Multispectral absorption algorithm for retrieving TSS concentrations in water

Abstract

The environmental problems caused by the increase of pollutant. It is the result of industrial waste and environmental accidents. One of the main sources of water pollution is suspended solids. When these suspended particles settle to the bottom of a water body, they become sediments. Optical methods offer two possibilities: scattering and transmission. The design of optical sensor systems is based on the interaction between the photons of the electromagnetic radiation and suspended particles in water. Pollution usually results in higher total suspended solids (TSS) concentrations or turbidity. Water pollution is caused by any chemical, physical or biological change in the quality of water. Suspended solids are small particles of solid pollutants that float on the surface of, or are suspended in waters. Water pollution has become increasingly critical in this present-day, whether in the developed or the developing countries. Total suspended solids (TSS) in water can be detected by a number of optical sensing techniques, which involve light interaction with suspended particles in water. The measurements of the transmittance give a method for determining the concentration of the particles. The objectives of this study are to derive multispectral absorption algorithm and to develop an optical system, which is based on absorption measurements for measuring the concentration of total suspended solids, TSS in water. The multispectral absorption algorithm has been developed and a new multispectral optical sensor system designed for measuring total suspended solids TSS concentrations in polluted water. The development of the optical algorithm was based on the Beer-Lambert law. Firstly, the water samples used for calibration were filtered and dried to obtain the TSS values. In this study, three light emitting diodes were used as sensing emitters (sources) and a silicon phototransistor as radiations detector. The radiation values were determined from the output voltage readings of the sensor system. An electronic circuit was designed and the readings were measured by using a digital multimeter. The major advantages in using an LED as the light sources are its relatively low power consumption and ability to be modulated electronically at rapid rates. Standard polluted samples were prepared for sensors calibration. As the concentration of total suspended solids P was increased, the intensity of the transmitted light decreased. The level of the photocurrent was linearly proportional to the pollutants concentration. The proposed multispectral algorithm was calibrated using the measured parameters. Its accuracy was determined based on correlation coefficient, R and the value of the root-mean square errors, RMSE. The results showed a good correlation between the radiation values and the total suspended solids concentrations. This optical system provides various advantages over the current portable turbidity meter, which uses a single infrared source. The main advantage is its capability provide water pollution levels accurately (i.e. total suspended solids concentration). It only requires inexpensive components and can be assembled easily. The proposed algorithm produced a high correlation coefficient and low root mean square error value. This new methodology is very important for measuring and monitoring TSS in polluted water areas.