Fate and role of fluorescence moieties in extracellular polymeric substances during biological wastewater treatment: A review

Biochar and hydrochar application influence soil ammonia volatilization and the dissolved organic matter in salt-affected soils

Biochar, which including pyrochar (PBC) and hydrochar (HBC), has been tested as a soil enhancer to improve saline soils. However, the effects of PBC and HBC application on ammonia (NH3) volatilization and dissolved organic matter (DOM) in saline paddy soils are poorly understood. In this research, marsh moss-derived PBC and HBC biochar types were applied to paddy saline soils at 0.5 % (w/w) and 1.5 % (w/w) rates to assess their impact on soil NH3 volatilization and DOM using a soil column experiment. The results revealed that soil NH3 volatilization significantly increased by 56.1 % in the treatment with 1.5 % (w/w) HBC compared to the control without PBC or HBC. Conversely, PBC and the lower application rate of HBC led to decrease in NH3 volatilization ranging from 2.4 % to 12.1 %. Floodwater EC is a dominant factor in NH3 emission. Furthermore, the fluorescence intensities of the four fractions (all humic substances) were found to be significantly higher in the 1.5 % (w/w) HBC treatment applied compared to the other treatments, as indicated by parallel factor analysis modeling. This study highlights the potential for soil NH3 losses and DOM leaching in saline paddy soils due to the high application rate of HBC. These findings offer valuable insights into the effects of PBC and HBC on rice paddy saline soil ecosystems.

Enhanced methane production from source-separated human feces (brown water) by single phase anaerobic co-digestion: Effects of different co-substrates

Based on the concept of source separation of brown water (BW, human feces with flushing water) and yellow water (urine) in rural area, anaerobic co-digestion of BW with agricultural waste is a promising and effective method for rural waste treatment and resource recovery. The purpose of this study was to investigate the performance of different agricultural wastes (peanut straw (PST), peanut shell (PSH), swine wastewater acting as co-substrate for anaerobic co-digestion with BW, and the relative mechanisms were explored. When the mixed ratio was uniformly set as 1:1 (mass ratio, measured by volatile solid (VS)) and initial VS load as 20 g/L, the maximum cumulative methane production obtained by co-digestion (21 days) of BW and PST was 688 mL/g-VS, which performed better than the individual substrates (341 mL/g-VS), as well as the average of the sole BW and sole PST groups (531.2 mL/g-VS). The most impactful advantage was ascribed to the promotion of hydrolytic and acidogenic enzyme activities. The addition of PST also reduced the production of endogenous humus, which is difficult for biodegradation. Microbial community analysis showed that different co-substrates would affect the microbial community composition in the reactor. The relative abundance of hydrolytic acidogens in the PST and PSH co-digestion groups were higher than that in the SW co-digestion and sole BW groups, and the methanogenic archaea were dominated by the acetate-trophic Methanotrichaceae. The overall results suggest that anaerobic co-digestion is a feasible method, and co-digestion of BW and PST can improve methane production potential.

Deciphering DOM-metal binding using EEM-PARAFAC: Mechanisms, challenges, and perspectives

Dissolved organic matter (DOM) is a pivotal component of the biogeochemical cycles and can combine with metal ions through chelation or complexation. Understanding this process is crucial for tracing metal solubility, mobility, and bioavailability. Fluorescence excitation emission matrix (EEM) and parallel factor analysis (PARAFAC) has emerged as a popular tool in deciphering DOM-metal interactions. In this review, we primarily discuss the advantages of EEM-PARAFAC compared with other algorithms and its main limitations in studying DOM-metal binding, including restrictions in spectral considerations, mathematical assumptions, and experimental procedures, as well as how to overcome these constraints and shortcomings. We summarize the principles of EEM to uncover DOM-metal association, including why fluorescence gets quenched and some potential mechanisms that affect the accuracy of fluorescence quenching. Lastly, we review some significant and innovative research, including the application of 2D-COS in DOM-metal binding analysis, hoping to provide a fresh perspective for possible future hotspots of study. We argue the expansion of EEM applications to a broader range of areas related to natural organic matter. This extension would facilitate our exploration of the mobility and fate of metals in the environment.

