| Abstract | 作为环境中一类重要的污染物，抗生素所带来的健康风险和生态环境问题引起了各国学者和公众的广泛关注。同时，抗生素诱导细菌抗性不断增强以及抗生素抗性基因（Antibiotic resistance genes, ARGs）大量增殖，ARGs能够在不同环境介质中传播和扩散，增加了病原菌获得抗生素抗性的机会，严重威胁人类健康。近年来，臭氧-生物活性炭（Ozone-biological activated carbon, O3-BAC）工艺被越来越多的应用到饮用水和污水处理中。基于此，本文研究了 O3-BAC工艺对饮用水和城市污水中多种抗生素及 ARGs的去除效果。此外，污泥是 ARGs的“汇”，ARGs的存在对污泥的处理与处置带来了较大的环境风险，本文也对污泥O3氧化过程中 ARGs的削减进行了研究，提出了优化组合工艺。主要结论如下：
（1）以上海给水技术验证基地滤后水为研究水体，开展了 O3-BAC工艺中试研究，考察了该工艺对磺胺类抗生素（ Sulfonamides, SAs）及磺胺类抗药菌（Sulfonamide resistant bacteria, SRB）的削减效果。结果表明，O3能够有效地去除水中 SAs，在 O3投加量为 2.5 mg L‒1时，8种目标 SAs在 O3-BAC工艺中的去除率超过了 90%。单独 BAC工艺中，较大的空床接触时间（Empty bed contact time,EBCT）能有效促进 SAs的去除，在 EBCT为 20 min时，8种 SAs的去除率为58%–83%。在 O3投加量为 0.5和 2.5 mg L‒1时，单独 O3对异养菌（Heterotrophicplate counts, HPCs）的去除率分别为 0.12和 0.47 logs。然而，经过 O3-BAC工艺后出水中 SRB出现了升高，表明后续消毒（如氯和氯胺）工艺对保障饮用水安全的重要性。同时，O3-BAC工艺能够有效降低氯代消毒副产物—三卤甲烷生成势（Trihalomethanes formation potential, THMsFP）和卤乙酸生成势（Haloaceticacids formation potential, HAAsFP）。此外，对于总有机碳（Total organic carbon,TOC）、254 nm UV transmittance（UV254）和浊度的去除，该工艺同样很有效。
（2）以某城市污水处理厂生物处理出水为研究水体，进行了 O3-BAC工艺去除抗生素、抗生素抗药菌（Antibiotic resistant bacteria, ARB）和 ARGs的中试研究。结果显示，生物处理出水中检出多种抗生素：四环素类抗生素（Tetracyclines,TCs）的浓度为 7.46–28.82（氧四环素，Oxytetracycline）和 1.18–24.09 ng L‒1（四环素，Tetracycline）；检出浓度较高的 SAs分别为磺胺甲恶唑（Sulfamethoxazole,25.87–104.92 ng L‒1）和磺胺噻唑（Sulfathiazole, 24.58–81.06 ng L‒1）；氟喹诺酮类抗生素（Fluoroquinolones, FQs）中浓度最高的是氧氟沙星（Ofloxacin, 160.77–450.83 ng L‒1）。运行初期未启动 O3，活性炭对多种抗生素的去除率在 90%以上，但对 TCs和 FQs去除率较低（20%-30%）；随着运行时间的延长，这两类抗生素的去除率接近 100%。单独 BAC对 HPCs的去除率为 0.08–1.50 logs；在 O3剂量为 5–20 mg L‒1，O3-BAC工艺能够实现 0.11–2.0 logs的 HPCs去除。然而，O3-BAC工艺出水中仍然含有一定数量的 HPCs和 ARB。BAC工艺对 ARB的截留作用较弱，而 O3-BAC整体工艺则能较有效地削减 ARB，在 O3剂量为 20 mg L‒1时，对四环素抗药菌（Tetracycline resistant bacteria, TRB）的灭活率为 1.3 logs。生物处理出水中，不同种类的 ARGs绝对含量差异较大，磺胺类抗性基因（Sulfonamide resistance genes, SRGs）、四环素类抗性基因（Tetracycline resistance genes, TRGs）和氟喹诺酮类抗性基因（Fluoroquinolone resistance genes, FRGs）的绝对含量较高。O3-BAC工艺对 ARGs和一类整合子（Class 1 integron, intI1）具有一定的削减能力。此外，O3-BAC工艺进出水中微生物群落结构发生了显著变化。
（3）对污泥中 ARGs的研究表明，SRGs和 TRGs被广泛检出，绝对含量分别为 6.45 × 108和3.61 × 107copies g–1dw（污泥干重）。在污泥 O3氧化过程中，O3剂量对污泥中 ARGs的削减具有一定的影响，在 O3剂量为185 mg g–1MLSS（Mixed liquor suspended solids）时，TRGs和 SRGs分别降低了 0.83和 0.52 logs。不同 pH条件影响 ARGs在污泥固、液两相中的分配，pH值为 5.0或 9.0时，污泥固相中 ARGs的绝对含量高于其在中性条件下的绝对含量。ARGs与intI1和二类整合子（Class 2 integron, intI2）均具有较强的相关性（p < 0.05），说明整合子是 ARGs发生迁移的重要载体。为了提升污泥 O3减量工艺中 ARGs的削减效果，考察了多种预处理技术与 O3的组合工艺对污泥中 ARGs的削减。结果表明，Ca(OH)2预处理能够有效地提高污泥 O3氧化对 ARGs的削减，在 Ca(OH)2投加量为 8.36 g L–1时，污泥固相中TRGs和 SRGs分别降低了 2.52和 1.73 logs。微波-双氧水预处理比单独微波预处理对污泥 O3氧化过程中 ARGs的削减更有效。 |
| Other Abstract | As an important class of emerging contaminants, antibiotics have been received increasing attentions for their potential threat to ecological environment and human health. Meanwhile, antibiotics would enhance the resistant level of microbes and promote the proliferation of antibiotic resistance genes (ARGs). ARGs could transport between different environmental media, thus increasing the opportunities for pathogen to acquire resistance and posing a severe threat on public health. Ozonation and biological activated carbon (O3-BAC) process is increasing applied in drinking water treatment plants (DWTPs) and wastewater treatment plants (WWTPs) in recent years.
