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岩溶区地下水资源的保护与修复是全球面临的重要环境问题[1]。燃油泄漏是地下环境常见的污染源之一,其组分苯(benzene, B)、甲苯(toluene, T)、乙苯(ethylbenzene, E)和二甲苯(xylene, X)是主要的有害物质。由于具有较高的溶解度与迁移性,BTEX不仅对环境和生态造成威胁,对人类的健康也构成严重危害,能诱发癌症等疾病[2-4]。因此,岩溶区燃油污染及其治理受到研究者的广泛关注,成为环境保护领域的重要议题。
原位化学氧化(in situ chemical oxidation, ISCO)是近年来常用的有机污染修复技术,通过向土壤或地下水中注入氧化剂,将有机污染物转化为无害或低毒性物质,从而达到修复目的[5]。过硫酸盐(persulfate, PS)是ISCO中常用的氧化剂之一,具有强氧化性、易溶于水、良好稳定性和适用范围广等特点[6]。然而,ISCO技术仍然存在一些不足,如氧化剂寿命受含水介质影响持久性变差,在岩溶水系统因为水流速度快而容易流失,因此,为达到持续治理目的通常需要进行多次投注[7]。随着修复技术的发展,缓释体(slow-release materials, SRMs)技术已成为当前的研究热点。SRM技术通过将氧化剂与粘合剂构成缓释体来减缓氧化剂的释放速率,达到延长使用寿命和增加利用率的目的[8]。缓释技术基本以物理法为主,作为载体的粘合剂不与氧化剂发生反应,将氧化剂混合、包裹在SRM内,使其缓慢释放。目前,按粘合剂的不同可分为石蜡类缓释体、混凝土类缓释体以及凝胶类缓释体等,这些缓释体在地下水原位修复中具有巨大的利用潜力[9]。其中,以石蜡为粘合剂的PS-SRMs技术有良好的应用前景,现有研究[10-11]已证明其具有降解有机污染物的性能。
为加强污染治理效果,研究者已经提出将ISCO技术与增强型生物修复(enhanced bioremediation, EBR)技术联合形成处理链,扬长避短,协同促进修复性能[12-14]。在微氧或厌氧的石油烃污染地下水环境中,硝酸盐、三价铁和硫酸盐常被微生物降解作用利用为电子受体[15-17],因此,这些化合物也可能成为ISCO-EBR处理链利用的电子受体。尽管PS-ISCO具有抑制微生物活性的缺点[18],但有研究[19-21]表明PS-ISCO产生的硫酸根离子可以被微生物利用继续降解BTEX。然而,通过添加电子受体促进EBR并与PS-SRM-ISCO协同处理BTEX的研究,至今仍未见相关报道,其研究可能对削减ISCO对微生物活性影响也具有积极意义。
为发展岩溶含水层石油污染修复技术,本研究以岩溶地下河中石灰石和砂粒混合物作为含水介质,以汽油饱和溶液为BTEX来源,以石蜡粘合剂制备PS-SRM,通过添加硝酸盐、三价铁以及利用PS氧化产生的硫酸盐来补充电子受体,开展了微元体研究,探究了不同过硫酸钠/石蜡质量比PS-SRM处理汽油BTEX的效果,更好地认识PS缓释情况下电子受体的可利用情况,为岩溶区EBR-ISCO-SRM技术联合处理地下水石油污染治理提供科学依据。
PS缓释处理岩溶水石油污染过程中电子受体的利用
Availability of electron acceptors in the persulfate slow-release treatment of petroleum pollution in karst groundwater
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摘要: 原位化学氧化与生物修复技术在石油污染地下水中具有联合的潜力,但化学氧化对微生物活性具有抑制影响,通过缓释氧化剂技术可能会缓解这种影响。为了更好地认识基于过硫酸钠的缓释技术在修复岩溶地下水石油污染过程中对生物降解作用的影响,本研究利用微元体实验在微氧/厌氧条件下,开展了过硫酸盐缓释处理石油污染修复中不同电子受体利用的研究。实验设置了未投加缓释体和添加缓释体(过硫酸钠/石蜡质量比分别为0.5、1、2和3)的不同工况,通过未添加电子受体、添加100 mg·L−1硝酸盐和添加100 mg·L−1三价铁作为电子受体,探究石油污染物苯、甲苯、二甲苯(简称BTX)以及乙醇(EtOH)处理及电子受体的可利用性。结果表明:BTX的降解速率与缓释体过硫酸钠/石蜡质量比呈正相关,在过硫酸钠/石蜡质量比为2和3时降解速率较高,比乙醇更容易被化学氧化;BTX降解以化学氧化为主,而乙醇的降解则以微生物作用为主。过硫酸盐缓释条件下,生物作用中硝酸盐还原作用较为明显,硫酸盐还原作用较为微弱,铁还原作用不明显;硝酸盐最容易被利用为电子受体,其次为硫酸盐,三价铁被微生物利用的可能性最小。