Synergistic enhancement of hydrophobic n-hexane biodegradation in a biotrickling filter: Role of hydrophilic VOCs in mass transfer and extracellular polymeric secretion

Abstract

Volatile organic compounds (VOCs) emitted from the pharmaceutical industry, such as n-hexane, dichloromethane (DCM), and N, N-dimethylacetamide (DMAC), pose significant environmental and health risks. This study evaluates the performance of a bamboo charcoal-based bio-trickling filter (BTF) in removing these VOCs, comparing two systems: BTF-a, treating only n-hexane, and BTF-b, treating a mixture of n-hexane, DCM, and DMAC. After 26 days of operation at an n-hexane concentration of 100 mg m⁻³, BTF-b achieved a removal efficiency (RE) of 87.25 % for n-hexane, significantly higher than the 62 % in BTF-a, showcasing the synergistic effects of multi-component VOCs. As the DMAC concentration increased from 100 mg L⁻¹ to 500 mg L⁻¹, the RE of n-hexane improved from 65.93 % to 82.08 %, with a significant enhancement in the mass transfer coefficient (K_La) from 1.75 × 10⁻⁶ to 6.34 × 1⁻⁵ s⁻¹, demonstrating the positive promotional effect of DMAC on n-hexane biodegradation. Conversely, high DCM concentrations (750 mg m⁻³) reduced the RE of n-hexane to 58.57 % due to substrate competition. The extracellular proteins (PN) content rose from 16.76 mg g⁻¹ to 18.73 mg g⁻¹. Microbial analysis after 220d operation revealed the enrichment of Mycobacterium (57.67 %) and Hyphomicrobium (5.38 %), key genera involved in VOCs biodegradation. Metabolic pathway analysis showed n-hexane and DMAC were transformed into intermediates, including hexanoic acid and acetic acid, demonstrating both pollutant removal and resource recovery potential. These findings highlight the synergistic role of hydrophilic VOCs, which are more hydrophilic than n-hexane, in promoting the biodegradation of hydrophobic pollutants, as well as the feasibility of BTF for treating multi-component VOCs.