UNCONVENTIONAL REAGENTS AS POLLUTION CATCHERS

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Опубликовано в библиотеке: 2021-09-19
Источник: Science in Russia, №3, 2011, C.14-18

by Tatyana BUDYKINA, Dr. Sc. (Tech.), South-Western State University (Kursk)

 

The contemporary industry cannot get along without utilization of enormous water volumes. When participating in a production cycle, water on its way absorbs a large quantity of contaminants including toxic ones for people and the environment. Search for efficient methods of their consequent removal is a topical problem faced by researchers. Hence, application of unconventional reagents is one of the promising approaches.

 

VANISHING WEALTH

 

The climate change on the planet results in draughts or long-term floodings in its territories, which leads to shortage of potable water. The United Nations data prove that around 700 mln people in 43 countries in the world remain permanently in the conditions of such shortage and stress caused by the latter. Approximately one third of the population on the Earth has no access to water for domestic needs, and its sixth part is in need of pure potable water. Annually 500 mln people get sick including 10 mln dead (mainly children) because of water shortage and poor quality.

 

According to Russian scientists, in 2035-2045 the volume of fresh water consumed by the planet's population

 
стр. 14

 

will come up to its resources. However, the global crisis can occur even before that time, as considerable stocks of water remain already today only in several countries (Russia including), while other countries experience acute shortage of water. That is why many experts confirm that in the near future water will be considered a third resource (after oil and gas) in volume of yielded revenues, and the world's leading states will launch competition for its possession.

 

Besides, an unrestrained and uncontrolled industrial growth observed over quite a long period in many regions of the planet implies many negative consequences. We can say without exaggeration that the Earth's river network has actually become a natural sewage system of the civilization, in which technogenic contaminants are abundant: mineral fertilizers, pesticides, surface-active substances, heavy metal salts, and oil products. Moreover, morbific bacteria get into water basins.

 

The danger of such kind would seem non-topical for Russia, whose territory contains 22 percent of the world stocks of potable water. Actually that is not so. The load on water resources has increased due to a considerable rate of production units connected with processing of minerals and decline in general ecological culture of the population. As a result, its quality deteriorates in many places. True, in our country anthropogenic impact is 4 times less than an average worldwide index (0.13 mln people per 1 km), the annual reduction of water stocks makes up around 1 percent (5 percent in the world), and a frequency of sewage dilution (58 times) exceeds the average worldwide more than twice. Nevertheless, the situation is unsatisfactory in the most habitable and populated areas of Russia. Though it cannot be accepted as satisfactory even where population is much less. For example, in the country north-east (a third part of the total territory) only 1/3 of river water resources can be accepted as pure.

 

As a whole, the geographical feature of all mentioned contaminants lies in the fact that our main industrial regions with high concentration of population are located in river upper reaches. That is why such great rivers as the Volga, the Don, the Ural, the Ob, the Yenisei, and the Pechora are assessed as contaminated along the whole length, and their tributaries the Oka, the Kama, the Tom, the Irtysh, the Tobol, and the Tura are recognized as highly contaminated. Besides, with the existing district water supply systems in most of our cities and townships, the condition of water sources cannot guarantee the required quality of potable water.

 

IS THERE A WAY OUT?

 

According to specialists, measures should be taken at least in two directions. On the one hand, striving to prevent contamination of surface and ground waters, and, on the other hand, to carry out water treatment prior to its utilization. Solution of the first problem is a subject for separate studies. We shall focus on the second problem in this paper.

 

More than 40 years ago, a member of the Ukrainian Academy of Sciences Leonid Kulsky, one of the founders of chemistry and technology of water treatment scientific trend, suggested to divide all contaminants into four groups depending on a form of their presence in water and classified methods of disposal of these substances. Thereafter, the respective technologies were updated noticeably, and new ones were developed.

 
стр. 15

 

 

Dependence of metal ion content on the time of contact with the reagent; schematic number 2 is a test with annealing at 800ºC by AQUAMAG.

 

 

Dependence of dyestuff content on the reagent contact duration.

 

At present, the most common methods are those, which are directed to recovery of suspended particles from water, removal of dissolved impurities, and water sterilization. Thus, use is made of coagulation*, sorption**, ultraviolet treatment, etc. To realize such processes, reagents as auxiliary substances are used, which ensure intensification of the treatment process, removal of contaminants and decolorization of water. The conventional reagents include salts of aluminum, iron, calcium, etc. Unfortunately, all of them have a number of disadvantages, namely, despite high costs they do not guarantee final purification up to the standards of the maximum permissible concentrations of harmful compounds, slightly oxidize or overalkalize water, which requires its further neutralization and, consequently, use of additional reagents. Besides, reagents are used in abundance, which leads to formation of their increased concentration in water and adversely affects living

 

* Coagulation is a process of adding of a chemical reagent (coagulant) to destabilize suspended colloidal particles with their consequent tlocculation.--Ed.

 

** Sorption is absorption of any substance from the environment by a solid body or a liquid.--Ed.

 

organisms. For example, use of aluminum salts is undesirable not only due to a high residual content of this chemical element proper but also to a negative action on human organism*, manifesting itself in breakage of metabolism, particularly, mineral metabolism, of functions of nervous system.

 

When choosing a treatment method, local peculiarities should also be taken into account. Say, reagents containing iron are unacceptable for the Kursk region due to its excessive content in local waters.

 

For the last few years there appeared new unconventional reagents in bioecological protection technology (they are discussed below), free from defects but information on their properties and a scope of application is still insufficient. To fill the vacuum, in 2008-2010 we carried on experimental studies to determine their efficiency, to choose optimal concentration, dosage, and replaceability of conventional reagents by them.

