Thermophilic waste air treatment of n‐alkanes in a two‐phase bubble column reactor: the effect of silicone oil addition

Abstract

BACKGROUND Thermophilic waste air biofiltration was developed to overcome the often observed drop in pollutant removal efficiency caused by classical reactor overheating above the mesophilic temperature range. To date, only a few studies have been reported on thermophilic biofiltration of airborne hydrophobic pollutants. In this work, a bubble column reactor (BCR) operated at 50 °C was used to treat waste air contaminated by a mixture of gasoline/kerosene range n‐alkanes with a microbial consortium acquired from burning coal dumps. RESULTS Several strategies were used to increase the low pollutant removal efficiency initially observed. Of these, only the addition of NAP (silicone oil) to the reactor led to increased removal efficiency, due to formation of water‐in‐oil emulsion. Analysis of the microbial consortium revealed bacteria from the Paenibacilaceae family (FN667384) and unidentified thermophilic fungi (HQ693517.1) to be the dominant organisms within the analyzed category, with 48% and 99% abundance, respectively. In the presence of NAP, longer‐chain n‐alkanes (C10–C12) were degraded efficiently, unlike their shorter‐chain homologs. After 7–10 days, the degradation of shorter‐chain C7–C8 n‐alkanes was observed at the expense of their longer‐chain homologs. CONCLUSION A two‐phase thermophilic BCR proved successful in treating an airborne n‐alkane mixture. With the NAP addition, the apparent mass transfer limitations were overcome, creating a suitable environment for thermophilic hydrocarbon biodegradation. As a result, efficient degradation of longer‐chain n‐alkanes was enabled upon emulsification, whereas the removal of shorter‐chain C7–C8 hydrocarbons occurred later, most likely as a consequence of the biomass adaptation. © 2021 Society of Chemical Industry

Styrene bioconversion by Pseudomonas putida utilizing a non‐aqueous phase for polyhydroxyalkanoate production

“…Notwithstanding, to evaluate the variation of the proportion of silicone oil in the mineral medium was not the object of this study, because most of the investigations of partition bioreactors that use silicone oil as the NAP have reported 5% (v/v) as optimal for styrene removal 11,46,47 and for other pollutants. 48,49 The styrene partition coefficient in the ionic liquid (1-hexyl-3-imidazolium tris(pentafluoroethyl)trifluorophosphate) mixed in the mineral medium at 5% (v/v) is 0.0035 ± 0.00056, is similar to that reported for different ionic liquids based on imidazolium that absorb VOCs. In this regard, some authors report that imidazolium-based ionic liquids have a high affinity for aromatic compounds, such as styrene, although their selectivity varies with the length of the alkyl chain.…”

“…Such an observation suggests that an increase in the proportion of silicone oil in aqueous medium can further increase the absorption of styrene, although it would be necessary to evaluate whether this increase is significant and economically feasible for a large‐scale system. Notwithstanding, to evaluate the variation of the proportion of silicone oil in the mineral medium was not the object of this study, because most of the investigations of partition bioreactors that use silicone oil as the NAP have reported 5% (v/v) as optimal for styrene removal 11,46,47 and for other pollutants 48,49 …”