Efficient Chemicals for High Salinity Oily Produced Water Treatment

Produced water (PW) is generated in a large amount worldwide and has complex compositions. Removing oil and is usually the main focus of the treatment to meet environmental regulations as well as reuse and recycling of PW. This study aims to investigate cost-effective chemicals for high salinity PW treatment with high oil removal efficiency, short treatment time and low chemical dosage. High salinity produced water (HSPW) and low salinity produced water (LSPW) with salinity of 102,290 mg/L and 65,680 mg/L, respectively, were used in this work. Three flocculants were tested with polymers with different molecular weights and charges. The efficiency of chemicals and the optimal dosage were evaluated by separation time and transmission intensity using stability analyzer which allows a step-by-step vertical scanning of the dispersions. Oil content was also measured to evaluate the chemical performance. Zeta potential and particle size were measured to investigate the mechanism of the synergism of flocculant and polymer. Transmission intensity was used to evaluate the oil-water separation in PW in this work. High transmission intensity indicates low oil content. Polymers could not efficiently remove the oil from PW. Flocculants could reduce the oil content in PW to less than 50mg/L. However, the treatment process needs 1 or 2 hours to reach equilibrium. The combination of polymer and flocculant presented synergistic effect in PW treatment for both HSPW and LSPW with shorter separation time, higher oil removal efficiency, and lower chemical dosage. The oil content was reduced to less than 20mg/L within 10 minutes. The reduction in chemical dosage significantly improves the chemical economy. Such synergism was observed in combination of different flocculants and polymers with different molecular weights and charges. The optimal concentration was determined by the transmission intensity curve with time. The increase of flocculant concentration leads to higher transmission intensity and increase of polymer concentration leads to faster separation of oil and water. The results of size distribution and zeta potential indicate that bridging is the main mechanism of polymer to improve treatment efficiency in this work. Large floc leads to fast separation of floc from aqueous phase. This work provides the insight of oily produced water treatment using flocculants and polymers. The results show that such combination could significantly improve the treatment efficiency of high salinity PW with low chemical dosage.