Parallel faction analysis combined with two-dimensional correlation spectroscopy reveal the characteristics of mercury-composting-derived dissolved organic matter interactions

Tanning wastewater restructured nitrogen-transforming bacteria communities and promoted N2O emissions in receiving river riparian sediments

Physicochemical and toxicological characterization of leather tanning wastewater has been widely documented. However, few reports have examined the response of denitrification N2 and N2O emissions in riparian sediments of tannery wastewater-receiving rivers. In this study, 15N-nitrate labeling was used to reveal the effects of tanning wastewater on denitrification N2 and N2O emission in a wastewater-receiving river (the old Mang River, OMR). OMR riparian sediments were highly polluted with total organic carbon (93.39 mg/kg), total nitrogen (5.00 g/kg) and heavy metals; specifically, Cr, Zn, Cd, and Pb were found at concentrations 47.3, 5.8, 1.6, 4.3, and 2.8 times that in a nearby parallel river without tanning wastewater input (the new Mang River, NMR), respectively. The denitrification N2 emission rates (0.0015 nmol N · g-1 h-1) of OMR riparian sediments were significantly reduced by 2.5 times compared with those from the NMR (p < 0.05), but the N2O emission rates (0.31 nmol N · g-1 h-1) were significantly increased (4.1 times, p < 0.05). Although the dominant nitrogen-transforming bacteria phylum was Proteobacteria in the riparian sediments of both rivers, 11 nitrogen-transforming bacteria genera in the OMR were found to be significantly enriched; five of these were related to pollutant degradation based on linear discriminant analysis (LDA >3). The average activity of the electron transport system in the OMR was 6.3 times lower than that of the NMR (p < 0.05). Among pollution factors, heavy metal complex pollution was the dominant factor driving variations in N2O emissions, microbial community structure, and electron transport system activity. These results provide a new understanding and reference for the treatment of tanning wastewater-receiving rivers.

Unravelling structure evolution of dissolved organic matter during oxidation by persulfate: Insights from aromaticity and fluorescence analysis

Persulfate advanced oxidation technology is widely utilized for remediating organic-contaminated groundwater. Post-remediation by persulfate oxidation, the aromaticity of dissolved organic matter (DOM) in groundwater is significantly reduced. Nevertheless, the evolution trends of aromaticity and related structural changes in DOM remained unclear. Here, we selected eight types of DOM to analyze the variation in aromaticity, molecular weight, and fluorescence characteristics during oxidation by persulfate using optical spectroscopy and parallel faction analysis combined with two-dimensional correlation spectroscopy analysis (2D PARAFAC COS). The results showed diverse trends in the changes of aromaticity and maximum fluorescence intensity (Fmax) among different types of DOM as the reaction time increases. Four types of DOM (humic acid 1S104H, fulvic acid, and natural organic matters) exhibited an initially noteworthy increase in aromaticity followed by a decrease, while others demonstrated a continuous decreasing trend (14.3%-69.4%). The overall decreasing magnitude of DOM aromaticity follows the order of natural organic matters ≈ commercial humic acid > fulvic acid > extracted humic acid. The Fmax of humic acid increased, exception of commercial humic acid. The Fmax of fulvic acid initially decreased and then increased, while that of natural organic matters exhibited a decreasing trend (86.4%). The fulvic acid-like substance is the main controlling factor for the aromaticity and molecular weight of DOM during persulfate oxidation process. The oxidation sequence of fluorophores in DOM is as follows: fulvic-like substance, microbial-derived humic-like substance, humic-like substance, and aquatic humic-like substance. The fulvic-like and microbial-derived humic-like substances at longer excitation wavelengths were more sensitive to the response of persulfate oxidation than that of shorter excitation wavelengths. This result reveals the structure evolution of DOM during persulfate oxidation process and provides further support for predicting its environmental behavior.

Characteristics of microplastic-derived dissolved organic matter and its binding with pharmaceuticals unveiled by fluorescence spectroscopy and two-dimensional correlation spectroscopy

Microplastics were an extensively detected pollutant in the environment, but microplastic-derived dissolved organic matter (MP-DOM) has received less attention, much less its impact on the binding behavior of pollutants (e.g., pharmaceuticals). In this study, DOM derived from two typical MPs, i.e., polyethylene terephthalate (PET) and polystyrene (PS) was generated by UV irradiation (a widely used way for MPs' aging treatment) and characterized by multiple spectroscopic techniques and methods. Chloramphenicol (CAP) and carbamazepine (CBZ) were selected to investigate the binding mechanism between MP-DOM and pharmaceuticals. After UV irradiation, the concentration of the dissolved organic carbon, colored DOM, and carboxyl/carbonyl groups of MP-DOM increased. Moreover, the humic-like substance released preceding and more under UV irradiation. Furthermore, the protein-like substances on PET-DOM and the humic-like substances on PS-DOM were positively correlated to the binding capacity to the pharmaceuticals, respectively. 2D-COS results revealed that the fluorescent materials having more oxygen-containing functional groups for MP-DOM preferentially interacted with the pharmaceuticals. Overall, the higher fluorescence quenching was related to the protein-like substance, CBZ, and PET-DOM as compared to the humic-like substance, CAP, and PS-DOM. It was verified by the relatively high binding ability (logKM) for them (the protein-like substance: 5.15; CBZ: 4.61; PET: 4.48). This study first proved the environmental reactivity of MP-DOM to the pharmaceuticals highlighting the significance of the spectral properties for the binding behavior of MP-DOM with pharmaceuticals and the competitive sorption role of MP-DOM to the pollutants in the natural environment.

Application of carbon-based adsorbents in the remediation of micro- and nanoplastics

Micro-nano plastics (MNPs) are emerging contaminants that can easily enter the food chain, posing risks to both the aquatic ecosystem and human health. Various physical, biological, and chemical methods have been explored to remove MNPs from water, and recently, adsorption technology has gained attention as an effective approach. Among the potential candidates, carbon-based adsorbent has emerged as a promising choice due to their low cost, eco-friendly nature, and sustainability. This paper summarizes recent advancements in MNP removal using carbon-based adsorbents, with a focus on the modification methods and adsorption mechanisms. Additionally, the factors influencing the adsorption performance and the methods for characterizing the adsorption mechanism are analyzed. Finally, the advantages and disadvantages of carbon-based adsorbents over other adsorbents are discussed, along with the current state of sustainable recycling and future research prospects.

