Characteristics in dissolved organic matter and disinfection by-product formation during advanced treatment processes of municipal secondary effluent with Orbitrap mass spectrometry.

Dissolved organic matter (DOM) is reported to be a precursor to disinfection by-products (DBPs), which have adverse effects on human health. Therefore, it is crucial to effectively remove DOM before water disinfection. Characteristics of DOM and DBPs formation during advanced treatment processes including coagulation, adsorption, ultraviolet (UV) irradiation, and ozone (O3) oxidation in municipal secondary effluent were investigated in this research. DOM was characterized by Fourier transform infrared spectroscopy (FTIR), excitation-emission matrix fluorescence spectroscopy (EEM), and Orbitrap mass spectrometry (Orbitrap MS). Moreover, DBPs formation potential under different advanced treatment processes was also discussed. FTIR results indicated that various functional groups existing in DOM may react with the disinfectant to form toxic DBPs. EEM analysis indicated that DOM in all water samples was dominated by soluble microbial product-like (SMPs) and humic acid-like (HA) substances. The municipal secondary effluent was abundant with DOM and rich in carbon, hydrogen, oxygen, and nitrogen atoms, contained a certain dosage of phosphorus and sulfur atoms, and the highest proportion is lignin. Most of the precursors (CHO features) had positive double bond equivalent subtracted oxygen per carbon [(DBE-O)/C] and negative carbon oxidation state (Cos) in all four different advanced treatment processes. DBPs formation potential (DBPFP) of coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes were 487 µg L-1, 586 µg L-1, 597 µg L-1, and 308 µg L-1, respectively. And the DBPs precursors removal efficiency of coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes were 50.8%, 40.8%, 39.8%, and 69.0%, respectively. This study provides in-depth insights into the changes of DOM in municipal secondary effluent at the molecular level and the removal efficiency of DBPs precursors during coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes.

Unveiling the transformation of dissolved organic matter during ozonation of municipal secondary effluent based on FT-ICR-MS and spectral analysis.

Ozonation is a well-recognized process in advanced treatment of municipal secondary effluent for water reclamation. However, the transformation of dissolved effluent organic matter (dEfOM) during ozonation of real effluents, particularly at molecular level, has been scarcely reported. In this study, we performed ozonation treatments on real secondary effluents from two municipal wastewater treatment plants, and used Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and various spectroscopic techniques to probe the transformation of dEfOM at four ozone dosage levels (0.28, 0.61, 0.89, and 1.21 mg O3/mg DOC). Most of the precursors were unsaturated and reduced compounds (positive double bond equivalent minus oxygen per carbon ((DBE-O)/C) and negative nominal oxidation state of carbon (NOSC)), whereas the products were mainly the saturated and oxidized ones (negative (DBE-O)/C and positive NOSC). As the ozone dosage increased, the relative abundance of O8-19 species gradually increased in the ozonated samples, whereas an opposite trend was observed for O5-7S1 species. Further, we employed 18 types of reactions to represent the ozonation process, and found that the oxygenation reaction (+3O) possessed the largest number of possible precursor-product pairs, and CHON compounds possessed the highest reactivity. Besides the dominant oxygenation reactions, decyclopropyl (-C3H4) was relatively common reaction for CHON compounds, while it was oxidative desulfonation (-SH2) for CHOS ones. In addition, the transformation of precursors to products accompanied with the drop of (DBE-O)/C, and the increase of NOSC and the O/C ratio. The precursors with aromaticity and fluorescence were mainly correlated with the compounds featuring higher (DBE-O)/C and lower NOSC values. This study is believed to help better understand and improve the application of ozonation process in advanced treatment of real wastewater.

Optimal regulation of N/P in horizontal sub-surface flow constructed wetland through quantitative phosphorus removal by steel slag fed.

