Spectroscopy Transmittance by LED Calibration

Abstract

Local administrations demand real-time and continuous pollution monitoring in sewer networks. Spectroscopy is a non-destructive technique that can be used to continuously monitor quality in sewers. Covering a wide range of wavelengths can be useful for improving pollution characterization in wastewater. Cost-effective and in-sewer spectrophotometers would contribute to accomplishing discharge requirements. Nevertheless, most available spectrometers are based on incandescent lamps, which makes it unfeasible to place them in a sewerage network for real-time monitoring. This research work shows an innovative calibration procedure that allows (Light-Emitting Diode) LED technology to be used as a replacement for traditional incandescent lamps in the development of spectrophotometry equipment. This involves firstly obtaining transmittance values similar to those provided by incandescent lamps, without using any optical components. Secondly, this calibration process enables an increase in the range of wavelengths available (working range) through a better use of the LED’s spectral width, resulting in a significant reduction in the number of LEDs required. Thirdly, this method allows important reductions in costs, dimensions and consumptions to be achieved, making its implementation in a wide variety of environments possible.

Performing Calibration of Transmittance by Single RGB-LED within the Visible Spectrum

“…A priori, one idea that would come to mind is to use LED technology, due to its low power consumption and lack of temperature problems. Nevertheless, for analyzing the entire spectrum would require the use of a huge number of LEDs [ 25 ], since each of them is designed to emit within a specific range of wavelengths. This would therefore result in an increase in both the size of the equipment as well as its cost.…”

“…Cost-effective spectrophotometers based on LEDs are being developed and spread to determine wastewater pollution with high accuracy [ 21 , 22 , 23 , 24 ], and their comparison with transmittance calculated from classical devices based on incandescent lamps shows good agreement [ 25 ].…”

“…The contributions of this work are as follows: First, we developed a novelty calibration process, in order to measure transmittance values between 510 and 645 nm using a single RGB-LED, without optical devices, and with a high level of accuracy. As indicated in the study [ 25 ], 18 individual LEDs are needed to be able to analyze water samples between 510 and 645 nm; therefore, a single RGB-LED enables us to significantly reduce the cost of the equipment. Secondly, we provide a simple way to define the red, green, and blue RGB-LED intensity combinations to be used in order to measure the transmittance values that are in agreement with those obtained using the commercial equipment.…”

Wastewater Quality Estimation through Spectrophotometry-Based Statistical Models

“…Deploying spectroscopic-based sensors throughout the sewerage system to monitor the pollution load in real time requires an enormous amount of equipment that must therefore meet the requirement of being cost-effective. The literature already describes the availability of compact and low-cost UV–Vis spectrophotometers to monitor WWTP processes [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. In addition, the installation of storm water storage and sedimentation tanks is usually economically unacceptable, thus a monitoring system to optimize the management of the sewer network is the most cost-effective and, probably, the most ecological variant as well [ 16 ].…”

“…About half of the samples corresponded to the input of the WWTP (raw water) and the rest to the output (treated water). The equipment used for the transmittance characterization in the UV–near visible and visible range is cost-effective, own developed and has been previously calibrated [ 29 ]. This is an offline research study, considered as the first step to reaching a continuous and online monitoring system, at sanitation-system scale, which allows assisting in the control of the pollutants that reach the treatment plant, as well as contributing to the improvement of the treatment processes carried out.…”