Sanitary and chemical indicators of wastewater pollution. Chemical indicators of water
The most important indicators of water quality that determine its suitability for drinking, industry and energy are:
3. concentration of hydrogen ions - pH;
4. general rigidity and its components;
5. oxidizability (organic matter content);
6. total alkalinity and its constituents;
In addition, for many processes it is necessary to control the content of sodium cations, chlorine anions, carbonate, sulfate and silicate compounds, as well as iron and aluminum compounds in water.
For drinking water, along with the first 5 indicators, the content of a number of ions, organic, biological contaminants and radionuclides is strictly standardized.
To determine the content of suspended solids in water, 1 liter of analyzed water is filtered through a dense paper filter, which is then dried at a temperature of 105-110 ° C to constant weight. An indirect, but more express, method is to determine the content of suspended matter by optical methods - nephelometric, transparency (font or cross) or turbidity of water by comparison with reference samples.
The dry residue is determined by evaporating 1 liter of a pre-filtered water sample and drying the residue at 105-110 ° C to constant weight. The dry residue does not include suspended solids, gases dissolved in water and volatile substances. If the dry residue is calcined at 800 ° C, its weight will decrease and a calcined residue will be obtained. The reduction in weight results from the combustion of organic matter and the decomposition of carbonates.
The alkalinity of water is the total concentration of anions of weak acids and hydroxyl ions in water, expressed in mg-eq / l. Depending on the type of anions that determine alkalinity, hydration, carbonate, silicate, humane and phosphate alkalinity are distinguished. In most natural waters, the concentration of bicarbonates significantly exceeds the concentration of anions of other weak acids, and the total alkalinity coincides with that of bicarbonate.
Since all of these substances react with acid, the total alkalinity of water is determined by the amount of acid consumed for titration with the indicator methyl orange or phenolphthalein. The color transition in methyl orange occurs at pH = 4.4, and in phenolphthalein at pH = 8.2. Comparing the amount of acid used for titration for methyl orange M with the amount of acid used for titration for phenolphthalein F, it is possible to determine the type of alkalinity.
Definition different types alkalinity
Chemical indicators
The chemical composition of water is the cause of non-infectious diseases.
Reasons for the change chemical composition water:
1) industrial and agricultural human activity - the flow of industrial and household Wastewater, precipitation containing harmful substances.
2) purification of drinking water - the use of chemical methods of water treatment and the content of residual amounts of reagents in the water.
Indicators:
1) dry residue
2) rigidity
3) chlorides
4) sulfates
5) nitrates and nitrites
6) pH value
7) trace elements
Dry residue.
The dry residue is the total dissolved solids in the water and gives an indication of the degree of mineralization of the water. The main ions that determine the dry residue are carbonates, bicarbonates, chlorides, sulfates, nitrates, sodium, potassium, calcium, magnesium. This indicator influences other indicators of drinking water quality such as taste, hardness, corrosive properties and tendency to scale formation.
Water with a dry residue of more than 1000 mg / l is called mineralized, up to 1000 mg / l - fresh. Water containing up to 50-100 mg / l is considered slightly mineralized (distilled), 100-300 mg / l is satisfactorily mineralized, 300-500 mg / l is optimal mineralization and 500-1000 mg / l is highly mineralized. Mineralized water is sea, mineral, fresh - river, rain, glacier water.
Solids value:
1) Water with a high content mineral salts unsuitable for drinking, as it has a salty or bitter-salty taste, and its use, depending on the composition of the salts, leads to unfavorable physiological changes in the body:
a) promotes overheating in hot weather,
b) leads to a violation of thirst quenching,
c) changes water-salt metabolism by increasing the hydrophilicity of tissues,
d) enhances the motor and secretory of the stomach and intestines.
2) Low-mineralized water tastes unpleasant, long-term use can lead to a violation of water-salt metabolism (a decrease in the content of chlorides in tissues). Such water, as a rule, contains few trace elements.
Rigidity
The total hardness of water is mainly due to the presence of calcium and magnesium in the water, which are in the form of bicarbonates, carbonates, chlorides, sulfates and other compounds; ions of strontium, iron, barium, manganese are also important.
Stiffness types:
1. Disposable - the amount by which the total hardness of water decreases when it is boiled for 1 hour. It is caused by calcium and magnesium bicarbonates, which break down and precipitate in the form of carbonates (scale).
2. Carbonate - this is the hardness caused by bicarbonates and slightly soluble carbonates. The removable hardness is approximately equal to the carbonate hardness, but when there are a lot of sodium and calcium bicarbonates in the water, the carbonate hardness significantly exceeds the removable hardness.
3. Constant - this is the hardness that remains after boiling and is due to chlorides, carbonates, and sulfates of calcium and magnesium.
Water with a total hardness of up to 3.5 meq / l is called soft, 3.5-7 - medium hardness, 7-10 - hard, over 10 - very hard.
The main natural sources water hardness are sedimentary rocks, filtration and runoff from the soil. Hard water forms in areas with a dense arable layer and calcareous formations. Groundwater is characterized by greater hardness than surface water. Groundwater, rich in carboxylic acids and dissolved oxygen, has a high dissolving capacity in relation to soils and rocks containing calcite, gypsum and dolomite minerals.
