Facile preparation of antifouling nanofiltration membrane by grafting zwitterions for reuse of shale gas wastewater

Biodegradation-assisted removal of sulfur-based odor compounds in rural drinking water using durable chitosan/polyvinyl alcohol biochar aerogels

Rural drinking water often suffers from unpleasant odors like dimethyl sulfide (DMDS) and dimethyl trisulfide (DMTS) due to poor raw water quality and limited treatment options. This study introduces durable chitosan/polyvinyl alcohol (PVA) biochar aerogels-supported bioflims in ultrafiltration (BAB-UF) reactors, where the incorporation of PVA significantly enhances structural integrity, biodegradation resistance, and functional lifespan, providing an efficient, sustainable solution for removing odorous compounds from rural water. Experimental results showed the enhanced chitosan/PVA porous biochar aerogels (CPPCA) displayed excellent biocapacity and structural stability. After 63 days of continuous operation, the degradation rate of biochar aerogels with 0.2 wt% PVA (CP2PCA) was only 8.2 %. The one-step membrane reactors utilizing PVA-enhanced aerogels achieved removal efficiencies for DMDS/DMTS pollutants of up to 98.4 %, surpassing systems without PVA. These findings indicate the potential for improved aerogels in rural drinking water treatment, providing a viable solution for effective and low-maintenance water purification.

Molecular comparison of organic matter removal from shale gas flowback wastewater: Ozonation versus Fenton process

Shale gas extraction process generates a large amount of shale gas flowback wastewater (SGFW) containing refractory organic compounds, which can pose serious environmental threats if not properly treated. However, the extremely complex compositions of organics in SGFW are still unknown and their transformation pathways in O3- and •OH-dominated systems are not well recognized, which restrain the selection of treatment technology and optimization of operational parameters. The removal characteristics and reaction mechanism of dissolved organic matter (DOM) in SGFW treated by ozonation and Fenton processes were comparatively investigated using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The results showed that both processes could degrade low-oxygen highly unsaturated and phenolic organics, polyphenolics and polycyclic aromatics, and transform them into aliphatic organics and high-oxygen highly unsaturated and phenolic organics. With increasing action of reactive oxygen species (O3 for ozonation and •OH for Fenton process), the degradation products (mainly aliphatic organics) increased during ozonation. However, in Fenton process, a wider range of DOM was removed without aliphatic organics accumulation. The degradation mechanisms of DOM during ozonation and Fenton processes included oxygen addition reactions (+3O, +H2O2, and +2O) as dominant pathways. However, ozonation showed more violent oxygenation, hydroxylation, and carboxylation, while Fenton process presented more violent chain-breaking reactions. These results revealed the selective oxidation of ozone and nonselective oxidation of •OH during SGFW treatment, and provided theoretical support for selecting SGFW treatment approaches.

Performances and mechanisms of the peroxymonosulfate/ferrate(VI) oxidation process in real shale gas flowback water treatment

Shale gas flowback water (SGFW), which is an inevitable waste product generated after hydraulic fracturing during development, poses a severe threat to the environment and human health. Managing high-salinity wastewater with complex physicochemical compositions is critical for ensuring environmental sustainability of shale gas development. Desalination processes have been recommended to treat SGFW to adhere to the discharge limits. However, organic fouling has become a significant concern in the steady operation of desalination processes, and the effective removal of organic compounds is challenging. This study aimed to develop an effective oxidation method to mitigate membrane fouling in real SGFW treatment process. It adopted the peroxymonosulfate (PMS)/ferrate (Fe(VI)) process, involving both free and non-free radical pathways that can alleviate the negative effects of high-salinity environments on oxidation. The operating parameters were optimized and removal effects were examined, while the synergistic oxidation mechanism and organic conversion of the PMS/Fe(VI) process were also analyzed. The results showed that the PMS/Fe(VI) process exhibited a synergistic effect compared with the PMS and Fe(VI) processes alone, with a total organic carbon (TOC) removal efficiency of 46.8% under optimal reaction conditions in real SGFW. In the Fe(VI)/PMS process, active species such as Fe(V)/Fe(IV), ·OH, and SO4-· were jointly involved in the oxidation of organic matter. Additionally, 99.5% of the total suspended solids and 95.2% of Ba2+ in the SGFW were removed owing to the formation of a coagulant (Fe3+) and SO42- during the reaction. Finally, an ultrafiltration membrane fouling experiment proved that oxidation processes can increase the membrane-specific flux and alleviate fouling resistance. This study can serve as a reference for the design of real SGFW treatment processes and is significant for the environmental management of shale gas development.

