Mineralization Of Humic Acid Research Articles

Photocatalytic activity of undoped and Ag-doped TiO 2-supported zeolite for humic acid degradation and mineralization

The hybrid materials based on natural zeolite and undoped and Ag-doped TiO 2, i.e., Z-Na-TiO 2 and Z-Na-TiO 2-Ag, were successfully synthesized by solid-state reaction in microwave-assisted hydrothermal conditions. Undoped TiO 2 and Ag-doped TiO 2 nanocrystals were previously synthesized by sol–gel method. The surface characterization of undoped TiO 2/Ag-doped TiO 2 and natural zeolite hybrid materials has been investigated by X-ray diffraction, DRUV-VIS spectroscopy, FT-IR spectroscopy, BET analysis, SEM microscopy and EDX analysis. The results indicated that anatase TiO 2 is the dominant crystalline type as spherical form onto zeolitic matrix. The presence of Ag into Z-Na-TiO 2-Ag was confirmed by EDX analysis. The DRUV-VIS spectra showed that Z-Na-TiO 2-Ag exhibited absorption within the range of 400–500 nm in comparison with Z-Na-TiO 2 catalyst. The enhanced photocatalytic activity of Z-Na-TiO 2-Ag catalyst is proved through the degradation and mineralization of humic acid under ultraviolet and visible irradiation.

Special Issue on Contaminant Mixtures: Fate, Transport, and Remediation

The fate and transport of mixed contaminants in subsurface environments can be quite complex because of various physical, chemical, and biological processes. In-depth understanding of geochemistry that influences the distribution, speciation, and transport is needed to understand the risk and develop remedial strategies. Joo et al. performed batch experiments to evaluate the sorption of six nonpolar and six polar organic compounds as mixtures to both hydrophilic mineral surfaces [uncoated, iron (hydr) oxide-coated, and aluminum (hydr)oxide-coated sands] and humic acid–mineral complexes with different fractions of organic carbon. The mixture effects on sorption of the nonpolar compounds were found to be not significant, whereas they were found to be significant for polar compounds depending on the mixture compositions and the type of sorbent. This implies the need for accurately quantifying and modeling mixture effects on fate and transport of multiple organic contaminants present at the site. Poly and Sreedeep performed batch sorption experiments and found that the presence of multiple contaminants affect the sorption of individual contaminants. The contaminant fate prediction based on linear isotherm is influenced by the range of concentration for single and multiple contaminants. For lower ranges of concentration, the contaminant fate prediction based on the Freundlich isotherm is greater than that of Langmuir, and vice versa for higher concentration range. Further, the difference in contaminant fate prediction based on Freundlich and Langmuir nonlinear isotherms decreases with an increase in concentration. The fate and transport parameters of soils vary in space because of soil heterogeneity, and such conditions require transport modeling using stochastic approaches. Nezhad and Javadi present an advective and diffusive-dispersive contaminant transport, using a stochastic finite-element approach. The need for expanding such approaches to multiple contaminant conditions is warranted.

Oxidation and coagulation removal of humic acid using Fenton process

The treatment of humic acid (HA) in water with Fenton reagents was carried out and the roles of oxidation and coagulation in removing HA during treatment were investigated. The removal efficiencies of HA by oxidation and coagulation were tested under various operating conditions: reaction time, initial pH, dosages of Fenton reagents, [H 2O 2]/[Fe 2+] molar ratio, initial HA concentration and reaction temperature. It is demonstrated that Fenton process can effectively remove HA. The values of 27.6% mineralization of HA and 78.9% reduction of UV absorbance at 254 nm (UV 254) by oxidation after 120 min reaction time indicated that HA was not completely oxidized to carbon dioxide but rather transformed to some organic intermediates. Moreover, the oxidation occurred mainly at the first 60 min and predominated the HA removal efficiency. Under the most favorable conditions (initial pH 4.0, H 2O 2 160 mM, Fe 2+ 40 mM, reaction time 120 min, reaction temperature 30 °C), 93.3% of UV 254 was reduced, the reduction of UV 254 by oxidation and coagulation were 78.9% and 14.4%, respectively. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of HA.

Humic substances cycling in a tropical oxbow lagoon (São Paulo, Brazil)

This study aimed at describing the cycling of humic substances (HS) in a tropical oxbow lagoon (São Paulo, Brazil). Humic substances were obtained from Oxycaryum cubense leachate submitted to degradation and fractionated into fulvic acid (FA) and humic acid (HA). Incubations were prepared using FA and HA and water from Infernão lagoon and maintained under high dissolved oxygen (HDO) and low dissolved oxygen (LDO) conditions at 16 °C, 22 °C and 26 °C. FA and HA decay was monitored (on a carbon basis) for 40 days. The results were fitted to first-order kinetics model and the effect of temperature and oxygen availability on mineralization of FA and HA was described and used on simulations of humic substance cycling. The simulations allowed us to infer that in the Infernão lagoon HS mineralization is faster under LDO than under HDO conditions, with higher mineralization occurring in February (summer) and HA presented lower mineralization coefficients. For the Infernão lagoon, HS decay is a slow process and these compounds are expected to be extensively incorporated into the sediments of this environment.

