油气开采是全球八大水密集型行业之一，产生了大量的油气开采废水（PW）亟需有效处理，以缓解油气开采地区的水资源短缺。在碳达峰碳中和背景下，页岩气这一战略资源的重要性愈发凸显。然而，在页岩气开采过程中，偏远井场产生了大量有害的页岩气废水（SGPW），因此亟需探索SGPW的分散式现场处理技术。

重力驱动膜（GDM）利用了膜面形成的生物膜对污染物进行降解去除，是一种低能耗的超滤技术，可实现农村和偏远地区的分散式水处理。然而，为实现SGPW回用和零液体排放，GDM常需与后续脱盐工艺相结合。膜蒸馏（MD）技术作为一种新兴的热驱动膜脱盐工艺，可有效地利用页岩气开采现场所产生的低级废热实现SGPW脱盐，但膜污染、膜润湿和渗透液水质恶化限制了膜蒸馏技术的应用。受非对称亲水性（Janus）MD抗污染抗润湿性能启发，亲水性的GDM与疏水性的MD存在着潜在的协同增效作用。因此，本研究首次提出了GDM-MD耦合的Janus双膜工艺以改善MD的脱盐性能，并系统评估了不同的预处理方法（氧化、混凝和颗粒过滤）对GDM-MD工艺的强化效果。本研究旨在探索SGPW的高效的处理工艺，为偏远的页岩气开采现场的分散式水处理提供了可行方案，有助于推动PW的可持续管理。主要的研究内容如下：

（1）GDM系统在运行30天后实现了通量稳定，GDM通量大致遵循着：混凝>过碳酸钠（SPC）氧化/沸石/石英砂/颗粒活性炭（GAC）>活性氧化铝（AA）/对照组的顺序。预处理和微生物活动的共同作用显著影响了GDM膜面污染层的形态，并影响着最终的通量表现。本研究中，在GDM膜面观察到两种与高通量密切相关的典型污染层的形貌，即含有较少生物成分的厚而非均质的污染层，以及薄而松散的污染层。此外，预处理可以显著改善GDM膜面污染层的亲水性并改善通量。

（2）预处理可有效改善GDM出水水质。吸附型颗粒过滤可以利用吸附-生物降解的协同效应，有效提高了氨氮（61.4-100%）和UV₂₅₄（6.2-52.61%）的去除率。评估了预处理-GDM系统对有机污染物的去除转化效果，发现预处理-GDM系统可有效截留疏水性（HPO）组分，并利用膜面持续性的生物降解作用而在长周期运行中保持了膜面的亲水性，从而有望保障后续疏水性的MD的脱盐性能。因此，GDM-MD工艺是一种Janus型双膜处理工艺，可利用GDM与MD工艺间的优势互补，实现难处理SGPW的高效处理。

（3）探究了GDM系统中原核生物和真核生物的群落构成。发现预处理-GDM系统可以对特定的功能性原核生物群落实现富集（例如变形菌（Proteobacteria）和亚硝化单胞菌（Nitrosomonadaceae）），有效确保了工艺对有机物和氨氮的去除，改善了GDM渗透液质量，并保证了后续MD的高效脱盐。此外，GDM膜面真核微生物的运动和捕食作用疏松了膜面的污染层，显著改善了GDM通量。

（4）对MD与GDM耦合时的脱盐效率进行分析，发现GDM可以有效地控制MD渗透液的电导率上升（1.39-19.90 μS/cm）并缓解MD膜污染（通量仅下降8.3%-27.5%）。此外，预处理-GDM-MD组合工艺在出水水质方面存在优势。MD渗透液水质中氨氮含量低于检测限，UV₂₅₄为0.002-0.007 cm^-1，浊度为0 NTU，水质接近于纯水标准。此外，GDM-MD工艺在降低MD污染和润湿方面与Janus MD膜存在着相似性。三维荧光光谱（EEM）显示仅有痕量的亲水性（HPI）有机物透过MD膜，证实了GDM可有效截留HPO污染物，从而避免MD膜的污染和润湿。

（5）评估了预处理-GDM-MD组合工艺的经济效益。发现石英砂过滤预处理工艺（80.79元/立方米）与混凝预处理工艺（80.80元/立方米）的成本最低，较先前文献报道的180元/立方米降低55%以上。考虑到MD能耗占总成本92%以上，未来可通过利用页岩气开采过程中产生的废热来进一步降低成本。

本研究所提出的预处理-GDM-MD组合工艺有着显著的环境意义与工艺创新。亲水性的GDM和疏水性的MD膜从处理工艺角度形成了Janus型双膜处理工艺并展现出与Janus MD相似的性能。相较于复杂的Janus MD膜制备方法，本工艺通过巧妙利用GDM膜面的生物降解作用实现了MD经济高效的稳定运行。

