Treatment of Water-Wash Paintbooth Effluents in the Automotive Industry

During the coating process of car bodies in water-wash spray booth, around 40% of the sprayed paint does not reach the support; these paint particles sprayed into the air are called “overspray”. By using a dawn-draft positive air pressure coming from the ceiling of the cabin, the polluted air is forced vertically downward toward a grating on the floor under which a constant stream of water is running. The paint particles are captured into the water flow and then drawn to a washwater pit located under the spray booth. Even after the overspray enters the water, it remains sticky and can plug holes, pipes, pumps, the creaming system… With time the water becomes contaminated with organic matter and requires disposal. To prevent these unfortunate occurrences, the water is treated with a detackifying reagent (removes the stickiness) and a flocculant (Aboulhassn, 2006). The floating paint sludge thus formed is removed at the end of the water-pit, whereas the cleanwater which remains in the pit is recirculated and used to clear the air stream again. Veolia Environmental Services - Industry and Services (VESIS) operates several wash-water pits in the automotive industry (water cycle and sludge management).

The management and control of the paint detackifying process is therefore a crucial issue in the automotive coating industry. A good knowledge of this process associated with a good management of the water-pit allows a better management of the paint sludge waste and a longterm recycling of the water in the booth reducing thus the frequency of the emptyings. In order to make sure that a well-adapted solution for the treatment of this type of effluents will be available, Veolia set up a methodology to study the different parameters influencing the detackifying process, to investigate the efficiency of different combinations of chemicals, as well from the point of view of the quality of water as of the paint sludge. This methodology allows to properly select the chemicals and to optimize the on-site treatment of this type of effluents.

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