缓释体质量比不同、电子受体类型不同可导致优势菌属存在明显的差异,鞘氨醇单胞菌属和罗尔斯通氏菌属相对丰度普遍较高,二者均可利用多种电子受体降解污染物,在生物降解上起到主要作用。Abstract: In situ chemical oxidation (ISCO) has the potential to combine with bioremediation techniques in the remediation of petroleum-contaminated groundwater, but it can decrease the activity of microorganisms, which may be buffered by slow-release material (SRM) techniques. To better understand the effect of SRM with persulfate (PS) on the biodegradation in the remediation of petroleum pollution in karst groundwater, a microcosm experiment under microaerobic and anaerobic conditions was conducted to explore the availability of different electron acceptors. In the test, different working conditions without or with slow release PS (persulfate/paraffin mass ratios of 0.5, 1, 2, and 3) were set as follows: no addition of electron acceptor, addition of 100 mg·L−1 nitrate as electron acceptor, addition of 100 mg·L−1 Fe3+ as electron acceptor, the treatment of benzene, toluene, xylene (referred to as BTX) and ethanol (EtOH) was investigated, as well as the availability of electron acceptors. The results showed that the degradation rate of BTX was positively correlated with the mass ratio of SRMs, and the highest degradation rate constants occurred at persulfate/paraffin mass ratios of 2 and 3. BTX was more preferentially oxidized by PS than EtOH. BTX degradation was dominated by chemical oxidation, while EtOH dgradation was dominated by microbial action. With the presence of SRMs, nitrate reduction was more significant in microbial action, while sulfate reduction was relatively weak, iron reduction was unconspicuous. Nitrate was more readily used as an electron acceptor by microorganisms, followed by sulfate. However, the possibility of ferric iron used by microbial was slight. Different mass ratios of SRMs and different types of electron acceptors could lead to significant differences in the dominant genera. Both Sphingomonas spp. and Ralstonia spp. had higher relative abundances than others and played a major role in utilizing various electron acceptors to degrade pollutants.
