Until alternative coating materials and depainting operations become available, treatment of fugitive volatile organic compound (VOC) contaminant releases during application or removal of coatings is necessary to maintain compliance with the Clean Air Act Amendments of 1990. Currently available VOC emission control technologies are costly at the high volumetric flow rates and low contaminant concentrations associated with the ventilation of aircraft hangars. Biofiltration of painting off-gas streams is limited because existing systems have not been designed to handle the operating conditions typical at these facilities.
This project will develop an innovative, high flow-rate biofiltration method for treating VOC-laden air emissions.
This project is evaluating the following innovative design features for their ability to improve biofilter performance for paint spray booth applications: (1) a recirculating inoculation method to shorten the bioreactor start-up period; (2) directionally-switching operation to improve biomass distribution and prevent clogging; (3) slip-stream feed to maintain high biomass activities during paint spray booth shutdown periods; and (4) an aerosol nutrient delivery system to efficiently deliver nutrients and moisture to the biofilm. Bioreactor performance is strongly influenced by the contaminants being treated. Therefore, the effectiveness of each design modification will be determined under single (e.g., ethyl acetate) as well as multiple (e.g. methyl ethyl ketone (MEK), methyl isobutyl ketone, toluene) contaminant conditions representative of paint spray emissions.
An experimental plan, test system, and experimental protocols for the project were developed and start-up experiments have been completed. The research team has constructed two stainless-steel laboratory-scale bioreactors The analytical methods that will be used have been developed and tested, including gas chromatography/ free induction decay for gas-phase volatile organic compounds. The research team also has developed and sucessfully used a new iodonitrotetrazolium chloride redox method for assessing biomass activity in the biofilter. Results from these tests indicate that the bioreactor acclimation period is very sensitive to the amount of nitrogen initially available in the system and the initial VOC contaminant feed supply. Other accomplishments include the development of microbial cultures capable of degrading the major contaminants found in paint spray emissions. To this end, the research team has isolated and developed microbial cultures that degrade toluene, ethyl acetate, and MEK.
The project will provide a stable biofiltration system for paint spray booth applications that operate intermittently and emit varying quantities of VOCs. Typical biofilter problems such as long acclimation times, slow response to load changes, and biomass clogging will be overcome. The innovative biofiltration process developed by this project will, therefore, be suitable for the venting of aircraft hangars during application or removal of coatings. This technology has the added advantages of operating at ambient temperatures and minimizing the generation of secondary wastes.