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Much remains unknown about compositional variations in soluble microbial products (SMP) with the shift of the substrate condition from a feast to a famine phase in biological treatment systems. This study demonstrated that the formation of SMP could be suppressed by up to 75% during the famine phase with the addition of essential nutrients. In contrast, presence of electron acceptor did not play any significant role during the stress condition, showing the similar amounts of SMP (r = 0.98, p < 0.05) formation between the bioreactors supplied with air and N 2. The SMP formed in the famine phase was more bio-refractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition (R 2 > 0.95). The fluorescence excitation–emission matrix coupled with parallel factor analysis (EEM-PARAFAC) revealed the presence of four different fluorescent components, including two protein-like (C1 and C4), fulvic-like (C2), and humic-like (C3) components, in the SMP and bEPS formed at different conditions. Both C1 and C4 showed increasing trends (R 2 > 0.95) with the length of starvation in the bioreactors without essential nutrients. Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers. This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules (particularly proteins), which typically exert many environmental concerns to effluent organic matter quality. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image • Indigenous persulfate activation was firstly presented for anaerobically digested sludge. • Indigenous activation was more effective for peroxymonosulfate versus peroxydisulfate. • The linkage between ADS dewatering and EPS compositional changes was explored. • Humic-like substances in EPS were correlated with the extent of dewaterability. [ABSTRACT FROM AUTHOR]

Spectroscopic techniques were used to examine the subtle changes in soluble microbial products (SMP) of batch activated sludge bioreactors working at different salinities (i.e., 0%, 1%, 3%, and 5% NaCl). The changes in different fluorescent constituent were tracked by excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC), and the sequential production was further identified by two-dimensional correlation spectroscopy (2D-COS). Greater enrichment of tryptophan-like component and large-sized biopolymer were found in SMP for higher saline bioreactors, suggesting the SMP sources from bound extracellular polymeric substances and excreted intercellular constituents. 2D-COS revealed the opposite sequences of the fluorescence changes in SMP between the low and the high saline bioreactors, following the order of “tyrosine-like > tryptophan-like > humic-like fluorescence” for the latter. This study clarified the dominant mechanisms involved in SMP formation during elevating salinity, which were well supported by the changes in SMP spectroscopic features, microbial activity, and organic degradation rates. [ABSTRACT FROM AUTHOR]

In this study, the spectroscopic indices of soluble microbial products (SMP) were explored using absorption and fluorescence spectroscopy to identify different distinctive biomass growth phases (i.e., exponential phase, pseudo-endogenous phase, and endogenous phase) and to describe the microbial activity of activated sludge in a batch type bioreactor under prolonged starvation. The optical descriptors, including UV absorption at 254 nm (UVA254), spectral slope, absorbance slope index (ASI), biological index (BIX), humification index (HIX), and the ratio of tryptophan-like to humic-like components (C1/C2), were examined to describe the dynamic changes in SMP. These indices were mostly associated with dissolved organic carbon (DOC) of SMPs and specific oxygen uptake rate (SOUR). Among those, ASI was the most strongly correlated with the SOUR data for the pseudo-endogenous and the endogenous periods. Although the three microbial phases were well discriminated using the spectral slope, BIX, and the C1/C2 ratio, the C1/C2 ratio can be suggested as the most preferable indicator as it can also trace the changes of the relative abundance of proteins to humic-like substances in SMPs. The suggested spectroscopic descriptors were reasonably explained by the general trends of decreased large-sized biopolymer fractions (e.g., proteins) and increased humic substrates (HS) with starvation time, which were detected by size exclusion chromatography. This study provides a novel insight into the strong potential of using optical descriptors to easily probe microbial status in biological treatment systems. [ABSTRACT FROM AUTHOR]