The main industrial sources of hardness are effluents from plants producing inorganic chemical substances, and the mining industry. Calcium oxide is used in the construction industry, the production of pulp and paper, sugar refining, oil refining, tanning and as a reagent for water and wastewater treatment. Magnesium alloys are used in foundry and stamping production, household products. Magnesium salts are used in the production of metallic magnesium, fertilizers, ceramics, explosives, medicines.
Hard water value:
· Organoleptic properties deteriorate - water has an unpleasant taste;
• absorption of fats in the intestine is disturbed as a result of the formation of calcium-magnesium insoluble soaps during saponification of fats;
In persons with sensitive skin contributes to the appearance of dermatitis due to the fact that calcium-magnesium soaps have an irritating effect
In the household aspect: consumption increases detergents, scale is formed during boiling, hair after washing becomes tough, clothing fabrics lose their softness and flexibility, the digestion of meat and vegetables worsens with the loss of vitamins as a result of their binding into indigestible complexes,
· There is evidence that drinking too hard water can lead to an increase in the incidence of urolithiasis; although there is evidence that rigidity can serve as protection against disease;
· With a sharp transition from the use of hard water to soft and vice versa, people may experience dyspeptic symptoms;
· Spoils the look, taste and quality of tea, which is the most important drink among the population, stimulating gastric secretion and quenching thirst;
There is evidence that drinking soft water can cause cardiovascular disease.
Chlorides.
Chlorides can be of mineral and organic origin. The presence of chlorides in natural waters may be associated with the dissolution of salt deposits, pollution caused by the application of salt to the roads in order to combat snow and ice, discharge of effluents by enterprises of the chemical industry, the operation of oil wells, wastewater discharge, irrigation drainage, pollution from washing out solid wastes and the invasion of sea water into coastal areas. Each of these sources can cause pollution of surface and ground waters. The high solubility of chlorides explains wide use them in all natural waters.
Impact on health. Chlorides are the most common anions in the human body and play an important role in the osmotic activity of the extracellular fluid; 88% of the chlorides in the body are found in the extracellular space. In healthy people, chlorides are almost completely absorbed.
Chloride value:
· Organoleptic properties deteriorate - water acquires a salty taste and, therefore, water consumption is limited;
· Affects water - salt metabolism; the level of chlorides in the blood rises, which leads to a decrease in urine output and the redistribution of chlorides in organs and tissues;
· Cause suppression of gastric secretion, as a result of which the process of food digestion is disrupted;
· There is evidence that chlorides have a hypertensive effect and in people suffering from hypertension, drinking water with a high chloride content can cause an aggravation of the course of the disease;
· Are an indicator of pollution of underground and surface water sources, since chlorides are contained in wastewater and human physiological excretions.
Sulfates.
Sulfates go to aquatic environment with waste water from many industries. Atmospheric sulfur dioxide (SO 2), formed during fuel combustion and released during roasting processes in metallurgy, can contribute to the sulfate content in surface waters... Sulfur trioxide (SO 3), formed during the oxidation of sulfur dioxide, in combination with water vapor form sulfuric acid, which falls out in the form of "acid rain" or snow. Most sulfates are water soluble.
With aluminum sulfate, which is used as a flocculant in water purification, an additional 20-50 mg / l of sulfates can enter the purified water. Sulfates are not removed from water conventional methods cleaning. Concentration in the majority fresh water very low.
The value of sulfates:
· Sulfates are poorly absorbed from the human intestine. They slowly penetrate cell membranes and are quickly excreted through the kidneys. Magnesium sulfate acts as a laxative at concentrations above 100 mg / L, leading to a cleansing of the gastrointestinal tract. This effect occurs in people who use water with a high sulfate content for the first time (when moving to a new place of residence where they use sulfate water). Over time, a person adapts to such a concentration of sulfates in the water.
· Water consumption is limited, since sulfates impart a bitter-salty taste to water in a concentration of more than 500 mg / l.
· Adversely affect gastric secretion, leading to disruption of the processes of digestion and absorption of food.
· Are an indicator of surface water pollution by industrial wastewater and groundwater by the waters of overlying aquifers.
Nitrates, nitrites.
Ammonia is the initial decomposition product of organic nitrogen-containing substances. Therefore, the presence of ammonia in water can be regarded as an indicator of epidemically dangerous fresh water pollution. organic matter animal origin. In some cases, the presence of ammonia does not indicate poor quality water. For example: in deep groundwater, ammonia is formed due to the reduction of nitrates in the absence of oxygen, or an increased content of ammonia in marshy and peat waters (ammonia of plant origin).
Salts of nitrous acid (nitrites) are products of incomplete oxidation of ammonia under the influence of microorganisms in the process of nitrification. The presence of nitrites indicates a possible contamination of water with organic substances, however, nitrites indicate a known age of pollution.
Nitric acid salts (nitrates) are the end products of the mineralization of organic matter by bacteria present in the soil and in water with a sufficient oxygen content. The presence of nitrates in water without ammonia and nitrites indicates the completion of the mineralization process.
