TREATMENT OF PRODUCED WATER WITH A SMZ-VPB SYSTEM: BUFFERING OF THE GAS PHASE REGENERATION STREAM

The oil and gas industry in the United States generates more than three billion tons of wastewater annually. This ‘produced water' is characterized by saline water containing a variety of pollutants, including soluble and insoluble organics as well as many inorganic species. Several of the dissolved contaminants, namely benzene, toluene, ethylbenzene, and xylenes (BTEX), are known to be hazardous at low concentrations. Although as much as 95% of this produced water is disposed via reinjection, a significant quantity is currently discharged to the surface. One potential treatment method for this produced water is to combine a surfactant modified zeolite (SMZ) adsorption system with a vapor phase bioreactor (VPB). In this process, the pollutants in the produced water are removed by sorption onto the SMZ which is subsequently regenerated with ambient air. The BTEX-laden waste gas stream is then treated in a downstream VPB.

The purpose of the current research was to evaluate the effectiveness of the VPB to treat the off-gas stream produced during the regeneration of the SMZ. Under steady feed conditions, the VPB can achieve greater than 90% removal of the BTEX contaminants. However, regeneration tests with the SMZ indicate that the BTEX concentrations in the waste gas stream vary significantly during the regeneration period and the initial BTEX concentrations are too high for a VPB to handle effectively. Placing a small adsorbent GAC bed upstream of the VPB was found to effectively buffer the inlet gas-phase concentration. At one second contact time, the GAC bed reduced the peak contaminant concentrations that occur early during the regeneration process by 97%. The contaminants on the GAC subsequently desorbed at a nearly steady rate over the next 45 hours resulting in a relatively steady concentration of approximately 25 ppmv. This lower concentration is readily degradable by the VPB and the steady nature of the feed stream will prevent the biomass in the VPB from enduring starvation conditions between SMZ regeneration cycles.