Acids are chemical compounds which tend to react by yielding hydrogen ions (H+). Acids act abravise to lime, corrosive and taste sour. Acid solutions are characterised by a low pH-value.
Acids and bases neutralise each other, and thereby react to salts and water.
Diluted in water, acids partly react with water to acid radicals (for example Cl-) as conjugated base and hydronium (H3O+) as the corresponding acid. The degree to which this reaction takes place depends upon the strength of the acid, characterised by the corresponding acid dissociation constant Ka or pKa respectively.
Strong acids, or mineral acids, are the acids of the anions chloride (Cl-), sulphate (SO4--) and nitrate (NO3-). The concentration of mineral acids in water is measured by the base capacity until pH 4.3 (KB 4.3). Mineral acids do usually not occur in natural waters.
Weak acids are for example carbonic acid (H2CO3) and silicic acid (Si(OH)4). The concentration of weak acids in water is measured by the base capacity until pH 8.2 (KB 8.2). Natural waters usually contain weak acids, especially carbonic acid.
De-alkalised water after a strongly acidic cation exchanger contains both strong and weak acids. Strong acids can be removed by both a strongly basic and a weakly basic anion exchanger, while weak acids are only removed by a strongly basic anion exchanger.
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The acid capacity KS 8.2 and KS 4.3 respectively is a measurement for the alkalinity or acid binding capacity of water.
The acid capacity is measured by titration with hydrochloric acid until a pH-value of 8.2 (KS 8.2) or a pH-value of 4.3 (KS 4.3) respectively is reached. The unit is usually mmol/l.
The colour transition point of indicators is pH 8.2 for phenolphtalein, and pH 4.3 for methyl orange. Accordingly, KS 8.2 is also called p-value, and KS 4.3 is also called m-value. The terms p-value and m-value are obsolete, but still used in practice.
The acid capacity approximately corresponds to the concentration of hydroxide ions (OH-), hydrogencarbonate ions (HCO3-) and carbonate ions (CO3--) diluted in water. The following table is valid for values ≥ 1 mmol/l.
| KS 8.2, KS 4.3 | OH- | CO3-- | HCO3- | ||
|
0 | 0 | KS 4.3 | ||
|
0 | 2 KS 8.2 | KS 4.3 - 2 KS 8.2 | ||
|
0 | 2 KS 8.2 | 0 | ||
|
2 KS 8.2 - KS 4.3 | 2 (KS 8.2 - KS 4.3) | 0 | ||
|
KS 8.2 | 0 | 0 |
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See cation conductivity.
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Adsorbable organically combined halogens (AOX) is a sum parameter including various halogenated hydrocarbons, especially chlorinated hydrocarbon. Individual substances can not be identified based on the AOX value alone. AOX is measured by an absorption test with activated carbon. Among other things, it serves for evaluation of industrial waste water. Notation as mg/l as Cl.
Some of the substances included into AOX are harmful to the environment and highly toxic, for example dioxin. In Germany, the limit value for AOX in industrial waste waters is 1 mg/l.
Natural waters contain only traces of AOX. Industrial waste waters can be polluted with higher amounts of AOX for various reasons. In relation to water treatment, ion exchange resins and brand new pvc pipelines will result in traces of AOX. Significant amounts of AOX can result from oxidation processes with chlorine compounds, for example resulting from desinfection of water with chlorine.
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Total alkaline earths means the sum of the concentrations of the alkaline earths or hardness builders diluted in water. These are calcium, magnesium, strontium and barium. In practice, the values of strontium and narium can usually be neglected compared to calcium and magnesium.
See water hardness.
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Alkalinity denotes the acid binding capacity or buffering capacity of water. The indication of alkalinity in a water analysis corresponds to the acid capacity for titration until pH 4.5. In natural waters, it approximately equals the concentration of hydrocarbonate (HCO3-) in that water.
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Aluminium (Al) is a chemical element belonging to the group of metal earths. The molar mass MAl is 26.98 g/mol. Diluted in water, it is a cation with a valency of three (Al +++).
The amounts of aluminium normally present in natural water are of little relevance for matters of health. However, various aluminium compounds are used as coagulation agents in water treatment, resulting in residual amounts of aluminium in the treated water.
