Changes In Humic Acids Research Articles

Hydrodynamic cavitation effects over complex organic mixtures

Hydrodynamic cavitation (HC) is a promising technology for the intensification of chemical and physical processes, with applications in wastewater treatment, extraction from suspended solids, and disinfection. In this study, the effects of HC on different model compounds for dissolved organic matter (DOM) were investigated. These compounds, such as lignin, humic acids, and protein-like compounds, are commonly present in organic wastewaters and were studied under various conditions. Specifically, changes in UV-Vis spectra and fluorescence properties resulting from HC treatments were analyzed. Results show that HC had distinct effects on the spectral indices, fluorescence intensity, and peak positions of the model compounds. Changes in humic acid and lignin were attributed to the oxidation and fragmentation of polymers, while changes in tryptone were explained by the polymerization and partial oxidation of its amino acids. Pyrolysis was found to be the dominant mechanism affecting non-polar substances, such as zwitterions in tryptone, whereas radical attack predominantly affects hydrophilic compounds like large, charged molecules like humic acids. Large molecules with both charged and non-charged groups, such as lignin, experienced a mixed effect. Findings in this work provide a comprehensive understanding of HC effects on various DOM model compounds. These results could aid in the development of more efficient HC-based treatment processes for organic pollutants.

Analysis of Molecular Structure Changes in Humic Acids from Manure-Amended Soils over 17 Years Using Elemental Analysis and Solid-State 13C Nuclear Magnetic Resonance Spectroscopy

Soil organic matter (SOM) plays an important role in regulating plant nutrient availability. Here, the effects of the long-term application of different forms of processed swine manure on the SOM structure are explored through the analysis of humic acid (HA) using elemental analysis and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. The HAs from soils amended with liquid swine manure (LSM) and swine manure compost (SMC) are found to be more humified compared to the soils treated with solid swine manure (SSM) and the control (CK). The H/C and O/C molar ratios suggest that carboxyl-rich aliphatic structures are the most important class of biomolecules contributing to the LSM- and SMC-HA structures, while lignin-like structures are the most important biomolecules contributing to the CK- and SSM-HAs. SSM promoted the formation of aliphatic polar structures, which are more susceptible to aerobic biodegradation, whereas the CK facilitated the inclusion of condensed aromatic structures into the HA. Apart from the LSM-HA, the proportion of carboxylic acid functional groups reduced with manure application, while the proportion of phenolic acid functional groups increased. LSM-HA has the highest potential to enhance plant nutrient availability.

Monitoring Organic Matter Humification during the Composting of Date Palm Wastes Using Chemical and Spectroscopic Analyses for Arid Soil Quality Improvement

ABSTRACT Soil organic matter (SOM) is the most important factor that affects soil quality. In arid areas, lack of SOM causes a major problem and farmers need to add organic amendments to restore the soil quality. Organic waste composting is an efficient and sustainable way to produce organic resource for soil amendment. The main objective of this study was to evaluate the effectiveness of compost derived from co-composting of date palm residues with goat manure to ameliorate soil quality in arid region in the southeast of Tunisia. Palm tree wastes were co-composted with goat manure (1/3 v:v) for 120 days. Chemical properties and structural changes of humic acids (HA) during the composting process were investigated using physicochemical and spectroscopic analyses: spectroscopic ultraviolet/visible (UV) analysis and Fourier Transform Infrared (FTIR) Spectroscopy. HA fractions extracted from different steps of composting process were monitored by measuring humification ratios CHA/CFA and E4/E6. Soil was amended with produced compost and manure during 3 months, and soil property evolution was evaluated using chemical and spectroscopic analyses. Results revealed that the date palm compost displayed neutral pH, a C/N ratio of about 12 and high levels of nutrients. FTIR spectra of HA extracted from produced compost and manure showed the abundance of aromatic structures with a high condensation and polymerization confirmed by a low E4/E6 ratio related to the increase in polymerization and polycondensation and a high CHA/CFA humification rate that improved the elevation of the humification degree. The application of the produced palm compost in soil improved soil quality by increasing levels of SOM and nutrients and showed a marked improvement of humification rate. The FTIR spectra of soil HA showed a clear increase in aromatic structures that improved soil stability. The input of palm compost is an efficient way to ameliorate arid soil quality by supplying highly humified organic matter restitution.

