(60e) Removal of DCM Vapours in a Combined Bioreactor-Photoreactor

The dramatic and debilitating effects of air pollution are a matter of increasing regulatory concern. The most recent version of Clean Air Act Amendments (CAAA – 1990) identify the pollutant of concern and set up the limits for their existence in atmosphere. Dichloromethane (DCM) is a potential VOC, most commonly used as a solvent and in aerosols. The majority of releases of this product are from chemical process industries, such as plastic product manufactures, manufacturers of synthetics, urethane foam production, the electronics industry (electroplating, circuit board manufacturing, and metal degreasing) and the paint industry. Among the various treatment methods developed for the degradation of VOCs, chemical and biological treatment systems and – (or) a combination of both, appears to be a highly effective to decompose high concentrations of VOCs to harmless end-products such as H₂O and CO₂ at ambient temperatures. Thus, the objective of the present work is to study the advantages of combining a non-biological treatment step (photocatalytic oxidation) and a biological process for the treatment of waste-gas containing DCM. Experimental results obtained in a continuously operated photoreactor, treating DCM vapours, both under steady and transient conditions are also presented. Besides, the operational strategies of combining the photoreactor with a biological system (biotrickling filter) in order to maximize the removal of gas-phase pollutants are also illustrated.

Experimental results show that the efficiency of using UV only is rather limited compared to a combined UV-TiO₂ system. A steady-state removal of DCM can be achieved using combined photocatalytic oxidation and biological processes in less than 20 min. The combined processes showed good ability to effectively withstand short-term shock-loads, and reduce pollutant to acceptable levels in effluents. Additionally, depending on the nature and composition of the waste-gas, and the degree of treatment attained in the bioreactor, a photocatalytic reactor can be designed/modified to be used a pre or post-treatment step.