A comparative study of the effect of compost/woodchips mixture, natural zeolite and zeolite/activated carbon mixture as packing materials on the biofilter performance

Formaldehyde is a dangerous compound that must eliminate from contaminated air. Different methods exist for removal of pollutants from the air that among them, the biological processes attracted a great deal of attention. Removal of formaldehyde from the contaminated air was investigated in three laboratory-scale biofilters packed with different materials (a mixture of compost and woodchips, the natural clinoptilolite zeolite particles in the original form, and the mixture of zeolite/activated carbon). The biofilters were inoculated by aerobic sludge. The average removal efficiencies of 97.5%, 90%, and 93.5% were obtained at 100s empty bed residence time (EBRT) and 20 mg/m3 inlet concentration of formaldehyde for the biofilter of configurations І, Ⅱ, and Ⅲ, respectively. Also, the performance of the reactors was investigated at different EBRTs of 20, 30, 60 and 100 s and the maximum elimination capacity of 2840 mg/m3.h was achieved at the lowest EBRT (20‌‌ s) for the biofilter of configuration Ⅱ. Increasing inlet formaldehyde concentration from 20 mg/m3 to 80 mg/m3 leads to obtaining the maximum formaldehyde removal efficiency of 82% for the biofilter of configuration Ⅲ. Therefore, the comparison of the results of the biofilters performances showed that the performance of the biofilters was approximately similar. However, the biofilter of configurations Ⅱ and Ⅲ were achieved to the steady-state conditions at the shorter time. Further, the higher performance of the biofilter of configurations Ⅱ and Ⅲ was approved by obtaining a higher mass transfer coefficient.