Humus Transformation and Compost Maturity Indexes in High-Temperature Composting of Livestock and Poultry Manure

Based on the variations of total humus, humic acid (HA), and fulvic acid (FA) during the manure composting process, the transformation of substances in humus was analyzed, and the compost maturity indexes were constructed by using the TC-TN ratio (C/N), ratio of total humus and total organic carbon (TOC), and humification index (HI). The results showed that: (1) The total humus content in the compost heap decreased firstly and then increased. When compost finished, the total humus content of R1, R2, and R3 was 8.33±0.31, 7.56±0.21, and 7.14±0.35%, respectively; (2) The changes of humic acid (HA) and fulvic acid (FA) concentrations in the three kinds of manure were basically consistent with the changes in total humic acid, which decreased first and then increased; (3) When experiments finished, the ratio of total humus and TOC decreased firstly and then increased. At the end of day 30, HI index was 1.25, 1.15, and 1.01, respectively, increasing by 48.8, 45.56, and 31.16%, respectively.

Dynamic Changes of Humic Acids in Chicken Manure Composting

Dynamic Changes of Humic Acids in Chicken Manure Composting

Assessing Factors Controlling Structural Changes of Humic Acids in Soils Amended with Organic Materials to Improve Soil Functionality

Humic acids (HAs) regulate soil chemical reactivity and improve many soil functions. The amendment of soil with organic materials increases soil organic matter (SOM) content and promotes the formation of HAs. However, the effect of the type, frequency and duration of amendment, and pedoclimatic conditions on SOM transformation and HA structural changes remains unclear. Herein, four experimental field sites (S1–4) with short-to-long-term organic fertilisation schemes were used to assess the effects of such factors, i.e., S1: loamy sand amended once with farmyard manure (FYM), brown coal waste (BCW), and biochar (BIO) for 0.5 and 1.5 years; S2: silt loam amended once with BIO for 8 years; S3: loamy sand amended every 5 years with FYM for 94 years; and S4: clayey silt amended every 2 years with FYM for 116 years. All HAs were extracted and analysed for structural differences by elemental analysis (EA), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), solid-state cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C-NMR), and differential scanning calorimetry (DSC). Results from EA, FTIR, and NMR showed that the long-term samples from S3 (treatments, T9–T10) and S4 (T11–T12) had the greatest aromatic characteristics, which increased with FYM amendment (T10 and T12). These agreed with DSC data, which indicated lower aliphatic contents compared with other samples. Samples from S2 (T7–T8), with receded amendment effects, had less aromatic and greater aliphatic characteristics compared with the short-term samples, S1 (T1–T6). In S1, structural changes were limited, but aromaticity increased with BIO (T3 and T6) compared with corresponding FYM (T1 and T4) and BCW (T2 and T5) amendments due to inherently high aromatic groups in the former. Overall, the results showed that the site (due to differences in pedoclimatic conditions), field age of OM, and amendment frequency were the main factors that influenced HA structure, and hence SOM transformation. Regular, long-term organic amendment increases the aromatic characteristics of HAs, which can improve soil functionality, but short-term structural improvements are achievable only when amending material is rich in aromatic compounds.

Combining humic acid with phosphate fertilizer affects humic acid structure and its stimulating efficacy on the growth and nutrient uptake of maize seedlings

This paper analyzed the compositional and structural changes of humic acid (HA) after combined with phosphate fertilizer (PHA), and investigated its effects on the growth of maize seedlings with four humic acid concentrations. The results showed that the atomic ratios of O/C and (O + N)/N of PHA were significantly lower than those of HA, which indicated that PHA had poor hydrophilicity compared with HA. The spectra of FTIR and NMR results suggested that the relative content of carboxyl group in PHA was higher than that in HA. X-ray photoelectron spectroscopy technology showed that the relative amount of C–C in PHA was lower than that in HA, while C–H was the opposite. The above changes were attributed to the crack of HA structure during the preparation of humic acid enhanced phosphate fertilizer, which was verified by the results from the determination of gel permeation chromatography that there were more low molecular weight components in PHA than that in HA. However, compared with HA, PHA showed a worse effect in promoting growth and the uptake of nitrogen, phosphorus and potassium by maize seedlings. This worse effect might be attributed to the poor hydrophilicity and unsuitable addition amount of PHA.

