Natural and anthropogenic dissolved organic matter in landfill leachate: Composition, transformation, and their coexistence characteristics.

A large number of natural and anthropogenic wastes were landfilled, and dissolved organic matter (DOM) were formed during landfill. However, the composition, transformation, and coexistence characteristics of natural and anthropogenic DOM in leachate remain unclear. Fourier transform ion cyclotron resonance mass spectrometry, size exclusion chromatography, gas chromatography coupled with mass spectrometry, and three-dimensional excitation-emission matrix spectrum were employed to clarify comprehensively the abovementioned question. The results showed that natural DOM in young leachate constituted mainly straight-chain organic acids, protein substances, and building blocks of humic substances (BB). Straight-chain organic acids vanished in old leachates, and the concentration of protein substances and BB decreased from 44% to 26% and from 47% to 12%, respectively, while CHON and CHONS were degraded to CHO and CHOS during the process. As to anthropogenic DOM, its types and relative content in leachate increased during landfill, and aromatic acids, terpenes, halogenated organics, indoles, and phenols became the main organic components in old leachate. Compared to natural DOM, anthropogenic DOM was degraded slowly and accumulated in leachate, and some of the natural DOM facilitated the dechlorination of dichlorinated organic compounds. This study demonstrates that landfill led to an increase in humic substances and halogenated organic compounds in old leachate, which was intensified with concentrated leachate recirculation.

Larger aggregate formed by self-assembly process of the mixture surfactants enhance the dissolution and oxidative removal of non-aqueous phase liquid contaminants in aquifer.

Surfactants can transfer non-aqueous phase liquid (NAPL) contaminants to the aqueous phase, and enhance the removal of the latter in groundwater. However, the extensive use of surfactants causes secondary contamination and increases the non-target consumption of oxidants. It is pressing to develop a surfactant with high phase transfer efficiency and sound compatibility with oxidants to minimize the use of surfactants for groundwater remediation. The phase transfer capability of different surfactants and their binary mixtures, their enhanced KMnO4 oxidation performance for NAPL contaminants as well as influencing factors were investigated to solve the above-mentioned question. The results showed that Tween20, SDBS and BS-12 perform best in terms of phase transfer capability among nonionic, anionic and amphoteric surfactants respectively, and only SDBS and BS-12 produce a synergistic effect among the binary mixtures. The CMC of SDBS/BS-12 was lower than its ideal CMC value, and the self-assembly process of SDBS/BS-12 also formed larger aggregates, which improved the phase transfer performance. Compared to other single surfactants, the removal efficiency of petroleum hydrocarbons in the aquifer sediments was raised by 7.4-33.8 % using the mixed surfactant. The SDBS/BS-12 mixture was compatible with KMnO4 and boosted the reaction of NAPL contaminants with KMnO4 by transferring from the NAPL phase to the aqueous phase. As a result, the NAPL toluene and phenanthrene removal efficiency increased from 37 % and 29 % to 80 % and 86 % respectively. Natural organic matters inhibited the phase transfer efficiency of the SDBS/BS-12 mixture, whereas anions and monovalent cations enhanced the phase transfer capability of the mixture. High-valent cations led to precipitation in the SDBS/BS-12, which could be eliminated by adding Na2Si2O5. The SDBS/BS-12 mixture delivered the same phase transfer efficiency with the dosage of 1.73-23.07 % of other single surfactants, and its cost was equivalent to 0.25-41.7 % of the latter, thus embracing bright application prospects.

Volatile and semi-volatile organic compounds in landfill leachate: Concurrence, removal and the influencing factors.