The forward osmosis (FO) membrane process is a good option for treating complex wastewater, such as landfill leachate, owing to its high rejection. However, organic membrane fouling and the generation of high-strength concentrate hamper efficient and environmentally friendly operation. To overcome these limitations, an integrated FO system combined with UV/H 2 O 2 oxidation is proposed in this paper. Changes in the heterogeneous organic composition of the leachate were tracked along the treatment processes via size exclusion chromatography and excitation emission matrix combined with parallel factor analysis, which allowed us to pinpoint the organic fractions responsible for FO membrane fouling and evaluate their removal efficiency. Three fluorescent components, including tryptophan-like (C1), fulvic-like (C2), and humic-like (C3) components, were identified in the landfill leachate. A separate UV/H 2 O 2 oxidation system led to selective removal of the organic leachate fractions, causing membrane fouling by ~80% along with the overall removal of bulk leachate by ~45%. Compared to traditional FO, the integrated system resulted in improved filtered volume (by 40%), decreased overall membrane resistance (by 30%), complete flux recovery after physical cleaning, and 50% reduction of organic carbon in the membrane concentrate. Moreover, the concentrate from the integrated FO system was characterized by a much lower abundance of large molecules, which is beneficial for the reclamation of concentrate due to its high biodegradability. This study demonstrated the effectiveness of UV/H 2 O 2 oxidation as an integrated option for an FO system used for extended filtration, membrane fouling mitigation, and the production of low-strength landfill leachate concentrate. Image 1 • First study to integrate UV/H 2 O 2 oxidation with FO for landfill leachate treatment. • Protein-like component and low MW acid fraction cause irreversible FO fouling. • UV/H 2 O 2 effectively removes the fouling fractions of landfill leachate. • It results in fouling mitigation, extended filtration, and low-strength concentrate. [ABSTRACT FROM AUTHOR]

In this study, the potential of osmotic backwashing was explored for the alleviation of the forward osmosis (FO) membrane fouling induced by landfill leachate. The normal osmotic backwashing employing NaCl as a draw solute resulted in an improved membrane flux (~ 4 LMH) and a reduction (45%) of the membrane resistance. We proposed an alternative way of osmotic backwashing based on the inherent osmotic potential of landfill leachate itself for the FO system. For the effort, intermittent osmotic relaxation (IOR) was newly introduced to the FO system to enhance the performance. This operation showed a comparable performance with fouling mitigation to the previous normal osmotic backwashing using NaCl as a draw solute. Under an optimized condition (4 h of filtration intervals and 20 min of backwashing time), the integration of the IOR with the FO system led to a 30% reduction in membrane resistance, a complete flux recovery, and 26% increment in the filtered volume. The IOR process does not require additional energy and/or chemical dosage. Therefore, it can be suggested as an innovative, practical, and energy-efficient osmotic backwashing strategy for a stable and the long-term operation of FO systems treating saline wastewater. Unlabelled Image • Intermittent osmotic relaxation (IOR) strategy was introduced to forward osmosis. • IOR is benefitted by the innate property of landfill leachate that contains high salts. • IOR resulted in extended filterability and membrane fouling mitigation. • IOR provides great benefits of no additional energy and a reduced operation cost. • 20-min backwashing and 4 h-filtration intervals are suggested to optimize IOR. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) has been adopted to treat complex wastewater such as landfill leachate due to its high rejection of organics. In this study, the in-line adsorptive process using biochar (BC) or powdered activated carbon (PAC) was applied to a cross flow FO system to enhance the mitigation of the FO membrane fouling from landfill leachate. The changes in the leachate composition along the treatments were tracked by excitation emission matrix-parallel factor analysis (EEM-PARAFAC) to identify tryptophan-like (C1), fulvic-like (C2), and humic-like (C3) components. After a single operation of FO, the C1 was found to be the main constituent responsible for membrane fouling irrespective of varying operation conditions regarding draw solute concentrations and flow rates. Both sorbents (i.e., BC and PAC) exhibited the preferential removal behavior towards C1 > C2 > C3, which was well supported by their individual adsorption isotherm model parameters. The addition of in-line adsorption treatment to FO resulted in substantial improvements in the filtered volume (>57%) and the flux recovery (>80%) compared to the single FO operation. Without chemical cleaning of membrane, the flux was fully recovered at a dose of 10 g/L BC or 0.3 g/L of PAC. A significant and negative correlation was found between the flux recovery and the C1 of the feed leachate or the corresponding spectral peak intensity (p < 0.05) for the integrated FO system, suggesting the potential of using on-line fluorescence monitoring for the performance of the integrated system in terms of fouling mitigation. This study provided a new insight into the effectiveness of BC or PAC adsorption as the in-line integration with an FO system for the targeted removal of FO membrane foulants in landfill leachate. Image 1 • Integrated FO system with BC adsorption is firstly presented for landfill leachate. • EEM-PARAFAC identified the main organic membrane fouling precursor. • Adsorption using BC or PAC led to targeted removal of organic fouling precursor. • Integrated FO resulted in improved flux recovery and lowered membrane fouling. • New insight is provided into BC or PAC effectiveness as in-line FO integration. [ABSTRACT FROM AUTHOR]

