IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at
IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C Report, Date: 13.01.2009 Table 5-1: Pro and Cons of different water treatment technologies (http://www.lenntech.com/water-treatment-chemicals.htm, 07.04.2009; 14:53) Technology Environm. friendly Byproducts Effectivity Investment Operational costs Fluids Surfaces Ozone + + ++ - + ++ ++ UV ++ ++ + +/- ++ + ++ Chlorine +/- +/- ++ ++ + ++ -- dioxide Chlorine gas -- -- - + ++ +/- -- Hypochlorite -- -- - + ++ +/- -- From the table above it can be concluded, that ultra violet light (UV) and Chlorine Dioxide are the most promising technologies for the application in small scale wet cooling towers because the investment and operational cost of the used technology are moderate or low and the effectivity against Legionella is high. Chlorine Dioxide offers further the advantage to be effective against biofilms. For large installations Chlorine Dioxide is usually manufactured on site because it is an unstable gas that dissociates into chlorine gas (Cl 2 ) and oxygen gas (O 2 ). For small applications Chlorine Dioxide is also commercial available in stabilized form as powder, tablet or solution. For the water treatment with Ozone an expansive reactor for production of the Ozone on site is necessary, thus this technology is applicable for high quantities of water only. The treatment with Chlorine or Hyperchloride is less effective compared to other options and does not act against biofilm formation. 5.4 Disinfection by UV-Radiation This chapter describes the principle structure of bacteria and the mechanism how they can be destroyed by ultra violet light (UV). Furthermore the design of market available lamps and there possible application are discussed. 5.4.1 General For a better understanding of the destruction mechanism in case of disinfection by UVradiation, of water or air, the Figure 5-2 shows the principle structure of bacteria. It consists of a cell nucleus, the cell fluid and the cell wall. The cell wall consists of a Murein membrane and an additional Lipid membrane. Murein is a biochemical strong net of Polysacharine chains and Peptide chains and build up a strong protection around the cell fluid. The chemist Gram discovered, that there are two groups of bacteria. The group 1, he calls it “negative”, do have a thin Murein membrane around the nucleus. The Murein membrane is lower than 10 % of the wall dry mass. The group 2, he calls it “positive” do have a Murein membrane with 30 to 70 % of the dry wall mass. page 31
IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C Report, Date: 13.01.2009 cell wall murein membrane lipid membrane cell nucleus Gram-nagative lower 10% of dry mass Proteobacteria Enterobacteria Escheria colli Salmonella Enterobacter Pseudomonas Legionella Neisserien Rickettsia Pasteurella Gram-positive between 30 and 70 % of dry mass Actinobacteria Actinimyzeten Firmicutes Streptokokken Enterokokken Stafylokokken Clostridien Lactobacilla Erysipelotrix Figure 5-2: Principle construction of Gram positive and Gram negative bacteria. Figure 4.1 characterizes a lot of well known bacteria which are assigned to the Grampositive and Gram-negative groups. The Legionella bacteria belong to the Gram-negative group and have therefore a thin protecting Murein membrane which opens the possibility to kill the dangerous bacteria by UV-disinfection. The ultraviolet (UV) radiation is an electromagnetic wave with a wave length in the range of 100 to 380 nm, or a frequency of more than 789 THz. Generally it is known that ultraviolet radiation is able to destroy bacteria. Especially the Gram-negative bacteria, which have only a relatively thin Murein membrane, can be destroyed by UV-radiation with a high lethal rate. Figure 5-3 shows the range of the ultraviolet radiation and the curve of effectiveness of destroying the Gram-negative bacteria. The highest effective destruction can be detected at 254 nm in the range of UV-C radiation (200 to 280 nm) X-ray Ultraviolett Visible Light Infrared Wafe length UV-radiation, 254 nm Killing of Microorgansms Figure 5-3: Position of the UV-C radiation in the frequency band from 100 to 750 nm page 32
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<strong>IEA</strong> SHC Task 38 <strong>Solar</strong> Air Conditioning <strong>and</strong> Refriger<strong>at</strong>ion Subtask C Report, D<strong>at</strong>e: 13.01.2009<br />
cell wall<br />
murein membrane<br />
lipid membrane<br />
cell nucleus<br />
Gram-nag<strong>at</strong>ive<br />
lower 10% of dry mass<br />
Proteobacteria<br />
Enterobacteria<br />
Escheria colli<br />
Salmonella<br />
Enterobacter<br />
Pseudomonas<br />
Legionella<br />
Neisserien<br />
Rickettsia<br />
Pasteurella<br />
Gram-positive<br />
between 30 <strong>and</strong> 70 % of dry mass<br />
Actinobacteria<br />
Actinimyzeten<br />
Firmicutes<br />
Streptokokken<br />
Enterokokken<br />
Stafylokokken<br />
Clostridien<br />
Lactobacilla<br />
Erysipelotrix<br />
Figure 5-2: Principle construction of Gram positive <strong>and</strong> Gram neg<strong>at</strong>ive bacteria.<br />
Figure 4.1 characterizes a lot of well known bacteria which are assigned to the Grampositive<br />
<strong>and</strong> Gram-neg<strong>at</strong>ive groups. The Legionella bacteria belong to the Gram-neg<strong>at</strong>ive<br />
group <strong>and</strong> have therefore a thin protecting Murein membrane which opens the possibility to<br />
kill the dangerous bacteria by UV-disinfection.<br />
The ultraviolet (UV) radi<strong>at</strong>ion is an electromagnetic wave with a wave length in the range of<br />
100 to 380 nm, or a frequency of more than 789 THz. Generally it is known th<strong>at</strong> ultraviolet<br />
radi<strong>at</strong>ion is able to destroy bacteria.<br />
Especially the Gram-neg<strong>at</strong>ive bacteria, which have only a rel<strong>at</strong>ively thin Murein membrane,<br />
can be destroyed by UV-radi<strong>at</strong>ion with a high lethal r<strong>at</strong>e. Figure 5-3 shows the range of the<br />
ultraviolet radi<strong>at</strong>ion <strong>and</strong> the curve of effectiveness of destroying the Gram-neg<strong>at</strong>ive bacteria.<br />
The highest effective destruction can be detected <strong>at</strong> 254 nm in the range of UV-C radi<strong>at</strong>ion<br />
(200 to 280 nm)<br />
X-ray Ultraviolett Visible Light Infrared<br />
Wafe length<br />
UV-radi<strong>at</strong>ion, 254 nm<br />
Killing of Microorgansms<br />
Figure 5-3: Position of the UV-C radi<strong>at</strong>ion in the frequency b<strong>and</strong> from 100 to 750 nm<br />
page 32
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