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Ammonium is a cation with a valency of one (NH4+). In water, it is mainly present as cation of ammonium hydroxide (NH4OH). The molar mass MNH4+ is 18 g/mol.
Drinking water does usually not contain any measurable ammounts of ammonium ions. The presence of ammonia can indicate hygienic problems, as they can be a result of faecal contamination. In case of significant amounts of ammonia within a water, hygienical and bacteriological analyses are suggested.
In boiler feed water, ammonium hydroxide (ammonia) is often used as volatile alkalinisation agent. Free carbonic acid and ammonia react to ammonium carbonate:
NH4OH + CO2 → NH4HCO3.
The measurement of the ammonium content of a water sample is best conducted right after sample taking, since otherwise changes are possible, similar to nitrite.
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Anions are negatively charged ions, meaning ions with an excess of electrons. The valency is indicated by appending minus symbols to the chemical symbol, for example OH-.
Diluted in water, anions are hydrated, meaning surrounded by water molekules according to the electric dipole of those.
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| Notation: |
absorp. coeff. Hg 436 nm in 1/m absorp. coeff. Hg 254 nm in 1/m absorp. coeff. Hg 245 nm in 1/m |
These values characterize the weakening of light with the respective wave lenght caused by a water sample with a thickness of 1 m. The yellowish to brownish colours primarily present in polluted waters show the highest weakening of light at a wave lenght of 436 nm, which makes it most suited in order to measure the colouring of water. The wave lengths 254 and 245 nm on the other hand are used to measure organic contamination of the water (humins, lignins).
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In pure water which is free of carbonic acid, calcium carbonate (CaCO3) can only be diluted up to a few milligramme. However, if a water absorbs carbonic acid while passing through air or layers of earth, the indissoluble calcium carbonate is diluted as calcium hydrogen carbonate (Ca(HCO3)2).
In order to dilute a certain amount of calcium carbonate, a certain amount of free carbonic acid is required. However, this correlation is not stoichiometrical. Instead, with increasing temperature, a certain amount of calcium hydrogen carbonate requires larger amounts of free carbonic acid in order to remain diluted. This correlation between calcium carbonate, calcium hydrogen carbonate, free carbonic acid and temperature is called balance between lime and carbonic acid. The respective amount of free carbonic acid required in order to keep a certain amount of calcium carbonate in dilution is called the correspondig carbonic acid.
If the values of free carbonic acid in a water exceed those required for the balance between lime and carbonic acid, the exceeding amount is called superfluous or aggressive carbonic acid.
If the balance between lime and carbonic acid is disrupted by an increase of temperature or a reduction of the concentration of carbonic acid, calcium carbonate (lime stone) will precipitate until the balance is restored.
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Bases or lyes are chemical compounds which tend to react by accepting hydrogen ions (H+). Bases are caustic, and feel soapy on the skin. Basic solutions are characterized by a high pH-value.
Bases and acids neutralise each other, and thereby react to salt and water.
Diluted in water, bases partly react with water to base radicals (for example Na+) as conjugated acid and hydroxide (OH-) as the corresponding base. The degree to which this reaction takes place depends upon the strength of the base, characterised by the corresponding base dissociation constant Kb or pKb respectively.
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The base capacity KB 8.2 or KB 4.3 respectively is a measurement for the base binding capacity of a water.
The base capacity is measured by titration with caustic soda until a pH-value of 4.3 (KS 4.3) or a pH-value of 8.2 (KS 4.3) respectively is reached. The unit is usually mmol/l.
The colour transition point of indicators is pH 4.3 for methyl orange, and pH 8.2 for phenolphtalein. Accordingly, KB 4.3 is also called negative m-value, and KB 8.2 is also called negative p-value. The terms negative m-value and negative p-value are obsolete, but still used in practice.
The base capacity approximately corresponds to the concentration of mineral acids and free carbonic acid diluted in water:
mineral acid [mmol/l] = KB 4.3
carbonic acid [mmol/l] = (KB 8.2 - KB 4.3)*2
carbonic acid [mg/l] = (KB 8.2 - KB 4.3)*44
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Barium (Ba) is a chemical element belonging to the group of alkaline earths. The molar mass MBa is 137.34 g/mol. Diluted in water, barium is a cation with a valency of two (Ba++).
