ПРИЛОЖЕНИЕ И
Chapter 3. (part 1) Natural and waste water impurities
Content
1 Natural and waste water impurities. 2
1.1 Water quality. 2
1.2 Classification of water impurities. 5
1.3 Methods of treatment 7
1.4 Conclusion. 8
List of sources. 10
Natural and waste water impurities
Water quality
The term water quality has to do with the description of given water in terms of its characteristics. Characteristics of water quality include temperature; concentrations of various kinds of particles; concentrations of dissolved materials; and parameters such as turbidity, pH, color, conductivity, etc. The term characteristic is more inclusive than the term contaminant and would include temperature, color, turbidity, conductivity, etc. Two of these categories of characteristics, i.e., particles and dissolved materials, would include thousands of species each. A particular combination, or set, of characteristics would comprise a water quality profile.
Let’s make some definitions clear: all impurities in water (of natural and anthropogenic origin) are called contaminants. When we talk about human impact on the environment, we usually use the term “ pollutant ”. A pollutant is a synonym of the word contaminant but is more often identified as an introduced contaminant from an anthropogenic source. Those contaminants that interfere with a particular use may be considered pollutants.
To add further to the definitions that circle about the same idea, the term parameter is used frequently. Water quality parameters might include temperature, BOD, pH, specific electrical conductance, UV254 absorbance, etc. With respect to uses of water, the terms criterion and standard are important. A water quality criterion is a contaminant concentration limit that, if exceeded, may impair a use or cause a toxic effect in certain animals or plants. As an example, a boron limit of 0.5 mg=L is considered appropriate for citrus crops. A criterion could also specify a contaminant or parameter range, e.g., 3,3 ≤ pH ≤ 10,7 for trout (McKee and Wolfe, 1963, p. 236).
A water quality standard is a quasi-legal limit for a contaminant concentration or parameter value, i.e., the value may be referenced in a law but may be either ‘‘recommended’’ or ‘‘enforced,’’ depending upon the severity of the effects and the levels that are economically achievable. Usually, there is nothing absolute about the foregoing definitions.
Table 1 illustrates a water quality description (надо ли вставлять сюда в качестве примеров наши стандарты из СанПиН и т.п.???) for a proposed industrial waste discharge. Points of interest in Table 2.1 are
(1) some 37 contaminants are listed;
(2) concentration limits are shown for each contaminant;
(3) two places for discharge—a publicly owned treatment works and a river— are shown, each with its own respective discharge limits;
(4) limits are given in terms of the monthly average and the daily maximums;
(5) a variety of organic compounds are listed; and
(6) a variety of heavy metals are listed.
Each treatment situation is different and would have a different list of contaminants and different limits. A similar tabular description, but with different constituents, would apply to a municipal wastewater discharge, a drinking water treatment plant product water, or another industrial waste situation [Hendricks David W. Fundamentals of water treatment unit processes physical, chemical and biological…]
Water quality standards
A water quality criterion refers to a contaminant level, which when not exceeded, will not impair a given beneficial use of water. A great deal of research and deliberation is involved in establishing a criterion for a particular contaminant. Seldom is the result definitive, and considerable uncertainty may be associated with any numerical value determined.
A criterion becomes the basis for a standard, which is a codified criterion. Water quality standards have evolved over the decades of the twentieth century. Usually, standards are normative in character, i.e., dependent not only on effects on uses but on economic and cultural factors.
The main water quality parameters using in potable water quality assessment are shown in Table 2. Table illustrates the threshold level of indicators in Russian sanitary and hygienic standards in comparison with European and American ecological and hygienic requirements
Table 2
| № | Contaminant | unit | State hygienic standards, value, less than | ||
| Name | Russian Federation1 | USA2 | Europe3 | ||
| Aluminum | mg/l | 0,5 | 0,05-0,2 | ||
| Arsenic | mg/l | 0,05 | 0,01 | ||
| Benzene | mg/l | 0,005 | |||
| BOD5 | mgO2/l | 5,0 | |||
| Bromate | mg/l | 0,01 | |||
| Cadmium | mg/l | 0,001 | 0,005 | ||
| Chlorine (residual, as Cl2) | mg/l | 0,3-0,5 | MRDLG=4,0 | ||
| Chromium total | mg/l | 0,1 | |||
| Chromium, hexavalent | mg/l | ||||
| Copper | mg/l | 1,0 | 1,0 | ||
| Hardness | mg-eqv/l* grade | 7,0 | |||
| Iron | mg/l | 0,3 | 0,3 | ||
| Lead | mg/l | 0,03 | Zero (0,0) | ||
| Manganese | mg/l | 0,1 | 0,05 | ||
| Mercury | mg/l | 0,002 | |||
| pH | 6,0-9,0 | 6,5-8,5 | |||
| Sulphate-ion | mg/l | ||||
| Total coliforms (including fecal coliform and EColi) | bac/l | zero (0,0) | zero (0,0) | ||
| Total Dissolved Solids | mg/l | < | n/a** (500) | ||
| Zink | mg/l | 0,005 |
Note: n/a – not assessed
1, 2, 3 - Sanitary and Hygienic Standards in Russian Federation, USA and Europe, respectively [];
The list of water contaminants “under control” was developed in the second part of XX century, and has been extended several times since 1950.
