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油田采出水(oilfield produced wastewater, OPW)指地下开采出的含水原油经油水分离技术处理后得到的油田污水[1]。随着我国大多数油田进入中、后期高含水开采阶段,各油田为稳定产量而不断加大开采力度,导致油田采出水产量也随之增加,自2010年起,我国每年约需处理的油田采出水就已超过10×109 m³,且呈逐年增加趋势[2-3]。扣除采出水回注后数据,近年来我国油田采出水的年外排量需求均超3 000×104 t,占油田生产废水处理总量的90%以上[4]。油田采出水主要含有以下种类的物质:溶解油和分散油、溶解矿物质、化学药剂、溶解气、固体颗粒物质,其中溶解油和分散油主要为各种烃类混合物,如苯、甲苯、乙苯、二甲苯、酚类、有机酸类化合物、多环芳烃(polycyclic aromatic hydrocarbons, PAHs)等[5]。PAHs指具有2个及以上的苯环结构的持久性有机污染物(persistent organic pollutants, POPs),对生物体具有致畸、致癌、致突变的三致效应,其中的萘、菲、芴、苊等16种PAHs属于美国环境保护署(environmental protection agency, EPA)认定的对人类和生态健康具有潜在影响的优先控制PAHs污染物[6-10]。为满足处理量大且低成本油田生产需求,目前国内大多数油田采出水的外排处理工艺普遍采用传统的物理分离联合生化处理法。有研究表明,生物处理工艺能够有效地去除绝大多数有机污染物,不能去除油田采出水中所含相对较高浓度的PAHs,且由于PAHs对微生物产生直接毒害作用,抑制了微生物的生长代谢,并具有较低的致死浓度,导致各水处理厂的生化工艺处理效能大大降低,外排水质波动大,外排水抽查达标率仅为50%左右[11-13]。
当前,石油开采生产面临环保排放压力日益增加,迫切需求对现有采油污水处理工艺进行升级增效以及开发应用高效率深度水处理新技术。对油田采出水中的PAHs类污染物的彻底去除成为了亟待解决的关键瓶颈问题之一,相关研究单位均致力于在该方向取得突破。
针对废水中PAHs的处理方法主要包括膜过滤、物理吸附、化学氧化、光催化氧化降解等[13-18]。光催化氧化法相对于上述其他PAHs降解技术具有反应条件温和、处理效率高、无二次污染、矿化彻底且适于处理低浓度污染物的优势,极具发展前景[19-21]。然而现有研究开展的工作大多集中在针对油田采出水中萘、菲、芴等低环PAHs物质中的单组分或双组分的光催化去除,实验水样主要为实验室人工自配模拟采油废水,鲜有针对实际油田采出水中多组分PAHs污染物共存条件下的光催化氧化竞争行为及降解效率的研究[22-23]。
本研究首先表征了所采用的g-C3N4/TiO2复合薄膜光催化剂的物理化学性质;后利用紫外光辐照g-C3N4/TiO2复合薄膜光催化剂,对取自采油现场的采出水水样进行降解,研究多组分PAHs污染物共存条件下的不同环数PAHs发生光催化氧化反应的规律及其降解动力学,以期为今后解决油田采出水中PAHs生物毒害问题探索新工艺方法并积累理论参考数据做贡献,从而推动我国石油开采废水处理行业早日实现技术升级。
g-C3N4/TiO2复合薄膜光催化降解石油采出水中多环芳烃
Degradation of polycyclic aromatic hydrocarbons in oilfield produced wastewater based on g-C3N4/TiO2 composite thin film photocatalyst
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摘要: 针对亟待解决的石油开采废水中的多环芳烃(polycyclic aromatic hydrocarbons, PAHs)污染物的生物毒害性问题,利用紫外光辐照g-C3N4/TiO2复合薄膜光催化剂,对取自内蒙某采油现场的采出水水样进行降解处理,研究多组分PAHs污染物共存条件下的不同环数PAHs发生光催化氧化反应的降解规律及降解动力学。采用扫描电子显微镜(scanning electron microscope, SEM)表征光催化剂表面微观形貌,采用固相微萃取法富集和萃取水样中的PAHs,采用气相色谱-质谱联用法(gas chromatography-mass spectrometry, GC-MS)检测分析PAHs含量。经UV/g-C3N4/TiO2光催化反应处理,采出水中不溶的颗粒态萘优先于溶解态萘被降解去除,经60 min后对萘的总去除率可达61.13%。大于4环不溶性高环PAHs,可被优先光催化降解,从而高毒性的PAHs污染物被逐级转化为相对较低生物毒性的苊烯、蒽、菲、萘等,其中苊烯的含量增长最显著。结论石油采出水的外排处理工艺中增加PAHs光催化脱毒工艺具有一定可行性,对于保障原有水厂中的生化工艺段高效率、稳定运行将极具价值。