Optimization of biopolymer addition in the clarification of waste-water containing emulsified

N.ZARITZKY; J. PEREZ CALDERON; M.V. SANTOS

Barcelona

Congreso; 10th World Congress of Chemical Engineering; 2017

A large amount of oily emulsified wastewater is generated by various industries such as petroleum refining. The use of biopolymers that can destabilize emulsions, producing clarification of the water is an interesting technological alternative. Chitosan (CH) is a linear polysaccharide with chains of β- (1-4) D-glucosamine (deacetylated units) and N-acetyl-D-glucosamine (acetylated unit). This biopolymer is obtained from solid waste from the fishing industry, which have an appreciable amount of chitin; it is obtained by deacetylating chitin and has multiple applications. CH is a biodegradable, non-toxic biopolymer; it has free amino groups forming a polycationic polymer that reacts with negative charges generating coagulation and flocculation phenomena( Zang et al., 2017).The objectives of this work were:(a) to study the action of CH for the clarification of emulsified waste-water from the petroleum industry; (b) to analyze the simultaneous effect of the addition of CH and a biodegradable anionic surfactant (dodecyl sodium sulfate, SDS), on the residual turbidity of the aqueous phase; (c) to describe the destabilization of the emulsions using different techniques: residual turbidity, image analysis, chemical oxygen demand, optical measurements based on static light scattering (Turbiscan) and zeta potential; (d) to optimize CH doses and SDS concentration in order to minimize residual turbidity by applying surface response methodology (SRM) and desirability tests. Stable oil/water emulsions (model system) were prepared using different crude-oil concentrations; the aqueous phase consisted in distilled water and SDS. In order to apply SRM a composite central design was proposed (SYSTAT 12.0). Clarification of the emulsions was measured by determining the percentage of residual turbidity (% TR) and volumetric fraction of the clarified fluid. The analyzed factors were SDS (concentration range below critical micelle concentration, 2.09 - 4.09 mM), and CH dose (1.483-8.578 g/L). The design had five replicates at the central point. Using micrographs the average diameters of the oil droplets D[4,3] were determined. The initial emulsion had a negative zeta potential; adding CH showed emulsion destabilization due to charge neutralization and flocculation ; however, an excess of CH caused re-stabilization of the emulsion due to the repulsion of positive charges. Optimal destabilization conditions were determined by applying mathematical procedures. Water clarification was produced in less than 3 hours, and the process kinetics was measured. Results obtained indicate that CH is a rapid-acting destabilizing agent and a sustainable alternative for waste-water treatment.