By the 1980s, the idea of water quality had moved well beyond the traditional notions prevalent in the 1950s.
Nowadays the spectrum of contaminants is very broad and might well include more than 200 in a typical analysis.
All kinds of water impurities can be classified into 4 main groups, mentioned in the slide below.
Classification of water impurities
Of practical interest is the classification of water contaminants proposed by the Russian Soviet scientist L. Kulsky. This classification is based on physicochemical characteristics of impurities [1]. The essence of the proposed classification is that all impurities of water are divided into 4 groups in relation to the dispersion medium (water), two of groups are heterogeneous systems and the other two are homogeneous. The former are formed by suspensions and colloids presented in water, the latter are formed by substances that give molecular and ionic solutions with water.
Such an arrangement of groups and systems with increasing dispersion of impurities is expedient from a technological point of view, since water purification begins with the removal of coarse impurities and colloidal dispersed substances. Methods for removing these contaminants are the most common; they are widely used in all wastewater treatment plants of industrial and municipal water supply systems and industrial wastewater treatment plants.
Processes that correct the content of molecular and ionic impurities belong to special water treatment systems and are used where necessary as additional to the main technological complex, ensuring the removal of heterogeneous impurities.
Impurities in water are classified according to the phase-dispersed state in the following 4 groups:
Group I - Suspension (particle size 10-7 - 10-6 m or more)
These suspensions cause turbidity of water and in some cases its color. The group includes particles of clay, sand, poorly soluble hydroxide precipitates of Fe, Mg, Al, Si, Ca and other elements, suspended organic matter, detritus, plankton, etc. The presence of pathogenic bacteria, spore microorganisms and viruses is possible in suspended particles. When a fluid moves, these substances are suspended, while slow motion they settle.
Group II - Colloid-dissolved impurities (particle size 10-8 - 10-7 m) or ‘ colloids’
This group of substances includes:
- so-called “thin sludge” colloidal mineral and organo-mineral particles of grounds and soils,
- natural humic and fulvic acids and their salts, insoluble high-molecular compounds, producing a color into the water;
These compounds are aggregatively stable. At rest, they practically do not precipitate and form a heterophase system.
Group III - molecularly dissolved impurities (particle size 10-9 - 10-8 m)
This category includes gases dissolved in water and soluble organic compounds of natural and artificial (made with industrial effluents) origin. Such compounds give water tastes and odors, sometimes coloring. It is important to note that this group includes metals that form complex compounds, including heavy metals: Fe, Al, Mg, Cu, Zn, Ni, Co.
Group IV - truly dissolved inorganic salts capable of dissociation into ions (particle size 10-9 - 10-10 m)
Impurities: electrolytes. The quantitative characteristics of the equilibrium state are the degree and constant of dissociation. Electrolytes, the degree of dissociation of which in 0.1N solutions is 30% or more, are called strong, and electrolytes with a degree of dissociation less than 3% − weak (all salts dissolved in natural water are included).
It should be noted that between the states of substances that clearly define their position in each of the above groups, there are also intermediate states due to the dynamic relationship between the systems described. For example, molecular solutions can be partially dissociated (weak electrolytes), and when particles are associated, they approach colloidal solutions. High-molecular compounds also occupy an intermediate space between colloidal and molecular solutions; they can also contain ionic groups capable (under certain conditions) of producing mobile ions in solution. The instability of such systems gives the developed classification a special flexibility, as it allows using physicochemical processes to translate, to the extent necessary, water pollutants from one phase-dispersed state into another.
Considering separately all four groups, we can conclude that the proposed classification fully includes all impurities that pollute water. Using the features of each group, it is possible to find effective ways to remove the entire complex of water impurities using a small amount of appropriately arranged elements of wastewater treatment plants.
Methods of treatment
For the purification of water from the first group of impurities, physicochemical processes are used: adhesion on the surface of sorbents and granular media in filters, aggregation using coagulants and flocculants, flotation. Also mechanical methods used – sedimentation, micro-percolation, centrifugation.
