Unveiling the Occurrence and Non-Negligible Role of Amino Sugars in Waste Activated Sludge Fermentation by an Enriched Chitin-Degradation Consortium.

Polysaccharides in extracellular polymeric substances (EPS) can form a hybrid matrix network with proteins, impeding waste-activated sludge (WAS) fermentation. Amino sugars, such as N-acetyl-d-glucosamine (GlcNAc) polymers and sialic acid, are the non-negligible components in the EPS of aerobic granules or biofilm. However, the occurrence of amino sugars in WAS and their degradation remains unclear. Thus, amino sugars (∼6.0%) in WAS were revealed, and the genera of Lactococcus and Zoogloea were identified for the first time. Chitin was used as the substrate to enrich a chitin-degrading consortium (CDC). The COD balances for methane production ranged from 83.3 and 95.1%. Chitin was gradually converted to oligosaccharides and GlcNAc after dosing with the extracellular enzyme. After doing enriched CDC in WAS, the final methane production markedly increased to 60.4 ± 0.6 mL, reflecting an increase of ∼62%. Four model substrates of amino sugars (GlcNAc and sialic acid) and polysaccharides (cellulose and dextran) could be used by CDC. Treponema (34.3%) was identified as the core bacterium via excreting chitinases (EC 3.2.1.14) and N-acetyl-glucosaminidases (EC 3.2.1.52), especially the genetic abundance of chitinases in CDC was 2.5 times higher than that of WAS. Thus, this study provides an elegant method for the utilization of amino sugar-enriched organics.

Unraveling the evolution of dissolved organic matter in full-scale A/A/O wastewater treatment process using size exclusion chromatography with PARAFAC and nonnegative matrix factorization analysis.

Changes in spectral features and molecular weight (MW) of dissolved organic matter (DOM) along the A/A/O processes in eight full-scale wastewater treatment plants (WWTPs) were characterized using size exclusion chromatography with a diode array detector, a fluorescence detector and an organic carbon detector in tandem (SEC-DAD-FLD-OCD) as well as bulk water quality parameters. The parallel factor (PARAFAC) and the nonnegative matrix factorization (NMF) analyses have been effectively applied to the postprocessing of SEC-FLD fingerprints and SEC-OCD chromatograms, respectively. Individual SEC-FLD-PARAFAC or SEC-OCD-NMF components may span a broad range of MW, indicating that these SEC fractions within the same component were cognate and varied coherently across the dataset samples. The SEC-FLD-PARAFAC modeling and SEC-OCD-NMF analysis have clearly and concisely presented that the dramatic decreases of dissolved organic carbon, UV absorbance at 254 nm and protein-like fluorescence at Ex280/Em350 nm in the anaerobic process were primarily associated with the degradation of the large MW proteinaceous and polysaccharide-like biopolymers. It has also revealed that fluorescence of humic acid-like fractions increased significantly during the anaerobic process, but fluorescence of fulvic acid-like and humic substances' building blocks decreased slightly. Laboratory experiments further confirmed the presence of the humification process in anaerobic processes, and the formation of humic acid-like fluorophores may be associated with carbohydrate metabolism. The combination of SEC-FLD-PARAFAC and SEC-OCD-NMF helped to establish the links between changes in bulk water quality parameters and the evolution of SEC MW fractions, which provides a more in-depth insight into wastewater DOM treatability and enables the optimization of wastewater treatment processes.

Changes of dissolved organic matter fractions and formation of oxidation byproducts during electrochemical treatment of landfill leachates: Development of spectroscopic indicators for process optimization.