PHOTOCATALYTIC ACTIVITY OF IN-SITU FE-DOPED TIO2 FOR NATURAL ORGANIC MATTER REMOVAL

Humic acids represent a major fraction of natural organic matter (NOM) in aquatic environments. Having undefined composition and complex ill-defined structures, their presence in natural waters is undesirable. In this study, solar photocatalytic activity of synthesized Fe-doped TiO2 photocatalysts was investigated for the degradation of a 100 kDa molecular size fraction of humic acid. For this purpose, catalysts comprised of 5 different molar ratios of Fe/Ti were prepared by in-situ sol gel method and characterized by FTIR and Raman spectroscopy. Optimum loadings of the catalysts were determined and the kinetics of humic acid removal was investigated focusing on UV–vis spectroscopic parameters. Moreover, fluorescence techniques such as excitation-emission matrix (EEM) were also acquired for elucidating induced structural changes of humic acid during photocatalytic degradation. Results revealed that, using photocatalysts prepared by in-situ sol-gel method 20 to 25% removal of humic acid could be attained after photocatalytic treatment of 120 min.

Influences of Nitrogen Application Levels on Properties of Humic Acids in Chernozem Amended with Different Types of Organic Materials

The objective of this study was to examine the structure changes in humic acids (HAs) in Chernozem after the application of different types of organic materials (OMs) under an indoor simulation condition for plastic mulched drip irrigation, measured with Fourier transform infrared (FTIR) spectroscopy. The biotechnological extract of fulvic acid (BFA), decomposed sheep manure (M), corn straw pellets (Ps) and corn straw powder (Pr) were used as the four OMs for testing, and they were applied to Chernozem at the same amount of actual material; three nitrogen (N) levels (no N, low N, and high N supply) were applied to each type of (OMs), separately. The total culture period was set to 90 days and soil sampling was taken at 0, 30, 60 and 90 days, respectively. The results showed that different types of OMs exerted different effects on Chernozem based on the FTIR spectra of HAs. The application of M combined with high N supply was the best way to fertilize Chernozem, under which the H-bonded OH groups and aromatic compounds were enhanced, resulting in increased soil carbon (C) sequestration; while the carbohydrates in HAs was easily consumed as microbial energy substance. The HAs from the Chernozem amended with BFA became more aliphatic, simpler and younger. High N supply was beneficial for increasing the complexity of HAs from Chernozem amended with Ps, but was not conducive to soil cation retention. Within a short time of incubation, the application of Pr combined with high N was detrimental to the C sequestration in Chernozem, and inhibited the consumption of carbohydrates by microorganisms.

Changes in bacterial community structure and humic acid composition in response to enhanced extracellular electron transfer process in coastal sediment.

Humic acids are one of the main organic matters in sediments and contribute importantly to the marine biogeochemical cycles. Extracellular electron transfer is a ubiquitous natural process and has potentials to change the macrostructure of humic acids which can act as an electron shuttle. By setting up marine sediment microbial fuel cells, the present study revealed that enhanced extracellular electron transfer process could increase the content of C and H, but decrease the O content in humic acids, which could result in an increased aromaticity and decreased polarity of humic acids, whereas no significant changes occurred to the humification degree of the humic acids. Specific bacterial groups as potential exoelectrogens including Proteobacteria (especially Pseudomonas strains) and Firmicutes were enriched under enhanced extracellular electron transfer process, indicatingthat they were active to exchange electrons and might play important roles during the changes of humic acids, while the relative abundance of Verrucomicrobia and Bacteroidetes was reduced during these processes. The results of the present research shed lights on the relation between exoelectrogens and the transformation of humic acids in coastal sediment, while the microbial process and mechanisms behind it require further study.

