Ozonation effects on emerging micropollutants and effluent organic matter in wastewater: characterization using changes of three-dimensional HP-SEC and EEM fluorescence data

Fluorescence sensor enabled control of contaminants of emerging concern in reclaimed wastewater using ozone-based treatment processes

Contaminants of emerging concern (CEC) pose significant challenges to environmental and human health. The development of the wastewater reuse sector, coupled with progressively stringent regulations, needs innovative systems that integrate advanced treatment processes with in-situ and real-time monitoring of CEC. This study investigates the use of a tryptophan-like fluorescence sensor for real-time and online monitoring of CEC within a pilot plant employing O3-based advanced oxidation processes (AOPs). Two tertiary wastewater effluents (WW-1 and WW-2) were tested, placing the pilot system downstream of two different wastewater treatment plants (WWTPs). Priority substances and micropollutants detected in the investigated water matrixes such as pharmaceuticals, per- and polyfluoroalkyl substances (PFAS) were selected as targeted compounds in this study. Fluorescence degradation was detected in real-time by the sensor, showing a high capability to detect fast changes in water quality induced by oxidation. Furthermore, the real-time fluorescence showed better sensitivity than lab-scale fluorescence in detecting the fast action of hydroxyl radicals (·OH) during the O3/H2O2 process, highlighting the importance of online monitoring. Selected CEC were degraded by AOPs with different percentages of removal efficiency (RE) (0% Collapse

Key Words

• Advanced oxidation process (AOP)
• Micropollutants
• Online fluorescence sensor
• Per- polyfluoroalkyl substances (PFAS)
• Peroxone
• Real-time monitoring

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Affiliation(s)

Luigi Marino Department of Civil Engineering and Architecture, University of Catania, Viale A. Doria 6, Catania, Italy
Erica Gagliano Department of Civil Engineering and Architecture, University of Catania, Viale A. Doria 6, Catania, Italy; Department of Civil, Chemical and Environmental Engineering, University of Genoa, Genoa, Italy
Domenico Santoro Department of Chemical and Biochemical Engineering, University of Western Ontario, London, Ontario N6A 5B9, Canada
Paolo Roccaro Department of Civil Engineering and Architecture, University of Catania, Viale A. Doria 6, Catania, Italy.

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Effect of Radio-Frequency Treatment on the Changes of Dissolved Organic Matter in Rainwater

Rainwater is a potential source of drinking water, but has various components of dissolved organic matter (DOM). DOM is a reservoir of potential hazards in drinking water. Therefore, a new method is required to purify rainwater as a drinking water source in terms of DOM aspects. A radio-frequency (RF) treatment system is introduced here to purify source water with a small possibility of contamination. RF is generated by applying a frequency of 1.5 MHz through a glass reactor with a diameter of 2 mm which is wrapped by a 2 mm copper wire. The results demonstrate that UV260 value and dissolved organic carbon (DOC) are reduced during RF treatment. DOC was reduced by a lower amount compared to UV260, suggesting the partial transformation of bio-refractory DOM. A fluorescence excitation-emission matrix showed that humic-like substances in rainwater were reduced faster than protein-like ones, indicating that humic-like substances are susceptible to reduction by RF treatment. The results offer information on the use of RF treatment in a rainwater purification process for the production of drinking water.

Use of spectroscopic indicators for the monitoring of bromate generation in ozonated wastewater containing variable concentrations of bromide

