Photoreactors for Solving Problems of Environmental Pollution

Abstract

Involvement of a huge amount of natural resources in the production sphere, synthesis of new materials and substances, and uncontrollable increase in the amount and volume of manufactured products engender a global problem of recycling and utilization of production and consumption wastes. The Earth atmosphere, hydrosphere and lithosphere are polluted. The atmosphere is a giant open reactor without walls in which hundreds of photochemical, dark, gas phase, liquid phase, homogeneous, and heterogeneous reactions take place with participation of all types of particles at various local temperatures and global pressure for different concentrations of substances and radiation intensities at different wavelengths. Hydroxyl radicals dominate in tropospheric chemistry as well as oxygen atoms and ozone dominate in stratospheric chemistry. Moreover, the photochemical processes proceed not only in surface waters, but also in the lithosphere in the upper soil layers [1, 2]. Anthropogenic effect on nature has already caused irreversible consequences. As a result of human activity, pollutants of many types are present in the environment. Chemistry of polluted urban atmospheres obligatory includes the photochemical processes. The typical pollutants presented in the photochemical (or Los Angeles) smog are ozone and nitrogen dioxide in combination with various organic compounds. The O3 and NO2 concentrations can be so high that ozone even smells, and large concentrations of aerosol particles cause the formation of grayish-brown haze in air. The pollution causes such consequences as destruction of materials, for example rubber, suppression of vegetation growth, reduction of the visibility range, and increase in the number of respiratory diseases. The most obvious consequence of the photochemical smog that manifests immediately is eye irritation caused by such compounds as formaldehyde, acrolein, and peroxyacetyl nitrate. The surface of solid aerosols and the inner volume of liquid-drop aerosols can also be the arena of various dark and photostimulated chemical reactions whose rates are largely determined by the catalytic properties of the surface and components forming particles. Many toxic impurities are detected in the aerosol composition, including compounds of heavy metals, carcinogenic polynuclear aromatic hydrocarbons, and polychlorinated compounds of different classes (pesticides, biphenyls, dibenzo-p-dioxins, and dibenzofurans). The largest amounts of these toxicants are contained in the smallest aerosol fractions capable of penetrating deep into the human respiratory tract and then into the blood system. Wide use of pesticides and herbicides in agriculture for the past few decades has significantly increased the number of persistent organic compounds in natural waters and soils [3–5]. For these reasons, the necessity arose to revise old technologies and to develop new ones aimed at resource saving and environmental protection. Experimental