Hypersaline produced water clarification by dissolved air flotation and sedimentation with ultrashort residence times.
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abstract
Treatment and reuse of some produced waters is made difficult due to their hypersalinity, high concentrations of myriad other dissolved and suspended components, specialized technology requirements (modularity, portability, and short residence times), and lack of existing information on their processing. In this work, produced water containing 100,000mg/L total dissolved solids from the Permian Basin was coagulated with aluminum chlorohydrate (ACH) and flocculated with an anionic high molecular weight organic polymer prior to dissolved air flotation (DAF) and sedimentation to reduce turbidity to < 4 NTU and iron < 0.8mg/L (>95% removal in both cases) with a total coagulation-flocculation-sedimentation/flotation residence time of only 5min. Two advantages of DAF over sedimentation were noted: (i) DAF required only half the dosage of the pre-hydrolyzed ACH coagulant to remove 90% of turbidity and iron even without the organic polymeric flocculant and (ii) DAF even operated successfully without ACH coagulation (i.e., using only the organic polymeric flocculant) evidencing its lower chemical dosing needs. Further, DAF attained all water quality and operational goals at a recycle ratio of only 12% demonstrating that it outperformed sedimentation to generate clean brine at relatively reduced excess energies necessary for air saturation. Higher DAF recycle ratios reduced turbidity and iron removal possibly due to floc breakage. Colloids were effectively destabilized by double layer compression (due to high water salinity), charge neutralization (via adsorption of Al13 polycations), and enmeshment (precipitation of amorphous aluminum). They were flocculated via interparticle bridging (by the anionic organic polymeric flocculant) to create large, compact flocs facilitating ultrashort flotation/sedimentation times. Direct evidence for these individual coagulation and flocculation mechanisms were obtained using electrophoretic mobility measurements, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, optical microscopy, computational image and video analysis, and scanning electron microscopy - energy dispersive X-ray spectroscopy.