 

The reagent Aquamag produced by the Russian Mining-and-Chemical Society (Moscow) and a titani-

 

See: N. Kaletina. G. Kaletin, "Trace Elements as Biological Regulators", Science in Russia. No. 1, 2007.--Ed.

 
стр. 16

 

um coagulant produced by Lukoil-Komi Ltd. (Ukhta, Republic of Komi), which appeared in the market of national environment protection services for the last 2-3 years, were tested. The former is designed for water decontamination and is a magnesium-containing compound with magnesium oxide predominance. It is obtained by cleavage of brucite mined at the Kuldur deposit (Jewish Autonomous Region), and the extent of its cleavage depends on current tasks. The latter is best applicable for removal of suspended particles from water and is a composition based on oxides, hydroxides, sulphates and oxyhydrosulphates of titanium and aluminum.

 

Efficiency of these two unconventional reagents was tested on natural waters of the Kursk region and sewage waters of machine-building and woodworking plants, knitted-goods factory, poultry plant, sugar mill, and dairy shop. Studied were contaminants of organic origin (dyestuffs and phenols) and inorganic origin (salts of heavy metals and suspended materials). We had to find out an extent of efficiency of unconventional reagents in protection of hydrosphere.

 

FIVE DIRECTIONS

 

First of all, we tried to answer the question, how Aquamag dealt with removal of heavy metal ions, namely, copper and trivalent chrome (Cr3+), from water. The point is that sewage water, which contains the above-mentioned ions and also ions of other heavy metals such as nickel, zinc, cadmium, etc., is very harmful to the environment as these components are preserved in biosphere for a long time (from several dozens to thousands of years), accumulate in food chains and in large quantities are toxic for living creatures. Therefore, strict requirements are set to clean sewage out of heavy metals. Usually such cleaning is carried out by reagent, ionexchange, sorption and other methods. The most common conventional method is a reagent plus lime. But can the above said Aquamag be used for this purpose? We have proved that it is fit to be used for cleaning of water from copper ions with their high concentration--30-35 mg/1. The level of purification 30 minutes after the start of the contact with a reagent makes up 72 percent, which permits its use for cleaning of sewage of galvanic works.

 

Of prime importance is a decrease in the amount of chrome ions (Cr3+) in sewage of mechanical-engineering plants and tanneries, where ion concentration of this metal reaches 11.2 mg/1, which is by an order of magnitude higher than the maximum permissible rate. Our tests proved that at the initial concentration of this contaminant 24.5 mg/1, already during the first 10 minutes from the start of the contact with Aquamag, 100 percent disposal of chrome ions (3+) was achieved. As a result, we developed treatment technologies, which did not require further water neutralization as it was not overalkalized in such case and finally allowed creation of a less expensive closed system of water supply.

 

The second direction of our research is application of unconventional reagents for water treatment from organic highly toxic compounds, namely, phenols. It is well-known that they are used for production of phenol-formaldehyde resins necessary for the production of phenoplasts, synthetic fiber, medical preparations, antiseptics, dyestuffs, detergents, pesticides, etc. and, therefore, are present in sewers of coke-chemical, oil-refining, chemical, paper-and-pulp, pharmaceutical and other industries.

 

The main disadvantages of the conventional methods of controlling these dangerous pollutants are duration of preparation of necessary sorbents and their high cost, insufficient degree of phenol disposal, and necessity for heating of solutions and reagents subject to treatment. We tried to use Aquamag for the same purpose and proved that, when passing sewage through this reagent at Izoplit woodworking enterprise (Oboyan, Kursk region), 100 percent disposal of phenol took place.

 

Science in Russia, No. 3, 2011

 
стр. 17

 

Besides, water oxidation level and salt content decreased, and it was proved later that this magnesium-containing reagent was applicable not only in woodworking but also in other industries requiring water treatment from phenols. (In January 2011, our proposal to use Aquamag for disposal of metal ions and phenols from water was proved by the patent for invention.)

 

The third direction of our research is connected with sewage treatment after dyeing and finishing operations at enterprises of light industry. Unfortunately, we usually fail to obtain 100 percent removal of dyestuffs, though these components are destructive for water fauna and flora. The tests with Aquamag showed that this reagent was suited for efficient treatment of colored solutions formed at textile and knitting factories, tanneries and dry-cleaning stores. In the course of tests a probabilistic mechanism of acidic dyestuff disposal from sewage was established, and the sorption capacity of reagent was determined. For example, 100 percent water cleaning from a blue dyestuff is reached during a 20 min contact with it and from a bright green one in 30 min. Based on these experiments, the corresponding technologies were suggested for application in industry.

 

The fourth direction of the research is neutralization of acid sewage. It has turned out that use of Aquamag does not imply formation of gypsum difficult to dissolve, water is not overalkalized as a result of treatment, and pH (acidity level) requires no adjustment before sewage is discharged into a manifold or a reservoir.

 

And, finally, the fifth direction is efficiency determination of titanium coagulant in removing of suspended substances from natural waters and sewage, as compared with a conventional coagulant (aluminum sulphate) and some other compounds of similar action. It was established in our tests conducted with sewage of a poultry farm and a dairy plant that titanium coagulant was comparable in efficiency to oxychlorides and aluminum sulphate. Besides, doses of the latter in terms of a marketable product, as a rule, are higher than doses of titanium coagulant given equal treatment effect.

 

Summing up, we shall note that our research has proved that conventional reagents in the bioecological protection engineering can be substituted by less expensive and modern ones. In this case, payment of enterprises will decrease not only for sewage sludge disposal but also for sewage discharge at the expense of creation of circulating water consumption systems.

 

The research was supported by a grant of the President of the Russian Federation for young scientists with a doctor's degree No. MD-563.2010.8.


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© Tatyana BUDYKINA () Источник: Science in Russia, №3, 2011, C.14-18

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