Treatment of mixed hydrogen sulfide and organic vapors in a rock medium biofilter

A pilot-scale biofilter was operated at a publicly owned treatment works to remove hydrogen sulfide and a mixture of volatile organic compounds (VOCs) from waste gas streams. Lava rock was used for the medium, which averaged pH 4 during the study. The study itself was conducted in three phases. The bed volume was 9.8, 6.5, and 3.3 m(3) in phases 1, 2, and 3, respectively, while the flowrate was approximately 17 m(3)/min throughout the study. The removal efficiency of hydrogen sulfide was consistently greater than 90% for all three phases and, despite low-pH conditions, weighted average VOC removal was greater than 70%. The lava rock provided a hospitable environment for microorganisms while causing low head loss (25 Pa at a load rate of 3.8 m/min). However, lava rock is susceptible to dissolution at low-pH conditions (the degree of dissolution depends on the source of the material).