As an oil field matures, it produces larger quantities of produced water. Appropriate treatment levels and technologies depend on a number of factors, such as disposal methods or usage aims, environmental impacts, and economics.
In this study, a pilot plant with a capacity of 50 m3/d was used to conduct flotation, filtration, and adsorption trials for produced-water treatment at a crude-oil gathering facility. The flexible design of the plant allows for the testing of different combinations of these processes on the basis of the requirements of the water to be treated. The subject water during this study was a complex and changing mixture of brine and oil from different oil fields.
Induced-gas-flotation (IGF) trials were conducted, with different coagulant [polyaluminum chloride (PAC)] -addition rates from 0 to 820 mg×L–1. Inlet-dispersed oil-in-water (OIW) concentrations were quite varied during the trials, ranging from 39 to 279 mg×L–1 (fluorescence-analysis method). Turbidity also varied, ranging from 85 to 279 FTU. Through coagulation/flocculation and flotation, dispersed oils were removed from the water. PAC addition ranging from 60 to 185 mg×L–1 resulted in the reduction of the dispersed-oil concentration to less than 50 mg×L–1 in treated water; and PAC addition ranging from 101 to 200 mg×L–1 resulted in the reduction of the dispersed-oil concentration to less than 15 mg×L–1 in treated water. Turbidity was also reduced through flotation, with trial average reductions ranging from 57 to 78%. Filtration further reduced turbidity at rates greater than 80% through the removal of any suspended solids remaining from flotation. Activated-carbon adsorption reduced OIW concentrations of flotation-/filtration-treated water to 5 mg×L–1 (infrared-analysis method) through the removal of dissolved oil remaining in the water. Results confirmed that such adsorption treatment would be more practical for water with lower chemical-oxygen-demand (COD) concentration because high-COD concentrations in water reduce the lifetime of activated carbon dramatically.