A review of the development in shale oil and gas wastewater desalination

The development of the shale oil and gas extraction industry has heightened concerns about shale oil and gas wastewater (SOGW). This review comprehensively summarizes, analyzes, and evaluates multiple issues in SOGW desalination. The detailed analysis of SOGW water quality and various disposal strategies with different water quality standards reveals the water quality characteristics and disposal status of SOGW, clarifying the necessity of desalination for the rational management of SOGW. Subsequently, potential and implemented technologies for SOGW desalination are reviewed, mainly including membrane-based, thermal-based, and adsorption-based desalination technologies, as well as bioelectrochemical desalination systems, and the research progress of these technologies in desalinating SOGW are highlighted. In addition, various pretreatment methods for SOGW desalination are comprehensively reviewed, and the synergistic effects on SOGW desalination that can be achieved by combining different desalination technologies are summarized. Renewable energy sources and waste heat are also discussed, which can be used to replace traditional fossil energy to drive SOGW desalination and reduce the negative impact of shale oil and gas exploitation on the environment. Moreover, real project cases for SOGW desalination are presented, and the full-scale or pilot-scale on-site treatment devices for SOGW desalination are summarized. In order to compare different desalination processes clearly, operational parameters and performance data of varying desalination processes, including feed salinity, water flux, salt removal rate, water recovery, energy consumption, and cost, are collected and analyzed, and the applicability of different desalination technologies in desalinating SOGW is qualitatively evaluated. Finally, the recovery of valuable inorganic resources in SOGW is discussed, which is a meaningful research direction for SOGW desalination. At present, the development of SOGW desalination has not reached a satisfactory level, and investing enough energy in SOGW desalination in the future is still necessary to achieve the optimal management of SOGW.

Safe purification of rural drinking water by biological aerated filter coupled with ultrafiltration

Water resources of many rural areas are usually lakes or reservoirs, which can be easily affected by run-off, non-point source pollution and are often of poorer quality compared with urban water sources. Drinking water supply in remote rural areas usually suffers from various challenges, such as the high cost of construction and maintenance of centralized drinking water treatment plants and pipe networks, due to the dispersed nature of villages, which are often located in varied and complex topographies. In this study, a combined process comprising biological aerated filter (BAF) combined with ultrafiltration was developed to treat polluted reservoir water. Organic matter indexes, turbidity, and chroma were used as indicators for the evaluation of the system performance. In a long-term experiment lasting 260 days, the combined process was tested under different values of critical operational parameters, including filler types and empty bed contact time (EBCT). Furthermore, the microbial communities in different BAF reactors were carefully evaluated at different times, finding that microorganisms with specific functions were enriched in the various BAF reactors. The combined process reached 85.5 % removal rate of DOC with an EBCT of 45 min and using granule active carbon (GAC) as filler. Most of the effluents of BAF reactors met the requirements for drinking water in China. The combined system showed practical potential for polluted water treatment in some rural areas.

Granular activated carbon (GAC) fixed bed adsorption combined with ultrafiltration for shale gas wastewater internal reuse