Quantitative source tracking for organic foulants in ultrafiltration membrane using stable isotope probing approach

Quantitatively identifying the primary sources of organic membrane fouling is essential for the effective implementation of membrane technology and optimal water resource management prior to the treatment. This study leveraged carbon stable isotope tracers to estimate the quantitative contributions of various organic sources to membrane fouling in an ultrafiltration system. Effluent organic matter (EfOM) and aquatic natural organic matter (NOM), two common sources, were combined in five different proportions to evaluate their mixed effects on flux decline and the consequent fouling behaviors. Generally, biopolymer (BP) and low molecular weight neutral (LMWN) size fractions - abundantly present in EfOM - were identified as significant contributors to reversible and irreversible fouling, respectively. Fluorescence spectroscopy disclosed that a protein-like component notably influenced overall membrane fouling, whereas humic-like components were predominantly responsible for irreversible fouling rather than reversible fouling. Fluorescence index (FI) and biological index (BIX), common fluorescence source tracers, showed promise in determining the source contribution for reversible foulants. However, these optical indices were insufficient in accurately determining individual source contributions to irreversible fouling, resulting in inconsistencies with the observed hydraulic analysis. Conversely, applying a carbon stable isotope-based mixing model yielded reasonable estimates for all membrane fouling. The contribution of EfOM surpassed 60 % for reversible fouling and increased with its content in DOM source mixtures. In contrast, aquatic NOM dominated irreversible fouling, contributing over 85 %, regardless of the source mixing ratios. This study emphasizes the potential of stable isotope techniques in accurately estimating the contributions of different organic matter sources to both reversible and irreversible membrane fouling.

Optimizing the hydrolysis-acidification stage in municipal wastewater treatment: comparison of immobilized fillers and granular sludge

The decomposition of organic macromolecules in sewage currently benefits substantially from hydrolysis-acidification. The full use of its qualities can help domestic sewage to biodegrade more quickly, which promotes the subsequent aerobic reactions. This study evaluated the hydrolysis-acidification performance of granular sludge and filler in residential sewage. Both forms were highly effective at producing volatile fatty acids (VFAs) at the beginning of the reaction, but the granular sludge gradually disintegrated over time, particularly at low temperatures. The production of VFAs decreased (68.08 mg/L), and the effluent dissolved organic nitrogen (DON) increased (6.23 mg/L). However, the effluent of fillers remained at a lower level (1.3 mg/L) and produced more VFAs (74.13 mg/L). High-throughput sequencing revealed that the filler included a greater quantity of hydrolytic-acidifying bacteria than the granular sludge, which resulted in higher performance. In this study, the optimal form of utilizing hydrolytic acidifying bacteria was discussed to provide a theoretical basis to improve the full utilization of organic matter in domestic sewage and the removal of as much total nitrogen as possible.

Microbial community and gene dynamics response to high concentrations of gadolinium and sulfamethoxazole in biological nitrogen removal system

The impact of high antibiotic and heavy metal pollution levels on biological nitrogen removal in wastewater treatment plants (WWTPs) remains poorly understood, posing a global concern regarding the issue spread of antibiotic resistance induced by these contaminants. Herein, we investigated the effects of gadolinium (Gd) and sulfamethoxazole (SMX), commonly found in medical wastewater, on biological nitrogen removal systems and microbial characteristics, and the fate of antibiotic resistance genes (ARGs), metal resistance genes (MRGs), and mobile genetic elements (MGEs). Our findings indicated that high SMX and Gd(III) concentrations adversely affected nitrification and denitrification, with Gd(III) exerting a strong inhibitory effect on microbial activity. Metagenomic analysis revealed that high SMX and Gd(III) concentrations could reduce microbial diversity, with Thauera and Pseudomonas emerging as dominant genera across all samples. While the relative abundance of most ARGs decreased under single Gd(III) stress, MRGs increased, and nitrification functional genes were inhibited. Conversely, combined SMX and Gd(III) pollution increased the relative abundance of intl1. Correlation analysis revealed that most genera could host ARGs and MRGs, indicating co-selection and competition between these resistance genes. However, most denitrifying functional genes exhibited a positive correlation with MRGs. Overall, our study provides novel insights into the impact of high concentrations of antibiotics and heavy metal pollution in WWTPs, and laying the groundwork for the spread and proliferation of resistance genes under combined SMX and Gd pollution.

Optical variations of dissolved organic matter due to surface water - groundwater interaction in alpine and arid Datonghe watershed

The direction and quantity of surface water - groundwater interaction (SGI) in alpine-arid zones can be tracked using multiple tracers. However, few studies have examined whether the optical indices of dissolved organic matter (DOM) can also track SGI. This study used excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC) to reveal the optical variations in dissolved organic matter (DOM) in groundwater and surface water with various SGIs in the Datonghe watershed. The results showed that the absorbance spectral indices of DOM did not vary with SGI, whereas DOM fluorescence varied with SGI. PARAFAC indicated that groundwater predominantly recharged by precipitation had significantly lower humic-like (C2 and C3) fluorescence than groundwater predominantly recharged by riverine water. Since humic-like substances were more likely to be retained in the aqueous phase than protein-like substances, significantly fewer protein-like substances (C4) were introduced when surface water was recharged to groundwater. This suggests that C4 can be used as an effective indicator to identify the SGI process from surface water to groundwater. Based on the principal component analysis of DOM and hydrochemical indicators, it was concluded that traditional chemical tracers were significantly and positively correlated with humic-like substances C2 and C3. Given that C3 is more stable and persistent in the environment, it could be used to track SGI processes midstream of the watershed. The findings of this study will assist in accurately identifying the processes and mechanisms of SGI on a regional scale and provide a basis for future water resource management and the protection of water ecosystems.

