Identification of visible colored dissolved organic matter in biological and tertiary municipal effluents using multiple approaches including PARAFAC analysis

This study provided insights into the persistent yellowish color in biological and tertiary effluents of municipal wastewater through a multi-characterization approach and fluorescence excitation-emission matrix-parallel factor(EEM-PARAFAC)analysis.The characterization was performed on three to five full-scale municipal wastewater treatment plants(WWTPs),including differential log-transformed absorbance(DLn A)spectroscopy,resin fractionation,size-exclusion chromatography for apparent molecular weight analysis(SECAMW),and X-ray photoelectron spectroscopy(XPS)analysis.Hydrophobic acids(HPOA)were abundant in visible colored dissolved organic matter(DOM).The SEC-AMW result showed that the molecular weight of the colored substances in the secondary effluents is mainly distributed in the range of 2–3 k Da.Through XPS analysis,C-O/C-N and pyrrolic/pyridonic(N-5)were found to be positively correlated with chroma.PARAFAC component models were built on biological(two components)and tertiary effluent(three components)and the correlation analysis revealed that PARAFAC component 2 in biological effluent(BE-C2)and component 1in tertiary effluent(TE-C1),which were ascribed to Hydrophobic acids and Humic acid-like,were the responsible visible colored DOM components cause yellowish color.In addition,component similarity testing found that the identified visible colored DOM PARAFAC BE-C2,and PARAFAC TE-C1 were identical(0.96)in physicochemical properties,with 4%removal efficacy on average,compared with 11%for invisible colored DOM.This implied that tertiary effluents containing colorants(TE-C1)were resistant to degradation/removal using different disinfection and filtration processes in advanced treatments.This sheds light on many physicochemical aspects of PARAFAC-identified visible colored DOM components and provides spectral data to build an online monitoring system.

Fractionation of soil organic carbon in a calcareous soil after longterm tillage and straw residue management

No-tillage(NT)and straw return(S)collectively affect soil organic carbon(SOC).However,changes in the organic carbon pool have been under-investigated.Here,we assessed the quantity and quality of SOC after 11 years of tillage and straw return on the North China Plain.Concentrations of SOC and its labile fractions(particulate organic carbon(POC),potassium permanganate-oxidizable organic carbon(POXC),microbial biomass carbon(MBC),and dissolved organic carbon(DOC)),components of DOC by fluorescence spectroscopy combined with parallel factor analysis(PARAFAC),and the chemical composition of SOC by 13C NMR(nuclear magnetic resonance)spectroscopy were explored.Treatments comprised conventional tillage(CT)and NT under straw removal(S0),return of wheat straw only(S1),or return of both wheat straw and maize residue(S2).Straw return significantly increased the concentrations and stocks of SOC at 0–20 cm depth,but NT stratified them with enrichment at 0–10 cm and a decrease at 10–20 cm compared to CT,especially under S2.Labile C fractions showed similar patterns of variation to that of SOC,with POC and POXC more sensitive to straw return and the former more sensitive to tillage.Six fluorescence components of DOC were identified,mainly comprising humic-like substances with smaller amounts of fulvic acid-like substances and tryptophan.Straw return significantly decreased the fluorescence index(FI)and autochthonous index(BIX)and increased the humification index(HIX).No-tillage generally increased HIX in topsoil but decreased it and increased the FI and BIX below the topsoil.Relative abudance order of the chemical composition of SOC was:O-alkyl C>alkylC>aromatic-C>carbonyl-C.Overall,NT under S2 effectively increased SOC and its labile C forms and DOC humification in topsoil and microbially-derived DOC below the topsoil.Return of both wheat and maize straw was a decisive factor in promoting SOC in the plow layer.The stratification of SOC under NT may confer a long-term influence on carbon sequestration.

Optical Characteristics of Chromophoric Dissolved Organic Matter(CDOM)in Upstream and Downstream Lakes of Taihu Lake Basin:New Insights for Water Environmental Management

Chromophoric dissolved organic matter(CDOM)is a key component of organic matter that contributes to the ecological functioning of lakes.The lakes in Taihu Lake Basin play an important role in maintaining regional ecological stabilities;however,the optical characteristics of the CDOM in the upstream and downstream lakes in this basin have not yet been systematically studied.Here,the optical characteristics of CDOM in ten lakes of upstream and downstream of the Taihu Lake Basin were studied using UV-Visible and excitation-emission matrix spectroscopies.Three different fluorophores consisting of two humic-like components(C1,C2)and one protein-like component(C3)were identified by parallel factor analysis.Soil or surface erosion was responsible for the higher abund-ance of C1 in the upstream lakes,and increased biological activities accounted for the higher abundance of C3 in the downstream lakes.Rainfall erosion in the wet season led to an increase in CDOM.We also found that the photodegradation and flocculation degree,which played a significant role in reducing CDOM,were higher in downstream lakes than in upstream lakes.Optical analysis of CDOM provides a promising method for monitoring water qualities(e.g.,total phosphorus and potassium permanganate index)in each lake.Re-ductions in soil or surface erosion in the upstream are needed to improve water quality.

