Spectral Characterization Of Dissolved Organic Matter:Towards Online Water Quality Monitoring And Smart Water Treatment

The objectives of this thesis were to:(1) characterize dissolved organic matter (DOM) in natural and engineered water systems with liquid chromatography and UV/fluorescence spectra; (2) use light emitting diode (LED) as light source to develop an online or portable UV absorbance and fluorescence sensor for frequent DOM monitoring; (3) apply UV and fluorescence indicators to assess the removal of DOM, degradation of micropollutants and formation of disinfection byproducts (DBPs) during water and wastewater treatment processes, such as enhanced coagulation, anion exchange, and ozonation. This work will contribute to the development of smart water treatment, which includes online monitoring of water quality and automatic optimization of treatment efficiency. The main contents and conclusions are as follows:Phase ?:characterization of DOMHigh-performance liquid chromatography (HPLC) or high-perfor mance size exclusion chromatography (HPSEC) with UV spectra scan and fluorescence excitation/emission spectra scan were established for characterization of DOM species, which relates their spectral characteristics to their hydrophobicity or molecular weight distribution.HPLC with multi-excitation fluorescence scan directly verified the prevalence of multi-peak fluorophores in EEM, which provides a corrective insight for the current fluorescence regional integration (FRI) methods; whereas HPLC/HPSEC-FLD with multi-emission scan provided more informative fluorescence fingerprints for identification of DOM species, which indicates that the EEM-PARAFAC analysis could not reflect the variety of DOM species with similar fluorescence but different physicochemical properties. In both surface water and wastewater effluents, some of protein-like fluorophores were found in combination with humic-like fluorophores; spectral indices including UVA254, UVA280 and fluorescence EEM reflected the same DOM species. In addition, the humic-like fluorescence with triple-excitation peaks at Em 460 nm presented as the specific fluorescence indicator in textile effluents and its critical fluorescence structure was identified as 1-amino-2-naphthol.Phase ?:Development of LED UV fluorescence sensorCalibrated by tryptophan and humic substances standards and verified by the lab benchtop spectroscopy, the newly developed portable/online LED sensor, which measures the UV280 absorbance, protein-like and humic-like fluorescence simultaneously, was feasible to monitor chromophores and fluorophores with good sensitivity and accuracy.Phase ?:application of LED UV fluorescence sensorUV and fluorescence spectroscopy as well as the UV LED sensor were applied for assessing the efficiency of enhanced coagulation and anion exchange for removal of DOM and control of DBPs formation. For all samples from 16 drinking water sources in Jiangsu province, enhanced coagulation was mainly effective for large molecular weight proteins; while anion exchange further substantially removed humic substances. During chlorination tests, UVA280 and UVA254 showed similarly good correlations with yields of disinfection byproducts (DBPs); the humic-like fluorescence obtained from LED sensors correlated well with both trihalomethanes and haloacetic acids yields, while the correlation between protein-like fluorescence and haloacetic acids was relatively poor.UV and fluorescence spectroscopy as well as the UV LED sensor were applied to predict the degradation of dissolved organic matter and trace organic contaminants (TOrCs) during ozonation. The online data from LED sensor showed that the degradation of chromophores and fluorophores in WWTP effluent complied with the second order kinetic models during ozonation and the protein-like and humic-like fluorophores, which showed similar reaction rates, were more prone to oxidation than chromophores. For TOrCs, their removal rates were well correlated with the decrease of the LED UV/fluorescence signals, and their elimination patterns were mainly determined by their reactivity with O3 and hydroxyl radicals. At approximately 50% reduction of humic-like fluorescence almost complete oxidation of TOrCs of group I and II was reached, a similar removal percentage (25-75%) of TOrCs of group III and IV, and a poor removal percentage (< 25%) of group V. In another way,90% reduction of humic-like fluorescence could reach the sufficient elimination of most TOrCs.UV and fluorescence indicators were further applied to assess the formation of bromate and biodegradable organic carbon during ozonation. With the increase of O3/DOC mass ratio, BDOC formed through three periods of lag, transition slope and plateau. With the decrease of UV absorbance and fluorescence, BDOC concentrations initially increased slowly and then rose more noticeably. Such 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. Data of size exclusion chromatography (SEC) with organic carbon detection and 2D synchronous correlation analysis showed that 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 and other smaller AMW species associated with BDOC. Appreciable bromate formation was observed only after the values of UVA254, UVA280 and humic-like fluorescence in 03-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.