High concentration of nitrogen and phosphorus and imbalance of N/P can lead to the formation of water and the malignant proliferation of toxic microalgae. This study put forward the advanced nutrient removal with the regulation of effluent N/P as the core in order to restrain the eutrophication and growth of poisonous algae. According to the preliminary study and review, the optimal N/P for non-toxic green algae was 50:1. The horizontal sub-surface flow constructed wetland was filled with steel slag and ceramsite to achieve the regulation of effluent N/P. The results showed that steel slag had the stable P removal capacity when treating synthetic solution with low P concentration and the average removal rate for 1.5, 1.0, and 0.5 mg/L synthetic P solution was 2.98 ± 0.20 mg kg-1/h, 2.26 ± 0.15 mg kg-1/h, and 1.11 ± 0.10 mg kg-1/h, respectively. Combined with P removal rate and P removal task, the filling amount of steel slag along the SSFCW (sub-surface flow constructed wetland) was 3.22 kg, 4.24 kg, and 4.31 kg. In order to ensure the stability of dephosphorization of steel slag, the regeneration of P removal capacity was investigated by switching operation of two parallel SSFCW in 20 days for cycle. The N removal was limited for the deficiency of carbon source (COD (chemical oxygen demand)/TN = 3-4), and was stable at 18.5-31.9% which was less affected by temperature. Therefore, by controlling the process of quantitative P removal of steel slag, the effluent N/P in SSFCW can be stable at 40-60:1 in the whole year, so as to inhibit the malignant proliferation of toxic algae.

Simultaneous sulfadiazines degradation and disinfection from municipal secondary effluent by a flow-through electro-Fenton process with graphene-modified cathode.

Conventionally the deep treatment and disinfection are fulfilled by different processes for municipal wastewater treatment, this work verified a breakthrough by one process of novel flow-through electro-Fenton (EF) with graphene-modified cathode, which is usually seemed to be ineffective. This process was firstly confirmed to be cost-effective for simultaneous sulfadiazines (SDZs) degradation and disinfection from municipal secondary effluent with a very low electrical energy consumption (EEC) of 0.21 kW h/m3, attributed to the high H2O2 production of 4.41 mg/h/cm2 on the novel graphite felt cathode modified by electrochemically exfoliated graphene (EEGr) with a low EEC of 3.08 kW h/(kg H2O2). Compared with the ineffective SDZs degradation by the conventional flow EF, this process was more cost-effective and overcame the harsh requirements on electrolyte concentration. It also showed good effectiveness in the degradation of different antibiotics, and the graphene-modified cathode still kept stable performance after eight consecutive runs. Account for the combined action of OH and active chlorine, the formation of hydroxylated and chlorine containing by-products was confirmed, and a possible degradation mechanism for SDZs was proposed. This flow-through EF process provided an alternative method for the disinfection and antibiotics degradation by one process for the treatment and reuse of municipal secondary effluent.

Fenton oxidation of municipal secondary effluent: comparison of Fe/Ce-RGO (reduced graphene oxide) and Fe2+ as catalysts.

The advanced treatment of municipal secondary effluent by heterogeneous and homogeneous Fenton processes using Fe/Ce-RGO (reduced graphene oxide) and Fe2+ as catalysts was studied and compared. Sulfamethazine (SMT) was spiked in the effluent to examine the effectiveness of the emerging contaminant removal. The Fe/Ce-RGO catalyst was characterized using a scanning electron microscope (SEM) and cycle voltammetry curves. The removal of dissolved organic carbon (DOC), soluble chemical oxygen demand (SCOD), SMT, and ultraviolet-visible spectroscopy in 254 nm (UV254) of municipal secondary effluents was examined. The DOC removal efficiency of secondary effluent (without addition of SMT) was 36.30% and 11.74% using Fe/Ce-RGO and Fe2+ as catalysts, respectively. The removal efficiency of DOC, SCOD, and SMT in heterogeneous Fenton process was higher than that in homogeneous Fenton process. The changes of three-dimensional excitation-emission matrix (3DEEM) fluorescence, soluble microbial products (SMPs), humic acids, and UV254 were determined, and the results indicated that UV254, aromatic proteins, and humic acids decreased rapidly in both processes; however, polysaccharides and protein-like substances were difficult to degrade. Although some toxic substances produced after Fenton-like treatment, the biodegradability of the treated effluent was enhanced.

[Mechanism on Enhanced Nitrogen Removal in Municipal Secondary Effluent via Internal-Electrolysis Constructed Wetlands at Low Temperature in Winter].