Insight into the dynamics of dissolved organic matter components under latitude change perturbation

Dissolved organic matter (DOM) which can help the transportation of nutrients and pollutants plays essential role in the aquatic ecosystems. However, the dynamics of individual DOM component under the change of latitude have not been elucidated to date. The composition and dynamics of DOM were assessed in this study. Two individual parallel factor analysis (PARAFAC) components were found in each sampling site in Heilongjiang. To further characterize the inner change of the identified PARAFAC components, two-latitude correlation spectroscopy (2DCOS) technique was applied to the excitation loadings data. Interestingly, not all the fluorophore in a PARAFAC component change in the same direction as the overall change of a component. From upstream to downstream, the peak A1 in PARAFAC component C1 showed a downward trend, but peak A2 presented an upward trend. In PARAFAC component C2, the peak T2 and peak T3 showed an inverse changing trend under latitude perturbation. Furthermore, basic nutrients parameters in Heilongjiang were also characterized in each sampling sites. The relationships between DOM and nutrients showed that component C1 made a significant contribution to chemical oxygen demand (COD) and biochemical oxygen demand (BOD5). The evolutions of DOM peak A1 and peak A2 were accompanied by the changing of Total phosphorus (TP). The findings in this study could make a contribution to explore the fate of DOM in high humic-like substance containing river.

Evolution from basic to advanced structure of fulvic acid and humic acid prepared by food waste

Fulvic acid (FA) and humic acid (HA) are common polyacids in nature. However, the evolutionary process of their basic and advanced structures is still unclear. FA and HA were separated into five molecular weight components to investigate the process of evolution from small to large molecules. The primary structure analysis showed that FA were rich in CN, COOH and OH content, while HA were rich in (CH2)n, NH2 and CC. Moreover, with the molecular weight increasing, the structures could complement each other to maintain the hydrophilic or hydrophobic balance. The 2D-COS spectroscopy demonstrated that during the growth of FA, COOH, NH2 and OH firstly respond. On the other hand, during the growth of HA, NH2 and (CH2)n firstly respond. In addition, advanced structure of FA was affected by intramolecular hydrogen bonds and π - π interaction. HA was affected by hydrophobic interactions due to the abundance of hydrophobic groups, primarily (CH2)n and benzene rings. 3D conformational fitting and particle size characterization confirmed that the interaction forces determine that FA and HA become tightly and loosely molecules respectively. This study is to further explore the geochemical formation and evolution process of FA and HA molecules.

Reducing the mass and decreasing the bioavailability of heavy mental from organic wastes treated by black soldier fly larvae

Black soldier fly larvae (BSFL), Hermetia illucens L., are widely used to reduce the mass of various wastes. However, the potential metal tolerance mechanisms during periods of waste bioconversion by BSFL remain largely unknown. To further reveal the mechanisms, BSFL were used to treat the agricultural organic wastes, including pig manure (PM), cow manure (COM), spent mushroom substrate (SMS), and wet distiller grains (WDG). After these individual and combined waste(s) were treated by BSFL, we investigated the waste reduction rates and evaluated the responses of BSFL gut microbes to heavy metals of agricultural organic wastes. Additionally, the colloidal particles of residual wastes were characterized by combing energy dispersive X-ray (EDX) spectroscopy, Size potential, Zeta potential, and excitation-emission matrix (EEM) spectroscopy. Results indicated that the waste reduction rates were up to 74% in COM+WDG and 69% in WDG, most of heavy metals (e.g., Zn and Co) from organic wastes were not accumulated in the bodies of mature larvae after treatment. Further, results obtained from the prediction of gene function on the basis of 16 S rRNA data revealed that the presence of multi-resistance genes in the gut of BSFL can help the larvae resist Zn and/or Co stress. In addition, the drug sensitivity test implied that BSFL5_L and BSFL6_L from BSFL gut bacterial strains have multi-resistance to Co and Zn. Additionally, EDX results revealed that the colloidal particles in five waste residues after BSFL treatment are mainly consisted of Fe, Ca and Si, which can capture heavy metals (e.g., Cu, Mn). Results from EEM spectroscopy and PARAFAC showed that tryptophan-like and humic-like accumulatively account for 56%- 68% of all components. Importantly, these two components could strongly bind the metal elements and form colloidal particles with high stability, and therefore reduce the heavy metal pollution of agricultural organic wastes. Our findings offered an environment-friendly method to treat agricultural organic wastes, which would be far-reaching influence to our environment.

Molecular complexation properties of Cd2+ by algal organic matter from Scenedesmus obliquus

A detailed understanding the metals binding with algal organic matter (AOM) is essential to gain a deeper insight into the toxicity and migration of metals in algae cell. However, the molecular complexation mechanism of the metals binding with AOM remains unclear. In this study, cadmium ion (Cd2+) binding properties of AOMs from Scenedesmus obliquus, which included extracellular organic matter (EOM) and intracellular organic matter (IOM), were screened. When Cd2+ < 0.5 mg/L, the accumulation of Cd2+ could reach 40%, while Cd2+ > 0.5 mg/L, the accumulation of Cd2+ was only about 10%. EOM decreased gradually (from 8.51 to 3.98 mg/L), while IOM increased gradually (from 9.62 to 21.00 mg/L). The spectral characteristics revealed that IOM was richer in peptides/proteins and had more hydrophilic than EOM. Both EOM and IOM contained three protein-like components (containing tryptophan and tyrosine) and one humic-like component, and their contents in IOM were higher than that in EOM. The tryptophan protein-like substances changed greatly during Cd2+ binding, and that the tryptophan protein-like substances complexed to Cd2+ before tyrosine protein-like substances in IOM was identified. Moreover, the functional groups of N-H, O-H, and CO in AOM played an important role, and the N-H group was priority to interacts with Cd2+ in the complexing process. More functional groups (such as C-O and C-N) were involved in the metals complexing in EOM than in IOM. It could be concluded that Cd2+ stress promoted the secretion of AOM in Scenedesmus obliquus, and proteins in AOM could complex Cd2+ and alleviate its toxicity to algal cell. These findings provided deep insights into the interaction mechanism of AOM with Cd2+ in aquatic environments.

Effects of different soil water holding capacities on vegetable residue return and its microbiological mechanism

With the gradual expansion of the protected vegetable planting area, dense planting stubbles and increasing labor cost, the treatment of vegetable residues has become an urgent problem to be solved. Soil bacterial community structure plays an important role in vegetable residue return and is susceptible to environmental changes. Therefore, understanding the influences of different soil water holding capacities on plant residue decomposition and soil bacterial communities is important for biodegradation. During the whole incubation period, the weight loss ratio of plant residue with 100% water holding capacity was 69.60 to 75.27%, which was significantly higher than that with 60% water holding capacity in clay and sandy soil, indicating that high water holding capacity promoted the decomposition of plant residue. The degradation of lignin and cellulose was also promoted within 14 days. Furthermore, with the increase in soil water holding capacity, the contents of NH4+ increased to 5.36 and 4.54 times the initial value in the clay and sandy soil, respectively. The increase in napA and nrfA resulted in the conversion of NO3- into NH4+. The increase in water holding capacity made the bacterial network structure more compact and changed the keystone bacteria. The increase in water holding capacity also increased the relative abundance of Firmicutes at the phylum level and Symbiobacterium, Clostridium at the genus level, which are all involved in lignin and cellulose degradation and might promote their degradation. Overall, these findings provide new insight into the effects of different soil water holding capacities on the degradation of plant residues in situ and the corresponding bacterial mechanisms.