This study investigated the influence of three different organic carbon sources including sodium acetate (SOD), glucose (GLU), and starch (STAR), on soluble microbial products (SMP), which presumably have dissimilar uptake rates and metabolic pathways, in sequencing batch reactors (SBR) and their subsequent effects on membrane fouling of ultrafiltration (UF). SMP were mainly characterized by fluorescence excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC) and size exclusion chromatography (SEC). SMP produced in SOD-fed SBR showed higher abundances of protein-like fluorescent component and large sized aliphatic biopolymer (BP) than GLU- or STAR-fed counterpart did, while the STAR-based operation resulted in more SMP enriched with humic-like fluorescence. The differences in SMP exerted marked effects on UF membrane fouling as indicated by the highest fouling potential with reversibility shown for the SMP from the SOD-fed reactor. Regardless of the carbon source, BP fraction and protein-like component exhibited the greatest extent of reversible fouling, suggesting that size exclusion plays a critical role. However, notable differences in the reversible fouling propensity of relatively smaller size fractions among the three SBRs signified the possible involvement of chemical interactions as a secondary fouling mechanism and its dependency on different carbon sources. Our results provide a new insight into the roles of carbon sources in the characteristics of SMP in biological treatment systems and their effects on the post-treatment using membrane filtration, which is ultimately beneficial to the optimization of biological treatment design and membrane filtration operation. Image 1 • Different organic carbon sources significantly alter SMP composition in SBRs. • Large sized biopolymers and protein-like component are more enriched in SOD-fed SBR. • SMP in SOD-fed SBR showed the highest reversible membrane fouling propensity. • Organic carbon source-dependent fouling is more pronounced for smaller sized SMP. [ABSTRACT FROM AUTHOR]

Membrane fouling by dissolved organic matter (EfOM) in secondary treated effluent is a problematic and inevitable issue during wastewater reclamation using low pressure membrane filtration. This study evaluates the performance of coagulation/flocculation (C/F) using two recently developed coagulants (namely TiCl 4 and ZrCl 4 ) in comparison to conventional alum (i.e. Al 2 (SO 4 ) 3 ) as pretreatment to remove EfOM for subsequent ultrafiltration (UF) membrane fouling mitigation. At the optimal dosage, TiCl 4 -based C/F pretreatment showed the greatest performance in membrane fouling mitigation, followed by ZrCl 4 and then alum. The underlying mechanisms were well explained by classical fouling models and the extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory, highlighting a dominant role of standard blocking in the fouling potential of the C/F treated EfOM. The interfacial free energy of cohesion and adhesion showed that C/F pretreatment using TiCl 4 and ZrCl 4 as coagulant can lower the binding affinity between EfOM molecules and between EfOM molecules and membrane surface, ultimately reduce membrane fouling. The results of size exclusion chromatography (SEC) and fluorescence excitation emission matrix- parallel factor analysis (EEM-PARAFAC) also supported the classical fouling mechanisms, providing additional insights into the potential roles of chemical interactions in the preferential removal of certain organic substances by C/F pretreatment and the chemical composition of subsequent membrane foulants. Protein-like components were highly associated with reversible fouling after the C/F, while the reversibility of humic-like substances was enhanced upon C/F pretreatment. After C/F pretreatment, small sized EfOM molecules became the dominant fraction responsible for UF membrane fouling. [ABSTRACT FROM AUTHOR]