Electrochemical oxidation (EO) is an attractive option for treatment of dissolved organic matter (DOM) in landfill leachate but concerns remain over the energy efficiency and formation of oxidation byproducts ClO3- and ClO4-. In this study, EO treatment of landfill leachates was carried out using representative active and nonactive anode materials, cell configurations and current densities. Size exclusion chromatograms coupled with 2D synchronous and asynchronous correlation analysis showed that the sensitivity of DOM fractions to EO degradation was dependent on the anode material. The nonactive boron-doped diamond (BDD) anode demonstrated the best performance for DOM oxidation. The humic acid-like fraction (HA, 2.5-20 kDa) predominated the visible absorbance of landfill leachates at λ ≥400 nm, and it generally had the highest reaction rates except the occurrence of the pH-induced denaturation and precipitation of the proteinaceous biopolymer fraction (BP, >20 kDa). During the EO treatment of landfill leachate with BDD anode, the UV absorbance spectra of landfill leachates at wavelengths <400 nm were affected by the formation of free chlorine. Instead, the decrease of Abs420 was found to be a good indicator of the shift of the oxidation from predominantly HA fraction to the proteinaceous BP fraction. The behavior of the Abs420 parameter was also indicative of the transition from the energy-efficient oxidation of DOM to the dominance of side reactions of chlorine evolution and the subsequent formation of ClO3- and ClO4-. These findings suggest that the EO treatment of landfill leachate can be optimized by adjusting the current density with feedback signals from the online monitoring of Abs420, to achieve a trade-off between degradation of DOM and control of ClO3- and ClO4-.

Formation of Nano- and Microplastics and Dissolved Chemicals During Photodegradation of Polyester Base Fabrics with Polyurethane Coating.

Polyurethane (PU) synthetic leathers possess an intricate plastic composition, including polyester (PET) base fabrics and upper PU resin, but the release of fragments from the complexes is unclear. Therefore, we investigated the photodegradation trends of PET base fabrics with PU coating (PET-U) as a representative of composite plastics. Attention was paid to the comparison of the photoaging process of PET-U with that of pure PET base fabric (PET-P). To reveal the potential for chain scission, physical and chemical changes (e.g., surface morphology, molecular weight, and crystallinity) of the two fabrics were explored. The generation of microplastic fibers (MPFs) and microplastic particles (MPPs) was distinguished. Compared with PET-P, PET-U showed a similar but delayed trend in various characteristics and debris release rate as the photoaging time prolonged. Even so, after 360 h of illumination, the generated number of MPs (including MPFs and MPPs) rose considerably to 9.32 × 107 MPs/g, and the amount of released nanoplastics (NPs) increased to 2.70 × 1011 NPs/g from PET-U. The suppression of MP formation from PET-U was potentially directed by the physical shielding of the upper PU layer and the dropped MPs, which resisted the photochemical radical effect. The components of dissolved organic matter derived from plastics (P-DOM) were separated by molecular weight using a size-exclusion chromatography-diode array detector-organic carbon detector/organic nitrogen detector (SEC-DAD-OCD/OND), and the results showed that a larger amount of carbon- and nitrogen-containing chemical substances were generated in PET-U, accompanied by more aromatic and fluorescent compounds. The results provided theoretical bases and insights for future research on the risks of plastic debris from PU synthetic leathers on aquatic organisms and indicated feasible directions for exploring combined pollution studies of plastics.

Simultaneous determination of dissolved organic nitrogen, nitrite, nitrate and ammonia using size exclusion chromatography coupled with nitrogen detector.

Accurate quantification of dissolved organic nitrogen (DON) has been a challenge due to the cumulative analytical errors in the conventional method via subtracting dissolved inorganic nitrogen species (DIN) from total dissolved nitrogen (TDN). Size exclusion chromatography coupled with an organic nitrogen detector (SEC-OND) has been developed as a direct method for quantification and characterization of DON. However, the applications of SEC-OND method still subject to poor separations between DON and DIN species and unsatisfied N recoveries of macromolecules. In this study, we packed a series of SEC columns with different lengths and resin materials for separation of different N species and designed an independent vacuum ultraviolet (VUV) oxidation device for complete oxidation converting N species to nitrate. To guarantee sufficient N recoveries, the operation conditions were optimized as oxidation time ≥ 30 min, injection mass (sample concentration × injection volume) < 1000 µL × mg-N/L for macromolecular proteins, and neutral pH mobile eluent. The dissolved O2 concentration in SEC mobile phase determined the upper limit of VUV oxidation at a specific oxidation time. Compared to conventional HW50S column (20 × 250 mm), HW40S column (20 × 350 mm) with mobile phase comprising of 1.5 g/L Na2HPO4·2H2O + 2.5 g/L KH2PO4 (pH = 6.85) could achieve a better separation of DON, nitrite, nitrate, and ammonia. When applied to river water, lake water, wastewater effluent, groundwater, and landfill leachate, the SEC-OND method could quantify DON as well as DIN species accurately and conveniently even the DIN/TDN ratio reached 0.98.

