Spectral in-situ analysis of NO2, NO3, COD, DOC and TSS in the effluent of a WWTP

Abstract

An in-situ UV spectrometer was applied to the effluent of a WWTP in Switzerland and calibrated using a multivariate calibration algorithm based on PLS regression. Except for nitrite, the calibration was based on comparative measurements of the effluent in the plant laboratory. Samples made of stock solution added to three different matrices prepared in the EAWAG laboratory were used for the nitrite calibration because the effluent concentrations were always in the range of 0.06-0.26 mg/l. The results show very good precision for nitrite and nitrate. The measuring range for COD and DOC was not completely covered by the measurements, so the meaningfulness of the results is limited. Nevertheless the precision obtained for soluble COD is high enough for most applications at WWTPs. The accuracy of the TSS measurement is unsatisfactory as regards effluent limits since the spectrometer used does not cover the wavelength region up to 700 nm, which gives better signals for TSS calibration due to its strong correlation with turbidity.

Technical Note: Field experiences using UV/VIS sensors for high-resolution monitoring of nitrate in groundwater

“…The recorded measurements at two different wavelengths at EM and ER are designed to compensate interference of organic and/or suspended matter (Thomas et al, 1990) by interpreting the difference between the absorbance values at EM and ER which is expressed by E. In comparison, a UV sensor using only one single wavelength is not able to compensate additional interferences (van den Broeke et al, 2006). The MWS measures absorbance at 256 different wavelengths between 200 and 750 nm within 15 s (Rieger et al, 2004). Both sensors feature the possibility to export the monitored absorbance values and the calculated concentrations.…”

“…Photometrical ultraviolet/visible light (UV/VIS) sensors have been first employed at municipal wastewater treatment plants to control NO 3 -N effluent concentrations Rieger et al, 2004). In addition, UV/VIS sensors have been recently used in groundwater and surface water applications to assess highly resolved NO 3 -N concentrations (Pu et al, 2011;Wade et al, 2012).…”

Estimate the densities of pollutions in water quality monitoring systems based on UV/vis spectrum

“…Instead of using the liner relation between absorption and density of single wavelengths, water quality monitoring system utilises the UV/vis range(200nm-710nm) for simultaneous measurement of numerous compounds. The UV/vis spectrum contains a huge amount of information about the water composition, they are used to monitor changes in the water composition through analysis of the general shape of the spectrum [3]. Furthermore the UV/vis spectrum are also used to derived more specific parameters such as total organic carbon(TOC), nitrate and turbidity [8], which are commonly used in water analysis ( Figure 1).…”

In situand high frequency monitoring of suspended sediment properties using a spectrophotometric sensor

“…It has only been in the last years that portable ultraviolet-visible (UV-VIS) spectrophotometers (220-730 nm), which are able to measure light absorption spectra directly submersed in a liquid media, have been developed and commercialized. They are often used in wastewater drainage systems for a fast and simple evaluation of wastewater quality (Brito et al, 2014;Gamerith et al, 2011;Rieger et al, 2004;Rieger et al, 2006;Rieger et al, 2008). They have been used to estimate turbidity, dissolved organic carbon (DOC), total organic carbon (TOC) and nitrates (NO 3 -N) in streams at a temporal resolution as high as several minutes (Avagyan et al, 2014;Bass et al, 2011;Grayson and Holden, 2012;Huebsch et al, 2014;Huebsch et al, 2015;Jeong et al, 2012;Koehler et al, 2009;López-Kleine and Torres, 2014;Strohmeier et al, 2013;Waterloo et al, 2006).…”