Volatile and semi-volatile organic compounds (VOCs and SVOCs) carried by landfilled wastes may enter leachate, and require appropriate treatment before discharge. However, the driving factors of the entry of VOCs and SOVCs into leachate, their removal characteristics during leachate treatment and the dominant factors remain unclear. A global survey of the VOCs and SOVCs in leachate from 103 landfill sites combined with 27 articles on leachate treatment was conducted to clarify the abovementioned question. The results showed that SVOCs such as polycyclic aromatic hydrocarbons (PAHs), phthalate acid esters (PAEs) and phenols were the most frequently detected in leachate on a global scale. However, four kinds of VOCs, i.e., toluene, ethylbenzene, xylenes and benzene, were frequently detected at high concentrations in landfill leachate as well. The concentrations of VOCs and SVOCs in leachate ranged from 1 × 10° to 1 × 108 ng/L. Solubility was a key factor driving the entry of VOCs and SOVCs into leachate, and higher solubility enables higher detectable concentrations in leachate (P<0.05). It was easiest to remove monocyclic aromatic hydrocarbons (MAHs) from leachate, followed by phenols and PAHs, and it was most difficult to remove PAEs. In terms of removing MAHs, the anoxic/oxic (A/O) process and the sequential batch reactor (SBR) process were comparable to the advanced oxidization process and far superior to the ultrafiltration and nanofiltration processes, and the removal rate increased with an increase in the Henry's constant and/or the hydrophilicity of the contaminants during the A/O and SBR processes (P<0.05). There were no significant differences among biological, advanced oxidation and reverse osmosis processes in the removal of phenolic. In terms of removing PAHs, the A/O process was comparable to the advanced oxidization process and more efficient than the other treatment processes. As to removing PAEs, the membrane bioreactor process was almost the same efficient as the advanced oxidization process and far more efficient than the other biological treatment processes. Future research should focus on the pollution of atmospheric VOCs and SVOCs near aeration units in leachate treatment plants, as well as the health risk assessment of VOCs and SVOCs in the treated leachate effluent. To the best of our knowledge, this is the first review regarding the occurrence and removal of VOCs and SVOCs from landfill leachates worldwide.

Volatile and semi-volatile organic compounds in landfill gas: Composition characteristics and health risks.

Gas emitted from landfills contains a large quantity of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs), some of which are carcinogenic, teratogenic, and mutagenic, thereby posing a serious threat to the health of landfill workers and nearby residents. However, the global hazards of VOCs and SVOCs in landfill gas to human health remain unclear. To quantify the global risk distributions of these pollutants, we collected the composition and concentration data of VOCs and SVOCs from 72 landfills in 20 countries from the core database of Web of Science and assessed their human health risks as well as analyzed their influencing factors. Organic compounds in landfill gas were found to primarily result from the biodegradation of natural organic waste or the emissions and volatilization of chemical products, with the concentration range of 1 × 10-1-1 × 106 µg/m3. The respiratory system, in particular, lung was the major target organ of VOCs and SVOCs, with additional adverse health impacts ranging from headache and allergies to lung cancer. Aromatic and halogenated compounds were the primary sources of health risk, while ethyl acetate and acetone from the biodegradation of natural organic waste also exceeded the acceptable levels for human health. Overall, VOCs and SVOCs affected residents within 1,000 m of landfills. Air temperature, relative humidity, air pressure, wind direction, and wind speed were the major factors that influenced the health risks of VOCs and SVOCs. Currently, landfill risk assessments of VOCs and SVOCs are primarily based on respiratory inhalation, with health risks due to other exposure routes remaining poorly elucidated. In addition, potential health risks due to the transport and transformation of landfill gas emitted into the atmosphere should be further studied.

Decreased CD57 expression of natural killer cells enhanced cytotoxicity in patients with primary sclerosing cholangitis.

Background/aims: Primary sclerosing cholangitis (PSC) is a chronic inflammatory biliary disease for which the immunopathological basis remains an enigma. Natural killer (NK) cells are key components of innate immunity and seemingly play diversified roles in different autoimmune disorders (AIDs). The aim of this study was to determine the role of NK cells in the pathogenesis of PSC. Methods: The frequency and phenotype of circulating NK cells in a large cohort of patients with PSC and healthy controls (HCs) were systematically examined. In addition, the functional capacity of NK cells including cytotoxicity and cytokine production was studied. Results: The frequency of CD3-CD56dimCD16+ (defined as CD56dim) NK cells in PSC patients was significantly lower in comparison to HCs. CD56dim NK cells from PSC displayed a more immature phenotype including high expression of the natural killing receptor NKp46 and downregulation of the highly differentiated NK cell marker CD57. Interestingly, the reduction of CD57 expression of NK cells was associated with the disease severity of PSC. In addition, PSC CD56dim NK cells exhibited increased CD107a degranulation and cytolytic activity toward target cells compared with HCs. Further analysis demonstrated that CD57-CD56dim NK cells from PSC had elevated expression of NKp46, NKp30, IL-2 receptor, and KLRG1 and higher cytotoxic capacity as compared to CD57+CD56dim NK cells. Conclusions: Our data demonstrate that the differentiation of PSC NK cells is dysregulated with enhanced cytotoxic activity. This change is likely to be functionally involved in pathogenesis and disease progression, deducing the potential of NK-directed immunotherapy for PSC.