The main methods of purification from second group- impurities: (fine) microfiltration, coagulation, sorption, membrane filtration. In addition, water treatment with various oxidizing agents (chlorine, ozone) improves its quality, as it oxidizes substances that give color to water, kills microorganisms, breaks down hydrophilic colloids, thereby creating favorable conditions for subsequent coagulation, accelerates the formation and precipitation of coagulant flakes. A significant increase in the coagulation effect is achieved by the introduction of flocculants of different composition. The type of flocculant (cationic, anionic, non-ionic) is determined based on the charge of colloidal impurities in the water.
The most effective methods for removing substances from the third group of contaminants from water are coagulation, sorption, membrane filtration, oxidation, distillation, ozonation, etc. It should be noted that these methods are effective only after the removal of larger impurities (group I and II).
The technique of water purification from impurities of the forth group consists in the binding of ions, which must be removed, into poorly soluble and weakly dissociated compounds. The following methods are used for this purpose: thermal (evaporation, freezing), ion exchange, electrodialysis, membrane methods - nanofiltration, reverse osmosis.
Conclusion
The main purpose of using this classification is to determine methods how to dispose each type of contaminant and treat the water containing impurities.
Some methods are presented in the picture and mentioned above, but let’s fix them one more time. Besides, one can determine the place for membrane processes application. The easiest way to correlate is using the prefix in titles: micro-, ultra-, and nanofiltration. Apart of reverse osmosis and dialysis, which do not have “size-look” prefixes, other methods can be correlate as following:
Using microfiltration one can dispose impurities of II and III (partially) groups, the treatment effect is XX% []. Ultra- and nanofiltration blocks may treat the water containing impurities of group III (ultrafiltration), nanofiltration – group III and IV. Treatment effects are XX% and XX% for ultrafiltration and nanofiltration respectively. The most effective methods providing so-called “deep purification” of water are reverse osmosis and electrodialysis. One can see in the slide the graphic illustration. Here we have the scale with size of contaminant particles and pore sizes of membrane. The smaller the pore size, the more particles are cut off and can be disposed. So we can provide the purification rate/efficiency demanded.
Table 2 Classification of membrane separation processes for liquid systems
| Name of process | Separation size range, m | Examples of materials separated | Group classification |
| Microfiltration | 10-0.1 * 10-6 m | Small particles, large colloids, microbial cells | I |
| Ultrafiltration | <0.1*10-6 – 5*10-9 m | Emulsions, colloids, macromolecules, proteins | II, III |
| Nanofiltration | ≈1*10-9 m | Dissolved salts, organics | III, IV |
| Reverse osmosis (hyperfiltration) | <1*10-9 m | Dissolved salts, small organics | IV |
| Electrodialysis | <5*10-9 m | Dissolved salts | IV |
List of sources
1. Кульский Л.А. Булава М.Н. Гороновский И.Т. Проектирование и расчет основных сооружений водопроводов (издание 2-е переработанное и дополненное), Киев, «Будiвельiнiк», 1972. – 424 с.
2. Й.Криш К-829 Мембраны и мембранные технологии: учебное пособие/ под общ.ред. Н.С. Попова –Тамбов: изд-во ИП Чеснокова А.В., 2011. – ХХ стр.
3. Nalco Water Handbook
4. Hendricks David W. Fundamentals of water treatment unit processes – physical, chemical and biological.
5. J.F. Richardson, J.H. Harker. Coulson and Richardson’s Chemical Engineering. V.2. Particle technologies and separation process. Fifth edition. Butterworth Heinemann, an imprint of Elsevier Publishing 2002. ISBN – 0-7506-4445-1
6. Й.Криш К-829 Очистка природных и сточных вод. Часть 2: Очистка воды. Очистка питьевой и технической воды: учебное пособие/ под общ.ред. Н.С. Попова –Тамбов: изд-во ИП Чеснокова А.В., 2011. – ХХ стр.
7. Дытнерский Ю.И. Обратный осмос и ультрафильтрация
8. Применение мембранных процессов. Часть 3: учеб. пособие / Е.В. Мигалатий, О.Б. Насчетникова, Г.Б. Браяловский и др; Под общ. ред. Н.С. Попова. – Тамбов: Изд-во ИП Чеснокова А.В.., 2011. – 108 с
9. Comprehensive membrane science and engineering. Second Edition. Editors in-Chief: Enrico Drioli, Lidietta Giorno, Enrica Fontananova. Institute on membrane technology of the National Research Counsil of Italy, ITM-CNR, V.1,Elseiver B.V, 2017. 1720 pages, p.87, ISBN – 978-0-444-63775-8