Long‐term mineral fertilization in paddy soil alters the chemical structures and decreases the fungistatic activities of humic acids

Fungistatic activity is a newly identified ecological function for soil humic acids. However, the relation between fungistatic activities of soil humic acids and their chemical structures is still unclear. In addition, how fertilizer application affects fungistatic activity is still unknown. We sampled paddy soils with different long‐term fertilizer schemes, namely: unfertilized control (CK), mineral fertilizer applied (NPK) and mineral fertilizer applied plus straw return (NPKRS). Soil humic acids were extracted and their fungistatic activities against 14 phytopathogenic fungi were investigated to evaluate their ecological functions. The humic acids from NPK and NPKRS treatments showed much smaller fungistatic effects than those from CK treatments. The chemical structures of humic acids were investigated by 13C nuclear magnetic resonance (13C NMR) spectroscopy. Long‐term fertilization significantly changed the chemical structure of soil humic acid, and the variation in chemical structure affected the fungistatic activities. The relative content of alkoyl C and alkyl C, the alkoyl C/alkyl C ratio and aliphaticity all had positive correlations with the fungistatic effects of humic acids. That indicated humic acids with more aliphatic and decomposable structures showed more fungistatic activity. From the results, we believe that long‐term application of mineral fertilizer in paddy fields makes the soil humic acids less aliphatic and more recalcitrant, and concomitantly weakens their ability to inhibit phytopathogenic fungi.Highlights We studied the inhibitory effects of paddy soil humic acids on 14 phytopathogenic fungi. Fertilization‐induced changes in humic acids affect inhibition of phytopathogenic fungi. Long‐term mineral fertilization significantly changed chemical structures of humic acids. Humic acid with more aliphatic and decomposable structures had more fungistatic activity.

The properties and dynamic changes of DOM subfractions during food waste and sugarcane leaves co-composting.

The purpose of this research was to evaluate the properties and dynamic changes of humic acids (HA), fulvic acids (FA), hydrophobic neutrals (HoN), and hydrophilic (Hi) fractions of dissolved organic matter (DOM) during food waste and sugarcane leaves co-composting process. The pools of HA, FA, HoN, and Hi were separated from DOM by fractionation method, and characterized using spectroscopic (UV-vis, FTIR) and pyrolysis-GC/MS analyses. The least peaks in the HA pool were found in FTIR spectra with the simple structure in HA. The highest value of SUV254 was observed in HA, indicating that the HA pool played a dominant role in aromaticity of DOM. Hydrophobic compounds (HA, FA, HoN) had higher percentages of alkanes and cyclo-alkanes at the end of composting, while lower contents in the Hi pool. Both DOM and its subfractions increased the Chinese flowering cabbage (Brassica campestris L.) seed germination rate (SGR), whereas HA had a significant effect on promoting the root growth.

Investigation of humic acids concentration in different seasons in a raw water canal, Bangkok, Thailand

Abstract This study presents an overview of the changes in humic acids, which are disinfection by-product precursors in a raw water canal, Bangkok, Thailand, during different seasons. Fluorescence excitation–emission matrix (EEM) spectroscopy was employed to characterize and quantify spatial and seasonal variations of dissolved organic matter (DOM) along a raw water canal of the Metropolitan Waterworks Authority (MWA) Bangkok, Thailand. A total of 276 raw water samples were collected from 23 stations during the winter, summer and rainy season. Results indicate that hydrophobic fractions made up the majority of DOM and this water source also had high specific UV absorbance (SUVA). Seasonal variation of DOM was found to be more pronounced than geographical variation along the canal. The presence of humic substances was the highest in the rainy season due to rainfall and surface runoff, while soluble microbial by-product-like substances were found only in summer. The results provide an insight into the prediction of humic acids in source water, which benefits the MWA in being aware of seasonal variation in water quality.

Induced structural changes of humic acid by exposure of polystyrene microplastics: A spectroscopic insight.

