A review of the issues and treatment options for wastewater from shale gas extraction by hydraulic fracturing
Abstract Since the beginning of this millennium, shale gas extraction by horizontal drilling and hydraulic fracturing has boosted U.S. gas production, changing the global energy markets and leading to low natural gas and oil prices. Following the expansion of this industry, other countries such as U.K. Poland or China are exploring and supporting its extraction as a way to secure energy independence in an increasingly unstable geopolitical context and as an effective transition substitute for coal while moving towards a renewable energy market. However, there are important environmental concerns associated to shale gas production including atmospheric pollution and air quality issues, risks of water pollution and nuisance to the population caused by road traffic and noise. Water management is one of the most challenging problems since hydraulic fracturing requires millions of liters of water and produces high volumes of liquid effluents at variable compositions and rates. The present review focuses on the characteristics of this wastewater and the options existing to minimize its environmental impacts. At the moment, deep well injection and re use are the most commonly employed strategies for this wastewater in the U.S. but the stricter regulations in other regions will require further treatment. Partial treatment and reuse is the preferred option where feasible. Otherwise, techniques such as mechanical vapor compression, thermal distillation or forward osmosis may be needed in order to meet the requirements for discharge.