Synthesis and Performance of Iron Oxide-Based Ceramsite in a Biotrickling Filter for Nitrogen Oxides Removal

A novel medium containing iron oxide-based porous ceramsite (modified ceramsite) and commercial ceramsite was used in two bench-scale biotrickling filter for nitrogen oxides removal to evaluate the performance of the modified ceramaite. In this study, we adopted the method of surface coating by choosing FeCl3·6H2O as modifier. Under the calcination time was 4 h at the temperature of 500°C, the modified filler presented excellent adsorption for microbial growth and the mass dry weight of biofilm reached a peak of 1.28 mg/g. Results showed that the density increased by 17% and porosity increased by about 15%, and the isoelectric point PI increased more than 4 times, while the surface pH value reduced to 3.46. The surface of pH is much lower than the isoelectric point, to ensure that its surface is electropositive, besides, the modified ceramsite had a more rough surface compared with ceramsite and changed the two-dimensional rough surface into three-dimensional surface. It only took 8 days for the biotrickling filter to start up with the modified ceramsite while the commercial ceramsite was about 22 days, which greatly shortened the start-up period. Packing with the modified filler, the NO removal performance stayed quite stable and efficient, the removal efficiency of NO did not apparently decrease under high inlet concentration of NO and basically maintained an average value of 92.8% during the whole operation period of treatment. While the commercial ceramsite presented an obvious removal decrease comparing with the modified, especially with the high NO inlet concentration of above 1600 mg/m3 and the removal efficiency was less than 80%. The iron oxide-based ceramsite proved to have the capability for improving the performance of the biofilter for NO removal. Furthermore, the fall off of the surface coating is not obvious under the experimental condition and the property of the coating is relatively stable in a long period of operation. Thus, our findings support the modified filler of iron oxide-based ceramsite as a material for use in filter media in in a biotrickling filter for pollutant gas removal.