(688b) Removal of Gaseous O-Xylene in the Two-Liquid Phase Biotrickling Filters and Airlift Bioreactors

Wu, C., Zhejiang University
Wang, X. Q., Technology Innovation and Training Center, Polytechnic Institute, Zhejiang University
Xu, B. L., Zhejiang University
Li, S. J., Zhejiang University
Li, W., Zhejiang University

O-xylene is the most recalcitrant among the three xylene isomers which are released into the atmosphere as a kind of fugitive emission from industrial production with healthy risk and environmental pollutions. Biotechnologies show off their advantages of completely degrading low-concentration contaminants into end-products like carbon dioxide, water, biomass, salts even biofuels since the 1920s. However, the practically insolubility of o-xylene may cause obvious deterioration in the mass transfer, thus reducing the performance of bioreactors.

Recently, an emerging biotechnology for removal of hydrophobic volatile organic compounds (VOCs) is the two-liquid phase bioreactor (TLPB). In a TLPB, an organic liquid-phase, which is always immiscible, non-biodegradable and biocompatible, is added to for an improvement of the VOC dissolution. A large variety of bioreactor configurations have been utilized in the research of TLPB so far, of which the continuous stirred tank bioreactor (CSTB) is the most popular system. Nevertheless, as a traditional bioreactor, the biotrickling filter (BTF) also showed an elimination capacity improvement of more than 100% relative to the one without silicone oil as non-aqueous phase. Although the airlift bioreactors (ALBR) didn’t have a significant enhancement after adding silicone oil, it would be different for the abatement of gas-phase o-xylene. Actually, the literatures about the removal of o-xylene from off-gas in the BTF and ALBR using silicone oil as non-aqueous phase are sparse.

The main aim of this research was to make a comparison observation on the performance of a two-liquid phase (TLP) BTF and ALBR for the biodegradation of o-xylene existing in contaminated air under different empty bed residence times (30-60 s), inlet loading rates (0-100 g m-3 h-1) as well as the response to shock-loads. The pilot plant consisted of two identical bioreactors with or without silicone oil to water phase ratio of 5% operating in parallel. Removal efficiency increased as the EBRTs were improved and inlet concentrations of o-xylene were decreased, exhibiting higher elimination capacities at higher inlet loading rate. Under shock-load condition, adding 5% silicone oil, removal efficiency of the biotrickling filter was dropped 23%, while that of the airlift bioreactors was essentially maintained at approximately 90%  when the inlet concentration was increased from 500 mg m-3 to 1500 mg m-3. When inlet concentration was recovered, the two-liquid phase airlift bioreactor could restore its removal efficiency to 100%, but the two-liquid phase biotrickling filter could not, which reveals that the former was more stable than the latter because of fully stirring and protection from silicone oil.