The occurrence of microplastics (MPs) as emerging contaminants in the environment may cause changes in water or sediment characteristics, and further affect their biogeochemical cycles. Thus, insights into the interactions between dissolved organic matter (DOM) and MPs are essential for the assessment of environmental impacts of MPs in ecosystems. Integrating spectroscopic methods with chemometric analyses, this work explored the chemical and microstructural changes of DOM-MP complex to reveal the mechanism of DOM-MP interaction at a molecular level. MPs were found to interact with the aromatic structure of DOM via π-π conjugation, then be entrapped in the DOM polymers by the carboxyl groups and C=O bonds, constituting a highly conjugated co-polymer with increased electron density. This induced the fluorescence intensity increase in DOM. The interaction affinity of DOM-MP was highly dependent on the MP size and solution pH. This work offers a new insight into the impact of MP discharge on environment and may provide an analytical framework for evaluating MP hetero-aggregation and the roles of MPs in the transportation of other contaminants. Furthermore, the integrated methods used in this work exhibit potential applications in exploring the fragmentation processes of MPs and formation of secondary MPs under natural conditions.

Vermicompost Incorporation into Soil Contaminated with Deltamethrin as an Attempt to Reduce the Toxicity Caused by this Pyrethroid: A Structural Study of Soil

The use of vermicompost for remediating soil contaminated with the commercial formulation containing deltamethrin was proposed. Biotoxicity tests with the goal of evaluating the potential remediation degree of the vermicompost after its addition to contaminated soils were performed. The tests lasted 56 days and involved Eisenia foetida earthworms. Possible structural changes in humic acids from these soils were evaluated by means of FTIR spectroscopy. The soil contaminated with deltamethrin offers toxicity to the earthworms. However, the vermicompost addition caused great positive impact on soil contamination level, which became quite similar to the reference soil. The vermicompost remedial effect depends on the source material. In this study the vermicompost were from filter cake and orange peel. The results obtained by FTIR pointed out for a weak interaction such as van der Waals type between the pyretroid and humic acids.

Specific UV–vis absorbance changes of humic acid in the presence of clay particles during photocatalytic oxidation

Photocatalytic oxidation of humic acid (HA) in the presence of clay particles (montmorillonite [Mt] or kaolinite [Kt]) followed using specific UV–vis parameters (SUVA365, SUVA280, SUVA254, and SCoA) calculated by respective absorbance measurements through conversion to mass of carbon. Non-selective oxidative degradation of HA could be displayed by the observed changes in the UV–vis spectral features in accordance with the successful elimination of the dissolved organic carbon. It was previously reported that fractional UV–vis parameters (E254/E365, E254/E436, E280/E365, E280/E436, and E365/E436) could signify the removal of color forming groups in relation to the removal of UV absorbing centers revealing information on the different oxidation pathways through photocatalysis. Regarding the results attained in this study, with respect to the changes attained in the specific UV–vis parameters, it could be indicated that the photocatalytic oxidation mechanism was significantly different for HA in the presence of either Mt or Kt. No noteworthy variation could be detected for fractional UV–vis parameters under photocatalytic conditions for sole HA as well as for HA in the presence of either Mt or Kt. However, a significant correlative interaction was observed between the specific UV–vis parameters (SUVA254 and SCoA) and the fractional UV–vis parameter (E254/E436) (r2 ##xgt; 0.80). Therefore, it could be concluded that E365/E436 parameter could be successfully used as a discriminative indicator parameter of the specific UV–vis parameters for the photocatalytic degradation of HA in the presence of either Mt or Kt.

Complexation of Copper(II) with Humic Acids Studied by Ultrasound Spectrometry

Copper biogeochemistry is controlled by bonding to natural organic matter. The soluble forms of bonded copper can be more biologically active due to the higher migration in environmental systems and instability of some copper-humic complexes. In this work, the interactions of copper(II) ions with humic acids are studied by means of high-resolution ultrasound spectrometry. It was found that the stoichiometry of the formed complexes is strongly influenced by the organization of humic acid in solution and by the final pH value in equilibrium. Although the ratio between the added copper and humic acids in all used concentrations was constant and the initial pH value was neutral, we observed significant differences between the individual systems. The highest binding ability was determined for a humic content of 0.5 g·dm−3. More diluted and more concentrated systems were able to bind lower amounts of copper. The implemented method is very sensitive and can be utilized not only for monitoring copper binding but also as an indicator of conformational changes of humic acid in solutions with varying concentration.

