The rapid development of the unconventional shale gas industry offers tremendous economic benefits while simultaneously posing a critical challenge of managing vast quantities of produced and flowback water. Approximately 10-25% of the water injected during hydraulic fracturing returns to the surface as highly contaminated water with total dissolved solids reaching as high as 350,000 mg/Liter with potential detrimental impacts on human health and ecosystems. Sustainable development of the shale gas industry will require economical management of wastewater while minimizing associated environmental impacts. Membrane distillation (MD) is an emerging technology for treatment of high salinity wastewater and offers promise owing to its lower energy requirements and capital investment when compared with existing competing technologies. By utilizing the concept of industrial ecology, the economic and environmental sustainability of the MD technology can be further enhanced by a systems-level integration of MD process with waste heat sources. One such source is the waste heat available at existing natural gas compressor stations. The U.S. Natural Gas (NG) pipeline network is a highly integrated transmission grid consisting of more than 300,000 miles of transmission pipeline and 1,400 Compressor Stations (CS). In most NG CS, a portion of NG is burned to meet the energy demands of the compression process. Concurrently, about two-thirds of the fuel energy is rejected as waste heat mainly in the form of high temperature flue gas.
We present a framework to evaluate the synergies and potential of utilizing waste heat available from existing natural gas compressor stations for a novel MD technology for treatment of saline wastewater in the Marcellus shale gas play. We determine the quantity and quality of waste heat available at existing NG CS based on capacity, thermodynamic constraints, and the inlet feed temperature for MD. We also estimate the amount of wastewater that could be treated at each compressor station in Marcellus shale gas play based on experimentally measured flux rates. A Geographic Information System (GIS) based optimization framework is developed for informing decision regarding optimal wastewater routing from existing shale gas wells to hypothetical MD plants collocated with compressor stations. The results and insights from this work will be helpful in characterizing regional opportunities and constraints for management of wastewater using MD technology and waste heat sources. The implications of the work for informing sustainable management of water-energy nexus for the shale gas industry will be discussed along with a comparison with existing treatment options.