As one of the eight most water-intensive industries globally, petroleum extraction generates substantial volumes of produced water (PW) that necessitating efficient treatment to alleviate water scarcity in extraction regions. Against the background of carbon peaking and carbon neutrality goals, shale gas has emerged as a strategic resource of growing significance. Nevertheless, considerable amounts of hazardous shale gas produced water (SGPW) generates in remote well sites. Therefore, achieving the efficient decentralized on-site treatment of SGPW is urgently needed.
Gravity-driven membrane (GDM) is a type of low-energy required ultrafiltration technology. GDM employs biofilm in the fouling layer for pollutant removal, making it suitable for decentralized water treatment, especially in rural and remote areas. When using single GDM for SGPW treatment, post desalination step is needed to achieve the purpose of zero liquid discharge. As an emerging thermally driven desalination process, membrane distillation (MD) can effectively utilize the low-grade waste heat during shale gas extraction to achieve desalination. However, membrane fouling, wetting, and permeate quality deterioration restricted the widely application of MD technology. Inspired by the high resistance of Janus MD towards fouling and wetting, the hydrophilic GDM and hydrophobic MD have potential synergistic effects. Accordingly, this study proposes a Janus dual-membrane process that couples hydrophilic GDM with hydrophobic MD to enhance desalination performance for the first time, and systematically evaluates the effects of various pretreatment methods (i.e., oxidation, coagulation, and granular filtration) on the efficiency of integrated GDM-MD process. The aim of this study is to develop an efficient process for SGPW treatment, thereby offering a viable solution for decentralized SGPW treatment and promoting the sustainable management of PW. The main research content and findings are listed as follows:
(1) The stable GDM flux were reached after 30 days operation. The GDM stable flux approximately following the order of coagulation > sodium percarbonate (SPC) oxidation /zeolite/silica sand/granular activated carbon (GAC) > activated aluminum oxide (AA)/control. The morphology of the fouling layer was greatly influenced by the combined effects of pretreatment and microbial activity, and influences the ultimate flux performance in stable stage. Two typical fouling layer morphologies were observed related with high GDM flux. Both thick and heterogeneous fouling layer with low bio-content as well as a thin and loose layer contributing to high GDM flux. Moreover, pretreatment can effectively improve the hydrophilicity of the fouling layer and overall flux performance.
(2) Pretreatment enhanced the permeate quality of the GDM system. Adsorptive granular filtration can utilize the synergistic effects of adsorption and biodegradation, therefore effectively increasing the removal rates of ammonia nitrogen (61.4-100%) and UV254 (6.2-52.61%). In addition, we analyzed the removal and transformation efficiency of pretreatment-GDM system on organic pollutants removal. Pretreatment-GDM system can effectively reject the HPO fractions, and utilize biodegradation to maintain the hydrophilicity of membrane surface during long-term operation, thereby ensuring the performance of hydrophobic MD desalination. Therefore, the GDM-MD process is a Janus dual-membrane process, which can utilize the complementary between GDM and MD, achieving efficient treatment of SGPW.
(3) The prokaryotic and eukaryotic community in GDM fouling layer were analyzed. The pretreatment-GDM system enriched certain functional prokaryotic microbes (e.g., Proteobacteria and Nitrosomonadaceae), which ensured the efficient removal of organic pollutants and ammonia nitrogen, improved GDM permeate quality, and ensured efficient desalination in MD. Moreover, the movement and predation of eukaryotic microorganisms in the GDM fouling layer significantly enhanced the GDM flux.
(4) MD desalination performance demonstrated that GDM can effectively control permeate conductivity (1.39-19.9 μS/cm) and mitigate fouling (flux decline=8.3%-27.5%). Moreover, the permeate quality of pretreatment-GDM-MD process achieved near pure water standards, with ammonia below detection limits, UV254=0.002-0.007 cm-1, turbidity=0 NTU. Moreover, the EEM spectra confirmed only trace hydrophilic (HPI) organics were observed in MD permeate, verifying GDM can efficiently reject HPO fractions and prevent membrane fouling and wetting. 
(5) Economic analysis revealed pretreatment-GDM-MD integrated process offers significant economic advantages. The GDM-MD process with pretreatment of silica sand filtration (80.79 CNY/m³) and coagulation (80.80 CNY/m³) reduced more than 55% cost than previous literature-reported 180 CNY/m³. Considering MD energy consumption accounts for more than 92% of the total cost, further reductions in total cost can be achieved by utilizing waste heat in shale gas extraction. 
The integrated pretreatment-GDM-MD process proposed in this study carries substantial environmental and innovative significance. The combination of hydrophilic GDM and hydrophobic MD membranes creates a Janus dual-membrane system, which has similarity with Janus MD. Considering the complex Janus MD membrane fabrication methods, this approach leverages the biodegradation in the GDM fouling layer to achieve stable MD operation, providing an economical and efficient alternative for high-salinity wastewater treatment.
 

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