Characterization of copper binding to different molecular weight fractions of dissolved organic matter in surface water

Dissolved organic matter (DOM) is a kind of substance with complex compositions and wide molecular weight distribution, which can strongly combine with various pollutants. Therefore, the binding characteristics of DOM and heavy metal pollutants can be studied specifically according to the binding characteristics of DOM and pollutants. In this study, DOM in surface water bodies was divided into three levels (MW < 1 kDa, 1 kDa < MW < 5 kDa, MW > 5 kDa) according to different molecular weights (MW). The binding properties were investigated by fluorescence spectrum analysis and complex model. Four components (C1-C4) were identified by PARAFAC. Among them, the contribution rate of protein-like components C1, C2 and C4 to the total fluorescence intensity reached more than 78%, and the log Ka values of low molecular weight components were the highest, which were 3.28, 3.14 and 3.47, respectively, indicating higher binding ability with Cu2+.With the decrease of molecular weight, the log Kb value increases, indicating that the complexation is more stable. The humic component C3 in high molecular weight has stronger binding stability with Cu2+, but the number of binding sites for C3 is 0.36, while that for C2 is 1.51, indicating that its binding sites and binding ability are relatively low. The results showed that the DOM ligand of Cu2+ in surface water showed a certain molecular weight dependence. In addition, different MW DOM lead to different pollution forms. Different properties of DOM ligand combined with Cu2+ were studied in order to control the migration, transformation, bioavailability, morphology and stability of heavy metal pollutants, and to provide theoretical support for the practical application management of surface water pollution control.

Molecular size-dependent compositions and lead (II) binding behaviors of two origins of organic fertilizers-derived dissolved organic matter

The application of organic fertilizers caused large amounts of dissolved organic matter (DOM) entering the soil environment and influencing the behaviors and fates of heavy metals. Here, we investigated the molecular weight-dependent (high molecular weight [HMW], 1 kDa-0.7 µm; low molecular weight [LMW], <1 kDa) compositions and lead (Pb) binding behaviors of DOM derived from sheep manure-based (SMOF) and shrimp peptide-based organic fertilizers (SPOF) using chromophoric and fluorescent spectroscopy, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and two-dimensional correlation spectroscopy (2D-COS). Results showed that SMOF released more DOM with higher aromaticity and hydrophobicity, containing more fluvic-like components, carboxylic-rich alicyclic molecules (CRAMs) and lignin phenolic compounds compared to SPOF-DOM with more microbially-transformed heteroatom-containing compounds (CHON, CHONS and CHOS). Furthermore, there was more aromatic compounds with ample carboxyl and hydroxyl groups in HMW-DOM but abundant protein-like components and heteroatom-containing compounds (CHONS and CHOS) in LMW-DOM. SMOF-DOM exhibited more obvious MW-dependent heterogeneity in molecular components compared to SPOF-DOM with higher molecular diversity. Moreover, 2D-COS indicated phenol and carboxyl groups in SMOF-DOM and polysaccharides in SPOF-DOM exhibited superior binding affinities for Pb. Pb binding to HMW-DOM derived from SMOF first occurred in the phenolic groups in fulvic-like substances, while polysaccharides in LMW-DOM first participated in the binding of Pb. In contrast, irrespective of MWs, polysaccharides and humic-like substances with aromatic (CC) groups in SPOF-DOM displayed a faster response to Pb. Furthermore, the polysaccharides which preferentially participated in the binding of Pb to SPOF-DOM and SMOF-derived LMW-DOM may pose a higher risk of Pb in the environment. These results were helpful to understand the effects of sources and size-dependent compositions of DOM on the associated risks of heavy metals in the environments.

Microbial metabolism and humic acid formation in response to enhanced copper and zinc passivation during composting of wine grape pomace and pig manure

Copper (Cu) and zinc (Zn) in piglet feed can lead to heavy metals (HMs) accumulation in pig manure (PM). Composting is crucial for recycling biowaste and decreasing HMs bioavailability. This study aimed to investigate the impact of adding wine grape pomace (WGP) on the bioavailability of HMs during PM composting. WGP facilitated the passivation of HMs through Cytophagales and Saccharibacteria_genera_incertae_sedis which promoted the formation of humic acid (HA). Polysaccharide and aliphatic groups in HA dominated the transformation of chemical forms of HMs. Moreover, adding 60% and 40% WGP enhanced the Cu and Zn passivation effects by 47.24% and 25.82%, respectively. Polyphenol conversion rate and core bacteria were identified as key factors in affecting HMs passivation. These results offered new insights into the fate of HMs during PM composting in response to the addition of WGP, which is helpful to practical application of WGP to inactivate HMs for improving compost quality.

Occurrence and source analysis of heavy metals and dissolved organic matter in Nanyi Lake, Anhui Province

Nanyi Lake is a tributary in the lower reaches of the Yangtze River and the largest freshwater lake in southern Anhui. Anthropogenic activities have significantly affected the lake with the rapid development of the surrounding economy in recent years. This study collected a total of 39 × 2 water samples of surface water and overlying water, detected the heavy metal concentrations (As, Cr, Cu, Mn, Ni, Pb, Sb, Zn, Fe, Cd), and analyzed the spectral characteristics of the dissolved organic matter (DOM). The results demonstrated that the concentrations of heavy metals (As, Cr, Cu, Mn, Ni, Pb, Sb, Zn, Fe, Cd) in the surface water were 1.00-7.78, 0.40-5.59, 0.20-4.52, 20.00-269.50, 0.40-5.56, 0.20-5.06, 1.00-7.64, 20.00-252.50, 60.00-590.00, and 0.04-0.60, respectively (unit: μg L^-1). The risk assessment showed that the carcinogenic risks of heavy metals (As, Cr, Cd) through drinking water were ranged from 10^-7 to 10^-4a^-1 in Nanyi Lake, and Cr was the main carcinogen which should be the focus of environmental health risk management. The average personal non-carcinogenic risks of heavy metals (Cu, Mn, Ni, Pb, Sb, Zn, Fe) were ranged from 10^-9 to 10^-13a^-1, and considered to be acceptable risk level. The contour map of spatial distribution demonstrated different degrees of heavy metals (except Zn) enrichment near the Langchuan River in the East Lake District. Parallel factor analysis showed that the main components of DOM in Nanyi Lake were tryptophan like, fulvic acid like, and tyrosine like, and the dissolved organic matter was primarily derived from autogenous endogenous sources. The heavy metals Cr, Ni, Pb, Fe, Cd, and HIX in the surface water of West Lake were significantly positively correlated, among which Ni, Fe and C2 were significantly negatively correlated (P < 0.05), Mn and BIX demonstrated extremely significant positive correlations (P < 0.01), while no significant correlation was observed between heavy metals and the DOM indexes in the surface water of the East Lake. The principal component and correlation analysis showed that the heavy metals in Nanyi Lake were primarily derived from the production wastewater discharged by the surrounding industrial and mining enterprises through the rivers input, followed by the non-point source runoff input of the surrounding agricultural production and lake aquaculture.

