Oil-Water Emulsion Flocculation through Chitosan Desolubilization Driven by pH Variation

Abstract

Water pollution is a major concern in our modern age. The contamination of water, as a valuable and often limited resource, affects both the environment and human health. Industrial processes such as food, cosmetics, and pharmaceutical production also contribute to this problem. Vegetable oil production, for example, generates a stable oil/water emulsion containing 0.5-5% oil, which presents a difficult waste disposal issue. Conventional treatment methods based on aluminum salts generate hazardous waste, highlighting the need for green and biodegradable coagulant agents. In this study, the efficacy of commercial chitosan, a natural polysaccharide derived from chitin deacetylation, has been evaluated as a coagulation agent for vegetable oil emulsions. The effect of commercial chitosan was assessed in relation to different surfactants (anionic, cationic, and nonpolar) and pH levels. The results demonstrate that chitosan is effective at concentrations as low as 300 ppm and can be reused, providing a cost-effective and sustainable solution for oil removal. The flocculation mechanism relies on the desolubilization of the polymer, which acts as a net to entrap the emulsion, rather than solely relying on electrostatic interactions with the particles. This study highlights the potential of chitosan as a natural and ecofriendly alternative to conventional coagulants for the remediation of oil-contaminated water.

Figure 1

(a) Particle size distribution and ζ potential measured in the emulsion obtained with different surfactants; (b) DLS characterization of SDS emulsion, particle size, and ζ potential distribution are shown from left to right, respectively; (c) DLS characterization of Tween 80 emulsion, particle size, and ζ potential distribution are shown from left to right, respectively; and (d) DLS characterization of the CTAB emulsion, particle size, and ζ potential distribution are shown from left to right, respectively.

Figure 2

ζ potential characterization of emulsions based on CTAB, Tween 80, and SDS at different pH values ranging from 2 to 8.

Figure 3

(a) Picture and schematic representation of the chitosan-driven flocculation on an oil–water emulsion. The photos specifically refer to the emulsion and coagulation of an SDS-based emulsion, where flocculation was carried out using 300 ppm chitosan at pH 11. (b, c) Histograms show the oil removal percentages obtained without the presence of chitosan (CTR) and with different concentrations of chitosan (300 and 450 ppm). The left side reports the oil removal obtained at pH 9, while the right side reports the oil removal obtained at pH 11. The pH was adjusted by adding 0.1 M NaOH. (d–f) Light microscopy images of the cell count plate of the CTAB emulsion, CTAB emulsion after treatment with 300 ppm of chitosan at pH 9, and CTAB emulsion after pH adjustment at 9 without chitosan, respectively, with a scale bar of 25 μm in each image.

Figure 4

Oil removal percentage of 300 ppm chitosan in a CTAB emulsion over three cycles of reuse.