Developing a Miniaturized Spectrophotometer Using 235 and 275 nm UVC-LEDs for Fast Detection of Nitrate in Natural Water and Wastewater Effluents

Abstract

In this study, miniaturized portable/online UVC-LED spectrophotometers have been developed for fast detection of nitrate nitrogen and dissolved organic matter, using 235 and 275 nm light-emitting diodes (LEDs) as the light sources and GaN-based photodiodes as UV detectors. The application of the wide-band gap GaN-based photodiodes eliminated the influences of parasitic visible emission of UVC-LEDs. Using Orange G as the test absorbing compound, the portable UVC-LED spectrophotometer showed high linear upper detection limits and a negligible stray light. The portable spectrophotometer showed good linearity for NO3 ––N concentration in the range of 0–15 mg/L (R 2 > 0.99), while a loss of sensitivity was observed at higher NO3 ––N concentration. This nonlinearity was attributed to the intrinsic stray light arising from the incomplete overlap between the 235 nm LED emission spectra and the nitrate absorption spectra. With the empirical correction coefficient α being determined from natural water and municipal wastewater samples, the UVC-LED spectrophotometers have comparable accuracy to the standard spectrophotometric method. The results of size exclusion chromatography further elucidated that it was the fraction of humic substances that determined the correction coefficient α for the UV spectrophotometric detection of nitrate in natural water and municipal wastewater samples.

Contactless Optical Liquid Identifier

“…Moreover, Han et al 27 have used only 235 and 275 nm light-emitting diodes (LEDs) as the light sources, which limit the selectivity of their device, and they used their system for measuring nitrate concentration in water, but not to identify different liquids.…”

“…In this work, we have used a principle that is similar to UV–visible spectroscopy ,, but with a cheaper and more suitable setup that can provide a contactless identification of a specific sample. The proposed system is mainly designed for liquid analysis and relies on the Beer–Lambert law. , The optical based electronic device was built using a set of SMD light emitting diodes (LEDs) that operates on different wavelength levels without the need to add a diffraction grid or monochromator. ,,, The operation principle of the system depends on sending a radiation from a light emitting source, then the emitted photons penetrates through the sample, part of them is going to be absorbed, and the rest is going to be passed through to the other side of the sample container. The amount of light passed through the sample to the other side is measured by specific photodetectors and the readings depend on the amount of absorption.…”

“…Recently, Han et al 27 developed a miniaturized portable/online UVC-LED spectrophotometer for fast detection of nitrate nitrogen and dissolved organic matter. They have used 235 and 275 nm light-emitting diodes (LEDs) as the light sources and GaN-based photodiodes as UV detectors.…”

An optoelectronic Portable Device for Real-Time Nitrate Detection in Water

“…The device achieved a limit of detection (LoD) ranging from 0 to 15ppm. Supplementary components included OPA314 and SM320105E [30]. Detection of nitrate and nitrite in drinking water was performed using 310nm for nitrate and 365nm for nitrite, employing a UV ML8511 UV sensor and achieving a limit of detection (LoD) of 50ppm.…”

Optimization of indirect wastewater characterization: a hybrid approach based on decision trees, genetic algorithms and spectroscopy

“…34,35 The versatility of this technology has led to the development of low-power equipment based on LED technology, such as the one developed by ref. 36, for detecting nitrates in natural waters and treated wastewater.…”