SDS–Chitosan Flocculant Systems in Oily Produced Water Treatment: Performance and Influence of Chitosan Properties

Abstract The increasing volume of produced water (PW) generated during oil production has intensified the demand for efficient and environmentally friendly technologies for oil and grease (O&G) removal. In this study, chitosan-based flocculant systems with different molar masses, combined with sodium dodecyl sulfate (SDS), were evaluated for the treatment of synthetic PW through flocculation and dissolved air flotation tests in jars, using a central composite rotatable design (CCRD). Experimental characterizations included the determination of the critical micelle concentration (CMC) of SDS and the charge densities of the components, parameters that helped elucidate the flocculation mechanisms. The evaluated systems achieved O&G removal efficiencies greater than 85%, reaching residual oil contents as low as 3.1 ppm, particularly at SDS concentrations close to three times the CMC. The combined analysis of the results allowed the identification of operational windows defined by the dimensionless parameter R (R = cchitosan/cSDS), associated with the condition of load equivalence between SDS and chitosan within the flocculant system. The operational range was R ≈ 0.48–0.75 for low molar mass chitosan and R ≈ 0.48–1.01 for high molar mass chitosan, indicating greater tolerance to excess polymer and delayed colloidal restabilization in the latter system. The results demonstrate that SDS/chitosan systems are promising and environmentally friendly alternatives for the treatment of produced water.