College of Architecture and Environment, Sichuan University, Chengdu 610207, China; Institute of New Energy and Low-Carbon Technology, Sichuan University, Chengdu 610207, China.
Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Institute of Environmental Research at Greater Bay, Guangzhou University, Guangzhou 510006, China.
Environ Int. 2019 Sep;130:104869. doi: 10.1016/j.envint.2019.05.063. Epub 2019 Jun 20.
Increasing attention is being paid to the treatment of shale gas fracturing wastewater, including flowback and produced water (FPW). Energy-efficient pretreatment technologies suitable for desalinating and reusing FPW are of paramount importance.
This work focused on enhanced fouling alleviation of ultrafiltration (UF) as a pretreatment for desalinating shale gas FPW in Sichuan Basin, China. The UF fouling behaviors under various backwash water sources or coagulant dosages were evaluated, and membrane surface characteristics were correlated with UF fouling. The feasibility of Fourier transform infrared (FTIR) microscope mapping technique in quantifying UF fouling was also assessed.
Various backwash water sources, including UF permeate, ultrapure water, nanofiltration (NF) permeate, reverse osmosis (RO) permeate, RO concentrate and forward osmosis (FO) draw solution, were used to clean UF membranes fouled by shale gas FPW. The UF fouling behaviors were characterized by total and non-backwashable fouling rates. Membrane surface characteristics were analyzed by scanning electron microscopy (SEM), total tension surface and FTIR spectra.
Protein-like substances in terms of fluorescence intensity in the backwash water decreased with the order of UF permeate, RO concentrate, NF permeate, RO permeate and FO draw solution. Compared with UF permeate backwashing, alleviated UF fouling was observed by using demineralized backwash water including ultrapure water and RO permeate, irrespective of hollow fiber and flat-sheet membranes. NF permeate and RO concentrate after NF used as backwash water resulted in low and comparable membrane fouling with that in integrated coagulation-UF process under optimal dosage. Among the backwash water tested, FO draw solution backwashing corresponded to the lowest UF fouling rates, which were even lower than that in the presence of coagulant under optimal dosage. The superiority of these backwash water sources to UF permeate was further confirmed by SEM images and FTIR spectra. The residual foulant mass on membrane surface and the total surface tension correlated well with non-backwashable and total fouling rates, respectively.
FTIR microscopy was a powerful surface mapping technique to characterize UF membrane fouling caused by shale gas FPW. Backwash water sources significantly influenced the fouling of UF membranes. In the integrated UF-NF-RO or UF-FO process, RO concentrate or FO draw solution were proposed as backwash water to enhance UF fouling control and decrease waste discharge simultaneously.
人们越来越关注页岩气压裂返排液和采出水（FPW）的处理。适用于 FPW 脱盐和再利用的节能预处理技术至关重要。
本工作重点研究了增强超滤（UF）作为四川盆地页岩气 FPW 脱盐的预处理技术，以减轻 UF 膜的污染。评估了不同反冲洗水源或混凝剂剂量下 UF 的污染行为，并将膜表面特性与 UF 污染相关联。还评估了傅里叶变换红外（FTIR）显微镜图谱技术定量 UF 污染的可行性。
采用 UF 渗透液、超纯水、纳滤（NF）渗透液、反渗透（RO）渗透液、RO 浓缩液和正向渗透（FO）汲取液等各种反冲洗水源对页岩气 FPW 污染的 UF 膜进行清洗。通过总污染率和不可反洗污染率来描述 UF 污染行为。采用扫描电子显微镜（SEM）、总张力表面和 FTIR 光谱对膜表面特性进行分析。
反冲洗水中的类蛋白物质荧光强度按 UF 渗透液、RO 浓缩液、NF 渗透液、RO 渗透液和 FO 汲取液的顺序依次降低。与 UF 渗透液反冲洗相比，使用去离子水和 RO 渗透液作为反冲洗水源可减轻中空纤维和平板膜的 UF 污染。NF 渗透液和 RO 浓缩液经 NF 处理后作为反冲洗水，在最佳剂量下与集成混凝-UF 工艺相比，膜污染程度较低且相当。在所测试的反冲洗水中，FO 汲取液反冲洗对应的 UF 污染率最低，甚至低于最佳剂量下投加混凝剂时的 UF 污染率。SEM 图像和 FTIR 光谱进一步证实了这些反冲洗水源优于 UF 渗透液。膜表面上残留的污染物质量与不可反洗和总污染率分别具有良好的相关性。
FTIR 显微镜是一种强大的表面图谱技术，可用于表征页岩气 FPW 引起的 UF 膜污染。反冲洗水源对 UF 膜的污染有显著影响。在 UF-NF-RO 或 UF-FO 工艺中，建议采用 RO 浓缩液或 FO 汲取液作为反冲洗水，以同时增强 UF 污染控制和减少废水排放。