Abstract: Aiming at the urgent problem regarding the biological toxicity of polycyclic aromatic hydrocarbons(polycyclic aromatic hydrocarbons, PAHs)pollutants in oilfield-produced wastewater, original wastewater samples from an oil production site in Inner Mongolia were degraded by using UV irradiation g-C3N4/TiO2 composite film photocatalyst. The photocatalytic oxidation behavior and degradation kinetics of PAHs with different benzene ring numbers were studied under the coexistence of multiple pollutants. The surface morphology of the photocatalyst was characterized by scanning electron microscopy (scanning electron microscope, SEM). PAHs in water samples were enriched and extracted by solid-phase microextraction. The content of PAHs was quantitatively analyzed by gas chromatography/mass spectrometry (gas chromatography-mass spectrometry, GC-MS). The results showed that after UV/g-C3N4/TiO2 photocatalytic reaction treatment, insoluble granular naphthalene was removed preferentially than dissolved naphthalene. The total removal rate of naphthalene could reach 61.13% after 60 min photocatalytic reaction. Insoluble PAHs with more than 4 benzene rings could be preferentially degraded by photocatalysis. Then the highly toxic PAHs were gradually converted into acenaphthene (Ace), anthracene (Ant), phenanthrene (Phe), naphthalene (Nap) and so on, of which the content of Ace increased significantly. The application of PAHs photocatalytic "detoxification" process in the efflux treatment of oilfield-produced water has a certain feasibility. More extensive research is worth carrying out in the future. It will be of great value to ensure the highly efficient and stable operation of the existing biochemical process in petroleum production wastewater treatment plants.
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Key words:
- produced wastewater /
- PAHs /
- photocatalytic degradation /
- solid-phase microextraction /
- GC-MS.
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表 1 油田采出水原水水样(0 min)中所含的PAHs质量浓度
Table 1. PAHs concentration in 0 min
PAHs
0 min水样(过滤分离) PAHs含量总和/(mg·L−1) 溶解态
/(mg·L−1)颗粒态
/(mg·L−1)萘(Nap) 1.194 07 4.337 38 5.531 45 苊(Acy) 0.021 742 0.056 49 0.078 232 苊稀(Ace) 0.010 052 0.230 318 0.240 37 芴(Fl) 0.021 92 0.267 536 0.289 456 菲(Phe) 0.046 805 0.669 296 0.716 101 蒽(Ant) 0.057 235 0.159 895 0.217 13 荧蒽(Flu) 0.029 166 0.251 054 0.280 22 芘(Pyr) 0.044 552 0.519 69 0.564 242 苯并[a]蒽(BaA) 0.063 517 0.163 323 0.226 84 䓛(Chr) 0.031 157 0.138 712 0.169 869 苯并(b)荧蒽(BbF) 0.072 649 0.155 904 0.228 553 苯并[k]荧蒽(BkF) 0.033 369 0.078 795 0.112 164 苯并芘(BaP) 0.024 312 0.082 777 0.107 089 茚苯(1,2,3-cd)芘(InP) 0.082 25 0.175 794 0.258 044 二苯并[a]蒽(DahP) 0.072 927 0.158 395 0.231 322 苯并[g,h,i]芘(BghiP) 0.008 501 0.001 767 0.010 268 ΣPAHs 1.814 224 7.447 127 9.261 351 -
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