H2S polluted airstreams were treated in two biotrickling filter columns packed with polyurethane (PU) foam cubes, one with cubes coated with a solution of 25 mg/L of polyethyleneimine (PEI, coated reactor) and the other containing just plain PU cubes (uncoated reactor) at empty bed residence times (EBRT) ranging from 6 to 60 s. and inlet H2S concentrations ranging from 30 to 235 ppm, (overall loads of up to 44 gH2S/m3bed/h), with overall removal efficiencies (RE) in the range of 90-100% over 125 days. The acclimatization characteristics of the coated reactor outperformed those of the uncoated one, and both the observed elimination capacity (EC) of 77 gH2S/m3bed/h and retention of volatile solids (VS) of 42 mgVS/cube were maxima in the coated reactor. Insights into the controlling removal mechanisms were also provided by means of dimensionless analysis of the experimental data. Denaturing gradient gel electrophoresis (DGGE) showed that the dominant surviving species in both units belonged to the genus Acidithiobacillus.
The removal efficiency of a pollutant being treated in a biofilter packed with macroporous units as biofilm media carriers can be maximized provided that more fouled air flows inside of the unit pieces of the media rather than around it, because the internal specific area of the carrier is several orders of magnitude higher than outside of it. A new model that accounts for the hydrodynamic distribution of a gas stream flowing inside of a macroporous packed bed, more specifically open-pore foams, is proposed. The model allows for the design of the carrier (pore size, media internal porosity, bed porosity, and external bed resistance coefficient) in the presence or absence of outer layers such as a biofilm and a liquid film so that a given pollutant removal efficiency can be attained or increased based on the amount of fouled gas flowing inside of the media rather than around it, whereas the clogging effects typically observed in the field can be avoided. The model can also be used for the special case in which the bed is packed with a monolithic open-pore carrier. Predicted values for the biofilter performance for a monolithic bed and a open-pore packed bed are in good agreement with experimental results obtained in systems treating toluene and hydrogen sulfide under a wide range (4-120 sec) of empty bed residence times and inlet concentrations (10-200 parts per million by volume).
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