Emulsion wastes destabilized by aluminum sulfate and cationic polyelectrolytes

PINOTTI, A; ZARITZKY, N

Food emulsions and dispersions

Editor: Marc Anton, Research Post

Año: 2002; p. 67 - 82

Emulsified oil in wastewater constitutes a severe problem in the different treatment stages. Aluminum salts have been traditionally used as coagulants in wastewater treatments; polyelectrolytes are used to coagulate and flocculate colloidal systems. The performance of aluminum sulfate in comparison to polyelectrolytes (chitosan and polyacrylamide) as conditioning chemicals for an emulsion waste was tested, and the predominant mechanisms acting in each case were analyzed. Turbidimetry, jar test, colloidal titration and microscopy were used to test emulsion destabilization. A coincidence between the doses necessary to reach zero colloidal charge and minimum turbidity was observed for polyelectrolytes. The increase of surfactant chain length increased the doses necessary to produce destabilization and to reach zero charge for all the tested destabilizers. This implies that the hydrophobic part of the surfactant plays an important role in the interaction between surfactant and flocculant. The time necessary to produce system clarification was larger for aluminum sulfate than for polyelectrolytes; this time was shortened for higher aluminum sulfate concentration. The pH showed a marked effect on aluminum sulfate performance with the optimum at pH 6; polyelectrolyte action was practically not affected by pH. Polyelectrolyte addition produced the minimum turbidity for the same doses that zero colloidal charge; at higher doses,  emulsion was restabilized and became turbid again. However, aluminum sulfate treatment did not produce emulsion restabilization. Charge neutralization by the electrostatic patch mechanism is important in chitosan treatment. For aluminum sulfate treatment the mechanism is based on electrostatic attraction chemical forces and adsorption of hydrolyzed metal ions