Application of UV absorbance and fluorescence indicators to assess the formation of biodegradable dissolved organic carbon and bromate during ozonation

Abstract

This study examined the significance of changes of UV absorbance and fluorescence of dissolved organic matter (DOM) as surrogate indicators for assessing the formation of bromate and biodegradable dissolved organic carbon (BDOC) during the ozonation of surface water and wastewater effluent. Spectroscopic monitoring was carried out using benchtop UV/Vis and fluorescence spectrophotometers and a newly developed miniature LED UV/fluorescence sensor capable of rapidly measuring UVA280 and protein-like and humic-like fluorescence. With the increase of O/DOC mass ratio, the plots of BDOC formation were characterized of initial lag, transition slope and final plateau. With the decrease of UV absorbance and fluorescence, BDOC concentrations initially increased slowly and then rose more noticeably. Inflection points in plots of BDOC versus changes of spectroscopic indicators were close to 35-45% loss of UVA254 or UVA280 and 75-85% loss of humic-like fluorescence. According to the data from size exclusion chromatography (SEC) with organic carbon detection and 2D synchronous correlation analyses, DOM fractions assigned to operationally defined large biopolymers (apparent molecular weight, AMW>20 kDa) and medium AMW humic substances (AMW 5.5-20 kDa) were transformed into medium-size building blocks (AMW 3-5.5 kDa) and other smaller AMW species (AMW<3 kDa) associated with BDOC at increasing O/DOC ratios. Appreciable bromate formation was observed only after the values of UVA254, UVA280 and humic-like fluorescence in O-treated samples were decreased by 45-55%, 50-60% and 86-92% relative to their respective initial levels. No significant differences in plots of bromate concentrations versus decreases of humic-like fluorescence were observed for surface water and wastewater effluent samples. This was in contrast with the plots of bromate concentration versus UVA254 and UVA280 which exhibited sensitivity to varying initial bromide concentrations in the investigated water matrixes. These results suggest that measurements of humic-like fluorescence can provide a useful supplement to UVA indices for characterization of ozonation processes.

Applying UV absorbance and fluorescence indices to estimate inactivation of bacteria and formation of bromate during ozonation of water and wastewater effluent

“…A range of studies have described indicator frameworks for ozonation process control, which are based on dissolved O 3 concentration integrated over time (CT), O 3 /DOC mass ratio, differential UV absorbance (e.g., ΔUVA254) and differential total/component fluorescence (e.g., ΔTF) (Chon et al, 2015;Gamage et al, 2013;Gerrity et al, 2012;Li et al 2016bLi et al , 2017Xu et al, 2002). As to wastewater, the conventional CT framework does not work well, as O 3 reacts rapidly with the effluent organic matter in the initial O 3 demand stage and the corresponding CT values are not typically measurable (Lee et al, 2013).…”

“…The development of miniaturized online UV absorbance/fluorescence monitor facilitates the application of spectroscopic indicator frameworks for the real-time optimization of ozonation dosage. Correlations between ΔUVA254, ΔTF or differential humic-like fluorescence, have been well developed in correlation with the oxidation of micropollutants and formation of bromate and biodegradable DOC (Gerrity et al, 2012;Li et al 2016bLi et al , 2017. In comparison with extensive studies focusing on the oxidation performance, few studies have applied the spectroscopic indicator frameworks for estimation of disinfection efficiency.…”

“…Ozone stock solution was dosed into each bottle at a range of specific O 3 doses (O 3 /DOC in the range of 0-1.5 g/g) at room temperature. The residual ozone was immediately determined by the indigo method (Bader and Hoigne, 1981;Li et al, 2017). After one hour, 20 mL of samples were filtered by 0.45 μm filter for chemical and spectroscopic analyses and the residual samples were taken for plating (E. coli experiments only) and FCM analyses immediately.…”

“…Referring to our previous literature (Li et al, 2017), bromate was determined using ion chromatography with MS/MS detection, using an Agilent 1290 series HPLC system coupled with an AB SCIEX QTRAP ® 5500 LC-MS/MS operating with negative mode electrospray ionization. Separation was performed using an ion exchange column Dionex IonPac AS-16 under isocratic conditions with a mobile phase comprising 25% of a 1 M aqueous methylamine solution and 75% of acetonitrile, at a flow rate of 0.30 mL/min and an injection volume of 10 μL.…”

“…UVA280 can also be used as a DOC indicator, by using commercially available 280 nm UV light emitting diodes (LED) (Li et al, 2016a). For DOM in water samples, the UVA280/UVA254 ratios are frequently ∼0.74 (Li et al, 2016a), but these ratios might decrease slightly with increasing ozone doses (Li et al, 2017).…”