摘要
为提高污水中17β-雌二醇(E2)的去除效率,筛选洱海沉积物中E2的优势降解微生物,并在不同环境条件下进行生物吸附和生物降解E2过程的研究。结果表明:大肠杆菌是E2降解的优势菌种,其对E2的生物去除是快速吸附及持续降解的共同作用过程。经大肠杆菌降解3 d后,1.00 mg/
类固醇雌激素(Steroid estrogens, SEs)对生态环境与人体健康的危害广受关注。17β-雌二醇(E2)是一种典型的SEs,仅在1 ng/L环境浓度时即可使水生生物产生慢性毒性,使其产生畸变或致
大多传统的生物法与物理化学法污水处理技术可去除一部分SE
微生物去除污染物有两种方法,即生物吸附和生物降
E2和标准品腐殖酸(HA)购买自Sigma-Aldrich公司。沉积物来自中国云南省大理市洱海,干燥后使用4.0 mm筛子筛分,用去离子水冲洗。采用国际腐殖酸物质学会的碱溶酸析法提取湖泊沉积物腐殖酸(LHA)和富里酸(LFA
称取100 g洱海底泥样品与150 mL无机盐培养基(MSM)混合置于500 mL锥形瓶中,充分振荡20 min后取上清液。其中,MSM成分为600 mg/L K2HPO4·12H2O、800 mg/L KH2PO4、1 000 mg/L NaCl、800 mg/L NH4NO3、200 mg/L MgSO4、50 mg/L CaCl2·2H2O和10 mg/L酵母提取
为阐明E2降解微生物对E2的吸附过程,进行了吸附平衡实验。生物量为1.00 g/L,E2浓度为1.00 mg/L,吸附时间为5 h。生物吸附在30.0 mL MSM中进行,并在30 ℃的旋转摇床上以160 r/min培养。在溶液中加入浓度为650 mg/L的叠氮化钠以抑制微生物活性。此后,取1.0 mL样品于离心管中,以12 000 r/min的速度离心10.0 min。离心后取样品上清液,使用高效液相色谱仪对E2进行分析。如无额外说明,所有吸附实验均在此条件下进行。
等温吸附实验使用1.00 g/L的生物量吸附不同浓度的E2溶液(0.25、0.50、0.75、1.00、1.50、1.75、2.00 mg/L)。E2吸附在微生物上,吸附量G(mg/g) 可用
(1) |
式中:为E2的初始浓度,mg/L;为E2的平衡浓度,mg/L;为微生物浓度,g/L。
为评估pH值、生物量对E2生物吸附的影响。分别对初始pH值范围为4.0~10.0和初始生物量为0.08~1.20 g/L的样品进行吸附实验。
为了评估碳源、H2O2、腐殖质及重金属对E2生物降解的影响,将1.00 mg/L E2和1.00 g/L微生物加入30 mL MSM的烧瓶中后,在避光条件下以160 r/min的转速在30 ℃的旋转摇床上培养。如无额外说明,所有生物降解实验均在此条件下进行。实验中,所加碳源为葡萄糖与甲酸钠,浓度为0.0、5.0、10.0、15.0、20.0、25.0、30.0、35.0、40.0、45.0、50.0 mg/L。H2O2的浓度为0.0、1.0、2.0、3.0、4.0、5.0、8.0、10.0、15.0、20.0 mmol/L,HA浓度梯度设为从0.0到50.0 mg/L不等。
为确定重金属(Z
所有实验在相同条件下进行,试剂及容器均在高压灭菌锅中以121 ℃灭菌30 min后使用。所有操作重复3次。
在对底泥样本中E2降解微生物Y2进行富集筛选后,对培养的菌株进行微生物种类鉴别,鉴别结果如

图1 E2降解菌Y2鉴定层次聚类树
Fig. 1 The phylogenetic tree of E2 degrading bacteria Y2 identification
为明确生物吸附和生物降解过程对水溶液中E2去除率的贡献,首先,在30 ℃下进行了1.00 g/L大肠杆菌对1.00 mg/L E2的生物吸附实验,结果如

图2 大肠杆菌对E2的吸附平衡曲线
Fig. 2 E. coli adsorption equilibrium curve for E2
为了更好理解大肠杆菌对E2的生物吸附作用,在30 ℃下进行等温吸附实验。并根据E2两种不同的吸附模型,分别使用Freundlich和Langmuir等温线吸附模型进行拟合,结果见

图3 两种不同的吸附模型拟合曲线
Fig. 3 The fitting curves of two different adsorption models
在72 h的1.00 g/L大肠杆菌对1.00 mg/L E2生物去除实验中,生物降解率为生物去除率减去生物吸附率,结果如

图4 E2的总去除率、生物吸附率及生物降解率
Fig. 4 Total removal efficiency, biosorption efficiency and biodegradation efficiency of E2
不同pH值和生物量对1.00 mg/L E2的生物吸附率如

图5 pH值与生物量对生物吸附的影响
Fig. 5 Effect of pH value and biomass on the biosorption
持久性有机污染物流入水生环境,可抑制微生物的生

图6 碳源对生物降解率的影响
Fig. 6 Effect of carbon sources on the biodegradation
efficiency
已有研究表

图7 H2O2对生物降解率的影响
Fig. 7 Effect of H2O2 on the biodegradation efficiency
E2具有稳定的芳香结构,表现出较强的疏水性和极低的水溶性,很难被生物体利用,从而限制了生物降解技术的应

图8 腐殖质对生物降解率的影响
Fig. 8 Effect of humic on the biodegradation efficiency
微量元素是维持微生物生长发育所必需的,可刺激微生物活动。但当单一微量元素过量时,对微生物具有很高毒性。研究了72 h内不同重金属对生物降解率的影响,见

图9 重金属对生物降解率的影响
Fig. 9 Effect of heavy mental on biodegradation efficiency
1)大肠杆菌是洱海底泥中的E2降解优势菌种,E2的生物去除过程由生物吸附及生物降解两部分组成。
2)生物吸附过程主要受pH值、生物量和E2浓度限制。其中吸附过程对pH值具有明显的依赖性,与生物量和E2浓度则呈明显正相关。弱碱性下(pH=8)吸附效率最为显著,约是酸性和强碱性的2~5倍,可达0.28 mg/g。
3)当葡萄糖、甲酸钠、H2O2、腐殖质、Z
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