Humic acid degradation in aqueous solution by the photo-Fenton process

The photodegradation of humic acid (HA) was carried out in the presence of the Fenton reagent. The absorbance decrease of HA was strongly influenced by the pH, and initial concentrations of H2O2 and Fe(II). An initial absorbances of HA (10 mg L −1 ) in 254 and 400 nm were completely disappeared after 8 h under the optimum conditions. The decrease of TOC as a result of mineralization of HA was observed during the photoFenton process. The degree of HA mineralization was about 80% under UV irradiation after 15 h. The molecular weight distribution changes of HA were evaluated by high performance size exclusion chromatography (HPSEC). The large molecular weight component in HA appears to be easily degraded by the photo-Fenton process than the smaller components. Furthermore, the photo-Fenton process was successfully applied to the degradation of HA in sea sediment of Ago Bay, Mie Prefecture, Japan. Based on these results, the photo-Fenton reaction could be useful technology for the treatment of environmental sample contaminated by HA. © 2007 Elsevier B.V. All rights reserved.

Sorption of humic acids and α‐endosulfan by clay minerals

Sorption of alpha-endosulfan by kaolinite and montmorillonite alone and in the presence of sorbed and dissolved humic acid (HA) was investigated (pH 8 and 25 degrees C). Three types of HA, Elliot soil HA (EHA), Peat HA (PHA), and Summit Hill HA (SHHA), were used to represent typical humic substances found in soils. For sorption of HA by either mineral, Freundlich sorption coefficient (K(f)) values appeared to decrease in the order of EHA > PHA > SHHA, which followed increasing polarity (expressed as the O/C atomic ratio) and decreasing percent-carbon content. For both clays, sorption of alpha-endosulfan by the HA mineral complex was greater than for sorption by the clay alone. Sorption of alpha-endosulfan by the HA mineral complexes followed the same order as the K(f) of the HAs (EHA > PHA > SHHA). Based on the amount of HA adsorbed by each mineral, organic carbon partition coefficients (K(oc)) were determined for sorption of alpha-endosulfan by two of the HA mineral complexes. The value of K(oc) for alpha-endosulfan sorption was greater for kaolinite EHA than kaolinite SHHA. However, the opposite trend was found with the montmorillonite HA complexes. Montmorillonite appeared to sorb alpha-endosulfan and/or HA with higher affinity than kaolinite, which likely is due to its 2:1 layer structure and higher surface area. Sorption of endosulfan diol, a hydrolysis product, by the minerals was much less than the parent pesticide.

Aspectos cinéticos da descoloração de substâncias húmicas durante a mineralização biológica

Assays were carried out to describe the kinetic aspects of biological bleaching of humic substances during its mineralization. Samples of aquatic plant and water ( Oxycaryum cubense ) were collected in the Infernao lagoon (21o 35' S and 47o 05' W; Sao Paulo State, Brazil). Experiments were carried out using fulvic acid (FA) and humic acid (HA) derived from leachates of O. cubense decay (120 days). FA and HA were added to 450 mL of lagoon water and incubated under high and low dissolved oxygen concentrations and at three temperatures. The optical density was monitored (95 days) and the data were fitted to first-order kinetic model. The processes involved with bleaching were favored with increasing temperature only during HA mineralization at low dissolved oxygen availability, indicating that in the Infernao lagoon, the biological bleaching of HA is more effective between November and April. Overall, FA presented higher bleaching coefficients than HA. Low HA bleaching coefficients are probably due to the complexity of the chemical structures and its transformation in FA

Transformation and mineralization of synthetic 14C-labeled humic model compounds by soil-feeding termites

The majority of termite species are considered to be humivorous, but the exact nature of their carbon and energy source, the mechanisms involved in digestion and the impact of this feeding habit on the humification of soil organic matter are largely obscure. We performed feeding trials with soil-feeding termites (Termitidae: Termitinae), using 14C-labeled humic model compounds as substrates. In the case of Cubitermes orthognathus, the components of chemically identical synthetic humic acids (HA), labeled either in their proteinaceous or aromatic building blocks, and synthetic fulvic acids (FA), labeled in the aromatic building blocks, all had similarly low mineralization rates (2.5, 2.2 and 2.7%, respectively) when incubated in soil for 10 days in the absence of termites. When termites were present, the mineralization rate of the aromatic component of HA and FA increased only slightly but significantly (2.4 and 3.1%, respectively; P < 0.05), whereas that of the proteinaceous component increased more than 10-fold (30.8%). Similar results were obtained when the protein was peptonized prior to polymerization (9.7 vs. 27.4% mineralization). Mineralization of HA was accompanied by a transformation of the residual peptide label to FA, whereas the aromatic label of HA and FA was partly transformed to humin during gut passage. High-performance gel permeation chromatography showed a strong shift in the size-class distribution of peptide label towards low-molecular-weight products, especially of the material ingested by the termites; the smallest molecules were recovered from the termite bodies. Similar results were obtained in feeding trials with Cubitermes umbratus and Thoracotermes macrothorax. Together with previous findings, the current results provide strong evidence that during gut passage, the combined action of extreme alkalinity in the anterior hindgut, autoxidative processes, and probably also proteolytic activities, renders a large reservoir of potential substrates accessible. While peptidic components of humic substances are selectively digested, aromatic components are apparently not an important food source for soil-feeding termites. These findings have important implications for the mobilization of organic nitrogen in tropical soils.