Barium compounds in small concentrations exist in all natural waters. Like Calcium and Magnesium, they belong to the hardness builders in water.
In water treatment, barium usually plays a neglectable role. However, in case of treatment with reverse osmosis, barium carbonate (BaCO3) and especially barium sulphate (BaSO4) can settle on the membranes. In water with a temperature of 20 °C, at most 2.3 ppm barium sulphate can be diluted, compared to 35 ppm barium carbonate.
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Calcium (Ca) is a chemical element belonging to the group of alkaline earths. The molar mass MCa is 40.08 g/mol. Diluted in water, calcium is a cation with a valency of two (Ca++).
Calcium compounds are present in all natural waters, in varying concentrations. Like magnesium compounds, they belong to the hardness builders in water. The solubility of calcium sulphate (plaster) in water with a temperature of 20 °C is 2004 ppm, that of calcium carbonate only 15 ppm (higher values at a higher concentration of CO2).
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Obsolete term for the amount of hardness builders or alkaline earths in water bound to hydrocarbonate (HCO3-). See hardness, balance between lime and carbonic acid and acid capacity capacity for pH-value 4.3.
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Carbonic acid (H2CO3) is an acid, and the product of the reaction of carbon dioxide (CO2) with water (H2O). The molar mass MH2CO3 is 62.03 g/mol. Diluted in water, carbonic either is either bound as ions, or free as molekules.
Natural waters contain carbonic acid, either bound as carbonat (CO3--) and hydrocarbonate (HCO3-), or free as diluted carbon dioxide (CO2) or carbonic acid (H2CO3).
Also see balance between lime and soda.
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Cation is a term for positively charged ions, meaning ions with a lack of electrons. The amount of charges = valency is indicated by appending plus symbols to the chemical formula, for example H+.
Diluted in water, cations are hydrated, meaning surrounded by water molecules according to the electric dipole of those.
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Cation conductivity is the conductivity of water, measured downstream of a strongly basic cation exchanger, at continuous flow.
In neutral waters, the value of thecation conductivity is usually higher than that of the directly measured conductivity, since the cation exchanger exchanges salts for strong acids. The conductivity value caused by acids and bases is about twice as high as that caused by equivalent salts. In alkaline waters however, the value of the cation conductivity is usually lower than that of the directly measured conductivity, since weak bases are removed by the cation exchanger.
When measuring the cation conductivity of boiler water, the cation exchanger removes bases like sodium hydroxide (NaOH), potassium hydroxide (KOH) or ammonia hydroxide (NH4OH), and only the conductivity caused by salts like chloride(Cl-), sulphate (SO4--), nitrate (NO3-) or phosphate (PO4---) is measured.
In case of high pressure steam generators, the cation conductivity of live steam condensate is measured. The cation exchangers removes bases like ammonia from the sample, and thus only the conductivity caused by weak acids is measured. Both the pH-value and the ammonia concent of the main steam can be calculated based upon the difference between the direct conductivity and acid conductivity of the main steam.
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Chloride (Cl-) is an anion with a valency of one.
Chlorides are the salts of hydrochloric acid (HCl). They exist in almost all natural waters, even in rain water. Their concentration varies depending upon the geological and local circumstances. They exist as for example calcium-, magnesium- or sodium chloride.
Larger amounts of chlorides can have a negative impact on the taste of water, and tend to increase corrosive abilities of the water.
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Elemental chlorine does not exist in natural waters. However, chlorine and chlorine compounds are often added to water for disinfection, as part of a water treatment process.
Chlorine causes damage to ion exchange resins and reverse osmosis membranes, and accordingly needs to be removed from water before plants of these types.
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Also see absorption coefficient. In case of qualitative denotation:
Intensity of the colour: colourless, very weak, weak, strong
Colour tint: yellowish, yellow-brown, brown-yellow, brown, light grey, dark grey, greenish, blueish, ...
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The electric conductivity σ is a measurement for the ability of a material to conduct an electric current. It is the reciprocal value of the specific electric resistance.