Sodium alginate/sinter gel spheres immobilized lysozyme producing strain SJ25 enhanced sludge reduction: Optimization and mechanism

In order to promote sludge hydrolysis and improve the efficiency of aerobic digestion, the sodium alginate immobilized gel spheres pellet B (SIP B) were prepared using sodium alginate (SA) and sinter as carrier to immobilize lysozyme producing strain SJ25. The optimal conditions for SIP B to promote sludge hydrolysis were 5.6 mg SS^-1 dosage and pH of 9.0. Under the optimal condition compared with the control group, the reduction efficiency of suspended solids (SS) in 24 h was increased by 26.89 %, the release of soluble chemical oxygen demand (SCOD) was increased by 517.79 mg L^-1, polysaccharide (PS) and protein (PN) concentrations were increased by 186.69 and 368.68 mg L^-1, respectively. SIP B enhanced the degradation efficiency of sludge by promote the release of lysozyme, prolonging the action time of the enzyme, enhancing the metabolism and membrane transport of xenobiotics, carbohydrate and amino.

Spectral change of dissolved organic matter after extracted by solid-phase extraction and its feasibility in predicting the acute toxicity of polar organic pollutants in textile wastewater

Spectroscopic parameters can be used as proxies to effectively trace the occurrence of organic trace contaminants, but their suitability for predicting the toxicity of discharged industrial wastewater with similar spectra is still unknown. In this study, the organic contaminants in treated textile wastewater were subdivided and extracted by four commonly-used solid-phase extraction (SPE) cartridges, and the resulting spectral change and toxicity of textile effluent were analyzed and compared. After SPE, the spectra of the percolates from the four cartridges showed obvious differences with respect to the substances causing the spectral changes and being more readily adsorbed by the WAX cartridges. Non-target screening results showed source differences in organic micropollutants, which were one of the main contributors leading to their spectral properties and spectral variations after SPE in the effluents. Two fluorescence parameters (C1 and humic-like) identified by the excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were closely correlated to the toxicity endpoints for Scenedesmus obliquus (inhibition ratios of cell growth and Chlorophyll-a synthesis), which can be applied to quantitatively predict the change of toxicity effect caused by polar organic pollutants. The results would provide novel insights into the spectral feature analysis and toxicity prediction of the residual DOM in industrial wastewater.

Continuing progress in the field of two-dimensional correlation spectroscopy (2D-COS), part II. Recent noteworthy developments

This comprehensive survey review compiles noteworthy developments and new concepts of two-dimensional correlation spectroscopy (2D-COS) for the last two years. It covers review articles, books, proceedings, and numerous research papers published on 2D-COS, as well as patent and publication trends. 2D-COS continues to evolve and grow with new significant developments and versatile applications in diverse scientific fields. The healthy, vigorous, and diverse progress of 2D-COS studies in many fields strongly confirms that it is well accepted as a powerful analytical technique to provide an in-depth understanding of systems of interest.

Continuing progress in the field of two-dimensional correlation spectroscopy (2D-COS): Part III. Versatile applications

In this review, the comprehensive summary of two-dimensional correlation spectroscopy (2D-COS) for the last two years is covered. The remarkable applications of 2D-COS in diverse fields using many types of probes and perturbations for the last two years are highlighted. IR spectroscopy is still the most popular probe in 2D-COS during the last two years. Applications in fluorescence and Raman spectroscopy are also very popularly used. In the external perturbations applied in 2D-COS, variations in concentration, pH, and relative compositions are dramatically increased during the last two years. Temperature is still the most used effect, but it is slightly decreased compared to two years ago. 2D-COS has been applied to diverse systems, such as environments, natural products, polymers, food, proteins and peptides, solutions, mixtures, nano materials, pharmaceuticals, and others. Especially, biological and environmental applications have significantly emerged. This survey review paper shows that 2D-COS is an actively evolving and expanding field.

