Conversion of chemical scrubbers to biotrickling filters for VOCs and H2S treatment at low contact times

The purpose of this work was to evaluate the technical and economical feasibility of converting three chemical scrubbers in series to biotrickling filters (BTFs) for the simultaneous removal of H2S and volatile organic compounds (VOCs). The conversion of the full-scale scrubbers was based on previous conversion protocols. Conversion mainly required replacing the original carrier material and recycle pumps as well as modifying the controls and operation of the reactors. Complete removal of H2S and VOCs on a routine basis was reached at neutral pH in a longer period of time compared to previous conversions reported. Biotrickling filters operated at a gas contact time of about 1.4 s per reactor and at pH controlled between 6.5 and 6.8. Inlet average concentrations below 10 ppm(v) of H2S and below 5 ppm(v) for VOCs were often completely removed. The first and second bioreactors played a primary role in H2S removal. Year-round operation of the biotrickling filters proved the ability of the system to handle progressive load increases of H2S and VOCs. However, fast, sudden load changes often lead to reduced removal efficiencies. Odor analyses showed average removal efficiencies above 80 %. Gas chromatography-mass spectrometry of selected samples showed that outlet odor concentration was due to limited removal of VOCs. The conversion showed was economically viable taking into account the theoretical consumption of chemicals needed for the absorption and oxidation of both H2S and VOCs.