Humic Substances Research Papers - Academia.edu (original) (raw)

The scientific understanding of the molecular size and shape of humic substances (HS) is critically reviewed. The traditional view that HS are polymers in soil is not substantiated by any direct evidence but is assumed only on the basis... more

The scientific understanding of the molecular size and shape of humic
substances (HS) is critically reviewed. The traditional view that HS are
polymers in soil is not substantiated by any direct evidence but is assumed
only on the basis of laboratory experiments with model molecules
and unwarranted results produced by incorrectly applying either analytical
procedures or mathematical treatments developed for purified and
undisputed biopolymers. A large body of evidence shows an alternative
understanding of the conformational nature of HS, which should be regarded
as supramolecular associations of self-assembling heterogeneous
and relatively small molecules deriving from the degradation and decomposition
of dead biological material. A major aspect of the humic
supramolecular conformation is that it is stabilized predominantly by
weak dispersive forces instead of covalent linkages. Hydrophobic (van
der Waals, -, CH-) and hydrogen bonds are responsible for the apparent
large molecular size of HS, the former becoming more important
with the increase of pH. This innovative understanding of the nature of
HS implies a further development of the science and technology for the
control of the chemistry and reactivity of natural organic matter in the
soil and the environment. (Soil Science 2001; 166:810–832)

Humic Substances (HS) occur naturally in our environment and are the remains of a process called humification, which is the biodegradation of biomass that then recombines and converts into dark colored complex compounds with no definite... more

Humic Substances (HS) occur naturally in our environment and are the remains of a process called humification, which is the biodegradation of biomass that then recombines and converts into dark colored complex compounds with no definite chemical structure. These are the end result of microbial degradation but resistant to further microbial degradation. It has a strong global presence as a dietary supplement and cosmetics applications for different beneficial uses. Till date its exploration as a pharmaceutical excipient has been limited to academic research only but the data being presented augurs a good commercial success.

Photocatalysis is a promising method for the disinfection of potable water in developing countries where solar irradiation can be employed, thus reducing the cost of treatment. In addition to microbial contamination, water normally... more

Photocatalysis is a promising method for the disinfection of potable water in developing countries where solar irradiation can be employed, thus reducing the cost of treatment. In addition to microbial contamination, water normally contains suspended solids, dissolved inorganic ions and organic compounds (mainly humic substances) which may affect the efficacy of solar photocatalysis. In this work the photocatalytic and photolytic

Increasing evidences have indicated that humic substances can induce plant growth and productivity by functioning as an environmental source of auxinic activity. Here we comparatively evaluate the effects of indole-3-acetic acid (IAA) and... more

Increasing evidences have indicated that humic substances can induce plant growth and productivity by functioning as an environmental source of auxinic activity. Here we comparatively evaluate the effects of indole-3-acetic acid (IAA) and humic acids (HA) isolated from two different soils (Inseptsol and Ultisol) and two different organic residues (vermicompost and sewage sludge) on root development and on activities of plasmalemma and tonoplast H+ pumps from maize roots. The data show that HA isolated from these different sources as well as low IAA concentrations (10−10 and 10−15 M) improve root growth through a markedly proliferation of lateral roots along with a differential activation not only of the plasmalemma but also of vacuolar H+-ATPases and H+-pyrophosphatase. Further, the vacuolar H+-ATPase had a peak of stimulation in a range from 10−8 to 10−10 M IAA, whereas the H+-pyrophosphatase was sensitive to a much broader range of IAA concentrations from 10−3 to 10−15 M. It is proposed a complementary view of the acid growth mechanism in which a concerted activation of the plasmalemma and tonoplast H+ pumps plays a key role in the root cell expansion process driven by environment-derived molecules endowed with auxinic activity, such as that of humic substances.

Studies have been conducted specifically to investigate the hypothesis that N-nitrosodimethylamine (NDMA) can be produced by reactions involving monochloramine. Experiments were conducted using dimethylamine (DMA) as a model precursor.... more

Studies have been conducted specifically to investigate the hypothesis that N-nitrosodimethylamine (NDMA) can be produced by reactions involving monochloramine. Experiments were conducted using dimethylamine (DMA) as a model precursor. NDMA was formed from the reaction between DMA and monochloramine indicating that it should be considered a potential disinfection by-product. The formation of NDMA increased with increased monochloramine concentration and showed maximum in yield when DMA was varied at fixed monochloramine concentrations. The mass spectra of the NDMA formed from DMA and 15N isotope labeled monochloramine (15NH2Cl) showed that the source of one of the nitrogen atoms in the nitroso group in NDMA was from monochloramine. Addition of 0.05 and 0.5 mM of preformed monochloramine to a secondarily treated wastewater at pH 7.2 also resulted in the formation of 3.6 and 111 ng/L of NDMA, respectively, showing that this is indeed an environmentally relevant NDMA formation pathway. The proposed NDMA formation mechanism consists of (i) the formation of 1,1-dimethylhydrazine (UDMH) intermediate from the reaction of DMA with monochloramine followed by, (ii) the oxidation of UDMH by monochloramine to NDMA, and (iii) the reversible chlorine transfer reaction between monochloramine and DMA which is parallel to (i). We conclude that reactions involving monochloramine in addition to classical nitrosation reactions are potentially important pathways for NDMA formation.