In this study, an integrated system of self-enhanced membrane distillation (MD) with H 2 O 2 oxidation was explored for the efficient treatment of landfill leachate, in which the heat energy required for MD operation was harvested for H 2 O 2 activation. Organic composition of the leachate was explored during the filtration processes via fluorescence excitation emission matrix combined with parallel factor analysis, which identified three different organic fractions (i.e., tryptophan-like C1, fulvic-like C2, and humic-like C3) in the extracted membrane foulants as well as in the membrane concentrate. C1 was the main organic fraction in the foulant, while C3 was dominant in the leachate concentrate. Moreover, H 2 O 2 was successfully activated by the in situ thermal energy (i.e., temperature difference) and pristine Fe ions in the leachate, resulting in significant (48%) oxidation of bulk organic matter. Preferential removal of the main fouling fraction (i.e., C1) from the bulk landfill leachate occurred under the optimal H 2 O 2 dose of 1.5 g/L. With respect to the H 2 O 2 dose on the feed side of the assisted MD setup, there was a considerable increase in the membrane flux, a 24% higher membrane flux recovery, and 1.5 times more filtered volume, as compared to the reference run without oxidation. The addition of H 2 O 2 to the conventional MD also led to a significant (93%) removal of the bio-refractory humic-like C3 fraction from the membrane concentrate. The results of this study demonstrated the successful operation of assisted MD based on the in-situ energy utilization for H 2 O 2 activation, which led to a drastic improvement in the performance of the system and the production of low-strength, reclaimable leachate concentrate. [Display omitted] • In-situ thermal energy was utilized to trigger H 2 O 2 oxidation in MD system. • Low MW (tryptophan-like) component was highly associated with organic fouling. • Assisted oxidation mitigated membrane fouling by 24% and enhanced filtered volume up to 1.5 times. • Produced membrane concentrate from assisted MD was lower in DOC (∼63%) and more biodegradable. [ABSTRACT FROM AUTHOR]

The two popular source tracing tools of stable isotope ratios (δ 13 C and δ 15 N) and fluorescence spectroscopy were used to estimate the relative source contributions to sediment organic matter (SeOM) at five different river sites in an agricultural-forested watershed (Soyang Lake watershed), and their capabilities for the source assignment were compared. Bulk sediments were used for the stable isotopes, while alkaline extractable organic matter (AEOM) from sediments was used to obtain fluorescent indices for SeOM. Several source discrimination indices were fully compiled for a range of the SeOM sources distributed in the catchments of the watershed, which included soils, forest leaves, crop (C3 and C4) and riparian plants, periphyton, and organic fertilizers. The relative source contributions to the river sediment samples were estimated via end member mixing analysis (EMMA) based on several selected discrimination indices. The EMMA based on the isotopes demonstrated that all sediments were characterized by a medium to a high contribution of periphyton ranging from ~ 30% to 70% except for one site heavily affected by forest and agricultural fields with relatively high contributions of terrestrial materials. The EMMA based on fluorescence parameters, however, did not show similar results with low contributions from forest leaf and periphyton. The characteristics of the studied watershed were more consistent with the source contributions determined by the isotope ratios. The discrepancy in the EMMA capability for source assignments between the two analytical tools can be explained by the limited analytical window of fluorescence spectroscopy for non-fluorescent dissolved organic matter (FDOM) and the inability of AEOM to represent original bulk particulate organic matter (POM). [ABSTRACT FROM AUTHOR]