Membrane processes are widely applied in shale gas flowback and produced water (SGFPW) reuse. However, particulate matters and organic matters aggravate membrane fouling, which is one of the major restrictions on SGFPW reuse. The present study proposed fixed bed adsorption using granular activated carbon (GAC) combined with ultrafiltration (UF) for the first time to investigate the treatment performance and membrane fouling mechanism. The adsorption of GAC for SGFPW was best described by the Temkin isotherm model and the pseudo-second-order kinetic model. GAC fixed bed pretreatment with different empty bed contact times (EBCT) (30, 60 and 90 min) showed the significant removal rate for dissolved organic carbon (DOC) and turbidity, which was 34.7%-42.4% and 98.1%-98.9%, respectively. According to characterization of UF membrane fouling layer, particulate matters and organic matters caused major part of membrane fouling. After being treated by GAC fixed bed, total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) respectively decreased by more than 32.5% and 18.3% respectively, showing the mitigation effect of GAC fixed bed on membrane fouling. According to the XDLVO theory, GAC fixed bed also mitigated membrane fouling by reducing the hydrophobic interactions between the foulants and the UF membrane. The integrated GAC fixed bed-UF process produced high-quality effluents that met the water quality standards of SGFPW internal reuse, which was an effective technology of the SGFPW reuse.

Nanomaterials and Technology Applications for Hydraulic Fracturing of Unconventional Oil and Gas Reservoirs: A State-of-the-Art Review of Recent Advances and Perspectives

The application of hydraulic fracturing stimulation technology to improve the productivity of unconventional oil and gas reservoirs is a well-established practice. With the increasing exploration and development of unconventional oil and gas resources, the associated geological conditions and physical properties are gradually becoming more and more complex. Therefore, it is necessary to develop technologies that can improve the development benefits to meet these challenges. In recent years, improving the effect of hydraulic fracturing stimulation in unconventional oil and gas reservoirs through the use of nanomaterials and technologies has attracted increasing attention. In this paper, we review the current status and research progress of the application of nanomaterials and technologies in various aspects of hydraulic fracturing in unconventional oil and gas reservoirs, expound the mechanism and advantages of these nanomaterials and technologies in detail, and provide future research directions. The reviewed literature indicates that nanomaterials and technologies show exciting potential applications in the hydraulic fracturing of unconventional reservoirs; for example, the sand-carrying and rheological properties of fracturing fluids can be significantly enhanced through the addition of nanomaterials. The use of nanomaterials to modify proppants can improve their compressive strength, thus meeting the needs of different reservoir conditions. The fracturing flowback fluid treatment efficiency and purification effect can be improved through the use of nanophotocatalysis and nanomembrane technologies, while degradable fracturing completion tools developed based on nanomaterials can effectively improve the efficiency of fracturing operations. Nanorobots and magnetic nanoparticles can be used to more efficiently monitor hydraulic fracturing and to accurately map the hydraulic fracture morphology. However, due to the complex preparation process and high cost of nanomaterials, more work is needed to fully investigate the application mechanisms of nanomaterials and technologies, as well as to evaluate the economic feasibility of these exciting technologies. The main research objective of this review is to comprehensively summarize the application and research progress of nanomaterials and technologies in various aspects of hydraulic fracturing in unconventional oil and gas reservoirs, analyze the existing problems and challenges, and propose some targeted forward-looking recommendations, which may be helpful for future research and applications.

Improvement of Antibacterial and Antifouling Properties of a Cellulose Acetate Membrane by Surface Grafting Quaternary Ammonium Salt

Through etherification reaction, epoxy propyl dimethyl dodecyl ammonium chloride (EPDMDAC) was grafted onto the surface of a cellulose acetate (CA) membrane to prepare a stable nonleaching antibacterial antifouling membrane (QCA-X). The results showed that with the extension of grafting reaction time, the quaternary ammonium salt groups on the membrane surface increased and the hydrophilicity was enhanced. Compared with those of the CA membrane, the filtration capacity and antifouling performance of the QCA-X membrane are improved. When the grafting time is 4 h, the water permeability and flux recovery rate of the QCA-4 membrane are increased by 139 and 21.5%, respectively. The QCA-X membrane showed excellent antibacterial performance, and the sterilization rate against S. aureus and E. coli was more than 99.99%. After four repeated antibacterial cycles, the bactericidal rates against S. aureus and E. coli were maintained at about 99.69 ± 0.02 and 99.98 ± 0.02%, respectively, with good antibacterial persistence. Moreover, the QCA-X membrane can effectively inhibit bacterial adhesion. Mild and simple EPDMDAC grafting modifications improve the antibacterial, antifouling, and antibioadhesion properties of the CA membrane, showing its application potential in long-term water treatment, especially in biofouling water treatment.