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. 2017 Nov;10(6):1628-1639.
doi: 10.1111/1751-7915.12741. Epub 2017 Jul 11.

Simultaneous valorization and biocatalytic upgrading of heavy vacuum gas oil by the biosurfactant-producing Pseudomonas aeruginosa AK6U

Wael Ahmed Ismail  1 , Magdy El-Said Mohamed  2 , Maysoon N Awadh  1 , Christian Obuekwe  3 , Ashraf M El Nayal  1
Affiliations

Simultaneous valorization and biocatalytic upgrading of heavy vacuum gas oil by the biosurfactant-producing Pseudomonas aeruginosa AK6U

Wael Ahmed Ismail et al. Microb Biotechnol. 2017 Nov.

Abstract

Heavy vacuum gas oil (HVGO) is a complex and viscous hydrocarbon stream that is produced as the bottom side product from the vacuum distillation units in petroleum refineries. HVGO is conventionally treated with thermochemical process, which is costly and environmentally polluting. Here, we investigate two petroleum biotechnology applications, namely valorization and bioupgrading, as green approaches for valorization and upgrading of HVGO. The Pseudomonas aeruginosa AK6U strain grew on 20% v/v of HVGO as a sole carbon and sulfur source. It produced rhamnolipid biosurfactants in a growth-associated mode with a maximum crude biosurfactants yield of 10.1 g l-1 , which reduced the surface tension of the cell-free culture supernatant to 30.6 mN m-1 within 1 week of incubation. The rarely occurring dirhamnolipid Rha-Rha-C12 -C12 dominated the congeners' profile of the biosurfactants produced from HVGO. Heavy vacuum gas oil was recovered from the cultures and abiotic controls and the maltene fraction was extracted for further analysis. Fractional distillation (SimDist) of the biotreated maltene fraction showed a relative decrease in the high-boiling heavy fuel fraction (BP 426-565 °C) concomitant with increase in the lighter distillate diesel fraction (BP 315-426 °C). Analysis of the maltene fraction revealed compositional changes. The number-average (Mn) and weight-average (Mw) molecular weights, as well as the absolute number of hydrocarbons and sulfur heterocycles were higher in the biotreated maltene fraction of HVGO. These findings suggest that HVGO can be potentially exploited as a carbon-rich substrate for production of the high-value biosurfactants by P. aeruginosa AK6U and to concomitantly improve/upgrade its chemical composition.

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Figures

Figure 1
Figure 1
Chemical structures of representative hydrocarbon components of HVGO.
Figure 2
Figure 2
A graph showing the changes in biomass formation and biosurfactants production (shown as decrease in surface tension) during growth of P. aeruginosa AK6U on HVGO (20% v/v) as the sole carbon and sulfur source in mineral salts medium.
Figure 3
Figure 3
A. The calculated number‐average (Mn) and weight‐average (Mw) molecular weights of the chemical species detected in the maltene fractions extracted from abiotic control and biotreated HVGO. B. Absolute number of sulfur‐containing and hydrocarbon compounds identified in the maltene fractions extracted from abiotic control and biotreated HVGO.
Figure 4
Figure 4
Difference map of hydrocarbon species. Blue dots represent species relatively enriched in the maltene fraction of the biotreated HVGO, and white dots represent species that are relatively more abundant in the maltene fraction of the abiotic control HVGO. The size of the dot reflects the abundance of a compound in the respective maltene fraction.
See this image and copyright information in PMC

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