In the water chemistry, the electric conductivity mainly serves for indirect measurement of the content of total dissolved solids of a water. The electric conductivity of a water mainly depends upon the ions diluted in that water, and to a lesser extend also upon the temperature. The lower the conductivity value, the less ions are diluted in that water.
Monitoring of the conductivity value mainly serves for observing changes in the salt content of water by repeated analyses, or for evaluating the quality of demineralised water.
A conductivity of 0.055 μS/cm ≈ 18 MΩ cm is the theoretical minimum of totally pure water with a temperature of 20 °C.
Unit: S/m = 104 μS/cm
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Copper (Cu) is a chemical element belonging to the group of metals. The molar mass MCu is 63.55 g/mol. Diluted in water, copper is usually a cation with a valency greater than one.
In natural waters, copper is extremely rare. In condensate, copper can exist as corrosion product. Boiler feed water may only contain traces of copper. The more noble copper tends to settle on steel surfaces, which results in corrosion caused by the ignoble iron.
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Fluoride (F-) is an anion with a valency of one, and the salt of hydrofluoric acid (HF). The molar mass MF is 18.99 g/mol.
Almost all natural waters contain fluorides in small amounts. The concentration varies depending upon geological and local circumstances. Appearance for example as calcium-, magnesium- and sodium fluoride. In some countries, fluorine is dosed to tap water for purposes of dental care.↑ Index
The salts of the alkaline earths dissolved in or sedimented from water are called hardness. The ions of the alkaline earths, especially calcium and magnesium, are called hardness builders. Strontium and barium also belong to this group, however their content in natural waters is usually negligible.
Calcium and magnesium diluted in natural waters are mostly bound to carbonic acid (hydro carbonate and carbonate), and are called carbonate hardness in this form. If they are bound to sulphates, chlorides or nitrates, they are called non-carbonate hardness.
The solubility of carbonate hardness in water mainly depends upon the temperature and basicity of the water. With increasing temperature or basicity, the solubility of the carbonate hardness decreases, resulting in hardness depositions. In case of high pressure and temperatues, for example during steam boiler operation, the non-carbonate hardness will precipitate as well. Also see balance between lime and carbonic acid.
According to SI conventions, the denotation of hardness as total alkaline earths in mmol/l is required. However, in practice, the terms total hardness and carbonate hardness in mval/l and °dH are still widely used. In English-speaking countries, hardness is often denoted as hardness in ppm CaCO3.
Units and conversion: 1 mmol/l total alkaline earths = 2 mval/l ≈ 5.6 °dH ≈ 100 ppm CaCO3
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Hydrochloric acid (HCl) or hydrogen chloride is an acid. The molar mass MHCl is 36.46 g/mol. Diluted in water, it exists as the cation hydrogen (H+) and the anion chloride (Cl-). Hydrochlorid acid is rather aggressive, and tends to dissolve calcium carbonate while forming CO2-bubbles.
Among other things, hydrochloric acid is used for regeneration of cation exchange resins in water treatment.
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See hydrochloric acid.
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The ionic strength N is a value for calculation purposes, which serves to determine the pH balance value, and the corresponding amount of carbonic acid.
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Iron (Fe) is a chemical element belonging to the group of metals. The molar mass MFe is 55.85 g/mol. Diluted in water, iron is a cation with a valency of either two as iron (II) (Fe++) or three as iron (III) (Fe+++).
Iron ions can exist in water if the water is free of oxygen, or if the pH value of the water is below 3. Oyxgen causes iron (II) ions to react to iron (III) ions, which tend to react to insoluble iron oxide hydrate (brown flakes).
This means that the amount of diluted iron in case of a later analysis will differ from the value at the time of sample taking. Only the total iron content will remain the same.
Before water treatment with reverse osmosis or ion exchange, iron needs to be removed from the water in order to prevent scaling on the membranes or blocking of the ion exchange resins respectively.
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The Langelier Saturation Indicator (LSI) is the difference between the measured pH-value and the calculated pH-equilibrium. If the index is negative, the water is aggressive towards lime. If the index is positive, calcium carbonate tends to precipitate from the water.
Among other things, the LSI serves for evaluation of waters to be used as cooling circulation water or reverse osmosis feed, and accordingly the design of required pre-treatment and dosing processes.