Comparison of three-dimensional fluorescence analysis methods for predicting formation of trihalomethanes and haloacetic acids

This work investigated the application of several fluorescence excitation–emission matrix analysis methods as natural organic matter（NOM） indicators for use in predicting the formation of trihalomethanes（THMs） and haloacetic acids（HAAs）. Waters from four different sources（two rivers and two lakes） were subjected to jar testing followed by 24 hr disinfection by-product formation tests using chlorine. NOM was quantified using three common measures： dissolved organic carbon, ultraviolet absorbance at 254 nm, and specific ultraviolet absorbance as well as by principal component analysis, peak picking,and parallel factor analysis of fluorescence spectra. Based on multi-linear modeling of THMs and HAAs, principle component（PC） scores resulted in the lowest mean squared prediction error of cross-folded test sets（THMs： 43.7（μg/L）^2, HAAs： 233.3（μg/L）^2）. Inclusion of principle components representative of protein-like material significantly decreased prediction error for both THMs and HAAs. Parallel factor analysis did not identify a protein-like component and resulted in prediction errors similar to traditional NOM surrogates as well as fluorescence peak picking. These results support the value of fluorescence excitation–emission matrix–principal component analysis as a suitable NOM indicator in predicting the formation of THMs and HAAs for the water sources studied.

A chemometric analysis on the fluorescent dissolved organic matter in a full-scale sequencing batch reactor for municipal wastewater treatment

Rapid monitoring of water quality is crucial to the operation of municipal wastewater treatment plants （WWTPs）. Fluorescence excitation-emission matrix （EEM） in combination with parallel lhctor analysis （PARAFAC） has been used as a powerful tool for the characterization of dissolved organic matter （DOM） in WWTPs. However, a recent work has revealed the drawback of PARAFAC analysis, i.e., overestimating the component number. A novel method, parallel lhctor framework-clustering analysis （PFFCA）,＂has been cleveloped in our earlier work to resolve this drawback of PARAFAC. In the present work, both PARAFAC and PFFCA were used to analyze the EEMs of water samples from a full-scale WWTP from a practical application point of view. The component number and goodness-of- fit from these two methods were compared and the relationship between the relative score change of component and the actual concentration was investigated to evaluate the estimation error introduced by 9 both methods. PFFCA score and actual concentration exhibited a higher correlation coefficient （R- = 0.870） compared with PARAFAC （R2〈 0.771）, indicating that PFFCA provided a more accurate relative change estimation than PARAFAC. The results suggest that use of PARAFAC may cause confusion in selecting the component number, while EEM-PFFCA is a more reliable alternative approach for monitoring water quality in WWTPs.

Simultaneous degradation of sulfadiazine and dissolved organic matter based on low-impact development facilities

Sulfadiazine(SD)is a common antibiotic administered to treat bacterial infections in livestock,and its fate andmigration are greatly affected by dissolved organicmatter(DOM).The soil infiltration system[a typical low-impact development(LID)facility]can significantly alterDOMproperties during runoff pollution,thus affecting the complexation of SDwithDOM.Here,the binding characteristics of different DOM components and SD in the soil infiltration system were explored using spectroscopic techniques(excitation–emission matrices,parallel factor analysis,and synchronous fluorescence spectroscopy).Combined with the weakening of DOM fluorescence intensity and 78.63%reduction in mean SD concentration following treatment,synchronous degradation may have occurred.The binding sequence of SD and DOM fluorophores was further explored using two-dimensional correlation spectroscopy.Effluent DOM showed greater sensitivity to SD and more binding sites than influent DOM.Moreover,hydrophobic protein-like substances exhibited higher log K_(M) values than other fluorescent components,indicating that protein-like components play significant roles in SD complexation.The soil percolation system improved the complexation stability and binding sequence of fulvic-like substances.Thus,SD–DOM can be intercepted and degraded using LID facilities to reduce the risk of SD in aquatic environments.

Degradation of dissolved organic matter in effluent of municipal wastewater plant by a combined tidal and subsurface flow constructed wetland

Dissolved organic matter(DOM)is an important constituent of wastewater treatment plant(WWTP)effluent.A novel combined tidal and subsurface flow constructed wetland(TF-SSFCW)of 90 L was constructed for a ten-month trial of advanced treatment of the WWTP effluent.Excitation emission matrix(EEM)fluorescence spectroscopy,parallel factor(PARAFAC)analysis and a two end-member mixing model were employed to characterize the composition and removal process of the effluent DOM(EfOM)from the WWTP.The results showed that the TF-SSF-CW performed an efficient EfOM removal with dissolved organic carbon(DOC)removal rate of 88%and dissolved organic nitrogen(DON)removal rate of 91%.Further analysis demonstrated that the EfOM consisted mainly of two protein moieties and two humic-like groups;protein moieties(76%)constituted the main content of EfOM in raw water and humic-like groups(57%)became the dominating contributor after treatment.The EfOM from the WWTP was mainly of aquatic bacterial origin and evolved to a higher proportion of terrigenous origin with higher humification in the TF-SSF-CW effluent.A common controlling treatment-related factor for determining the concentrations of the same kind of substances(protein groups or humic-like groups)was revealed to exist,and the ratio of removal rates between the same substances in treatment was calculated.Our study demonstrates that the TF-SSF-CW can be a novel and effective treatment method for the EfOM from WWTPs,and is helpful for understanding of the character of EfOM in wetland treatment.