Molecular Insights into the Transformation of Dissolved Organic Matter in Landfill Leachate Concentrate during Biodegradation and Coagulation Processes Using ESI FT-ICR MS

High resolution fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for the characterisation of enzymatic processing of commercial lignin

Lignin and lignin components of woody biomass have been identified as an attractive alternative to fossil fuels. However, the complex composition of this plant polymer is one of the drawbacks that limits its exploitation. Biocatalysis of lignin to produce platform chemicals has been receiving great attention as it presents a sustainable approach for lignin valorisation. Aligned with this area of research, in the present study we have applied ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to identify the preferred lignin substrates of a ligninolytic enzyme, a laccase produced by the terrestrial fungus Trametes versicolor. A commercial lignin was incubated with the laccase and acetosyringone (a laccase mediator) for up to 168 h and direct infusion electrospray FT-ICR MS enabled the identification of thousands of molecular species present in the complex lignin sample at different incubation time points. Significant changes in the chemical composition of lignin were detected upon laccase treatment, which resulted in a decrease in the molecular mass distribution of assigned species, consistent with laccase lytic activity. This reduction was predominantly in species classified as lignin-like (based on elemental ratios) and polymeric in nature (>400 Da). Of particular note was a fall in the number of species assigned containing sulfur. Changes in the chemical composition/structure of the lignin polymer were supported by FT-IR spectroscopy. We propose the use of FT-ICR MS as a rapid and efficient technique to support the biotechnological valorisation of lignin as well as the development and optimization of laccase-mediator systems for treating complex mixtures.

Transformation of dissolved organic matter during advanced coal liquefaction wastewater treatment and analysis of its molecular characteristics

Coal liquefaction wastewater (CLW) contains numerous toxic and biorefractory organics. A series of advanced treatment processes were designed to remove the dissolved organic matter (DOM) from CLW. Here, the reactivity and state of the DOM in the treatment train were studied in relation to its chemical composition by a Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis. Within an isobaric group, the raw CLW possessed a high average double-bond equivalent (DBE_wa) and low H/C_wa values with the N- and S-containing compounds accounting for approximately 77% of the raw CLW, which represented lignin (73.6%) and condensed aromatic structures (19.8%). In addition, the flotation process removed some hydrophobic DOM compounds with highly unsaturated states, which were biorefractory compounds. Ozonation and catalytic oxidation processes preferentially removed the highly unsaturated compounds and produced more oxidized molecules. The biofiltration process impacted the organics composition by consuming oxygen-rich substances, whereas the anoxic/oxic (A/O) process converted the reactive compounds into newly formed compounds through the loss of hydrogen (unsaturation) from the original compounds. The membrane bioreactor (MBR) process was more efficient in removing the N-containing compounds with higher unsaturated states. The compounds resistant to the applied CLW treatment processes were characterized by lower molecular weights (approximately 250-350 Da), higher oxidation states (O/S > 6), numerous carboxylic groups, and non-biodegradable features.

Combination of self-organizing map and parallel factor analysis to characterize the evolution of fluorescent dissolved organic matter in a full-scale landfill leachate treatment plant

The dissolved organic matter (DOM) characterization in a full-scale landfill leachate treatment plant is of great importance for the design and operation of treatment processes. In this study, the long-term removal behaviors of DOM during landfill leachate treatment were explored using excitation emission matrix fluorescence spectroscopy (EEMs) coupled with parallel factor analysis (PARAFAC) and self-organizing map (SOM). Results indicated that the application of combining PARAFAC and SOM on EEMs analysis effectively characterized long-term removal behaviors of DOM during leachate treatment. The DOM in raw leachate was dominated by humic substances, while its composition exhibited significant seasonal differences. A large proportion of protein-like fluorescent dissolved organic matter (FDOM) and bulk DOM were removed within membrane bioreactor (MBR) system. Meanwhile the humic-like FDOM removal capacity in nanofiltration (NF) process was well comparable with those in the MBR system owing to the bio-recalcitrant nature of humic substances. The protein-like FDOM and bulk DOM were removed synchronously in both the process of MBR and NF. Moreover, samples distribution exhibited obvious differences among NF concentrate samples. In general, the performance of MBR-NF treatment for landfill leachate displayed reasonable stability in DOM removal irrespective of seasonal variations. This study enhanced our understanding of EEMs application in characterizing leachate-derived DOM composition and has potential implications for the associated monitoring investigations in engineered systems.

Separation and characterization of marine dissolved organic matter (DOM) by combination of Fe(OH)3 co-precipitation and solid phase extraction followed by ESI FT-ICR MS

Marine dissolved organic matter (DOM) constitutes a major carbon pool in the global carbon cycle. Characterization of its chemical composition will improve our understanding of its role in global biogeochemical cycles. Currently, solid phase extraction (SPE) followed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis has become a powerful approach to characterize the molecular composition of DOM. However, some components in marine DOM, such as highly oxygenated tannin-like molecules, were lost during the SPE process. In this study, a sequential combination of co-precipitation and SPE procedure was proposed to improve the yield of marine DOM extraction. Ferric hydroxide was used as the co-precipitation agent to separate marine DOM, and SPE was carried out for the extraction of DOM from dissolved and precipitate fractions. The total yield in total organic carbon (TOC) and the number of assigned molecules of SPE-DOM increased by 25% and 51%, respectively, compared with those by direct SPE process. The combined process has good selectivity on tannin-like compounds. The result is instructive for the understanding of DOM molecular composition and potential for a routine method for DOM extraction from environmental water samples, especially for marine DOM containing a small amount of tannin-like compounds.

