Optimal Pretreatment System of Flowback Water from Shale Gas Production

Toxicity identification evaluation for hydraulic fracturing flowback and produced water during shale gas exploitation in China: Evidence from tissue residues and gene expression

Hydraulic fracturing flowback and produced water (HF-FPW) from shale gas extraction processes is a highly complex medium with potential threats to the environment. Current research on ecological risks of FPW in China is limited, and the link between major components of FPW and their toxicological effects on freshwater organisms is largely unknown. By integrating chemical and biological analyses, toxicity identification evaluation (TIE) was used to reveal causality between toxicity and contaminants, potentially disentangling the complex toxicological nature of FPW. Here, FPW from different shale gas wells, treated FPW effluent, and a leachate from HF sludge were collected from southwest China, and TIE was applied to obtain a comprehensive toxicity evaluation in freshwater organisms. Our results showed that FPW from the same geographic zone could cause significantly different toxicity. Salinity, solid phase particulates, and organic contaminants were identified as the main contributors to the toxicity of FPW. In addition to water chemistry, internal alkanes, PAHs, and HF additives (e.g., biocides and surfactants) were quantified in exposed embryonic fish by target and non-target tissue analyses. The treated FPW failed to mitigate the toxicity associated with organic contaminants. Transcriptomic results illustrated that organic compounds induced toxicity pathways in FPW-exposed embryonic zebrafish. Similar zebrafish gene ontologies were affected between treated and untreated FPW, again confirming that sewage treatment did not effectively remove organic chemicals from FPW. Thus, zebrafish transcriptome analyses revealed organic toxicant-induced adverse outcome pathways and served as evidence for TIE confirmation in complex mixtures under data-poor scenarios.

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.

Evaluating the potential for sustainable development of China's shale gas industry by combining multi-level DPSIR framework, PPFCI technique and RAGA algorithm

This work was aimed to comprehensively evaluate the potential for sustainable development of China's shale gas industry. It will contribute to the sustainable development of China's energy and economic. Factors of resource, technology, economy and environment were selected to develop the DPSIR framework evaluation indicators in system for shale gas based on the previous research. Next, The PPFCI (projection pursuit fuzzy clustering model) technique was developed by combining the projection pursuit model with a fuzzy clustering iterative model. So that it can deal with the multi-source, high-dimensional, fuzzy data of the proposed evaluation indicators. And then, the RAGA (accelerated genetic algorithm based on real coding) algorithm was developed to run the PPFCI technique. The results show that core technical capability, investment in projects of prevention of geological disasters, and ecological environment damage indicators were the key factors affecting the sustainability of China's shale gas industry. The potential for sustainable development of China's shale gas industry was relatively low. And it was unbalanced in different provinces. The potential for sustainable development of the southwest region was better than the northwest region. Among them, the development of Sichuan was more stable than Chongqing, with a 99% probability of maintaining a stable and sustainable development state, while Chongqing province has a 15%-20% probability to fluctuate towards the poles.

Environmental and Economic Water Management in Shale Gas Extraction

This paper introduces a comprehensive study of the Life Cycle Impact Assessment (LCIA) of water management in shale gas exploitation. First, we present a comprehensive study of wastewater treatment in the shale gas extraction, including the most common technologies for the pretreatment and three different desalination technologies of recent interest: Single and Multiple-Effect Evaporation with Mechanical Vapor Recompression and Membrane Distillation. The analysis has been carried out through a generic Life Cycle Assessment (LCA) and the ReCiPe metric (at midpoint and endpoint levels), considering a wide range of environmental impacts. The results show that among these technologies Multiple-Effect Evaporation with Mechanical Vapor Recompression (MEE-MVR) is the most suitable technology for the wastewater treatment in shale gas extraction, taking into account its reduced environmental impact, the high water recovery compared to other alternatives as well as the lower cost of this technology. We also use a comprehensive water management model that includes previous results that takes the form of a new Mixed-Integer Linear Programming (MILP) bi-criterion optimization model to address the profit maximization and the minimization Life Cycle Impact Assessment (LCIA), based on its results we discuss the main tradeoffs between optimal operation from the economic and environmental points of view.

Potential for Beneficial Reuse of Oil and Gas-Derived Produced Water in Agriculture: Physiological and Morphological Responses in Spring Wheat (Triticum aestivum)

Produced water (PW) from oil and gas operations is considered a potential resource for food crop irrigation because of increasing water scarcity in dryland agriculture. However, efforts to employ PW for agriculture have been met with limited success. A greenhouse study was performed to evaluate the effects of PW on physiological and morphological traits of spring wheat (Triticum aestivum). Plants were irrigated with water treatments containing 10 and 50% PW (PW10 and PW50, respectively) and compared to a matching 50% salinity (NaCl50) and 100% tap water controls. Compared to controls, plants watered with PW10 and PW50 exhibited developmental arrest and reductions in aboveground and belowground biomass, photosynthetic efficiency, and reproductive growth. Decreases in grain yield ranged from 70 to 100% in plants irrigated with PW compared to the tap water control. Importantly, the PW10 and NaCl50 treatments were comparable for morphophysiological effects, even though NaCl50 contained 5 times the total dissolved solids, suggesting that constituents other than NaCl in PW contributed to plant stress. These findings indicate that despite discharge and reuse requirements focused on total dissolved solids, salinity stress may not be the primary factor affecting crop health. The results of the present study are informative for developing guidelines for the use of PW in agriculture to ensure minimal effects on crop morphology and physiology. Environ Toxicol Chem 2019;38:1756-1769. © 2019 SETAC.