 原子占比/% 质量比/% Mg 5.17 6.69 N 3.03 2.26 P 1.91 3.15 Si 17.60 26.32 表 3 纯土和SD吸附Pb(II)和CTC的Langmuir和Freundlich模型参数
Table 3. Langmuir and Freundlich isotherm parameters for adsorption of Pb(II) and CTC on soil and SD
吸附质 吸附剂 Langmuir 模型 Freundlich 模型 qmax
/(mg·g−1)KL
/(L·mg−1)R2 KF
/( (mg·g−1) · (mg·L−1) −n)n R2 Pb(II) 纯土 45.71 0.01 0.987 2.15 0.43 0.998 SD 689.40 0.15 0.985 304.27 0.11 0.918 CTC 纯土 47.11 0.01 0.989 1.06 0.71 0.992 SD 104.27 0.03 0.982 7.32 0.55 0.981 表 4 OTU水平下土壤样品的Chao指数和Shannon指数
Table 4. Chao index and Shannon index of soil samples on OTU level
组别 Chao Shannon 原土 4578.3 6.87 对照组 3945.8 6.44 +0.2%SD 3986.2 6.79 +1%SD 4301.5 6.82 +3%SD 4268.4 6.83 -
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