Simultaneous Removal of N, N-Dimethylacetamide and N-Hexane in Rotating Drum Biofilters: Enhancement of Functional Microorganisms

Abstract

This study investigated the interaction during biodegradation between hydrophilic N, N-dimethylacetamide (DMAC) and hydrophobic n-hexane, both of which are common volatile organic compounds (VOCs) in the pharmaceutical industry. A rotating drum biofilter (RDB) was utilized to remove DMAC and n-hexane simultaneously. The results indicated that the addition of 800 mg/L DMAC shorten the start-up time from 23 days to 18 days of RDB, and increased the n-hexane removal efficiency from 42% to 60%, compared with the biodegradation of n -hexane alone. Further, the protein (PN)/polysaccharide (PS) ratio in the extracellular polymer substance (EPS) was increased from 1:5.62 to 2.25:1. Interestingly, microbial community analysis revealed that the addition of DMAC led to an increase in the proportion of Proteobacteria, which tended to secrete EPS with a high proportion of PN. This PN-rich EPS enhanced the adhesive force of the biofilm and lowered the surface tension of the liquid, which led to the improvement of biofilm trapping of n-hexane. Meanwhile, the excitation-emission-matrix results suggested that the tryptophan-like compounds and tyrosine-like substances provided protection during acid stress and acted as a carbon source for cellular life activities during starvation. Finally, as a further validation, the molecular ecological network also showed that Proteobacteria had the most positive connections (65.47%). Overall, this study found that the removal of hydrophobic compounds could be facilitated by the addition of hydrophilic compounds in the bioreactor, which contributes to the biological treatment of mixed VOCs in practical exhaust gases.

Keywords: N, N-dimethylacetamide, n-Hexane, Extracellular polymer substances, Biofilm