Unravelling relationships between fluorescence spectra, molecular weight distribution and hydrophobicity fraction of dissolved organic matter in municipal wastewater.

The characteristics of dissolved organic matter (DOM) in the influent and secondary effluent from 6 municipal wastewater treatment plants (WWTPs) were investigated with a size exclusion chromatogram (SEC) coupled with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as a function of molecular weight (MW). The SEC chromatograms showed that biopolymers (>6 kDa) and humic substances (0.5-6 kDa) comprised the significant fraction in the influent, while humic substances became the abundant proportion in the secondary effluent. Direct linkages between MW distribution and hydrophobicity of DOM in the secondary effluent were further explored via SEC analysis of XAD resin fractions. DON and DOC with different hydrophobicity exhibited significantly distinct MW distribution, indicating that it was improper to consider DOC as a surrogate for DON. Different from DOC, the order of averaged MW in terms of DON was hydrophobic neutral ≈ transphilic neutral > hydrophobic acid > transphilic acid > hydrophilic fraction. Fluorescence spectral properties exhibited a significant semi-quantitative correlation with MW and hydrophobicity of DOC, with Pearson's coefficients of -0.834 and 0.754 (p < 0.01) for biopolymer and humic substances. Meanwhile, regional fluorescence proportion was demonstrated to indicate the MW and hydrophobicity properties of DON at the semi-quantitative level. The fluorescence excitation-emission matrix (EEM) could be explored to provide a rapid estimation of MW distribution and hydrophobic/hydrophilic proportion of DOC and DON in WWTPs.

Controlling volatile fatty acids production from waste activated sludge by an alginate-degrading consortium.

It is desirable to control volatile fatty acids (VFAs) recovery from waste activated sludge (WAS) while avoiding the release of N and P. Structural extracellular polymeric substances (St-EPS), with typical components of alginate and polygalacturonic acid, resist the biodegradation of extracellular polymeric substances (EPS) in WAS. Previously, we purposely enriched an alginate-degrading consortium (ADC), but, both controlling VFAs production and cell integrity after dosing with ADC were not investigated. In this work, ADC with a high percentage of the genus Bacteroides (~67%) was further enriched with alginate utilization above 95%. The St-EPS content in WAS was 109.7 ± 3.3 mg/g-VSS, accounting for 31% of EPS. After dosing ADC in the WAS, the main metabolites were acetate (1.6 g/L) and propionate (0.7 g/L), the hydrolysis efficiency was increased to 38%, and the acidification efficiency was increased to 72%. Cell integrity was maintained during WAS fermentation by dosing with ADC according to no P release and unchanged lactate dehydrogenase activity. VFA production was mainly from the EPS, and protein degradation in EPS resulted in low N release (e.g., 212 mg/L from casein and no P release). Consequently, ADC doing offers the advantages of controlling VFAs production from EPS while maintaining cell integrity.

Elucidating the production and inhibition of melanoidins products on anaerobic digestion after thermal-alkaline pretreatment.

The refractory organics released from waste activated sludge (WAS) are unwanted produced in thermal-alkaline pretreatment, which are not well documented. In this study, we refer to them as melanoidins products (MPs) with characteristics of high molecular weight and inhibition to microbes. The results showed that these MPs from thermal-alkaline (80 °C and pH 10) pretreatment of WAS were identified with a broad molecular weight (>1000 Da). Dark-colored MPs were further verified from glucose and tryptophan as the model components, with values of UV280 and UV420 increasing. The produced MPs with a molecular weight of 1220, 6835, and even 21,200,000 Da were confirmed by SEC-HPLC. Unexpectedly, MPs were found to be electroactive with higher redox peak values than that of humic acids, which were almost not degraded by anaerobes as revealed by SEC-HPLC and 3D-EEM spectra. For the first time, the results demonstrated that MPs delayed volatile fatty acids production and reduced the methane yield (22-26% lower), which was likely attributed to the toxicity and/or electrons competition with anaerobes such as Methanosaeta. Thus, it is clear that MPs negatively impact anaerobic digestion after thermal-alkaline pretreatment, which shall be re-evaluated to minimize MPs when producing biochemicals from WAS.