Variation of glomalin-metal binding capacity in 1 m soil profiles from mangrove forests to mudflat and affected factor analysis

Glomalin-related soil protein (GRSP) plays an important role in soil metal sequestration in coastal wetlands. Additionally, it can release dissolved organic matter (GDOM) in water-soaked condition. The purpose of this study was to clarify the variation of GRSP's heavy metal immobilisation capacity at soil profiles of coastal wetland, and explore the compositional characteristics of GDOM and its influence on the heavy metals' environmental behaviour. The results indicated that the metal immobilisation capacity of GRSP decreased with increasing burial depth. The contributions of GRSP to soil Cr, As, and Pb were higher in both mangrove soils (K. obovata and A. marina forests) than in the mudflat. Oxygen-containing functional groups of GRSP (CO, -COO^-, etc.) played a positive role in heavy metals accumulation. Redundancy analysis (RDA) showed that high soil pH was not conducive to the enrichment of heavy metals by GRSP. Besides, the concentrations of GRSP-Fe showed a significant positive correlation with the concentrations of other metals (Cu, As, and Pb) in GRSP. It is speculated that the Fe minerals in GRSP contributed the enrichment of heavy metals. Based on PARAFAC modelling, four fluorescent components of GDOM were identified, including three humic-like fluorescent components and one tyrosine-like fluorescent component. The contributions of GDOM to GRSP-bound heavy metals fluctuated between 4.05 % and 88.80 %, which could enhance the fluidity of heavy metals in water and weaken the soil heavy metal immobilisation capacity of GRSP. High salinity exerted an inhibitory effect on the heavy metal content of the GDOM. This study comprehensively explored the potential of GRSP to immobilise heavy metals in wetland soils and highlighted the potential heavy metal risks associated with the GDOM component in water, which could contribute to the multidimensional assessment and control of heavy metal pollution in coastal wetlands.

The coexistence of copper ions and TC affected the binding ability and the reaction order between extracellular polymeric substances of aerobic granular sludge and exogenous substances

As a barrier against external toxic effects, extracellular polymeric substances (EPSs) directly affect the toxicity and removal efficiency of exogenous substances. The reaction of EPSs with exogenous substances has been taken into consideration. The contents of EPSs in sludge cultivated by different influent water vary greatly, which leads to great differences in the binding ability and reaction sequence between EPSs and exogenous substances. However, the results in this respect are very limited. In this study, the binding characteristics between exogenous tetracycline (TC)/copper ions (Cu²⁺) and EPSs from aerobic granular sludge cultured under single and coexisting TC/Cu²⁺ were assessed by three-dimensional fluorescence-parallel factor analysis. The pollutants in the influent water could directionally induce microorganisms to secrete more EPSs, while fluorescence substances in EPSs could combine with the exogenous substances to lessen their effects. In the presence of coexisting TC and Cu²⁺ in the influent water, the ability of fluorescence substances in EPSs to combine with exogenous TC or Cu²⁺ weakened, and humic substances in EPSs were more susceptible than protein substances to binding with exogenous substances. However, the reaction order between EPSs components and exogenous TC or Cu²⁺ was opposite, and the ability of fluorescence substances in EPSs to combine with exogenous TC or Cu²⁺ was enhanced under individual TC or Cu²⁺ existing in the influent water. This study provided new insights into the interaction between EPSs and exogenous substances.

Unveiling the Role of Dissolved Organic Matter on the Hg Phytoavailability in Biochar-Amended Soils

Biochar can effectively reduce the phytoavailability of mercury (Hg) in soil, but the mechanisms are not fully understood. In this study, the dynamic changes in Hg content adsorbed by the biochar (BC-Hg), Hg phytoavailability in the soil (P-Hg), and soil dissolved organic matter (DOM) characteristics were determined over a 60-day treatment period. Biochar obtained at 300 °C, 500 °C and 700 °C reduced the P-Hg concentration assessed by MgCl2 extraction by 9.4%, 23.5% and 32.7%, respectively. However, biochar showed a very limited adsorption on Hg, with the maximum BC-Hg content only accounting for 1.1% of the total amount. High-resolution scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) results showed that the proportion of Hg atoms in biochar after 60 d was barely detectable. Biochar treatment can shift soil DOM toward higher aromatic content and molecular weight. Additionally, the addition of high-temperature biochar increased more humus-like components, but low-temperature biochar increased more protein-like components. Correlation analysis and partial least squares path modeling (PLS-PM) showed that biochar promoted humus-like fractions formation to reduce the Hg phytoavailability. This research has deepened the understanding of the mechanisms by which biochar stabilizes Hg in agricultural soils.

Pb0 flue gas biosorption in denitrifying MBfR: Characteristics and binding ability of extracellular polymeric substances

Pb⁰ in flue gas which is ubiquitous in the environment, poses a certain threat to human and ecology, but the study on EPS-dependent stabilization of lead to remove Pb⁰ from flue gas remains insufficient. In this investigation, the characteristics and heavy metals-binding ability of four EPS fractions were evaluated. The EPS were extracted from denitrifying membrane biofilm reactor (MBfR) and divided into slime EPS (S-EPS), loosely-bound EPS (LB-EPS), tightly-bound EPS (TB-EPS) and EPS in circulating flow (Y-EPS). The S, LB, TB-EPS related to Pb stabilization on biofilm need more attention. Compared to Pb-S-EPS (0.013 mg g^-1) and Pb-LB-EPS (0.13 mg g^-1), the Pb-TB-EPS (0.26 mg g^-1) was mainly stable form of vapor Pb⁰, since TB-EPS's higher content (30.67-82.44 mg g^-1 VSS), proteins (13.47-36.32 mg g^-1 VSS) and polysaccharides (9.37-32.48 mg g^-1 VSS) concentration. Particularly, proteins related ligands were more effective in S, LB, TB-EPS dependent adsorption of Pb, complexing with hydrophobic acid ligands further strengthened in TB-EPS adsorption. The Pb-EPS complex formed via binding with functional groups (such as O-H, N-H, C-H and CC) on EPS, also facilitated by loose structure of proteins. This study enlightens the researchers on the bio-treatment and EPS-dependent biosorption of Pb⁰ in flue gas in denitrifying MBfR.

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.

