Abstract
The performance of a hybrid bubble column/biofilter (HBCB) bioreactor for the removal of dichloromethane (DCM) from waste gas streams was studied in continuous mode for several months. The HBCB bioreactor consisted of two compartments: bubble column bioreactor removing DCM from liquid phase and biofilter removing DCM from gas phase. Effect of inlet DCM concentration on the elimination capacity was examined in the DCM concentration range of 34–359 ppm with loading rates ranged from 2.2 to 22.8 g/m3.h and constant total empty bed retention time (EBRT) of 200 s. In the equal loading rates, the elimination capacity and removal efficiency of the biofilter were higher than the corresponding values of the bubble column bioreactor. The maximum elimination capacity of the HBCB bioreactor was determined to be 15.7 g/m3.h occurred in the highest loading rate of 22.8 g/m3.h with removal efficiency of 69%. The overall mineralization portion of the HBCB bioreactor was in the range of 72-79%. The mixed liquor acidic pH especially below 5.5 inhibited microbial activity and decreased the elimination capacity. Inhibitory effect of high ionic strength was initiated in the mixed liquor electrical conductivity of 12.2 mS/cm. This study indicated that the HBCB bioreactor could benefit from advantages of both bubble column and biofilter reactors and could remove DCM from waste gas streams in a better manner.
Highlights
Dichloromethane (DCM, CH2Cl2), so-called methylene chloride, is an environmental contaminant of concern causing both acute and chronic health effects
The experimental set composed of three parts: gas loading units, the hybrid bubble column/biofilter (HBCB) bioreactor including the bubble column bioreactor and the biofilter and conditioning unit for humidification of the biofilter medium and nutrient and trace element supply
The higher elimination capacity of bioreactors removing pollutant in a gas phase comparing with
Summary
Dichloromethane (DCM, CH2Cl2), so-called methylene chloride, is an environmental contaminant of concern causing both acute and chronic health effects. This compound is a synthetic volatile organic compound (VOC) without known natural sources. The health effects of acute (short-term) exposure to DCM through inhalation consist mainly of nervous system effects including decreased visual, auditory, and motor functions and the production of carboxyhaemoglobin (COHb), but these effects are reversible once exposure ceases. Long-term exposure to DCM has the potential to cause chronic health effects including central nervous system (CNS) damages, cardiac effects, liver and lung cancers and mammary gland tumors.
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