Biofuel
processing applications require concentration measurement of bio-ethanol during
its evolution by algae in a proprietary chemical process to optimize the
chemical parameters and the resulting yield of bio-ethanol. The production rate
of bioethanol is initially very low with correspondingly minute concentration
changes. This study presents a highly sensitive U-bend evanescent wave plastic
optical fibre sensor for ethanol concentration measurement in water
corresponding to the production rate limit of bio-ethanol by algae
(cyanobacteria) i.e. 0.1‒0.5gL-1day-1
or 0.0126%v/v ‒ 0.0633%v/v in terms of percent volume concentration of a
solution or % volume/volume concentration. The sensor
was fabricated using low cost, large core (1000 µm diameter) plastic optical
fibre (POF) and investigated in the broadband visible light spectrum (VIS) and
specifically at 630nm wavelength. Real-time measurements show that the sensor
provides a significant response in the range of 0.00633%v/v to 0.0633%v/v
concentration of ethanol in water which corresponds to detection of change in
refractive index as low as 10-7. Moreover, sensitivity of sensor was
derived for the above range as 0.6448 O.D/%v/v with 97.14% of linearity in
results at 630nm wavelength, here O.D refers to optical density ‒ unit of
absorbance. It indicates that the proposed sensor represents a viable solution
for real time and very low level concentration sensing in bio-fuel processing
applications.