Current Organic Chemistry - Volume 22, Issue 11, 2018

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are toxic, mutagenic and carcinogenic, causing great concern in the public. This review analyzes the properties, toxic effects and sources of PCDD/Fs. The distribution in various environmental compartments, including air, water, soil and sediments, are described. Further, the transformation of PCDD/Fs in the environment was emphatically discussed. The result shows that the fate of PCDD/Fs is mainly controlled by their gasparticle distribution behavior. For gas-phase PCDD/Fs, they are primarily depleted by photolysis and reactions with atmospheric oxidants. For particle-phase PCDD/Fs, dry and wet deposition are the effective removal mode. In the water body, the PCDD/Fs will be inclined to deposit in the sediment. Biodegradation may be a possible environment fate for the PCDD/Fs in sediments. Moreover, PCDD/Fs can enter into the atmosphere in the form of volatilization, especially in the summer. In the soil, the PCDD/Fs can be degraded through anaerobic dechlorination and aerobic dioxygenation, as well as by gas exchange across the air-soil interface. It has a strong net volatilized from the soil into the air for the PCDD/Fs with six or fewer chlorine atoms, while the hepta- and octachloroisomers are approached to the main air-soil exchange balance.

Polycyclic Aromatic Hydrocarbons (PAHs) are persistent organic pollutants (POPs) structurally composed of 2-7 fused aromatic rings. They are released from all processes involving incomplete combustion of organic materials. In the ambient air, they are present as vapors or adsorbed onto airborne particulate matter. They undergo several physicochemical reactions and photochemical reactions with atmospheric ozone, NOX, SOX and OH radicals. They have been recognized as priority pollutants by the United States Environmental Protection Agency and the European Commission due to their toxic properties being mutagenic and carcinogenic. This article presents the state-of-the-art knowledge on atmospheric PAHs concerning their sources, mechanism of formation and properties including current understanding and models employed to investigate their gas-particle partitioning. This article also briefly reviews their chemical reactions, deposition processes, bioconcentration, routes of exposure to humans and biomonitoring with a particular focus on their toxicity and associated health effects. Finally, the limits and standards imposed by various agencies and countries are addressed.

The occurrence of micro-pollutants in natural waters (surface and groundwater) as well as in wastewaters, has become a worldwide issue of a great importance for environmental protection strategies. First of all, disinfection by-products, endocrine disrupting, pharmaceuticals and personal care products are taken into account. The paper gives a brief outline on recent advances in the detection and removal of this pollutants in/from water and wastewater. Conventional and advanced treatment technologies capable of removing these trace organic compounds, with a specific focus on membrane technology, i.e. reverse osmosis and nanofiltration, microfiltration and, ultrafiltration, as well as membrane bioreactors and forward osmosis have been described. Reverse osmosis and nanofiltration can remove nearly all discussed compounds to the levels below permissible limits, but some hydrophobic and small organic trace contaminants may not be effectively rejected by nanofiltration membranes. Double systems, such as reverse osmosis/advanced oxidation processes or double pass reverse osmosis and membrane bioreactor/reverse osmosis are found to be the most suitable in the removal of micro-pollutants. Microfiltration and ultrafiltration, while considered to organic micropollutants removal, has to be integrated with coagulation, adsorption, chemical complexion or biological reactors. A specific emphasis on the emerging forward osmosis process, which can potentially be a major platform for the next generation water and wastewater treatment technologies, has been made.

In the last decades, the development of advanced analytical techniques has revealed the presence of micro-contaminants (MCs) in effluents from municipal wastewater treatment plants (MWTPs), which represents a significant challenge to wastewater reclamation as biological treatments attain only partial removal of MCs. The application of tertiary treatments for refining these waters so as to avoid MCs reaching both irrigation systems and water natural bodies is widely studied. In this chapter, an overview of the combination of different membranes with advanced oxidation processes and conventional physicochemical treatments for the improvement of MCs removal efficiency is assessed. In addition, membrane fouling effects, progress in analytical monitoring techniques and brief economic considerations have been also tackled. Pressure-driven membrane processes for MCs retention is discussed focusing microfiltration (MF)/ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO) and membrane distillation (MD) systems. Reviewed physicochemical processes included adsorption on activated carbon; coagulation/flocculation and chlorination/ozonation also integrated with membranes processes. Membrane bioreactors integrated with other membrane systems as NF or RO showed high removal rates (99%) for all compounds looked over. Different advanced oxidation processes as pre-treatment stage for mainly avoiding fouling and as post-treatment of the membrane rejection stream is also discussed. Integration of membranes with photo-reactors by both photocatalytic membranes and hybrid systems coupling photocatalysis and membrane processes (for retaining the powdered TiO2 in the photoreactor) has been also addressed in this chapter. Economical and regulation considerations in different countries and EU are discussed as the final and conclusive section of this work.

This mini-review will describe the recent applications of tert–butyl nitrite (TBN) in organic synthesis. Due to its unique structural feature and wide application, TBN holds a prominent and great potential in organic synthesis. Since the applications of TBN is too wide and developments have been too fast, Part-I of the present mini-review has surveyed the studies carried out to date in three areas viz. aerobic oxidation, annulation, and diazotization, which is demonstrated by the work outlined in this mini-review. The mechanisms of these transformations will be briefly described in this mini-review. TBN has been utilized in other organic transformations, such as nitrogenation, nitrification, nitrosylation, multifunctionalization, nitrodecarbocyclization, nitro-aminoxylation and etc. which will be presented as part- II in mid-2018.