Effect of aluminum sulfate and cationic polyelectrolytes on the destabilization of emulsified wastes

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 flocc ulate 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 m icroscopy were used to test emulsion destabilization. Both charge neutraliz ation and bridge formation were identified and confirmed as mechanisms of i nteraction of polyelectrolytes with waste constitutents. Charge neutralizat ion would be more important for chitosan than for polyacrylamide treatment. A coincidence between the doses necessary to reach zero colloidal charge a nd minimum turbidity was observed for polyelectrolytes. The time necessary to produce system clarification was larger for aluminum sulfate than for po lyelectrolytes; this time was shortened for higher aluminum sulfate concent ration. 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 d oses that zero colloidal charge; at higher doses, emulsion was restabilized and became turbid again. However, aluminum sulfate treatment did not produ ce emulsion restabilization. (C) 2001 Elsevier Science Ltd. All rights rese rved.