Integrated Coagulation-Adsorption Dissolved Air Flotation Treatment for Oily Wastewater

Abstract

Produced water is the largest wastewater stream generated by the petroleum industry, and contains a range of petroleum hydrocarbons in free, dispersed and dissolved form. In the offshore environment, produced water management often consists of treatment and discharge into the ocean. The most common treatment technologies in use only target the free and dispersed phase, despite environmental concerns arising from the discharge of dissolved aromatic compounds. Thus, the primary objective of this research was to investigate a produced water treatment train which incorporates dissolved aromatics removal into a gravity separation process. Specifically, this research investigated an integrated adsorption-coagulation pre-treatment process for dissolved air flotation (DAF), which is a common gravity separation technology used for offshore produced water treatment. This thesis reports the results of bench-scale jar test or batch adsorption experiments conducted on a synthetic saline, oily wastewater containing two soluble aromatic compounds, phenol and naphthalene. The first experimental study focused on coagulation alone as a pre-treatment for DAF, and demonstrated that this treatment was not effective for the removal of the dissolved aromatics, particularly phenol. These findings confirmed the premise of this thesis that additional pre-treatment would be necessary for enhanced dissolved aromatics removal. The second study compared the proposed integrated adsorption-coagulation pre-treatment to separate adsorption and coagulation treatments. The results of this study indicated that the integrated pre-treatment could combine the high naphthalene removals observed in the adsorption treatment with the high dispersed oil removals provided by the coagulation treatment. However, the adsorbent material used in this study was not effective for phenol removal. Thus the objective of the third study was to identify an appropriate adsorbent for both phenol and naphthalene removal. This research concluded that powdered activated carbon (PAC) and an aromatic-containing organoclay (BTMA) were both effective adsorbents for both phenol and naphthalene. Finally, experiments were conducted to investigate the impact of adsorption addition on downstream clarification. It was concluded that both sedimentation and DAF were appropriate clarification processes for adsorbent-floc aggregates in oily-saline wastewater.