Increased use of humic substances in agriculture has generated intense interest among producers, consumers, and regulators for an accurate and reliable method to quantify humic acid (HA) and fulvic acid (FA) in raw ores and products. Here... more

Increased use of humic substances in agriculture has generated intense interest among producers, consumers, and regulators for an accurate and reliable method to quantify humic acid (HA) and fulvic acid (FA) in raw ores and products. Here we present a thoroughly validated method, the new standardized method for determination of HA and FA contents in raw humate ores and in solid and liquid products produced from them. The methods used for preparation of HA and FA were adapted according to the guidelines of the International Humic Substances Society involving alkaline extraction followed by acidification to separate HA from the fulvic fraction. This is followed by separation of FA from the fulvic fraction by adsorption on a nonionic macroporous acrylic ester resin at acid pH. It differs from previous methods in that it determines HA and FA concentrations gravimetrically on an ash-free basis. Critical steps in the method, e.g., initial test portion mass, test portion to extract volume ...

The use of vermicompost (humified material) for treating wastewaters, remediating polluted soils, improving agricultural productivity, protecting crop production, and developing sensitive analytical methods is reviewed here, covering the... more

The use of vermicompost (humified material) for treating wastewaters, remediating polluted soils, improving agricultural productivity, protecting crop production, and developing sensitive analytical methods is reviewed here, covering the past 17 years. The main advantages of vermicompost, considering all applications covered in this paper, comprise (i) easy acquisition, (ii) low costs, (iii) structural, chemical, and biological characteristics responsible for exceptional adsorptive capacities as well as pollutant degradation, and (iv) the promotion of biocontrol. Specifically, for wastewater decontamination, a considerable number of works have verified the adsorption of toxic metals, but the application of vermicompost is still scarce for the retention of organic compounds. Problems related to the final disposal of enriched vermicompost (after treatment steps) are often found, in spite of some successful destinations such as organic fertilizer. For decontaminating soils, the use of ...

We size fractionated a soil humic acid (HA) by preparative high performance size exclusion chromatography (HPSEC) and evaluated the analytical capacity of humeomics to isolate and identify humic molecular components in the separated... more

We size fractionated a soil humic acid (HA) by preparative high performance size exclusion chromatography (HPSEC) and evaluated the analytical capacity of humeomics to isolate and identify humic molecular components in the separated size-fractions. HA and its three size-fractions were chemically fractionated to extract non-covalently bound organosoluble compounds (ORG1), weakly ester-bound organosoluble (ORG2) and hydrosoluble constituents (AQU2), strongly ester-bound organosoluble components (ORG3), and final unextractable residues (RES4). According to their solubility, the extracts were characterized by either GC–MS or on-line thermochemolysis/GC–MS techniques. The humeomic sequence showed that the analytical yields of identified compounds in either ORG or AQU extracts of size-fractions were invariably larger than for the unfractionated HA. This was attributed to a weaker conformational stability of humic suprastructures obtained by HPSEC fractionation, thereby enabling an improved separation and identification of single humic molecules. In line with the supramolecular understanding of humic substances , we found that hydrophobic compounds were mainly distributed in the largest size-fraction, while hydrophilic components were eluted in the smallest size-fraction. Furthermore, compounds with linear chains or stackable aromatic rings associated in regular structures were more abundant in the former fraction, whereas irregularly shaped compounds, that hindered association in larger size, were mostly found in the latter fraction. Thus the structural characteristics of single humic molecules determined their mutual association in humic suprastructures, as well as their conformational strength and shape. The lack of de novo synthesized macropolymers in the unfractionated soil humic matter was confirmed by the absence of RES4 fractions in the separated size-fractions. Our results indicate that humeomics capacity to reveal the complex molecular composition of humic suprastructures was significantly improved by subjecting humic matter to a preliminary HPSEC fractionation.