Enhanced nitrate and cadmium removal performance at low carbon to nitrogen ratio through immobilized redox mediator granules and functional strains in a bioreactor

The coexistence of multiple pollutants and lack of carbon sources are challenges for the biological treatment of wastewater. To achieve simultaneous removal of nitrate (NO₃^--N) and cadmium (Cd²⁺) at low carbon to nitrogen (C/N) ratios, 2-hydroxy-1,4-naphthoquinone (HNQ) was selected from three redox mediators as an accelerator for denitrification of heterotrophic strain Pseudomonas stutzeri sp. GF2 and autotrophic strain Zoogloea sp. FY6. Then, halloysite nanotubes immobilized with 2-hydroxy-1,4-naphthoquinone (HNTs-HNQ) were prepared and a bioreactor was constructed with immobilized redox mediator granules (IRMG) as the carrier, which was immobilized with HNTs-HNQ and inoculated with the two strains. The immobilized HNQ and the inoculated strains jointly improved the removal ability of NO₃^--N and Cd²⁺ and the removal efficiency of NO₃^--N (25.0 mg L^-1) and Cd²⁺ (5.0 mg L^-1) were 92.81% and 93.94% at C/N = 1.5 and hydraulic retention time (HRT) = 4 h. The Cd²⁺ was removed by adsorption of iron oxides (FeO(OH) and Fe₃O₄) and IRMG. The electron transport system activity (ETSA) of bacteria was improved and the composition of dissolved organic matter in the effluent was not affected by HNQ. The HNQ promoted the production of FeO(OH) and up-regulated the proportion of Zoogloea (54.75% in the microbial community), indicating that Zoogloea sp. FY6 was dominant in the microbial community. In addition, HNQ influenced the metabolic pathways and improved the relative abundance of some genes involved in nitrogen metabolism and the iron redox cycle.

Nickel-Cobalt Oxide Nanoparticle-Induced Biohydrogen Production

The positive effects of metal oxide nanoparticles (NPs) on dark fermentation (DF) for biohydrogen synthesis have been increased, and the mechanism still needs to be further revealed. In this study, nickel-cobalt oxide (NiCo₂O₄) NPs were prepared to increase H₂ yield via DF. The highest (259.67 mL/g glucose) and the lowest (188.14 mL/g glucose) yields were achieved at 400 and 800 mg/L NiCo₂O₄ NPs added, respectively, with their corresponding 33.97% increase and 2.93% decrease compared with the control yield (193.82 mL/g glucose). Meanwhile, the microbial community further confirmed that NiCo₂O₄ NPs increased the abundance of the dominant H₂-producing Clostridium sensu stricto 1 by 23.05%. The gene prediction also showed that NiCo₂O₄ NPs increased the abundance of genes encoding the rate-limiting enzyme pyruvate kinase in glycolysis, thus increasing the substrate conversion. Moreover, the gene abundance of key enzymes directly related to H₂ evolution was also increased at different levels.

Molecular-level characterization of natural organic matter in the reactive electrochemical ceramic membrane system for drinking water treatment using FT-ICR MS

Applications of electrochemical advanced oxidation processes are rising in drinking water treatment for effective mitigation of refractory organic compounds. This study explored the fate of natural organic matter (NOM) (lake water and standard NOM (SRNOM solution)) at molecular-level in the reactive electrochemical membrane (REM) system utilizing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Fluorescence spectroscopy showed above 90 % removal of the humic-like component in both lake water and SRNOM solution in 10 min of REM operation compared to 70-80 % removal of the fulvic-like component after 30 min. REM-based treatment effectively eliminated (>70 %) the disinfection byproduct precursors. The lake water, sharing ~70 % of similar compounds with SRNOM, displayed a different propensity toward electrochemical oxidation, and its finished water was characterized with relatively lower double-bond equivalent (DBE), nominal oxidation state of carbon (NOSC), and aromaticity compared to that of SRNOM. The chloride ions in the water matrix of lake water impacted the electrochemical oxidation and generated significantly different transformation products than SRNOM solution. The heteroatoms (N and S) containing compounds (CHON and CHOS) were preferentially degraded in lake water; however, CHOS compounds were removed fewer in SRNOM. The electrosorption and electrochemical oxidation on the REM surface were the significant contributors for NOM removal. The newly formed compounds were mostly retained on the REM surface and fewer were released in finished water. This study is believed to help understand the fate of NOM in real source drinking water during electrochemical treatment.

DOM tracking and prediction of rural domestic sewage with UV-vis and EEM in the Yangtze River Delta, China

Compared with the urban sewage treatment plants, the operation of rural decentralized sewage facilities is trapped by the absence of professionals, thus having to be run dependently on the self-adaptive operation of the facilities, which makes timely monitoring particularly important. In this study, organic pollutants in rural domestic sewage and urban domestic sewage are analyzed using ultraviolet-visible (UV-vis) absorption spectroscopy, fluorescence excitation-emission matrix (EEM) and Fourier transform infrared reflectance (FTIR). Compared with the UV-vis absorption spectrum, EEM can not only make up the deficiency in the detection of some easily degradable organics in sewage, but also reveal the transformation of different components, thus indicating timely the treatment progress of rural sewage. Linear fitting of COD and spectrum shows that UV₂₅₄ combined with fluorescence excitation-emission at Ex/Em = 250/330 nm might be more suitable for the prediction of COD in rural water than the UV₂₅₄ alone. This is of great significance for guiding the self-adaptive operation of rural domestic sewage facilities, improving their stability and efficiency, so as to improve the rural living environment.

