Rhamnolipid Production By Pseudomonas Aeruginosa Usm-Ar2 In Fed-Batch Fermentation And Application In Crude Oil Distillation
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Date
2014-07
Authors
Md Noh, Nur Asshifa
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Fed-batch cultivations of Pseudomonas aeruginosa USM-AR2 producing
rhamnolipid have been investigated in a 3.0 L stirred tank bioreactor, using diesel as
carbon source. The highest oxygen transfer in the oil-water-surfactant system was
achieved at agitation rate of 500 rpm or impeller tip speed of 1.31 m/s, due to the
highest dispersion of diesel at this speed rate compared to 400 and 600 rpm. At any
agitation rate, the oxygen supplied in the bioreactor was sufficient to meet the
highest possible oxygen demand by the cells. Following batch cultivation, different
fed-batch strategies of DO-stat, pulse-pause and feeding based on the maximum
substrate uptake rate (MSUR) were carried out and compared in enhancing
rhamnolipid production by P. aeruginosa USM-AR2. The MSUR is the maximum
substrate consuming ability of the cells. The strategy depends on real-time
measurements of substrate consumption rate, estimated from dissolved oxygen (DO)
measurements. The yield of product on biomass was enhanced from 0.421 (g/g) in
batch, 0.496 (g/g) in DO-stat fed-batch to 3.098 (g/g) in pulse-pause fed-batch and
finally 3.471 (g/g) via feeding at the MSUR. Productivity was recorded to be 0.029
g/L/h in batch, 0.023 g/L/h in DO-stat fed-batch, 0.054 g/L/h in pulse-pause fedbatch,
and increased to 0.076 g/L/h in MSUR-fed batch. The highest rhamnolipid
production of 23.6 g/L was achieved using the MSUR-fed batch, which depicted
higher substrate utilization rate by the cells and effective strategy in improving
rhamnolipid production by P. aeruginosa USM-AR2. The sharp increase of
rhamnolipid titre during fermentations was dictated by the emulsification of diesel
when rhamnolipid concentration reached 4 to 5 g/L. Rhamnolipid effect was
assessed on distillation of crude oils. Nine out of 12 crude oil samples showed
reduced distillation time, temperature, or increased volume of distillate collected
with retained distillate quality upon simple mixing with the culture containing
rhamnolipid. Characterization of the crude oils based on chemical composition and
physical properties using viscosity, surface tension, emulsification and SARA
(saturate, aromatic, resin and asphaltene) analyses showed no correlation with
rhamnolipid effect on distillation. The CHNS (carbon, hydrogen, nitrogen and
sulphur) analysis showed enhanced distillation by rhamnolipid addition for crude oils
with higher carbon content (~80% - 90%), whereas crude oils with lower carbon
(~70%) are irrelevant to predict distillation performance. The inconsistency in crude
oil distillation might be due to the complex behaviour of crude oil composition.
However, the findings are anticipated to play important role to improve the existing
conventional oil refinery.
Description
Keywords
Oil Distillation