The simultaneous content of ammonia, nitrites and nitrates in water testifies to the incompleteness of this process and the ongoing, epidemically dangerous pollution of water. However, the increased nitrate content may be of mineral origin. Nitrates are used as fertilizers (saltpeter), in explosives, in chemical production, and as food preservatives. Some nitrates are the result of atmospheric nitrogen fixation in the soil (bacterial synthesis). Nitrites are used as food preservatives. Some nitrates and nitrites are formed when the rain leaches out nitrogen oxides, which are the result of lightning strikes or come from anthropogenic sources.
Nitrates and nitrites are widespread in environment, they are found in most foods, in the atmosphere and in many water sources. The entry of these ions into the water is facilitated by the use of fertilizers, decay of plant and animal material, domestic wastewater, disposal of sewage sludge into the soil, industrial discharges, washing out of landfills and washing out from the atmosphere. In natural clean waters nitrates, as a rule, are few. However, in groundwater within settlements, livestock farms and in other places where the soil is long and massive
gets dirty, nitrate content can be high.
Since none of the commonly used water purification and decontamination methods change significantly the nitrate level, and since the nitrate concentration does not change appreciably in the water distribution system, the levels in tap water are often completely similar to those for water sources. The content of nitrites in tap water is lower than in water sources, which is caused by their oxidation during water purification, especially during chlorination.
Metabolism. Nitrates and nitrites are readily absorbed by the body. Nitrates are absorbed in the upper parts of the small intestine, concentrated mainly in saliva through the salivary glands, and excreted through the kidneys. Nitrate can easily be converted to nitrite by bacterial reduction. The reduction of nitrates to nitrites occurs throughout the body, including the stomach. This transformation
depends on the pH value. Infants, whose stomach acid is normally very low, produce large amounts of nitrite. In adults, acidity in the stomach is characterized by a pH value of 1-5, and to a lesser extent, the conversion of nitrate to nitrite occurs. Nitrite can oxidize hemoglobin to methemoglobin. Under certain conditions, nitrites can react in the human body with secondary and tertiary amines and amides (food) to form nitrosamines, some of which are considered carcinogens.
The value of nitrates, nitrites:
· Cause the development of "water-nitrate methemoglobinemia" due to the oxidation of hemoglobin by nitrites to methemoglobin. Basically, this disease occurs in children. The sensitivity of infants to the action of nitrates was attributed to their high intake into the body relative to body weight, the presence of nitrate-reducing bacteria in the upper gastrointestinal tract, and easier oxidation of embryonic hemoglobin. In addition, hypersensitivity is observed in infants with gastrointestinal dysfunction, in which the number of bacteria that can convert nitrates to nitrites increases. The use of artificial formula for feeding children is also seen as a reason for the increase in morbidity, since the water used to prepare the formula may contain an increased amount of nitrates. In infants, a near-neutral pH in the stomach promotes bacterial growth in the stomach and in the upper intestines. In children, there is a deficiency in two specific enzymes that reverse the conversion of methemoglobin into hemoglobin. Prolonged boiling can exacerbate the problem by increasing the amount of nitrate when the water evaporates. Most often, the cause of the disease was the use of private wells with microbiological pollution as a source of water (they do not contain algae that actively consume nitrates). The disease is characterized by the development of shortness of breath, cyanosis, tachycardia, seizures. In children over 1 year old and in adults, the disease in the form of acute toxic cyanosis is not observed, but the content of methemoglobin in the blood increases, which worsens the transport of oxygen to the tissues - this is manifested by weakness, pallor of the skin, and increased fatigue.
· Cause the formation of nitrosamines, some of which may be carcinogenic. The formation of these substances occurs in the mouth or elsewhere in the body, where the acidity is relatively low.
· Are an indicator of water pollution by organic substances.
PH value (active reaction).
Acidic are swampy waters containing humic substances, alkaline - The groundwater rich in bicarbonates.
Meaning:
· Defines natural properties water;
· Is an indicator of the pollution of open water bodies when acidic or alkaline industrial wastewater is released into them;
· PH value is closely related to other indicators of drinking water quality. The growth of iron bacteria is highly pH dependent. They form iron oxide hydrate as an end product of metabolism, which gives the water a red color. At high pH values, the water tastes bitter.
· The efficiency of the processes of coagulation and disinfection depends on the pH. The disinfecting effect of chlorine in water is lower at high pH values; this is due to a decrease in the concentration of hypochlorous acid.
Trace elements.
Various trace elements are found in natural waters: bromine, boron, copper, zinc, manganese, cobalt, molybdenum, lead, arsenic, beryllium, fluorine, iodine, etc.
Fluorine.
The main source of fluoride intake in the human body is drinking water. The source of fluorine in water is the soil and the underlying rocks, where there are soluble fluorine-containing mineral compounds. Open water bodies can be contaminated with fluorine-containing compounds when industrial wastewater is discharged into them. The water of open reservoirs contains a reduced amount of fluorine. High concentrations of fluorine are more common in the waters of artesian wells.