The calcium cyanamide and polyethylene blocks the secondary transmission and infection of vegetable leaf diseases

Continuous cropping obstacles, especially soil-borne diseases can cause serious harm to agricultural production and limit the sustainable development of modern agriculture. However, Corynespora blight is an important air-borne disease on cucumber leaves caused by Corynespora cassiicola. The pathogen also could survive in air-dried soil or plant residue for at least one month. However, it is not clear whether soil Corynespora blight residues can infect plants. We detected the dynamic change of C. cassiicola content in soil and air after returning the diseased and residual straw to the field in real time by PMA-qPCR detection method. In this study, we reveal for the first time a new mode of transmission in which leaf blade disease residues in soil can spread again into the air and infect plants. In polyethylene (PE) treatment, cucumber plants grew healthily without disease. However, the content of C. cassiicola in the soil still existed in the PE treatment at 10³ spore·g^-1. The disease index (DI) of cucumber was less than 3 in calcium cyanamide (CaCN₂). After fumigation and film removal and the whole growth period was controlled at a safe level. In addition, the PMA-qPCR detection method of Corynespora blight of cucumber was established for the first time in this study. In summary, CaCN₂ and PE treatments are effective ways to block the infection of cucumber leaves by Corynespora blight residues in soil. These treatments are considered to comprise a feasible and sustainable technique for vegetable leaf residues in greenhouses.

Insight into the Soil Dissolved Organic Matter Ligand-Phenanthrene-Binding Properties Based on Parallel Faction Analysis Combined with Two-Dimensional Correlation Spectroscopy

Dissolved organic matter (DOM) can strongly bind to organic contaminants and control phenanthrene in soil. Herein, four individual parallel factor analysis (PARAFAC) components were found in soil DOM. Component C1 was the humic-like component ligand T, and component C2 was a combination of humic fluorophore ligands M1 and M2. Furthermore, components C3 and C4 were characterized as terrestrial and ubiquitous humic substances. Then, the modified Stern-Volmer complexation model was used to reveal soil DOM component-phenanthrene-binding properties. The overall binding characteristics of a PARAFAC component could not express the phenanthrene-binding properties. Therefore, two-dimensional correlation spectroscopy was used to reveal DOM ligand-phenanthrene-binding properties. After binding with phenanthrene, DOM ligands T, M2, A2, and C1 were quenched but DOM ligands M1, A1, and C2 were excited. The ligands with higher humification presented higher phenanthrene-binding ability. With these promising results, the DOM ligand-phenanthrene-binding characteristics offered theoretical support for soil pollution control.

Quantitative study on the structure-bioavailability relationship of dissolved organic nitrogen in wastewater treatment plant effluent

This study systematically investigated the relationship between the structure properties and biological characteristics of dissolved organic nitrogen (DON) in the effluents from municipal wastewater treatment plants. Ultrafiltration, Fourier transform infrared (FTIR) spectroscopy, ultraviolet (UV) spectroscopy, and excitation-emission matrix (EEM) fluorescence spectroscopy were used to characterize the structure of organic matters in the effluent samples, and the bioavailability of DON was determined by algal/bacterial-based bioassay. The quantitative analysis of EEM spectra conducted by fluorescence regional integration method showed that the organic portion of all samples was mainly consistent with fulvic acid and protein. Combined with the bioassay results, a positive correlation between the DON bioavailability and the protein content (sum of region I and region II) (r = 0.80, P < 0.02) and soluble microbial byproduct-like materials (region IV) (r = 0.76, P < 0.03) were observed. Nevertheless, the humic substances content represented by the region III and V would negatively affect the DON bioavailability. High humification degree (high HIX value) (r =  - 0.77, P < 0.03) was related to low bioavailability. Furthermore, according to UV spectroscopy results, strong aromaticity (high UV254 values) (r =  - 0.78, P < 0.03) suggested low DON bioavailability. One protein-like component (C3) and two humic-like components (C1 and C2) were identified via fluorescence excitation-emission matrices-parallel factor analysis (EEM-PARAFAC), and component C3 values were positively correlated to the BAN/DON ratio (r = 0.74, P < 0.03). The ultrafiltration showed that the low molecular weight DON (< 3 kDa) accounted for 30-73% of the total DON, and no notable relationship was observed for DON molecular weight and its bioavailability.

Critical evaluation of the interaction between fluorescent dissolved organic matter and Pb(II) under variable environmental conditions

Dissolved organic matter (DOM) can strongly influence the behavior and risk of metal pollutants in aquatic ecosystems. However, a comprehensive study on the effects of DOM level and environmental factors on the binding of DOM with Pb(II) is lacking. This study examined the DOM-Pb(II) interaction in the river water under variable DOM level, pH, and major ions, using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Four humic-like and one protein-like component were identified, and the abundant humic-like components showed higher Pb(II)-binding fractions (f) than the protein-like component. The f of PARAFAC components decreased while the conditional stability constants (logK_M) increased for the diluted DOM, indicating the influence of DOM level on its metal binding. The DOM-Pb(II) interaction was sensitive to changes in pH, with generally higher f and lower logK_M at the alkaline condition due to changes in the DOM conformation. The addition of major ions significantly decreased the fluorescence quenching by Pb(II), due to competitive effects and potential DOM conformation changes at elevated ions. Overall, our results show that the DOM-Pb(II) complexation is highly dependent on both the DOM properties and environmental factors, which have implications for optimizing the experimental conditions and for comparing the results in different environments.

Characteristics of oxytetracycline stress-sensitive microbe-dissolved organic matter component interactions during composting

Dissolved organic matter (DOM) has important impacts on the transportation of antibiotics through chemical and biological processes in composting. The interaction between DOM and antibiotics is reciprocal. The interaction between DOM ligands and antibiotics could be characterized based on a technique combining parallel factor analysis (PARAFAC) and microbial community structure analysis. However, PARAFAC cannot reveal the dynamic changes in each DOM peak in one PARAFAC component under antibiotic stress. In this study, two-dimensional correlation spectroscopy (2DCOS) combined with PARAFAC and bacterial community diversity analyses were employed to reveal the effects of oxytetracycline (OTC) stress and the key microorganisms on the transformation of different fluorescent peaks from DOM PARAFAC components during chicken manure composting. The results showed that OTC inhibits the transformation between DOM PARAFAC components by inhibiting the core microbial activities involved in the transformation of DOM components. Protein-like components (C1 and C2) were more sensitive to OTC residue, and components with a high humification degree promoted the degradation of OTC. The interaction between special DOM PARAFAC components and certain bacteria affects the degradation of OTC. The DOM PARAFAC components A2(C1), B1(C2), B2(C2) and Z1(C4) enhanced OTC degradation by stimulating the genera Pseudomonas, Glycomyces and Hyphomicrobium. With these promising results, the true effect of DOM PARAFAC components on the degradation of OTC can be revealed, which is helpful for addressing antibiotic contamination to improve the bioavailability of compost products.

