Inhalt:

Nr.1
The redox potential as a way to determine the effect of disinfectants on the example of a Twin Oxide Process 1% Solution

Nr.2
Temperaturabhängigkeiten

Nr. 3
Elektrochemische Spannungsreihe

Nr.4

Beispiel aus einem Schwimmbadprojekt

Nr.1

The redox potential as a way to determine the effect of disinfectants on the example of a Twin Oxide Process 1% Solution

Dr. -Ing. Wolfgang Storch -2014-03-19

The redox potential is dissolved in the water oxidizing and reducing

Substances caused if these are effective at the electrode surface . It is expressed as a voltage between an internal electron conductor and of the standard hydrogen electrode . " This is the definition of the redox potential , as in DIN 38404 , Part 6 , listed . It is further stated in this standard : " The redox potential is an indication for states and processes in a water in which oxidizing and reducing agents are effective" .

What do these statements mean in terms of drinking water disinfection ? The reducing substances present in a drinking water contaminants and organic load materials can be viewed while the disinfectants such as chlorine , chlorine dioxide or ozone present as oxidising substances.

The ORP , e.g., present in a chlorinated water, so is a measure of the oxidizing and disinfecting effect of a water at the same time , while taking into account the currently present pollution of the water with impurities .

This can also be referred to as disinfection capacity of a water. The amount of the redox potential depends on the case of the application of twin oxide chlorine dioxide solutions in the first instance of the chlorine dioxide from , as well as well as the type and concentration of possible reaction partner of the chlorine dioxide and the other oxidizing and reducing substances in the water .

Furthermore, the redox potential of the pH - value and to a small extent dependent on the temperature of the water . The redox potential is thus a more comprehensive measure than the concentration of chlorine dioxide , for it includes except the disinfectant concentration , other parameters , which to the disinfection

able effect of water.

The relationship between ORP and the concentration of the disinfectant is not linear.

So water with the same concentration of chlorine dioxide can have different redox potential and then have a different disinfecting action . When waters of different chlorine dioxide have the same redox potential , and their disinfecting action is the same. For many years, the redox potential for the control of drinking water disinfection is being used.

In the waterworks practice, the redox potential as a measure of the disinfectant property offers particularly where such waters are treated , where at times, with a greater occurrence of organic pollutants , such as algenbürtigen substances or ammonium , must be expected . In these periods, the indication of the disinfectant concentration loses its significance , while the measurement of the redox potential allows an accurate statement about the still existing disinfection assets.

Another aspect arises out of the difficult analysis of chlorine and chlorine dioxide at very low concentrations . To lowest possible disinfectant levels to control , but to still ensure safe disinfection , the redox potential offers itself as an appropriate measure because they most responsive in very low concentration ranges to changes in the concentration of disinfectant .

Figure 1 shows the redox potential with increasing content of free chlorine.

In Figure 2 you can see the change in the redox potential in an extremely germ-laden water. Here it is shown that at low concentrations of chlorine dioxide initially dominate the reducing effects of the germs , then comes a range of stagnation , which merges into a region of rapidly increasing redox potential . In this area the disinfection takes place. In the upper section , a lower increase of the redox potential can be observed. In a redox potential of 805 mV finally all germs ( 259000/100ml ) were inactivated .

Limits or ranges for the redox potential required for safe disinfection , are nowhere defined.

To find out in a waterworks which redox potential for reliable disinfection is necessary trials are required. Here, the microbiological testing , the amount of disinfectant , and the pH value associated with the value of the redox potential should be seen .

In the alternative, may initially be determined as a function of the redox potential of the dose of disinfectant (twin Oxide 0, 3 % solution or twin Oxide Process Solution) for the water to be treated . This results in the dose range of the disinfectant. Microbiological tests with test bacteria can then follow .

Important: The increase in the redox potential indicates the oxidizing effect on all water constituents , organic and inorganic . If there is no increase in the redox potential , despite increasing dosage of disinfectant, then the disinfectant is consumed by the water constituents ( consumed ) .

In the picture part, the correlations are illustrated.

Although in DIN 38404 , Part 6 ( determining the redox potential ) , the redox potential as a tension between an inert electronic conductor and the standard hydrogen electrode is to be specified, for practical reasons, the measurement with a platinum electrode against a silver / silver chloride (Ag / AgCl) reference electrode performed.