Fluoride consumed with water is almost completely absorbed, retained in the skeleton and in small amounts in dental tissues. At a concentration of fluorine above 1.5 mg / l, people who drink such water develop dental fluorosis, over 5 mg / l skeletal fluorosis is possible. Dental fluorosis is characterized by the appearance on the enamel of the teeth porcelain-like or pigmented in yellow or Brown color stains or erosion, as well as increased tooth wear. With a decrease in the concentration of fluorine below 1 mg / l in the population, the incidence of caries increases, since it reduces the solubility of enamel under conditions of increased acidity of the environment. In high doses, fluoride is acutely toxic to humans: hemorrhagic gastroenteritis, acute toxic nephritis and damage to the liver and heart muscle develop.
Iron.
In surface waters, iron is present in a trivalent state, although under reducing conditions, ferrous iron may also be present in groundwater. The presence of iron in natural waters is associated with the dissolution of rocks and minerals, drainage of acidic mine waters, filtration from landfills, wastewater discharge and effluents from metallurgical enterprises.
Iron value:
· Ferrous salts are unstable and precipitate in the form of insoluble iron hydroxide, which settles in the form of a rusty coating. Iron gives water turbidity, yellow-brown color. Such water tastes unpleasant (has a bitter metallic taste), stains linen and plumbing fittings.
· Iron sediment reduces the flow of water and accelerates the growth of iron bacteria. They receive energy from the oxidation of ferrous iron to ferric, and during this process sludge is deposited, covering the pipelines.
Copper.
Copper is often found in surface waters and imparts an unpleasant astringent taste and color to the water. The presence of copper in water does not pose a health hazard, although it may interfere with the use of water for domestic purposes. Copper increases the corrosion of aluminum and zinc cookware and fittings.
Manganese.
Manganese, present in surface waters, occurs in both soluble and suspended form. Higher manganese concentrations are usually associated with industrial pollution. Manganese intoxication from drinking water, not described. Manganese imparts an undesirable aftertaste to beverages and stains fittings and laundry during washing. If the manganese compounds in solution undergo oxidation, the manganese precipitates, causing scale problems.
Zinc.
Zinc carbonates, oxides and sulfides are poorly soluble in water, although highly soluble chloride and sulfate salts are prone to hydrolysis to form zinc hydroxide and carbonate. As a result, the concentration of zinc in natural waters is usually low. The concentration of zinc in tap water is higher due to its leaching from galvanized pipes, brass and zinc-containing fittings. Due to the low toxicity of zinc and effective homeostatic mechanisms of regulation, the danger to humans of chronic toxicity of zinc from drinking water and diet is unlikely. Zinc imparts an undesirable astringent taste to the water, and can also become opalescent and form an oily film when boiled.
Aluminum.
Aluminum enters the water as a result of industrial wastewater discharge, erosion, leaching of matter from minerals and soil, atmospheric dust pollution and precipitation. Aluminum salts are widely used in water purification to eliminate its color and turbidity. Ingested aluminum salts do not cause any harmful effects in humans. Normally, they are not absorbed from food and water, but form complexes with phosphates and are excreted in feces. Aluminum can impair the organoleptic properties of water - an unpleasant, astringent taste appears.
Chromium.
Drinking water usually contains very low concentrations of chromium. Water pollution occurs as a result of the use of chromium in human economic activities and as a result of the discharge of effluents containing chromium compounds. The adverse effects of chromium present in water to humans are associated with hexavalent chromium. Chromium in the range of 10 mg / kg body weight causes liver necrosis, nephritis and death in humans; lower doses lead to irritation of the gastrointestinal mucosa. There is evidence that chromium can cause the development of malignant neoplasms.
Lead.
The presence of lead in surface waters is due to the discharge of industrial effluents. IN drinking water The lead content is relatively low, but when lead pipes are used, its concentration can increase significantly. There is information in the literature on intestinal absorption of lead from aqueous solutions containing dissolved lead. Lead in high doses is a cumulative metabolic poison of general action.
Mercury.
Mercury can be present in the environment as a metal, in the form of salts and in the form of organomercury compounds, the most important being methylmercury. Methylmercury can be produced from inorganic mercury by the action of microorganisms found in sediments and sewage sludge. The presence of elevated concentrations of mercury indicates water pollution. Fish and mammals absorb and retain mercury, and in areas where water is contaminated with mercury and where fish constitutes a significant part of the diet, intake of the element can be significant.
Mercury has no physiological function in the body. Methylmercury is completely absorbed in the gastrointestinal tract. Mercury poisoning is manifested by neurological and renal impairment, gonadotoxic and mutagenic effects.
Nickel.
Many nickel salts are soluble in water, which can lead to water pollution, and industrial effluents containing nickel compounds can also be discharged into rivers. Some nickel is removed with traditional water treatment methods, so the nickel content of treated water is lower than that of untreated water. Nickel is an essential element, absorption from the gastrointestinal tract is low. Nickel is relatively non-toxic. The levels of nickel found in food and water are not believed to pose a serious health hazard.
Water temperature surface sources depends on air temperature, humidity, speed and nature of water movement and a number of other factors. It can vary considerably. The water temperature of underground sources is relatively constant and is usually 4-8 ° C.
The optimum water temperature for drinking purposes is 7-11 ° C.
