Monitoring of water quality using fluorescence technique: prospect of on-line process control

Abstract

The wastewater from sewage processing plants shows characteristic fluorescence signatures when excited by UV light in the 240–300 nm wavelength band. A typical signature is a spectrum having a broad band centered at about 350 nm and two relatively less intense bands centered at about 390 and 430 nm. Samples of settled sewage, treated in an aerobic digester, show a substantial reduction of the intensity of the 350 nm band and comparatively much smaller reduction of the strength of the other two bands. The biodegradable chromophoric constituent species are, therefore, considered to be the major contributors to the overall fluorescence within this band. The intensity of this band has been found to have a good correlation with the biochemical oxygen demand (BOD) parameter. This parameter is universally used for assessing the sewage strength and the suitability of the treated effluent for discharge into rivers or reservoirs. Therefore, the fluorescence technique is considered to have the potential for use in noninvasive continuous water quality monitoring thereby, enabling on-line process control in sewage treatment plants. However, fluorescence strength is affected by the pH of the sample, particularly at higher values. This has to be taken into account for the practical utilization of this technique.