Comparing biotransformation of extracellular polymeric substances (EPS) under aerobic and anoxic conditions: Reactivities, components, and bacterial responses

This study aimed to better understand the transformation behaviors of extracellular polymeric substances (EPS) and their roles in regulating bacterial community in biological wastewater treatment processes. Herein, well-controlled bioassays under aerobic and anoxic conditions were performed to investigate degradation dynamics, composition variations, and bacterial response during EPS transformation. Reactivity continuum modeling showed that organic pools of EPS had continuous reactivity distributions, and most labile organic fraction with a degrading rate >0.1 h^-1 was substantially higher under aerobic (20.47%) than anoxic (2.02%) condition. Rapid degradation of protein-like substances in the initial degradation stage was accompanied by the humification process, as revealed by UV absorption spectroscopy, fluorescence spectroscopy, and size exclusion chromatography with continuous organic carbon detection analysis. The 16S rRNA gene sequencing results showed that the selection effect of EPS in controlling abundant populations during their transformation, e.g., Acinetobacter was enriched, and Candidatus Competibacter was washed out relative to the source community. Furthermore, taxonomic normalized stochasticity ratio-based null model and bacterial ecological network analysis indicated higher relative importance of deterministic process in shaping the EPS-degrading communities under aerobic than anoxic condition, likely explaining the faster EPS biotransformation under aerobic condition. Intriguingly, the keystone populations driving EPS metabolism showed the environmental filtering characteristics (e.g., capable of degrading refractory and aromatic compounds or adapting to harsh environments) and cooperative interactions with the co-occurring species under both conditions. This work is expected to reveal the fates and roles of EPS in wastewater treatment plants extensively.

Effect of aniline and antimony on anaerobic-anoxic-oxic system with novel amidoxime-modified polyacrylonitrile adsorbent for wastewater treatment

There has been increasing concern over the mixed discharge of municipal-textile composite wastewater, which remains challenging for typical wastewater treatment plant (WWTP) using anaerobic-anoxic-oxic process (AAO). Highly-toxic aniline and antimony, typical co-contaminants in textile wastewater, usually lead to increased chemical oxygen demand (COD) in influent and deteriorated effluent quality. Amidoxime-modified polyacrylonitrile (amPAN) adsorbent was prepared and added to adsorb antimony and facilitate substrate removal. With amPAN dosage at 6.0 g L^-1 in oxic bioreactor, 64.2 ± 5.6% of antimony was removed from influent. Extracellular polymeric substance release was simultaneously changed with residual antimony concentration. Meanwhile, amPAN promoted the proliferation of Proteobacteria, Bacteroidetes and Epsilonbacteraeota serving as microorganism carrier. As a result, removal efficiencies of COD (94.4 ± 0.6%), ammonium (NH₄⁺-N, 92.6 ± 3.3%), total nitrogen (TN, 76.4 ± 6.3%) and total phosphorus (TP, 93.4 ± 2.1%) were enhanced to meet Class 1A discharge standard in China. These results indicate that AAO with amPAN is promising for municipal-textile composite wastewater treatment.

Study on the mechanism of inhibiting the calcification of anaerobic granular sludge induced by the addition of trace signal molecule (3O-C6-HSL)

Microbiota quorum sensing (QS) induced by 3O-C6-HSL (N-(β-ketocaproyl)-DL-homoserine lactone) inhibited the calcification of anaerobic granular sludge (AnGS), and the mechanism of promoting the activity recovery of calcified AnGS was studied in this paper. Through research, it was speculated that 3O-C6-HSL acted on calcified AnGS residual microorganisms to trigger QS. It enriched many functional microorganisms. For example, it promoted the growth of Methanospirillum. The CO₂ could be consumed quickly by Methanospirillum and reduced the calcium carbonate formation. The increase of microbial biomass would promote the activity of sludge. What's more, the pore size and porosity of sludge would increase, so the mass transfer channel will be broadened at same time. All those, could help the calcified AnGS quickly restore the activity and anaerobic system recover normal, which provided a new idea for the emergency rescue of anaerobic system in the future.