Water color- color intensity, expressed on the platinum-cobalt scale. One degree of the scale corresponds to the color of 1 liter of water, colored by the addition of 1 mg of cobalt chloroplatinate salt. The color of groundwater water is caused by iron compounds, less often by humic substances (primer, peat bogs, permafrost waters); the color of the surface - by the flowering of reservoirs.
According to the norms of SanPiN 2.1.4.559-96 for drinking water, the color of water should not be higher than 20 o.
Turbidity is determined by the content of suspended solids in the water. Comparing under the same illumination a sample of the investigated water and samples of distilled water of the same volume, artificially turbid with a certain amount of a standard suspension, a sample with the most suitable concentration is selected. Turbidity can be expressed in milligrams per liter (mg / L), formazin turbidity units, or NTU turbidity units. Turbidity of water in underground sources, as a rule, is low and is caused by a suspension of iron hydroxide. In surface waters, turbidity is often caused by the presence of phyto- and zooplankton, clay or silty particles; therefore, the value depends on the flood (low-water) time and changes throughout the year.
According to the norms of SanPiN 2.1.4.559-96, the turbidity of drinking water should not exceed 1.5 mg / l.
Taste caused by the presence of solutes in the water and can be salty, bitter, sweet and sour... Natural waters usually have only a salty and bitter taste. The salty taste is caused by the sodium chloride content, the bitter taste is caused by the magnesium sulfate. A large amount of dissolved carbon dioxide gives the water a sour taste. Water can also have inky or glandular taste caused by iron and manganese salts, or astringent taste caused by calcium sulfate.
According to the norms of SanPiN 2.1.4.559-96, the taste should be no more than 2 points.
Smells waters are determined by living and dead organisms, plant residues, specific substances released by some algae and microorganisms, as well as the presence of dissolved gases in the water - chlorine, ammonia, hydrogen sulfide, mercaptans or organic and organochlorine contaminants. There are natural smells: aromatic, marsh, putrid, woody, earthy, moldy, fishy, herbaceous, indeterminate and hydrogen sulfide. Smells of artificial origin are called according to the substances that determine them: phenolic, chlorophenolic, petroleum, resinous etc. The intensity of the odor is measured organoleptically on a five-point scale:
0 points - smell and taste are not detected
1 point - very faint smell or taste (only an experienced researcher detects)
2 points - faint smell or taste that attracts the attention of a layman
3 points - noticeable smell or taste, easily detectable and causing complaints
4 points - a distinct smell or taste that can make you refrain from drinking water
5 points - so much strong smell or a taste that the water is completely unsuitable for drinking.
According to the norms of SanPiN 2.1.4.559-96, the smell of water should be no more than 2 points.
CHEMICAL INDICATORS OF WATER QUALITY
Active reaction water - the degree of its acidity or alkalinity - is determined by the concentration of hydrogen ions. Usually expressed in terms of pH - the negative logarithm of the concentration of hydrogen ions. At pH = 7.0, the reaction of water is neutral, at pH 7.0, the medium is alkaline.
According to the norms of SanPiN 2.1.4.559-96, the pH of drinking water should be in the range of 6.0 ... 9.0
Rigidity water is determined by the content of hardness salts (calcium and magnesium) in the water. It is expressed in milligram equivalents per liter (meq / l). The following types of stiffness are distinguished:
Carbonate- characterized by the content of calcium bicarbonate in water, which, when boiled, decomposes into practically insoluble carbonate and carbon dioxide... Therefore, it is also called temporary stiffness.Non-carbonate or constant stiffness- the content of non-carbonate calcium and magnesium salts.
General- the sum of carbonate and non-carbonate hardness.
Surface water is usually relatively soft (3 ... 6 mg-eq / l) and depends on geographic location- the farther south, the higher the water hardness. The hardness of groundwater depends on the depth and location of the aquifer and the annual precipitation. The hardness of water from limestone layers is usually 6 meq / l and higher.
According to SanPiN 2.1.4.559-96, the hardness of drinking water should not exceed 7.0 mg-eq / l
Alkalinity of water. The total alkalinity of water means the sum of the hydrates and anions of weak acids (carbonic, silicic, phosphoric, etc.) contained in it. In the overwhelming majority of cases, for groundwater, we mean bicarbonate alkalinity, that is, the content of bicarbonates in the water.
Chlorides are present in almost all waters. Basically, their presence in water is associated with the washing out of the rocks of the most common salt on Earth - sodium chloride (table salt). The increased content of chlorides in combination with the presence of ammonia, nitrites and nitrates in the water may indicate contamination with domestic wastewater.
MPC of chlorides in water potable quality- 300… 350 mg / l (depending on the standard).
Sulphates enter groundwater mainly by dissolving gypsum in strata. The increased sulfate content in the water leads to indigestion (the trivial names for magnesium sulfate and sodium sulfate (salts that have a laxative effect) are "Epsom salts" and "Glauber's salt", respectively).
MPC of sulfates in drinking water - 500 mg / l.
Nitrogen-containing substances (NH4 +, NO2- and NO3- ions) are formed in water mainly as a result of the decomposition of urea and proteins that enter it with domestic wastewater. The first decay product is ammonia (ammonium nitrogen)... In natural water, ammonium ions are oxidized by the bacteria Nitrosomonas and Nitrobacter to nitrite and nitrates... By the presence, quantity and ratio of nitrogen-containing compounds in water, one can judge the degree and duration of water contamination with human waste products. Drinking water with a high content of nitrites and nitrates leads to a violation of the oxidative function of the blood.