Recent progress on in-situ chemical oxidation for the remediation of petroleum contaminated soil and groundwater.

Accidental oil leaks and spills can often result in severe soil and groundwater pollution. In situ chemical oxidation (ISCO) is a powerful and efficient remediation technology. In this review, the applications and recent advances of three commonly applied in-situ oxidants (hydrogen peroxide, persulfate, and permanganate), and the gap in remediation efficiency between lab-scale and field-scale applications is critically assessed. Feasible improvements for these measures, especially solutions for the 'rebound effect', are discussed. The removal efficiencies reported in 108 research articles related to petroleum-contaminated soil and groundwater were analyzed. The average remediation efficiency of groundwater (82.7%) by the three oxidants was higher than that of soil (65.8%). A number of factors, including non-aqueous phase liquids, adsorption effect, the aging process of contaminants, low-permeability zones, and vapor migration resulted in a decrease in the remediation efficiency and caused the residual contaminants to rebound from 19.1% of the original content to 57.7%. However, the average remediation efficiency of ISCO can be increased from 40.9% to 75.5% when combined with other techniques. In the future, improving the utilization efficiency of reactive species and enhancing the contact efficiency between oxidants and petroleum contaminants will be worthy of attention. Multi-technical combinations, such as the ISCO coupled with phase-transfer, viscosity control, controlled release or natural attenuation, can be effective methods to solve the rebound problem.

Molecular structure and evolution characteristics of dissolved organic matter in groundwater near landfill: Implications of the identification of leachate leakage.

Landfills can cause groundwater contamination, the pollution characteristics in groundwater near landfill sites have been extensively investigated, while the rapid identification of leachate leakage remained unclear. Comprehensively characterizing dissolved organic matter (DOM) is crucial for tracing the source, species, and migration of contaminants within groundwater and protecting groundwater sources. Here, we showed that DOM composition from newer landfills was mainly composed of newly-produced tryptophan and tyrosine, and protein-like and humic-like substances were more abundant in landfills that were relatively older. DOM in landfill groundwater was initially dominated by outputs from microbial activities, followed by terrigenous input. Leaked leachate contained an additional dye-derived fluorescent matter at the excitation/emission wavelength of 240-260/440-460 nm that was absent in uncontaminated groundwater. Leachate leakage increased the concentrations of humic-like substance, DOM molecular weight, and microbial activity in the downstream groundwater, resulting in the microorganisms rapidly multiply and secrete large amounts of microbial metabolism by-products, making them suitable indicators of groundwater pollution. Three criteria were proposed to establish an interpretable fluorescence method to identify leachate pollution. The obtained results provide a novel insight into not only the monitoring, early warning, and identification but also the transport, fate and removal or transformation of groundwater leachate in landfills.

Influence of moisture content on chicken manure stabilization during microbial agent-enhanced composting.

Moisture content (MC) influences substance transformation during composting and the function of exogenous microbial agents. Unsuitable MC could cause leaching, nutrient loss, and secondary contamination. In this study, chicken manure composting with varied MC (45-61%) was conducted under functional microbial agent inoculation to explore the optimum condition for composting and the potential mechanism. Due to the enhanced decomposing, nitrosation, and nitrification effect lead by the functional microorganism, treatment with the optimal MC (53%) exhibited the highest composting temperature (61 °C) and longest high-temperature period (15 days), achieving a final carbon-nitrogen ratio (C/N), humic acids and fulvic acids ratio (HA/FA), and NH4+-N/NO3--N at 19.20, 2.00, and 0.93, respectively. After composting, the total nitrogen (TN) increased by 13.01-22.10% in the treatments with microbial agent inoculation compared with original stack, while it decreased by 7.76% in control. The highest nutrient (5.63%, 5.63-14.20% higher than the other composts) and better product safety (11.43-23.58% higher seed germination than others) were observed in treatment with MC at 53%, exceeding the Chinese national standard for organic fertilizer. Obviously, under optimum MC, microbial agent augmentation lead to high quality and safe compost products after a short composting period (25 days) without any leaching, which suggested an efficient way to promote the recycling and recovery of husbandry waste.

