Q110624183 Dotaz Zobrazit nápovědu
A group of pollutants denoted to as per- and polyfluoroalkyl substances (PFAS) currently comprises more than 4,700 identified substances. Their structure consists of a per- or polyfluorinated hydrocarbon chain forming the hydrophobic part of the molecule and a functional group which in turn forms a hydrophilic part. Depending on the type of functional group, PFAS can be divided into sulfonates, carboxylates, sulfonamides, phosphonates, acrylates, acetates and other minor groups. These substances are nowadays ubiquitous in the environment. In general, they are considered as highly persistent in nature. However, under suitable environmental conditions, some of them may degrade due to the presence of highly polar functional groups. The intermediates or final products of the degradation first step are less or non-polar. These are not readily (bio)degradable and can accumulate in the environment. Current technologies are not able to remove per- and polyfluorinated compounds from drinking water efficiently. It is therefore necessary to develop new technologies or efficient sorption materials that will enable the removal of both per- and polyfluorinated compounds, micropollutants and residual organic substances and thus to eliminate or at least to decrease the risk associated with human exposure to these substances in drinking water.
This paper looks at chemistry of individual oxyhalogens such as chlorite, chlorate, perchlorate and bromates, their origin in drinking water and health effects which restrict their concentrations. It is concluded that with understanding of mechanisms of formation of individual oxyhalogens and undertaking practical steps during water treatment and disinfection processes their concentration can, in the majority of cases, be controlled within the drinking water guideline limits.
Humic matter is the prevailing constituent of natural organics in many surface water resources. Humic matter is a class of complex polyclic high-molecular-weight compounds with molecular weights ranging from ten thousands to hundred thousands. Humic matter often varies in different types of surface water and for that reason different treatment technologies are used. The most common method is chemical water treatment based on coagulation/ floculation of humic substances. Besides, chemical processes and other methods can be used for removal of humic matter in water treatment, such as sorption, ion exchange, membrane filtration, oxidation and biological methods.
A comprehensive review on in situ chemical oxidation, which ranks among progressive methods of remediation of contaminated ground, in particular by the removal of organic pollutants from soil and groundwater. The method is based on direct injection of an aqueous solution of the oxidant (mostly KMnO4 or H2O2) into the subsurface. The main advantage of the method consists in fast destruction of organic pollutants. The method is well applicable to grounds showing high hydraulic permeability, without preferential pathways. Its main drawback is the nonselectivity of the oxidant, a significant part of which is consumed by oxidation of natural soil and groundwater components.