MPC in ammonium water is 2.0 mg / l; nitrites - 3.0 mg / l; nitrates - 45.0 mg / l
Phosphates usually present in water in small amounts, therefore their presence indicates the possibility of contamination by industrial effluents or effluents from agricultural fields. The increased content of phosphates has a strong effect on the development of blue-green algae, which release toxins into the water when they die.
The maximum concentration limit for phosphorus compounds in drinking water is 3.5 mg / l.
Fluorides and iodides. Fluorides and iodides are somewhat similar. Both elements, with a deficiency or excess in the body, lead to serious diseases. For iodine, these are diseases of the thyroid gland ("goiter") that occur with a daily diet of less than 0.003 mg or more than 0.01 mg. To replenish the iodine deficiency in the body, it is possible to use iodized salt, but the best way out is to include fish and seafood in the diet. Seaweed is especially rich in iodine.
Lack of fluoride in water leads to caries, its excess - to fluorosis ("stained tooth enamel"), rickets and anemia. The optimal dose of fluoride in drinking water is 0.7 ... 1.2 mg / l. If the content of fluoride in drinking water is low, it is recommended to use a toothpaste with added fluoride. Fluoride is one of the few elements that the body absorbs better from water, although it can also be obtained from pineapples.
Oxidizability is due to the content of organic substances in the water and can partly serve as an indicator of the pollution of the source with wastewater. Distinguish oxidizability permanganate and dichromate oxidizability(or COD- chemical oxygen demand). Permanganate oxidation characterizes the content of easily oxidized organic matter, bichromate - the total content of organic matter in water. By the quantitative value of the indicators and their ratio, one can indirectly judge the nature of organic substances present in water, the path and effectiveness of the purification technology.
According to SanPiN, the permanganate oxidizability of water should not exceed 5.0 mg O2 / l.
Total salt content and dry residue characterize mineralization (the content of dissolved salts in water).
According to SanPiN 2.1.4.559-96 for drinking water, the dry residue should be no more than 1000 mg / l
Truly dissolved form (ferrous iron, clear colorless water)
Undissolved form (ferric iron, clear water with a brownish-brown sediment or pronounced flakes)
Colloidal state (colored yellowish-brown opalescent water, no sediment precipitates even after long standing)
Iron organics - salts of iron and humic and fulvic acids (clear yellowish brown water)
Iron bacteria (brown mucus on water pipes Oh)
Manganese found in similar modifications.
The increased content of both elements in the water causes drips on plumbing fixtures, stains the laundry during washing and gives the water an iron or ink flavor. Long-term use of such water for drinking causes the deposition of these elements in the liver and significantly outperforms alcoholism in terms of harmfulness.
MPC in iron water is 0.3 mg / l; manganese - 0.1 mg / l.
Hydrogen sulfide found in groundwater, predominantly of inorganic origin. It is formed as a result of the decomposition of sulfides (pyrite, pyrite) by acidic waters and the reduction of sulfates by sulfate-reducing bacteria. Hydrogen sulfide has a sharp unpleasant odor and is a general cellular and catalytic poison. For these reasons, as well as due to the intensification of corrosion processes, hydrogen sulfide should be completely removed from the water for household and drinking purposes (according to GOST 2874-82 "Drinking water").
SanPiN 2.1.4.559-96 for drinking water not only allows the presence of hydrogen sulfide in water up to 0.003 mg / l, and sulfides up to 3 mg / l, so these figures still do not agree with elementary knowledge of chemistry: according to the dissociation of hydrogen sulfide and sulfides in water, at pH = 9.0 (the upper limit of the standard for drinking water), the proportion of sulfides is approximately 98.5-99%, that is, in hundred times higher than hydrogen sulfide, and the maximum permissible concentration of sulfides, respectively, should not be higher 0.3 mg / l.
Who and how made such a mistake in normative document?
Chlorine appears in drinking water as a result of its disinfection. The essence of the disinfecting effect of chlorine is the oxidation or chlorination (replacement) of molecules of substances that make up the cytoplasm of bacterial cells, which causes bacteria to die. Pathogens of typhoid fever, paratyphoid fever, dysentery, cholera are very sensitive to chlorine. Even water that is heavily contaminated with bacteria is largely disinfected with relatively small doses of chlorine. However, some chlorine-resistant individuals remain viable, so complete sterilization of water does not occur.
Residual chlorine(remaining in the water after disinfection) is necessary to prevent possible secondary contamination of water while passing through the network. The content of residual chlorine in tap water should be at least 0.3 mg / l and not more than 0.5 mg / l.
Dissolved oxygen absent in groundwater, content in surface water corresponds to partial pressure, depends on water temperature and intensity of processes enriching or depleting water with oxygen and can reach 14 mg / l
Sodium and potassium fall into groundwater due to the dissolution of bedrock. The main source of sodium in natural waters is the salt deposits of NaCl, formed on the site of ancient seas. Potassium is less common in waters because it is better absorbed by the soil and extracted by plants.
