Long‐term VOC and siloxane removal in an anoxic biotrickling filter inoculated with Methylibium sp.

Background Volatile methyl siloxanes in biogas hinder energy recovery due to abrasive silica deposits formed during combustion. Biological removal in biotrickling filters (BTFs) is constrained by low gas–liquid mass transfer, yet few studies separate transport from biological limitations in anoxic conditions. This study evaluates the long‐term performance of a BTF inoculated with Methylibium sp. for the removal of D4, D5, hexane, toluene and limonene under anoxic and microaerobic conditions over 265 days. Results Batch assays showed that co‐substrate availability was the primary factor enhancing Methylibium growth ( P = 0.002), strongest under microaerobic conditions (interaction P = 0.005), while nitrate had no effect ( P ≥ 0.75). In the BTF, toluene (RE > 97%) and limonene (RE 86%–98%) were consistently removed throughout operation. Hexane removal responded strongly to electron acceptor supply (RE 17–100%). In contrast, D4 and D5 RE were largely invariable (13.1 ± 0.7% and 27.6 ± 1.1%; ranges 8.8%–17.9% and 18.9%–30.3%) regardless of EBRT (4.4–15.5 min) or electron acceptor regime, with elimination capacities increasing proportionally with loading, a behavior characteristic of gas–liquid mass transfer limitation. The higher RE of D5 than D4, opposite to the ranking predicted from air–water partitioning, indicates that other factors also contribute. Conclusion The BTF achieved near‐complete VOC removal and partial siloxane abatement under biogas‐compatible conditions. Siloxane removal, relatively stable and largely independent of EBRT and electron acceptor, is constrained primarily by mass transfer rather than by biological capacity. These results support using the BTF as a first purification stage coupled with a downstream adsorption polishing step.