Insight into complexation of Cd(II) and Cu(II) to fulvic acid based on feature recognition of PARAFAC combined with 2DCOS

Fulvic acid which could govern the environmental geochemistry behavior of heavy metals is considered as the eco-friendly substances for controlling heavy metal pollutants in environment. Knowledge on the individual fulvic acid ligand is crucial to characterize the effect of fulvic acid on the migration and toxicity of metal pollutants. Herein, fulvic acid substances were analyzed by fluorescence quenching associated with parallel factor analysis (PARAFAC). Three components were identified based on PARAFAC. Furthermore, two-dimensional correlation spectroscopy (2DCOS) associated with complexation model were used to elucidate the Cd(II)- and Cu(II)-binding characteristics of the individual fulvic acid ligand. The Cd(II)- and Cu(II)-binding capability and speed of different fulvic acid ligands were revealed and theoretical guidance and technical support were provided for the practical application. The Cd(II) contaminated soil could be amended with high fulvic acid ligands A1 and Y2 containing composting products and the Cu(II) contaminated soil could be amended with high fulvic acid ligands Y1, T1 and A1 containing composting products to control the pollution and improve the soil condition. Based on these excellent results, the different fulvic acid ligands-contaminants-binding properties was characterized for the theoretical supporting of environmental pollution control.

Effects of exogenous cellulose-degrading bacteria on humus formation and bacterial community stability during composting

This study aimed to reveal the potential mechanism of influence exogenous cellulose-degrading bacteria (ECDB) exerted on humus synthesis during the co-composting of corn straw and cattle manure. By measuring the changes in physicochemical factors and bacterial communities, it was revealed that inoculation with ECDB enhanced the driving force of cellulose degradation and humus synthesis. ECDB not only directly participated in cellulose degradation as degrading bacteria, but also changed the bacterial community succession, and increased the abundance of bacterial communities associated with cellulose degradation. The results showed that ECDB stimulated the potential functions and interactions of bacterial communities. Structural equation modeling confirmed that ECDB acted mainly as a bioactivator to promote humus formation in co-composting of corn straw and cattle manure. Taken together, these findings offered new strategies which can be effectively utilized to increase the efficiency and quality of corn straw composting.

FT-IR and synchronous fluorescence two-dimensional correlation spectroscopic analysis on the binding properties of mercury onto humic acids as influenced by pH modification and sulfide addition

Mercuric Hg²⁺ ion forms strong complexes with dissolved organic matter (DOM) in natural waters. The complexation of Hg²⁺ by sulfhydryl groups of DOM was regarded as the main mechanism for Hg²⁺-DOM interactions, particularly in anoxic sulfur and DOM-rich environments. In the present study, the influences of pH and sulfide addition on the molecular structure of Hg²⁺-DOM complexes and the characteristics of Hg²⁺ binding to DOM were investigated using FT-IR and synchronous fluorescence two-dimensional correlation spectroscopic analysis. Results showed that, during the Hg²⁺ binding process, the aromatic hydrogen CH in humic acids (HA) gave the fastest responses to pH perturbation and the S-reacted HA (S-HA) exhibited different reaction patterns from the unreacted HA. In S-HA, the esters/alcohols CO and carboxyl CO gave the fastest responses to Hg²⁺ binding. In the process of S-HA binding to Hg²⁺, the protein-like fractions including proteins, amino acids or monoaromatics played the leading role. Sulfide addition of HA enhanced the reactivity of small molecular weight compounds with low aromaticity and improved the binding ability of protein-like fractions to Hg²⁺. These findings provide a better understanding of the interaction mechanisms between Hg²⁺ and DOM at a molecular level and have important environmental implications in Hg²⁺ biogeochemical transformation, transport and cycling.

Effects of photo-irradiation on mercury binding to dissolved organic matter: Insights from FT-IR and synchronous fluorescence two-dimensional correlation spectroscopy

The binding interactions between Hg and dissolved organic matter (DOM) affect the fate and transport of Hg in the aquatic environment. Here, we investigate the effects of photo-irradiation on the binding characteristics of dissolved organic matter with Hg(II) using FT-IR and synchronous fluorescence two-dimensional correlation spectroscopy (2D-COS). Results showed that the binding of Hg(II) onto humic acid (HA) followed the order of humic-like fraction > fulvic-like fraction > protein-like fraction and photo-irradiation did not affect this order. The binding affinity of each site within the fluorescent fraction was affected by the photoreaction patterns. Pre-irradiation of HA before Hg(II) binding changed its structures and binding ability. UV irradiation showed a more obvious effect on Hg(II)-HA complexes than solar irradiation, and UV irradiation enhanced the reactivity of aromatic groups of HA. The amine or amide N-H of HA played a leading role in binding with Hg(II) in the dark, whereas the aromatic amine C-N became dominant after UV irradiation. In fulvic acid (FA), the aromatic hydrogen C-H played a leading role in Hg(II) binding in the dark, but solar irradiation promoted the binding ability of polysaccharide C-O and the carboxyl CO became dominant after UV irradiation. The response sensitivity of the fulvic-like fraction to Hg(II) was higher than that of the protein-like fraction in FA. Multiple types of sites binding to Hg(II) were verified in the fulvic-like fraction and protein-like fraction of FA. These findings provide new insight into photo-induced structural changes of DOM upon Hg binding.

Cattle manure compost humification process by inoculation ammonia-oxidizing bacteria

The effectiveness of newly isolated ammonia-oxidizing bacteria (AOBs; T-AOB-2, M-AOB-4 and MT-AOB-2-4) in promoting organic matter degradation and humification of cattle manure compost was explored. The results show that, compared with the control, the inoculation of AOBs (5%, v/w) promoted the humification process, particularly in the MT-AOB-2-4, which showed the lowest total organic carbon (19.13%) and dissolved organic carbon (2.61%), whereby humic substances (C_EX) and humic acid (C_HA) increased to 89.84 g/kg and 85.20 g/kg, and fulvic acid (C_FA) decreased to 4.63 g/kg. The high-throughput sequencing and quantitative PCR showed that the abundance of Bacillaceae, amoA and nirS had a significant correlation with humification factors. Among the treatments, the inoculation of MT-AOB-2-4 provided the driving force for the composting process by enhancing the bacterial activity and had the most significant effect on the formation of humic substances and the efficiency of organic matter decomposition.

Insight into interactions of heavy metals with livestock manure compost-derived dissolved organic matter using EEM-PARAFAC and 2D-FTIR-COS analyses

Dissolved organic matter (DOM), as the most active ingredient in compost, directly determines the speciation and environmental behavior of HMs. Here, the binding properties of DOM derived from chicken-manure compost (CHM), cow-manure compost (COM) and pig-manure compost (PIM) with HMs were explored by analyses of Fluorescence excitation-emission matrix parallel factor (EEM-PARAFAC) and two-dimensional correlation Fourier transform infrared spectroscopy (2D-FTIR-COS). Results showed that the binding characteristics vary with origin of DOM and type of HMs. The fulvic-like component dominated the transformation of HMs speciation, and CHM-DOM had higher affinity with HMs and greater risk causing pollution due to its higher aromaticity, molecular weight and distribution of fluorescent components. Moreover, Cu(II) can efficiently bind to DOM with the stability constants (log k_M) ranging from 4.53 to 5.38, followed by Pb(II) (3.34-3.57), whereas Cd(II) can hardly bind to DOM. The amide and polysaccharide were the predominant sites for HMs binding in CHM-DOM, and polysaccharide and phenolic in COM-DOM, while phenolic and amide in PIM-DOM, respectively. Although the proportion of protein-like components and non-fluorescent polysaccharides in DOM were low, their role in HMs binding should not be ignored. In brief, the environmental risk caused by livestock manure compost may originate from interactions between DOM and HMs.