Humic acids (HA) have a colloidal character whose size and negative charge are strictly dependent on surface functional groups. They are able to complex large amount of poorly ordered iron (hydr)oxides in soil as a function of pH and... more

Humic acids (HA) have a colloidal character whose size and negative charge are strictly dependent on surface functional groups. They are able to complex large amount of poorly ordered iron (hydr)oxides in soil as a function of pH and other environmental conditions. Accordingly, with the present study we intend to assess the colloidal properties of Fe(II) coprecipitated with humic acids (HA) and their effect on Fe hydroxide crystallinity under abiotic oxidation and order of addition of both Fe(II) and HA. TEM, XRD and DRS experiments showed that Fe-HA consisted of Ferrihydrite with important structural variations. DLS data of Fe-HA at acidic pH showed a bimodal size distribution, while at very low pH a slow aggregation process was observed. Electrophoretic zeta-potential measurements revealed a negative surface charge for Fe-HA macromolecules, providing a strong electrostatic barrier against aggregation. Under alkaline conditions HA chains swelled, which resulted in an enhanced stabi...

Landfill leachate consists mostly of a high content of refractory organic matter, ammonia and toxic compounds. All of these compounds, regardless of their nature, have a potential pollution effect on local ground and surface waters. In... more

Landfill leachate consists mostly of a high content of refractory organic matter, ammonia and toxic compounds. All of these compounds, regardless of their nature, have a potential pollution effect on local ground and surface waters. In this context, the purpose of the present study was to evaluate a treatment process (coagulation-flocculation with lime coupled with nanofiltration) applied to landfill leachate from Seropédica, Rio de Janeiro (Brazil). Jar tests were conducted to determine the optimum dosage of lime (ranged from 0 to 10 g L-1) and, at optimum lime dose, ammonia nitrogen was removed during coagulation-flocculation process due to high pH. The process was settled for 6 h with slow stirring (50 rpm) to promote air entrainment and NH3-N stripping before using the final treatment step of nanofiltration at 8 bar. After ammonia stripping, NH3-N was reduced from 1236 mg.L-1 to 353 mg.L-1 (71% removal efficiency). At the end of the combined treatment, TOC (Total Organic Carbon), HS (Humic Substances) and COD (Chemical Oxygen Demand) removals were 89%, 80% and 94%, respectively. The results showed that the combined process was effective in the removal of recalcitrant compounds and NH3-N.

• Using humic acids and fulvic acids as chelating agents to improve EK efficiency. • HSs-enhanced EK efficiency was about 2–3 times greater than that in unenhanced EK. • Fulvic acids provided higher HMs removal than humic acids. • Results... more

• Using humic acids and fulvic acids as chelating agents to improve EK efficiency. • HSs-enhanced EK efficiency was about 2–3 times greater than that in unenhanced EK. • Fulvic acids provided higher HMs removal than humic acids. • Results indicate the suitability of HSs-enhanced EK in real HMs contaminated soil. a b s t r a c t The effects of catholyte conditioning and the use of humic acids (HAs) and fulvic acids (FAs) as chelating agents to improve electrokinetic (EK) remediation efficiency were investigated using a real and highly contaminated soil. By applying a constant voltage (2.0 V/cm) to the soil, pH and current changes and heavy metals (HMs) concentration were investigated through a range of durations and positions. The observations demonstrated that both catholyte conditioning with 0.1 N HNO 3 and using humic substances (HSs) enhance remediation efficiency. After 20 days of EK treatment, the removal efficiency of HMs in HS-enhanced EK remediation was about 2.0–3.0 times greater than when unenhanced. The quantity of HMs moving toward the cathode exceeded the anode, from which it could be reasonably inferred that most negatively charged HM-HS complexes were moved by electroosmotic forces. Further, free HM cations and positively charged complexed HMs migrated to the catholyte compartment by electromigration. The results obtained in this study, demonstrate the suitability of HS-enhanced EK remediation in HMs contaminated soil.

Recently, ultrafiltration membrane technology is challenged to maintain their sustainability and favourable economics by improving their flux, selectivity and durability. Polysulfone membrane constitute the most extensively studied class... more

Recently, ultrafiltration membrane technology is challenged to maintain their sustainability and favourable economics by improving their flux, selectivity and durability. Polysulfone membrane constitute the most extensively studied class of membrane materials due to its commercial availability, excellent chemical and thermal resistance, good mechanical properties and easy processing. However, polysulfone ultrafiltration membrane is susceptible to fouling and has low permeate flux due to hydrophobicity properties of the materials. Membrane modifications become unavoidable in order to reduce the fouling susceptibility. One simple and attractive method is blending polysulfone with additives. Previous studies show that the addition of additives in membrane solution could enhance membrane performances with higher porosity and flux. Meanwhile in surface water treatment application, humic substance has brought particular interest due to its nature which could produce some carcinogen substances that have negative effects on the human health in long term period. Therefore, the investigation to remove humic substances is considered as a sustainable solution in the field of surface water treatment. Many studies have been conducted with polysulfone based ultrafiltration membrane to remove humic substance from water, thus the factors that influenced humic substances fouling on polysulfone-based membrane and the effect of additive concentration on the improvement membrane performance for humic substance removal will be reviewed further in this paper.