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Magnesium (Mg) is a chemical element belonging to the group of alkaline earths. The molar mass MMg is 24.1 g/mol. Diluted in water, magnesium is a cation with a valency of two (Mg++).
Magnesium compounds exists in practically all natural waters. See hardness.
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Manganese (Mn) is a chemical element belonging to the group of transition metals. The molar mass MMn is 54.94 g/mol. Diluted in water, manganese is a cation with a valency of either two, three or four.
In natural waters, manganese can appear diluted with valency of two, or colloidal with a valency of three or four.
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Obsolete denotation - see acid capacitiy for pH 4.3.
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Nitrates (NO3-) are univalent anions, and the salts of nitric acid (HN03). The molar mass MNO3- is 62 g/mol.
Nitrate in water is often an indicator for biological contamination, together with nitrite and ammonium.
Usually, natural waters contain between 5 and 10 ppm nitrate. However, much higher values can still be a result of edaphic conditions. Even concentrations up to 200 ppm are measured in ground water in some areas, with otherwise normal conditions.
Higher amounts of nitrate in water can cause corrosion to galvanised pipelines.
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Nitrite (N02--) is a bivalent anion and a reaction product of nitrate. The molar mass MNO2- is g/mol.
In natural waters, only small traces of nitrite ions are present. An exception to this are ground and swamp waters with a high iron content.
Nitrite in water is often an indicator for biological contamination, together with nitrate and ammonium.
The analysis is best conducted right during sample taking, since otherwise, changes due to reduction and oxixdation processes are possible.
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Odour is denoted according to intensity and type.
Intensity: without, weak, strong
Type: earthy, mouldy, putrid, fishy, aromatic, chlorine, tar, petrol, mineral oil, ...
A fishy odour of demineralised water can indicate the presence of trimethylamine.
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The oxidability value is an indicator for the amount of organic and anorganic substances in water which can be oxidated by potassium permanganate (KMNO4) under certain circumstances. The obsolete denotation is potassium permanganate consumption.
For the denotation as oxidability Mn VII - II, the required amount of potassium permanganate is converted to the corresponding amount of oxygen (O2). The conversion factor from KMNO4-consumption to O2 is 1/4.
Ground waters usually only display low values of oxidability, however higher values can occur depending upon edaphic conditions, for example in swamp waters.
If the analysis is not conducted with a raw water sample, but instead with a pre-filtrated or sedimented water sample, this needs to be noted down seperately.
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Oxygen (O) is a chemical element belonging to the group of non-metals. The molar mass MO is 15.99 g/mol. In water, oxygen exists either as a free gas (for example O2), diluted as various ions (for example OH-), or as part of molecular water (H2O).
Molecular oxygen (O2) appears in surface and ground waters in various amounts. Real ground water from huge depths, which is not influenced by surface water, is free of oxygen.
Oxygen is rather reactive, and plays a role in several continuous as well as self-inhibiting corrosion processes. Also, oxygen encourages organic growth in water.
The oxygen content of a water sample must be analysed right during sample taking in order to be meaningful.
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Phosphates are multivalent anions, and the salts of various phosphoric acids. Denotations in water analyses usually refer to PO4---. The molar mass MPO4--- is 95 g/mol.
A distinction can be made between:
1. monophosphates (salts of the O-phosphoric acid)
2. condensed phosphates and polyphosphates respectively
Usually, only the total phosphate concentration is measured in a water analysis. In special cases, the monophosphate concentration can be measured seperately.
Natural waters contain phosphates in concentrations of normally up to 0.03 ppm PO4. An exception are swamp waters, which sometimes contain up to 0.5 ppm PO4.
However, phosphates are often used for water treatment in order to prevent corrosion and hardness scaling. To this end, monophosphates as well as condensed phosphates or mixtures of both are used.
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The calculated pH value for each water where that water is neither aggressive to lime nor precipitating carbonate hardness is called pH equilibrium. This value mainly depends upon the temperature of the water, as well as upon the concentrations of carbonic acid and carbonate hardness. Also see balance between lime and carbonic acid.
In natural waters, the pH equilibrium usually lies in the range from pH 6 to pH 8.