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Key words:
- petroleum pollution /
- persulfate /
- slow-release material /
- groundwater /
- biodegradation
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表 1 实验采用含水介质的化学成分
Table 1. Chemical constituents of aqueous media used in experiments %
含水介质 Al2O3 CaCO3 SiO2 Fe2O3 Na2O MgCO3 K2O 其他 石灰石 0.41 88.22 1.38 0.24 0.01 9.63 0.02 0.09 河砂 23.21 0.29 56.15 11.15 0.11 2.02 5.13 1.94 表 2 微元体设置
Table 2. Design of the microcosms
电子受体 过硫酸钠/
石蜡质量比组别 添加物及目标质量浓度/(mg·L−1) S2O82− BTX EtOH SO42− NO3− Fe3+ 未添加电子受体 — S1 — 20 100 — — — 0.5 S2 791 20 100 * — — 1 S3 791 20 100 * — — 2 S4 791 20 100 * — — 3 S5 791 20 100 * — — 添加硝酸盐电子受体 — N1 — 20 100 — 100 — 0.5 N2 791 20 100 * 100 — 1 N3 791 20 100 * 100 — 2 N4 791 20 100 * 100 — 3 N5 791 20 100 * 100 — 添加三价铁电子受体 — F1 — 20 100 — — 100 0.5 F2 791 20 100 * — 100 1 F3 791 20 100 * — 100 2 F4 791 20 100 * — 100 3 F5 791 20 100 * — 100 注:“—”表示未添加相应组分;“*”表示SRMs释放的PS会产生硫酸盐离子;汽油饱和溶液未能检出乙苯(E)。 表 3 各组缓释体PS释放情况
Table 3. Release of sustained-release materials in each group
电子受体 组别 质量比 拟合时间/d 拟合方程 PS增长速率/(mg·(L·d)−1) R2 缓释率/% 未添加电子受体 S2 0.5 0~70 y=8.9x+18.7 8.9 0.931 9 59.7 S3 1 0~63 y=14.4x−18.1 14.4 0.937 5 69.2 S4 2 0~20 y=34.3x−19.4 34.3 0.916 6 77.4 S5 3 0~13 y=64.9x+98.6 64.9 0.956 1 96.1 添加硝酸盐 N2 0.5 0~70 y=6.9x+8.7 6.9 0.989 3 54.6 N3 1 0~70 y=10.4x−39.6 10.4 0.977 3 67.7 N4 2 0~13 y=71.4x−57.1 71.4 0.920 1 98.6 N5 3 0~13 y=69.0x+131.6 69.0 0.931 2 100.0 添加三价铁 F2 0.5 0~49 y=12.4x−45.3 12.4 0.915 4 58.2 F3 1 0~42 y=13.9x−3.7 13.9 0.947 5 60.0 F4 2 0~27 y=34.6x−38.9 34.6 0.934 0 87.1 F5 3 0~13 y=61.8x+50.0 61.8 0.948 7 93.4 表 4 各组分浓度准一级动力学拟合结果
Table 4. Pseudo-first-order kinetic fitting results of each component concentration
组分 Kobs/d−1 未添加电子受体 添加硝酸盐 添加三价铁 S1 S2 S3 S4 S5 N1 N2 N3 N4 N5 F1 F2 F3 F4 F5 BTX 0.007 0.023 0.036 0.036 0.066 0.018 0.023 0.032 0.032 0.055 0.009 0.019 0.020 0.038 0.069 EtOH 0.079 0.018 0.028 0.010 0.014 — 0.062 0.077 0.021 0.020 0.091 0.012 0.011 0.003 0.011 B 0.004 0.014 0.024 0.021 0.045 0.012 0.014 0.023 0.021 0.053 0.005 0.011 0.011 0.022 0.048 T 0.006 0.021 0.041 0.053 0.091 0.018 0.021 0.035 0.042 0.061 0.010 0.021 0.023 0.048 0.241 X 0.030 0.046 0.056 — — 0.111 0.057 — — — 0.051 0.062 — — — 注:“—”表示可供拟合点数少于5个,不具有代表性。 表 5 各组Alpha多样性指数分析
Table 5. Alpha diversity index analysis of each group
未添加电子受体 添加硝酸盐电子受体 添加三价铁电子受体 缓释体质量比 组别 丰富度 均匀度 覆盖度 组别 丰富度 均匀度 覆盖度 组别 丰富度 均匀度 覆盖度 S1 1117.8 4.2 1 N1 758.0 4.2 1 F1 221.5 2.0 1 0 S2 549.1 2.3 1 N2 186.0 2.9 1 F2 164.6 1.6 1 0.5 S3 577.2 2.7 1 N3 262.9 3.0 1 F3 575.9 1.3 1 1 S4 508.9 3.2 1 N4 641.6 2.2 1 F4 490.0 2.0 1 2 S5 512.6 0.8 1 N5 567.2 2.6 1 F5 158.2 1.4 1 3 -
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