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by Alexander GRECHКО, Dr. Sc. (Tech.), leading researcher, GINTsVETMET Institute
Humankind has scored staggering achievements in unlocking the mysteries of the world we live in. It has solved the riddles of the atom, it has built space stations, it has designed artificial intelligence...
But there is also the reverse side of the coin.
That is mountains of waste, the waste products.
Some are known well enough, and we know how to get rid of them - e.g. through prevention, utilization or annihilation. However, many toxic substances are still an enigma-say, compounds of the dioxin or furan type. Pretty dangerous compounds!
Small wonder they have been dubbed "chemical AIDS", "degradation hormones" and "the arch enemy of ecology".
The first publications on dioxins (C 4 H 4 O 2 ) appeared way back in 1956-1957. These highly toxic compounds were found to be responsible for the occupational disease among chemical industry workers caused by an excess of chlorine and its compounds in the organism. But then this problem was "shelved" and forgotten up until 1968 when dioxins were detected in solid household wastes.
Dioxins, furans and other substances belong to a large group of high-toxicity compounds known as xenobiotics, i.e. substances alien to living organisms and contained in various industrial wastes and even products. From the chemical standpoint, dioxins are a family of homologues* and isomers** of tri- and bicyclic halogenorganic compounds. Their number depends on the level of saturation with chlorine and bromine atoms, and it may come into thousands. That is to say, dioxins exhibit a great structural complexity and variety.
Dioxins are similar to radiation in that they can accumulate in the human organism and cause genetic mutations in the progeny. The medics say there are no safe dioxin doses - even at low concentrations dioxins are harmful to all forms of living matter. Just one dioxin molecule can interfere with the normal cell activity and trigger reactions disturbing the functions of the organism. Dioxins also impair the receptors of cells responsible for the work of hor-
* Homologous series - a sequence of organic compounds with identical functional groups and single-type structure; each member of the series (homologue) differs from its neighbor in one constant structural unit, usually the methyl group СН 2 . - Ed
* Izomers - chemical compounds identical in the molecular mass composition and different in the structure or in the spatial arrangement of atoms and, consequently, in their properties. - Ed.
monal systems. Thereby they upset the endocrine and hormonal systems - specifically, the reproductive organs, the thyroid gland and the pancreas, and pave the way for sugar diabetes and many other pathologies.
Children contract such disorders in infancy with the mother's milk and, as a result, develop mental and physical deficiencies; slow pupils at school, they show symptoms of premature ageing afterwards, in adulthood. Women run the higher risk of sterility, miscarriages and the like. Congenital defects and other anomalies are also common. To add insult to injury, dioxins have an adverse effect on immunity and prepare the ground for infections, allergies, malignancies and many other grave diseases.
These toxic agents are resistant to chemical, biological and photolytic effects. They are temperature stable too up to the point of 1,200 0 - 1,250 0 C. Dioxins are found not only in household garbage, they are also present in products of the chemical, petrochemical and paper-and-pulp industries, in medical paraphernalia, in military hardware and related items, and so forth.
Many countries are eliminating such toxic compounds actually in one and the same mode, that is either by dumping wastes on special sites (garbage dumps) or burning them up. Yet neither method conforms to the present-day standards of ecological safety. For instance, the garbage dumps are a breeding-ground of deleterious processes like aerobic and anaerobic decomposition, sedimentation, evaporation, etc. Toxic agents thus escape into the ambient environment, especially in the case of unsanctioned, "wildcat" dumping. Besides, the dumps keep sprawling and take up more and more of the land.
The other technique - that of burning, incineration-is even worse. The process takes place at rather low temperatures (600 0 -900 0 C) - say, in incinerators or boiler units equipped with fire bars. Such incineration stimulates intensive formation of dioxins; besides, the slag and ashes, which make up 25 to 30 percent of the total mass, come to be contaminated with toxic agents. Still worse, this solid residual is carried away to the selfsame dumps, something that may result in disastrous consequences. It's a paradox indeed: incinerators cause further deterioration of ecology, as shown by the record of countries that have built all too many garbage disposal plants like that. Judging by the data of a case study in Germany and Sweden, the filtrate of the waste in one of the dumps had a 100-fold higher concentration of dioxin than that in decontaminated discharges released by industrial enterprises. And so, incinerators have turned into a kind of "suppliers" and "producers" of high- toxicity compounds. What's the way out?
But first, a few words about the scope of the problem. The point is that dioxins and other harmful substances are drawn into natural circulation - from garbage dumps they get into the atmosphere, bodies of water and soil; subsequently they are accumulated in fodder, fruits and vegetables. And sure enough, in milk, meat, eggs and other products consumed by man.
Chlorine-containing wastes reprocessed in the Vanyukov smelter:
4-waste particles and jets of melt;
6-feed of solid household wastes;
The circle comes full swing. One way of dealing with this problem is the recultivation of polluted tracts of land. Yet even the most effective techniques, such as thermal or light radiation "attacks" on dioxins in the topsoil, are quite costly. Besides, such techniques are still in their infancy.
Since we cannot close down the industries that involve dioxins as a by-product, the only way out is to utilize industrial and household wastes through recycling. What we need is a correct and comprehensive strategy that could render them harmless. Accordingly, their space lattice should be destroyed. In this fashion the toxic agents will decompose into elementary components posing no danger.
Now, how should we go about that? To begin with, by high-temperature treatment (at t 0 > 1,250 0 C) for no less than 2 s, without any pretreatment.
This can be done in a bubble bath furnace named after its maker - Vanyukov (the Vanyukov furnace).* This smelter consists of a tall caisonned shaft, at the bottom end of which there are heater blowers for blowing jets of hot gas through the melt. The melt begins to seethe, and this greatly intensifies the heat and mass exchange, and boosts the technological parameters of smelting.
The space lattice of dioxins treated this way is destroyed irreversibly, as shown by tests carried out at the Ryazan-based pilot smelter capable of reprocessing as much as 50 tons of solid wastes daily.
Samples were assayed for toxic agents by a panel of experts from the K.D. Pamfilov Academy of Utilities and an independent research center specializing in this field. The methods of such assays
* See: A. Grechko, "Copper Smelter of the Future", Science in Russia, No. 3, 1998. - Ed.
were in conformity with the international classification No. 1613 of EPA (Environmental Protection Agency, USA).
Even given the most unfavorable conditions, the concentration of dioxins and associated noxious substances was found as a result to be insignificant, far below permissible levels, if present at all. According to chromatography studies, the discharged gas contained harmless elementary components (N 2 , O 2 , CO 2 , H 2 O), while micro-impurities (such as HCl, HF, SO 2 , etc.) were much below permissible levels, with no secondary dioxins being formed.
So that's that: we have developed an ecologically safe and waste-free technology for the reprocessing (utilization) of toxic wastes. A panel of the State Ecological Examination Board has given a positive verdict. And our innovative technology has been awarded state patents.
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