Organic pollutants in shale gas flowback and produced waters: identification, potential ecological impact and implications for treatment strategies

Abstract

Organic contaminants in shale gas flowback and produced water (FPW) are traditionally expressed as total organic carbon (TOC) or chemical oxygen demand (COD), though these parameters do not provide information on the toxicity and environmental fate of individual components. This review addresses identification of individual organic contaminants in FPW, and stresses the gaps in the knowledge on FPW composition that exist so far. Furthermore, the risk quotient approach was applied to predict the toxicity of the quantified organic compounds for fresh water organisms in recipient surface waters. This resulted in an identification of a number of FPW related organic compounds that are potentially harmful namely those compounds originating from shale formations (e.g. polycyclic aromatic hydrocarbons, phthalates), fracturing fluids (e.g. quaternary ammonium biocides, 2-butoxyethanol) and downhole transformations of organic compounds (e.g. carbon disulphide, halogenated organic compounds). Removal of these compounds by FPW treatment processes is reviewed and potential and efficient abatement strategies are defined.