Copper, zinc, cadmium, lead, arsenic, nickel, chromium and mercury predominantly end up in water supply sources with industrial wastewater. Copper and zinc can also enter during corrosion of respectively galvanized and copper water pipes due to the increased content of corrosive carbon dioxide.
All of the above compounds are heavy metals and have a cumulative effect, that is, the property of accumulating in the body and triggering when a certain concentration in the body is exceeded.
MPC in copper water is 1.0 mg / l; zinc - 5.0 mg / l.
Aluminum can get into water during its processing with coagulants and during discharge of wastewater from bauxite processing. Maximum concentration limit in water of aluminum salts is 0.5 mg / l.
Boron and selenium are present in some natural waters as trace elements in very low concentrations, however, if they are exceeded, serious poisoning is possible.
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Sanitary and chemical indicators of wastewater pollution
The composition of wastewater and their properties are assessed according to the results of sanitary-chemical analysis, including, along with standard chemical tests whole line physical, physico-chemical and sanitary-bacteriological definitions.
The complexity of the composition of wastewater and the impossibility of determining each of the pollutants leads to the need to select such indicators that would characterize certain properties of water without identifying individual substances. Such indicators are called group or total. For example, the determination of organoleptic characteristics (odor, color) avoids the quantitative determination in water of each of the substances that have odor or give color to water.
A complete sanitary-chemical analysis involves the determination of the following indicators: temperature, color, odor, transparency, pH value, dry residue, solid residue and loss on ignition, suspended solids, settling substances by volume and mass, permanganate oxidizability, chemical need for oxygen (COD), biochemical oxygen demand (BOD), nitrogen (total, ammonium, nitrite, nitrate), phosphates, chlorides, sulfates, heavy metals and other toxic elements, surfactants, oil products, dissolved oxygen, microbial count, bacteria of the Escherichia coli group (BGKP), helminth eggs. In addition to the listed indicators, the determination of specific impurities entering the drainage network of settlements from industrial enterprises can be included in the number of mandatory tests of a complete sanitary-chemical analysis at city treatment plants.
Temperature is one of the important technological indicators, the function of temperature is the viscosity of the liquid and, consequently, the force of resistance to settling particles. Therefore, temperature is one of the determining factors in the sedimentation process. Temperature is of paramount importance for biological purification processes, since the rates of biochemical reactions and the solubility of oxygen in water depend on it.
Color is one of the organoleptic indicators of wastewater quality. Domestic and fecal wastewater is usually weakly colored and has yellowish-brownish or gray tints. The presence of intense color in various shades is evidence of the presence of industrial wastewater. For colored wastewater, determine the color intensity by dilution to colorless, for example 1: 400; 1: 250, etc.
Smell is an organoleptic indicator characterizing the presence of odorous volatile substances in the water. Usually, the smell is determined qualitatively at a sample temperature of 20 ° C and is described as fecal, putrefactive, kerosene, phenolic, etc. If there is an unclear odor, the determination is repeated by heating the sample to 65 ° C. Sometimes it is necessary to know the threshold number - the smallest dilution at which the odor disappears.
The concentration of hydrogen ions is expressed in terms of pH. This indicator is extremely important for biochemical processes, the rate of which can significantly decrease with a sharp change in the reaction of the environment. It was found that the wastewater supplied to the facilities biological treatment, should have a pH value in the range of 6.5 - 8.5. Industrial waste water (acidic or alkaline) must be neutralized before being discharged into the drainage network to prevent its destruction. Urban waste water usually has a slightly alkaline reaction of the medium (pH = 7.2-7.8).
Transparency characterizes the overall contamination of waste water with undissolved and colloidal impurities, without identifying the type of contamination. The transparency of municipal wastewater is usually 1-3 cm, and after treatment it increases to 15 cm.
The dry residue characterizes the total pollution of wastewater with organic and mineral impurities in various states of aggregation (in mg / l). This indicator is determined after evaporation and further drying at t = 105 ° C of the waste water sample. After calcination (at t = 600 ° C), the ash content of the dry residue is determined. These two indicators can be used to judge the ratio of organic and mineral parts of pollution in the dry residue.
Solid residue is the total amount of organic and mineral substances in the filtered wastewater sample (in mg / l). Determined under the same conditions as the dry residue. After calcining the dense residue at t = 600 ° C, it is possible to roughly estimate the ratio of the organic and mineral parts of soluble wastewater contaminants. When comparing the calcined dry and solid residues of urban wastewater, it was determined that most of the organic pollutants are in an undissolved state. In this case, mineral impurities in to a greater extent are dissolved.
Suspended substances - an indicator that characterizes the amount of impurities that are retained on the filter paper when filtering a sample. This is one of the most important technological indicators of water quality, which makes it possible to estimate the amount of precipitation formed in the process of wastewater treatment. In addition, this indicator is used as a design parameter in the design of primary sedimentation tanks. The amount of suspended solids is one of the main standards when calculating the required degree of wastewater treatment. Losses on ignition of suspended solids are determined in the same way as for dry and solid residues, but are usually expressed not in mg / l, but as a percentage of the mineral part of suspended solids to their total dry matter. This indicator is called ash content. The concentration of suspended solids in urban wastewater is usually 100 - 500 mg / l.
