New technology will help disposal waste technogenic

Scientists have proposed a new way to eliminate polychlorinated biphenyls – toxic industrial waste that accumulates in the adipose tissues of humans and animals and pollutes the environment. The new two-step approach is environmentally safe and can be implemented on the basis of existing disposal facilities. A description of the methodology and experimental results have been published at Chemical Papers.

Polychlorinated Biphenyls (PCB) are highly hazardous chloroaromatic compounds. These compounds can accumulate in the human body, causing cancer, allergies, and severe poisoning, including death. The most effective way of destroying PCB is incineration, but for successful elimination of substances it is necessary to follow the rules: high turbulence, presence of the substance in the reaction zone for two or three seconds and the temperature in the combustion zone above 2000 Degrees Celsius. High temperature is necessary to avoid formation of dioxins and furans - cumulative poisons formed from PCB at high, but insufficient for complete combustion, temperatures. Creation of furnaces with all the requirements requires separate design measures and high-tech capacities, that is why the scientists have developed a two-stage method, facilitating the process of PCB elimination. The technology is advantageous in that it does not require construction of special plants with furnaces capable of maintaining the temperature of at least 2000 Degrees Celsius. The new approach will require lower temperatures that can be maintained in existing furnaces at waste disposal plants.

“The first step is chemical functionalization - replacing the chlorine atoms in the original PCB structures with the hydroxyl group OH. It is chlorine that is dangerous in combustion, making it important to minimize its amount in the composition of the substance. Unfortunately, it is impossible to replace all chlorine atoms by traditional chemical methods, but it is possible to replace a few atoms with more neutral chemical groups. Then the combustion of functionalized PCB will produce only water and compounds that are safe for health,” says Tatiana Gorbunova, coauthor of the study and leading researcher of the Laboratory of Organofluorine Compounds at RAS Institute of Organic Synthesis.

The decisive step in the destruction scheme is thermal destruction. After functionalization, the combustion of new polychlorinated biphenyl derivatives is more efficient and at lower temperatures. Scientists have found that a temperature of 600-700°C is sufficient to incinerate chemically processed PCBs. The end products of thermal destruction are mineral substances: water, carbon dioxide, hydrochloric acid, which do not pose direct danger to humans. Dioxins and furans are not formed in the final products.

“The results of our experiments show that hydroxy derivatives of polychlorinated biphenyls can be incinerated at any waste incineration plant. For example, at plant for the disposal of hazardous waste, the main technology there is represented by just thermal methods. But in the furnaces of the plant only solid waste contaminated with PCB is destroyed: oiled consumables and contaminated soil. Liquid technical mixtures are forbidden, because of danger of formation of cumulative poisons. Therefore, we propose to solve this problem by a comprehensive approach and neutralize the original hazardous substances. Cooperation of scientific potential of our group and capacities of waste incineration plants may become the optimal solution of the problem of liquid stockpiles of PCBs,” says Tatiana Kulikova, senior researcher of the Research Laboratory of Advanced Functional Inorganic Materials at UrFU.

Note

Polychlorinated biphenyls are a group of organic compounds including 1-10 chlorine atoms bonded to any carbon atom of a biphenyl (organic compound, aromatic hydrocarbon). PCB have high thermal and electrical insulation characteristics, thermal and fire resistance, good solubility in fats, oils and organic solvents. This has contributed to their wide use as dielectrics in transformers and condensers, hydraulic fluids, coolants and coolants, lubricating oils, components of paints, varnishes, adhesives, etc.

PCB are one of the most widespread anthropogenic pollutants and are classified as persistent organic pollutants (POP) - a class of highly hazardous chemical agents posing a serious threat to human health and the environment. POP are characterized by resistance to degradation, acute and chronic toxicity, and long-range transboundary transport by air, water, or with migratory species.

In 2001, after a series of international negotiations within the framework of the Intergovernmental Committee under the UN Environment Program, the Stockholm Convention was adopted. It provides for the reduction or elimination of emissions from the intentional production and use of persistent organic pollutants, as well as the reduction or elimination of emissions from their unintentional production.