Photocatalytic oxidation of humic acid and its effect on haloacetic acid formation potential: a fluorescence spectrometry study

By fluorescence spectrometry method, molecular conformation changes of humic acid (HA) during the photocatalytic oxidation process were studied. Haloacetic acids formation potential (HAAFP) changes during the oxidation process were also measured. The results indicated that aromatic rings of HA decreased and conjugated double bonds were destroyed at the beginning of the process. Meanwhile, organic matter with large molecular weight decomposed into intermediates with smaller molecular weight, such as tryptophan and tyrosine. HA can be degraded almost completely, but not be mineralized thoroughly. Structures of the intermediates were changing during the oxidation process. Molecular structure transformation of HA led to the fluctuation tendency of the HAAFP changes during the photocatalytic oxidation process. HAAFP increased to 1.22 times that in raw water after 30 min of ultraviolet (UV) radiation, and decreased to 0.66 times that in raw water after 60 min of photocatalytic oxidation.

Conformational changes in humic acids in aqueous solutions

AbstractConformational changes in humic acids in two different aqueous solutions (NaCl and NaOH) are studied by means of high resolution ultrasound spectrometry. The method is based on the measurement of parameters of ultrasonic waves propagating through the sample. The attenuation describes the decay of the amplitude of the ultrasonic wave with the distance travelled. The velocity is the speed of this wave and is related to the wavelength and the frequency of oscillation of the deformation. It is determined by the density and elasticity of the sample, which is strongly influenced by the molecular arrangement. The minimal velocity of ultrasound was observed at 1 g dm−3 for lignitic humic acids and at 0.5 g dm−3 for IHSS Leonardite standard. The values of compressibility as computed are almost constant up to humic acids’ content corresponding to the minimum velocity of ultrasound and then decrease with the increase in concentration. This shows that the organisation of particles in diluted and concentrated humic acids sols is different. The decrease in compressibility points to the formation of a more rigid structure, which could lead to the decrease in humic acids’ binding ability. It was confirmed that the method employed was very sensitive and could be utilised as an indicator of conformational changes in humic acids in solutions with varying concentrations.

Structural changes of humic acids from sinking organic matter and surface sediments investigated by advanced solid-state NMR: Insights into sources, preservation and molecularly uncharacterized components

Knowledge of the structural changes that particulate organic matter (POM) undergoes in natural systems is essential for determining its reactivity and fate. In the present study, we used advanced solid-state NMR techniques to investigate the chemical structures of sinking particulate matter collected at different depths as well as humic acids (HAs) extracted from these samples and underlying sediments from the Saguenay Fjord and the St. Lawrence Lower Estuary (Canada). Compared to bulk POM, HAs contain more non-polar alkyls, aromatics, and aromatic C–O, but less carbohydrates (or carbohydrate-like structures). In the two locations studied, the C and N contents of the samples (POM and HAs) decreased with depth and after deposition onto sediments, leaving N-poor but O-enriched HAs and suggesting the involvement of partial oxidation reactions during POM microbial degradation. Advanced NMR techniques revealed that, compared to the water-column HAs, sedimentary HAs contained more protonated aromatics, non-protonated aromatics, aromatic C–O, carbohydrates (excluding anomerics), anomerics, OC q, O–C q–O, OCH, and OCH 3 groups, but less non-polar alkyls, NCH, and mobile CH 2 groups. These results are consistent with the relatively high reactivity of lipids and proteins or peptides. In contrast, carbohydrate-like structures were selectively preserved and appeared to be involved in substitution and copolymerization reactions. Some of these trends support the selective degradation (or selective preservation) theory. The results provide insights into mechanisms that likely contribute to the preservation of POM and the formation of molecules that escape characterization by traditional methods. Despite the depletion of non-polar alkyls with depth in HAs, a significant portion of their general structure survived and can be assigned to a model phospholipid. In addition, little changes in the connectivities of different functional groups were observed. Substituted and copolymerized carbohydrates and fused-ring aromatics detected in the present study likely represented an important part of molecularly uncharacterized components (MUC).