Online removal of volatile siloxanes in solid-state anaerobic digester biogas using a biofilter and an activated carbon filter

Abstract

This study tested the feasibility of using a low-cost biofilter and an activated carbon filter to remove siloxanes from solid-state anaerobic digesters that had unsteady biogas production. The digesters were dosed with three commonly found siloxanes, D3 (Hexamethylcyclotrisiloxane), D4 (Octamethylcyclotetrasiloxane), and D5 (Decamethylcyclopentasiloxane). The removal efficiency of siloxanes by a biofilter and an activated carbon filter integrated system was compared to that using an activated carbon filter only. All solid-state anaerobic digesters were healthy throughout the 42-day test. The results showed that both methods removed siloxanes at a relatively consistent level, regardless of the fluctuating biogas yields. On average, the biofilter-activated carbon filter system showed 98.13%, 96.61%, and 78.58% removal efficiency for siloxanes D3, D4, and D5, respectively, while the ones with an activated carbon filter only gave 91.39%, 81.54%, and 69.43%. Likely, the biofilter either directly captured siloxanes from biogas or partially removed water vapor from biogas which enhanced siloxanes removal in the subsequent activated carbon filter.