Settling substances - part of suspended substances that settle to the bottom of the settling cylinder during 2 hours of settling at rest. This indicator characterizes the ability of suspended particles to settle, allows you to estimate maximum effect sedimentation and the maximum possible volume of sediment that can be obtained under resting conditions. In urban wastewater, settling substances on average account for 50-75% of the total concentration of suspended solids.
Oxidizability is understood as the total content of organic and inorganic reducing agents in water. In urban wastewater, the overwhelming majority of reducing agents are organic substances; therefore, it is believed that the value of oxidation is completely related to organic impurities. Oxidation is a group indicator. Depending on the nature of the oxidizing agent used, a distinction is made between chemical oxidation, if a chemical oxidizer is used in the determination, and biochemical, when the role of an oxidizing agent is played by aerobic bacteria - this indicator is the biochemical oxygen demand - BOD. In turn, the chemical oxidizability can be permanganate (oxidizing agent KMn04), dichromate (oxidizing agent K2Cr207), and iodate (oxidizing agent KJ03). The results of determining the oxidizability regardless of the type of oxidizing agent are expressed in mg / l 02. The dichromate and iodate oxidizability is called the chemical oxygen demand or COD.
Permanganate oxidizability is the oxygen equivalent of easily oxidized impurities. The main value of this indicator is the speed and ease of determination. Permanganate oxidizability is used to obtain comparative data. Nevertheless, there are substances that are not oxidized by KMn04. By determining the COD, it is possible to fairly fully assess the degree of water pollution with organic substances.
BOD is the oxygen equivalent of the degree of wastewater pollution with biochemically oxidizable organic substances. BOD determines the amount of oxygen required for the vital activity of microorganisms involved in the oxidation of organic compounds. BOD characterizes the biochemically oxidized part of wastewater organic pollutants, which are primarily in the dissolved and colloidal states, as well as in the form of suspension.
For the mathematical description of the process of biochemical oxygen consumption, the kinetic equation of the first order is most often used. To derive the equation, we introduce a number of designations: La is the amount of oxygen required for the oxidation of all organic matter, i.e. BODtotal mg / l; Lt - the same consumed by the time t, i.e. BOD mg / l; La - Lt - the same remaining in the solution by the time t, mg / l.
Nitrogen is found in wastewater in the form of organic and inorganic compounds. In urban wastewater, the bulk of organic nitrogenous compounds are protein substances - feces, food waste. Not organic compounds nitrogen is represented by reduced - NH4 + and NH3 oxidized forms NO2 "and NO3" Ammonium nitrogen in large quantities is formed during the hydrolysis of urea - a product of human vital activity. In addition, the process of ammonification of protein compounds also leads to the formation of ammonium compounds.
In urban wastewater before its purification, nitrogen in oxidized forms (in the form of nitrites and nitrates) is usually absent. Nitrite and nitrate are reduced by a group of denitrifying bacteria to molecular nitrogen. Oxidized forms of nitrogen can appear in wastewater only after biological treatment.
The source of phosphorus compounds in wastewater is physiological excretion of people, waste of human economic activity and some types of industrial wastewater. Concentrations of nitrogen and phosphorus in wastewater - the most important indicators | agents of sanitary-chemical analysis, which are important for biological treatment. Nitrogen and phosphorus - necessary components composition of bacterial cells. They are called biogenic elements. In the absence of nitrogen and phosphorus, the biological treatment process is impossible.
Chlorides and sulfates are indicators, the concentration of which affects the total salt content.
The group of heavy metals and other toxic elements includes big number elements, which increases with the accumulation of knowledge about the cleaning processes. Toxic heavy metals include iron, nickel, copper, lead, zinc, cobalt, cadmium, chromium, mercury; toxic elements that are not heavy metals - arsenic, antimony, boron, aluminum, etc.
The source of heavy metals is industrial wastewater from machine-building plants, electronic, instrument-making and other industries. Wastewater contains heavy metals in the form of ions and complexes with inorganic and organic substances.
Synthetic surfactants (surfactants) - organic compounds consisting of hydrophobic and hydrophilic parts, causing the dissolution of these substances in oils and water. Anionic-active substances account for about 75% of the total amount of synthetic surfactants produced; nonionic compounds occupy the second place in production and use. In urban wastewater, these two types of synthetic surfactants are determined.
Petroleum products are non-polar and low-polar compounds extracted with hexane. The concentration of oil products in water bodies is strictly standardized, and since the degree of their retention at urban treatment facilities does not exceed 85%, the content of oil products in the wastewater entering the station is also limited.
Dissolved oxygen in the inlet sewage treatment plant waste water is absent. In aerobic processes, the oxygen concentration should be at least 2 mg / l.
Sanitary and bacteriological indicators include: determination of the total number of aerobic saprophytes (microbial number), bacteria of the Escherichia coli group and analysis for helminth eggs.
The microbial count assesses the general contamination of wastewater by microorganisms and indirectly characterizes the degree of water pollution with organic substances - the sources of nutrition for aerobic saprophytes. This indicator for urban wastewater ranges from 106 to 108.