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The pH-value is a measurement to determine wether a water reacts acidic, neutral or alkaline. The measuring range is 0 to 14. pH-values below 7 are considered as acidic, pH 7 is considered as neutral, and values above 7 are considered as alkaline.
Strictly speaking, the pH-value equals the negative common logarithm of the concentration of hydrogen ions in water. The lower the pH-value, the higher the concentration of hydrogen ions, and the lower the concentration of hydroxide ions, and vice versa.
At a temperature of 25 °C, the ion product of the water, meaning the product of the concentrations of hydrogen ions (H+) and hydroxide ions , is 10-14 mol²/l². For example, a pH-value of 6 equals a hydrogen ion concentration of 10-6 mol/l, and accordingly a hydroxide ion concentration of 10-8 mol/l. At pH 7, both concentrations values are 10-7 mol/l, and the water reacts neutral.
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Potassium is a chemical element belonging to the group of alkaline metals. The molar mass MK is 39.10 g/mol. Diluted in water, potassium is a monovalent anion (K-).
In natural waters, potassium occurs in low concentrations.
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Obsolete denotation - see oxidability Mn VII - II.
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Obsolete denotation - see acid capacity for pH 8.2.
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If a water contains substances which tend to convert into each other via oxidation and reduction processes, this is called a redox environment. There can be strongly and weakly oxidising as well as reducing substances present.
The redox potential is a measurement for the oxidation and reduction potential of the water. It is usually measured via voltage metering at special electrodes (noble metal/standard hydrogen electrode).
This measurement is mainly of releveance for biological processes, for removal of iron and manganese and disinfection processes.
In contaminated waters, the redox potential is usually low (reducing). Higher values indicate oxidising behaviour.
The redox potential depends upon the pH-value and the temperature of a water. Accordingly, those need to be measured as well for a significant analysis.
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Salts are chemical compounds, composed of cations and anions. Among other things, salts are a neutralisation product of acids with bases. As solids, salts form crystal structures, while diluted in water, they are hydratised cations and anions.
The salt content of a water sample is often measured indirectly via the conductivity.
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See Langelier Saturation Indicator (LSI).
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In case of water samples with sediments, the qualitative denotation includes the amount, colour and appearance of the sediments.
Amount: little to strong
Colour: white, grey, brown, black, ....
Appearance: flaky, slimy, granular, ...
Sediments are a result of floating particles or sedimentable substances like iron oxide or manganese oxide.
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Silicates (SixOy4x-2y) are the salts of silicic acid (Si(OH)4). In water analyses, the concentration of silicon dioxide (SiO2) is usually measured, the molar mass MSiO2 is 60.1 g/mol.
Silicates (silicic acid) are weakly dissociated anions. They exist in all natural waters, partly diluted as ions, partly as colloids. Silicates can cause serious malfunctions to steam boiler operation by forming insoluble depositions. Depending upon the operation pressure, silicic acid becomes volatile in higher concentrations, and can for example cause severe damage to steam turbines. Accordingly, boiler feed water treatment for high pressure boilers requires removal of silicic acid.
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The Silt Density Index (SDI) is a measurement for the concentration of filtratable particles within a water. The SDI is determined by a filtration test as defined in ASTM D 4189-82.
In practice, the SDI mainly serves to evaluate wether a certain water will cause fouling to reverse osmosis membranes. For spiral wound membranes, the maximum permitted SDI value usually is 5. In case of higher values, the osmosis feed water needs to be treated by appropriate filtration processes. The SDI of town or well water normally is less than 3.
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Sodium (Na) is a chemical element belonging to the group of alkaline metals. The molar mass MNa is 22.99 g/mol. Diluted in water, sodium is a monovalent cation (Na+).
Natrium commonly occurs in natural waters in the form of various salts. The most well-known natrium salt is common salt or sodium chloride (NaCl) respectively.
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Sodium bicarbonate (NaHCO3) is a sodium salt of carbonic acid. The molar mass MNaHCO3 is 84 g/mol.
Sodium bicarbonate occurs in natural waters. The concentration of sodium bicarbonate equals the difference between acid capacity for pH 4.3 and the double value of the total alkaline earth concentration.
Sodium bicarbonate is also a product of softening water by ion exchange, see soda fission.