Molecular Characterization of Organics Removed by a Covalently Bound Inorganic-Organic Hybrid Coagulant for Advanced Treatment of Municipal Sewage

Coagulation is an important process to remove organics from water. The molecular composition and structure of organic matter influence water quality in many ways, and the lack of information regarding the organics removed by different coagulants makes it challenging to optimize coagulation processes and ensure reclaimed water safety. In this paper, we investigated coagulation of secondary biological effluent from a municipal sewage treatment plant with different coagulants. We emphasized investigation of organics removal characteristics at the molecular level using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with electrospray ionization (ESI). We found that conventional coagulants can only partially remove condensed polycyclic aromatics and polyphenols with low H/C (H/C < 0.7) and highly unsaturated and phenolic compounds and aliphatic compounds with high O/C (O/C > 0.6). A new coagulant, CBHyC, had better removal efficiencies for all organics with different element compositions and molecular structures, especially organics that are resistant to conventional coagulants such as highly unsaturated and phenolic compounds and aliphatic compounds located in 0.3 < O/C < 0.8 and 1.0 < H/C < 2.0 regions and sulfur-containing compounds with higher O/C (e.g., anionic surfactants and their metabolites or coproducts). This study provides molecular insights into the organics removed by different coagulants and provides data supporting the possible optimization of advanced wastewater treatment processes.

Investigating organic matter properties affecting the binding behavior of heavy metals in the rhizosphere of wetlands

Soil organic matter (SOM) is a crucial factor affecting the immobilization of heavy metal in wetlands. Recent studies have shown that the rhizosphere SOM has great ability to immobilize heavy metals. However, there existed few works on studying molecular characteristics of SOM to explore the mechanisms. Electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry (ESI-FTICR-MS) combined with FTIR spectroscopy were applied to investigate the characteristics of SOM in rhizosphere and nonrhizosphere samples and to find out what characteristics the rhizosphere SOM embodies conducive to metal binding in this paper. The rhizosphere contained higher C, P, Mn, and other metal concentrations. The adsorption of Cr on rhizosphere SOM was greater than that on nonrhizosphere SOM. Compared to nonrhizosphere SOM, rhizosphere SOM contained less saturated and more oxidized compounds, greater overall molecular weights (MW), more condensed aromatic structures (56.59% VS 51.56% by peak intensity), less carboxylate and N-containing COO functional groups (25.98% VS 56.63% by peak intensity), more hydrophilicity, and the latter four are conducive to metal binding. This study showed that the rhizosphere SOM had unique compositional and structural characteristics. These results provided evidence for the phytoremediation technologies of heavy metal contaminated wetlands.

Molecular Characterization of Cloud Water Samples Collected at the Puy de Dôme (France) by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Cloud droplets contain dynamic and complex pools of highly heterogeneous organic matter, resulting from the dissolution of both water-soluble organic carbon in atmospheric aerosol particles and gas-phase soluble species, and are constantly impacted by chemical, photochemical, and biological transformations. Cloud samples from two summer events, characterized by different air masses and physicochemical properties, were collected at the Puy de Dôme station in France, concentrated on a strata-X solid-phase extraction cartridge and directly infused using electrospray ionization in the negative mode coupled with ultrahigh-resolution mass spectrometry. A significantly higher number (n = 5258) of monoisotopic molecular formulas, assigned to CHO, CHNO, CHSO, and CHNSO, were identified in the cloud sample whose air mass had passed over the highly urbanized Paris region (J1) compared to the cloud sample whose air mass had passed over remote areas (n = 2896; J2). Van Krevelen diagrams revealed that lignins/CRAM-like, aliphatics/proteins-like, and lipids-like compounds were the most abundant classes in both samples. Comparison of our results with previously published data sets on atmospheric aqueous media indicated that the average O/C ratios reported in this work (0.37) are similar to those reported for fog water and for biogenic aerosols but are lower than the values measured for aerosols sampled in the atmosphere and for aerosols produced artificially in environmental chambers.

A review of bottom-up vs. top-down control of sponges on Caribbean fore-reefs: what's old, what's new, and future directions

Interest in the ecology of sponges on coral reefs has grown in recent years with mounting evidence that sponges are becoming dominant members of reef communities, particularly in the Caribbean. New estimates of water column processing by sponge pumping activities combined with discoveries related to carbon and nutrient cycling have led to novel hypotheses about the role of sponges in reef ecosystem function. Among these developments, a debate has emerged about the relative effects of bottom-up (food availability) and top-down (predation) control on the community of sponges on Caribbean fore-reefs. In this review, we evaluate the impact of the latest findings on the debate, as well as provide new insights based on older citations. Recent studies that employed different research methods have demonstrated that dissolved organic carbon (DOC) and detritus are the principal sources of food for a growing list of sponge species, challenging the idea that the relative availability of living picoplankton is the sole proxy for sponge growth or abundance. New reports have confirmed earlier findings that reef macroalgae release labile DOC available for sponge nutrition. Evidence for top-down control of sponge community structure by fish predation is further supported by gut content studies and historical population estimates of hawksbill turtles, which likely had a much greater impact on relative sponge abundances on Caribbean reefs of the past. Implicit to investigations designed to address the bottom-up vs. top-down debate are appropriate studies of Caribbean fore-reef environments, where benthic communities are relatively homogeneous and terrestrial influences and abiotic effects are minimized. One recent study designed to test both aspects of the debate did so using experiments conducted entirely in shallow lagoonal habitats dominated by mangroves and seagrass beds. The top-down results from this study are reinterpreted as supporting past research demonstrating predator preferences for sponge species that are abundant in these lagoonal habitats, but grazed away in fore-reef habitats. We conclude that sponge communities on Caribbean fore-reefs of the past and present are largely structured by predation, and offer new directions for research, such as determining the environmental conditions under which sponges may be food-limited (e.g., deep sea, lagoonal habitats) and monitoring changes in sponge community structure as populations of hawksbill turtles rebound.