[Display omitted] • First application of a magnetic visible light photocatalyst for NOM treatment. • The composite integrates the individual benefits of mpg-C 3 N 4 , Bi 2 WO 6 , and CuFe 2 O 4. • Optimal composite CBC-5 showed the highest performance in NOM removal. • First molecular-level investigation of NOM under a visible-light mediated photocatalysis. Despite growing interest in research on visible-light-driven photocatalysts, reusable photocatalysts have not been extensively developed for the treatment of natural organic matter (NOM), because such development requires an understanding of the complex NOM structures. In this study, we combined the individual benefits of CuFe2O4, Bi2WO6, and mesoporous graphitic carbon nitride (mpg-C3N4) to prepare a magnetic, visible-light-driven photocatalytic composite, CBC-5, for effectively removing NOM in a short period of time. The degradation mechanisms were further explored at the molecular level through ultra-high-resolution mass spectrometry. Broad light absorbance and charge transmission based on a dual S-scheme pathway allowed CBC-5 to generate multiple active agents, OH (49.7 %), O2− (27.6 %), and h+ (24.8 %), which ultimately led to the removal of 7.9 mgC of NOM per 0.9 g of CBC-5 in 6 h. Humic-like fluorophores were preferentially degraded, followed by the generation of simple phenolic components as by-products. Molecular-level investigation revealed that the NOM structures with high degree of unsaturation and functionalization were preferentially attacked by the radicals. Oxygenic groups were formed upon the oxidation of the unsaturated bonds and the functional groups having a low oxidation state of carbon (OSc) before the degradation of the carboxyl-rich alicyclic molecules. NOM degradation was prioritized in the following order: CHON > CHO > CHOS. Oxidative deamination is attributed to the preferential degradation of N -containing compounds, which are partially transformed to CHO compounds. CHOS compounds enriched with aliphatic organosulfates were recalcitrant to photocatalytic oxidation. Thus, CBC-5 demonstrated convenient magnetic recovery, stable performance, and high recyclability and can be applied as a promising NOM treatment agent. [ABSTRACT FROM AUTHOR]

In this study, a nano-sheet C 3 N 4 -WO 3 composite (nsCW21) was applied as a visible-light active photocatalyst to degrade natural organic matter (NOM). The nsCW21 photocatalyst exhibited a higher removal efficiency for NOM than the bare host and other composite counterparts due to the effective separation of the charge carriers in the Z-scheme pathway. The addition of H 2 O 2 resulted in the enhanced photocatalytic performance via the generation of hydroxyl radicals from the catalyst with an NOM removal rate of up to 71% for 5 h. The catalyst showed a considerable stability, which held a good NOM degradation efficiency during five cycle runs. The complex NOM removal behavior was unraveled by using a fluorescence excitation emission matrix-parallel factor analysis and a two-dimensional correlation spectroscopy (2D-COS) combined with Fourier-transform infrared spectroscopy (FT-IR). The large sized and the terrestrial humic-like component exhibited a high adsorption tendency toward the catalyst and was degraded primarily by h+, while a typical humic-like component, which is mainly removed by .OH, displayed a high degradation rate constant (k = 0.159 h−1). The 2D-COS revealed the sequence of the preferable removal among the different NOM functional groups in the nsCW21 system with H 2 O 2 addition, which occurred in the order of open ring reaction > oxygenated functional groups > the transformation into aliphatic compounds/inorganic moieties. Meanwhile, the hybrid system that employed ultrafiltration as a post-treatment demonstrated synergetic effects on the improved effectiveness for NOM removal in the overall system, which was a total of 91%, of the residuals from the precedent photocatalysis as well as alleviating the membrane fouling. [ABSTRACT FROM AUTHOR]