Based on this, the present study investigated the performance of O3-BAC in removing different kinds of antibiotics and ARGs from water and wastewater. Moreover, sludge is an important “reservoir” of ARGs, the existence of ARGs in sludge incurs the environmental risks during the treatment and disposal of sludge, therefore, O3-based
processes were selected to investigate the removal of ARGs in the sludge. The main results are as follows:
(1) Taking the filtered water from water supply test base of Shanghai as the water matrix, a field pilot-scale study was carried out on the removal of sulfonamides (SAs) and sulfonamide resistant bacterial (SRB) by O3-BAC process. The results indicated that O3 could effectively remove SAs from water and the removal of eight SAs exceeded 90% at the O3 dose of 2.5 mg L‒1. In BAC process alone, higher empty bed contact time (EBCT) greatly enhanced the removal of SAs and at EBCT of 20min, the removal of eight SAs reached 58%–83%. The inactivation of heterotrophic plate counts (HPCs) at the O3 dose of 0.5 and 2.5 mg L‒1 reached 0.12 and 0.47 logs,respectively. However, the amount of SRB increased after the O3-BAC process, which highlights the importance of subsequent disinfection process (such as chlorination and chloramine disinfection) for ensuring the safety of drinking water. Meanwhile,O3-BAC process could effectively reduce chlorinated by-products: trihalomethane formation potential (THMsFP) and haloacetic acid formation potential (HAAsFP). In addition, the process was also effective for the removal of total organic carbon (TOC),UV254 and turbidity.
(2) The effluent from biological treatment of a WWTP was selected as the test water, a pilot-scale test was carried out for the removal of antibiotics, antibiotic resistance bacteria (ARB) and ARGs by O3-BAC process. The results indicated that various kinds of antibiotics were detected: the concentration of tetracycline was 7.46-28.82 ng L‒1 (Oxytetracycline, OTC) and 1.18-24.09 ng L‒1 (Tetracycline, TCN);
SAs with higher concentrations were sulfamethoxazole (SMX, 25.87–104.92 ng L‒1)and sulfathiazole (STZ, 24.58–81.06 ng L‒1); the highest concentration of fluoroquinolone antibiotics was ofloxacin (OFL, 160.77–450.83 ng L‒1). At the beginning of the operation, O3 was not added and the removal of most kinds of antibiotics by activated carbon exceeded 90%, but low removal was achieved for TCs and FQs (20%–30%). As the operation time extended, the removal of these two antibiotics was close to 100%. The inactivation of HPCs by BAC process alone was 0.08–1.50 logs and at the O3 dose of 5–20 mg L‒1, the inactivation could reach 0.11–2.00 logs. However, a certain amount of HPCs and SRB was still detected in the effluent of O3-BAC process. BAC process alone could not inactivate the ARB, while the O3-BAC process could achieve effective inactivation. The inactivation rate of tetracycline resistant bacteria (TRB) was 1.3 logs at the O3 dose of 20 mg L‒1.Different kinds of ARGs showed distinct distribution patterns in the effluent of biological treatment: sulfonamide resistance genes (SRGs), tetracycline resistance genes (TRGs) and fluoroquinolone resistance genes (FRGs) were dominant. O3-BAC process had a certain reduction capacity towards ARGs and class 1 integron (intI1). In addition, the microbial community structure changed significantly in the influent and effluent of O3-BAC process.
(3) The investigation on ARGs of sludge revealed that SRGs and TRGs were widely detected in sludge, the absolute gene copies were 6.45 × 108 and 3.61 × 107 copies g–1dw (dry weight), respectively. O3 dose had a certain influence on the quantity of ARGs in sludge ozonation. At the O3 dose of 185 mg g-1 MLSS, the quantities of TRGs and SRGs were reduced by 0.83 and 0.52 logs, respectively.Different pH values affected the distribution of the liquid phase and solid phase of the sludge. The quantity of ARGs in solid phase of sludge was higher at pH 5.0 or 9.0 than that under neutral condition. The target ARGs were strongly correlated with intI1 and class 2 integron (intI2) (p < 0.05). The integrons were important vectors for the migration of ARGs. With the aim of enhancing the reduction of ARGs during sludge ozonation, the present study combined different pretreatment processes with O3 to investigate the reduction of ARGs. The results indicated that pretreatment with Ca(OH)2 could effectively promote the reduction of ARGs in the sludge ozonation
and the quantities of TRGs and SRGs were reduced by 2.52 and 1.73 logs,respectively, at the Ca(OH)2 dose of 8.36 g L–1 . Microwave combined with hydrogen peroxide pretreatment showed higher reduction capacity than microwave process alone on ARGs reduction during sludge ozonation.
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