Effects of landfill refuse on the reductive dechlorination of pentachlorophenol and speciation transformation of heavy metals.

Landfill refuse is a mixture of inorganic minerals and organic matter that is capable of undergoing complexation and redox reactions due to its active functional groups. Organic matter often combines with minerals in landfill refuse and it remains unclear whether this combination involves electron transfer. Therefore, the effects of landfill refuse composition on reductive dechlorination and speciation transformation of heavy metals were investigated in this study. Results show that landfill refuse comprises protein- and humic-like substances, aliphatic structures, and a large number of hydroxyl, carboxyl, quinoid and other active functional group. The electron donating capacity (0.09-0.26 µmol/g(C)) of landfill refuse was found to be higher than its electron accepting capacity (0.03-0.23 µmol/g(C)), indicating that electron donating groups (hydroxyl) were the main redox-active moieties, facilitating the reductive dechlorination of pentachlorophenol (PCP) by microorganism. Fe2O3, FeO and SiO2 were the main inorganic minerals affecting PCP dechlorination. The speciation distribution of heavy metals in landfill refuse was determined by the BCR sequential extraction method. Results showed that Zn and Ni have high potential migration capacity, poor stability and the highest bioavailability, while Cr, Cu and Pb are relatively stable and have weak migration potential. The oxygen- and nitrogen-containing functional groups, aliphatic structures and aromatic carbon in landfill refuse can promote the transformation of Ni and Cr from an unstable to stable state. Protein-like substances exhibit a strong Cu binding ability, allowing Cu to combine with organic matter more easily than other assessed heavy metals. Both Fe2O3 and FeO affected the stability of Cu. FeO promoted the stabilization of Zn, whereas Fe2O3 and SiO2 promoted Cu instability. These results could provide some references for the treatment of organic chlorides and the stabilization of heavy metals in landfill refuse in China.

Surfactant-enhanced remediation of oil-contaminated soil and groundwater: A review.

Oil leakage, which is inevitable in the process of extraction, processing, transportation and storage, seriously undermines the soil and groundwater environment. Surfactants can facilitate the migration and solution of oil contaminants from nonaqueous phase liquid (NAPL) or solid phase to water by reducing the (air/water) surface tension, (oil/water) interfacial tension and micellar solubilization. They can effectively enhance the hydrodynamic driven remediation technologies by improving the contact efficiency of contaminants and liquid remediation agents or microorganism, and have been widely used to enhance the remediation of oil-contaminated sites. This paper summarizes the characteristics of different types of surfactants such as nonionic, anionic, biological and mixed surfactants, their enhancements to the remediation of oil-contaminated soil and groundwater, and examines the factors influencing surfactant performance. The causes of tailing and rebound effects and the role of surfactants in suppressing them are also discussed. Laboratory researches and actual site remediation practices have shown that various types of surfactants offer diverse options. Biosurfactants and mixed surfactants are superior and worth attention among the surfactants. Using surfactant foams, adding shear-thinning polymers, and combining surfactants with in-situ chemical oxidation are effective ways to resolve tailing and rebound effects. The adsorption of surfactants on soils and aquifer sediments decreases remediation efficiency and may cause secondary pollution, Therefore the adsorption loss should be noticed and minimized.

Urolithin A Prevents Focal Cerebral Ischemic Injury via Attenuating Apoptosis and Neuroinflammation in Mice.

