A composition and method for treating oversprayed paints in paint spray booths is provided. The method includes contacting the paint overspray with a wash water system comprising an agitated solution containing a microorganism concentrate so as to collect the paint overspray in the agitated solution. The solution containing the paint overspray is passed to a holding area for phase separation into an organic phase containing paint overspray and an aqueous phase. The organic phase containing the paint overspray, which contains the paint solids portion, and, optionally, an organic solvents portion, is separated from the aqueous phase. The wash water system for treating paint overspray in paint spray booths contains a microorganism concentrate in an amount effective in precipitating the paint solids and, optionally, organic solvents, from the system.