On measuring module, the actual measured voltage UG ( vs. Ag / AgCl) is displayed.

The redox measurement system consists of the ORP Einstabmesselektrode with Ag / AgCl - reference system , the impedance transformer , the measuring cable and the plug- measuring module . As a flow-through fitting the same flow valve is used in combination with the chlorine measurement.

Sources:

/1/Umweltforschungsplan des Bundesministeriums für Umwelt, Naturschutz und Reaktorsicherheit

Förderkennzeichen 380 01 005

„Modellhaftes technologisches Konzept für die Verbesserung der Sicherheit bei der Chlorlagerung am Beispiel eines Moskauer Großwasserwerkes in Verbindung mit Maßnahmen zur Verbesserung des anlagenbezogenen Gewässerschutzes“ von Dr. Klaus Ritter Dr. Michael König Euro Institute for Information and Technology Transfer in Environmental Protection GmbH, Hannover

S. 539 f

/2/ Interner Laborbericht März-2014

Die Desinfektionswirkung eines Stoffes, also auch von Chlordioxidgas, TwinOxide-Solutions,... ist vom Redoxpotential abhängig.
Die geringe Temperaturabhängigkeit des Redoxpotentials von Chlordioxid weist auf dessen hohe Temperaturstabilität der Desinfektion hin.

Maschelein,Use Chlorine Dioxide,

Redoxpotentiale

Nr.2 Temperaturabhängigkeiten

Maschelein,Use Chlorine Dioxide, Redoxpotentiale

http://www.umweltbundesamt.de/sites/default/files/medien/publikation/long/2361.pdf

Nr. 3

Elektrochemische Spannungsreihe

nach: http://de.wikipedia.org/wiki/Elektrochemische_Spannungsreihe

The electrochemical series is a collection of oxidants on the oxidation strength and at the same time a reverse listing of reducing agents by reducing strength.
In addition, the electrochemical series contains a gradation of metals ("very noble metal", "noble metal", "less noble metal", "ignoble metal", "very ignoble metal") to their quest to can be oxidized into acids. The standard potentials of the noble metals have a positive sign that the ignoble on the other hand a negative. The base metals therefore dissolve in acids because acids contain H +. (The arguments, for example, Zn / Cu analogously apply.)

Die elektrochemische Spannungsreihe ist damit eine Auflistung von Oxidationsmitteln nach Oxidationsstärke bzw. gleichzeitig eine umgekehrte Auflistung von Reduktionsmitteln nach Reduktionsstärke.
Außerdem enthält die elektrochemische Spannungsreihe eine Abstufung der Metalle („sehr edles Metall“, „edles Metall“, „weniger edles Metall“, „unedles Metall“, „sehr unedles Metall“) nach ihrem Bestreben, sich in Säuren oxidieren zu lassen. Die Standardpotentiale der edlen Metalle haben ein positives Vorzeichen, die der unedlen dagegen ein negatives. Die unedlen Metalle lösen sich daher in Säuren auf, weil Säuren H⁺ enthalten. (Die Argumente zum Beispiel Zn/Cu gelten analog.)

Elektrochemische Spannungsreihe

(Standardpotentiale bei 25 °C; 101,3 kPa; pH=0; Ionenaktivitäten= 1)