Aiming at the low pollutant removal efficiency of constructed wetlands (CWs) at low temperature in winter, three laboratory-scale vertical-flow CWs, namely unplanted CWs, ordinary CWs, and internal-electrolysis CWs, were used to investigate the nitrogen removal efficiency of municipal secondary effluent when the water temperature was 3-12℃. Moreover, the mechanism of enhanced denitrification of the new wetland was revealed through analysis of the microbial community diversity and community structure. The results showed that the internal-electrolysis CWs could make better use of the carbon sources in the municipal secondary effluent and had a higher removal rate. The effluent TN concentration was maintained at about (9±0.29) mg·L-1. The average TN removal rate was 42.27%, which was 17.91% and 17.33% higher than those of the unplanted CWs and ordinary CWs, respectively. The microbial activity was detected using fluorescein diacetate (FDA), and the result revealed that the microbial activity of the internal-electrolysis CWs could reach 0.224 mg·g-1, which was 2.6 times and 3.4 times of that of the unplanted CWs and ordinary CWs, respectively. The microbial denitrification intensity of the internal-electrolysis CWs was 2.8 times and 3.3 times of that of the unplanted and ordinary CWs, respectively. The results of high-throughput sequencing showed that the microbial community diversity of the internal electrolysis CWs was higher than those of the unplanted and ordinary CWs. Denitrification microorganisms were detected, mainly Dechloromonas, Rhizobium, Hyphomicrobium, and Rhodobacter, as well as Thiobacillus, which is an autotrophic denitrifying bacterium. There were obvious advantages in the total amount of denitrifying microorganisms in the internal-electrolysis CWs, as the denitrification microorganisms accounted for 7.13% of the total microbial biomass, which was 3.8 times and 8.7 times of that of the unplanted CWs and ordinary CWs, respectively.

Adsorption of selected emerging contaminants onto PAC and GAC: Equilibrium isotherms, kinetics, and effect of the water matrix.

The removal of three emerging contaminants (ECs) (amitriptyline hydrochloride (AH), methyl salicylate (MS) and 2-phenoxyethanol (PE)) dissolved in several water matrices by means of their adsorption onto powdered activated carbon (PAC) and granular activated carbon (GAC) has been investigated. When dissolved in ultrapure water, adsorption of the ECs followed the trend of AH > MS > PE, with a positive effect of the adsorbent dose. According to the analysis of the adsorption isotherms and adsorption kinetics, PAC showed strongly higher adsorption efficiency in both capacity and velocity of the adsorption, in agreement with its higher mesoporosity. Equilibrium isotherm data were fitted by Langmuir and Freundlich models. Pseudo-second order kinetics modeled very successfully the adsorption process. Finally, the effect of the presence of dissolved organic matter (DOM) in the water matrices (ultrapure water, surface water and two effluents from wastewater treatment plants) on the adsorption of the selected ECs onto PAC was established, as well as its performance on the removal of water quality parameters. Results show a negative effect of the DOM content on the adsorption efficiency. Over 50% of organic matter was removed with high PAC doses, revealing that adsorption onto PAC is an effective technology to remove both micro-pollutants and DOM from water matrices.

[Removal of Nitrogen in Municipal Secondary Effluent by a Vertical Flow Constructed Wetland Associated with Iron-carbon Internal Electrolysis].

Aiming at the problem of high concentration of total nitrogen (TN) and low available carbon source for microorganisms in municipal secondary effluent, the vertical flow constructed wetland associated with iron-carbon internal electrolysis (ICIE-VFCW) was applied to investigate the removal efficiencies of pollutants in municipal secondary effluent. Moreover, the mechanism for enhanced nitrogen removal was primarily discussed by the applications of UV visible spectrum (UV-VIS) and gel filtration chromatography (GFC). The results showed that the ICIE-VFCW could improve the COD removal efficiencies and the effluent COD of less than 30 mg·L-1could be stably obtained. The average COD removal efficiencies of the whole year, warm months, and cold months could be increased by 10.16%, 9.81%, 11.22%, respectively, compared to the control group. The effluent TN of the ICIE-VFCW could be maintained below 10 mg·L-1, and the average TN removal efficiencies of the whole year, warm months and cold months could be increased by 13.72%,12.90%,16.17%, respectively. Besides, compared to the influent, the humification, aromaticity and average relative molecular weight (Mr) in the effluent obviously decreased, and the Mr decreased more significantly in the ICIE-VFCW. The ICIE-VFCW could promote the conversion of refractory organics in municipal secondary effluent to the small and readily biodegradable molecules, which could enhance the utilization of organic compounds by microorganisms, thus improving the removal efficiency of nitrogen.