DESTABILSATION OF DISPERSANTS USED IN PAINT PRODUCTION D. GINA, 1 L.L.JEWELL, 1 B. COORAY 2 1 School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa. 2 PLASCON PAINTS (Barloworld Plascon South Africa (PTY) Limited) Correspondence to: Dr. L.L. Jewell, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg Private Bag 3, WITS 2050, South Africa Tel: +27(0)11 717 7507, Fax: +27(0)11 717 7557 E-mail: linda.jewell@comps.wits.ac.za Paint production is a batch process and vessels and lines are washed between batches. This generates paint waste water, which is treated by means of coagulation and flocculation. Dispersants are used to stabilise the suspension of particles in paint. In coagulation, the effect of the dispersants must be counteracted in order to allow particles to settle out. Due to environmental pressure a new range of low solvent paints is being introduced and the dispersants used in these paints differ from previously used stabilisers. The behaviour of these dispersants in coagulation and flocculation treatment processes has not been investigated previously. The ability of aluminium sulphate to destabilise the dispersants used in the production of paint has been investigated. Changes in redox potential have been found to be associated with good flocculation. In this work redox potential has been evaluated as an indicator for destabilisation of the dispersants. The ease with which the dispersants can be destabilised increases with decreasing dispersant concentration so that no problems are expected in the flocculation of paint wastewater, which will contain even lower concentrations of the dispersants. INTRODUCTION The composition of wastewater from a paint production process, like most wastewater, varies depending on which products are being washed out of the system at the time that the waste is generated. The wastewater under consideration is coagulated and flocculated so that the water can be recovered and the sludge disposed of. The dosage of a flocculent is generally determined by trial and error and is known to depend on the solid concentration, the particular flocculent being used and the nature of the water being treated; Thomas et al. (1) have provided a thorough review of the factors that affect flocculation.