Element im Redox-Paar,
dessen Oxidationsstufe
sich ändert	oxidierte Form	+ z e⁻	⇌ reduzierte Form	Standardpotential E °
Fluor (F)	F₂	+ 2 e⁻	⇌ 2 F⁻	+2,87 V
Sauerstoff (O)	S₂O₈²⁻	+ 2 e⁻	⇌ 2 SO₄²⁻	+2,00 V
Sauerstoff (O)	H₂O₂ + 2 H₃O⁺	+ 2 e⁻	⇌ 4 H₂O	+1,78 V
Gold (Au)	Au⁺	+ e⁻	⇌ Au	+1,69 V
Gold (Au)	Au³⁺	+ 3 e⁻	⇌ Au	+1,42 V
Gold (Au)	Au²⁺	+ 2 e⁻	⇌ Au	+1,40 V
Chlor (Cl)	Cl₂	+ 2 e⁻	⇌ 2 Cl⁻	+1,36 V
Chrom (Cr)	Cr⁶⁺	+ 3 e^-	⇌ Cr³⁺	+1,33 V
Sauerstoff (O)	O₂ + 4 H₃O⁺	+ 4 e⁻	⇌ 6 H₂O	+1,23 V
Platin (Pt)	Pt²⁺	+ 2 e⁻	⇌ Pt	+1,20 V
Brom (Br)	Br₂	+ 2 e⁻	⇌ 2 Br⁻	+1,07 V
Quecksilber (Hg)	Hg²⁺	+ 2 e⁻	⇌ Hg	+0,85 V
Silber (Ag)	Ag⁺	+ e⁻	⇌ Ag	+0,80 V
Eisen (Fe)	Fe³⁺	+ e⁻	⇌ Fe²⁺	+0,77 V
Iod (I)	I₂	+ 2 e⁻	⇌ 2 I⁻	+0,53 V
Kupfer (Cu)	Cu⁺	+ e⁻	⇌ Cu	+0,52 V
Eisen (Fe)	[Fe(CN)₆]³⁻	+ e⁻	⇌ [Fe(CN)₆]⁴⁻	+0,361 V
Kupfer (Cu)	Cu²⁺	+ 2 e⁻	⇌ Cu	+0,35 V
Kupfer (Cu)	Cu²⁺	+ e⁻	⇌ Cu⁺	+0,16 V
Zinn (Sn)	Sn⁴⁺	+ 2 e⁻	⇌ Sn²⁺	+0,15 V
Wasserstoff (H₂)	2 H⁺	+ 2 e⁻	⇌ H₂	0
Blei (Pb)	Pb²⁺	+ 2 e⁻	⇌ Pb	−0,13 V
Zinn (Sn)	Sn²⁺	+ 2 e⁻	⇌ Sn	−0,14 V
Molybdän (Mo)	Mo³⁺	+ 3 e⁻	⇌ Mo	−0,20 V
Nickel (Ni)	Ni²⁺	+ 2 e⁻	⇌ Ni	−0,23 V
Cadmium (Cd)	Cd²⁺	+ 2 e⁻	⇌ Cd	−0,40 V
Eisen (Fe)	Fe²⁺	+ 2 e⁻	⇌ Fe	−0,44 V
Schwefel (S)	S	+ 2 e⁻	⇌ S²⁻	−0,48 V
Nickel (Ni)	NiO₂ + 2 H₂O	+ 2 e⁻	⇌ Ni(OH)₂ + 2 OH⁻	−0,49 V
Chrom (Cr)	Cr³⁺	+ 3 e⁻	⇌ Cr	−0,76 V^[1]
Zink (Zn)	Zn²⁺	+ 2 e⁻	⇌ Zn	−0,76 V
Eisen (Fe)	Fe³⁺	+ 3 e⁻	⇌ Fe	−0,77 V
Wasser	2 H₂O	+ 2 e⁻	⇌ H₂ + 2 OH⁻	−0,83 V
Chrom (Cr)	Cr²⁺	+ 2 e⁻	⇌ Cr	−0,91 V
Niob (Nb)	Nb³⁺	+ 3 e⁻	⇌ Nb	−1,099 V
Vanadium (V)	V²⁺	+ 2 e⁻	⇌ V	−1,17 V
Mangan (Mn)	Mn²⁺	+ 2 e⁻	⇌ Mn	−1,18 V
Titan (Ti)	Ti³⁺	+ 3 e⁻	⇌ Ti	−1,21 V
Aluminium (Al)	Al³⁺	+ 3 e⁻	⇌ Al	−1,66 V
Titan (Ti)	Ti²⁺	+ 2 e⁻	⇌ Ti	−1,77 V
Beryllium (Be)	Be²⁺	+ 2 e⁻	⇌ Be	−1,85 V
Magnesium (Mg)	Mg²⁺	+ 2 e⁻	⇌ Mg	−2,38 V
Cer (Ce)	Ce³⁺	+ 3 e⁻	⇌ Ce	−2,483 V
Lanthan (La)	La³⁺	+ 3 e⁻	⇌ La	−2,522 V
Natrium (Na)	Na⁺	+ e⁻	⇌ Na	−2,71 V
Calcium (Ca)	Ca²⁺	+ 2 e⁻	⇌ Ca	−2,76 V
Barium (Ba)	Ba²⁺	+ 2 e⁻	⇌ Ba	−2,90 V
Kalium (K)	K⁺	+ e⁻	⇌ K	−2,92 V
Lithium (Li)	Li⁺	+ e⁻	⇌ Li	−3,05 V