Wasserparameter bei der Wasseraufbereitung/en

Chemical Oxygen Demand (mg/L) The Chemical Oxygen Demand (COD) indicates the amount of oxygen that is required for the chemical oxidation with potassium dichromate in the substances contained in water. <ref name="isa">ISA – Institut für Siedlungswasserwirtschaft der RWTH Aachen</ref>

Note: The COD is always higher than the BOD5; the ratio COD / BOD₅ lies at 1.5 – 2 with well biologically degradable materials.

Biochemical Oxygen Demand 5 (mg/l) The Biochemical Oxygen Demand BOD₅ is the amount of oxygen consumed in biochemically oxidizable organic substances contained in one litre of water in 5 days under the corresponding metabolic activity of the microorganisms at 20 °C in dark (in mg O2/l).

Note: If the BOD_{5</sub value attains a value of <10 mg / litre (organically biodegradable load), then it is no longer putrefactive under normal conditions. <ref name="H.M.">Hans Mönnighoff, 1993, Ökobuchverlag</ref>}

This value is critical if the water is to be stored for a longer period, without formation of any odour. (For instance, absence for few days).

The Total Organic Carbon TOC (mg/l) content is the amount of organic carbon compounds in a sample. These are burnt during the analysis and the amount of the resulting CO2 is measured. <ref name="isa">ISA – Institut für Siedlungswasserwirtschaft der RWTH Aachen</ref>

Note: The TOC is a sum parameter in the water analysis as well as run-off water analysis and reflects the contamination of water with organic matter. Clean spring waters indicate a TOC content of 1 - 2 mg/l. slightly contaminated rivers and streams show values around 2 - 5 mg/l. The mesotrophic lakes already have the values of 5 - 10 mg/l, and a productive carp pond has a typical value around 15 - 25 mg/l. The value many exceed over 100 mg/l in highly contaminated sewage water.

Spectral Absorption Coefficient 245nm SAK (1/m) The UV absorption is a sum parameter for water pollution by dissolved organic substances such as aromatic compounds and humic substances. The Spectral Absorption Co-efficient and Extinction per meter is converted with a measurement wavelength of 254 nm. <ref name="isa">ISA – Institut für Siedlungswasserwirtschaft der RWTH Aachen</ref>

Note: Thus, Spectral Absorption Co-efficient 245nm corresponds as sum parameter for the inorganic salt contamination in approximate electrical conductivity. A number of organic substances absorb ultraviolet light. It is based on DIN 38404-3 (2006), which enables measurement at a wavelength of 254 nm. The light attenuation per meter of water (hence the dimension 1 / m) simultaneously functions as a measure of organic contamination of the water. Thus, it is also possible to convert the measured value into approximately related carbon parameters such as TOC (Total Organic Carbon), COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand). (State Office for Nature, Environment and Consumer Protection, North Rhine-Westphalia).

Oxygen

As the water becomes colder, the amount of O₂ that can be dissolved increases and decreases depending on the salinity or decrease in the atmospheric pressure. Examples:

0 °C, standard pressure, fresh water: 14.6 mg/l = 100% saturation

10 °C, standard pressure, fresh water: 11.3 mg/l = 100% saturation

20 °C, standard pressure, fresh water: 9.1 mg/l = 100% saturation

The following environments can be distinguished depending on the percentage of oxygen in the water:

• Aerobic environment = Presence of dissolved molecular oxygen (O₂) and chemically bound oxygen, > 0.5 mg O₂/l
• Anoxic environment = Presence of a nitrogen bound oxygen (for instance, NO₃- ; NO₂- ), < 0.5 mg O₂/l
• Anaerobic environment = neither dissolved molecule nor nitrogen bound oxygen is present, < 0.5 mg O₂/l

If there is less oxygen in water, then it could be attributed to the presence of certain microorganisms for formation of unpleasant smells and toxic gases. In this process, the oxygen required for respiration of bacteria is separated from oxygen-containing compounds such as sulphates, sulphites, etc. which leads to the formation of sulphides and H2S in significant quantities and are released. <ref name="Schikowski">Diplomarbeit Schikowski, 10'1988, Prof. Olschewski</ref>

Counter action: aeration, the content of oxygen must always be high in enough quantity.

Conductivity [µS/cm]

The chemically pure water with pH of 7 is dissociated only to a limited extent in the H3O+ and OH-electric charge carriers. Therefore, it has a specific high resistance of 18.2 M Ω •cm (= 1.82×1013 Ω •mm²/m) at 25 °C. This corresponds to a specific conductance value of 54.9 nS•cm−. Thereby the effect of variation of temperature is about 1.5 to 2% per Kelvin. Dissolved salts and acids intensify the concentration of charge carrier. Already the mains water reaches up to about 10,000 times the conductivity of an average of 500 µS•cm−1 depending on the mineral content. <ref name="Wiki">Wikipedia</ref>

The pH value is a measure of the acidic or basic character of an aqueous solution. The pH value is a non-dimensional unit. The ionic product of water at 25 °C gives following results with autoprotolysis.

K_W = c(H₃O+) • c(OH−) = 10^(−14) mol²/l²

und teilt pH-Werte von verdünnten wässrigen Lösungen ein in:

• pH < 7 als saure wässrige Lösung, hier ist cH₃O+ > cOH−
• pH = 7 als neutrale wässrige Lösung, hier ist cH3O+ = cOH−; auch eine Eigenschaft von reinem Wasser
• pH > 7 als basische (alkalische) wässrige Lösung, hier ist cH₃O+ < cOH−

Chemisch reines Wasser von 22 °C hat einen theoretischen pH-Wert von 7 (die Gleichgewichtskonstante für die Dissoziation von Wasser beträgt dann genau 10^(−14)). Dieser Wert ist als chemisch neutral definiert. Allerdings hat chemisch reines Wasser keinen Puffer und reagiert damit auf geringste Verunreinigungen mit einer deutlichen pH-Wert-Änderung. So stellt sich in zuvor chemisch reinem Wasser bei Luftzutritt infolge Lösung von CO₂ sofort ein pH-Wert zwischen 4,5 und 5 ein.<ref name="Wiki">Wikipedia</ref>

Die Trübung (1/m) ist ein Maß für den Anteil von fein verteilten Partikeln und ungelösten Stoffen in der Wasserprobe. Sie wird bei 860 nm Wellenlänge bestimmt.<ref name="isa">ISA – Institut für Siedlungswasserwirtschaft der RWTH Aachen</ref>

• i.d.R. handelt es sich um ungefährliche Sedimente, ungelöste Partikel, sogenannte. Schwebstoffe
• Wasserinhaltsstoffe, die Kleinlebewesen als Nährsubstanz dienen und so deren Wachstum fördern
• sie verhindern eine effektive Desinfektion (Chlorzehrung, Chlor lagert sich an den Partikeln an), daher muss trübes Wasser vorher gefiltert werden
• Maßeinheit für Trübung: NTU, nach WHO soll TW < 1 NTU aufweisen (Katadyn Wasserfibel)

Schwermetalle sind Blei, Cadmium, Chrom, Nickel, Kupfer, Zink, Quecksilber. Gelangen über das Regenwasser, welches durch die Gesteinsschichten gefiltert wird, in das Grundwasser. Schwermetalle können sich im menschlichen Körper ablagern.<ref name="WHO">WHO Richtlinien für TW</ref> Schwermetalle lassen sich nur über aufwändige Verfahren, wie der Destillation oder der Flockung, aus dem Wasser entfernen. Schwermetalle können aber auch aus Metalldächern gelöst werden und so in den Regenwasserspeicher gelangen

Quellen

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