Shale gas exploitation by hydraulic fracturing involves a number of environmental hazards, among which the neutralization and management of fracturing flowback waters is of particular importance. Chemical compounds present in the flowback water mainly constitute a threat to surface waters. The aim of our research was to determine the effects of these compounds on the state of activated sludge in a wastewater treatment plant employing biological treatment processes. Based on the obtained results, it was concluded that prior to the transfer of flowback water to a biological wastewater treatment system, it should be diluted with fresh water to lower the chloride ion concentration to the level of 1,000 mg Cl-/dm³. Although such a procedure would ensure the proper performance of a biological wastewater treatment system, it would not limit the migration of phthalates and thihalomethanes to surface waters.