Toward zero waste production in the paint industry

Abstract

Wastewater is generated in the batch production process of water-based paints when vessels and filling lines are washed between batches. This results in a diluted paint wash water stream. The wash water is currently treated in a flocculation process using ferric chloride as a coagulant. An opportunity was identified for re-using wash water from white, non-textured paints. It is necessary to stabilise the wash water with biocides. This water is then used in place of fresh feed water for lower quality paints. Since the wash water originates from high quality products, adding this water to the lower quality paints results in a quality improvement. In addition, treatment costs of the wash water are reduced. This wash water represents approximately 65% of total effluent from the plant. With respect to the remainder of the wash water, the concentration of paint solids in the wastewater stream can vary widely. For effective treatment different solids content in the wastewater requires different dosage levels of the coagulant. If ferric chloride is used as the coagulant overdosing results in waste that must be disposed of as toxic. Ferric chloride dosing can be more easily controlled by using a dilute feed solution. This paper presents the findings of the effect of concentration of the coagulant on the coagulation process. Both the solids content of the wash water and the concentration of the coagulant have been found to be important variables to ensure efficient flocculation and coagulant utilisation.