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Strontium (Sr) is a chemical element belonging to the group of alkaline earths. The molar mass MSr is 87.62 g/mol. Diluted in water, strontium is a trivalent cation (Sr+++).
Strontium exists in all natural waters, however only in very small concentrations. Like calcium and magnesium, it belongs to the hardness builders in water. For water treatment, strontium usually plays only a negligible role, same as barium. However, in case of treatment with a reverse osmosis plant, strontium sulphate compounds can result in scaling on the membranes.
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Sulphates (SO4--) are the salts of sulphuric acid. The molar mass MSO4-- is 96 g/mol.
Most natural waters contain sulphates only in a concentration of up to about 50 ppm. However values of serval 100 ppm are also possible depending upon edaphic conditions.
A high sulphate concentration (especially as alkali sulphate or magnesium sulphate) results in a bitter taste of the water. Waters with a high sulphate content are also often a cause for damage to water buildings made of concrete, and are unsuited for mixing of concrete. In case of non-protected metals, a high sulphate concentration tends to assist corrosion.
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Among other things, the temperature of a water influences the pH-value, the redox potential, the conductivity, the pH equilibrium and the saturation indicator. Accordingly, the water temperature always needs to be mentioned as part of a water analysis.
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Obsolete denotation for total alkaline earths. Also see hardness.
Unit: 1 °dH = 10 mg/l CaO ≈ 0.1783 mmol/l (total alkaline earths)
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The values for TOC (total organic carbon) and DOC (dissolved organic carbon) are quantitative measurements for the amount of carbon of organic substances in the water.
TOC is measured in the original water sample including colloids, while DOC is measured in a filtrated sample.
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Trimethylamine (C3H9N) is an easily flammable, colourless gas. It is easily soluted in water, and has a strong fish-like odour even in small concentrations. The molar mass MC3H9N is 59.1 g/mol.
Trimethylamine can be released by washing of strongly alkaline groups from fresh anion exchange resins. This also causes a fish-like odour. The odour threshold value in air is 0.001 mg/m³, the maximum permitted workplace concentration value is 4.9 mg/m³. Trimethylamine can not be removed with activated carbon. However, it will be absorbed by a cation exchanger.
A notable reduction of the concentration can be achieved by:
- Lowering of the water temperature (as far as possible).
- Filtration of the demineralised water with a mixed bed filter. This caused the trimethylamine to be bound by the cation exchange resin, from where it will be removed with the regeneration.
- A regeneration of the anion exchanger with hydrochloric acid (HCl) will increase the rate of trimethylamine decomposition. The regeneration can be conducted as follows:
Suction of the hydrochloric acid like with the cation exchanger, first with a concentration of about 1%, after 5 minutes with an increased concentration of about 5%. After suction of the hydrochloric acid, the plant needs to be shut down for 60 minutes, so that the acid can take effect. Afterwards, the plant needs to be washed for 120 minutes, and then normally regenerated with caustic soda (NaOH).
The release rate of trimethylamine can be increased by:
- brand new resins
- higher water temperature (condensate treatment)
- too frequent regeneration with caustic soda, without salt load on the resins
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The turbidity of water is influenced by the content of non-dissolved particles.
Qualitative denotation for example: clear, almost clear, weakly opalescent, opalescent
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Water (H2O) is a chemical compound, composed of the lements oxygen and hydrogen.
Water is of crucial importance for the climate and eco system. Furthermore, water is used in various technical applications, for example for storing and transportation of heat, as well as in various chemical and physical processes.
In the nature, water can appear in all three physical conditions solid, liquid and gaseous. At a temperature of 4 °C, water has its highest density, with a specific volume of 1000 kg/m³. The compressibility of liquid water is small enough that it can be neglected for most technical calculations.
In natural waters, various substances are diluted, depending upon the origin of the water. There is a distinction to be made between fully diluted substances which exist as hydrated cations and anions, colloid particles and diluted gases.
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Zinc (Zn) is a chemical element belonging to the group of transition metals. The molar mass MZn is 65,41 g/mol. Diluted in water, zinc is a cation with a valency of two (Zn++).
Traces of zinc are quite common in natural waters. Larger amounts can exist in the underground waters of for example zinc mining areas.
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