China
Africa
Explore chapters and articles related to this topic
Organic Matter
Published in Michael J. Kennish, Ecology of Estuaries Physical and Chemical Aspects, 2019
Humic substances, which comprise the bulk of DOC in river water and seawater, have been defined as macromolecular phenolic carboxylic acids that are carried in natural waters as hydrophilic colloids or as true solutions of polyelectrolytes.38-41 Stevenson (p. 261)2 evaluates the structure of humic acids as a “type molecule consisting of micelles of a polymeric nature, the basic structure of which is an aromatic ring of the di- or trihydroxyphenol type bridged by -O-, -CH2−, −NH-, −N=, -S−, and other groups and containing both free OH groups and the double linkages of quinones.” Figure 1 depicts a hypothetical structure for humic acid. Despite the numerous structural formuli postulated as a representative model of humic acids, none has been universally accepted. This is so because of the heterogeneous mixture of compounds comprising humic substances. As stated by Stevenson (p. 258),2 “Each fraction (humic acid, fulvic acid, etc.) must be regarded as being made up of a series of molecules of different sizes, few having precisely the same structural configuration or array of reactive groups”
Radionuclide Concentrations in Soils lution-Processed Organic Solar Cells
Published in Michael Pöschl, Leo M. L. Nollet, Radionuclide Concentrations in Food and the Environment, 2006
Humic substances such as humic acid (HA) and fulvic acid (FA) are a fraction of the organic matter in a soil. These have a high affinity for actinide and lanthanide metal ions in a terrestrial system. Chung et al. [17] investigated the possibility of retaining fallout radionuclides in an organic matter-rich soil of Jeju Island, Korea. In order to simulate the behavior of actinide metals, Eu(III) was used as a tracer. Synchronous fluorescence spectroscopy (SyFS) was used to characterize the Eu(III) binding to humic substances. The element composition of HA and FA (carbon, hydrogen, nitrogen, and sulfur) was determined by a combustion method.
Formulation design, optimization and in vivo evaluation of oral co-encapsulated resveratrol-humic acid colloidal polymeric nanocarriers
Published in Pharmaceutical Development and Technology, 2021
Rahul Hasija, Sundeep Chaurasia, Swati Gupta
Humic acid (HA) falls under the category of humic substances as an affluent resource of shilajit, and the most governing fraction of natural organic matters (Kong et al. 1987; Acharya et al. 1988). Humic substances are omnipresent: in the soil, in the river and in the sewage water, and macromolecular negatively charged polyelectrolytes. Intensive studies have highlighted humic substances as constituent components which are primarily comprised of humus approximately 60%–80% and other components such as benzoic acid, hippuric acid, fatty acid, ellagic acid, resin, triterpenes, sterols, aromatic carboxylic acid, amino acids, 3–4 benzocoumarins, and phenolic lipids (Agarwal et al. 2007; 2010). The average molecular weight of the HA is reported to be 6500 Da (Ghosal 2003). HA serves as a potent bioenhancer for poorly water-soluble active molecules. HA consists of dark brown to blackish colour and is insoluble under acidic conditions (pH < 2) but freely soluble at higher pH.
Effect of aeration rate on the anti-biofouling properties of cellulose acetate nanocomposite membranes in a membrane bioreactor system for the treatment of pharmaceutical wastewater
Published in Biofouling, 2019
Figure 10 shows the removal of COD for activated sludge (bioreactor tank) and membranes under various aeration rate conditions. The COD removal for activated sludge under high aeration rates is lower than under low aeration rates, suggesting that the high shear condition will cause more EPS and especially SMP release into the bioreactor tank by the erosion of activated sludge flocs (Kim et al. 2001). In other words, large sludge flocs would be broken into smaller particles and soluble EPS would be released from the sludge flocs, resulting in the increase in the supernatant COD. The total COD removal efficiencies in the effluent for the nanocomposite membrane could be kept over 90% regardless of aeration rates. One of the mechanisms responsible for the removal of pharmaceutical compounds in MBR is physical retention by the membranes. For example, some toxic compounds in pharmaceutical wastewater could be adsorbed on humic substances (Tambosi et al. 2010), which are themselves retained by the membrane due to their hydrophobic nature. As humic substances are mainly hydrophobic materials, improvement in membrane hydrophilicity and increased antifouling properties subsequently result in removal of toxic compounds.
The toxicology of air pollution predicts its epidemiology
Published in Inhalation Toxicology, 2018
Andrew J. Ghio, Joleen M. Soukup, Michael C. Madden
Humic substances (HS) are ubiquitous, heterogeneous, amorphous, organic materials occurring in all terrestrial and aqueous environments including composts, sediments, peat bogs, coals, rivers, lakes, and oceans (Stevenson, 1985). The molecular weights for HS can range from a few hundred to millions of daltons. Chemically, they are a complex mixture of many different acids with prominent numbers of carboxylate and phenolate groups (Figure 1). HS include three different fractions: humic acid, fulvic acid and humin. Humic acid is the major extractable component of soil HS; it is insoluble in water under acidic conditions (pH <2) but soluble at higher pH values and dark brown to black in color. Fulvic acid is that fraction of HS soluble in water under all pH conditions and remains in solution after removal of humic acid by acidification; it is light yellow to yellow-brown in color. Humin is the fraction of HS that is not soluble in water at any pH value and is black in color.