Difference and interplay of microbial communities, metabolic functions, trophic modes and influence factors between sludge and bulking agent in a composting matrix

The difference and interplay of microbial communities, metabolic functions and influence factors between sewage sludge and bulking agent were evaluated in 60 days composting. Results showed that fungal communities were mainly affected by pH (42.4%) and ORP (35.9%) of sludge but by VS (41.1%) and temperature (34.7%) of sawdust in a composting system. Bacterial communities were primarily affected by VS (43.5%) and C/N (34.8%) of sludge but by ORP (44.5%) and temperature (31.0%) of sawdust. Tepidimicrobium dominated in the sludge at thermophilic period, while Alcaligenes prevailed in the sawdust. Bacterial carbon metabolism was significantly higher in the sludge than that in the sawdust except carbohydrate metabolism. Saprophytic fungi were the main trophic mode both in the sludge and sawdust. Water transfer facilitated Aspergillus and Trichosporon moving from sludge to sawdust to decompose lignocellulose. Ammonia transfer promoted the migration of Alcaligenes and Pseudomonas from sludge to sawdust and facilitated ammonia assimilating.

δ-MnO2 changed the structure of humic-like acid during co-composting of chicken manure and rice straw

Improving the structure and quantity of humus is important to reduce agriculture organic waste by composting. The present study was aimed to assess the role of δ-MnO₂ on humus fractions formation during co-composting of chicken manure and rice straw. Two tests (control group (CK), the addition of δ-MnO₂ (M)) were carried out. The results showed that organic matter content decreased by 34% and 29% at M and CK, suggesting the process of organic waste disposal was accelerated by adding δ-MnO₂. The structures and quantity of fulvic acid (FA) and humic acid (HA) (as the main fractions of humus) were investigated. The δ-MnO₂ had no significant effect on improving the concentration of FA and HA (p > 0.05). However, the addition of δ-MnO₂ caused different effects on the FA and HA structure. The humification degree of FA improved, while bioavailability of HA increased through adding δ-MnO₂. The addition of δ-MnO₂ rephased the bacterial community structure, slowing down the succession rate of the bacterial community in M composting. After adding δ-MnO_2, the structural equation modeling results showed that environmental factors could directly drive changes in FA and HA by modulating the bacterial community. Furthermore, the role of FA and HA in the soil amendment was also demonstrated. Therefore, the addition of MnO₂ might be promising for agriculture organic waste treatment and environmental repair during composting.

Phosphorus sorption - Desorption behaviors in the sediments cultured with Hydrilla verticillata and Scripus triqueter as revealed by phosphorus fraction and dissolved organic matter

The migration of sediment phosphorus (P) could be affected by the existence of aquatic plants. To explore the effects of aquatic plants on the P sorption-desorption behaviors in the sediments, sediment in Caohai wetland was collected and cultured with the submerged plant (Hydrilla verticillata) and emerged plant (Scripus triqueter). Then the sorption and desorption experiments were performed, and physicochemical properties, P fractions, and dissolved organic matter (DOM) characteristics were evaluated. Results showed that the treated sediments exhibited similar P sorption kinetic process fitted well with the two-compartment first-order model. Nevertheless, H. verticillata cultured sediment could be well described by the modified Langmuir isotherm model, while S. triqueter cultured sediment fitted the modified Freundlich equations well. The obvious changing P fractions in cultured sediments were BD-P and NaOH-SRP during sorption. H. verticillata and S. triqueter displayed different sorption-desorption behaviors by altering BD-P, humification index, fluorescence intensity, and PARAFAC component contents in sediments. Compared to raw sediment, H. verticillata presented higher P sorption and lower P release from sediments by decreasing BD-P and increasing DOM (fulvic acid-like and humic-like components) content, while S. triqueter showed adverse P sorption and release effects by reducing DOM components. The growth of submerged plants was suggested to make a positive influence on the high efficiency of P retention capacity and low release risk.

New insights into mechanisms of sunlight- and dark-mediated high-temperature accelerated diurnal production-degradation of fluorescent DOM in lake waters

The production of fluorescent dissolved organic matter (FDOM) by phytoplankton and its subsequent degradation, both of which occur constantly under diurnal-day time sunlight and by night time dark-microbial respiration processes in the upper layer of surface waters, influence markedly several biogeochemical processes and functions in aquatic environments and can be feasibly related to global warming (GW). In this work sunlight-mediated high-temperature was shown to accelerate the production of FDOM, but also its complete disappearance over a 24-h diurnal period in July at the highest air and water temperatures (respectively, 41.1 and 33.5 °C), differently from lower temperature months. Extracellular polymeric substances (EPS), an early-state DOM, were produced by phytoplankton in July in the early morning (6:00-9:00), then they were degraded into four FDOM components over midday (10:00-15:00), which was followed by simultaneous production and almost complete degradation of FDOM with reformation of EPS during the night (2:00-6:00). Such transformations occurred simultaneously with the fluctuating production of nutrients, dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and the two isotopes (δ¹⁵N and δ¹⁸O) of NO₃^-. It was estimated that complete degradation of FDOM in July was associated with mineralization of approximately 15% of the initial DOC, which showed a nighttime minimum (00:00) in comparison to a maximum at 13:00. FDOM identified by excitation-emission matrix spectroscopy combined with parallel factor analysis consisted of EPS, autochthonous humic-like substances (AHLS) of C- and M-types, a combined form of C- and M-types of AHLS, protein-like substances (PLS), newly-released PLS, tryptophan-like substances, tyrosine-like substances (TYLS), a combined form of TYLS and phenylalanine-like substances (PALS), and their degradation products. Finally, stepwise degradation and production processes are synthesized in a pathway for FDOM components production and their subsequent transformation under different diurnal temperature conditions, which provided a broader paradigm for future impacts on GW-mediated DOM dynamics in lake water.

