Pretreatment of Shale oil Produced Water with Softening, Coagulation and Flocculation
Abstract: Hydraulic fracturing of shale formations to extract oil and gas consumes high volume of freshwater and generates flowback and produced water (PW). Produced water (PW) is contaminated with high concentrations of salts, oil residues, fracking fluids and other chemicals in the shale formation. Research is currently underway to improve the treatment processes targeted for removal of emulsified oil and grease, suspended solids and multivalent ions in PW. In the current study, we focus on evaluating softening, coagulation and flocculation as preliminary treatment methods for PW from the Permian basin in Texas. PW are pH-adjusted with sodium hydroxide (NaOH) and softened with sodium carbonate (Na2CO3) to reduce water hardness. Multiple cationic poly (aluminum chlorides) (PAC) and polyacrylamides (PAM) are applied as coagulants and flocculants to remove suspended solids (SS) and reduce chemical oxygen demand (COD) in the PW. Varying doses of PAC and PAM are tested at different pH, and the effect on COD and turbidity is observed. The research conducted is aimed to test the various coagulants and flocculants. Specifically, a comparison will be made with pretreatment solution that has a higher level of reduction for COD and turbidity in produced water samples from Permian Basin. The treatment process includes the addition of appropriate doses of coagulants and flocculants to PW, and stirring the solution continuously for 2 minutes at 400 rpm, and 10 min at 80 rpm using a magnetic stirrer. Out experimental results demonstrate that with the softening process applied, most Ca2+ and Mg2+ as well as multivalent cations can be removed from PW, and COD can be reduced by about 30% with the optimized doses of coagulants and flocculants.
Brittani Turner* and Raghava R. Kommalapati
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