Time-resolved monitoring of bromate and other by-products formed into effluents treated with ozone or advanced oxidation processes in wastewater treatment plants (WWTPs) is time-consuming and expensive. This study examined whether concentrations of bromate formed in wastewater after ozonation in the presence of widely varying bromide levels (from ca. 0.7-21.2 mg/L) can be quantified based on measurements of changes in optical properties (differential UV absorbance (ΔUVA), spectral slopes, total or regional fluorescence) of the ozonated samples. Batch ozonation was carried out using a secondary effluent produced at a major wastewater treatment plant located in the Metropolitan Seattle Area. The tests involved raw and bromide-spiked samples treated with ozone doses from 0.1 to 1 mg O₃/mg DOC. Measurements of the absorbance at 254 nm (UVA254), fluorescence and bromate concentrations were performed on the treated samples. In the ozonated wastewater the concentration of bromate increased approximately linearly, from <10 ppb to ca. 200 ppb, without showing the lag phase characteristic for lower ozone doses (<0.4 mg O₃/mg DOC) that was observed in previous studies carried out with concentrations of bromide in the range of 0.05-0.5 mg/L. The highest bromide concentrations used in this study (>10 mg/L) tended to inhibit the generation of bromate. Relative reduction of UVA254 and total fluorescence (TF) were found to be good predictors of bromate generation. Specifically, exponential curves could adequately fit the non-linear relationships found to exist between the concentrations of bromate and the relative reductions of the UV254 and TF, for any initial bromide concentrations used in this study. Little formation of bromate was found to occur for reduction ranges for UVA254 and TF of 30-40% and 70-80% respectively. Conversely, rapid increases in bromate generation were observed when the decrease of UVA254 or TF exceeded these threshold values.

Improved dewaterability of anaerobically digested sludge and compositional changes in extracellular polymeric substances by indigenous persulfate activation

In this study, an indigenous activation of persulfate by iron-bearing minerals was examined using peroxymonosulfate (PMS) and peroxydisulfate (PDS) for the dewaterability and extracellular polymeric substances (EPS) composition of anaerobically digested sludge (ADS). Iron minerals originally present in the ADS seemed to operate as an initiator of the persulfate activation, which was indicated by an increase in the total dissolved iron in the supernatant. The PMS showed higher performance in improving the ADS dewaterability compared to the PDS, with more reduction in the average microbial flocs size. The extracted EPS consisted of three different fluorescent components of tryptophan-like (C1), humic-like (C2), and fulvic-like (C3) components. In the tightly bound (TB)-EPS, two humic-like components (C2 and C3), which were resistant to degradation, exhibited a strong linkage with dewaterability; whereas, in both the PMS and the PDS systems, the C1 was preferentially degraded by the radical-based oxidation, with a greater extent for the PMS-based treatments. The results showed that prior to the actual EPS degradation, the produced radicals were initially involved in cell disruption. The SEC results during the oxidation clearly demonstrated the degradation of a large-sized biopolymer fraction, followed by the production of relatively small sized molecules. They also revealed in the TB-EPS a close association between the ADS dewaterability and the degradation of humic substances.

A new methodology to assess the performance of AOPs in complex samples: Application to the degradation of phenolic compounds by O3 and O3/UV-A-Vis

A methodology combining experimental design methodology, liquid chromatography, excitation emission matrixes (EEM) and bioassays has been applied to study the performance of O₃ and O₃/UVA-vis in the treatment of a mixture of eight phenolic pollutants. An experimental design methodology based on Doehlert matrixes was employed to determine the effect of pH (between 3 and 12), ozone dosage (02-1.0 g/h) and initial concentration of the pollutants (1-6 mg/L each). The following conclusions were obtained: a) acidic pH and low O₃ dosage resulted in an inefficient process, b) increasing pH and O₃ amount produced an enhancement of the reaction, and c) interaction of basic pH and high amounts of ozone decreased the efficiency of the process. The combination of O₃/UVA-vis was able to enhance ozonation in those experimental regions were this reagent was less efficient, namely low pH and low ozone dosages. The application of EEM-PARAFAC showed four components, corresponding to the parent pollutants and three different groups of reaction product and its evolution with time. Bioassys indicated important detoxification (from 100% to less than 30% after 1 min of treatment with initial pollutant concentration of 6 mg/L, pH = 9 and ozone dosage of 0.8 g/h) according to the studied methods (D. magna and P. subcapitata). Also estrogenic activity and dioxin-like behavior were significantly decreased.

