Quantification of chloride and iron in sugar factory effluent using long period fiber grating chemical sensor

This paper is an effort to introduce application of Long period fiber grating (LPG) sensors in perpetual monitoring of industrial waste water effluent. A change in ambient refractive index (RI) of an LPG causes a shift in its resonant wavelength. This RI sensitivity of LPG has been used to design a simple and highly sensitive chemical sensor to determine the concentration of Chloride (Cl) and Iron (Fe) ions present in the treated waste water effluent of sugar factories. The concentrations of Cl and Fe ions in the effluent sample determined by our sensor are 97.85 ppm and 0.274 ppm respectively. The results are in good agreement with that of two standard techniques used for the purpose, thus proving the reliability of the LPG sensor. Limit of detection of Cl and Fe ions are found to be as low as 0.038 ppm and 0.007 ppm per pm shift in wavelength respectively, reflecting enormous potential of the sensor in detection of trace elements in waste water with accuracy. Sensitivity of the sensor for Fe ions being about 5 times greater than that for Cl ions, suggests a higher sensitivity of sensor in lower range of concentration in ppm. Miniaturization, cost-effectiveness and ability of online measurement are the most important features of LPG chemical sensors that give them an edge over existing techniques for the purpose.