Optimization of the Coagulation Process to Remove Total Suspended Solids (TSS) from Produced Water

Produced water is the largest waste stream generated in oil and gas industries. The disposal of this hypersaline wastewaters containing a mixture of different organic and inorganic compounds is a relevant issue. In this study the removal of total suspended solids (TSS) from a real Produced Water, sampled at a full scale oil refinery plant, was optimized. Coagulation experiments were conducted simulating the coagulation, flocculation and sedimentation phases. Ferric chloride and aluminium sulphate were used as alternative coagulants at doses from 5 to 100 ppm while the pH was varied from 6.68 (ambient pH) to 8 and 9. A cationic and an anionic polyelectrolyte, DF 492 and DF 973 were used as flocculants at doses from 2 to 30 ppm. Finally the produced sludge was quantified in order to select the optimal process conditions for fulfilling the required effluent standard while minimizing the sludge production. Obtained results showed a better performance of aluminium sulphate in the TSS removal, compared with ferric chloride, while the cationic polyelectrolyte (DF 492) performed better than the anionic polyelectrolyte (DF 973). Overall, the best performance was achieved dosing 5 ppm of Al2(SO4)3, 30 ppm of DF 492, at ambient pH (6.68), while the optimal process condition was found dosing 5 ppm of Al2(SO4)3, 5 ppm of DF 492, at ambient pH. The optimized condition can be used at full scale plant in the chemical-physical treatment units designed to remove the TSS.