Emerging novel polymeric adsorbents for removing dyes from wastewater: A comprehensive review and comparison with other adsorbents

Dye molecules are one of the most hazardous compounds for human and animal health and the excess intake of these materials can create toxic impacts. Several studies show the practicality of the adsorption process for dye uptake from wastewaters. In recent years, various adsorbents were used to be efficient in this process. Among all, polymeric adsorbents demonstrate great applicability in different environmental conditions and attract many researchers to work on them, although there is not enough reliable and precise information regarding these adsorbents. This study aims to investigate some influential parameters such as their type, physical properties, experimental conditions, their capacity, and further modeling along with a comparison with non-polymeric adsorbents. The influence of the main factors of adsorption capacity was studied and the dominant mechanism is explained extensively.

Using stable isotope probing and fluorescence spectroscopy to examine the roles of substrate and soluble microbial products in extracellular polymeric substance formation in activated sludge process

In this study, we used stable isotope-labeled soluble microbial products (SMP) and substrates to explore their assimilation into the formation of new biological products (i.e., extracellular polymeric substances and biomass) in two adjacent sequencing batch reactors. The isotope labeling approach along with fluorescence spectroscopy allowed us to distinguish between refractory and labile portions of SMP constituents as well as their roles in the formation of extracellular polymeric substances (EPS). Comparison of SMP fluorescence and the specific UV absorbance values between the two reactors revealed the presence of humic-like aromatic substances in the non-consumable part of SMP, which can be ultimately released as effluent organic matter. Parallel factor analysis modeling of fluorescence spectra showed that the hydrolysis of EPS contents mostly resulted in humic-like components in SMP rather than protein-like components, which were initially abundant in EPS (>80%). From variations in carbon and nitrogen isotopic contents in EPS and biomass, it was found that carbon-containing substrates were enriched faster than their nitrogenous counterparts. The contributions to new EPS formation reached 87.5% for carbon and 60.5% for nitrogen. Meanwhile, the isotopic tracking of the labeled SMP revealed that only 11.0% and 11.9% of carbon and 13.3% and 11.6% of nitrogen from the influent SMP were finally assimilated into EPS and biomass, respectively. In contrast, the isotopic enrichment in SMP was higher (~50%) than that of EPS and biomass, indicating the low bioavailability and refractory nature of the feed SMP. This study proposed a promising approach for estimating the relative contributions of different forms of labile substrate and SMP to the formation of EPS in activated sludge processes. This approach could be suggested as a versatile method for establishing the kinetics, substrate element flow, mass balance on organic substrates and nutrients, as well as for tracking the consumption and uptake pathways of hazardous materials.

Advanced treatment of secondary effluent organic matters (EfOM) from an industrial park wastewater treatment plant by Fenton oxidation combining with biological aerated filter

This study investigated the advanced treatment of secondary effluent organic matters (EfOM) from an industrial park wastewater treatment plant (IPWTP) by Fenton oxidation process and its combination with biological aerated filter (BAF). The constituents of EfOM were characterized by using fluorescence excitation-emission matrix, and the results showed that the major components included aromatic proteins, soluble microbial products, humic and fulvic acid-like substances, and compounds associated with fluorescent region of Ex 250-300 nm/Em 600-700 nm. The EfOM was strongly resistant to biodegradation (biochemical oxygen demand (BOD₅):chemical oxygen demand (COD) ratio at 0.11), resulting in less than 15% dissolved organic carbon (DOC) removal efficiency by the BAF reactor. The advanced treatment of EfOM by Fenton oxidation process led to maximum ~50% mineralization efficiency of EfOM under the optimal conditions of 2.0 mM Fe^II, 10 mM H₂O₂, pH 3.0 and 3.0 h of the reaction time. Particularly, Fenton oxidation treatment effectively improved the biodegradability of EfOM in the IPWTP secondary effluents, e.g., increasing the BOD₅:COD ratio from 0.11 to 0.42. A synergistic combination of Fenton oxidation process with the BAF reactor offered desirable mineralization efficiencies of EfOM (>70%) at lower dosages of Fenton's reagents. The present results suggest that Fenton oxidation process combining with the BAF reactor can be a promising strategy for the advanced treatment of EfOM in IPWTP secondary effluents. This study provides guidance for the characterization and advanced treatment of EfOM in IPWTP secondary effluents for practical purpose.

