Performance of a hybrid bubble column/biofilter bioreactor for removal of dichloromethane from waste gas streams

Abstract

Background and objectives: Dichloromethane (DCM) is one of the hazardous contaminants of the environment, especially ambient air that threatens human health at both acute and chronic exposures. In this study, the performance of a pilot-scale hybrid bubble column/biofilter (HBCB) bioreactor was studied for the removal of DCM from waste gas streams at steady state. Materials and methods: The experiments were conducted in four stages with relatively constant concentrations of DCM (approximately 240 ppm) and variable empty bed residence time (EBRT) of 50, 100, 150 and 200 s. In addition to determining DCM removal rate and efficiency, quality parameters of mixed liquor of the bubble column bioreactor were studied and kinetic of biofiltration was analyzed. Results: The average DCM removal efficiency of the HBCB bioreactor at EBRT of 200 and 150 s were 79 and 71% respectively. However, further reduction of EBRT resulted in significantly decreased DCM removal efficiency, so that at EBRT of 50 s, the DCM removal efficiency decreased to 32%. In addition, the EBRT reduction from 200 s to 50 s through increasing DCM loading rate resulted in increasing DCM removal rate from 12.1 to 19.6 g/m3.h. The results of kinetic analysis showed that the kinetic data of biofiltration were in the best fitness with the first order rate equation (R2>0.99 and ε%<2.2) and the DCM removal rate constant was determined 0.0114 s-1. The mixed liquor characterization indicated that the daily adjustment of pH and EC was sufficient to prevent any limitation in the performance of the HBCB bioreactor. Conclusion: This study indicated that the DCM removal rate and efficiency of the HBCB bioreactor were relatively high and the HBCB bioreactor had reliable performance during the variable operational conditions.

Keywords

• Dichloromethane
• Waste gas stream
• Hybrid bioreactor
• Empty bed retention time
• Kinetic