Shale gas fracturing flowback water deep treatment engineering – a case study

Abstract

The exploitation of shale gas produces fracturing flowback fluid (SG-FFF) containing salt, organic matter, ammoniacal nitrogen (NH₃-N) and heavy metals which can be harmful to the environment. A process consisting of oil isolation and de-hardening, Fenton oxidation, vapor compression evaporation (MVR), and an anoxic/oxic membrane bioreactor (A/O-MBR) and reverse osmosis (RO) membrane filtration was used to treat the SG-FFF, and the removal process of pollutants in each unit was analyzed. The results of 30 days' operation show that the effluent can stably meet the class III standard of “Surface Water Environmental Quality Standard” GB 3838-2002, and the direct operational cost is about 58.74 Yuan per m³. COD_Cr is removed by air flotation, Fenton oxidation, MVR evaporation and the A/O-MBR biochemical unit, and the removal rates of each unit are 12%, 43%, 87% and 95.5%, respectively; NH₃-N is removed in the MVR, AO/MBR biochemical and RO membrane units, and the removal rates are 8%, 89.8 and 93%; TN is removed by MVR, AO/MBR and RO membrane units, and the removal rates are 68.7%, 16% and 98%; As is removed by the Fenton oxidation, MVR evaporation and RO units, with removal rates of 80%, 92.31% and 99%. TDS is reduced by MVR (98.7%) and RO membrane (99.3%) units. Gas Chromatography-Mass Spectrometry (GC-MS) and Excitation–Emission-Matrix Spectroscopy (EEM) analysis were used to determine the change process of organic compounds in each unit. This study provides a method for deep treatment of SG-FFF.