[Removal Behavior of Protein-like Dissolved Organic Matter During Different Water Treatment Processes in Full-Scale Drinking Water Treatment Plants].

Protein-like dissolved organic matter (pDOM), which is ubiquitous in natural waters, is a critical precursor of nitrogenous disinfection byproducts. Recently, the control and elimination of pDOM have been a growing concern during drinking water treatment processes. In this study, a high-performance size exclusion chromatography system coupled with photo-diode array, fluorescence detector, and online organic carbon detector (HPSEC-PDA/FLD/OCD) was used to determine the removal behaviors of different-sized pDOM from two full-scale drinking water treatment plants (DWTPs). Coagulation and activated carbon adsorption were selected for bench-scale experiments to further assess the removal behavior of pDOM during conventional water treatment processes. The results showed that different-sized pDOM fractions exhibited different removal characteristics. Pre-oxidation can effectively remove some tyrosine-like and tryptophan-like components with high MW, and as the oxidization effect was enhanced, more high MW fractions decomposed into low MW ones. Conversely, some aliphatic pDOM fractions in high MW (e.g., aliphatic proteins) were not subject to pre-oxidation removal. The coagulation-sedimentation unit was efficient in removing high MW fractions, specifically tryptophan-like fractions. Additionally, some pDOM components may be released during coagulation. pDOM with low MW and high hydrophobicity were easily removed during activated carbon filtration. However, long-term operation of the activated carbon filter may breed microorganisms, resulting in the partial release of pDOM fractions. Moreover, UV disinfection processes promoted the degradation of low MW pDOM components. Due to the complex water quality and uncontrollable microbial activities, the aforementioned water treatment units did not exhibit a synergistic effect on pDOM removal. In comparison with humic-like substances, pDOM was susceptible to water quality changes, and its removal was limited in the surveyed DWTPs. Therefore, DWTPs must strengthen pDOM monitoring in influent and effluent and adjust the operating parameters of different treatment units in a timely manner. Moreover, the combination of advanced water treatment processes, such as ozone-biological activated carbon process and nanofiltration, should also be considered to strictly control pDOM component removal.

[Control of Coagulant Dosing for Humic Substances Based on Ultraviolet Spectrum Analysis].

Humic substance (HS) is a main component of dissolved organic matter in the aquatic environment and significantly affects water treatment processes. To investigate the applicability and principle of UV spectrum analysis for coagulation control, laboratory jar tests were conducted with synthetic waters that had varying concentrations of HS and kaolinite. Thus, the influence of water quality conditions on the optimal coagulant dose (OCD) was determined and further correlated to Specific Ultraviolet Absorbance (SUVA254) and the ultraviolet spectral slopes of the coagulated water. Subsequently, the relationship between the UV spectral slopes and organic fractionation was further identified by using size exclusion chromatography (SEC). The results showed that the coagulant demands of the synthetic waters were positively related to dissolved organic carbon (DOC). Consequently, a stoichiometric relationship (0.61 mg·mg-1 calculated as Al/DOC) was found between the coagulant demand and initial DOC of the synthetic water. As the coagulant dose increased, SUVA254 decreased from 8.9 L·(mg·m)-1 to a steady level of 2.0 L·(mg·m)-1 and the removal efficiency of DOC was positively correlated with SUVA254. Spectral slopes in different wavelength ranges had showed similar tendencies, with S275-295 having the best correlation with SUVA254 (R2=0.81). Furthermore, SEC results demonstrated that coagulation preferentially removed humic substances, leading to reduced humification. As a result, S275-295 had the highest correlation with the portion of UVA254 contributed by humic substances in water. Therefore, online measurement of ultraviolet spectral slopes was an important aspect in the control of coagulant dosing.