Fluorescent Characteristics and Metal Binding Properties of Different Molecular Weight Fractions in Stratified Extracellular Polymeric Substances of Activated Sludge

The combination of heavy metals and extracellular polymeric substances (EPSs) affects the distribution of heavy metals in microbial aggregates, soil, and aquatic systems. This paper aimed to explore the binding mechanisms of EPSs of different molecular weights in activated sludge with heavy metals. We extracted the stratification components of activated sludge EPSs and divided the components into five fractions of different molecular weight ranges. In the three-dimensional fluorescence analysis of each fraction, the EPSs of activated sludge had two peaks, peak A (representing low-excitation tryptophan) and peak B (representing high-excitation tryptophan), and static quenching was the main reason for the fluorescence quenching between the compounds attributable to peak A in activated sludge EPSs and Pb2+ and Cu2+. Further exploration suggested that the EPSs of activated sludge interacted with Cd2+, Pb2+, Cu2+, and Zn2+ to form new substances. The quenching effect of the EPSs with the highest molecular weight (100 kDa–0.7 μm) was more significant, and the binding ability was more stable. This study implies that the application of EPSs from activated sludge is promising. While effectively binding heavy metals, it can also reduce the volume of the excess activated sludge.

Determining the leading sources of N-nitrosamines and dissolved organic matter in four reservoirs in Southern China

The presence of carcinogenic N-nitrosamines and dissolved organic matter (DOM) in freshwater is a significant concern from the perspective of public health and drinking water treatment plant operation. This study investigated the N-nitrosamines concentration and their precursors' distributions, and DOM composition in four reservoirs located in a southern city of China. A total of 22 renowned precursors were identified. Precursors from industrial and pharmaceutical origins were found to be dominant in all reservoirs; however, traces of pesticide-based precursors, i.e. pirimicarb and cycluron were also found. The distribution of nine N-nitrosamines was substantially different among the reservoirs. N-Nitrosodibutylamine (NDBA), N-Nitrosopiperidine (NPIP), N-Nitrosodimethylamine (NDMA), and N-Nitrosopyrrolidine (NPYR) were abundantly present in all reservoirs. Most of N-nitrosamines except NDMA and N-nitrosodiethylamine (NDEA) were far below the generally accepted cancer risk of 10^-6, and NDMA/NDEA were found close to the risk level (10^-6). Anthropogenic DOM was dominant in three reservoirs as depicted by a higher biological index (BIX) than the humification index (HIX). By the principle component analysis, BIX appeared as an indicator of N-nitrosamines (except NDEA and NPIP). A strong and direct relationship was observed between the NDMA-formation potential (FP) and concentration of total N-nitrosamines (∑NA), and BIX. These results confirmed that the anthropogenic activities were the leading source of DOM and N-nitrosamines in this city based on land-use.

Comparison of mesophilic and thermophilic dark fermentation with nickel ferrite nanoparticles supplementation for biohydrogen production

In this work, nickel ferrite nanoparticles (NiFe₂O₄ NPs) was prepared to improve hydrogen (H₂) production by dark fermentation. Moderate amounts (50-200 mg/L) promoted H₂ generation, while excess NiFe₂O₄ NPs (over 400 mg/L) lowered H₂ productivity. The highest H₂ yields of 222 and 130 mL/g glucose were obtained in the 100 mg/L (37 °C) and 200 mg/L NiFe₂O₄ NPs (55 °C) groups, respectively, and the values were 38.6% and 28.3% higher than those in the control groups (37 °C and 55 °C). Soluble metabolites showed that NiFe₂O₄ NPs enhanced the butyrate pathway, corresponding to the increased abundance of Clostridium butyricum in mesophilic fermentation. The endocytosis of NiFe₂O₄ NPs indicated that the released iron and nickel favored ferredoxin and hydrogenase synthesis and activity and that NiFe₂O₄ NPs could act as carriers in intracellular electron transfer. The NPs also optimized microbial community structure and increased the levels of extracellular polymeric substances, leading to increased H₂ production.

A year-long cyclic pattern of dissolved organic matter in the tap water of a metropolitan city revealed by fluorescence spectroscopy

Delivering drinking water with stable quality in metropolitan cities is a big challenge. This study investigated the year-long dynamics of dissolved organic matter (DOM) in the tap water and source water of a metropolitan city in southern China using fluorescence spectroscopy. The DOM detected in the tap water, and source water of Shenzhen city was season and location-dependent. A year-long cyclic trend of DOM was found with predominate protein-like fluorescence in the dry season compared to the humic-like enriched DOM in the wet season. A general DOM pattern was estimated by measuring the shift in dominant fluorescence regions on the excitation-emission matrix (EEM). The difference in fluorescent DOM (FDOM) composition (in terms of the ratio of protein-like to humic-like fluorescence) was above 200% between wet and dry seasons. The taps associated with reservoirs receiving water from the eastern tributary of Dongjiang River showed significant changes in protein-like contents than the taps with source water originating from the western part of the river. This study highlights the importance of optimizing drinking water treatment plants' operational conditions after considering seasonal changes and source water characteristics.

