Book Description

This report describes feasibility tests of a two-step strategy for air pollution control applicable to exhaust air contaminated with volatile organic compounds (VOCs) from painting aircraft. In the first step of the two-step strategy, the VOC-contaminated exhaust air passes over coated, polypropylene, hollow-fiber membranes while an involatile liquid (silicone oil, mineral oil, decanol, octanol) is pumped counter-current through the filters. The organic liquid captures the VOCs, and their concentration in the circulating liquid increases whenever exhaust air circulates. In the second step, the circulating organic loop passes through a second set of hollow-fiber membranes that support a culture of microorganisms, which remove and metabolize the VOCs, on their exterior surfaces. The concentration of VOCs in the circulating loop oscillates as the painting process starts and stops because VOC capture by the liquid is a fast process whereas removal and metabolization by microorganisms is a slow process. Despite constraints caused by limited availability of commercial membrane packages, adequate rates of removal and transport into and out of circulating octanol were shown to be adequate to support the proposed technology. Biodegradation was also qualitatively validated, although each of the organisms used in these tests selectively metabolized specific classes of solvents; however, other cultures or sequential treatment stages are expected to provide satisfactory removal. Scale-up revealed material incompatibility of the membranes and adhesives with octanol. Silicone oils and vegetable oils were briefly tested as the circulating organic liquid at the end of the project. Pressure drop also remains as an engineering challenge unless ventilation exhaust rates are decreased.