Biological removal of gaseous VOCs from automotive painting operations

Among the pollutants that automotive plants produce, volatile organic compo und (VOC) emissions due to paint solvents from painting operations are the largest in quantity. The current control process, based on vapor-phase adso rption followed by thermal oxidation, is costly to install and operate. At Ford, a cost-effective method of removing VOCs has been investigated that i nvolves converting an existing spraybooth scrubber system to a biological r eactor. This paper reports the results of a pilot-scale investigation in wh ich two activated-sludge bioreactors, one with and the other without powder ed activated carbon (PAC), were operated in parallel for 16 months. The pri mary findings include (1) The biological VOC removal process was technicall y feasible, and a scrubber system at a typical assembly plant is sufficient ly large to handle the solvent loading used under normal vehicle-production conditions; (2) as compared to the adsorption/thermal oxidation process, t he 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 bio reactors effectively captured and degraded hydrophilic paint solvents (meth yl ethyl ketone, n-butanol, and butyl cellosolve) that were fed via the vap or phase. Toluene, a hydrophobic solvent, was also well-captured and degrad ed (74 to 91% without PAC and 86 to 93% with PAC).