Effects of chlorination on the fluorescence of seawater: Pronounced changes of emission intensity and their relationships with the formation of disinfection byproducts

Chlorination of coastal (CS) and deep ocean (DO) seawater was accompanied by a prominent decrease (of up to 70%) of the intensity of its emission which was measured using a 315 nm excitation wavelength. Deconvolution of the emission spectra of CS and DO seawater showed that these spectra comprised three Gauss-shaped bands. The intensities of two of these bands decreased rapidly as the halogenation proceeded. For both DO and CS seawater, two stages of changes of their fluorescence were observed. The first stage in which the relative changes of the fluorescence intensity (ΔF/F) were between zero to 0.30 and 0.40 was not accompanied by the release of individual disinfection byproduct (DBP) species. For ΔF/F values above the corresponding thresholds, the relative changes of fluorescence intensity were well correlated with the concentrations of individual DBP species such as trihalomethanes and haloacetonitriles. R² values for CHBr₃, CHBr₂Cl and CHBrCl₂ formed in DO seawater were 0.83, 0.80 and 0.68, respectively while for CS seawater, the corresponding R² values were 0.91, 0.93 and 0.92. The presented data demonstrate that the intrinsic chemistry of DBP formation and dissolved organic matter (DOM) halogenation in seawater can be well quantified based on the examination of changes of its fluorescence. This approach can also be employed for practical monitoring of changes of properties of marine DOM and generation of DBPs in desalination, marine aquaculture and other processes.

Tracking the reactivity of ozonation towards effluent organic matters from WWTP using two-dimensional correlation spectra

The characteristics of effluent organic matter (EfOM) from a wastewater treatment plant (WWTP) during ozonation were investigated using excitation and emission matrix (EEM) spectra, Fourier transform infrared spectroscopy (FT-IR) and high-performance size exclusion chromatography (HPSEC) at different ozone dosages. The selectivity of ozonation towards different constituents and functional groups was analysed using two-dimensional correlation spectra (2D-COS) probed by FT-IR, synchronous fluorescence spectra and HPSEC. The results indicated that ozonation can destroy aromatic structures of EfOM and change its molecular weight distribution (MWD). According to 2D-COS analysis, microbial humic-like substances were preferentially removed, and then the protein-like fractions. Terrestrial humic-like components exhibited inactivity towards ozonation compared with the above two fractions. Protein-like substances with small molecular weight were preferentially reacted during ozonation based on 2D-COS probed by HPSEC. In addition, the selectivity of ozone towards different functional groups of EfOM exhibited the following sequence: phenolic and alcoholic CO groups > aromatic structures containing CC double bonds > aliphatic CH. X-ray photoelectron spectroscopy (XPS) further elucidated the preferential reaction of aromatic structures in EfOM during ozonation.

PARAFAC Modeling of Irradiation- and Oxidation-Induced Changes in Fluorescent Dissolved Organic Matter Extracted from Poultry Litter

Parallel factor analysis (PARAFAC) applied to fluorescence excitation emission matrices (EEMs) allows quantitative assessment of the composition of fluorescent dissolved organic matter (DOM). In this study, we fit a four-component EEM-PARAFAC model to characterize DOM extracted from poultry litter. The data set included fluorescence EEMs from 291 untreated, irradiated (253.7 nm, 310-410 nm), and oxidized (UV-H₂O₂, ozone) poultry litter extracts. The four components were identified as microbial humic-, terrestrial humic-, tyrosine-, and tryptophan-like fluorescent signatures. The Tucker's congruence coefficients for components from the global (i.e., aggregated sample set) model and local (i.e., single poultry litter source) models were greater than 0.99, suggesting that the global EEM-PARAFAC model may be suitable to study poultry litter DOM from individual sources. In general, the transformation trends of the four fluorescence components were comparable for all poultry litter sources tested. For irradiation at 253.7 nm, ozonation, and UV-H₂O₂ advanced oxidation, transformation of the humic-like components was slower than that of the tryptophan-like component. The opposite trend was observed for irradiation at 310-410 nm, due to differences in UV absorbance properties of components. Compared to the other EEM-PARAFAC components, the tyrosine-like component was fairly recalcitrant in irradiation and oxidation processes. This novel application of EEM-PARAFAC modeling provides insight into the composition and fate of agricultural DOM in natural and engineered systems.