Characterization of dissolved organic matter for understanding the adsorption on nanomaterials in aquatic environment: A review

Nanomaterials (NMs) have received tremendous attention as emerging adsorbents for environmental applications. The ever-increasing release into aquatic systems and the potential use in water treatment processes heighten the likelihood of the interactions of NMs with aquatic dissolved organic matter (DOM). Once DOM is adsorbed on NMs, it substantially modifies the surface properties, thus altering the fate and transport of NMs, as well as their toxic effects on (micro)organisms in natural and engineered systems. The environmental consequences of DOM-NMs interaction have been widely studied in the literature. In contrast, a comprehensive understanding of DOM-NM complexes, particularly regarding the controlling factors, is still lacking, and its significance has been largely overlooked. This gap in the knowledge mainly arises from the complex and heterogeneous structures of the DOM, which prompts the urgent need to further characterize the DOM properties to deepen the understanding associated with the adsorption processes on NMs. This review aims to provide in-depth insights into the complex DOM adsorption behavior onto NMs, whether they are metal- or carbon-based materials. First, we summarize the up-to-date analytical methods to characterize the DOM to unravel the underlying adsorption mechanisms. Second, the key DOM characteristics governing the adsorption processes are discussed. Next, the environmental factors, such as the nature of adsorbents and solution chemistry, affecting the DOM-NM interactions, are identified and discussed. Finally, future studies are recommended to fully understand the chemical traits of DOM upon its adsorption onto NMs.

Seasonal occurrence of N-nitrosamines and their association with dissolved organic matter in full-scale drinking water systems: Determination by LC-MS and EEM-PARAFAC

N-nitrosamines have been identified as emerging contaminants with tremendous carcinogenic potential for human beings. This study examined the seasonal changes in the occurrence of N-nitrosamines and N-nitrosodimethylamine formation potential (NDMA-FP) in drinking water resources and potable water from 10 drinking water treatment plants in a southern city of China. The changes in N-nitrosamines are well correlated with dissolved organic matter (DOM), particularly fluorophores, which were measured and compared between traditional fluorescence indices and excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Four of N-nitrosamine species including N-nitrosodimethylamine (NDMA), N-Nitrosodibutylamine (NDBA), N-Nitrosopyrrolidine (NPYR), and N-Nitrosodiphenylamine (NDPhA) are found to be abundant compounds with an average of 29.5% (26.7%), 20.0% (25.2%), 18.9% (16.0%), and 9.0% (9.9%) in the source (and treated) water, respectively. The sum of N-nitrosamines concentration is recorded to be low in the wet season (July-September), whereas the dry season (October-December) provided opposite impacts. EEM-PARAFAC modeling indicated the predominance of humic-like component (C1) in the wet season while in the dry season the water was dominant in protein-like component (C2). All the N-nitrosamines excluding NDPhA and N-Nitrosomorpholine (NMOR) showed a strong association with protein-like component (C2). In contrast, humic-like C1, which was directly influenced by rainfall, was found to be a suitable proxy for NMOR and NDPhA. The results of this study are valuable to understand the correlation between different N-nitrosamines and DOM through adopting fluorescence signatures.

Effects of Solids Retention Time on the Anaerobic Membrane Bioreactor with Yttria-Based Ceramic Membrane Treating Domestic Wastewater at Ambient Temperature

The effects of solid retention times (SRTs) (100 days, 50 days, 25 days) on the performance, microbial community, and membrane fouling of a lab-scale anaerobic yttria-based ceramic membrane bioreactor (AnCMBR) treating synthetic domestic wastewater at ambient temperature (31.2 ± 2.7 °C) were examined. The soluble chemical oxygen demand (SCOD) removal was higher (89.6%) at 25 days SRT compared with 50 days (39.61%) and 100 days (34.3%) SRT. At 100 days SRT, more Bacteroidetes, Firmicutes, and Proteobacteria were present in the microbial community. At 25 days SRT, more Chloroflexi, Synergistetes, and Pastescibacteria emerged, contributing to the stable performance. The SRT of 25 days has resulted in a more stable microbial community compared with 50 days and 100 days SRT. Both bacterial and archaeal community diversities were higher at 25 days SRT, and the specific production of soluble microbial by-products (SMPs) and extracellular polymeric substances (EPSs) were higher at 25 days SRT as well. Consequently, the membrane flux was lower at 25 days SRT with the increased particle size and the enhanced SMPs and EPSs production. Fourier transform infrared spectroscopy analysis (FTIR) and three-dimensional excitation and emission matrix (3D-EEM) analysis showed that protein and SMPs were the major membrane foulants at all SRT stages. In this study, SRT at 25 days was favorable for the stable operation of an AnCMBR treating domestic wastewater at ambient temperature.