Presence Of Humic Matter Research Articles

Effects of humic matter on the anaerobic digestion of sewage sludge: New insights from sludge structure.

A sludge structure perspective of the effects of humic matter (HM) on the anaerobic digestion (AD) of sewage sludge was proposed and investigated in this study. It was observed that the net cumulative methane production of sludge was significantly lower in the presence of HM. The fractal dimension values of sludge samples were increased by the addition of HM, whilst their total surface energy values were decreased, indicating that HM reinforced the stability of the sludge structure. Analyses of the physicochemical properties of different sludge samples revealed that HM enhanced the structural stability of sludge organic substances and restricted its organic solubility by interacting with the biopolymers to form a dense granular aggregate, thereby reducing the random-coil degree of extracellular organic substances and its active sites for enzymes, which suggested that HM could inhibit AD by changing the sludge structure. It was further confirmed by the biochemical methane potential (BMP) assay process. The BMP tests and corresponding kinetic analyses revealed that HM can restrict the potentials of sludge organic solubilisation, hydrolysis and acidification processes, but not necessarily the rates of these processes by enhancing the structural stability of high molecular weight readily biodegradable organic matter (RBOM) and restricting the mobility of low molecular weight RBOM (i.e., hydrolysis products). These findings can enrich understanding of the AD of sludge and may thus aid in the development of more effective methods to improve sludge treatment.

Identification and characterization of photodegradation products of metoprolol in the presence of natural fulvic acid by HPLC-UV-MSn

Metoprolol is a β-blocker highly prescribed for the treatment of heart diseases. It is not efficiently removed in wastewater treatment plants and it has been detected not only in the treated effluents, but also in natural waters. Thus, the knowledge of its fate in the environment is an important issue, and photodegradation is an important degradation pathway. While direct photodegradation of metoprolol by solar light is not relevant, there is evidence in the literature that it suffers indirect photodegradation and a few studies have been published showing the important role of dissolved humic matter as photo-sensitizer. However, the identification of the photoproducts formed in the presence of humic matter is very poor, since only 2 photoproducts had been identified. This study investigated the degradation of metoprolol under simulated solar radiation and in the presence of fulvic acids (FA) extracted from a river. During the photodegradation experiments we observed the formation of new compounds which were separated and tentatively identified by HPLC-UV-ESI-MSn. At least 16 compounds were tentatively identified, including the 2 compounds previously identified in the literature and 4 new compounds which had not been detected by other authors as degradation products of metoprolol, even when submitted to artificial degradation processes.

A ω-mercaptoundecylphosphonic acid chemically modified gold electrode for uranium determination in waters in presence of organic matter

A chemically modified electrode (CME) on a gold surface assembled with a ω-phosphonic acid terminated thiol was investigated for its capability to complex uranyl ions. The electrode, characterized by electrochemical techniques, demonstrated to be effective for the determination of uranyl at sub-μgL−1 level by differential pulse adsorptive stripping voltammetry (DPAdSV) in environmental waters, also in presence of humic matter and other potential chelating agents. The accuracy of the measurements was investigated employing as model probes ligands of different complexing capability (humic acids and EDTA).

Effect of humic matter on metal adsorption onto clay materials: Testing the linear additive model

Migration of contaminants with low affinity for the aqueous phase is essentially governed by interaction with mobile carriers such as humic colloids. Their impact is, however, not sufficiently described by interaction constants alone since the humic carriers themselves are subject to a solid–liquid distribution that depends on geochemical parameters. In our study, co-adsorption of the REE terbium (as an analogue of trivalent actinides) and humic acid onto three clay materials (illite, montmorillonite, Opalinus clay) was investigated as a function of pH. 160Tb(III) and 131I-labelled humic acid were employed as radiotracers, allowing experiments at very low concentrations to mimic probable conditions in the far-field of a nuclear waste repository. Humate complexation of Tb was examined by anion and cation exchange techniques, also considering competitive effects of metals leached from the clay materials. The results revealed that desorption of metals from clay barriers, occurring in consequence of acidification processes, is generally counteracted in the presence of humic matter. For all clay materials under study, adsorption of Tb was found to be enhanced in neutral and acidic systems with humic acid, which is explained by additional adsorption of humic-bound Tb. A commonly used composite approach (linear additive model) was tested for suitability in reconstructing the solid–liquid distribution of Tb in ternary systems (Tb/humic acid/clay) on the basis of data determined for binary subsystems. The model can qualitatively explain the influence of humic acid as a function of pH, but it failed to reproduce our experimental data quantitatively. It appears that the elementary processes (metal adsorption, metal–humate complexation, humic acid adsorption) cannot be considered to be independent of each other. Possible reasons are discussed.

Impact of humic matter on sorption of radionuclides by montmorrilonite

The paper has analyzed the impact on sorption by montmorrilonite of the chemical nature of radionuclides, forms of their finding and concentration of humic matter. It has been found that for Eu(III) and Th(IV) in the presence of humic matter one can observe reduction of sorption within the pH wide interval, which is determined by the formation of fulvate and various ligand hydroxofulvate complexes, while for U(VI)—in an acid region, which indicates the formation of only fulvate complexes. It has been shown that in the presence of humic matter in the aqueous medium an increase of migration of radionuclides is determined by a decrease of their sorption on mineral suspensions and precipitation on the surface of silt sedimentations as a result of the formation of soluble complex compounds, while the presence of humic matter on the surface of clayey components of soils substantially increases immobilization of radionuclides, i.e., reduced migration of the latter to the environment.

Effects of organic and inorganic matter on pesticide rejection by nanofiltration

This work explores the performances of two types of nanofiltration (NF) membranes (Desal DK and NF200) in the elimination of some selected pesticides presents in water (triazines and urea herbicides). Experiments were carried out on synthetic waters composed from distilled water to which has been added organic (humic acids) or inorganic (CaCl 2 or CaSO 4) matter and on a real water matrix collected at the outlet of the grain activated carbon. These matrices are fortified at a level of 1 μg/L of each pesticide and were treated on a NF pilot unit. The pesticides removal percent and that of their adsorption on the membrane have been calculated. A difference in the behaviour of the two membranes was observed, together with an improvement in the removal percent of some pesticides in the presence of humic matter. On the contrary, inorganic matter exercises little influence. The results obtained with the real water matrix reveal an increase in the rate of pesticides adsorbed on the membranes in comparison with those of the synthetic waters. This phenomenon facilitated the transition of these molecules in the direction of the permeate and led to an identical reduction percent except for diuron, which was furthermore the most poorly eliminated by the two membranes.

Influence of metal concentration at the electrode surface in differential pulse anodic stripping voltammetry in the presence of humic matter

The influence of metal concentration in bulk solution and of deposition time on voltammograms obtained by differential pulse anodic stripping voltammetry in the presence of humic matter is discussed based on the slow diffusion of complexes, adsorption of the ligand on the electrode and ligand to metal concentration ratio during the stripping step. The conditional stability parameters at pH 5, in the bulk solution and in the absorbed layer, are determined. The concentration of adsorbed sites i calculated from the saturation of th sites at the electrode surface with metal ions, estimated either from the critical deposition time or from the height of the shoulder presented in the voltammogram.