Neuroinflammation contributes to neuronal death in cerebral ischemia. Urolithin A (UA), a gut microbial metabolite of ellagic acid, has emerged as a potential anti-inflammatory agent. However, its roles and precise mechanisms in stroke remain unknown. Here we found that UA treatment ameliorated infarction, neurological deficit scores, and spatial memory deficits after cerebral ischemia. Furthermore, UA significantly reduced neuron loss and promoted neurogenesis after ischemic stroke. We also found that UA attenuated apoptosis by regulating apoptotic-related proteins. Meanwhile, UA treatment inhibited glial activation via affecting inflammatory signaling pathways, specifically by enhancing cerebral AMPK and IκBa activation while decreasing the activation of Akt, P65NFκB, ERK, JNK, and P38MAPK. Our findings reveal a key role of UA against ischemic stroke through modulating apoptosis and neuroinflammation in mice.

Evolution properties and dechlorination capacities of particulate organic matter from a landfill.

Particulate organic matter (POM) includes humin and non-degradable residues, and the knowledge about its composition, evolution and environmental behavior is limited. The composition, evolution and its influence on dechlorination of the POM in landfill was studied. The results show that POM accounts for 27 %-57 % of the organic matter in landfill cell, which is mainly composed of protein-, fulvic- and humic-like components. Firmicutes and Proteobacteria were the main microorganisms driving the compositional evolution of POM during the landfilling process. The electron acceptance capacities (EAC) and electron donating capacities (EDC) of POM were in the range of 0.05-0.51 µmol/gC-1 and 0.13-0.66 µmol/gC-1, respectively, and the average EAC and EDC of POM in the intermediate and old stage of landfill were higher than those in the initial stage. The combined action of MR-1 and POM increased the degradation rate of PCP by 20 %-40 %, which was ascribed to the reduction capacities and electron transfer process of POM. POM derived from the intermediate and old stages promoted PCP dechlorination more effectively when compared with the initial stage due to its high electron transfer capacities (ETC), which are of great significance for soil in-situ bioremediation.

Mechanisms of potentially toxic metal removal from biogas residues via vermicomposting revealed by synchrotron radiation-based spectromicroscopies.

Biogas residues (BR) contaminated with potentially toxic metals pose environmental risks to soils and food chains, and strategies are needed to decrease the concentration and bioavailability of potentially toxic metals in BR. Here, metal fractions and removal mechanisms were quantified by synchrotron radiation-based Fourier transform infrared and micro X-ray fluorescence spectromicroscopies on BR and earthworms subject to vermicomposting. Vermicomposting resulted in decreases in concentrations of potentially toxic metals in BR and increases in metal removal efficiencies due to uptake by earthworms. Prior to vermicomposting, Zn, Cu and Pb were associated with N-H, O-H, aromatic C, aliphatic C, and amide functional groups, but following maturation during vermicomposting, metals were associated with N-H, O-H, aliphatic C and polysaccharide functional groups. Following vermicomposting, Zn and Cu were mainly distributed in the dermal portions of earthworms, whereas Pb was more homogeneously distributed among the inner and outer portions of the earthworms, revealing that different metals may have different uptake routes. These findings provide a new strategy for safe utilization of BR by using earthworms via vermicomposting to remove potentially toxic metals and in situ insights into how metals binding and distribution characteristics in BR and earthworms during compost and vermicomposting processes.

Interaction and coexistence characteristics of dissolved organic matter with toxic metals and pesticides in shallow groundwater.

The long-term and large-scale utilization of fertilizers and pesticides in facility agriculture leads to groundwater pollution. However, the coexistence and interactions between organic fertilizers (i.e., organic matter), toxic metals, and pesticides in shallow groundwater have seldom been studied. Thus, the study sought to characterize said interactions via fluorescence, ultraviolet-visible spectroscopy (UV-Vis), and Fourier-transform infrared spectroscopy coupled with two-dimensional correlation spectroscopy and chemometric techniques. The results indicated that groundwater DOM was comprised of protein-, polysaccharide-, and lignin-like substances derived from organic fertilizers. Protein-like substances accounted for the binding of Co, Ni, and Fe, while polysaccharide- and lignin-like substances were mainly responsible for Cr and Mo complexation. Moreover, lignin- and polysaccharide-like substances played a key role in the binding of pesticides (i.e., dichlorodiphenyltrichloroethane [DDT], endosulfan, γ-hexachlorocyclohexane [γ-HCH], monocrotophos, chlorpyrifos, and chlorfenvinphos), rendering the conversion of γ-HCH to ß-hexachlorocyclohexane (ß-HCH) and the degradation of DDT to dichlorobenzene dichloroethylene (DDE) ineffective. However, the presence of protein-like substances in groundwater benefited the degradation and conversion of γ-HCH and α-endosulfan. Redundancy analyses showed that lignin- and polysaccharide-like matter had the most impacts on the coexistence of DOM with toxic metals and pesticides.

