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污染物通常是以多种共存的形式被释放在生态系统中,一般具有伴生性和综合性[1]。因此,某一污染物在生态系统(土壤、水体、沉积物等)中的吸附行为必定会受到其他共存污染物的影响。共存的多环芳烃和重金属是环境中典型的2种污染物[2-3]。多环芳烃由2个或2个以上的碳和氢原子的聚合芳香烃环组成,其分子质量越大,水溶性越低,属于难降解的持久性有机污染物[4-5]。重金属-多环芳烃复合污染主要来源于家庭和工业废物不完全燃烧,直接或间接从空气和水中释放进入河流和土壤中[6]。根据重金属和多环芳烃与吸附剂结合方式的不同,重金属和多环芳烃之间可能存在的作用有互不影响、竞争吸附、共沉淀等[7]。二者在环境中的滞留会产生严重的生物毒性危及所有生物,并且研究发现复合污染的毒性机理也更加复杂。所以探究复合污染吸附影响机制刻不容缓。
生物膜能够有效结合重金属且对有机污染物具有较强的亲和力。水体生物膜由微生物和细胞外聚合物质组成,通常存在于几乎所有水生环境系统中[8-9]。有研究[10-11]表明,生物膜对有机污染物(包括疏水性和亲水性)的吸附与生物膜的有机质含量呈线性相关,有机质部分被认为是影响生物膜吸附的一个重要因素。不同水体、不同季节生长的生物膜被认为是微量污染吸附的关键因素[12]。HUANG等[13]研究发现生物膜对微量有机污染物的吸附机理较为复杂,吸附可由静电、阳离子交换和络合相互作用等多种机制参与。重金属对疏水性有机污染物的吸附存在争议,有研究[14]表明,重金属通过与疏水性有机污染物争夺吸附表面活性位点来抑制疏水性有机污染物的吸附。有研究表明,某些重金属如Ag+、Cu2+、Fe3+和Cd2+有助于芳香族有机化合物(多环芳香烃在木质碳[15]、蓝藻[16]和细菌[17])的吸附。
目前,重金属和多环芳烃复合污染对生物膜吸附性能的影响机制仍不清楚。因此,本研究选取新疆乌鲁木齐市某含油污水库的生物膜,以镉Cd(Ⅱ)和菲(PHE)为重金属和PAHs的模型化合物,探究了污水生物膜在有Cd2+和无Cd2+条件下对PHE的吸附影响及机理,以期能为新疆含油污染水体中重金属-多环芳烃复合污染防治提供参考。
重金属镉对污水生物膜吸附菲的影响机制
The influence mechanism of heavy metal cadmium on phenanthrene adsorption onto sewage biofilm
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摘要: 为了探究重金属镉(Cd)对污水生物膜吸附菲(phenanthrene,PHE)的影响及机制,以新疆乌鲁木齐某含油污水库生物膜为研究对象,通过对比有Cd2+和无Cd2+条件下,污水生物膜对PHE的吸附性能,Cd2+的存在对污水生物膜吸附PHE有促进作用。有Cd2+和无Cd2+条件下,在pH=6、温度为35 ℃时污水生物膜对PHE的吸附效果最好;吸附动力学和吸附等温线方程均符合拟二级动力学和Langmuir模型,说明吸附以单分子层的化学吸附为主,并且有Cd2+时污水生物膜对PHE的最大吸附量比无Cd2+时高出21.8%。SEM、FTIR和XPS的表征分析结果表明,有Cd2+和无Cd2+条件下污水生物膜表面与PHE发生作用的基团基本相同,吸附过程中的主要官能团为有机质中的羟基、羧基和酰胺基团。Abstract: To explore the effect and mechanism of cadmium (Cd) on phenanthrene (PHE) adsorption onto sewage biofilm, Urumqi oil reservoir biofilm was taken as the research object, then the PHE adsorption performance onto the sewage biofilm was compared with and without Cd2+. The results showed that PHE adsorption onto the sewage biofilm was promoted in the presence of Cd2+. Whether with or without Cd2+, the best PHE adsorption effect onto the sewage biofilm occurred at pH 6 and 35 ℃. The simulated kinetics and isotherm equations were consistent with the pseudo-second-order kinetics and Langmuir model, indicating that the adsorption is dominated by the chemisorption of monolayers, and the maximum PHE adsorption amount with Cd2+ was 21.8% higher than that in the absence of Cd2+. The result of SEM, FTIR, and XPS characterization indicated that the groups on the sewage biofilm surface absorbing PHE with or without Cd2+ were basically same, and the main functional groups in organics were hydroxyl, carboxyl, and amide ones.
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Key words:
- cadmium /
- phenanthrene /
- sewage biofilm /
- adsorption
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表 1 污灌区采样水质测定分析表
Table 1. Analysis table for water quality determination at sampling sites
项目 采样坐标 pH 溶解氧/(mg·L−1) COD/(mg·L−1) 氨氮/(mg·L−1) 总氮/(mg·L−1) 总磷/(mg·L−1) 污灌区水体 44°11'24〃N,87°42'27〃E 7.4 4.6 31 8.4 5.9 0.18 水环境质量标准(GB3838-02)Ⅳ类 — 6~9 3 30 1.5 1.5 0.3 超标倍数 — — 0.53 0.03 4.6 2.93 — 表 2 污水生物膜吸附PHE的拟一级动力学及拟二级动力学参数
Table 2. Parameters of pseudo-first-order kinetics and pseudo-second-order kinetics fitting PHE adsorption onto sewage biofilm
有(无)Cd2+ 拟一级动力学模型 拟二级动力学模型 a b R2 q k R2 无Cd2+ 1.507 0.043 0.986 2 1.60 0.043 0.989 9 有Cd2+ 1.515 0.037 0.955 7 1.62 0.035 0.990 1 表 3 生物膜吸附PHE的Langmuir和Freundlich吸附拟合参数
Table 3. Parameters of Langmuir and Freundlich adsorption model fitting PHE adsorption onto sewage biofilm
有(无)Cd2+ Langmuir 模型 Freundlich 模型 k q R2 a b R2 无Cd2+ 0.109 15.53 0.988 4 1.588 1.339 0.974 6 有Cd2+ 0.079 18.91 0.977 5 1.445 1.255 0.953 4 -
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