The quality of dissolved organic matter extracted at different times from pig compost and its copper binding capacity based on EEM-PARAFAC

Dissolved organic matter extracted from compost tea, can be regarded as alternatives to inorganic fertilizers as well to be used as a washing agent for heavy metal polluted soil. However, the composition and quality of compost tea produced under different extraction time are still unknown. The objective of the current study was set to explore the influence of different extraction time (i.e., 6, 12, and 24 h) on the composition, quality, and copper binding capacity of compost tea originated from pig manure compost. The results indicated that the extraction time obviously influenced the phenolic, aromatic carboxylic, and polycyclic aromatic groups of compost tea. In addition, the compost tea undergo the shorter extraction time (i.e., 6 and 12 h) contained more protein and humic-like compositions. Among the all treatments tested herein, the compost tea produced from 12 h extraction time obviously exhibited higher aromaticity, molecular weight, and humification degree than other two treatments. The highest stability constant value (log K_M) was observed for the shortest extraction time, i.e., 6.08. According to the quality measures and copper binding capability, shorter extraction times (i.e., 6 and 12 h) would be suggested for compost tea production from pig manure compost.

Oxytetracycline stress reconstruct the core microbial community related to nitrogen transformation during composting

This study investigated oxytetracycline (OTC) effects on nitrogen (N) transformation and bacterial community diversity during chicken manure composting. The addition of OTC inhibited nitrifying bacteria, resulted in a decrease in the transformation of NH₄⁺-N to NO₃^--N during composting, and affected in the order T3 (32.76%) > T2 (28.76%) > T1 (17.02%) > CK. The OTC could act as an inhibitor against core microbial growth, leading to a delay effect during composting. 16S rRNA sequencing was employed for the functional prediction, and results indicated the bacterial community related to N transformation reconstructed under OTC stress. The core microorganisms were changed after OTC addition, with the emergence of Bacillus and Thermobifida, which could inhibit the N transformation by network analysis. Therefore, core microorganisms could be regulated to reduce the negative of OTC impacts on N transformation and thus reduce N loss during composting.

Reconstruction of core microbes based on producing lignocellulolytic enzymes causing by bacterial inoculation during rice straw composting

The aim of this paper was to identify the core microbes of producing lignocellulolytic enzymes during rice straw composting with functional bacterial agents inoculation. The results indicated that inoculation functional bacterial agents accelerated the degradation of organic matter and coarse fiber content by 7.58%, 8.82%, which were due to the fact that key enzymes and core microbes were stimulated. In addition, inoculation have reconstructed core microbes of producing lignocellulase. Meanwhile, inoculation functional bacterial agents not only as core bacteria to produce cellulase, xylanase and manganese peroxidase (MnP), but also increased most core microbial abundance. Redundancy analysis indicated that CMCase, xylanase, total nitrogen and MnP as key factors to affect the degradation of organic fractions in the core bacterial communities, while in the core fungal communities, were mainly affected by environmental factors (except for MnP). This study provided a theoretical basis for the efficiently degradation during agricultural wastes composting.

Humus formation driven by ammonia-oxidizing bacteria during mixed materials composting

The aim of this study was to identify the effects of ammonia-oxidizing bacteria (AOB) inoculation on humus formation. Both nitrogen conversion and humus formation were considered as the main processes, because NH₄⁺-N-like compounds not only substrates of nitrification, but also precursors of humus. During composting, the inoculation of AOB indeed increased humus concentration by fixing NH₃ emission as NH₄⁺-N, but it has also promoted nitrogen transformation. While the main reason was the changed bacteria community structure caused by inoculating AOB. Moreover, the relationship between bacteria and nitrogen transformation and humus formation has become closer. And bacteria were more likely to synthesize humus. Therefore, it is conjectured that AOB inoculation could not only provide NH₄⁺-N for humus formation, but also enhance the anabolism of microorganisms. This suppose has been confirmed by structural equation model in this study. Therefore, AOB inoculation has a driving effect on promoting humus formation.

Revealing the Inner Dynamics of Fulvic Acid from Different Compost-Amended Soils through Microbial and Chemical Analyses

The formation of fulvic acid (FA), an aromatic compound, is affected by the compost amendment. This study aimed to assess the extent of the humification of FA in soil amended with seven different composts. Results showed that composts improved the FA concentration in soil. Parallel factor (PARAFAC) analysis, combined with hetero-two-dimensional correlation spectroscopy (hetero-2DCOS), indicated that the inner changes in FA components determined the evolution of mineralization. The diversity in the composts used and the dominant microbes present might be responsible for the evolution of different mechanisms of FA transformation. Structural equation models (SEMs) demonstrated that the FA components were transformed directly by microbes, or indirectly via changes in the total organic carbon (TOC) and total nitrogen (TN) contents, C:N ratio, humic substance (HS) levels, and humic acid (HA): FA ratio, which regulate the microbial community structure. Our results will be useful for improving the bioavailability of compost products and realizing sustainable utilization of the soil.

Indirect effect of nutrient accumulation intensified toxicity risk of metals in sediments from urban river network

The levels of metals in sediments of urban river ecosystems are crucial for aquatic environmental health and pollution assessment. Yet little is known about the interaction of nutrients with metals for environmental risks under contamination accumulation. Here, we combined hierarchical cluster, correlation, and principal component analysis with structural equation model (SEM) to investigate the pollution level, source, toxicity risk, and interaction associated with metals and nutrients in the sediments of a river network in a city area of East China. The results showed that the pollution associated with metals in sediments was rated as moderate degree of contamination load and medium-high toxicity risk in the middle and downstream of urban rivers based on contamination factor, pollution load index, and environmental toxicity quotient. The concentration of mercury (Hg) and zinc (Zn) showed a significant correlation with toxic risks, which had more contribution to toxicity than other metals in the study area. Organic nitrogen and organic pollution index showed heavily polluted sediments in south of the study area. Though correlation analysis indicated that nutrients and metals had different input zones from anthropogenic sources in the urban river network, SEM suggested that nutrient accumulation indirectly intensified toxicity risk of metals by 13.6% in sediments. Therefore, we suggested the combined consideration of metal toxicity risk with nutrient accumulation, which may provide a comprehensive understanding to identify sediment pollution. Graphical abstract Toxicity rate of metals in sediments from urban river network indirectly intensified by nutrients accumulation.

Roles of different humin and heavy-metal resistant bacteria from composting on heavy metal removal

This study aims to assess the roles of different humin and heavy-metal resistant bacterial community from composting on heavy metal removal. The results showed that the concentration of Cu²⁺, Zn²⁺, Ni²⁺, Pb²⁺, Cr³⁺ and Cd²⁺ decreased with adding the compost-derived humin, but the removal rates were relatively low (<30% on average). The heavy metal resistant bacteria from composting have better metal binding capacities than humin, and the combined addition of humin and bacteria could further stimulate the biosorption of heavy metals with 60-80% removal of metals and improve the diversity and biomass of bacterial community. There was obviously increased synergy between the humin from maturity phase and bacteria for metal biosorption ("1 + 1 > 2"). Structural equation modeling showed that microbial biomass and humin humification are the key factors for the biosorption of heavy metals. Combining humin from maturity phase with heavy-metal resistant bacteria was suggested to control heavy metal pollution in composts.