Redox properties and dechlorination capacities of landfill-derived humic-like acids.

Electron transfer capacities (ETC) of humic-like acids (HLA) and their effects on dechlorination are dependent on their redox-active properties. Aging and minerals can affect the chemical compositions and structures of HLA. However, the underlying mechanism and the impacts on the dechlorination capacities of HLA are poorly understood. We investigated how redox properties change in association with the intrinsic chemical natures and exterior minerals of the HLA extracted from landfilled solid wastes. Furthermore, the ETC of the landfill-derived HLA could be strengthened by increasing landfill age and demineralization, thereby facilitating the dechlorination of pentachlorophenol (PCP). The HLA molecules started to polymerize aromatic macromolecules during landfilling, leading to an increase in ETC and dechlorination capacities. Macromolecular HLA were dissociated to smaller molecules and exposed more aromatic and carboxyl groups when separated from minerals, which enhanced the ETC and the dechlorination abilities of the HLA. Microbial-mediated dechlorination was an effective way to degrade PCP, and almost 80% of the PCP was transformed after 40 days of demineralized HLA and Shewanella oneidensis MR-1 incubation. The demineralization and aging further facilitated the microbial-mediated PCP dechlorination. The findings provide a scientific base for improving in-situ bioremediation of chlorinated compound-contaminated soils using freshly synthesized HLA.

Polarity and Molecular Weight of Compost-Derived Humic Acids Impact Bio-dechlorination of Pentachlorophenol.

Compost-derived humic acids (HAs) as cheap soil conditioners have potential to facilitate pentachlorophenol (PCP) bio-dechlorination but lack proof and studies. To clarify this, PCP bio-dechlorination mediated by compost-derived HAs under Fe(III) reduction conditions was investigated. Reverse phase high-performance liquid chromatography and high-performance size exclusion chromatography were employed to identify the functional components within compost-derived HAs. Our results showed that compost-derived HAs facilitated the bio-dechlorination of PCP under Fe(III) reduction conditions, and four kinds of byproducts were detected during the process. The relatively hydrophilic and high molecular weight (MW) components within compost-derived HAs presented significant associations with the concentration of byproducts from bio-dechlorination of PCP in Fe2O3 reduction conditions. In contrast, the hydrophobic and low MW components were the main functional components for PCP bio-dechlorination in Fe3O4 reduction environment. These findings clarified the effects of polarity and MW of compost-derived HAs on PCP bio-dechlorination, giving clues to optimize composting technology to utilize compost products for in situ contamination remediation of paddy soil.

Influenza Virus Vaccination Elicits Poorly Adapted B Cell Responses in Elderly Individuals.

Influenza is a leading cause of death in the elderly, and the vaccine protects only a fraction of this population. A key aspect of antibody-mediated anti-influenza virus immunity is adaptation to antigenically distinct epitopes on emerging strains. We examined factors contributing to reduced influenza vaccine efficacy in the elderly and uncovered a dramatic reduction in the accumulation of de novo immunoglobulin gene somatic mutations upon vaccination. This reduction is associated with a significant decrease in the capacity of antibodies to target the viral glycoprotein, hemagglutinin (HA), and critical protective epitopes surrounding the HA receptor-binding domain. Immune escape by antigenic drift, in which viruses generate mutations in key antigenic epitopes, becomes highly exaggerated. Because of this reduced adaptability, most B cells activated in the elderly cohort target highly conserved but less potent epitopes. Given these findings, vaccines driving immunoglobulin gene somatic hypermutation should be a priority to protect elderly individuals.

Redox properties of compost-derived organic matter and their association with polarity and molecular weight.

