Biological Removal of Gaseous VOCs from Automotive Painting Operations

Among the pollutants that automotive plants produce, volatile organic compound (VOC) emissions due to paint solvents from painting operations are the largest in quantity. The current control process, based on vapor-phase adsorption followed by thermal oxidation, is costly to install and operate. At Ford, a cost-effective method of removing VOCs has been investigated that involves converting an existing spraybooth scrubber system to a biological reactor. This paper reports the results of a pilot-scale investigation in which two activated-sludge bioreactors, one with and the other without powdered activated carbon (PAC), were operated in parallel for 16 months. The primary findings include (1) The biological VOC removal process was technically feasible, and a scrubber system at a typical assembly plant is sufficiently large to handle the solvent loading used under normal vehicle-production conditions; (2) as compared to the adsorption/thermal oxidation process, the biological process was found to be comparable in VOC removal efficiency, an order of magnitude more cost-effective in capital cost, and a factor of two more cost-effective in operating and maintenance cost; and (3) the bioreactors effectively captured and degraded hydrophilic paint solvents (methyl ethyl ketone, n-butanol, and butyl cellosolve) that were fed via the vapor phase. Toluene, a hydrophobic solvent, was also well-captured and degraded (74 to 91% without PAC and 86 to 93% with PAC).