Compost-derived dissolved organic matter (DOM), which has a wide distribution of molecular weight (MW) and polarity, has a potential application in the remediation of the contaminated soil due to its redox-active functional groups. Composting treatment can change the MW and polarity of the DOM through microbial transformation and degradation. However, the relationship between the redox properties of compost-derived DOM and its MW and polarity is still unclear. DOM was extracted from municipal solid wastes with different composting times in this study, and it was further fractionated into humic acids (HA), fulvic acids (FA) and hydrophilic (HyI) fractions based on its hydrophobicity and XAD-8 resin. Electron transfer capacities [including electron accepting capacities (EAC) and electron donating capacities (EDC)] of the HA, FA and HyI fractions and their associations with polarity and MW were studied. The results showed that the EAC of the HA, FA and HyI all increased after composting. The EDC of the HA and HyI exhibited an increasing trend as well, though that of the FA decreased remarkably after composting. The MW, polarity and redox-active functional groups of the HA, FA and HyI fractions were determined using high performance liquid chromatography and excitation-emission matrix fluorescence spectra coupled with parallel factor analysis. The result showed that the quinone-like groups were mainly detected in the medium MW and transphilic sub-fractions of the HA, FA and HyI, and were the main functional groups responsible for the EAC. The low MW sub-fractions, which consisted mainly of tyrosine-like matter, were the main functional components accounted for the EDC. The results advance our understanding of the influence of MW and polarity on the redox properties of organic substances, and facilitate to reveal the important redox-active functional groups when compost is utilized to remediate the contaminated soil.

Hydrophobicity-dependent electron transfer capacities of dissolved organic matter derived from chicken manure compost.

The electron transfer capacities (ETC) of dissolved organic matter (DOM) are related to their hydrophobicity. However, the underlying mechanism is poorly understood. The DOM was extracted from chicken manure compost, and fractionated into four fractions based on hydrophobicity, i.e., hydrophobic acid (HOA), hydrophobic base (HOB), hydrophilic matter (HIM) and acid insoluble matter (AIM) fractions. The composition, structure and ETC of the four fractions were measured using spectral technology and electrochemical methods. The results showed that the HOA and AIM fractions consisted mainly of fulvic- and humic-like substances, the HOB fraction comprised mainly organic nitrogen compounds, and the HIM was mainly composed of carbohydrates and protein-like matter. The electron donating capacities (EDC) and electron accepting capacities (EAC) of the four fractions were in the range of 616.90-5224.66 and 7.30-191.20 µmoL/g(C), respectively, The HOB fraction exhibited the highest EDC among the four fractions, followed by the HOA, AIM and HIM fractions. The EAC of the four fractions was characterized by the order of AIM, HOB, HOA and HIM. The tryptophan- and humic-like substances and organic nitrogen compounds accounted for the EDC, whereas the carboxyl group on aromatic substance responsible for the EAC.

The binding properties of copper and lead onto compost-derived DOM using Fourier-transform infrared, UV-vis and fluorescence spectra combined with two-dimensional correlation analysis.

Three dissolved organic matter (DOM) samples were obtained from municipal solid wastes at the initial (C0), high-temperature (C7) and mature (C51) period during composting. Two-dimensional correlation spectroscopy (2D-COS) analysis on Fourier-transform infrared (FTIR), ultraviolet visible (UV-vis), and synchronous fluorescence spectra (SFS) were used to investigate the metal binding properties of compost-derived DOM. Synchronous and asynchronous maps of 2D-FTIR-COS of DOM-Cu(II) and DOM-Pb(II) were similar, however, the susceptibility and binding sequence of the corresponding spectral region was different. The N-H (amide I), phenolic OH, and C-O of alcohols, ethers, and esters were the most susceptive in the C0, C7, and C51 samples, respectively. 2D absorption COS indicated that the preferential binding with Cu(II) was shown to be at 305 nm for C0, at 236 nm for C7 and C51, and with Pb(II) at 247 nm for C0, at 233 nm for C7 and C51. 2D-SFS-COS indicated that protein-like matter showed a higher susceptibility and preferential binding with Cu(II) than humic-like substances. DOM showed a higher complexing affinity with Cu(II) than Pb(II) on the basis of the log K values. Spectral techniques combined with 2D-COS are useful to understand the binding heterogeneities of ligand sites within DOM-Cu(II) or Pb(II) during the composting.